report of committee on ovens and furnaces · the report of the committee on ovens and furnaces is...

C O M M I T T E E P E R S O N N E L OF=I

Report of Committee on Ovens and Furnaces .James T. Blackmon, Jr., Chairman

Union Carbide Corp., Nuclear ])iv., Bldg. K-1001, MS 18.3 Oak Ridge, TN 37830 .

E. C. Bayer, Holcrnft & Co. W . J . McEIhaney , Lectrome!t Corp. Roger F. Beal, Continental Can Co., Inc. T h o m a s L.-Nabora, American Iron & Stee! John P. Benedict , Benedict-Miller, I n d . . Institute L. M. Bolz, Improved Risk Mutuals Ray Ostrowski, Protection Controls, Inc. Robert R. Brining, Caterpillar Tractor Co. H . E . Parker , The Electric Furnace Co. Robert C~" Davis, NFPA Industrial Fire W . F . Parker , Surface Combustion Div., Protection Section Midland-Ross Corp.

S. B. Gamble, Flinn and Dreffein Engi- H.R. Richards, Industrial Ovens, Inc. neering Co. Paul N. Rick, Ford Motor Co.

Paul H. Goodell~ J . M . S i m m o n s , Factory Mutua| Research Corp.

Robert F. Gunow, Metal Treating Institute A r t h u r Sp iege lman , American Insurance John R. HixSon, Maxon Corp. Assn. Fred K. Jensen , Jensen, Inc. Geort~e S t u m p h , Industrial Heating Equip- Will iam R. Jones, Abar Corp. ment Assn. K. N. Lawrence , National Electlical Mfrs. . A b r a h a m Wlllan, Aerospace Industries

Assn. Assn. Floyd B. McCoy, Reynolds Metals CorD. D.E. Winp, atc !pson Industries Robert" H. McCreery, Forging Industry George~M. Woods, Jr., Kemper Insurance

Association Co.

AI t e rna te s

R. C. Brown, Factory Mutual Research Wi l l i am F. Pat ' ton, Aerospace Industries Corp. (Alternate to J. M. Simmons) Assn. (Alternate to Abraham Willan)

J a m e s Knodel , Industrial Heat ing Equip- F r ank E. R a d e m a c h e r , Industrial Risk In- ment Assn. (Alternate to George Stumph) surers (Alternate)

.Joseph A. Lincoln, Metal Treating In- J a m e s M. Sull ivan, National Electrical stitute (Alternate to Robert F. Gunow) Manufacturers Assn. (Alternate to K. N.

Wallace D. Ma lms ted t , American Insur- Lawrence) ance Assn. (Alternate. to Arthur Spiegel- N. L. Ta lbot , Improved Risk Mutuals man) . (Alternate "to L. M. Bolz)

T h o m a s J . Mlll igan, American Iron & Steel George W. Weln fu r tne r , Forging Industry Institute (Alternate to Thomas L. Nabors) Assn. (Alternate to Robert H. McCreery)

tNonvoting

NOTE: Industrial Risk Insurers have one voting ~dternate, but no principal representative.

S e c t i o n a l C o m m i t t e e o n C las s A O v e n s a n d F u r n a c e s

A r t h u r Spiege lman, Chairman American Insurance Assn., 85 John St., New York, NY 10038

Fr~ l K, Jensen , Vice Clu3ir~nan Jensen, Inc., 24115 Industrial Park Dr., Farmington, MI 48024

4t~ ~ t m t

O F - 2 C O M M I T T E E O N O V E N S A N D F U R N A C E S

P a u l H. Gcmdel l t Robert H. McCreery, Forging Industry As-

sociation H. R. R i c h a r d s \ Industrial Ovens, Inc.

P a u l N. Rick, Ford Motor Co.

George S t u m p h , Industrial Heating Equip- , meat Association

Alternates

J a m e s Knode l , Industrial Heating Equip- George W. W e i n f u r t n e r , Forging Industry meat Association (Alternate to George Assn. (Alternate to Robert H. McCreery) Stumph)

Wallace D. M a l m s t e d t , American Insur- ance Assn. (Alternate to Arthur Spiegel- man)

tNonvot ing

S e c t i o n a l C o m m i t t e e o n C las s C F u r n a c e s

George M. Woods, J r . , Chairman Kemper Insurance Co., Route 22, Long Grove, IL 60049

E. C. Bayer , Holeroft & Co. John P. Benedict , Benedict-Miller, Inc. Robert C. Davis, NFPA Industrial Fire Pro-

tection Section

W. F. Pa rke r , Surface Combustion Div., Midland-Ross Corp.

D. E. W i n g a t e , Ipsen Industries

Thin lint represents the membership at the time the Committee wan balloted on the text of this edition. ~inee that time, changes in the membership may have occurred.

The report of the commi t tee on Ovens and Furnaces is in two parts.

Part I proposes for official adoption a complete revision of NFPA 86A-1973. Ovens and Furnaces. This Standard was prepared by the Sectional Committee on Class A Ovens and Furnaces.

Par t I has been submitted to letter ballot of the Sectional Committee which consists of six voting members, of whom /Tve have voted affrmatively, and one has voted negatively. Mr. McCreery has voted negatively.

Par t I has also been submitted to letter ballot of the Ovens and Furnaces Committee which consists of 29 voting members, of whom 20 have voted affrmatively, eight negatively and one has asked to be recorded as not voting. Messrs. Bayer, Benedict, McCreery, H. E. Parker, W. F. Parker, Willan, Rademacher, and Talbot have voted negatively, and Mr. Gunow has asked to be recorded as hot voting.

V O T ~ S T A T E M E N T O F - 3

Part I I proposes for official adoption the addition of a chapter covering Molten Salt Bath Furnaces to NFPA 86C-1974, Indus t r l a l Furnaces Using a Special Processing Atmosphere. This chapter was prepared by the Sectional Committee on Class C Furnaces.

Part "II has been submitted to letter ballot of the Sectional Committee which consists of six voting members, oJ whom four have voted affrmatively and two have voted negatively. Messrs. Bayer and Wingate have voted negatively.

Part I I has also been submitted to letter ballot of the Ovens an'd Furnaces Committee which consists of 29 voting members, .of whom 23 have voted aj~rmatively, four negatively, and two have not returned ballots. Messrs. Bayer, McCreery, Wingate, and Rademacher have voted negatively, and Messrs. Hixson and Nabors have not returned ballots.

tram t ~

86A-6 O V E N S A N D F U R N A C E S

b

Foreword =

Explosions and fires in fuel-fired steam and electric heat utilization equipment constitutes a loss potential in life, property, and production. This standard is a compilation of guide lines, rules and methods applicable to safe operation of this type of equipment.

T h e r e are other regulations and conditions that should be con= sidered when designing and operating ovens and furnaces tha t are not covered in this standard, such as toxic vapors, noise levels; heat stress, and local, state, and federal regulations (EPA and OSHA).

Causes of practically all failures can be traced back to human failure. The most significant failures have been found to be:

(a) Inadequate training of operators

(b) Lack of proper maintenance

" (c) Improper application of equipment.

Users and designers must utilize engineering skill to bring together that proper combination of controls and training necessary for the safe operation of the equipment.

The standard for the location, design, and construction of ovens and. furnaces is set forth under classifications as follows:

Class A ovens or furnaces are heat utilization equipment operating at approximately atmospheric pressures and temperatures below 1400°F (760°C) where there is an explosion hazard from either, or a combination of, the fuel in use of, f lammable volatiles from material in the oven or catalytic combustion system; i.e., f lammable volatiles from paints, and other finishing processes such as dipped or sprayed material, impregnated material, coated fabrics, curing applications, drying, water dry off, etc.

Class B ovens or furnaces are those operating at or above atmospheric pressure and temperatures exceeding 1400°F (760°C).

Class C furnaces are those in which tt~ere is an explosion hazard due to a flammable special atmosphere being used for treatment of material in process. This type of furnace may use any type o f heating-system and includes the atmosphere generator.

i

• Class D furnaces are vhcuum furnaces which operate at temperatures above ambient to over 5000°F (2760.°C) and at pressures below atmosphere, using any type of heating system. These furnaces may include the use of special processing atmospheres.

i

Notes in this standard'are for informational purposes only, and are not mandatory.

I N T R O D U C T I O N 86A-7

P~rt !

: Standard for

Ovens and Furnaces

Design, Location, and Equipment

NFPA No. 8 6 A - - 1 9 7 7

Chapter 1 Introduct ion

1-1 Scope. This standard applies to Class A ovens or furnaces. The words ovens and furnaces shall be used interchangeably.

Within the scope of this standard, an oven shall be any heated enclosure operating at approximately atmospheric pressure used by industry for the processing of materials.

This standard also applies to bakery ovens in all. respects and reference is made to those sections of the American National Standard Safety Code for Bakery Equipment, ANSI Z50.1-1977, which covers bakery oven construction and safety.

1-2 Purpose . Since the drying or baking of material containing flammable volatiles such as sprayed or dipped paint work, impregnated material and coated fabrics may involve a serious fire and explosion hazard endangering the oven and the building in which the process is located, and possibly the lives of employees, adequate safeguards shall be provided as appropriate for ,the location, equipment, and operation of such ovens.

1-3 Application. This standard shall apply to new installations or alterations or extensions to existing, equipment.

1-4 Definitions. For the purpose of this Standard, the following definitions shall apply:

After-burner System means a separate or independent combustion system usually removed from the processing area of an oven, or elevated temperature fume producing device, but intended to entrain the process exhaust vapors o r f u m e s as they are generated, for the purpose of thermal decomposition and /o r heat recovery.

NOTE: Such after-burners are usually similar in design and.construction to remote oven heaters or Class B furnaces (NFPA 86B), except for the temperature and combustibility of gases entrained.

86A-8 OVENS AND FURNACES

Air F low Swi tch means a device ac tua ted by the flow of a i r in a duct" sys t em.

N O T E 1 : Vane-type air flow switches consist 6f a vane or paddle mounted - on a movable arm. The vane is so located that a differential pressure or air flow against the vane will cause the vane arm assembly to move and actuate a switch contact.

N O T E 2: Diaphragm-type air flow switches consist generally of a diaphragm with one side open to room pressure and the other connected to the exhaust or,ventilation duct. Movement of the d iaphragm by a pressure differential will actuate switch contact.

A i r - G a s M i x e r means a device into which the fuel gas and the p r i m a r y combust ion air are in t roduced, mixed, and then del ivered to the burner nozzle(s) .

N O T E : The kinetic energy of the gas under pressure may be used' to inject part or all" of the air required for combustion as pr imary air. Conversely, all, or part of the pr imary combustion air may be pressurized, as by a centrifugal blower, and used to cause injection of the fuel gas.

Atmospheric (Venturi) Inspirator means a device which utilizes the kinetic energy of the fuel gas under pressure, to in jec t all or pa r t of the combust ion a i r . r equ i r ed 'as p r i m a r y air f rom the amb ien t (see Figure 7-d. I).

NOTI~: "Low pressure inspirators" operate at about 1 psig gas pressure, or less, and cannot inject 100 percent combustion air. "High pressure inspirators" operate in the approximate range of 1 to 30 psig gas pressure, and may or may not inject 100 percent primary air.

Secondary Air - - • e q i s t e r ' ~ • / / v r , m a r y

. . . . ~ insRira~0rBody / Air"

.... I <<. p.o.o oe V [ ~ u r n e r _L Mixer

Figure 1-4.1 Atmospheric Inspiring Burner Mixer.

INTRODUCTION 8 6 A - 9

A i r J e t M i x e r means a device which utilizes a i r under pressure, to enti 'ain all or pa r t of the fuel gas Which m a y be suppl ied at, or below, or above a tmospher ic ( "zero") pressure.

N O T E : Air jet mixers have internal or external means for varying the flow of pr imary combustion air. In addition and simultaneously, provision is made for corresponding flow control of the fuel gas.

Branch Circuit'-- I n d i v i d u a l means a b ranch ci rcui t tha t supplies only one ut i l iza t ion equipment .

Burner (or Nozz le ) means a device th rough which combust ion ai r and fuel are released into the combust ion zone.

N O T E : If the fuel gas and air are introduced separately, the burner is said to be "nozzle-mixing," otherwise, an air-gas mixing device- is used to supply the nozzle, which then is said to be of the (partial) premixing- type. Either way, additional means are required to control or limit the flow of the fuel and a~. Oil burners are always "nozzle-mixing," even if air is used for atomization.

Atmospheric Burner means a burner used in the low pressure gas or " A t m o s p h e r i c " system which r e q u i r e s s e c o n d a r y - a i r for comple te combust ion.

Blast Burner means a bu rne r del ivering a combust ib le mixture unde r pressure, normal ly above 0.3 in. w.c. to the combus t ion zone:

Blast T i p means a small metal l ic or ceramic bu rne r nozzle so made tha t flames will not b low away f rom it, even ,with high mixture pressures.

Burner Turndown means the rat io of m a x i m u m to m i n i m u m burne r fue l - input rates.

Combination Gas and Oil Burner means a bu rne r which Can burn ei ther gas or oil or bo th together.

Diaphragm Burner means a burner which util izes a porous r e f r ac to ry d i a p h r a g m as the po r t so that the combust ion takes place over 3he ent i re a rea of this refractory d i a p h r a g m .

D u a l F u e l B u r n e r means a burner designed to bu rn ei ther gas or oil, bu t not bo th together.

Enclosed Combustion Burner means a burne r which con- fines the combust ion in a small chamber of min ia tu re furnace and only the high t empe ra tu r e comple t e ly combus ted gases; in the form

o f high veloci ty je ts or streams, are used for hea t ing .

i

86A-10 OVENS AND FURNACES \

Ex'cess Air Burner means a, nozzle mixing burner delivering a fixed volume of air and a variable volume of gas such that complete combust ion of gas occurs at all rates of firing, to provide a relatively uniform flow of air and products regardless of firing rates.

Flame Retaining Nozzle means any burner nozzle with built- in features to hold the flame at high mixture pressures.

H i g h - L o w Fi r ing means provision for tWO firing rates, high ancl low, according to load demand.

L ine B u r n e r m e a n s . a burner whose flame is a continuous " l ine" f rom one end to the o t h e r . (Normally applied to a blast burner.)

L u m i n o u s F lame B u r n e r means a burner which discharges nonturbulent parallel strata of air and gas to produce an extended flame of high luminosity.

Luminous Wall Burner means a porous refractory liner to permit gas-air mixtures to flow through, forming a luminous wall.

Modulated Fi r ing means provision for gradual ly varying the firing rate between high-fire and low-fire, according to load .demand.

Mul t i je t B u r n e r means a form of burner which generally consists of gas manifolds with a large number of jets arranged t o fire hor izonta l ly through openings in a vertical refractory plate.

NOTE: These openings are of various s h a p e s - round, square, clover- leafed, etc. Combustion" air may be supplied by natural, induced, or forced draft. Complete assemblies combining burner, refractory plate, wind box, blower, and controls are generally known, as forced draft boiler burners.

Mul t ip0 r t B u r n e r means a burner having two or more separate discharge openings or ports. (These ports may be either flush or raised.)

Nozz le Mix ing B u r n e r means a burner in which the gas and air are kept separate until discharged f rom the burner into the combustion chamber or tunnel.

NOTE: Generally used with low pressure gas (up to 1/6.psig or 14 in. w.c.) and low pressure air (up to 5 psig).

O p e n Port Burner means any type of burner that fires across ' gap into "an opening in the furnace or combustion chamber wall

and is not sealed into the wall..

P i p e •Burner means any type-of atmospheric or blast burner in the form of a tube or pipe with ports or tips spaced over its length.

INTRODUCTION 86A-11

Power Burner means a gas burner in which either gas or air, or .both, are supplied at pressure exceeding, for gas, the lin~ pres- " sure, and ior air, atmospheric pressure. (This added pressure is applied at the burner.) .

NOTE: Examples are gas burners having zero governor inspirator mixers, those supplied by blower mixers or approved gas-mixing machines, imd those supplied with air by a blower, compressor, or forced-draft fan.

P r e m i x e d B u r n e r means a burner that utilizes a positive and dependable air-gas mixer to furnish the air needed for complete combustion of the fuel supplied to the burner independently of t h e concent ra t ion or pressure of the atmosphere inside the enclosure where the burner fires.

NOTE: The zero governor inspirator mixer,.~ high-pressure (gas pressure 1.0 psi or higher) atmospheric inspirator mixer, blower mixer, and the approved gas-mixing machine are illustrative of such a mixer.

Pressure Burner. Same as Blast Burner.

R a d i a n t B u r n e r means a burner designed to transfe'r a significant par t of the combustion heat in the form of radiation from " surfaces of various shapes which are usually of refractory material.

Radiant Tube Burner means a burner of either the atmospheric or nozzle mixing type specially designed to provide a long flame within a tube of.given length. to assure substantially u n i f o r m radiation f rom the tube surface.

R i b b o n B u r n e r means :a burner having many small elose.ly spaced ports usually made up by' pressing corrugated metal ribbons in a slot or o the r shaped opening.

R i n g B u r n e r means a form of atmospheric burner made with one or more concentric rings.

NOTE: Combustion air may be .supplied by natural, induced, or forced draft.

Serf-piloted B u r n e r means a burner where the pilot fuel is issued f rom the same ports as main flame a n d / o r merge with the main flame to form a common flame envelope with a common flame base.

NOTE: In effect, the pilot flame is simply enlarged to become the main ~ flame.

Single Port Burner means a burner having only one dis- . cha rge opening or port. . ,

Tunnel Burner means a burner sealed in the furnace wall in which combustion takes place mostly in a refractory tunnel or tuyere which is really part of the burner. t ~

k '-

8 6 A - 1 2 OVENS AND F U R N A C E S

Catalytic Combustion System (Direct or Indirect Heater) m e a n s an oven h e a t e r of any cons t ruc t ion tha t employs catalysts to acce le ra t e the ox ida t ion or c o m b u s t i o n of fue l -a i r o r f u m e - a i r m ix tu re s for e v e n t u a l release of h e a t to an o v e n process.

Combustion Safeguard m e a n s a safety con t ro l respons ive di- r ec t ly to f l ame p rope r t i e s ; i t senses the p resence a n d / o r absence of f l ame a n d de -energ izes the fuel safety v a l v e in the e v e n t of f l ame fa i lu re w i th in 4 seconds of the loss of f l ame sigfial.

Commercial Manufactured Gas means a m i x t u r e of gases usua l ly c o m p o s e d of va r ious p ropor t ions of some of the fo l lowing gases :

(a) C o a l gas, f o r m e d by dis t i l la t ion or " c r a c k i n g " of b i t u m i n o u s coal .

(b) C o k e - o v e n gas, p r o d u c e d in a s imi la r m a n n e r as a by- p r o d u c t in m a n u f a c t u r e of coke.

(c) C a r b u r e t e d w a t e r gas, f o r m e d by f lowing s t e a m t h r o u g h i n c a n d e s c e n t ca rbon . I t has a low h e a t c o n t e n t w h i c h is inc reased by b r i n g i n g the ho t gas in to c o n t a c t w i t h oil so t h a t some of the oil is b roken d o w n or " c r a c k e d " in to a gas. T h i s p r o d u c t , ca l led c a r b u r e t e d w a t e r gas, is some t imes m i x e d w i t h coke -oven gas.

('d) O i l gas, m a d e by " c r a c k i n g " p e t r o l e u m oils, is used oc- cas iona l ly in m a n u f a c t u r e d gases.

Continuous Vapor Concentration' Indicators and Controllers m e a n s devices w h i c h m e a s u r e a n d ind ica te , d i r ec t ly o r i nd i r ec t l y in p e r c e n t a g e of the l ower explos ion l imi t , the c o n c e n t r a t i o n of a f l a m m a b l e v a p o r - a i r m i x t u r e .

NOTE: They may be of the portable or fixed location continuous operating type. The continuous indicators are mostly used throughout the period of operation of a process wherein flammable vapor is evolved. In addition to indicating or recording concentrations to aid in safe and efficient process control, they can be arranged through'suitable controls automatically to sound an alarm, open or close dampers, start or stop motors, conveyors, and ventilating fans, when the concentration of a flammable vapor-air mixture has reached a predetermined dangerous level.

Dielectric Heater m e a n s a h e a t e r s imi la r to an i n d u c t i o n hea te r , b u t the f r equenc i e s used a re genera l ly h i g h e r (in the o r d e r of th ree megacyc l e s o r more ) t h a n those in induc t ion , hea t ing .

NOTE: This type of heater is useful for heating materials which are commonly thought of as being nonconductive.

Examples: Heating plastic 'preforms before molding, curing glue in plywood, drying rayon cakes, and for many similar applications.

co

INTRODUCTION 8 6 A - 1 3 .

Direct Fired m e a n s any h e a t i n g system w h e r e the p roduc t s of c o m b u s t i o n en t e r the oven c h a m b e r and c o m e in c o n t a c t w i t h the w o r k in process (see Figures 1-4.2, 1-4.3, 1-4.4, and 1-4.5).

Direct Fired External Heater m e a n s a n y oven h e a t i n g sys tem in w h i c h the bu rne r s are in a c o m b u s t i o n c h a m b e r e f fec t ive ly s e p a r a t e d f r o m the oven c h a m b e r a n d so a r r a n g e d tha t p roduc t s of c o m b u s t i o n f r o m the burne r s a re d i s cha rged in to the o v e n c h a m b e r by a c i r cu l a t i ng fan o r b lower . T h e r e a r e two classes of these hea te r s as fo l lows:

Direct Fired External Nonrecirculating Heater m e a n s any" d i r e c t f i red ex te rna l h e a t e r so a r r a n g e d tha t p r o d u c t s of c o m b u s t i o n w i t h o u t a n y r e t u r n o r r e c i r cu l a t i on f r o m the o v e n c h a m b e r a r e d i s cha rged in to the o v e n c h a m b e r (see Figure 1-4. 3).

Direct Fired External Recirculating Heater m e a n s a d i r ec t f i red ex t e rna l h e a t e r so a r r a n g e d t h a t o v e n a t m o s p h e r e is re- c i r c u l a t e d to the o v e n h e a t e r a n d in con t ac t w i t h the b u r n e r f l ame (see Figure 1-4.4).

N O T E 1: A heating system so constructed that the oven atmosphere circulated through a blower with products of combustion admitted to the recirculating duct work, but without the oven atmosphere actually passing through the combustion chamber, is designated as "direct fired external, recirculating not through heater" (see Figure 1.4.5). N O T E 2: A combustion chamber of a recircuaating oven heater may be built within an oven chamber but substantially separated from the oven atmosphere by gas-tight construction. This type of heater is classed as direct fired external and may be either nonrecirculating or recirculating.

N O T E 3: Attention is called to some advantages of direct fired external heaters either recirculated or non/'ecirculated for ovens which are to be direct fired because of the use of a single burner for each heater.

N O T E 4: The type of operation permits the installation of a single combustion safeguard for each heater; usually a less complicated and less expensive installation than can be secured in any design using multiple burners, particularly those designs making use of multiple line burners where it is not ordinarily possible to secure ignition over the entire length of each burner by reliable automatic controls. In general, any design which makes use of the smallest possible number of burners is preferred to multiple burner installations.

Direct Fired Internal Heater m e a n s any oven h e a t i n g s y s t e m in w h i c h the bu rne r s a re w i t h i n the oven c h a m b e r a n d in c o n t a c t w i t h the oven a tmosphe re .

Dustproof means so cons t ruc t ed or p ro t ec t ed tha t dus t will n o t • in te r fe re w i t h its successful opera t ion .

86A-14 OVENS AND F U R N A C E S I N T R O D U C T I O N 8 6 A - 1 5

• " p Y e n t ~ IF' • I

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o...o....,, lq" z:,:° I * Ed.IRN E R DETAI L

Burner Noz:le. \ -

Eefraclory ~ Eurner ~ B l o c k

A'A

~ EM.

f - - L " - - - - -

- Pilot No]e: ~ v e f n o r Suppl;es Tunnel .Several Eurn~.rs

Figure 1-4.2 Typical piping, direct internal-fired multiburner furnace.

Figure 1-4.3 Direct Fired Figure 1-4.4 Direct Fired External Nonrecirculating. External Recirculating

Through the Heater.

Figure 1-4.5 Direct' Fired External Recirculating Not Through Heater.

Figure 1-4.6 Indirect Fired Internal Explosion

Resisting.

f

Electr ical V e n t i l a t i o n I n t e r l o c k i n g means a fan that is" motor • driven by, direct shaft or at least two " V " belts which is interlocked with the safety control circuit by energizing the circuit f rom the load side of an overcurrent protected starter for the fan motor, through an extra contact of the starter or a suitable relay or trans- f o r n 2 e r .

Explosive R a n g e (Limits of F l ammab i l i t y ) means the range of concentrat ion of a f lammable gas in air within which flame is propagated.

NOTE: The lowest flammable concentration is the lower explosive limit• Within the range, the maximum rate of flame propagation occurs when the combustible gas and air are mixed in proportions for complete combustion or often with the gas at a slightly higher concentration (see Table 1-4.1).

F l ame Detec t ion Device means a device which will detect the presence or absence of flame and will cause automat ic shutoff of the fuel supply in event of flame outage.

NOTE: Flame detection devices may be based on: (a) Flame'rectification. (b) Ultra-violet radiation produced by burning gases. (c) Infrared radiation produced by burning gases.

, b ~a


Table 1-4.1 Properties of Typical Commercial Gases

Gas

Cu. Ft. ,of Limits of Explosive S~vecifie Air Required Range Per cent in (Iravily To Burn

Btu Per Air by Volume Compared 1.0 C u. Ft. Cu. Ft. Lower Upper To Air--1.0 of Gas

Natural (High Btu type) 1115 4.6 14.5 .64 10.6

Natural (High methane

type) 960 4.0 15.0 .56 9.0

Natura[ (High inert type) 1000 3.9 14.0 .70 9.4

Coke Oven 575 5.0 28.0 .44 5.1.

Carbureted Water (Heavy oil with

blow run) 530 6.5 37.5 .70 4.1

Carbureted Water (Gas oil) 530 6.4 37.7 .67 4.5

Oil Gas (Pacific Coast) 496 4.5 29.6 .47 4.0

Coal Gas 536 5.6 30.8 .47 4.9

Water Gas (Blue gas) 287 6.9 69.5 .57 2.1

Producer Gas (Anthracite) 136 20.7 73.7 .86 1.1

Producer Gas (Bituminous) 153 16.8 64.0 .86 1.2

Propane 2500 2.4 9.5 1.52 " 24.0

Butane 3200 1.9 8.5 1.95 31.0

Flame Propagation (Rate of) means the speed at which a flame progresses through~a combustible gas-air mixture under pressure, temperature, and mixture conditions, existing in the combustion space, burner, 'or piping under consideration (see Figure 7-4.7).

NOTE: The rate of flame proi)agation has practical significance in the design and operation of premixing gas biJrners. If the velocity of the mixture at the burner diminishes, the tendency of the flame to flash back into the burner body is increased. Conversely, if the gas velocity leaving the burner is much greater than the rate of flame propagation, the flame may be blown away from the burner. For this reason, a burner which has been used on a manufactured gas, with a relatively high rate of flame propagation, may not be suitable for natural gas or butane which" has a low rate: Fortunately, the relation between burner discharge velocity and flame propagation

INTRODUCTION 86A- 17 \

.rate is not critical, so that neither variation in the rate of flow nor changes in mixture adjustment over a fairly-wide range will cause the flame to blow away from the burner or to flash back.

)

,0 / \ N 0

\

/i . . . . . \ ' "

/ A " ~ ' , - / -,~ " .0

/ / , ¢ ] - - - - , ~ - : ~ . . ~ ~_ h

PAII, t t ~ AIA - Pz.q~Jrf 01 r Tt~o~'rICAt. Iq.QUIAI[tlIMT I g l COItPIATI£ (~OtllUSTIO~

Figure 1-4.7 Theoretical Ignition Velocity Curves for Various Gases.

Flame Rod means a detector which employs an electrically insulated rod of temperature resistant material that extends into the flame being supervised, with a voltage impressed between the rod and a ground connected to the nozzle of the burner, and the electrical current passing through the flame is rectified and this rectified current is detected and amplified by the "combustion safeguard.

Fuel Oil means Nos. 2, 4, 5 or 6 in accordance with Specificatlons for Fuel Oils, ASTM D-396-73.

Fuel Safety Controls means devices such as safety shutoff valves, flame detection units, pressure s~vitches (high and low), combustible gas detectors, flowmeters, firechecks, reliable ignition sources, and supervisory cocks.

Gas Pressure Regulator means a diaphragm-operated valving device that attempts to maintain a constant outlet pressure despite varying flow.

NOTE : A "zero governor" is a special type of gas regulator that has an outlet pressure at, or near, atmospheric.

t aJ

86A-18 O V E N S A N D ' F U R N A C E S

Guarded means covered, shielded, fenced, enclosed or otherwise n r n t e e t e ~ t h v h ~ e ~ n ~ n f c l l i t ~ h l e c n v e r ~ o r r ~ i n ~ R _ h ~ r r l e r R r ~ i } R n r r" . . . . . . . . ~ -i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o - , -- - - - , . . . .

screens, mats or platforms, to remove the l iabili ty of dangerous contact or approach by persons or objects to a point of danger.

H i g h P r e s s u r e Air System (air pressure 5 psig or higher) means a system using the m o m e n t u m of a je t of high pressure air to ent ra in gas, or air and gas, to produce a combust ible mixture.

H i g h P/-essure Gas System (gas pressure 1 psig* or higher) means a system using the m o m e n t u m of a je t of high pressure gas to ent ra in from the atmosphere all; or near ly all, of the air required for combustion•

Ignition Temperature means the lowest temperature at Which a gas-air mixture may ignite and cont inue to b u r n .

NOTE: This is also referred 'to as the auto-ignition temperature• When burners supplied with a gas-air mixture in the flammable range are heated above the auto-ignition temperature, flash backs may occur. In general, such temperatures range from 870 ° F to 1300 ° F. A much higher temperature is needed to ignite gas dependably. The temperature necessary is slightly higher for natural gas than for manufactured gases, but for safety _with manufactured gases a temperature of about'1200 ° F is needed and for natural gas a temnerature of about 1400 ° F is needed. • L

Ignition Systems.

Automatic-lgnited'Burner means a bu rne r ignited by direet electric ignition, or by an electric-ignited o r c o n t i n u o u s pilot.

Automatic-lighted Industrial Heating Equipment means gas- or oil-fired industr ial heat ing equ ipmen t such as a furnace or oven where fuel to the main burner(s) is tu rned on automatical ly and ignited automatical ly (see Automatic-ignited Burner).

NOTE: Firing of the main burner(s) may be high-low, modulated to off, or on-off.

Direct'Electric Ignition means ignit ion of an oil flame (and in some cases a gas flame) by an electric-ignition source such as a high-voltage spark or hot wire.

Manual-ignited Burner means a burney ignited by a po{table gas- or o i l -burner torch or by an oil-soaked swab torch, placed in proximity to the bu rne r nozzle by the bu rne r man.

Manual-lighted Industrial Heating Equipment means gas- or oil-fired equ ipment such as a furnace or oven where fuel to the

*Equipment will not function satisfactorily at pressures less than 1 psig.

I N T R O D U C T I O N 8 6 A - 1 9

main burner(s) can be turned on only by hand and is manua l ly ............. i~n~terJ nnAor the nr ~emlmltnmntlrally -o .................. supervisio_ n_ of the burner

man (see Manual-ignited Burner and Semiautomatic-ignited Buiner). NOTE: Once ignited, firing of the main burner(s) may be high-low or modulated.

Proved Low-f i re-s tar t In t e r lock means a burner s t a r t in v~hieh a control Sequence ensures that a -h igh- low or modula ted burner is in the low-fire (firing rate not exceeding 33 percent of the maximum) position before the burner can be started, as for example by ineans of an end switch mounted on the drive shaft of the modu- lat!ng motor, which is wired into the safety-control circuit.

Semiautomatic-ignited Burner means a bu rne r ignited by direct electric ignition, or by an electric-ignited pilot, electric ignition being manua l ly activated. • -

\

Semiautomatlc-llghted Industrlal Heating Equipment means the same as automatic- l ighted except that on each lighting-off, placing the equ ipment in service from cold condit ion, fuel to the main burner(s) can be - tu rned on only by hand and is manua l ly or semiautomatical ly ignited under the supervision of the burner man (see Manual-ignited Burner and" Semiautomatic-ignited Burner). • NOTE: Once ignited, firing of the main burner(s) may be high-low, ' modulated to off, or on-off.

Indirect Fired External Heater means, an oven heater in which burners and combust ion chamber are outside of the oven chamber

.and the oven atmosphere is kept separate f rom combust ion gases. These heaters may be of three types as follows:

Indirect Fired, External Heater, Recirculating, not Through Heater rffeans a system in which air is d r a w n or blown through the radiator of a heater without any recirculat ion of the oven atmosphere through the heater (see Figure 1-4. 9).

- Indirect Fired, External Heater, Recirculating means a system in which oven atmosphere is recirculated through radiators outside the oven chamber (see Figure 7-4. 10).

Indirect Fired, External Heater, Internal Radiator means a system in which products of combust ion from a heater located outside the oven chamber are circulated .through radiator tubes located,within the oven" (s'ee Figure 1-4. l l).

NOTE: Heaters of these types are well adapted to low temperature drying operations and practically eliminate the possibility of explosion in the oven or dryer from fuel gases, but do not in any way reduce the possibility of explosion from vapors given off by the work being dried.

W~

8 6 A - 2 0 OVENS AN~ FURNACES

5'[ Pc, dud.* d } Cembushbn ...~H ( 4"~ " L./Kxhausl fan ~ooutdoora - Iq M* 13

j l 1I [" " gxhauM£an-

IPl ', I t II I ~ .d , ; , . . r ,~ .

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Figure 1-4.8 Indirect Fired Internal Nonexplosion-

Resisting.

Pan to ou/~Qov$

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t l t e h a ~

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Figure 1-4.9 Indirect Fired External Recirculating Not Through Heater.

~z&taetPen y £MmuelPan~

I . ~ u l a ! , ' ~ re,

Id ,.,,..~'t.,",,~.~.~l ",~*~,"

Figure 1-4.10 Indlrek:t Fired External Recircu-

lating.

P reduc4seP f,d tee# #metea/e~'an fo ou/door, - 6tt~ ~ ;

Figure 1-4.11 Indirect Fired External Internal

Radiator.

I n d i r e c t Fired Heating S y s t e m m e a n s a sys tem so a r r a n g e d t h a t the p roduc t s of c o m b u s t i o n do no t en te r the w o r k c h a m b e r , hea t i ng be ing a c c o m p l i s h e d by r a d i a t i o n or c o n v e c t i o n f r o m tubes o r muffles.

I n d i r e c f Fired Internal Heater m e a n s a hea t i ng sys tem of gas- t i gh t rad ia to rs con ta in ing , gas bu rne r s no t in c o n t a c t w i t h the oven a tmosphe re . T h e s e systems m a y be of the types as fol lows:

Explosion Resisting means an ind i r ec t f i red in te rna l h e a t e r so cons t ruc t ed as to w i t h s t a n d exp los ion pressure f r o m igni t ion of a gas-a i r m i x t u r e in the rad ia to r s (see Figure 1-4.6).-

INTRODUCTION 8 6 A - 2 1

N o n e x p l o s i o n R e s i s t i n g m e a n s an ind i r ec t f i red i n t e rna l h e a t e r w i th gas - t igh t r ad ia to r s which , however , a re no t des igned to w i th s t and an in te rna l explos ion (see Figure 7-4.8).

Muffles means enc losures w i th in a f l ! rnace w h i c h s epa ra t e the p roduc t s of c o m b u s t i o n f r o m the work and f r o m any special a t m o - sphere wh ich m a y be r e q u i r e d for the process.

NOTE: Burners may be used for direct-firing of the space within the furnace but outside the muffle, or heating of the muffle may be by indirect means using radiant tubes or external furnace heaters (see Figure 1-4.12).

//////////////A I ! CROSS SE:CTION 1

~ ~ x x x x ~ x ~ x x x x x ~ , ~x~, D ~ Q H

I I II I! ~ - HORIZONTAL ~ E C . T I O N ~

Figure 1-4.12 Muffle-type internal-fired multlburner furnace.

Radiant Tubes means t u b u l a r e lements o p e n a t one o r b o t h ends, cons t ruc t ed gas - t igh t of su i tab le hea t - res i s tan t ma te r i a l , a n d c a p a b l e of w i t h s t a n d i n g explos ion pressure f r o m igni t ion of fue l -a i r " mix tures .

NOTE: The tube has an inlet and/or burner arrangement where combustion is initiated, a suitable length where combustion occurs, and an. outlet for the combustion products formed. The fuel-air .mixture can be mixed before, during or after introduction into the tube. The introduction can be accomplished under high pressure, under slight pressure, or under suction. Ignition can be accomplished at either the inlet or the outlet of the tube.

Radiant tubes can be located in the actual heating chamber of the furnace or remotely in another chamber. In the latter instance, heat transfer is accomplished by recirculation of heated gases (see Figure 1-4.13).

/ Induction Heater m e a n s a hea t i ng system by m e a n s of w h i c h a

current-c~ r ry ing c o n d u c t o r induces the t ransfer of e lec t r ica l ene rgy to the w o i k by eddy currents . (See Article 665 of NFPA 70-1978.)

Infrared Lamp and Tubular Heaters means a f o r m of res is tance h e a t e r in wh ich the resist ive conduc to r s a re enc lo sed in glass, q u a r t z , o r . c e r a m i c enve lopes t h a t m a y o r may n o t c o n t a i n a special gas a tmosphere .

O

" 8 6 A - 2 2 OVENS AND FURNACES INTRODUCTION 8 6 A - 2 3

6 To Prod.Of (o rn b, [ | i f Exhaust Sys~ern I I

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CROSS SECTION

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NORIZONIAL S'E'CTION

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/G, ' - ~ ' - ' ~ _ .C'-" (t . . . . . . . ~ A ? r Pressure

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TYPICAL P U L L - T H R O U G H RADIANT-TUBE BURNER

Figure 1-4.13 Typical indirect fired r ad ian t - tube furnace (car-bottom type).

L i m i t S w i t c h (for use o n o v e n d o o r s or v e n t i l a t i o n s y s t e m d a m - pers ) m e a n s , a d e v i c e cons i s t i ng of a l e v e r a n d s u i t a b l e c o n n e c t i n g m e c h a n i s m to a s w i t c h c o n t a c t .

N O T E : By swinging"the door or damper to a predetermined position, usually wide open, where it moves the lever, the switch contact is made. Limit switches are used mostly for safe lighting-off sequence to ensure the doors or dampers will be wide open or positioned for preventilation before electric-ignition or fuel will 'be made available for lighting up burners, or power is available for energizing electric-heaters.

L i q u e f i e d P e t r o l e u m G a s m e a n s a n y m a t e r i a l w h i c h is c o m p o s e d p r e d o m i n a n t l y of a n y of t h e f o l l o w i n g h y d r o c a r b o n s , o r m i x t u r e s of t h e m : p r o p a n e , p r o p y l e n e , b u t a n e s ( n o r m a l b u t a n e o r i s o - . b u t a n e ) , a n d b u t y l e n e s .

N O T E : The composition of liquefied petroleum gases varies, but in all the established grades the predominant compounds are propane and butane (iso-butane and normal butane). Under moderate pressure, the gases liquefy, but upon relief of the pressure are readily converted into the gaseous phase. Advantage of this characteristic is taken by the' industry, and for convenience, the gases are shipped and stored under pressui'e as - liquids. When in the gaseous state, these gases present a hazard comparable to any flammable natural or' manufactured gas, except tha t being heavier than air, ventilation requires added attention. The range of combustibility is slightly narrower and lower than that of natural gas. When below 30 ° F, butane is a liquid and the hazard is similar to that of a flammable liquid.

Propane is liquid at atmosphere pressure at temperatures below minus 44 ° F. Flash vaporization takes place at temperatures above the boiling points (butane above 30 U F; propane above minus 44 ° F).-

Mixtures of liquefied petroleum,gases and air are distributed by public utilities through gas systems for use in place of commercial manufactured gas or natural gas and may satisfactorily be used in equipment designed for use with those gases. Such mixtures shall be considered equivalent of com- mdrcial manufactured gas or natural gas except that provision should be made for ventilation based on these mixed gases being heavier than air.

Low P r e s s u r e A i r S y s t e m ( a i r p r e s su re u p to 5 psig) m e a n s a sys tem u s i n g t h e m o m e n t u m of a j e t of low p r e s s u r e a i r to e n t r a i n gas to p r o d u c e a c o m b u s t i b l e m i x t u r e , w h e r e all, o r n e a r l y all, o f the a i r r e q u i r e d ' f o r c o m b u s t i o n is s u p p l i e d b y s e p a r a t e m e a n s s u e h as a c o m b u s t i o n a i r b lower .

Low P r e s s u r e G a s o r " A t m o s p h e r i c " S y s t e m (gas p r e s s u r e less t h a n 0.5 p s ig ) m e a n s a s y s t e m u s i n g t he m o m e n t u m of a j e t of low p re s su re gas to e n t r a i n f r o m t h e a t m o s p h e r e a p o r t i o n of the a i r r e q u i r e d for c o m b u s t i o n . '

• M e c h a n i c a l M i x e r m e a n s a m i x e r u s ing m e c h a n i c a l m e a n s to mix gas a n d air , n e g l e c t i n g e n t i r e l y a n y k i n e t i c e n e r g y in t he gas a n d a i r , a n d c o m p r e s s i n g t he r e s u l t a n t m i x t u r e to a p r e s su re s u i t a b l e for d e l i v e r y to i ts p o i n t of use.

N O T E : Mixers in this group utilize either a centrifugal fan or some other type of mechanical compressor with a proportioning device on its intake through which gas and air are drawn by the fan or compressor suction. The proportioning device may be automatic or require manual adjustment fo maintain the desired air/gas ratio as rates of flow are changed.

Mechanical S y s t e m m e a n s a s y s t e m w h i c h p r o p o r t i o n s a i r a n d gas a n d m e c h a n i c a l l y c o m p r e s s e s t h e m i x t u r e for c o m b u s t i o n p u r p o s e s . .

N O T E : A central mixing unit may be used or individual appliances may each have its own mixer.

M i x i n g B l o w e r m e a n s a m o t o r - d r i v e n b l o w e r to p r o d u c e a i r - gas m i x t u r e s fo r c o m b u s t i o n t h r o u g h o n e o r m o r e gas b u r n e r s o r nozzles o n a s ingle z o n e i n d u s t r i a l h e a t i n g a p p l i a n c e or o n e a c h con t ro l z o n e of a m u h i - z o n e i n s t a l l a t i o n .

N a t u r a l G a s m e a n s a m i x t u r e of gases, p r i n c i p a l l y . m e t h a n e a n d e t h a n e O b t a i n e d f r o m gas wells, a n d f r o m w h i c h less vo la t i l e h y d r o - c a r b o n s s u c h as p r o p a n e a n d b u t a n e h a v e b e e n r e m o v e d , l e a v i n g a m i x t u r e of gases w h i c h wi l l r e m a i n in t he gaseous s t a t e a t a l l p ressures a n d t e m p e r a t u r e s e n c o u n t e r e d in t he d i s t r i b u t i o n sys tem.

O i l B u r n e r T y p e s .

A i r o r S t e a m A t o m i z i n g m e a n s oil ' d i v i d e d i n t o a f ine s p r a y b y an a t o m i z i n g a g e n t , s u c h as s t e a m or a i r .

d~

86A-24 OVENS AND F U R N A C E S

Rotary means oil atomized by centrifugal force, such as applied by a whirling cone or plate.

Pressure Atomizing means oil under high pressure forced through small orifices.

Vapor means oil vaporized by heat.

Operator means the individual responsible for the light-up, operation, shutdown, and emergency handling of the specific installation, consisting of the oven and the associated, equipment.

O v e n means any heated enclosure operating at approximately atmospheric pressure used by industry for the processing of materials. (Except where specificall3/stated, the words ovens and furnaces are used interchangeably.)

Batch Process Ovens means ovens into which the work charge is introduced all.at one time so that the ev.aporation of f lammable volatiles within the oven is not at a constant rate.

Continuous Process Ovens means ovens into which the work charge is more or less continuously introduced, 'as by a conveyor, so that the evaporation of f lammable volatiles within the oven ap- proaches a constant rate.

Photoelectric, Infrared and..', Ultraviolet Detecting Device means a detector based on the radiant energy of specific wave lengths

-gf. the flame, and the current passing through the detector is amplified by the combustion safeguard to actuate suitably arranged relays to make or interrupt the .power to the fuel safety shut-off valves.

Pi lot means a flame that is issued to light the main burner.

Continuous Pilot means a pilot that burns without turndown- throughout the entire period that the heating equipment is in service whether or not the main burner is firing.

Expanding Pilot means a pilot tha t burns at a set turndown throughout the entire p e r i o d that the heating equipment is in service whether or not the main burner is firing, but during lighting- off, it is expanded (burns without turndown) to ignite the main burner reliably.

InterrMttent Pilot means a pilot .which burns during lighting- off and while the main burner is firing, and which is shut off with the main burner.

Interrupted Pilot means a pilot which burns during the entire pilot-flame-establishing period a n d / o r trial-for-ignition period, and which is cut off (interrupted) at the end of this period(s) or during firing.

I N T R O D U C T I O N 8 6 A - 2 5

Proved Pilot means a pilot flame supervised by a combustion safeguard which senses the presence of the pilot flame and which is located where it will reliably ignite the main burner before per- mitting the main-burner fuel safety shutoff valve to be opened.

Pilot-flame-establlshing Period means the interval of time during lighting-off in which a safety-control circuit permits the pilot fuel safety shutoff valve to be open before the combustion safeguard is required to prove the presence of the pilot flame.

Pressure Switch.

Bellow-Operated Pressure Switch means a pressure switch used for higher pressures, and generally similar in operat ing prin- ciple to the d iaphragm type, except that a flexible metal bellows replaces the diaphragm.

H i g h Fuel Pressure Switch means a pressure activated device arranged to effect a safety .shutdown of the burner or burners or prevent the burner or burners from starting in the event of abnormal ly high fuel pressures.

Low Fuel Pressure Switch means a pressure activated device arranged to effect a safety shutdown of the burner or burners f. or prevent the burner or burners f rom starting in the event of abnormal ly low fuel pressure.

A tomiz ing Medium Pressure Switch means a pressure activated device arranged to effect a safety shutdown or to prevent the oil burner or burners f rom starting in the event of inadequate atomizing medium pressure.

Combus t ion Air Pressure Switch means a pressure activated device arranged to effect a safety shutdown or to prevent the burner or burners f rom starting in the event the combust ion air supplied to the burner or burners falls below that recommended by the burner manufacturer .

Diaphragm-operated Pressure Switch means a pressure switch used for low pressures, generai ly not exceeding several pounds per square inch.

NOTE: The diaphragm suitable for the fluid being handled bears against. a lever controlling a switch contact. A spring/with tension adjtugtment.for pressure setting, provides cotinterthrust to the diaphragm..

Preventilatlon T i m e De lay Re lay means a switch which is closed automatical ly after a preset time interval usually measured by a timing device.

NOTE: Such a relay should be arranged to reset instantly to the starting. position when the current'supply is interrupted.

86A-26 O V E N S A N D F U R N A C E S .

P r i m a r y Air means all air supplied through the burner, including ~ L I O I I I I Z I I I ~ ~ l l l k l Et.)I~tJLkJLIDLI'OII ai]X ~,

Producer Gas means any gas formed by blowing air through incandescent coal, coke, or charcoal.

NOTE: Such gases often contain solid particles and carry liquids which cause difficulty in burner operation. Special design is needed and automatic control is often difficult.

The use of producer gas for heating systems should be restricted" to equiprn.ent under constant supervision of a qualified operator. Plans for producer gas equipment, distribution systemsand oven heating systems should be submitted to the 'authority having jurisdiction for approval. The use of other types of gases is recommended.

Proper Vent i l a t ion means a Sufficient supply of fresh air and proper exhaust to outdoors with a sufficiently vigorous and properly distributed air circulation to ensure that the f lammable vapor concentrat ion in all parts of the oven or dryer enclosure will be safely below the lower explosive limit at all times.

Proportioning In sp i r a to r means an inspirating tube which, when supplied with gas, will draw into the gas stream all the air necessary for combustion.

P r o p o r t i o n i n g Mixe r means a mixing device comprised of an inspirator which, when supplied with air, will draw into the air s tream all the gas necessary for combustion and a gas governor, zero regulator, or ratio valve which reduces incoming gas pressure to approximately atmospheric (see Figure 1-4. 14).

t• NSPIRATOR

~ M~xvu~E N ~ / c ° " ' " ° L

I;122Z I ~ ' ~ " VALVE

Figure 1-4.14 Typical Low Pressure Air System.

/

INTRODUCTION 86A-27

Proportioning System (automatic proport ioning system) means a combinat ion of one or inore burner tips,, nozzms or other• firing heads and a -propor t ion ing device intended to supply a gas-air mix tu re to the firing point in proper proportions for combustion.

NOTE: Similar devices with additional controls to permit operation with control d~vices between burner and proportioning device are governed by 3-3.6.3.

Resis tance H e a t e r means any elecfi'ie heater in which, heat is produced by current flow through a resistive conductor.

NOTE: Resistance heaters may be of "open" type with ]6are heating

Rotat ional S w i t c h (for ventilation interlocking) is a device which is usually driven directly by the fan wheel or fan motor shaft, and when the speed of the fan shaft or drive motor reaches a certain predetermined rate, which will give a safe m in imu m air flow, a switch-contact closes.

Safe-start Check means a checking circuit incorporated in a safety control circuit that prevents iighting-off if the flame-sensing

"relay of the combustion safeguard is i n t h e unsafe (flame-present) position due to component failure within the combustion safeguard or due to the presence of actual or simulated flame.

Safety Shu to f f Valve means a normally closed (closed when de- en&gized) automat ic valve installed in the fuel piping to shut. off the fuel in the event of unsafe conditions or during shutdown periods.

Electric, Manual-openlng, .Automatic Closing Safety Shut- off Valve means a valve which can be opened only after the valve -solenoid coil is energized and must be opened manual ly by means of a suitable "free-handle" and de-energizing the valve solenoid coil

• automatical ly closes the valve.

Electric. Opening, Automatic Closing Safety Shutoff Valve means a valve which opens automatical ly on energizing the valve actuating device, and closes automatically on de-energizing the actuating device.

Mechan ica l , Pressure-operaied Safety Shutoff Valve means a valve, wh ich must be opened manual ly but atitomatically shuts off the fuel supply if the fuel a n d / o r air pressure necessary for proper.atomization or combustion falls below predetermined values.


NOTE: These pressure settings are usually the minimum values for stable combustion and safe operation. These valves must be reopened manually but will reclose when the hand is removed unless the fuel and/or air pressure has been restored to above the set point.

Secondary Air means all of the air tha t is intentionally al lowed to enter the furnace, but which does not pass through the burner nozzle.

Suction System means a system apply ing suction to a combust ion chambe r to draw in the air a n d / o r gas necessary to produce the desired combust ible mixture.

Supervised Flame means a flame whose presence or absence is detected by a combust ion safeguard.

Supervising Cock means a special approved cock incorpora t ing in its design means for positive inter locking with a main fuel safety shutoff valve so that before the main fuel safety shutoff Valve can be opened all individual burners supervising cocks must be in the full closed position.

E lec t r i c I n t e r l o c k i n g T y p e of Supervising Cock means a convent iona l s t ra ight- through cock with a special buil t - in switch assembly protected against tamper ing, and arranged so that switch contacts are closed only when the cock is in the fully closed position.

NOTE: This type of supervising cock is suitable for both gas or oil fuels (see Figure 1-4.15). The switch contacts of all cocks are wired in series in the safety control circuit so that all supervising cocks must be closed before the main fuel safety shutoff valve can be opened.

Figure 1-4.15.

T~TR~TT~T~T Q~ A ~Ck

Pneumatic T y p e of S u p e r v i s i n g Cock means a special approved cock similar to the usual burner gas cock, except that it has two side outlets which furnish a small independen t passageway which is opened only after the main gas passage is complete ly closed.

NOTE: The key way width is narrow enough in respect to the size and proportions of the main gas ports to ensure positive closure of the main gas way before opening the side outlets. This particular type of supervising cock is not suitable for fuel oil (see Figure 1-4.16).

To Burner

%, 11 /k

J

| Handle riveted to ke~ ~ er~lequipped w i t h / I I quarter-turn stop*. U

• igure i-4.16 Supervising Cock (F.M. Cock).

Temperature Controller means a device which measures the t empera tu re au tomat ica l ly and controls the heat input of the burner .

Excess Temperature Controller means a similar uni t designed to cut off the source of hea t if the t empera tu re control ler fails to operate proper ly on fai lure of the p r imary sensing element.

qT~ t,O


Trial-for-ignit ion Period (Flame-establishing Period) means that interval of time during lighting-off in which a safety control circuit permits the fuel safety shutoff valve to be open before the combustion safeguard is required to supervise the flame.

T w o V a l v e System means a system ' using separate control of air and gas, both of which are under pressure.

NOTE: The valves controlling the air and gas flows may or may no.t be interlocked.

Vent i la ted means provided with a method to permit circulation -of air sufficient to remove-an excess of heat, fumes or vapors.

Vent i lat ion Controls means devices such as flow switches, pressure. switches, "fan shaft rotation detectors, dampers, position limit switches, time delay relays and electrical interlocks which are placed in the system'to ensure adequate ventilat]on-prior to establishing the source of heat and during the operation of the heating equipment.

Zero Governor , also called "atmospheric regulator," means a diaphragm-type regulator that maintains the fuel-gas pressure at atmospheric or zero gage pressure.

1-5 Approvals, Plans, and Specifications.

1-5.1 Before new equipment is installed or existing equipment remodeled, complete plans and specifications shall be submitted for approval to the authority having jurisdiction. Plans shall be drawn to an indicated scale, and show all essential details as to location, consti'uction, ventilation duct work, volume of fresh air at 70°F introduced for safety ventilation, heater equipment, fuel piping, heat input, and safety control wiring diagrams. The plans shall include a list of all equipment giving manufacturer and type number.

NOTE: For illustration purposes only and not to show sequencing of devices.

1-5.2 Wiring diagrams and sequence of operations for all safety controls including "ladder type" schematic drawings shall be provided (see Figure 7-5.2):

1-5.3 All wiring in and around ovens shall be in accordance with the National Electrical Code (NFPA 70-1978) and as described hereafter.

• 1-5A Any material deviation from this standard will require special permission from' the authority having jurisdiction.

INTRODUCTION 86A:-31

I' ~ o ~ ' R o - c , R c u , T VOLTAGE ~I CL~E ELECT~C~

SCANNER ASSEMBLY

' ~ ~ G A S

P I L O o P E R A T I N G $1GNAL~" FROM FLAME

LINE TERMINALS OF I S C A N N E R OR FLAME ROB O FLAME SUPERVISION O

l . . . . . . . . . . . , . . . . . . . I . . . . . . . . I SUPERVISION CONTROL TO OPEN WITH F L A M E PRESENT A L A R M SILENCER SWITCH A L A R M

V E N T I L A T I N G DOOR L I M I T A'IR FAN STARTER ~" SWITCH E FLOW . " I N T E R L O C K BATCH 0VENI 1 SWITCH ' .)~ f

T -. E . . . . . L . . . . . . . . . [ :. I AIR GAS GAS R

TEMPERATURE ~, / SWITCH • ~ ! P ILOT

PRESSURE SWITCHES COMBUSTION START P R AIR BLOWER

[ ~ IO_..~,_~ B U T T O N IGNIT ION " , U GE INTERLOCR ~ . ~ T R A-NS.

" TIMER CONTACT . . . . . . . . . . C L O S E S / ~ ~ ~ ' - , ! ~ . . . . . . AT END OF P U R G I N G - - ~ "~ f% IS 'SEC t

4 . . . . . . . . . E i~ C.NOES F . . . . . .

P[LOT SOL, VALVE NOTE: ~ TO CLOSE ONLY WHEN RESPECTIVE MOTORS ARE ENERGIZED WITH POWER

" OFF VALVE N,O, CONTACTS OF FLAME i

AUX, GIG. SW. ON S,S,O.) '1 I . . . . . . . . E . . . . . . . . . . . . ÷ . . . . - - o ~ o - - ~,

MOTORIZED ~ I t I

. . . . . . . . . . . . . T: AL/E ,--~1

DE&D- MAN TYPE "O~ 'C~-I

I MOMENTARY SWITCH FOR VALVE LEAKAGE TESTING

Figure 1-5.2 Typical "Ladder Type" Schematic Diagram.

1-6 Operator Tra in ing .

1-6.1 New operators shall be thoroughly instructed and shall demonstrate an adequate 'understanding of the equipment and its operations.

NOTE: It is fully recognized that the most essential safety consideration is the selection of alert and competent-operators. Their knowledge and training are vital to continued safe operation.

1-6.2 Regular operators slaall receive scheduled retraining to maintain a high level of proficiency and effectiveness.

d;L

t ~

86A-32 OVENS AND FURNACES,

1-6.3 Operators shall have access to operat ing instructions at all times.

1-6.t Opera t ing instructions shall be provided by the equip- men t manufacturer . These instructions shall include schematic piping and wiring diagrams. Light-up, shutdown, and emergency procedures shall be available in a suitable location near the facility.

1-6.5 Opera to r t ra ining shall include:

(a) Combust ion of air-gas mixtures.

(b) Explosion hazards.

(c) Sources of ignit ion and ignition temperature.

(d) Funct ions of control and safety devices.

1-7 S a f e t y D e s i g n D a t a F o r m f o r S o l v e n t A t m o s p h e r e O v e n s .

1-7.1 A suitable, clearly worded, and prominent ly displayed oven safety design data form shall be provided by the bui lder of each oven stating the safe operat ing conditions for which the oven was designed and built , and disregard of which m a y - p u t the ap- paratus in jeopardy of failure to funct ion safely, and cause it to become liable to destruction by fire or explosion.

1-7.2 Da ta shall be furnished on approved forms similar to Figure 1-7.2. They shall be prepared in quintupl icate , the original to be on a good qual i ty l ightweight card which is to be inserted in a metal frame fastened to the equ ipment and protected either with a glass or clear plastic cover. The other f6ur sheets, which are to be exact duplicates and serve as file copies of the original, may be a l ightweight paper of sufficiently good qual i ty to preserve as a record:

INTRODUCTION 86A-33

MANUFACTURERS SERIAL NUMBER ~AFETY DESIGN FORM

. . . . . . . . . . . . . . . . . . . . . . . . FOR SOLVENT ATMOSPHERE OVENS"

THIS OVEN IS DESIGNED FOR THE CONDITIONS kS INDICATED BELOW, AND IS APPROVED FOR SUCH USE ONLY

W A R N I N G - - D o n o t d e v i a t e f r o m t h e s e c o n d i t i o n s

NAME OF OWNER ..................................................................................................

. LOCATION .................................................... ' ............................ : ................................. City State Plant Building Floor

PURPOSE .............. : ....................................... : .......................................................... : For Example: Baking: Paint, Enamel, Japan, Food. Dehydrating-- Heat Treat ing- Curing.

KIND OF MATERIAI~ HANDLED .............................................. : ................... For Example: Wood, Paper, Textiles, Foods, Metal, Mineral8

LBS. OF MATERIAL PER HOUR OR PER BATCH .......................................

TYPE OF HEATING 'SYSTEM ........................ HEAT MEDIUM .................... For Example: Convection, Radiant, Induction For Example, Gas, Oil, Electricity, Steam

SOLVENTS USED .................................................................................................... For Example, Alcohol, Naphtha, Benzol, Turpentine

SOLVENTS AND VOLATILES ENTERING OVEN .................................... Gallons Per Batch or Per Hour

PURGING INTERVAL ............................................................................................

DO PRODUCTS OF COMBUSTION ENTER OVEN? ................................ Yes No

OVEN TEMPERATURE, DEG. F .........................................................................

OVEN DIMENSIONS .................................................... VOLUME .................... Inside Length, Width, Height In Cubic Feet

FRESH AIR ADMITTED INTO OVEN IN CU. FT./MIN. (70°F.) ................

(THIS SPACE RESERVED FOR MANUFACTURER'S NAME)

Abo~'e information is for checking safe performance and is not a guarantee of this equipment in any form, implied or otherwise, between buyer and seller relative to its performance.

F ig ur e 1-7.2 Typ ica l Safety De s i gn F o r m

t ~


t

f'k---~---- 0 • ^ ~ - d - " . . . . .] /'~^--.4. . . . . ~.'----,

2-1 Location.

2-1.1 General.

NOTE: Ovens, oven heaters, and related equipriaent should be located with consideration to the possibility of fire resulting from overheating or from the escape of fuel and the" possibility of building damage and personal injury resulting from an explosion.

2-1.2 G r a d e Location.

2-1.2.1 Special considera t ion shall be g iven . to t he locat ion of Class A equ ipmen t processing f l ammable mater ia ls or when using fuels wi th a specific g rav i ty grea ter than air.

NOTE: Class A ovens and furnaces should be located at or above grade to make maximum use of natural ventilation and to minimize restrictions to adequate explosion relief. However, Class A equipment may be located in basements where additional consideration has been given to ventilation and the ability to safely provide the required explosion relief. (See NFPA 68-1974, Explosion Venting Guide.)

2-1.3 Structural Members of the Building.

2-1.3.1 O v e n s and furnaces shall be located and erected so tha t the bui ld ing s t ruc tura l members will not be adverse ly affected by the m a x i m u m an t i c ipa ted tempera tures (see 2-/. 5).

2-1.3.2 S t ruc tu ra l members passing th rough ovens having an opera t ing t empera tu re less than 500°F shall be of noncom- bust ible mate r ia l and fireproofed.

2-1.4 Location in Regard to Stock and Other Processes.

• 2-1.4.1 Valuable Stock.

NOTE: Ovens and furnaces should be well separated from valuable stock, • important power equipment, machiner)/and sprinkler risers, thereby secur-

hag a minimum interruption to production and protection in case of accidents to the oven or furnace.

2-1.4.2 P e r s o n n e l . Furnaces and ovens shall be located to" minimize exposure to people f rom the possibil i ty of i n j u r y f rom fire, ~explosion, asphyxia t ion, and toxic mate r i a l s , and shall no t obst ruct personnel t ravel to exitways.

• 2-1.4.3 F i n i s h i n g Operations.

2-1.4.3.1 Indus t r i a l •ovens and furnaces ( e x c e p t - t h o s e hea ted by steam) shall be safely located and pro tec ted f rom exposure to d ip tanks, spray booths, s torage and mixing rooms for f l ammable

LOCATION AND CONSTRUCTION 86A-35

liquids, or s torage a r e a s used for readi ly f l ammable mater ia ls , or exposure f rom or to the diffusion of f l ammable vapor a i r mixtures•

NOTE 1: The hazard is particularly severe when vapors from dipping operations may flow by gravity to heating units at or near the floor level• (,See NFPA 30-1976, NFPA 33-1973, and NFPA 34-I974.)

NOTE 2: The use of combined dipping and. baking, and spraying and baking, units is permissible when adequately ventilated.

2-1.4.3.2 T h e room in which f l ammable vapors a re produced shall b e vent i la ted in such a m a n n e r tha t the a tmosphere in the vic ini ty of pa in t ing opera t ions will be kep t well below the lower explosive l imit . F low of vent i la t ing a i r f rom pa in t room or a rea shall be away f rom the ovens or heaters.

2-1.5 Floors and Clearances.

2-1.5.1 Ovens shall b e located so as to be readi ly accessible with a d e q u a t e space above oven to pe rmi t ins ta l la t ion of automat ic sprinklers, the p roper funct ioning of explosion vents, inspection and main tenance . Roofs ,and floors of.ovens shall be insulated, and the space above and below vent i la ted, to keep t empera tu re s at combust ib le ceilings and floors below 160°F.

2-1.5.2 I f oven locat ions On noncombus t ib le f loo~ are not avai lable , then sufficient insulat ion and vent i la t ion shall be provided to pro tec t t h e combust ib le floor f rom d a m a g e by fire, and wood de te r io ra t ion due to l o n g - t i m e hea t exposure2

2-1.5.3 T h e follow!ng procedure shall b e - o b s e r v e d if the oven is located in contac t wi th a wood or o ther combus t ib le floor and the olSerating t empe ra tu r e is above 160°F:

(a) Remove the wood or o ther combus t ib le floor and re- place it wi th a concrete slab extending a t least 12 in. beyond the

• oven outl ine.

(b) I f the combust ib le floor is not removed, provide hol low tile or steel tunnels on top of floor ex tending to oven oud ine and laid to fo rm cont inuous air channels para l le l wi th short ax i s of the oven wherever possible, open at both ends; for air movemen t so tha t the surface t empe ra tu r e of the floor will not exceed 160 ° F. I f the t empe ra tu r e at the combust ib le floor surface exceeds 160 ° F, then the a i r channels shall be connected on one end t o ' a vent duct , of a d e q u a t e size, l ead ing to a stack d ischarging to the a tmosphere and p rov ided wi th mechan ica l vent i la t ion.

(c) W h e n the s u p p o r t i n g f l o o r is of concrete, s t ee lchanne l s , or hol low tile, for opera t ing t empera tu res above 300 ° F , the oven floor shall be fur ther insulated w i t h s u i t a b l e ma te r i a l eqt i ivalent in insulat ing value to tha t used for oven walls and roof, and sui tably


enclosed or covered for protect ion against mechanica l d a m a g e or abrasion. T h e external t empera tu re of the floor near the oven shall not exceed 250 ° F.

NOTE: Insulating cement for 700°F oven heat may be diatomaceous earth or its equivalent mixed with cement, and the thicknesses used-should be : 2 in. for 300 ° F oven heat 4 in. for 500 ° F oven heat 3 in. for 400 ° F oven heat - 5 in. for 600 ° F oven heat

6 in. for 700 ° F oven heat

(d) W h e r e electr ical wir ing will be present in the channels of cer ta in types of floors, the wir ing shall be instal led in accordance with Art icle 356, Cel lu lar M e t a l F loor Raceways , of the National Electrical Code ( N F P A 70-1978).

(e) Combus t ib le floors in immedia t e a rea of oil burners shall be covered with noncombus t ib le mate r ia l in such a m a n n e r tha t the floor cannot become oil soaked. (See the building code having iurisdiction.) A d e q u a t e protec t ion f rom heat and f rom fuel spil lage shall be provided for combust ib le floors under heaters.

2-1.5.4 W h e r e oven ducts or stacks pass th rough combust ib le walls, floors or roofs, adequa te insulat ion and clearances shall be provided to prevent surface t empera tu res of combust ib le mater ia l s exceeding 160 ° F.

2-1.5.5 Combus t ib le work benches and o ther combust ib le equ ipmen t shall n o t b e located within two feet of an oven, oven heater , or ductwork.

2-2 Construct ion .

2-2.1 Genera l .

2-2.1.1 Ovens and re la ted equ ipmen t shall be bui l i in a substant ia l m a n n e r wi th due regard to the" fire haza rd inherent in equ ipmen t opera t ing at e levated temperatures , the haza rd to operators f rom high tempera tures , open flames and mechanica l equipment and the need of ensuring rel iable, safe opera t ion over the expected m a x i m u m life of the equipment .

2-2.2 Materials .

2-2.2.1 Ovens and furnaces shall be const ructed of noncom- bust ible mater ials .

2-2.2.2 Fu rnace s t ructura l supports and conveyors shall be designed with adequa t e factors of safety at the m a x i m u m opera t ing temperatures , considerat ion being given to the strains imposed by expansion.

LOCATION A N D C O N S T R U C T I O N 86A-37

2-2.2.3 Adequa t e facilities for access shall be provided to pe rmi t p roper inspection and maintenance.

2-2.2.4 Burners and hea t ing elements of al! types shall be substant ia l ly const ructed or gua rded to resist mechanica l damage .

2-2.2.5 W h e r e ref rac tory mater ia ls are used, they shall be adequa te ly suppor ted .

2-2:2.6 Corrosion Resistan/ze. Where subject to corrosion, metal par ts shall be protected.

2-2.2.7 Access ib i l i ty a n d M o u n t i n g of Controls . Provision shall be made for the rigid a t t achmen t of control devices. Com- bustion safeguard mounts shall be a r ranged so tha t the e lect rode or o ther f lame de tec t ing e lement is correct ly posi t ioned. Valves and control panel shall be so located tha t all necessary observation. and ad jus tmen t m a y be readi ly made.

2-2.2.8 All par ts of equ ipment opera t ing at e levated tempera tures shall be instal led in accordance with 2-1.5.

2-2.2.8.1 W h e r e imprac t ica l to guard , warn ing signs or p e r m a n e n t floor markings shall be provided or moun ted to be visible to personnel enter ing the area.

NOTE 1 : Exterior of furnaces in excess of 160 ° F (71 ° C) should be guarded by location, guard rails, shields or insulation to prevent accidental contact with personnel.

NOTE 2: Bursting discs or panels, mixer openings, or other parts of the furnace from which flame or hot gases may be discharged should be located or guarded to prevent injury to personnel..

2-2.2.9 Proper ly located observat ion ports shall be provided to pe rmi t the opera to r to observe the l ight ing of indiv idual burners.

2-2.2.10 Devices such as relief valves, open sight drains, and water flow switches f rom water cooling systems shall be designed and instal led for ready observation by opera tor .

2-2.2.11 Fuel-f i red heaters shall not be located di rec t ly under the p roduc t being hea ted where combust ib le mater ia l s may drop and accumula te . Nei ther shall they be loca ted di rec t ly over readi ly igni ted mater ia l s such as cot ton unless for contro l led exposure time, as in cont inuous processes where fur ther a u t o m a t i c provisions a n d / o r a r r angemen t of gua rd baffles preclude the possibil i ty of ignition.

2-2.2.12 T h e metal frames of ovens shall in all cases be electr ical ly g rounded th roughout "for the safe removal of static

\


electric charges. (See Recommended Practice on Static Electricity, NFPA 77-1972.)

2-2.3 Explosion Vents.

2-2.3.1 Ovens which may contain f l ammable l iquids, ~;apors, or gases shall be equ ipped with unobs t ruc ted relief vents for freely rel ieving internal• explosion pressures, and cons t ruc ted " in accordance with N F P A 68-1974.

2-2.3.2 Explosion relief panels shall be p ropor t ioned in the ra t io of their a r e a in square feet to the explos ion-conta in ing volume of the oven, due a l l owance being made for o p e n i n g s or h inged panels or access doors equ ipped with app roved explosion: rel ieving ha rdware .

NOTE' The preferred ratio is 1:15, i.e., one square foot of relief panel area to every fifteen cubic feet of oven volume. For those fuel-fired ovens in which there is no flammable or explosive solvent hazard, equipped with

• all recommended fuel safety devices, an explosion venting ratio'of 1:30; i.e., one square foot of vent ratio to every thirty cubic feet of oven volume should be permitted.

2-2.3.3 Arrangement of Explosion Vents.

2-2.3.3.1 Explosion vent ing panels or doors shall be arranged so that , when open, the full vent opening will be an efl'ective rel ief area. In instal lat ion, care shall be taken to make sure tha t the opera t ion of relief vents to their full capac i ty is not obs t ruc ted by l o w ceilings, piping, bui ld ing columns, or walls, ins t rument panels, or o ther fixed equipment .

NOTE 1 : These vents should preferably be provided in the form of gravity retained roof "panels designed .to afford adequate insulation and possess the necessary structural strength• ,

NOTE 2: Guard rails may be needed to prevent movable equipment from being placed so as to obstruct such vents.

NOTE 3: Explosion relief vents, where possible, should be placed in the top of the oven or in side walls and located so that employees will not be

• exposed to injury.

2-2.3.3.2 Exp los ion relief vents for long ovens shall be reasonably d is t r ibu ted th roughou t the ent ire oven length.

2-2.3.3.3 See N F P A 68-1974, Explosion Venting Guide.

2-2.4 Duct Work.

2-2.4.1 Wheneve r oven ducts or stacks pass th rough combust ible walls, floors, or roofs, noncombus t ib le insulat ion or c lear- ance or both shall be provided to prevent surface , t empera tures eXceeding 160 ° F.

LOCATION AND CONSTRUcTIoN 86A-89

NOTE: The oven "location should permit the shortest and most direct path for ducts (exhaust or relief) to discharge to atmosphere.

2-2.4.2 Ducts shall be const ructed ent i re ly of sheet steel or o ther noncombus t ib le mater ia l , and of adequa t e s t rength and r igidi ty to meet the condi t ions of service and insta l la t ion requirements, and shall be pro tec ted w h e r e s u b j e c t to physical damage .

2-2.4.3 No rooms or por t ions of the bu i ld ing shall be used as an in tegra l pa r t of the system.

NOTE: The entire duct system should be self-contained.

2-2.4.4 All ducts shall be made t ight th roughou t and shall have no openings o ther than those requi red for the opera t ion and main tenance of the system.

2-2.4.5 All ducts shall be thoroughly braced where requi red and substant ia l ly suppoi-ted by meta l hangers or brackets .

NOTE :. All laps in the duct joints should be made in the direction of the air flow.

2-2.4.6 W h e r e ducts pass th rough noncombus t ib le walls; 1f loors , or par t i t ions , the space a round the duc t shall be sealed wi th

n o n c o m b u s t i b l e mate r ia l to prevent the passage of f lame and smoke.

NOTE: The passing of ducts through fire wails should be avoided.

2-2.4.7 Ducts handl ing fumes which leave a combus t ib le deposi t shall be p rov ided with c leanout doors. Such ducts shall be const ructed of not less than 16 gage steel or equivalent .

2-2.4.8 H a n d holes for dampe r , sprinkler , or fusible link • inspection or resett ing, and for purposes Of residue c leanout shall be equ ipped with t ight-f i t t ing doors or covers provide d with sub- s tant ial latches, except in the case of ver t ical sl iding door s held in place by gravity.

2-2.4.9 D a mper s in the ducts which affect the volume of fresh a i r admi t t ed to and vapors or gases exhaus ted f rom the oven shall be designed so that , when in closed position, they wiB pass the vo lume requi red for safe vent i la t ion. I f e lectr ical ly or mechanica l ly control led damper s are used, l imi t switches shall be uti l ized to assure p rope r pos i t ion of the dampers , inc luding those used as gas barr iers on carbon d ioxide ext inguishing systems.

2-2.4.10 T h e oven and its locat ion shall be designed to prevent excessive emission of ob jec t ionable fumes into the building.

2-2.4.11 All ~xposed hot fan casings and hot ducts wi th in 7 feet of the b u i l d i n g floor shall be pro tec ted to prevent in jury tO p e r s o n n d ( t empera tu re n o t t o exceed 160°F).

86A-40 O V E N S AND F U R N A C E S

2-2.4.12 Exhaust ducts shall not discharge near doors, windows, or other air intakes in a manner that ,will permit re- entry of vapors into the building.

NOTE: All air inlets outside the oven should be protected by coarse screens and so guarded that they cannot be obstructi:d.

2-2.4.13 All external exhaust duct work shall conform to NFPA 91-1973, Blower and Exhaust Systems.

2-2.5 Access, Mountings, and Auxiliary Equipment. 2-2.5.1 Adequate facilities for access shall be provided to

permit proper inspection and maintenance.

NOTE: When such openings are intended to permit persons to climb inside for inspection and cleaning, there should be provided such additional equipment as ladders, Steps, and:grab-rails to permit safe and easy access and egress.

2-2.5.2 Mountings for auxiliary equipment shall provide for rigid mounting of control instruments and safety devices protected against injury by heat, vibration, and mechanical equipment.

2-2.5.3 Where ladders or steps are needed to reach valves or other controls, 'they shall be noncombustible and provided as an integral part of the equipment.

2-2.5.4 Auxiliary equipment such as conveyors, racks, shelves, baskets, and hangers shall be noncombustible and designed, to facilitate cleaning.

2-2.6 Hydraul ic Systems. 2-2.6.1 When petroleum oils or other combustible fluids

must 'be used for door operation, lifts for work loads, and conveyor systems, the hydraulic system shall be designed to minimize the possibility of fluid release which may result in a fire or explosion.

NOTE: The use of fire resistant fluids is recommended.

2-2.6.2 All components of the hydraulic system shall conform to the standards of the National Fluid Power Association

"and/or ANSI standards in the B93 series.

NOTE: Drawings for fluid power diagrams should follow ANSI Standards Y14.17-1966, and Y32.10-1967.

2-2.7 Fans. 2-2.7.1 Any fan not directly connected to the motor shall

be multiple V-belt driven, suitably interlocked as described in Chapter 5.

2-2.7.2 All moving parts shall be guarded from mechanical accidents or possibility of causing personal injury.

H E A T I N G SYSTEMS 86A-41

Chapter 3 Heating Systems

3-1 Scope.

(a) For the purposes of this standard, the term "heating sys-, tern" shall include the heating source (and assbciated piping/ wiring) and the circulating fans (and associated duetwork) used to convey heat to the furnace and for the work therein. Exhaust systems and ductwork are not included.

(b) The source of heat may be either internal (within the unit) or external (outside the unit). The unit may be direct fuel fired (when the products of combustion contact the work) or indirect fuel fired (where the products of combustion do not contact the work).

(c) The transfer of heat into and throughout the unit may be by convection, conduction or radiation ; or by combinations of these.

(d) Coal (or other solid fuel) firing systems and hot liquid circulating systems are not included in this standard.

3-2 Electrical Wiring. All electrical wiring, and applicable electrical components, shall be in accordance with NFPA 70- 1978, National Electrical Code, and as described hereafter.

3-3 Gas Fired Units.

3-3.1 General.

(a) This section includes combustion systems for ovens/ furnaces fired with standard, commercially distributed t~uel gases such as natural, mixed, manufactured, liquefied petroleum gas (LP-Gas) in the vapor phase and LP-Gas/air systems, and the gas burning portions of dual fuel or combination burners.

(b) For fuel gas data and properties, see Table 1-4.1.

(c) Additional safety considerations which are beyond the scope of this standard shall be given to dirt-laden gases, sulfur-laden gases, high-hydrogen gases, low Btu waste gases, etc., where used.

3-3.2 Burner System Selection. Burners, along with associated m!xing, valving and safety controls and other auxiliary components, shall be properly selected for the intended application, suitable for the type and pressure 'of the fuel gases to be used, and for the temperatures to which they will be subjected.

t ~ O

86AZ42 O V E N S A N D F U R N A C E S "

3-3.3 Gas Supply Pipingl ,9 ,9 *9 ~ r~_'___" _ _ r . . . . . . 1 c ~ _ ~ .I 1, " o-o.o.x r , p , , ~ .ore u,c point of ue,vevy, to the ourner

system shall comply with N F P A 54-1974, National Fuel Gas Code.

3-3.3.2 Installation of L PG storage and handling systems shall comply with N F P A 58-1976, Standard for Liquefied Petroleum Gases.

3-3.3.3 Emergency Shut-off Valves. Valves shall be provided t o permit turnin.g off the fuel in an emergency and shall be loca;,ed,so that fires, explosions, etc., at ovens/fuimaces will not prevent access to these valves. .'

3-3.3.4 Manual Shut-off Valves and Cocks.

3-3.3.4.1 Manua l shut-off valves and cocks shall be provided for shut-off of the fuel to the pilot a n d / o r burner for extended periods of shut down.

3-3.3.4.2 Valves and cocks shall be maintained in accordance with the manufacturer ' s instructions.

NOTE: Particular zittention is directed to the frequency of need for a proper lubricant for lubricated plug cocks.'

3-3.3,4.3 Consideration shall be given to the use of quar ter turn valves.

3-3.3.4.4 I t shall be the user's responsibility to see that separate wrenches (handles) remain affixed to the valve, and that they are properly oriented with respect to the valves port."

3-3.4 Gas Train Piping.

3-3.4.1 Gas train piping is d~fined as that piping which connects f rom the user's gas supply piping (see 3-3. 3. l and 3-3. 3.2) to the air-gas mixing device (or to the burner, if nozzle-mixing).

3-3.4.2 Mater ia l . Material for pipe and fittings shall comply wi th ' the National Fuel Gas Code (NFPA 54-1974).

3-3.4.3 Sizing. Pipe, fittings and valving equipment shall be sized to prevent excessive pressure losses at the max imum rate of flow.

3-3.4.4 M a i n Gas Cock. A main gas shut-off cock shall be located upstream from all other gas line train components to shut off all flow of gas for servicing and for other shutdowns.

3-3.4.5 Pressure Regulator.

3-3.4.5.1 A pressure regulator shall be furnished whenever the p lan t supply pressure exceeds that required for proper

, l

~ J

H E A T I N G S Y S T E M S 8 6 A - 4 3

burner operation or whenever the plant supply pressure is subject to excessive fluctuations.

NOTE: A zero governor is a special type of regulator, "the primary difference being in the outlet pressure delivered.

3-3.4.5.2 Regulators shall be vented to Outdoors or other safe location, with terminating end protected against water entry and bug screened. Vent pipe" shall be of adequate size to not lengthen response time.

Exception: Regulators need not be vented when used with lighter-than-air fuel gases at 1 psig inlet pressure or less, provided that the vent connection contains a restricted orifice and discharges into a space large enough, or ventilated well enough, so the gases ~escaping will not p~esent a hazard.

3-3.4.5.3 V e n t lines f rom multiple regulators, where manifolded together, shall be piped in such a manner t h a t diaphragm rupture of one ~vill not backload t h e others.

NOTE-1': Vents from gas pressure switches, but from no other devices, may be vented into the regulator vent lines .provided that switch failure cannot backload regulator.

NOTE 2 :" Regulators and zero governors may be backloaded from combustion air lines, air-gas mixture lines, and combustion chambers nrovided that gas escapement- through the restricted vent opening will, "in itself, create no additional hazard. • '

3-3.4.5.4 The gas vent line Connected to the normal ly open vent valve, located between the two safety shut-off valves (refer to 5-5.2.5), shall be piped separately into atmosphere.

3-3.4.5.5 Positive shut-off devices shall not be used in the impulse line to the regulator.

3-3.5 Gas Burners.

3-3.5.1 All burners shall maintain a stable flame, with neither flash back nor blow-off, over the entii'e range of tu rndown that will be encountered dur ing operation when supp l i ed with combustion air and the designed fuel gases in the proper proportions and in the proper pressure ranges.

-NOTE: Burner operation may be adversely affected with other than the designed fuel gases.

3-3.5.2 Multiple-port Burners. Line, ribbon, pipe, ring, radiant and d iaphragm type burners "shall perform in accordance with the provisions of 3-3.5.1. In addition, they shall maintain flame stability throughout their entire length ( and /o r surface)- uhder all operat ing conditions that will be encountered. t ~

86A-44 O V E N S AND FURNACES

3-3.5.3 B u r n e r Igni t ion . Burners shall ignite completely, smoothly, and re l iab ly f rom the ignition source provided. If a burner cannot be safely ignited at all firing rates encountered, positive provision shall be made to assure a firing rate suitable for safe light-off at the time of ignition (low fire start).

N O T E : Safety Warning: Multiple small burners manifolded together and mounted on a single heater are usually spaced too far apart to flash across from burner to burner from a single ignition'source, and require that extreme caut ion be exerc ised - - especially at light-off.

3-3.5.4 Seconda ry Air Ad jus tmen t . I f provided, adjustment shall include a locking device to prevent unintentional change in setting.

3-3.6 Air-Gas Mixers .

N O T E : Certain burner/nozzle designs Utilize a full (stoichiometric) or a partial (gas-rich) mixture of air and gas. An appropriate device is then used to mix the air and gas for subsequent delivery to the nozzle(s) or to the mixture piping connecting to the nozzle(s).

3-3.6.1" Air-Gas M i x t u r e P ip ing .

3-3.6.1.1 In the design, fabrication and utilization of mixture piping, continuous consideration shall be given to the fact that the mixture is in the f lammable (i.e., explosive) range and all due precautions shall be exercised.

3-3.6.1.2 Piping shall be designed to provide uniformity of transverse velocity at the nozzle(s) to the degree required by the nozzle(s).

N O T E : This generally requires a minimum straight run of approximately four pipe diameters immediately upstream from the nozzle.

3-3.6.1.3 Piping shall be sized to prevent excessive pressure losses (and a t tendant capacity reduction) and to present essentially-uniform mixture pressures at multiple r~ozzles.

3-3.6.1.4 Total length of mixture piping shall be as short as practical within the limits of established good practice.

3-3.6.1.5 Devices which can, or may, result in pressure loss or may adversely affect the flow velocity pattern shall not be installed in the mixture piping. Fixed balancing orifices shall be installed in the mixture piping only under the direction of the responsible manufacturer .

3-3.6.1.6 Flow control valves shall not be used in the air-gas mixture piping.

Exception: Individual control of one or more nozzles can be achieved as provided in 3-,3. 7 and ,3-,3. 9.

H E A T I N G SYSTEMS 8 6 A - 4 5

3-3.6.2 Mixer Adjus tments . I f any field adjustable device is built into the mixer (gas orifice, air orifice, air shutter, etc.) an appropriate locking device to prevent unintentional changes in the setting shall be provided. ~

3-3.6.3 Mix ing B l o w e r s .

3-3.6.3.1 Mixing blowers shall not be used to function as gas mixing machines, which are covered in 3-3.9.

3-3.6.3.2 Air-gas piping and air-gas control adjustments for mixing blowers shall comply with 3-3.6.1 and 3-3.6.2. Mixing blowers shall be subject to the same limitations as are other air- gas mixers (3-3.6.1.1 through 3-3.6.1.6).

3-3.6.3.3 Mixing blowers shall not be used with fuel gases containihg more than 10 percent free hydrogen (H2).

3-3.6.3.4 Mixing 'blowers. shall not be utilized where 10 in. w. c. or more mixture pressure is required.

3-3.6.3.5 Mixing blowers shall be equipped with a permanent but adjustable inlet air limit stop to assure that a mini- m u m mixture pressure can be field established to suit the requirements of the burners, the manifold, and the combustion environ- ment.

3-3.7 Flow Cont ro l Valves.

3-3.7.1 Flow control valves of appropriate design shall be used to change the rate of flow of pressurized combust ion air a n d / or the fuel gas where applicable.

3-3.7.2 Where the min imum and /o r the ma x imu m flow of combustion a n d / o r the fuel gas is critical to the safe operation of the burner, flow valves shall be equipped with an appropriate limiting means and with a locking device to prevent an unintentional change in the setting.

3[3.8 Combus t ion Air.

3-3.8.1 Whether supplied as primary or secondary ale, and whether u n d e r positive, negative or atmospheric pressure, the quali ty and quant i ty of the combustion air shall be equal to, or better than, that r equ i red 'for proper operat ion of the mixer and /o r burner, and for the subsequent combustion.

3-3.8.2 Fuel burning systems shall be assured of an adequate supply of combustion air. Inlet air filters shall be used on combustion blowers where required to screen out solid matter.

t ~

86A-46 OVENS AND FURNACES HEATING SYSTEMS 86A-47

3-3.8.3 Special precautions shall be taken, when necessary, to prevent insufficiently diluted products of combust ion from short circuit ing back into the combustion air inlet of the burner or mixer.

3-3.8.4 C o m b u s t i o n Air. W h e n provided mechanical ly as pr imary a n d / o r secondary air, combust ion air pressure a n d / o r volume shall be proven electrically a n d / o r pneumatical ly , and interlocked with the safety shut-off valve so that gas. cannot be admit ted prior to establishment of combust ion air, and the gas will be shut off in the event of combust ion air failure. The quant i ty of the combust ion air for combust ion shall be adequate for proper bu rne r perform~mce.

3-3.9 Gas M i x i n g Machines.

3-3.9.1 Gene ra l . Any combinat ion of proport ioning control devices, blowers, or compressors which supply mixtures of gas a~d air to burners where control devices or other obstructions are installed between the mixing device ~fnd burner is defined as a "gas mixing machine" and the provisions of 3-3.9.2, 3-3.9.3, and 3-3.9.4 shall apply.

NOTE: The essential difference between the mixing devices used with air- gas mixers (3-3.6) and the ga~ mixing machines is the provision for a proportioning valve which responds to changes in rate of gas delivery controlled at any point between the machine and burner. There are several distinct types of gas mixing devices which come within the scope of this section and may supply premixed gas within the explosive range or with only part of the air required for complete combustion.

A gas mixing machine usually comprises a pressure regulator or "zero governor" which reduces the gas supply pressure to atmospheric and a proportioning valve and compressor.

Gas mixing machines may deliver gas-air mixtures which are not within the explosive range, additional combustion-air being secured at the burner, either from a burner mixer or directly from the combustion space. They also may supply mixtures within the explosive range and, wheri so installed, means to prevent flash backs OCCUlTing in piping containing the flammable mixture, or to prevent damage if flash back should occur, should also be pl:ovided.

3-3.9.2 Nonexplosive Mixtures (outside f l ammabi l i ty l imits) . ,Gas mixing machines supplying gas-air mixtures which are above the upper explosive limit shall be installed as follows:

(a) A stop or other m e a n s shall be provided which will effectively prevent ad jus tment of the machine within or approaching the explosive range.

(b) I f t h e machine is located in a small detached buikt ing or cut-off room, explosi0n vents shall be provided in the ratio of 1 sq. ft. of vent area to each 20 cu. ft.. of room volume (see NFPA 68-197d, Guide Jor Explosion Venting).

NOTE 1: The choice of location varies considerably in individual in- s'tallation. In large, well-ventilated manufacturing areas there is relatively

such conditions, the machine may well form an integral part of a furnace heating system.

NOTE 2: In Considering small rooms where dangerous gas-air mixtures could be formed, the machine is better located in a detached building or in a small room cut off by concrete walls bonded into the floor and ceiling and provided with explosion relief vents to outdoors. Entrance to this room should be directly from outdoors.

NOTE 3: Machines should, if practical, be constructed so that, in the event of an explosive mixture forming and flash back resulting, the machine casing will not be ruptured.

NOTE 4: Air intakes for gas mixing machines ~md blowers using compressors or blowers should be taken from outdoors wherever practical.

(C) When gas mixing machines are installed in well- venti lated areas, the type of electrical equ ipment shall be governed by the National Electrical Code requirements for general service conditions unless other hazards in the area prevail.

When gas mixing machines are installed in small detached build- ings- or cut-off rooms, the elecirical equ ipmen t and wiring shall be installed in accordance with N F P A 70-1978, National Electrical Code, requirements for hazardous locations (Article 500, Class i , * " 2) L n I V I B I O I I

3-3.9.3 Explosive Mixtures (within flammability limits). Gas mixing machines supplying gas-air mixtures within the explosive range shall be installed in accordance with 3-3.9.2 (b) and (c) and the following shall also apply:

(a) Automat ic fire checks and sa f e ty blowouts shall be provided.

(b) Burners used with explosive mixtures shall be designed with port areas and length of gas passage through each port such that the possibility of backfire is largely el iminated.

NOTE: When necessary to. secure stability of operation, water-cooled burners may be used.

3-3.9.4 Controls for gas mixing machines shall include interlocks and safety shutoff valves of the manua l ly opening automat ic closing type in the gas supply connect ion to each machine ar ranged to automat ical ly shut off the gas supply in event of air a n d / o r gas supply failure (see Chapter 5).

3-3.10 Fuel Ignition.

3-3.10.1 w h e n e v e r fiiling of the combust ion chamber with f lammable (i.e., explosive) air-fuel mixture can result in an.unsafe

t ~ t ~


condition, the length of time allotted for flame ignition and the rate of fuel input at ignition shall be correlated so that the LEL, with respect to the combustion chamber volume, is not exceeded.

N O T E : Fuel-air mixtures of a ratio within the f l ammable range are ignited by means of electric arc, hot wire, pilot bu rne r flame, hand held torch, etc. A bu rne r is sui tably ignited when combus t ion of the fuel-air mixture is establ ished and stable at the discharge port(s) of the nozzle(s) or in the cont iguous combus t ion tunnel .

3-3.10.2 Ignition shall be effectively applied at the proper point in sufficient quantity, and with sufficient intensity to safely ignite the fuel-air mixture.

3-3.10.3 Pilot Burners . The provisions of 3-3.5 (Gas Burners) shall also apply to pilot burners.

3-3.10.3.1 Special precautionary measures shall be taken with large capacity pilot systems in the range of 400,000 Btu/each hour and upward, as directed by the manufacturer and/or the authority having jurisdiction.

N O T E : Pilot capacities are generally in the range of 5,000 to 50,000 B tu /each hour:

3-3.10.4 Pilot Mixers. I f pilot mixers are used, the provisions of 3-3.6 (air-gas mixers) shall also apply to pilot mixers.

3-3.10.5 Combust ion Air. The provisions of 3-3.8 shall apply.

3-3.10.6 Fixed Pilots.

3-3.10.6.1 The pilot burner shall be located as required to reliably ignite the main flame, and as directed by the manufacturer.

3-3.10.6.2 The pilot shall be so mounted to prevent unintentional changes in location, and in direction with respect to the main flame.

3-4 Oil-fired Units.

3-4.1 Scope.

(a) This section includes combustion systems for ovefis/ furnaces fired with No. 2, No. 4, No. 5, and No. 6 industrial fuel oils as specified by ASTM D-396-73, Specifications for Fuel Oils. I t also includes the oil-burning portions of dual-fuel and combination burners.

(b) Additional safety considerations which are beyond the scope of this standard shall be given to other combustible liquids not specified in 3-4.1 (a).

HEATING SYSTEMS 8 6 A - 4 9

3-4.2 Special Safety Considerations. In the design of, and the use of, oil-fired units, continuous considerations shall be given to the following facts:

(a) Unlike the standard fuel gases, many important physical/ chemical characteristics are not available for fuel oil which, being a complex mixture of complex hydrocarbons, is relatively unpre- dictable.

(b) Fuel oil must be vaporized prior to combustion. Heat generated by the combustion is commonly utilized for this purpose, and oil will remain in the vapor phase as long as sufficient temperature is present. Under these conditions, oil vapor can be treated like fuel gas.

(c) Unlike fuel gas, oil vapor will condense into liquid when the temperature falls too low; and will re-vaporize whenever the temperature rises to a certain undeterminate point.

(d) Therefore, oil in a cold oven can lead to a hazardous condition; for it cannot be purged out as gas can, but it may vaporize (to become a gas) when, or because, oven operating temperature is reached.

(e) Unlike water, for example, there is no published relation- ship between temperature and vapor pressure for fuel oil. For purposes of comparison, a gallon of fuel oil is equivalent to 140 cu. ft. of natural gas (hence 1 oz. equals approximately 1 cu. ft.).

: 3-4.3 Burner System Selection. Burners, along with associated valving, safety controls and other auxi l ia rycomponents , shall be suitable for the type and pressure of the fuel oil to be used,. and for the temperatures to which they will be subjected.

3-4.3.1 This shall• not be interpreted to imply that a burner system selected for No. 2 fuel oil must be capable of handling No. 4, No. 5, or No. 6 fuel oil, or vice versa.

3-4.4 Oil Supply Piping.

3-4.4.1 Storage tank and installation shall comply with Standard for the Installation oJ Oil-Burning Equipment, NFPA 31-1974.

3-4.4.2 Piping materials shall be wrought iron, steel, brass or copper. Pipe shall be connected with standard fittings, tubing with listed fittings. Connectors made of oil utilizing combustible materials shall not be used. Unions requiring gaskets .and sweat fittings employing solder having a melting point of less than 1000°F (537°C) shall not be used. Cast iron fittings shall not be used.

3-4.4.3 Oil pump, if not an integral part of the burner, shall be :

8 6 A - 5 0 O V E N S A N D F U R N A C E S

(a) O f the positive d i sp lacement type which au tomat ica l ly shuts off the fuel when stopped.

(b) Listed or app roved by the au thor i ty having jur isdic- tion

(c) E q u i p p e d with an integral safety relief valve, or with an external remote safety relief valve connected ups t r eam from all shut-off v.alves in the discharge line and a r ranged to re turn surplus oil to the suctioff side of the p u m p or to the storage tank.

3-4.4.4 M a n u a l Shut -of f V a l v e s an d Cocks.

3-4.4.4.1 M a n u a l shut-off valves shall be instal led where requ i red to avoid oil spillage dur ing servicing of supply p ip ing and associated components .

3-4.4.4.2 M a n u a l shut-off valves and cocks shall be pro- v ided for shut-off of the fuel to the pi lot a n d / o r bu rne r for ex tended per iods of §hutdown.

3-4.4.4.3 Valves and cocks shall be ma in t a ined in ac- co rdance with the manufac tu re r ' s i.nstructions.

3-4.4.4.4 Considera t ion shall be given to the use of q u a r t e r turn valves.

3-4.4.4.5 I t shall be the user 's responsibi l i ty to see tha t separa te wrenches (handles) r emain affixed to the valve, and tha t they are p roper ly or iented with respect to the valve 's port .

3-4.4.5 E m e r g e n c y Shut -o f f Valves . Valves shrill be pro- v ided to pe rmi t turn ing off the fuel in an emergency and shall be located so tha t fires, explosions, etc., at ovens / furnaces will not prevent access to these valves.

NOTE: A positive displacement oil pump can serve as one valve by shutting off the power to it.

3-4.4.6 Ful l considerat ion shall be given to the necessity to in i t ia l ly purge all a i r f rom the supply and re turn piping, and to the safety advantages of minimiz ing ai r en t r a inmen t in the oil. The inheren t ad;cantages of a long c i rcula t ing loop, consisting of a supp ly leg, a back-pressure regula t ing valve, and a re turn line b a c k to the storage tank, shall not be overlooked.

NOTE :-Manual ventvalves may be needed to bleed air from the high points of the oil supply piping.

3-4.4.7 Suction, supply a n d re turn p ip ing shall be ade- "quately sized w i t h respec t - to oil p u m p c a p a c i t y .

3-4.4.7.1 Oi l shall be suppl ied to the oven / fu rnace site p roper ly condi t ioned (pressure, t empera ture , f i l t e red , air-free, water-free) as d i rec ted by the equ ipmen t manufac turer .

. H E A T I N G S Y S T E M S 86A-51

3-4.4.8 W h e n e v e r a section of oil p ip ing can be shut off at both ends, considerat ion shall be given to the use of relief valves a n d / o r expansion chambers to release the pressure caused by thermal expansion of the oil.

NOTE: The'weight of the oil is "~ilways a consideration in vertical runs. When going up, pressure will be lost (100 psig with a 100 ft. lift will net only 63 psig). When going down, pressure will be adde~t (100 psig with a 100 ft. drop will nix 137 psig). This also occurs with fuel gas, but it is most often . of no importance. However, i~ can never be overlooked when handling oil (see Table 3-4:4.8).

Table 3-4-4.8 Useful Conversion Data

(14.7 PSIG = 29.92 ~ HG = 33.9 Ft. H20 = 39.89 Ft..85 SG OIL)

TO PSIG "HG FT H20

One PSIG = 1 2.04 2.31

• One u HG = 0.'49 1 1.13

One FT H20 = 0.43 0.88 1

One FT .85 SG OIL-= 0.37 "[ 0.75 0.85

NOTE: 14.7 psig & 29.92 in. HG are sea level figures.

FT .85 SGOIL

2.71

1.33

1.18

3-4.5 Branch Circuit Oi l P ip ing .

3-4.5.1 Branch ci rcui t oil' p ip ing means tha t p ip ing which connects f rom the supp ly leg of the c i rcula t ing loop to one or more burner systems.

3-4.5.2 Piping shall connect to the bo t tom of the supply l eg (to min imize a i r en t ra inment ) .

3-4.5.3 Mate r i a l s shall be in accordance wi th 3-4.4.2.

3 - 4 . 5 . 4 Pip ing shall be adequa te ly sized for m a x i m u m flow rate.

3-4.5.5 ConsideratiQn shall be given to shut-off valves (refer to 3-4.4.4, 3-4.4.5 and 3-4.4.8) .

3-4.6 Oi l T r a i n Piping. 34 .6 .1 Oi l t ra in p ip ing means tha t p ip ing which connects

from the b ranch ci rcui t p ip ing to the burner .

3-4.6.2 T h e provisions of 3-4.5.3 and 3-4.5.4 shall app ly .


3-4.6.3 Manual Shut-off Valve. A manual shut-off valve ha,)ing provision for position indication shall be located upstream from all other components to shut off the flow of oil for,servicing, and for other shut-downs.

3-4.6.4 Pressure Regulator.

3-4.6.4.1 A pressure regulator shall be furnished whenever the plant supply pressure exceeds that required for proper burner system operation, or whenever the plant supply pressure is subject to excessive fluctuation.

3-4.6.4.2 Regulator shall be suitable for the service.

3-4.6.5 Oil Filters and Strainers.

3-4.6.5.1 An oil filter shall be installed in the oil train piping to protect the downstream components.

3-4.6.5.2 The degree of filtration shall be compatible with the size of the most critical clearance being protected.

3-4.6.5.3 The filter housing and cartridge shall be suitable for the intended pressure, temperature, and service.

NOTE: Customarily, a filter/strainer is installed in the suction piping to protect the pump. A secondary filter/strainer is often installed in the discharge line. However, neither of these are-usually fine-meshed to the point required for burner and valving protection.

3-4.7 Oil Burners.

3-4.7.1 Oil burners shall be of a type and design suitable for the intended service.

3-4.7.1.1 The burner shall accept fuel oil of the proper grade, preconditioned to the degree it requires, for subsequent combustion.

3-.4.7.1.2 The burner shall self-sustain combustion be- ginning at the designed flame base, and throughout the firing range, Without external stimulation, mechanical or otherwise.

3-4.7.2 Oil Atomization.

3-4.7.2.1 Oil shall be atomized to the droplet size as required for proper combustion throughout the firing range.

NOTE: The atomizing medium may be steam, compressed air, low-pressure air, air-gas mixture, fuel gas, or other gases. Atomization may also be mechanical (mechanical-atonfizing tip or rotary cup).


3-4.7.2.2 The atomizing device shall be accessible as may be required for inspection, cleaning, repair, replacement, and other maintenance.

3-4.7.3 Burner Ignition.

3-4.7.3.1 Burners shall ignite completely, smoothly, and reliably from the ignition source presented• If a burner cannot be safely ignited at all firing rates encountered, positive provision shall be made to assure a firing rate suitable for safe light-off at the time of ignition (low-fire start).

NOTE: Safety warning multiple small burners manifolded together are usually spaced too far apart to flash across from burner to burner from a single ignition source, and require that extreme caution be exercised - - especially at light-off.

3-4.7.4 Burner Shut-down. If clearance of oil passages upon normal termination Of a firing cycle is required, it shall be done prior to safety shut-down with the initial ignition source (pilot flame) present and with all allied fans and blowers in operation.

3-4.7.5 All pressures involved in the safe operation of the combustion system shall be maintained within the proper ranges throughout the firing cycle.

3-4.8 Flow Control Valves.

3-4.8.1 Flow control valves of appropriate design shall' be used to change the rate of flow of pressurized combustion air and/or the fuel oil where applicable.

3-4.8.2 Where the minimum and/or the maximum flow of combustion air and/or the fuel oil is critical to the safe operation of the burner, flow valves shall be equipped with an appropriate limiting means and with a locking device to pre~eent an unintentional change in the setting.

3-4.9 Combustion Air.

3-4.9.1 Whether supplied asprimary, secondary, or atomizing air, and whether under positive, negative or atmospheric pressure, the quality and quantity of the air shall be equat to, or better than, that required for proper operation of the mixer and/or burner, and for the subsequent combustion.

3-4.9.2 Fuel burning systems shall be assured of an adequate supply of combustion air. Inlet air filters shall be used on combustion blowers where required to screen out solid matter•


3-4.9.3 Special precaution s shall be taken, when necessary, to prevent insufficiently diluted products of combustion from

3-4.9.4 Combust ion Air. When provided mechanically, air pressure and /or volume shall be proven electrically and/or pneumatically, and interlocked with the safety shut-off valve so that oil cannot be admitted prior to establishment of combustion air, and the oil will be shut off in the event of combustion air failure. The quantity of the combustion air for combustion shall be adequate for proper burner performance.

3-4.10 Units Heated with Dual-fuel and Combination Burners.

3-4.10.1 When fuel gas and fuel oil are to be fired individually (dual-fuel) or simultaneously (combination) the provisions of 3-3 and 3-4 shall apply equally to the respective fuels.

3-5 Electrically Heated Units.

3-5.1 General .

3-5 .1 .1 Scope. This section includes all types of heating systems where electrical energy is used as the source of heat.

3-5.1.2 Definitions. The following definitions apply to the several types of electrical heating systems included in 3-5.

Resistance Heater means any electric heater in which heat is produced by current flow through a resistive conductor. R e - sistance heaters may be of "open" type with bare heating conductors or "insulated sheath" type with heater conductors covered by a protecting sheath which may be filled with electrical insulating material.

Infrared Lamp and Tubular Heaters means a form of resistance heater in which the resistive conductors are enclosed in glass, quartz, or ceramic envelopes that may or may not contain a special gas atmosphere.

Induction Heater means a heating system by which a current-carrying conductor induces the .transfer of electrical energy to the work by eddy currents. (See Article 665 oJ NFPA 70-1978.)

Dielectric Heater means a heater similar to an induction heater, except that the frequencies used are generally higher (in the order of three megacycles or more) 'than those in induction heating.

HEATING SYSTEMS " 8 6 A - 5 5

NOTE:" This type of heater is useful for hea t ing mater ia ls which are c o m m o n l y t hough t of as being nonconduct ive , such as hea t ing plast ic preforms before molding, cur ing glue in plywood, d ry ing rayon-cakes , ana mr m a n y simiiar appiieations.

3-5.1.3 Safety Equipment. Safety equipment including air flow interlocks, time relays, and temperature switches shall be

-in accordance with Chapter 5.

3-5.1.4 Electrical Installation. All parts of the electrical installation shall be in accordance with the National Electrical Code, NFPA 70-1978.

• 3-5.2 Resistance Heat ing Systems.

3-5.2.1 General . The following paragraphs shall apply to resistance heating systems including those of the infrared lamp (quartz, ceramic, and tubular glass types).

N O T E : Resis tance hea t ing systems are sui table for Class A ovens bu t as the surfaces of all types of resistance heaters operate above ignition tempera tures of mos t f inishing materials , the fire and f l ammable vapor hazards are comparable to tha t o f direct fuel fired hea t ing sys tems .

3-5.2.2 Enclosure.

.,- . . . . . . . . . . . c . used with flammable vapors, the use of an enclosed oven shall be considered. (See 3-7, Unenclosed Heating Systems.)

3-5.2.2.2 All parts of heaters operating within an oven at elevated temperatures and all energized parts shall be protected to prevent contact by persons and also to prevent accidental contact by work in process and metal objeets as by drippage from work goingthrough the oven.

3-5.2.2.3 External electric heating systems shall have the electric elements encased in a sufficiently insulated chamber to prevent injury to personnel and property.

3-5.2.2.4 The heater housing shall be so constructed as to provide easy accessibility to heating elements and wiring.

3-5.2.2.5 Heating elements shall be fastened securely to a supporting frame and the f r a m e shall be grounded.

3-5.2.3 Heater Locations.

3-5.2.3.1 Heaters shall not be located direct ly under the product being heated where combustible materiMs may drop and accumulate. Neither shall they be located directly over readily ignited materials, such as cotton, unless for controlled exposure rime, as in continuous processes, where further automatic provisions

t ~


a n d / o r a r rangement of guard baffles preclude the possibility of ignition.

3-5.2.3.2 Parts of oven heaters which operate at temperatures in excess of 160°F or which are energized at potentials in excess of 20 volts shall be guarded. Wher~ impractical to guard, warning signs shall be mounted or permanent floor markings shall be provided to be visible to personnel entering the area.

3-5.2.4 Construction.

3-5.2.4.1 Resistance heaters of all types shall be constructed to resist, or protect against damage f rom falling work, o r other mechanical hazards.

3-5.2.4.2 Where insulators are used, they shall be supported so they will resist falling out of place.

3-5.2.4.3 Corrosion Resistance. Where subject to corrosion, metal parts shall be protected.

3-5.2.4.4 All parts of equipment operat ing at elevated temperatures shall be installed in accordance with 2-1.5, Floors and Clearances.

3-5.2.5 Safety Devices for Resistance Heaters. Refer to Chapter 5.

3-5.3 Induction and Dielectric Heating Systems.

3-5.3.1 G e n e r a l . The following paragraphs shall apply to induction and dielectric heating systems. This type of heating shall be designed and installed in accordance with N F P A 70-1978, National Electrical Code, with special reference to Article 665, en- tiffed " Induc t ion and Dielectric Heat ing Equipment . "

NOTE: To prevent spurious radiation caused by this type of equipment and to ensure that the frequency spectrum is utilized equitably, the Federal Communications Commission (FCC) has established rules (Code of Federal Regulations, Title 47, Part 18) which govern, the use of industrial heating equipment of this type operating above 10kHz.

3-5.3.2 Instal lat ion. High-frequency induction equipment and dielectric heating systems shall not be installed in hazardous locations. (See Article 665 of N F P A 70-1978. )

3-5.3.3 Construction.

3-5.3.3.1 Frames, enclosures, and shelves shall be of noncombustible construction and shall be sufficiently strong to resist physical damage.

3-5.3.3.2 Combustible electrical insulation shall be reduced to a minimum.


NOTE: Transformers should be of the dry or nonflammable liquid type. Dry transformers should be in compliance with NEMA TR27-4.03, 150°C rise insulation.

3-5.3.3.3 Protection shall be installed to prevent overheating of any par t of the equipment, in accordance with N F P A 70-1978.

3-.5.3.3.4 When water cooling is used for transformers, capaci tors , electronic tubes, spark gaps, or high-frequency conductors, cooling coils and connections shall .be arranged so that leakage or condensation will not damage the electrical equipment. The cooling-water supply shall be interlocked with the power supply so that loss of water will cut off the power supply. Consid- eration shall be given to providing individual pressure flow interlocks for parallel water flow paths.

3-5.3.3.5 When forced ventilation by motor-driven fans is necessary, the air supply shall be interlocked with the power supply. An air filter shall be provided at the air intake.

3-5.3.3.6 The conveyor motor and the power su'pply of dielectric heaters of the conveyor type used to heat combustible materials shall be interlocked to prevent overheatirig of the material being treated.

3-5.3.3.7 Dielectric heaters used for treating highly combustible materials shall be designed to prevent a disruptive discharge between the electrodes.

3-6 Steam Heating Systems.

3-6.1 Scope: This section includes all types of heat ing systems where steam is used as the source of heat and refers spe- cifically to the steam heat exchangers, which are usually supplied f rom a central steam generating source.

NOTE: The construction and controls for steam boilers are covered by ASME. Rules for the Installation of Heating Furnaces, Boilers, and Fire Boxes of Power Boilers, and by any applicable local or state regulations. Burners and controls for boilers using gas, oil, or pulverized coal are covered by NFPA Standards for Off Burning Equipment (No. 31 ), and Pulverized Fuel Systems (No. 60), and also by any applicable requirements of the authority " having jurisdiction.

3-6.2 Coflstruction.

3-6.2.1 Piping and fittings associated with steam heat exchangers shall be in accordance with the American National Stan- dard CodeJor Power Piping, ANSI B31.1-1967. Suitable relief valves shall be provided where needed in this system.

hO


3-6.2.2 Enclosures or duct work for heat exchanger coils shall be of noncombustible construction with suitable access openings provided for maintenance and cleaning. ~

/

3-6.2.3 Heat exchangers or steam coils shall not be located on the floor of an oven or in any position where paint drippage or combustible material can accumulate on the coils.

3-6.3 Safety Devices. Refer to Chapter 5 for control equipment and application to s team heating systems.

3-6.4 To avoid abnormally high temperature at coil surfaces , steam pressure in heat exchanger coils shall be mainta ined at the minimum pressure necessary to provide the required drying .temperature.

N O T E : Th i s is usual ly accompl ished by an au tomat ic pressure regu la t ing device.

3-6.5 'Recirculation dfi'ectly over the heat exchanger 'coils shall not be used if lint or other light combustibles may be c~irried- back to and deposited on the steam coil surfaces unless the recireulated atmosphere is properly filtered.

3-7 Unenclosed Heating Systems.,.

3-7.1 The use of "oven-less" or ~ unenclosed heating systems e m p l o y i n g lamps, resistance-type electric, elements, or gas-fired

infrared heaters in processes responsible for the vaporization of flammable, toxic or corrosive liquids and their thermal decomposition products shall be subject to the approval of the authority having jurisdiction.

3-7.2 To avoid the escape of flammable, toxic, or corrosive vapors into the general area, an oven enclosure shall be considered as ventilation and personnel safeguards can be more readily' applied.

Exception: Heating systems having an .energy input of under dO0,O00 Btu/hr. or lO0 K W are excluded if adequate area ventilation is provided.

3-7.3 The applicable provisions relating to fire, fuel, and ex- plosiofi hazards in Chapters 4 and 5 Of thisstandard shall be utilized by the authorities responsible for the approval of unenclosed driers and heating systems as discussed in 3-7.1.

VENTILATION 8 6 A - 5 9

Chapter 4 Ventilation

4-1 Scope. T h e proper ventilation of ovens is of prime "im- p o r t a n c e . Proper ventilation within the scope of this chapter

, means a sufficient supply of fresh air and proper exhaust to outdoors with a sufficiently vigorous and properly distributed air circulation to ensure that the flammable vapor concentration in all parts of the oven or dryer enclosure shall be safely below the lower explosive limit at all times.

4-1.1 The determination of safe oven ventilation shall be based on : '

(a) The vo lu me of combustion products (if any) entering, the oven heating chamber.

(b) The weight of flammable constituents, f rom organic powder or liquid coatings, released during the heating process.

(c) Design of the oven heating and ventilation system as to: 1. Materials to be processed. -

"2. Temperature to which these materials will be raised. 3. Method of heating as to direct or indirect venting of

combustion products vs. alternate use of steam or electrical energy. 4. General design of oven as to continuous or batch-type

operation. 5. Type of fuel and chemicals to be used and consequent

" by-products that may be generated in the heating chamber during normal or excessive temperature cycles.

N O T E : Ovens used to fuse organic powders will require safety venti lat ion on the same basis as ovens used to evapora te f l ammable solvents, when expressed in te rms of cubic feet of s t anda rd 70 ° F air requi red per p o u n d of

• the var ious organic mater ia ls being released.

4-1.2 Careful consideration shall be given to the safe removal, dilution, or other disposal of flammable-;eapors or vapor-air mixtures. To do this, all necessary consideration shall be given" to temperatures of. operation, periods of dripping and predrying, speed of conveyor travel, safe disposal of flammable drippings, safe escape of flammable vapors or gases, safe-control of combustion and the safety of chains, carrier belts, hoods, racks and "carts.

4-1.3 T h e consideration of all these factors and their evalu- ation; the selection of the equipment and its design including arrangement to meet safely all requirements of safe operation, and adequate ventilation, shall be done by. a qualified person familiar with oven design and basic rules of safety. ~O


4-1.4 In general , the need for and type of vent i la t ion requi red for safety in ovens covered by this s t andard is as follows:

(a) Ovens in which f l ammable or toxic vapors are l ibera ted shall be mechanica l ly vent i la ted to ou tdoor a tmosphere regardless of the type of hea t ing equ ipmen t employed.

(b) T h e safe disposal of the products of combust ion shall be a pa r t of the engineer ing considerat ion.

Exception No. l: Ovens with 64 cu. f t . volume or less need not be equipped with mechanical ventffation except when..it is known that the products or materials processed in the oven give off flammable vapors or toxic fumes.

Exception No. 2: Ovens using steam or electrical energy for heat, or gas or oil fired indirect heating equipment, and which do not at any time lib- erate combustible or injurious (toxic).fumes, do not reqube fresh air ventilation for safety. Also, such ovens may be arranged to recirculate any portion of the air supplied.

4-1.5 Genera l basic requi rements for oven vent i la t ing systems hand l ing f l ammable or toxic vapors are as follows:

(a) Exhaus t duc t openings shall be located in the a rea of greatest concent ra t ion of vapors.

(b) Exhaus t duc t openings shall be p laced and sized so tha t they will ga the r and discharge vapors to ou tdoor a tmosphere as d i rec t ly as prac t ica l in accordance with app l icab le local, state, and federal regulat ions, such as the Env i ronmen ta l Pro tec t ion Agency (EPA).

(e) All exhaust shall be by mechanica l means, using power- . dr iven fans.

NOTE: Each oven should be'equipped with an individual exhaust system not connected to an exhaust system serving other equipment.

(d) Mani fo ld exhaust systems shall be designed so t h a t - t h e fa i lure or nonopera_tion of one or more exhausts shall not adversely affect the r ema in ing exhaus ts , and tha t the opera t ing units will not create a haza rd in the fai led or nonopera t ing unit(s) .

NOTE: Groups of ovens or ovens divided into several compartments may be exhausted by a common exhaust fan or individual oven exhaust fans connected to a common exhaust system.

(e) Ovens in which the t empe ra tu r e is control led by damper s (manua l or au tomat ic ) which affect the volume of hot air admi t t ed to the oven shal l .be designed so tha t a reduct ion in the volume of hot a i r suppl ied does not result in a reduct ion of the vo lume of fresh a i r suppl ied to meet the requi rements for safety vent i la t ion.

VENTILATION 86A-61

NOTE: It is recommended that a separate draft fan, not connected with the oven ventilation, be used for exhausting the products of combustion from indirect gas or oil fired air heaters.

(f) O n small instal lat ions subject to the approva l of the au- thor i ty having jur isdic t ion, it may be permissible to connect the draf t flue to the oven exhaust system, provid+ed tha t : T h e tem- pe ra tu re of the products of combust ion shall be reduced (if necessary) by the add i t ion of fresh a i r to a point where i t will p revent ignit ion of any combust ib le fumes in the oven exhaust system.

(g) Ai r suppl ied into the oven shall be c i rcula ted to p roduce a thorough dis t r ibut ion and movemen t in all par ts of the oven and through the work in process.

NOTE: For typical unacceptable safety ventilation systems, see Figure 4-1.5.

4-1.6 W h e n vent i la t ion is required for ovens and furnaces, the following shall be compl ied wi th :

(a) Interlocks. (See 5-2 and 5-5.) 1. Mechan ica l interlocks ac tua ted by devices such as a i r

flow or pressure switches, or centr i fugal switches ac tua ted by the fan shaft.

2. Electr ical interlocks ob ta ined th rough in terconnect ion with a mo to r starter .

(b) F r e s h A i r . S u p p l y . 1. Ovens in which f l ammable vapors a re being l ibera ted

shall be assured of receiving the full r equ i r ed a m o u n t o f f r e s h air for safe di lut ion of vapors (see d-2 and 4-3).

2. Ovens hea ted by electr ic resistance heaters or by combustion of any fuel shall have the air supply fans electr ical ly or mechanica l ly in ter locked in such a manner as to prevent operat ion" of the hea t ing units unless t h e a i r supply fans are running.

3. Vo lume control damper s in the ducts which affect the volume of fresh a i r admi t t ed to and vapors or gases exhausted f rom t h e oven shall be designed so tha t when in closed posit ion they

• will pass the volume requi red for safe venti lat ion.

(c) Exhaus t . 1. Ovens in which f l ammable vapors are being p roduced

or into which the products of combust ion of fuels are pe rmi t t ed to enter shall be assured of having the required a m o u n t of exhaust for safe vent i la t ion (see 4-2 and 4-3).

2. Ovens hea ted by electric or infrared l amps or by combustion of any fuel shall have the exhaust fans electr ical ly and me-


chanically interlocked in such a m a n n e r as to prevent operat ion of the heating units unless the exhaust fans are running .

3. Volume control dampers in the ducts which affect the volume of fresh a i r admit ted to and vapors or gases exhausted from the oven shall be designed so that when in closed position they will pass the volume required for safe venti lat ion.

(di P u r g i n g In t e rva l . Purging cycle or prevent i la t ion shal l be in accordance with 5-2.

Damper ~'- ~ ~ } • . Inlet Blast I~ rl Fan~ " ~a~e"~-o r. ImL I I ~ ~ Fresh Air

/1 m 'r" ::;/'/ L . > . . . . . ; 2 Z . ; . .

~1~ Reclrculatin 9

. , . L-Z . .

Oub~OOr

r ' t ~ ' , . ' - - - ~ ' - I fresh

" ,p po.r ,

- I 1 I ~ ~" ", I . i ~ - _ . , ~ _ s

BF, e,h I '~ ' , ' '~ - '~ I BAir /o,L, / ~._~q ~] In x,.I.O~-Direct Gas Line Burner

. I r ~ i i i i i i / 1 1 1 / 1 1 / / / / / / /

. N I I t , ' 1 ~ I~KResiatance ~l I~f ~ II Heaters

/ i / / 1 1 ~ ' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 / . . / / 1 1 /

,I. Air . Inlet 8hst~ie Xir ~ '~ '~ LLock L Oven \ _Llagk . I IT[

[/f ~ ~ ' ~ - ~l{'r~ F~'-'.~X'-_SP litter

I I / / / / / I / / / / / / / / / / / 1 1 / / / / / 1 1 / / / / / / I / 1 1 1 1 1

K E Y

- ~ Safety Ventilwtidn

- - - ~ Reci reulat ion

Figure 4-1.5 Typical unacceptable safety ventilation systems using dual- purpose fans alone (reclreulation combined with spill exhaust).

VENTILATION 86A-63

4~1.7 Forced Ven t i l a t i on .

of and in addition to (a) remrculation within the oven enclosure, and (b) exhaust for removal of products of combustion in an indirect heating system.

4-1.7.1 Mechanica l means for reliable and adequate venti lation of ovens shall be provided except as specified in 4-1.8.

4-1.7.2 O n complet ion of an oven installation air-flow tests shall be conducted on the vent i la t ion systems unde r operat ing conditions of oven in balanced condit ion a n d adjustable dampers a t m i n i m u m opening, and tests of safety devices shall be made to assure proper venti lat ion and operat ion of the system. These ' tests shall be repeated periodically.

NOTE: The user should make arrangements to have these tests conducted by qualified personnel if not equipped to do so himself.

4-1.8 Natura l venti lat ion-shal l not be used on Class A ovens when f lammable volat i les o r toxic fumes are given off f r o m the work in process.

NOTE: Subject to the approval of the authority having jurisdiction, natural ventilation may be used in ovens having only the fuel hazard providea the burner-mlxer design is such that all air necessary for complete combustion of the fuel is reliably obtained" by means independent from and not adversely affected by the natural draft.

4-1.9 T e m p e r a t u r e Correc t ions . Tempera tu re conversion factors shall be taken into considerat ion of the applicat ion of the following requirements since the vo lume of gas var ies in direct

p ropo r t i on to its absolute temperature (0°F e q u i v a l e n t to 460°F absolute) (see Table d-7.9).

NOTE: For example, in order to draw 9,200 cfm of fresh air referred to 70°F (530°F absolute) into an oven operating at 300°F (760°F absolute), it is necessary to exhaust 760/530 x 9,200 or 13,150 cfm of 300°F air.

T a b l e 4-1.9 T e m p e r a t u r e - V o l u m e C o n v e r s i o n T a b l e

Temp. Factor Temp. Factor 7O o 1 350 ° 1.53

100 1.06 400 1.62 110 1.075 450 1.72 120 1.09 500 1.81 130 1.11 550 1.90 140 1.13 600 2.00 150 1.15 650 2.09 175 1.20 700 2.19 200 1.24 750 2.28 225 1.29 850 2.47 250 1.34 900 2.57 275 1.38 300 1.43

Temp. Factor 950 ° 2.66

1000 2.75 1050 2.85 1100 2.94 1150 3.04 1200 . 3.13 1250 3.23 1300 , 3.32 1350 3.42 1400 3.51

l:


4-1 .10 D i l u t i o n o f V a p o r s . V e n t i l a t i o n sha l l b-e a r r a n g e d in a n o v e n e n c l o s u r e in s u c h a w a y t h a t t h e r e a r e n o zones in w h i c h c i r c u l a t i o n does n o t t ake p lace . I n c o m p l i a n c e w i t h th i s r e q u i r e - m e n t , d u e c o n s i d e r a t i o n sha l l b e g i v e n to t he p r o p o r t i o n i n g of f r e sh a i r a n d r e c i r c u l a t e d a i r in le t s a n d e x h a u s t ou t l e t s in s u c h a w a y t h a t m a x i m u m d i l u t i o n is o b t a i n e d a t p o i n t s of m a x i m u m s o l v e n t e v a p o r a t i o n , a n d also to t he specif ic g r a v i t y of the so lven t v a p o r a n d fue l gas.

N O T E : The vapors of all volatile solvents and thinners commonly used in finishing materials are heavier than air; consequently, bottom ventilation is of prime importance (see Table 4-2). Liquefied petroleum gases are heavier than air and other fuel gases are lighter than air (see Table 1-4.1).

4-1.11 A i r D r y i n g o r D r i p p i n g . I n a r ea s ou t s i de of t h e o v e n w h e r e vo la t i l es a r e g i v e n off b y m a t e r i a l p r i o r to e n t e r i n g t he oven , a d e q u a t e p rov i s ions s h a l l b e m a d e to e x h a u s t v a p o r s to t h e a t m o - s p h e r e in a c c o r d a n c e w i t h a p p l i c a b l e local , s ta te , a n d f e d e r a l r e g u l a t i o n s , s u c h as E P A .

4-1.12 Methods for Calculation of Ventilation for Con- tinuous and Box or Batch Ovens.

N O T E 1: This contains explanatory material relative, to the methods for • calculating venti lat ion in continuous and box or bateh type ovens. The air

delivered into an oven by the supply system to do the work required may be all fresh air (from a source outside the oven), or i t may be part ly fresh air and part ly recireulated air from the oven. A volume of air equivalent to the fresh air supplied, must be exhausted from the oven to keep the system in balance. I t is this portion of the air supplied to the oven which provides the ventilation. .

• The minimum amount of fresh air delivered into the oven for venti lat ion is based on the amounts of solvent vapor which is l iberated f r o m t h e work in process. The method for determining the minimum volume of fresh air required for venti lat ion is demonstrated by the following examples:

N O T E 2: Measurement of Quantity of Air Exhausted from an Oven. The amount of air discharged irom an oven by the exhaust system is gen-

erally a fair indication of the safety ventilation, assuming t ha t supply and exhaust are properly designed.

A simple method ma X be used to determine the quant i ty of air being exhausted from an oven. Establish the velocity of the air through the discharge duct by means of a velometer, anemometer, p i to t tube, or other suitable means, and calculate the cubic feet of air per minute by multiplying the velocity in lineal feet per minute by the cross sectional area of the exhaust duct in square feet. The temperature of the exhaust air should glso be read and the volufne referred to 70°F.

The resultant quant i ty of air is an indication of the volume exhausted from the oven provided the exhaust air does not mix with air external to the oven. In many ovens, particularly of the continuous type, the exhaust ducts are of ten placed in a location which permits air from the outside of the oven to enter the exhaust system toge the rwi th the venti lat ion air exhausted from the oven. I t is necessary t ha t only the venti lat ion air exhausted from the oven be considered in calculating the safety volume.


The temperature of the air discharged from the exhaust will be the average of the temperatures of the air exhausted from the oven and the air exhausted from the space outside the oven in proportion to their volumes. Temperature readings should be noted within the oven in the area of the exhaust, outside the oven in the area of the exhaust, and at the fan discharge. From these temperatures the proportion of oven air and outside air can be determined with a fair degree of accuracy.

Only the air exhausted from the oven should be considered. For example (Continuous Oven) :

Temperature reading of mixed air in exhaust duct of oven: 242.5°F.

Temperature of air in oven within exhaust area: 300°F.

Temperature of air outside of oven exhaust system, short circuited into oven: 70°F.

Problem: How many parts of air a t 300°F. and a t 70°F. when mixed will produce

a resultant temperature of 242.5°F.? x = parts @ 300°F. y - -pa r t s (~ 70°F. 242.5 (x % y) =300x + 70y 242.5x -{- 242.5y L- 300x + 70y 172.5y = 57.5x 3y = x

Therefore, 3 parts (~ 300 ° -{- 1 par t (~ 70°F. = 4 parts total.

Therefore, 75% of the air being discharged by the exhaust fan in this example is from inside the oven. Correcting this 'volume for 70 ° F., we have the actual amount of venti lat ion air being exhausted, or the equivalent amount of fresh air being admit ted into the oven.

In case all of the fresh air is admit ted to the oven through an opening or openings where i t can be measured directly, it will not be necessary to go through the preceding exhaust calculations.

N O T E 3: Theoretical Determination of Required Ventilation.

I. Determine the number of gallons of paint or coating which will be baked in oven per hour (for example, 10 gallons).

2. Determine the total percentage of solvent in coating (for example, 60% = 6 gallons).

3. Determine air volume rendered barely explosive by vapor from one gallon of solvent.

For this example, use toluol as the solvent.

a. The lower explosive limit (L.E.L.) = 1.4% by volume in air. (See Table 4-2. ) As given, this value for the lower explosive limit is at the ordinary ambient temperature (approximately 70°F.). (See 4-3.3.)

b. The specific gravity of this liquid (Sp.Gr)=0.9 (water=l.0).

c. The vapor density (V.D.) =3.1 (air = 1.0).

dl The weight per cubic foot of dry air at 70°F. and 29.9 inchesHg =0.0751bs.

e. One gallon of water weighs 8.33 Ibs. at 70°F.

4~ 4~ [,J

8 6 A - 6 6 - OVENS ANDFURNACES

To determine the cubic feet of vapor per gallon of solvent, use the following formula:

8.33 x Sp.Gr. cu. ft. per gallon @ 70°F.

0.075 x V.D.

For this example,

8.33 x 0.9 32.2 eu. ft.

0.075 x 3.1

The L.E.L. being 1.4%, the cubic feet of air rendered explosive by one gallon of toluol is

• (100 -- 1.4)'x 32.2 2,268 cu. ft. @ 70°F.

1.4

This 70°F. volume, if handled at a higher temperature, must be corrected for the higher temperatures by the use of an expansion factor in which t = the exhaust temperature. Assume the exhaust temperature to be 300?F.

For example,

t°F. + 4 6 0 300 + 4 6 0 1.43= ratio of 'absolute temperatures at

70°F. + 460 70 + 460 70 ° and 300°F.

At oven exhaust temperature, the volume of air rendered barely explosive by vapor from one gallon of toluol is

2,268 x 1.43 =3,243 cu~ ft. per gallon of solvent at 300°F.

NOTE 4: Another Method of Computation.

For this example, use xylol (or xylene) as the solvent.

Sp.Gr. =0.9

Then:

Weight of 1 gallon liquid =8.33 x 0.9 =7.5 lbs. Molecular weight of CeI-I,(CHs)~ = 106

If the vapor density is not known, ' the volume of the vapor can be determined from the molecular weight. The molecular weight in pounds of any gas or vapor occupies 388 cubic feet at 70°F. and 29.9 inches of mercury.

The volume of one gallon of xylol, when vaporized, is, therefore:

7.5 x 388 - - =27.5 cu. ft. @ standard condition~.

106

L.E.L. for xylol =1.0% by volume.

(100 - - 1.0) x 27.5 2,723 cu. ft. per gallon @ 70°F. at L.E.L.

1.0


For a higher exlaaust temperature, t, this 70°F. voiume must be corrected by an expansion factor. Assume t =300°F.

300 + 460 Expansion factor~ = l . 43=ra t i o of absolute temperature at

70 + 460 70 ° and 300°F.

Then: 2,723 x 1.43=3,894 cu. ft. of air rendered barely explosive per gallon

of solvent at 300°F.

4 - 2 C o n t i n u o u s Process O v e n .

4-2.1 R a t e o f V e n t i l a t i o n . I n cont inuous , process ovens, t he safet]7 v e n t i l a t i o n ra te shal l be des igned a n d m a i n t a i n e d to p r e v e n t t h e 7 a p o r c o n c e n t r a t i o n in the oven f r o m exceed ing 25 p e r c e n t o f the l o w e r explos ive l imi t .

Exception: The safety ventilation rate may be decreased when a continuous vapor concentration indicator ahd controller is provided (see 4-4). For such installations the continuous vapor concentration indicator' and "controller shall be arranged to alarm and shutdown the oven heating systems or operate additional exhausters at a predetermined vapor concentration not to exceed 50 percent o f the lower explosive limit.

i~Ir~: l ne recirculation and exhaust fans and other devices should be operated in such a manner that the vapor concentration is maintained at or less than the safe predetermined concentration.

4-2.2 E s t i m a t e d R a t e o f V e n t i l a t i o n M e t h o d . "In c o n t i n u o u s process ovens the ra te of safety v e n t i l a t i o n shall n o t be less t h a n 10,0.00 cu. ft. of f resh a i r r e fe r red to 70°F p e r ga l lon of so lven t e v a p o r a t e d in the o v e n excep t as p e r m i t t e d in 4-2.3.

NOTE: The basis for the above general rule is that one gallon of common solvent produces a quantity of flammable vapor which will diffuse in air to form roughly 2,500 cu. ft. of the leanest explosive mixture. (See calculation 4-2. 3.)

Since a considerable portion of the ventilating air may pass through the oven without traversing the zone in which vapors are given off and on account of a possible lack of uniform distribution of the ventilation air, and also to provide a margin of safety, four times this amount of air, or 10,O00 cu. ft. (refer:red to -'/0OF), for each gallon of solvent evaporated should be allowed.

Warning: I t shou ld be n o t e d t h a t w i t h ce r t a in solvents, w h e n the v o l u m e of a i r r e n d e r e d ba re ly explos ive exceeds 2,500 cu. ft . ( C o l u m n J , T a b l e 4-2), the f ac to r of safety in this e s t i m a t i o n m e t h o d decreases in p ropo r t i on .

T h e to ta l v o l u m e of air , in cub i c feet p e r m i n u t e , r e q u i r e d fo r ven t i l a t i on of the o v e n is o b t a i n e d by m u l t i p l y i n g the cub i c fee t

" - o f a i r r e q u i r e d p e r ga l lon of so lvent by th e ga l lons of so lven t p e r minu te .

T a b l e 4 -2

T A B L E O F P R O P E R T I E S O F C O M M O N L Y U S E D F L A M M A B L E L I Q U I D S I N U N I T E D S T A T E S C U S T O M A R Y A N D E N G L I S H U N I T S

, , , , T ~ e d s ~ in this ~ b l e have been obtained, with few exceptions as noted, f rom N F P A Pamphle t .No. 325 ! 1960 Edit ion) "F i re Haza rd Propert ies of F lamm~ble Liquids, Gases, ano .vmatne ~OllO.,8. , Av~l.lable fi~ures f rom numerous sources will be found to vary over a wtde range in many.instances, depending on the pur i ty or grade of samples and on the test conmtmns prescnneo by different observers. The figures presented are for information and general guidance out7 and are no t to be regarded as official etandards.

The importance of obtaini.ng precise da ta on the ra te of evaporat ion by aetuul tests on part icular pa in t formulat ions in use needs to be emphasised. Some of these mut t componen t preparat ions may contain seTeml solvents with w i d d y different values of "lower explomve l imi t , " "epecifie gravity/," and "vapor dens i ty ." Unt i l su.:L de terminat ions are made, the operat ion should be on the side of safety. Therefore, the individual solvent, whose da t a result in the largest reqmred volume of air per gallon, should be used as the "~asis for safe ventilation. Corrections ~.nd factors of safet r for final vent i lat ion values are to be applied as indicated in the footnotes.

A Moleeuhr Weight (a)

58 130 88

88

78

118 74 74

118 130 152 76 00

132 113

108

84 313

134

278 147 68 73

18 I 40 ~4

310

B Flash Point

DegbF.

77 77

01

<O 12

72 84 82

141 00

180 - 2 2 104 124 90

480 202

- 4 I11

117

60 016 161

130

5t ~4 55

--49 110

C Ign.

Temp. De~. Y.

100O 714 713

572

550 1044

790 65O 800

473 80O 871 212 460 715

1180

950 1038

500 788

817

780 757

1198

833

350 8O0 793 Z59 752

Acetone Amyl Acetate n

, Amyl Acetate l~O

Amyl Acohol n

Benzine (Petroleum ]~th~') Benzol (Benzene)

Butyl Acetate n Butyl Alcohol n Butyl Alcohol - - tso

Butyl Cello~olve Butyl Proplonato Camphor Carbon Disulphldc Cellosolve (Ethyl C e l l c ~ . ) Cellosoh'e Acetate Chlorobenzenc-meso

Cottonseed Oil (Refined) Cresol m or p

Cyclohexane Cyelohexanone

Cymene-pora

Denatured Alcohol Dibutylph thalato o Diehiorobenzene O ~ Diethyl Ketone Dimethyl Formamlde

Dioxane - - 1,4 E (Diethytene Dles~e~ 'thyl Acetate

Ethyl Alcohol Ethyl Ether Ethyl Lactate

D Explo Limits

Lo~rbY /olume 2.6 UP2.~r

• 1.1 i 7.3 1.0 , 7.5 •

~ 212°P. 1,2 I0.0 1.1 ~ 212°]" 1 4 " 212 ° F. 1.7 7.0 1.4 11.2 1.7 10.9 213°F. ~0 212°F.

1.3 44 2.6 15.7 1.7 . . . . 1.3 7.1 212°F. (~ 302°P.

1.I . . . . • 302°F. 1.3 0 1.1 . . . . 2120F. 0.70 . . . .

(q~ 312°F.

2.2 .0*2

0.3 . . . . (~ 212°F.

2.0 2,5 9 4.3 10 1.9 40 1.5 . . . . 013°¥.

E SpedL

Gmvi~ (Wate~ t ) ~8 0.9 0.9

0.8 "

0.8 0.9

0.9 0.8 0.8

0.902 0.9 1.0 1.3 0.031 0.975 1.I

0.9 1.0

0.8 0.9

0.9

0.8 1.0+ 1.3 0.010(O o.9

1.0+ 0.0 0.8 0.7 1 ~ +

F Vapor

DcnfiW (Air~'~ I) 2.00 4.5 4.5

3.0

2.0 2.8

4.00 2.6 2.0

4.07 4.5 5.2 2.0 6.10 4.73 3.9

2.9 3.4

4.6

1.6

8.I

2.5

3.0 3.0 4.6 3.6 4.t

G Boiling Point

De~. F. 131 300 290

290

95-140 170

290 243 225

340' 295 408 116 275 313 270

395

179 313

349

175 890 356 218.9(0 307

914 174 173 90

o00

l l Lbs. Per Gal. 0.66 7.50 7.80

0.66

6.00 7.50

7.50 6.66 0.66

7.5t 7.5 8.33

10.83 7.76 8.13 9.16

7.5 8.33

6.06 7.60

7.90

6.66 8.33

10.33 8.70(a) 7.50

8.33 7.50 0.68 6.83 &33

Cu. Fk of Vapor Per Gal. Per Lb. Liquid Liquid 44.4 6.66 22.2 2.96 22.9 2.96

29.6 4.44

26.6 5.30 36.7 4.76

24.9 3.33 34,2 6.18 34.2 5.18

24.6 3.26 22.3 2.98 21.4 2.57 55.5 5.13 33.3 4.32 23.0 2.83 31.3 3.43

29.8 3.58

30.6 4.69 29.1 3.83

21.8 2.91

55.5 &34

28.3 2.61

39.9 0.32

36.6 4.39 32.9 4.38 55.5 8.34 39.9 5.12 27.0 8.28

J *Approximate Ce. P t. ofAwrenderedbarely

exploaivep& gal. of Solvent

1663 1976 2198

2437

2392 2503

1435 2408 1978

"4214 1248 1327 2376

2670

2323 2616

3092

1258

1774

' 1703 1283 1235 3543 1778

C~

Z C~

Z

~O

Z a"

Ethyl Methyl Ether Ethyl Propionata Ethylene Dichloride Gasoline Hexane n Kerosene Linseed Oil - - Raw Methyl Acetate Methyl Alcohol Methyl Carhitol Methyl Cellosolve Methyl Cellosolve Acetate Methyl Ether Methyl Ethyl Ketone Methyl Lactate

Mineral SpiriLs So. 10

Naphtha (V.M. & P. Regnhr) Naphthalene Nitrobenzol

Nitroethane Nitromethane (b) Nitropropane - - I Nitropropane - - 2 Paraffin Oil Petroleum Ether (See Benzine) Propy] Acetate - - ~o Propyl Alcohol n Propyl Alcohol - - ins Propyl Ether - - is9 Pyridine Rosin Oil Soy Bean Oil Tetrachloroethsae (a/m) Toluol Turpentine Vinyl Acetate Xylene (Xylol)

A Molecular Weight (a)

60 102 99

86

74 32

120 79

118 49 72

104 '

128 133

73 61 89 89

102 60 6O

102 79

168 92

86 106

B FInch Point

Dog, F. --33

64 56

--45 --7 100 432

14 82

'200 105 132 (]as 21

191

104

20 174 190

82 96 (0. c.) 120(o, e.) 103 (o. c.)

444 ~.0 4O 59 53

--IS 68

266 040

95 18 03

C Ign,

Tern . Deg. ~.

374 890 775 495 453 444 650 935 867

551

662 950 725

473

450 979 900

779 785 789 803

"516 860 700 750 830 900 648 83!

'o9~ 488 8O0 887

D Explo. Limiu % by Vohlme

Lower Upper 2.0 10.1 1.9 I1 6.2 16 1.4 7.6 1.2 7.5 0.7 5

'~i se" 7.3 36

3'.i l'S'" 1.8 10 3.2 . . . . . 212°P. 0.8 . . . .

('~ 212°F. 0.92 6.0

. 0 .9 5.9 1.8 . . . .

@ 200OF. 4.0 . . . . 7.3 . . . . 2.6 . . . . 2,9 . . . .

. , , , . "I~i" 5.9 1.8 8 2.1 13.5 2.0 12 1,4 21 1.8 12.4

1.4" 6,7 0.8 . . . . 2.6 13.4 1.0 6.0

Note: Column J gives the cubic "feet of air rendered barely explosive by 1 gallon of solvent. However, for meat practical calculations, th is value is close enough to the actual volume of the vapor-air mixture. .

*For final required safety venti lat ion values in each par t icular oven operat ion these fi~ are mult ipl ied by the following factors as they app ly (see 410 and 420 of tex t and

t ion examples Appendix C, page* 86A-06- I00) :

( ! ) Tempera ture - - Volume Conversion (see table - - 400-10).

E Specif.

Gravity Water=i) [ 0.7 0.9 1.3 0.8 0.7 <].O 0.9 0.9 0.8 1.035 0.966 1.003

0.8 IA

0.8

0.75 1.1 1.2

I.I I.I 1.0 1.0

0.6 0.9 0.8 0.8 0.7 1.0 1.0 0.9 1.6 (s) 0.9

0.9 0.9

F Vapor

Density (Air=i) 2.1 3.5 3.4 3--4 3.0

2.6 I.I 4.14 2.62 4.07 1.6 2.5 3.8

3.9

3.73 4.4 4.3

3.6 2.1 3.1 3.1

2.5 3.5 2.1 2.1 3.5 2.7

3.1

3.0 3.7

G Boiling Point

Deg. F. 50 210 183

100-400 156

304-574 600 140 147

• 379 255 289

--11 176 293

300

212-330 424 412

237 214 268 248

95-140 194 207 181 156 239

>68O

295.3 (a) 231 300 161 292

II Lbs. Per Gal. 5.83 7.50

10.83 6.66 5.83

7.50 6.66 8.62 8.05 8.38

6.66 9.15

6.66

6.24

Cu. Ft. of Vapor Per GpI. Per Lb. Liquid Liquid 37.0 6.35 28.5 3.8 42.5 3.92 29.6 4.41 25.9 4.44

38.4 5.12 80.7 13.12 27.9 " 3.23 40.9 8.08 37.4 3.27

3.33 5.0 33.9 3.70

22.6 3.43

22.3 3.58 9.18 37.7 3.02 10.0 31.0 3.10

9.16 9.16 58.1 6.34 8.33 35.8 4.29 8.33 35.8 4.29

5.00 26.6 6.37 7.5 28.5 3.80 6.68 42.3 6.35 6.66 42.3 0.35 5.83 22.2 3.81 8.33 41.1 4.93 8.33 . . . . . . . . 7.50 . . . . . . . . 13.3(a) . . . . . . . . 7.5 32.2 4.29

7.5 33.3 4.44 7.5 27.0 3.6

J *Approximate Cu. Ft, of Air rendered barely

exploaiveper gal. dso lvent

1813 1472 680

2080 2132

1188 1024

1762 1507

2802

3052 1889

738 1341 1341

2392 1555 1972 2073 1663 3239

2388

1248 3673

(2) S tandard factor of safety of 4 for cont inuous procesa ovenL

(3) L.E.L. Correction factor for batch ovens between 250°F. and 500°F . mult i* ply by 1.4 (see 420-2).

(4) The max imum number of gallons of solvent evaporated per un i t of ~ e on the b a ~ of m a x i m u m p o ~ b l e load inga

(a) " H a n d b o o k of Chemis t ry" Nin th Edi t ion - - 1956 - - Lange. (b) Clamified as a potent ia l ly explosive chemic91 (see N B F U Research. Repor t No.

12 Ni t ropamffms and their Hazards ) . ~D

Tab le 4-2 TABLE OF P R O P E R T I E S OF C O M M O N L Y USED FLAMMABLE L I Q U I D S

• IN M E T R I C UNITS The data in this table have been obtained, with few exceptions as noted, from NFPA Pamphlet No. 325 (1960 Edition). "Fire Hazard Propert es of Flammable Liquids,

Gases. and Volat~e Solids." Available figures from numerous sources will be found to vary over a wide range in many instances, depending on t he purity or grade of samples a ad on the test conditions p r~enbed by different observers. The figures presented are for information and general guidance only and are not to be regarded as official standanis.

A ne amportance o: obtaining preeme aata on the rate of evaporation by actual tests on particular pa n t Iormulat on n use needs to be emphasized Some of these mu ti- component preparations may contain several solvents with widely different values of "lower explc~ive limit " "specific gravity," and "vapor density." Until such determlnaticns are magi. e; the operation .should be on the side of safety'. Therefore, the individual solvent, whose data result in the largest required volume of air per liter, should be used as the o&sm mr sale ventimtion. Corrections and factors olsafety for final ventilation values are to be applied as indicated in the footnotes.

J

A Molecular Weight (a)

58 130 88

88

78

116 74 74

118 130 152 75 90 132 113

108

84 312

134

278 147 89 73

88 88 46 74 118

B Fh~h Point

oo_~isC- 25

- 25

33

< - - 1 8 --11

22 29 28

6O 32 66

--30 40 51

. 3 2

252 94

--20 44

48

16 157 08

58

12 --4 13

--44 46

C Igh.

Temp. Deg. C.

538 378 379

300

288 562

421 343 427

244 427 466 100 238 379 638

343 559

260 420

436

399 403 648

445

180 427 423 180 4O0

Acetone - Amyl Acetate n Amyl Aecetate iso

Amyl Alcohol n

Benzine (Petroleum Ether) Benzol (Benzene)

Butyl Acetate n B u t y l Alcohol n Butyl Alcohol - - mo

Butyl Cellosolve Butyl Propionate Camphor Carbon Disulphide Ceilosolve (Ethyl Cello6olve) • Ceilosolve Acetate ' Chlorobenzene°mono

Cottonseed 0il (Refined) Cresol m or p

Cyelohexane Cyclohexanone

Cymene-para

Denatured Alcohol Di~utylphthalate o Dichlorobenzene ortho Diet hyl Ketone Dimethyl Formamide

Dioxane - - 1 4 (D ethylene D o x de)

Ethyl Acetate Ethyl Alcohol' Ethyl Ether Ethyl Lactate

D Ex 1o. Limits % ~y Volume

Lower Upper 2.6 12.8 1.1 7.5 1.0 7.5

~} 100°C. 1.2 I0.0

@ 16O°C. 1,1 5.9 1.4 7.1

@ 100°C. 1.7 7.6 1.4 11.2 1.7 10.9

@ 1000C. @ IO0*C

1.3 44 2.6 15.7 1.7 . . . . 1.3 7.1

@ 16O*C. @ 160*C.

1.1 . . . . @ 160°C.

1.3 8 1.1 . . . .

@ lO0*C. 0.70 . . . .

@ 100"C.

2.2 9.2

2.2 . . . . @ 100*C.

2.0 22 2.5 9 4.3 19 1.9 48 1.5 . . . .

@ I00"C.

E Specif.

Gravity IWater

0.8 0.9 0.9

0.8

0.6 0.9

0.9 0.8 0.8

0.902 0.9 1.0 1.3 0.931 0.975 1.1

0.9 1.0

0.8 0.9

0.9

0.8 1 .0+ 1.3 0.816(a) 0.9

1.0"]- 0.9 0.8 0.7 1 .0+

F Vapor

Density (Air = I)

2.00 4.5. 4.5

3.0

2.5 2.8

4.00 2.0 2.6

4.07 4.5 5.2 2.6 3.10 4.72 3.9

2.9 3.4

4.6

1.0

5.1

2.5

3.0 3.0 1.0 2.6 4.1

G Boiling Point

Deg. C. 56

159 144

138

35 --60 8 0

126 117 110

171 146 209 46

135 156

H Kg. Per

Liter 0.797 0.399 0.899

0.797

0.598 0.899

0.899 0.797 0.797

0.898 0.897 0.996 1.295 0.928 0.974

132 1.097

. . . . 0.899 202 0.998

82 0.728 156 0.899

176 0.899

80 0.798 360 0.998 180 1.297 102(a) 0.813 153 0.899

101 0.998 77 0.899 I 78 0.798 I 35 0.698 '

154 0.998 I

Cu. Meters of Vapor Per Liter Per Kg.

Li0uid Liqutd 0.332 0.416 0.166 0.185 0.166 0.185

0.221 0.277

0.199 0.332 0.267 0.297

0.186 0.208 0.256 0.323 0.256 0.323

0.184 0.203 0.167 - 0.186 0.160 0.160 0.415 0.320 0.249 0.270 0.172 0.176 0.234 0.214

0.223 0.223

0.229 0.286 0.218 0.242

0.163 0.182

0.415 0.520

0.212 0.163

0.298 0.332

0.274 0.274 0.245 0.273 0.415 0.520 0.224 0.319 0.202 0.205

Approx., Cu. Meters of Air

rendered barel ~" explosive per

Liter of Solvezt 12.44 14.78 16.44

18.23

17.89 18.72

10.73 18.01 14.80

31.52 9.34 9.93

17.77

20.04

17.38 19.57

23.13

9.4i lZ.~

13,41 9.60 9.24

11.54 13.26

o < t~

Ethyl Methyl Ether Ethyl Fropionate Ethylene Dichloride Gasoline Hexane n Kerosene Linseed Oil ~ Raw Methyl Acetate Methyl Alcohol Methyl Carbitel Methyl Ceilceolve Methyl Cellosolve Acetate Methyl Ether Methyl Ethyl Ketone Methyl Lactate

Mineral Spirits No. 10

Naphtha (V.M. & P. Regular) Naphthalene Nitrobenzal

Nitroethane Nitromethane (b) Nitropropane - - 1 Nitro re a n e - 2 Para~n ~il Petroleum Ether (See Benzine) Propyl Acetate - - iso Propyl Alcohol n Propyl Alcohol - - iso PropEl Ether - - iso Fyndine Rosin Oil Soy Bean Oil Tetrachloroethane (sym) Toluol Turpentine Vinyl Acetate Xylene (Xylol)

A Molecular ~eight (a)

60 102 99

86

74 32

120 76

118 46 72

104

128 123

75 61 89 89

102 6O 60

102 79

168 92

86 106

B Flash, Point Peg. C.

--37 12 13

~43 -22 38

222 --10 11 94 ~0 56

Gas -9 50

40

-6 78 88

28 35 (o. e.) 49 (o. c.) 39 (o. e.)

228 < --18

4 15 12

--28 2O

130 282

35 12 17

. C Ign.

Temp De8. C

12O 477 413 257 234 229 343 502 464

288

360 616 385

245

232 529 482

414 418 420 428

288 460 371 399 443 482 342 445

539 253 427 464

D Ex 1o. Limits % ~y Volume

Lower Upper 2.0. lO.I 1.9 11 6.2 16 1.4 7.6 1.2 7.5 0.7 5

3.1 10 7.3 36

3.4 18 1.8 10 2.2 . . . .

@ 100°C, 0.8 . . . .

@ 100*C. 0,92 6.0 0.9 5.9 1.8 . ..

@ 93°C. 4.0 . . . . 7.3 . . . . 2.6 . . . . 2 .8 . . . .

1.1 '5.9 1.8 8 2.1 13.5 2.0 12 1.4 21 1.8 12.4

1.4 6.7 0.8 . . . . 2.6 13.4 1.0 0.0

~Note: Column J gives the cubic meters of air rendered barely explosive by 1 liter of solvent. However, for most practical calculations, this value is elo~e enough to the actual volume of the vapor-air mixture.

*For final required safety ventilation values in each particular oven operation these figures are multiplied by the following factors as they apply (see 410 and 420 of text and calculations examples Appendix C):

(1) Temperature - - Volume Convention (see table - - 400-10):

• E Specif.

Gravity a~,rater = 1 )

0 .7 0.9 1.3 0.8 0.7

<." 1.0 0.9 0.9 0.8 1.035 0.966 1.005

0.8 1.1

0.8

0.75 1.1 1.2

1.1 .1.1 1.0 1.0

0.6 0.9 0.8 0.8 0.7 1.0 1.0 0.9 1.6 (a) 0.9 <1

0.9 0.9

F Vapor

Density '~Air = 1)

2.1 3.5 3.4 3 - - I 3.0

2.6 1.1 4.14 2.62 4.07 1.6 2.5 3.6

3.9

3.73 4.4 4.3

2.6 2.1 3.1 3.1

2.5 3.5 2.1 2.1 3.5 2.7

3.1

3.0 3.7

G Boiling Point

Deg. C. ! 10 99 84

38 --204 89

151-301 316

60 64

193 124 143

--24 80

145

149

100 --160 218 211

114 101 131 120

35 - 6 0 90 97 83 59.

115 <300

146 (a) 111 149

72 144

H Kg. Per

Liter 0.998 , 0.899 ' 1.297 I 0.798 0.698 '

0.899 0.798 1.033 0.964 1.004

0.798 1.097

0.798

0.748 1.097 1.198

1.097 1,097 0.998 0.998

0.599 0.899 0.798 0.798 0.698 0.998 0.998 0.899 1.593 0.899

0.899 0.899

Cu. Meters of Vapor Per Liter Per Kg.

Liquid Liquid 0.277 0.39@ 0.213 0.237 0.318 0.245 0.221 0.275 0.194 0.275

0.287 0.319 0,604 0.756 0.209 0.202 0.306 0.317 0.205 0.204

0.025 0.312 0.254 0.231

0.189 0.214

0.167 0.223 0.207 0.188 0.232 0.193

0.435 0.396 0.268 0.268 0.268 0.268

0.199 0.335 0.213 0,237 0.316 0.396 0.316 0.396 0.156 0.238 0.307 0.308

0.241 0.268

0.249 0.277 0.202 0.225

J Approx., Cu. Meters of All'

rendered barely explosive er

Liter of So~ea t 13.56

. 11.01 5.09

15.56 15.98

7.66

13.i8 11.27

20.96

22.~ 12.63

~.~2 10.03 10.03

i¢.sb 11.63 14.75 15.51 11.69 10.75

16.96

9.34 19.99

(2) Standard factor of safety of 4 for continuous process ovens. (3) L.E.L. Correction factor for batch ovens between 121 C., and 260 C.,'

multiply by 1.4 (see 420-2).

(4) The maximum number of liters of solvent evaporated per uni t of time on the basis of maximum possible loedings.

(a) "Handbook of Chemletry" Ninth Edition - - 1958 - - Lange.

(b) Classified as a potentially explc~ive chemical.

o o Q ,

I " 4

8 6 A - 7 2 OVENS AND FURNACES

4-2.3 C a l c u l a t e d R a t e o f V e n t i l a t i o n M e t h o d . I n con t inuous process owens w h e n the ra te of ven t i l a t i on is ca l cu la t ed the fo l lowing m e t h o d shall be used.

NOTE 1: This method is usually applied when an oven is designed to operate with a particular solvent and when ventilating air may be ac- curately controlled.

. 444X Sp.Gr. X (100-L.E.L.) Required ventilation= V.D. X L.E.L. cu. ft. of. air re-

ferred to 70 ° F. per gallon solvent evaporated, where:

Sp. Gr. = Specific gravity of solvent (water = 1).

V.D. = Vapor density of solvent vapor (air = 1).

L.E.L. = Lower explosive limit expressed in per cent by volume. (For example, L.E.L. of gasoline written 1.3, not .013.)

NOTE 2: The derivation of the above formula is as follows :

One gallon of solvent produces 8.33 XSp. Gr. .075 XV.D. cu. ft. of flammable vapor

where:

8.33 = Weight of one "gallon of water in lbs. .075 = Weight of 1 cu. ft. of air in lbs.

Tl~e volume of air required to render this amount of vapor barely ex-

(100-L.E.L.) X this figure, or 1 gallon of solvent will form plosive is L.E.L.

8.33 XSp.Gr. X (100-L.E.L.) 0.075 X V.D. X L.E.L. cu. ft. of the barely explosive mixture.

Providing a factor of safety of 4 (maintaining an average concentration of 25% of the lower limit) then the equation becomes 4X8.33XSp.Gr .X (100--L.E.L.) 444X Sp.Gr. X (100--L.E.L.)

.075 X V.D. X L.E.L. or V.D. X L.E.L.

The total volume of air, in cubic feet per minute, required for ventilation of the oven is obtained by multiplying the cubic feet of air required per gallon of solvent by the gallons of solvent per minute entering the oven. (See 4-1.12 and 4-2.4 for calculation examples. ) ""

A c o n v e n i e n t l is t ing of the p roper t i e s and a p p r o x i m a t e v o l u m e s o f a i r r e q u i r e d to r e n d e r one ga l lon of c o m m o n solvefits •bare ly explos ive appea r s in d a t a tables f o u n d in T a b l e 4-2.

4-2.4 I n con t inuous process ovens w h e n a d i rec t - f i red c o m - bus t ion sys tem (wi th in the oven c h a m b e r o r r emote ) is used to h e a t a p a i n t o r p o w d e r cu r ing oven , the v o l u m e of c o m b u s t i o n p roduc t s f r o m bu rne r s shall be d e t e r m i n e d for s to ich iomet r i c o p e r a t i o n by • the f o r m u l a :

B t u / h r (To ta l B u r n e r R a t i n g ) C u b i c feet of a i r p e r m i n u t e = ( S C F M ) re fer red to 70°F

95 x 60 ( S t a n d a r d densi ty)


W h e r e 95 B t u / c u . ft. = the a p p r o x i m a t e h e a t c o n t e n t of a gas- a i r m i x t u r e wi th sl ight excess air .

W h e n this ca l cu l a t i on for 70°F e q u i v a l e n t v o l u m e is g r e a t e r t han one - th i rd ( ½ ) of the v o l u m e d e t e r m i n e d for r e m o v a l of c h e m i c a l by -p roduc t s ( f rom .4-2.1, 4-2.2, o r 4-2.3), the m i n i m u m exhaus t v o l u m e for the o v e n wil l be the s u m of the two c o m p u t a t i o n s , ad ju s t ed for t h e r m a l expans ion as pe r 4-1.9. W h e n the c o m b u s t i o n p roduc t s a re less t h a n o n e - t h i r d of the v o l u m e d e t e r m i n e d for re- m o v a l of c h e m i c a l by -p roduc t s , the m i n i m u m exhaus t v o l u m e for t h e oven shall be based on the v o l u m e for r e m o v a l of c h e m i c a l by- p roduc t s only, w i t h a d j u s t m e n t for t he rma l expans ion as pe r 4-1.9.

NOTE 1: Example For a Continuous Liquid Solvent Paint Oven. This direct gas-fired oven has a 21~ million Btia/hour burner system and the

heating process is intended to evaporate 14 gallons per hour of toluol from a dipped liquid finish on sheet steel products being baked at 400°F.

When this calculation for 70°F equivalent volume is shown to be more than one-third of the volume determined for the removal of chemical by- products (from 4-2.1, 2 or 3), the minimum exhaust volume for the oven will be the sum of the two computations adjusted for thermal expansion as per 4-1.9. When the combustion products are shown to be less than one-third of the volume determined for removal, of chemical by-products, the minimum oven exhaust volume shall be based on the volume determined for removal of chemical by-products only with adjustment for thermal expansion as pep 4-1.9.

(a) The exhaust indicated for combustion products is (see 4-2.4): 2,250,000 - - = 395 SCFM (70°F condition)

95 x 60 (b) Ventilation for solvent vapors is (see 4-2.2): '

14gph x 10,000 = 2,331 SCFM 60

(c) The adjustment for thermal expansion is based on item "h" only: 2,331 x 1.62 = "3,776 CFM (at 400°F)

NOTE 2: Example 1. For a Continuous Powder Coating Oven. This direct gas fired oven has a 2 million Btu/heur burner system being used

to fuse an organic powder finish on steel products at 450°F. Seven thousand square feet (7,000 sq. ft.) of surface is to be covered hourly to a depth of 3 mils with a powder intended to provide 135 square feet of 1 mil coating per pound.

(a) The exhaust indicated for combustion products is (see 4-2.4): 2,000,000

351 SCUM 95 x 60

(b) The amount of powder to enter the oven is: 7000 x 3

---- 156 lb. per hour 135

(c) Ventilation for constituents released from powders will be (see 4-2.5):

1 5 6 x 0 . 0 9 x 3 6 0 x 4 = 33'75CFM 6O

(d) The adjustment for thermal expansion is based on the sum of a and b: (351 + 337) x 1.72 = 1183 CFM (at 450°F)


NOTE 3: Example 2. For a Continuous Powder Coating Oven. (a) Th i s 450°F, electrichlly-heated oven is required to cure 156 pounds

~ t . . . . . J . . . . . t . . . . . - l o . . . . . . I ^ t l _ I . . . . . . . . . . L . . . . . . . . . . . L _ . - ~ : _ _

products to be'considered. Accordingly, the.ventilation rate for constituents released from powders will be:

156 x 0.09 x 360 x 4 = 336 SCFM

60

(b) The adjustment for thermal expansion will be: 337 x 1.72 = 580 CFM (at 450°F)

If this is adequate to avoid undesirable fume spill at oven work openings, no additional ventilation will be required.

4 - 2 . 5 C a l c u l a t e d R a t e o f V e n t i l a t i o n M e t h o d fo r P o w d e r F u s i n g o r C u r i n g O v e n s . I n c o n t i n u o u s p rocess o v e n s w h e n t h e r a t e of v e n t i l a t i o n fo r p o w d e r fu s ing o r c u r i n g is c a l c u l a t e d t h e f o l l o w i n g m e t h o d shal l b e used.

Dilution of the powder constituehts released at theoretical minimum ex- . plosive condition shall require ventilation of :

W-x R x 360 .= cubic'feet per hour referred to 70°F (standard density). \

Provide a factor of safe'ty of 4 and convert • to cubic feet per minute, the equation above becomes:

W x R x 3 6 0 x 4 = SCFM (standard density)

6O

Determine the weight of powder for use in the above caclculation, as follows:

S x T W -- Weight of powder in pounds entering oven per hour

C

Where: W = Maximum intended hourly rate of powder delivery into the oven.

R = Percent of powder constituents released during oven cure cycle. A generally accepted value for'characteristic powders and operating conditions is 9.0% based on exper!mental determination.

360 = Cubic feet of air-rendered barely explosive per pound of powder " constituent released (based on xylol - - see Table 4-2).

S = Surface area of parts to be coated in square feet per hour.

T = Maximum powder coating thickness in mils.

C -- Manufacturers ' recommended coverage in square feet per pound for one rail thickness (135 typical).

4-3 B a t c h P r o c e s s O v e n .

4-3.1 E s t i m a t e d . R a t e o f V e n t i l a t i o n M e t h o d . I n ba_tch o v e n s for c o a t e d s h e e t m e t a l t y p e work , t he safe ty v e n t i l a t i o n r a t e sha l l b e des{gned a n d m a i n t a i n e d to p r o v i d e a t l eas t 380 c f m of v e n t i l a t i o n a i r p e r m i n u t e r e f e r r e d to 70°F p e r g a l l o n of f l a m - m a b l e vo la t i l e s e x c e p t as p e r m i t t e d in 4-3.2.

V E N T I L A T I O N 8 6 A - 7 5

NOTE 1 : Industrial experience indicates that the nature of the work being baked is the main factor in determining the ventilation rate. Different" t y p ~ $ n f w n r k n r n d l l f ' e ~ d l l ~ ' e ~ r e ' n t o v : ~ n a r : ~ t l n n r : ~ t a ¢ w h i l ~ h ~ k l n ~ unc l f i p I r l

. . . . x- . . . . . . . . . . . . . . . . . . . . r . . . . . . . . . . . . . . . . . . . . . . . . . . . o . . . . . . . . .

tests show" that sheet metal or metal parts coated by dipping produces the highest evaporation rates ordinarily encountered• Tests and years of experience have shown that 380 cu. ft. of ventilation air per minute referred to 70°F per gallon of flammable volatiles in the batch, is reasonably safe for dipped.metal. _ NOTE 2: Tests of dipped sheet metal in batch process ovens show that in typical one-hour bakes practically all the solvent is evaporated in the fibst twenty minutes. Further, the peak evaporation rate occurring from four to eight minutes after loading is about three times the twenty-minute average. With one gallon of solvent in the batch, the twenty-minute average evaporation rate is 1/20 gpm and the peak rate three times this or 3/20 gpm. Using one gallon of solvent whose vapor requires approximately 2,500 cu. ft. of air referred to 70°F to keep the mixture barely below the lower explosive limit, the rate of ventilation required in order. to be safe under the worst condition would be 3/20 x 2,500 or approximately 380 cfm referred to 70°F.

4-3 .2 C a l c u l a t e d R a t e o f V e n t i l a t i o n ' M e t h o d . I n b a t c h ovens p r o c e s s i n g o t h e r t h a n c o a t e d s h e e t m e t a l t y p e work , t h e f igure of 380 c f m r e f e r r e d to 70°F sha l l b e u sed un less t h e r e q u i r e d v e n t i l a t i o n r a t e s c a n b e c a l c u l a t e d o n t he basis of re l iab le" p r e v i o u s . e x p e r i e n c e o r t h e m a x i m u m e v a p o r a t i o n r a t e d e t e r m i n e d in tests. r u n u n d e r a c t u a l o v e n o p e r a t i n g c o n d i t i o n s . O n t h e basis of t h e m a x i m u m e v a p o r a t i o n r a t e d e t e r m i n e d b y test~ suf f ic ien t v e n t i l a - t ion sha l l b e f u r n i s h e d to p r e v e n t t he v a p o r c o n c e n t r a t i o n in t h e oven f r o m e x c e e d i n g 25 p e r c e n t of t h e l o w e r exp los ive l imi t .

• Exception No. 1: The safety ventilation rate may be decreased when a continuous vapor concentration indicator and controller is provided. For such installations the continuous vapor concentration indicator and controller shall be arranged to alarm, shutdown the oven heating system, and operate additional exhausters at a predetermined vapor concentration not to exceed50 percent o.f the lower explosive limit.

NOTE: The recirculation and exhaust fans and other devices should be operated in such a manner that the vapor concentration is maintained at or less than the safe predetermined concentration. .

Excep'tion No. 2: All types of work. I f the maximum number of gallons evaporated during any one hour of the total heating period is known, this figure may be used to calculate the required amount o.f ventilation as.follows: The required amount oJ ventilation air in cubic .feet per minute referred to 70°F shall be at least equal to the gallons of solvent evaporated during the maximum hour multiplied'by the volume of air (referred to 70°F) com- puted as rendered flammable at "the lower explosive limit'(per .formula in 4-_2.3) then multiply by an empirical'.factor of 70 and divide by 60.

Warning: U s e c a u t i o n in a p p l y i n g t h i s m e t h o d to w o r k of low • mass w h i c h wi l l h e a t u p q u i c k l y (such. as p a p e r , t ex t i l es ) , o r w o r k

c o a t e d w i t h m a t e r i a l s con t~ / in ing h i g h l y vo la t i l e so lvents . E i t h e r c o n d i t i o n m a y g i v e too h i g h a p e a k e v a p o r a t i o n r a t e . f o r th i s m e t h o d .

• 7 /

8 6 A - 7 6 OVENS AND F U R N A C E S

NOTE 1: Application of Examples for Box or Batch Ovens.

(a) Coated Metal.

A batch oven takes a load of dipped metal at 300°F. There are 3 gal lors of volatiles, mostly xylol, contained in the paint used to coat the lo-td. The ventilation, required in sections 420-1(a) and 420-2, is ligured as follows:

Required Ventilation efm. referred to 70°F =380 x 3 (gallons of xylol) x 1.4 (L.E.L. correction factor - - see 420-2) = 1596 efm. referred to 70°F

or Required Ventilation at the oven teml)erature of 300°F would be:

300 -t- 460 1,596 x =2,290 cfm. of air :tt 300°F.

70 -t- 460

(b) .Types of Work other than Coated IXletal where Evaporation Rate Tests Have Been Made.

A batch oven operates at 255°F with load of small transformer coils impregnated with material containing 4.8 gallons of volatiles, mostly toluol. Tests under plant operating conditions indicate that over five hours were required to evaporate all volatiles arid that the peak evaporation rate, occurring in the first 5 minutes after loading, was .06 gallons per minute. The ventilation, required in 420-1(b) would be figured as follows:

Required Ventilation efm. referred to 70°F = - ' Peak evaporation rate gpm. (determined by test) x cu. ft. of air to form a barely explosive mixture per gallon of toluol (see Example A) x Factor of 4 (to prevent vapor concentration exceeding 25 percent L.E.L. x L.E.L. Correction Factor (see 420-2) or =.06 x 2,268 (From Example A) x 4 x 1.4

=762 cfm. referred to 70°F.

or Required Ventilation at the oven temperature would be:

255 -I- 460 762 x 1,029 cfm. air at 255°F.

70 -t- 460

(c) Alternate Estimation of Ventilation - - All Types of Work.

A batch oven cures at 480°F a load of asbestos rings impregnated with thinned asphalt, the volatiles being mostly Mineral Spirits No. 10. I t is known from weight tests of samples removed progressively throughout the cure, that the maximum amount of volatiles evaporated in any one hour is 2.3 gallons, and the total loss of weight throughout the cure is equivalent to 6.6 gallons. The estimated ventilation, required in 423.2, Exception 2, is figured as follows:

Estimated Ventilation cfm. referred to 70°F=gallons of solvent evaporated during maximum hour x cu. ft. of air rendered barely explosive per gallon of Mineral Spirits No. 10 (see Table 4-2) x empirical factor of 10 x L.E.L. Correction Factor (see 4-3.3, Note 2)

or=2.3 x 2,802 x 10 x 1.4 = 1,504 cfm. referred to 70°F.

60

or Estimated Ventilation at the oven temperature of 4800F would be:

480 -t- 460 1,504 x =2,667 cfm. at 480°F.

70 -F 460

V E N T I L A T I O N 8 6 A - 7 7

NOTE 2: Important Suggestions for Securing Data.

Rate of Evaporation (a) The maximum number of gallons of solvent evaporated per unit of time

in ovens must be figured on the basis of maximum possible loadin[gs; i.e., if the baking cycle is 20 minutes and 2 gallons of solvent enter the oven in this period, then the number of gallons of solvent per hour for purpose of figuring fresh air for safe ventilation must be assumed to be 6 gallons per hour, whether actual loadings are continued for the entire hour or not.

b (b) It has been shown in the foregoing examples that the volume of air

m cubic feet per pound of air increases with rise in temperature and that correction must be made for this increase in order to provide the required volume at 70°F.

(c) Air also increases in volu'me at elevated altitudes due to lower baro- metric pressures, even though the temperatures are constant. While no correction is ordinarily made at altitudes in the lower levels (say-up to 1,000' above sea level) such a correction is necessary at higher altitudes. The correction figure m~y be obtained from available tabulated data.

(d) .Every effort should be made to obtain the information on the exact solvents, and their characteristics, to be used in a proposed coating operation. When a combination of solvents is used, that solvent, which requires the greatest amount of air per gallon for ventilation, should be used as the basis for calculation.

4-3.3 V o l u m e s of air speci f ied or c a l cu l a t ed as p e r 4-3.1 or • 4-3.2 c o r r e c t e d for o p e r a t i n g t e m p e r a t u r e , shal l a p p l y for oven

t e m p e r a t u r e s up to 250°F. F o r b a t c h ovens o p e r a t i n g a t t e m p e r a - tu res ove r 250°F, the v o l u m e shal l be i nc reased by a m u l t i p l i e r o f 1.4 a n d c o r r e c t the t e m p e r a t u r e as ou t l i ned in 4-1.9.

NOTE 1 : The 1.4 multiplier is not required on continuous process ovens.

NOTE 2: Extensive tests have been conducted by the Underwriters .Laboratories Inc. to obtain data as to the effect of elevated temperatures on the L. E. L. of many of the solvents commonly used in connection with ovens. These tests show that the L. E. L. of all solvents tested decreases as the temperature increases, the conclusion being that more air (referred to 70°F) is required for safety per gallon of solvent as the oven temperature increases. The actual figures vary considerably with different solvents, but for the sake of simplicity the preceding requirement applies.

4-4 Vai3or C o n c e n t r a t i o n Indicators a n d Control lers .

4-4.1 C o n t i n u o u s v a p o r c o n c e n t r a t i o n i n d i c a t o r s a n d con- t ro l lers _means dev ices w h i c h m e a s u r e and ind ica t e , d i r ec t ly or in- d i r ec t ly in p e r c e n t a g e of the l ower explos ion l imi t , the c o n c e n t r a - t ion of a f l a m m a b l e v a p o r - a i r mix tu re .

NOTE: They may be of the portable or fixed location'continuous operating type. The continuous indicators are mostly used throughout the peri~cl of operation of a process wherein flammable vapor is evolved. In addition t6 indicating or recording concentrations to aid in safe and efficient process control, they can be arranged through suitable controls automatically to

t: lm

86A-78 OVENS AND F U R N A C E S S A F E T Y E Q U I P M E N T AND A P P L I C A T I O N 86A-79

sound an alarm, open or close dampers, start or stop motors, conveyors, and ventilating fans, when the concentration of a flammable vaporTair

These-devices are ordinarily used with continuous process ovens and dryers or coating machinesevaporating relatively large amounts of flammable liquids where the character of the process is such that evaporation rates may fluctuate widely or the normal working vapor concentration level is unusually high. Ovens connected to solvent recovery systems are frequently equipped with these instruments.

Only approved devices should be used and plans covering the application of the instrument to the process in question should be submitted to the authority having jurisdiction.

4-4.2 F l a m m a b l e vapor concent ra t ion indicators shall be used to test f l ammable vapors having a flash poin t below 70°F unless it is possibl e to ma in ta in the sampl ing line and measur ing assembly at the t empera tu re of the vapors, so tha t condensa t ion will not occur.

4-4.3 M a i n t e n a n c e of cont inuous f l ammable vapor indicators and controls shall be done per iodical ly , th rough a ma in tenance service by the ins t rument manufac tu re r or equivalent . P roper ly t ra ined personnel, compe ten t to make necessary da i ly adjus t - ments in accordance with the manufac tu re r ' s exact instruct ions or equiva len t shall .be made responsible for re l iable opera t ion .

• . ~ x ~ . A rehabte auxhlary racans tot frequenuy C£1U1.,1~.211~ mdmator calibrations is imperative. It should be noted that some flammable vapor indicators are designed for use on specific materials, and that new calibrations must be made for each change in material tested. Maintaining sampling lines clean and airtight and prompt renewal of filaments when necessary are essential.

~nap~vr 5 oaxc ty-x .quxpmcnt a n u ,~plJt lcalzon

5-1 Genera l .

5-1.1 Fo r safety of personnel and pro tec t ion of proper ty , careful considera t ion shall be given to the supervision a n d / o r moni tor ing of condit ions which m a y cause, or m a y lead to, a real or potent ia l haza rd on any given instal lat ion.

5-1.1.1 Fuel-f i red units, and units where combust ib le or f l ammable vapors or gases are invoFced, shall be p rov ided wi th all safety devices in accordance with establ ished good and safe prac- tices.

5-1.1.2 Safety considerat ions shall extend to al l ied equipment, and to o ther p rox ima te equ ipment , to a v o i d - a d d i t i o n a l con t r ibu tory hazards .

5-1.1.3 A safety shu tdown of the hea t ing system by any of the prescr ibed safety features or devices shall requi re e i ther :

(a) M a n u a l in tervent ion of an opera to r for i-e-establish- " . . . . . . . . . . . . . . . .

ment of n o r m a l opera t ion of the system, or

(b) Au toma t i c .recycling of the system by an approved au toma t i c p r o g r a m m i n g system.

\

5-1.2 Areas of concern shall include, bu t shall not be l imi ted to:

(a) Fresh vent i la t ion air.

(b) Ree i reu la ted air.

(c) Combus t ion air.

(d) F l ame presence.

(e) Fuel pressure and tempera ture .

( f ) S t eam and electr ic units.

5-1.3 I t shall be con t inua l ly borne in r a i n d tha t :

(a) T h e mere presence Of sa fe ty equ ipmen t on an instal lation cannot , in itself, assure absolute safety of opera t ion .

(b) T h e r e is no subst i tute for a di l igent , eapab!e , wel l - t ra ined opera tor .

(c) Highly repet i t ive opera t iona l cycl ing Of any safety device m a y reduce its life span.

(d) Au toma t i c s team valves, electr ic relays and fuel safety , [~ shutoff valves are n o t substi tutes for ma in shutoff cocks (valves) . and disconnects. ~


5-1.4 Regularly scheduled inspection and maintenance of all safety deyices shall be performed as required to insure that the intended protection against the anticipated hazards, real or potential, is available at all appropriate times.

5-1.4.1 I t shall be the sole responsibility of the user to establish, schedule and enforce the frequency of and the extent of the inspection/maintenance program (as well as the corrective action to be taken) because only the user can know what the actual field conditions of operation are.

5-1.4.2 I t shall be the responsibility of the equipment manufacturer to provide suitable recommendations and/or suggestions on maintenance and inspection procedures.

5-1.5 Safety devices shall be properly installed, and maintained in accordance with the manufacturer 's instructions.

5-1.6 Safety devices shall be guarded against physical damage and inadvertent tampering.

5-1.7 Safety devices shall not be shorted-out nor shall they be bypassed.

Exception: Deadman switch usage on vent valve, to leak test the safety shut-off valve.

5-2 Preventilation (Pre-purge, Purging Cycle).

5-2.1 Prior to each operational cycle, t~ositive provision shall be made for the removal of, or for dilution to a point below the LEL of, all combustible/flammable vapors and/or gases which may have entered during the shutdown period.

5-2.1.1 At least four (4) standard cubic feet (SCF) of fresh air per cubic foot of oven volume shall be introduced during the purging cycle.

5-2.1.2 Timed preventilation shall be provided for all ovens and heaters in which flammable vapors or fuels can accumulate during a shutdown period.

Exception: Timed preventilation can be omitted on ovens of less tha.n 350 cu. f t . volume provided:

(a) Fans are proven operating, and

(b) Doors are proven open before admitting heat, and

(c) Door area is at least one (1) sq..ft, per fifteen (15) cu..ft, of o v e n

volume.

S A F E T Y E Q U I P M E N T AND A P P L I C A T I O N 86A-81

5-2.1.3 Timed preventilation cycle shall be repeated after " each and every shutdown of the recirculating and /or exhaust fans.

5-3 Ventilation Safety Devices.

5-3.1 Whenever any fan is essential to safe operation of the oven or allied equipment, fan operation shall be proven;

5-3.1.1 Electrical interlocks and/or flow switches shall be ar~'anged in the safety control circuit so that loss of ventilation or air flow will immediately shut down the heating sys tem of the particular oven section affected; or if necessary loss of ventilation should shut down the entire oven heating system as well as the conveyor.

5-3.1.2 Air pressure switches and air suction switches shall not be used to prove air flow if dampers can be closed to the point of reducing flow to an unsafe operating level.

5-3.2 Air flow pressure switches shall not be installed on the pressure side of a fan handling air contaminated with any substance that might condense or otherwise deposit and inter- fere with the switches' sensing or performance.

5-3.3 Adjustable or motorized dampers capable of being moved to a position which might contribute to, or result in, an unsafe condition shall be equipped with mechanical stops, and /or limit switches interlocked into. the safety circuitry to assure that dampers are in a safe operating position.

5-4 Combustion Air Safety Devices (Fuel-fired Units).

5-4.1 I f all, or a portion of, the air required for combustion of the fuel is contingent upon air movement, caused by the exhaust and /or recirculating fans, air flow shall be proven prior to ignition a t tempt and reduction of air flow to an unsafe level shall result in de-energization of the safety shut-off valve (see 5-3).

5-4.2 When a combustion air blower is used, presence of the minimum combustion air pressure required for safe burner operation shall be established prior to each at tempt at ignition.

• 5-4.2.1 Motor starter shall be interlocked (5-3.1.1).

5-4.2.2 An approved low pressure combustion air switch (N.O. Contact) shall be used to sense and monitor pressure, interlocked into the safety circuitry.

t ~


5-4.3 Wheneve r i't is possible for combust ion air pressure to exceed a m a x i m u m safe opera t ing pressure, as might occur when compressed ai r is ut i l ized, a pressure reducing valve and app roved high pressure switch (N.C. Contact ) and an app roved low pressure swi tch (N.O. Contac t ) shall be used.

5-4,4 Combust ion air shail be established dur ing the prevent i la t ion (pre-purge) cycle whenever necessary to provide cooling a i r for the burner or to otherwise establish a i r flow th rough the bu rne r for reasons of safety.

5-4.5 Use of Combustion air for a post -purge per iod (following shut-down) shall be considered whenever exhaus t / r ec i r eu la t ing fans cont inue in opera t ion a n d / o r whenever expostire to res idual hea t can lead to excessive ra te of burner de ter iora t ion .

5-5 Fue l Safety D e v i c e s .

5-5.1 G e n e r a l .

5-5.1.1 As with all safety devices, full considera t ion shall . cont inua l ly be given to the fact that i m p r o p e r : a p p l i c a t i o n a n d / o r

ad jus tmen t can result in repea ted and unscheduled shutdowns. I m p r o p e r correct ive act ion (by-passing, j umper ing -ou t , etc.) can lead to a hazardous condi t ion, and shall not be taken to sustain

• p roduct ion .

5-5.1.2 One or more safety devices shall be p rov ided to pre- venf un in ten t iona l recycl ing of the safety system, or any por t ion of it.

5-5.2 Safety Shut -o f f v a l v e s (Gas or Oil) . ,

5-5.2.1- Genera l .

NOTE 1 : The safety shut-off valve is the "Key Unit" of all the safety controls used to protect against the explosion Or fire hazards which could result from accidental interruption to various services~or operations, such as flame failure, failure of fuel pressure, failure of combastion air pressure, failure of exhaust or recirculation fans, excessive temperatures, or power failure.

NOTE 2: Safety shut-off valves are designed to automatically shut off the fuel to the burner system within 5 seconds after interruption of the holding _, medium by any one of the interlocking safety devices. They are self- closing (usually by means of an internal spring) and cannot be readily bypassed or blocked open. Most approved valves have an open/shut indicator actuated by the closure element. They are available with end switches, actuated at both the closed and the open end of the stroke for signal and alarm purpose.

5-5.2.1.1 Valve components shall be of a m a t e r i a l suitable for the fuel handled .

SAFETY EQUIPMENT AND APPLICATION" 8 6 A - 8 3

5-5.2.1.1.1 I t ' s h a l l be the user 's responsibi l i ty to in- form the equ ipmen t manufac tu re r of any devia t ion f rom the s tandard , clean fuel.

5-5.2.1.2 Valves shall not be subjected to pressures in excess of manufac tu re r ' s rat ing.

5-5.2.1.2.1 I f no rma l inlet pressure to the fuel pressure regu la to r immedia t e ly ups t r eam f rom the valve exceeds valve 's pressure rat ing, a relief valve shall be pi~oyided and shall be vented to a safe location.

5 - 5 . 2 . 1 . 3 Posit ion indica t ion shall be p rov ided for safety shut-off valves to main burners in excess .of 150,000 B tu /hou r . T h e use of signal lights shall be pe rmi t t ed for valves not e q u i p p e d with posi t ion indicat ion.

5-5.2.1.4 Safety shut-off valves shall not be used in lieu o f manua l cocks/vaFces when shut t ing down.

5-5.2.2 Gas Safety Shut -o f f V a l v e s .

5-512.2.1 If. main or p i lo t gas bu rne r capac i ty exceeds 400,000 B tu /h r . , two safety shut-off valves (p iped in series) shall be used. In addi t ion , a vent wi th an a p p r o v e d no rma l ly open vent valve shall be loca ted b e t w e e n them, and sized in accordance with T a b l e 5-5.2.2 (or larger) .

5-5.2.2.1.1 Ven t p i p e shall t e rmina te in a safe locat ion where vented gas cannot re-enter the bu i ld ing wi thou t ex- t reme di lut ion, a n d out le t shall be su i tab ly p ro tec ted against foreign mat te r , ra!n, etc.

Table 5-5.2.2 Vent Pipe Size

Fuel Line Vent Line Diameter Diameter

Up to l l~ ~ 2" 2½" 3 ~ 3½" 4 v 5 ~ 6 u 8 ~

~ ty

, 1 u

1 ~ • 1½" 2 u _

2½ ~

tJI t,m


5-5.2.2.2 I f main or pilot gas burner capacity is 400,000 Btu/hr. or less, a sir~gle approved safety shut-off valve may be used in place of the double safety shut-off valves as required in 5-5.2.2.1.

Exception No. 1: I f spring loaded solenoid valves may be used as the primary safety.shut-off valve with fuel flow up to "400,000 Btu's per hour, or as the secondary safety shut-off valve with the double safety shut-off valve and vent system provided:

(a) The sealing force of the spring is a minimum of five pounds, ex- clusive of "dead weight" of the assembly and fuel pressure exerted.

(b) Their use does not necessitate any abnormal settings of either the high or low gas pressure switches to counter any transient pressure .fluctuations created by sudden operations of the valve.

Exception No. 2: Other solenoid valves, not meeting the above specifications may be used when all three of the following conditions prevail:

(a) The flow is less than 150,000 Btu's per hour.

(b) The valve size and pipe size is a/~ in. or less.

(c) The gas pressure is five (5) psig, or less.

5-5.2.2.3 A permanent and ready means for making tightness checks of all main burner gas safety shut-off valves "shall be provided (see Chapter 7, Inspection and Maintenance).

5-5.2.3 Oil Safety Shut-off Valves.

5-5.2.3.1 An approved safety shut-off valve or valves shall be provided for shutting off fuel to the burner or burners being protected.

5-5.3 Fuel Pressure Switches (Gas or Oil).

5-5.3.1 At least one low pressure switch. (N.O.) shall be provided for, and interlocked with, each burner, system's safety shut-off valve.

5-5.3.2 Whenever the normal fuel pressure to the pressure regulator immediately upstream from the safety shut-off valve exceeds the design limits of the burner system, at least one high pressure (N.C.) switch shall be provided, and interlocked with burner system's safety shut-off valve, as in 5-5.3.1.

5-5.3.3 Pressure switch settings shall be made in accordance with design limits of the burner system and/or the heating unit, whichever is the more stringent.

SAFETY EQUIPMENT AND APPLICATION 86A-85

5-5.4 Combustion Safeguards (Flame Supervision).

5-5.4.1 Each burner flame shall be supervised by an approved Combustion Safeguard, having a nominal flame response timing of 4 seconds or less, interlocked with the safety circuitry.

Exception No. 1: Neither interrupted pilot nor second flame sensor are requ#ed for self-piloted burners, as defined in 1-4.

Exception No. 2: Multiple burners where combustion safeguards for each burner are too numerous to be practical, but continuous line-burner type pilots

for groups of burners (see 3-3.5.2) can be used: An approved practically instantaneous combustion safeguard shall be provided at the far end of each line-burner type pilot, away from the pilot fuel source, with sensing element located at the junction of the flame paths of both pilot ~nd last main burner.

The pilot safety shut-off valve must be initially opened by a manual momentary push button.

Exception No. 3: Where two burners, which will reliably ignite one from -the other, are used, it shall be permissible to use a single approved instantaneous combustion safeguard, supervising one of the burners; the supervised burner shall burn continuously at a firing rate at all times }ufficient to reliably ignite the unsupervised burner.

' i

Exception No. 4: Burners for direct fired heating system which supply a furnace at a fuel rate not exceeding 750,000 Btu/hour may be equipped with heat actuated combustion safeguards or safety pilots. For small equipment under constant attendance, approaching in size the household ga s range~ or very small laboratory test furnace, combustion safeguards may be omitted, subject to approval of the authority having jurisdiction.

Exception No. 5: In general, for greatest security, all burners should be protected with combustion safeguards as outlined in the foregoing sections. When this is not technically feasible the maximum practical protection shall be furnished by providing a reliable continuous pilot at each burner, and/or operating burners on high-low flame, and by installing devices (pressure switches and safety shut-off valves) to assure, where practical, closure of all individual burner cocks before the main burner safety shut-off valve can be opened, and to shut off all fuel in case of high and low fuel pressure and low air pressure, where a# pressure is necessary for operation of burners and controls, subject to the approval of the authority having jurisdiction.

Exception No. 6: Radiant tube heating systems utilizing explosion resistant tube construction do not require combustion safeguards.

5-5.4.1.1 Consideration shall beg iven to the supervision of the main flame, which can be done by:


(a) Use Of a second sensor a p p l i e d o n l y to t h e m a i n l i ~ l i i l ~ l or

(b) In terrupt ing the pilot .

" , . . . . o . o . . i , o ~ . t h n . . * * . ~ o ~ l ~ ' ¢ . : . , ~r, M~..OC#

h e i r P i lo t Presl ~=.w~ - ,

. Main Furna IJ4" 0 n

, . . . . . "

' P ~ " r ' - ~ ~ - - " ~ - ~ ~i. i ii u ,~ ivlra,

---- Common L i n e / "Gas / ] [ I (~ I ~ d) ~ Y8" Pil¢^-~" I I [ Chickmq Pressure J~ Filter n o t s h o w n Low-Air -/ I . t .~.~ _~ ~ /- ir~'~ " '~ [ L / Sw i i ch - -_~ . I I~'~_) .

• . 6~;s:$W. I.L; lkt~ - ~ [ - ,[ I I ~ . ' Ml lnSa fe tyShu i .o f l / ISupcrvislnl(lU)C~ck Whereseveralbutnersaresupp~'d J. . . . . . . . Vi l i i ,Manua l Reset tor l e i k i q e t ~ , t o f through one zero o~vernor, u~e ~ . li].~me,e~utrjii¢ e

" $ i f e t ~ $11u~,off Valve i , lp l ra tor and a,%~irvi$1n~(EM.) • I - C0{k i t {.~ch burner, 110 p 1 ~'~ Ili

indiv idual l i l h i l n ~ .

Figure 5-5.4.1.i(a) Supervising Cock and Gas Safety Control System.

NOTE: • A method of assuring closure of all individual gas burner cocks before the main burner gas safety shut-off valve can be opened is the supervising cock and gas safety control system. A typical piping and wiring arrangement using the pneumatic type supervisifig cock is illustrated in Fig. 5-5.4.1.1(a). (See 1-4, Supervising Cock.) The number and location of pressure switches, arrangement of tubing and other details will vary with the individual installation. In the illustration, the main burner safety shut-off valve cannot be opened until all supervising cocks are closed, combustion air pressure is normal, and normal gas pressure present in the pilot burner manifold. Power failure, loss of combustion air, and/or gas pressure failure during normal firing will shut and lock out the main burner and pilot safety shut-off valves. Once the initial check has been completed and the main burner safety shut-off valve is opened, the low gas pressure switch downstream from the safety shut-off valve shunts the checking pressure switch so that, after lighting the pilots, the supervising cocks can be opened to light off.

. A typical piping and wiring arrangement for the electric interlocking type supervising cock is also illustrated in Fig. 5-5.4.1.1(b). The main burner safety shut-off valve cannot be opened until all supervising cocks are closed (cock switch contacts in series are all closed), ventilation fails operating, preventilation purge completed and other interlocks satisfied.

5-5 .4 .1 .2 L i n e burners a n d p i p e burners shall h a v e at least one C o m b u s t i o n Sa feguard per 50 ft. of c o n t i n u o u s s ingle p a t h l e n g t h [see Fig. 5-5.4.1./(a)]. R a d i a n t c u p burners m a y utilize o n l y one C o m b u s t i o n Sa feguard w h e n e q u i p p e d w i t h - f l a m e propa- gat ion t u b e s / d e v i c e s p r o v i d e d that c u p spac ing does not exceed 30", a n d f l a m e p r o p a g a t i o n path does no t exceed 50 ft. a n d that there are not m o r e than 50 radiant c u p burners [seeFig. 5-5.4. 1.2(b)].

SAFETY EQUIPMENT AND APPLICATION 8 6 A - 8 7

H,GHPRESS RE ¢' To tlBU.NE.S II • ATMOSPHERIC ~ t I

"P"ROVEOELECT,,DALLY INTERLOCKED SUPERVISING COCK II

APeROVED MANUAL ~ 1 1 OPENING SAFETY ~ k J - I SHUTOFF VALVE WITH END SWITCH u . ~

GAs PRESSqRE ~ . ^ II

GAS AT l P S I G OR i ~ ~ B L E E D TAP FOR

LEAKAGE TEST OF SAFETY SHUTOFF VALVE

PIPING (MULTI-BURNER SYSTEM WITH HIGH PRESSURE

ATMOSPHERIC I N S P I R A T O R S )

=r.. HoT

l

VENT FAN ~ ' INTERLOCK __~ i2OV. AC

--r-- COCK SWITCH CONTACTS CLOSE WHEN COCK IS GAS PRESSURE . . . . . .

AND OTHER , ~ / ~,LU~.U

INTERLOCKS ~ . . 1 ~ 1 ~ 1 L 4 l

END SWITCH ON - . L - ° SAFETY SHUTOFF VALVE-CLOSED / I ONLY WHEN VALVE OPEN . " r

C O M M O I ~ _ ~"

APPROVE,?,~ [ TIMER {TIME DELAY SWITCH \

TT~MER LOAD CONTACT [CLOSED ATEND OF

_L_ PURGE PERIOD T ~ / ' ~ . . APPROVED

/ MANUAL OPENING

v

WIRING {DETAILS WILL VARY DEPENDING ON TYPE OF BURNER 8rCONTROLS USED)

SAFETY SHUTOFF VALVE (WITH END SWITCH)

Figure 5-5.4.1.1(b) Safety Control System Piping and Wiring, Electric Inter- lock Type Supervising Cock.

5-5 .4 .2 T h e r e shal l be no a u t o m a t i c a t t e m p t at re l ight after acc identa l f l a m e failure.

5-5.4.3 Tr ia l for ignition of pilots or m a i n burners shal l not e x c e e d 15 seconds.

Exception: Longer time, up to a maximum oJ 60 seconds, may be per- f,~ matted .for ignition provided: (,~


(a) Written request .for extension of trial for ignition is filed with the authority having jurisdiction and,

(b) It is determined that 25% of the L.E.L. will not be exceeded in the extended time.

5-5.5 Oi l A tomiza t ion , other than M e c h a n i c a l Atomiza t ion .

5-5.5.1 Adequa t e pressure/ f low of the a tomiz ing m e d i u m shall be proven to exist before the oil enters the burn ing zone.

5-5.5.2 If a low pressure switch is used to sense/supervise this pressure, considerat ion shall .be given to loc'ating it down- s t ream f rom all cocks, v/dyes, and o ther obstruct ions which can shut off flow or cause excessive pressure d rop of a tomiza t ion medium.

MANIFOLD

1. Approved main gas safety shutoff valve. Manual-opening automatic- closing valve or automatic-opening automatic-closing valve, to suit firing method used. /

2. Permanent and ready means for making periodic checks of main gas safety shut-off valve.

3. Approved pilot gas safety shut-off valve.

4. Pilot flame-sensing element. Wired into safety-control circuit so that it is automatically cut out of combustion safeguard's flame-detecting circuit at end of trial-for-ignition period. (Flame rod shown, but a photoconductive cell may be used.)

5. Main flame-sensing element. Wired into combustion safeguard's flame-detecting circuit. Unlike pilot flame-sensing element 4, it is not cut out but remains in the flame-detecting circuit during lighting-off and firing. (Flame rod shown, but a photoconductive cell may be used.)

Figure 5-5.4.1.2(a) Example of application of an approved combustion safeguard supervising a pilot for a continuous fine burner during fighting-

off and the main flame alone during firing.


RADfANT CUP BURNERS " ( ~ ' ~ F ~ I (SHOULD NOT EXCEED 50 ~ G A ~ . S CUP BURNERS PER BURNER #" - GROUP.) [h~O"MA)L[ PILOT.~,, .- m . ~

II r . . . . . . . . . ~ - - _ ~ 1 ~ , \ TOTAL PREM,XED ' , 2~ LE, ' ( ~ GAS . . . . .~/ ,_p,, v

FLAME PRO P A G A T ~ (SHOULDNOT EXCEED SOFT.) ~ v . _

1. Approved main gas safety shutoff valve. "Manual-opening automatic- closing valve or automatic-opening automatic-closing valve, to suit firing method used.

2. Permanent and ready means for making periodic tightness'checks of main gas safety shut-off valve.

3. Approved pilot gas safety 'shut-off valve. 4. Main flame-sensing element. (Flame rod shown, but a photocon-

ductive cell may be used.)

Figure 5-5.4.1.2(b) Example of application of an approved combustion safeguard supervising a group of radiant-cup burners having reliable flame-propagation characteristics from one to the other by means of flame-

propagation devices.

5-5.6 Low Oi l T e m p e r a t u r e L imi t Dev i ce s (N.C.) .

5-5.6. t A p p r o v e d l imit devices shall be provided whenever the t empera tu re of the fuel oil can drop below a safe level for p rope r a tomizat ion.

5-5.6.1.1 Devices shall be provided when oil p rehea ters are used.

5-5.6.1.2 Devices shall be required for NO. 2 fuel and No. ~ fuel o i l when its t empe ra tu r e may reach congeal ing point , whe ther or not preheaters are used.

5-5.6.2 T h e l imi t device Shall be inter locked to de-energize the oil safety shut-off valve whenever oil t empera tu re falls below a safe p rede te rmined level.

5-5.7 Mdl t i p l e fuel systems require safety devices for the secondary fuel(s) tha t are equivalent to those devices ~ used for the p r ima ry fuel; i.e., the fact tha t oil or gas m a y be considered to be a s t andby fuel for a d u a l fuel b~rner system shall not lessen the safety requi rements for tha t port ion.

5-5.7.1 W h e n dua l fuel burners are used, positive provision shall be made to prevent s imultaneous in t roduct ion of both fuels.

NOTE: Not applicable to combination burners.

t ~


5-6 Gas Mixing Machines.

5-6.1 Safety equipment and installation shall comply with NFPA. 54-1974, National Fuel Gas Code.

5-7 Ignition of Main Burners.

5-7.1 Burners shall be ignited by a fuel-fired pilot burner or by direct electrical means.

5'-7.1.1 Sufficient effergy shall b e presented for safe and proper light-off at the burners' input at light-off.

5-7.1.2 If any specific input, or a limited range of i.nputs is 'required for safe light-off, the fuel control valve shall be properly positioned prior to each and every at tempt at ignition.

,5-7.2 Electrical ignition energy for direct spark ignition systems shall be terminated after main burner trial for ignition period.

Exception." Repetitibe sparking of multiple burners is allowed where the input per burner does not exceed 150, 000 Btu/hour.

5-7.3 UV scanners, if used as the combustion safeguard's flame sensor, shall be shielded mechanically or electrically from spark excitation when a spark-ignited pilot burner is used.

5-7.4 Line burners, if used as runner pilots for multiple main burners, shall be single-path and proven ignited, end-to=end,prior to main burner ignition attempt.

5-7.5 If orie or more main burners is/are to be ignited from another main burner, the burden for proof of reliability shall rest with the equipment manufacturer.

5-8 .Excess T e m p e r a t u r e Limit (ETL).

5-8.1 One or more approved excess temperature limits shall be used on any heating unit where it is possible for the controlled temperature to exceed a safe limit.

5-8.1.1 The thermal element of the ETL shall be suitable for the atmosphere to which it will be exposed.

5-8.1.2 The ETL shall be fail safe.

5-8.2 The ETL shall be interlocked with the safety circuitry to cut off the source of heat when safe temperature is exceeded.

(

J

SAFETY EQUIPMENT AND APPLICATION 86A-91

5-8.3 Exact location of thermal element of the ETL within

that temperature most critical to safe operation.

5-8.4 The operating temperature controller shall not be used as an excess-temperature limit.

. .

-5-9 Conveyor interlocks shall be provided in conveyor ovens having a flammable volatile hazard so that the conveyor cannot move unless ventilating fans are operat ing and discharging the proper amount of air, as required in Chapter 4, and purge cycle completed.

5-9.1 An audible and/or visible alarm shall be provided in the safety circuit to give warning of unsafe conditions and interruption of the safety circuit.

Exception No. 1: It is permissible to install provision for operating the conveyor manually Or by means of a constant pressure push button for the purpose of removing material from the oven in event of conveyor stoppage from ventilation failure.

Exception No. 2: When an automatic material feeding system supplies a conveyor at a point adjoining the oven entrance, such as a lithograph oven coater, the material feeding syitem may be interlocked with the ventilation system and the conveyor interlocks omitted.

"Exception No. 3: Certain "one line conveyor systems supplying several processes may prevent a practical ventilation interlocking arrangement. Omitting the interlocks in such cases is subject to the approval of the authority having jurisdiction.

5-10 Power . Safety control circuits shall be single phase, one side grounded, with all breaking contacts in the " H o t " ungrounded, fused ( o r circuit breaker) protected.line, which shall not exceed 120 volt potential.

N O T E : Th i s control circuit an d its " n o n f u r n a c e or oven m o u n t e d control and Safety eomponef i t s" should be housed in a dus t - t ight panel, o r

cabinet, protected by part i t ions or secondary barr iers f r o m electrical controls employed in the h igher vol tage furnace or oven power system. Related ins t ruments m a y or m a y not be instal led in the Same control cabinet.

T h e door providing access to this control enclosure m a y include m e a n s "for mechan ica l interlock with the ma in disconnect device requ i red in the fu rnace power supply circuit (see 5-11.2.2).

T e m p e r a t u r e s wi thin this control enclosure should be limiteci to 125°F for sui table operat ion of plastic componen t s , t he rma l e lements , f u s e s ,

• and var ious mechan i sm s as m a y be employed in the control circuit .


5-11 Safety Devices for Systems L a c k i n g Fue l Hazards.

5-11.1 General.

5-11.1.1 Safety control appl ica t ion for furnaces lacking fuel hazards shall provide protect ion f rom excess temperatures , loss of secondary systems (cooling, mater ia l handl ing, etc.) essential to normal opera t ion of the furnace. Controls and a r rangement shall be as out l ined in the safety control app l ica t ion for electric furnaces. Ins t ruments shall be of the fail-safe type.

5-11.2 Safety Control Application for Electrical Heating Systems.

5-11.2.1 Each furnace~ or hea t p rocess ingsys tem ( including resistance, induct ion, electric arc or p lasma device) shall be provided with the following Control devices and safety control circuits for p roper operat ion.

5-11.2.2 Heating Equipment Controls.

5-11,2.2.1 Electr ic hea t ing equ ipmen t of o ther than the por tab le type shall be equ ipped with a main disconnect device, capab le of de-energiz ing the_entire hea t ing system under load to provide safety for secondary measures necessitated by one or more of the following condi t ions :

(a) A s~Tstem short circuit not c leared by supp lementa l b ranch circui t protect ion.

(b) Excess furnace tempera ture .

(c) Fa i lu re of normal opera t ing controls.

(d) Comple te or pa r t i a l loss of power, such as single phas ing of a mul t ip le phase power system.

5-11.2.2.2 T h e in te r rup t ing capac i ty of the main disconnect device (see Table 5-1 1.2.2.2) shall be adequa te to clear the m a x i m t i m faul t cu r ren t .capabi l i ty of the immed ia t e power supply system (f/mlt cur ren t shall be de te rmined f rom the vol tage and impedance of the furnace power supply circuit , not f rom the sum- ma t ion of the opera t ing load currents) .

NOTE: Other disconnect means in this power supply circuit may be used as the heating equipment "main disconnect" provided furnace operation can be terminated without affecting operation of other essential equipment.

5-11.2.2.3 A u t o m a t i c versus supervised opera t ion of the " m a i h heat ing system disconnect" shall be governed by the furnace size, design character is t ics and the .potential hazards involved.


NOTE: When operation of a multiple phase "main disconnect" is to be manually supervised, each phase of the power supply circuit should be equipped to" show electrical potential on the protected or load side, as an

. indication of intended operation, partial or complete loss of power.

Table 5-11.2.2.2 Main Disconnect to Power Supply System

Manual switclaes, powered (electrical opening, manual closing) switches, plastic case circuit breakers, and steel case circuit breakers are among the devices used to provide the "main disconnect" function. The use of switches will require the proper selection of fuses to handle the normal equipment load current, some short term overcurrent for starting motors and an interrupting capacity suffmient to extinguish an arc as may be caused by a short circuit fault. National Electrical Code up.torequirements for Class "H" fuses should be followed for current ratings 600 amperes and for Class "L" fuses above 600 amperes. Typical current ratings and interrupting capacities for 600- volt class fuses and circuit breakers are as follows:

Identification or Trade Name Plastic Case Breakers* A. Std. Industrial Duty B. High Interrupting Capacity with

Current Limiting Fuses Steel -Case

Air Circuit Breakers

Current Carrying C~pacity-Amperes

70-2,500

100-1,600

100-4,000

Symmetrical Interrupting

Capacity-RMS

22,000 to 65,000

200,000

14,000 to 85,000

Typical Current Limiting - - Time Delay - - Fuses

Fusetron 1-600 100,000 Low Peak 1-600 200,000 Limitron 600-6,000 200,000 H i-Cap 600-6,000 200,000

High Interrupting Capacity - - Pressure Switches

Manually and Electrically Operated Types • 800-4,000 200,000

The above symmetrical interrupting capacities may be increased by a factor of 1.3 when equipment is operated at 480 volts, or for asymmetric fault currents at 600 volts.

*Available with numerous optional features for furnace and/or oven protection from ground faults, short-circuit faults, over-temperature, single/or multiple phase power failure.

For proper selection of "main disconnect" equipment it is necessary to know: (a) The full load operating current and voltage of the equipment to be

served. (b) The impedance of the furnace and/or oven power supply system in-

cluding its transformer.

86A-94 OVENS. AND FURNACES

5-11.2.2.4 Por tab le furnaces m a y be equ ipped with main disconnect devices to meet the above requirements , bu t if not, the power supply circuit to the furnace shall be so equipped. Supp lemen ta l electr ical controls (contactors, c ircui t breakers, relays, s ignaling devices, etc.) shall be provided in accord with safety, t empera tu re control, b ranch ci rcui t and at /xi l iary system requirements .

5-11.2.2.5 T h e capac i ty of all e lectr ical devices used to control energy for the hea t ing load shall be selected on the basis of cont inuous du ty load rat ings when ful ly equ ipped for the loca t ion and type of service proposed.

NOTE: This may require de-rating some components as listed by manufacturers for other types of industrial service, motor control, etc., and shown in Table 5-11.2.2.5.

5-11.2.2.6 All controls, using the rmal protec t ion or t r i p mechanisms, shall be so located or pro tec ted as to prec lude faul ty opera t ion due to abnorma l t empera tu res or o ther furnace hazards.

5-11.2.3 V e n t i l a t i o n Cont ro ls . W h e n removal of by- p roduc t vapors is essential to the safe opera t ion of the furnace, controls and interlocks s h a l l be p rov ided as out l ined in 5-2.

Table 5-11.2.2.5

Control Device

Resistance Type Infrared Lamp and Quartz Heating Devices Tube Healers

Rating in % Permissible Rating in % Permissible of-Actual Current in % of Actual Current in %

Load of Rating Load of Rating Fusible Safety Switch

(% rating of Fuse employed) 125 80- 133 75

Individually Enclosed Circuit Breaker 125 80 125 80

Circuit Breakers in En- closed Panelboards - 133 75 133 75

Magnetic Contactors " 0-30 Amperes 111 90 200 50

30-100 Amperes 111 90 167 60 150-600 Amperes 111 90 125 80

NOTE: The above applies to "maximum load" or open ratings for safety switches, cilcuit breakers, and industrial controls approved under current NEMA standards.

' SAFETY EQUIPMENT AND APPLICATION 86A-95

5-11.2.4 Ma te r i a l hand l ing or posi t ioning controls shall be a r r anged for p rope r sequence of opera t ion with other f t : rnaee (special a tmosphere and safety controls) , and also to assure emergency act ion as m a y be needed in the event of mal func t ion of the mater ia l hand l ing system.

Exception: It is permissible to install provision for operating conveyors manually or by means of a constant pressure pushbutton for the purpose of removing material from the furnace in event of malfunction in the automatic system.

5-11.2.5 Where a furnace is subject to damage , an excess furnace t empe ra tu r e l imi t control shall be provided for annunci - ation and in te r rup t ion of power supply to the furnace heat ing system.

5-11.2.5.1 M a n u a l reset shall be provided to prevent au tomat ic res torat ion of power.

5-11.2.5.2 These controls shall be in addi t ion to a n y normal opera t ing t empe ra tu r e control devices.

5-11.2.6 Branch circuits and b ranch ci rcui t protec t ion for all e lectr ical circuits in the furnace hea t ing system shall be provided in accordance with N F P A 70-1978, National Electrical Code.

iS1


Chapter 6 Af t er -burner a n d Ca ta ly t i c C o m b u s t i o n Sys tems

6-1 Af t er -burner System.

6-1.1 Fue l systems and controls for a f t e r -burners sha l l comply with the requi rements for direct-f i red oven heaters. Addi t iona l ly , concur ren t opera t ion with the fume genera t ing process shall also be gua ran teed by p rope r inter locking means, usual ly requir ing in tended opera t ing t empera tu res wi th in the a f t e r -burner for proving per iods both before and after fumes m a y be en t ra ined for thermal destruct ion.

NOTE: After-burner systems ma; or may not eml31oy catalysts and various heat exchange principles to aid the combustion process.

6-1.2 W h e r e the relat ive locat ion of equ ipmen t a n d / o r the type of fumes genera ted is such tha t they m a y condense between the or ig ina t ing process and the af te r -burner , to form combust ib le l iquids or solids, fu r ther safeguards shall be taken to avoid fire h a z a r d or to guaran tee de l ivery to the a f t e r -burner in t rue vapor form or combus t ib le par t i cu la te form.

6-1.3 Excess- tempera ture pro tec t ion shall b e p rov ided in the fo rm of increased ai r d i lu t ion or in te r rup t ion of the feed to the or ig ina t ing process, as the rmal expansion of gases m a y otherwise cause the system to spiral out of control . (Energy release exceeding the designed volume di lut ion ra te of the t rea ted exhaust gases.)

NOTE: Proper design of the stacking or heat recovery system from the after-burner exhaust is also important as the latent energy in some hydro-carbon fumes (although diluted.to 25 percent L.E.L.) may add as much as 650°F to the effluent temperature during after-burner treatment.

6-1.4 W h e n port ions of the potent ia l energy are re tu rned to -ear l ier stages of the hea t ing system (oven, fume del ivery manifold or a f te r -burner ) , safeguards shall be p rov ided to avoid recycl ing un- t rea ted gases in the event of system malfunct ion.

6-2 Ca t a ly t i c C o m b u s t i o n System.

6-2.1 Ca ta ly t i c - type systems, whe ther employed for oven hea t supply , exhaust energy recovery or for air pol lu t ion control shall be subject to the same safety precaut ions as o ther direct-f i red oven heaters or a f t e r -burner systems.

NOTE 1 : Heaters of this type may be employed to burn a fuel gas with substantial portions of the energy being released as radiation to the processing zone (or oven, if enclosed) similar to direct fired internal heaters.

A F T E R - B U R N E R A N D C A T A L Y T I C C O M B I N A T I O N 86A-97

Alternately, Catalytic heaters may be installed in the oven exhaust stream to release heat from evaporated oven by-products with available energy being returned via heat exchange and recirculation to the oven processing zone (see 1-4, Direct Fired External Heater). [See Figures 6-2.1(a), (b), (c), and (d).]

I DOR FREE EXHAUST

PAINT FINISHING l~J~l -- 400"F ~ ~'X~ OVEN-/

CATALYST--'~_--_~'L/ i l l FPREHEAT " l t l ./

FA J

-------:/ENTRANCE . . . . . . . . . . . . . . . . ~ k\ /I ~_.L~a_z.~.z.~_~ EXIT B U R N E R " ~ I ~ ' ~ - - ~ RECIRCUL'ATION

FRES ~,D ~V~OVE N - - AIR INTAKE HEATER

Figure 6-2.1(a) Catalyst System Independent of Oven Heater for Air Poilu- _ tion Control.

EXHAUST ¢ • FAN ~

i i / i i / i i i / / , / / / / / g / / / / d " ~ . ~ - , - - - i ----

f : I I \ \ , , ~ I / W O R K I t . z ~ " - - ~ ,.L"v':_~\ I WORK ~ - - J ENTRANCE rz/_zz/_uJj~ j' I " - ' 7 " L"4 -~ I'-t-Y/r~Y, " / / ' ' ' / ! ' ' ' EXIT

• .,C,TALY I BED

BURNER J r / , . - . - . . . . . . . . . I J ~ . ¢ ~ ~ . ~ - - I FAN . . . . .

CATAt.YTIC / ~-FRESH AIR HEATER ~ ' . INTAKE

Figure 6-2.1(b) Direct Type Catalytic Oven Heater for Partial Air Pollution Control.

tJ~


i EXHAUST

I SOLVENT J l COR, O ZONE

_ ~ I I ZONE ikX,~ [

g

FAN " F A N - " ~ / x ~ , / ; 5 / : / / ~ I ~ / x / ~ ~ ~ ~ - RECIRCULATION

CATALYTIC J \ ' / \ \ OVEN HEATER CATALYST --~ /- HgAT ..L__ xx\ FRESH

EXCMAN~.N Alibi

Figure 6-2".1(c) Indirect Type Catalytic Oven Heater for Full Air Pollution Control. ,

EXIT

tEXHAUST FRESH AIR | /

CATALYST \ HEAT .L I E X H A U S I ~

BURNE R RECIRCL LATING FAN

Figure 6-2.1(d) Batch Oven Catalytic Heater for Full Air Pollution Control.

N O T E 2: Three basic types of Catalytic Combustion elements are available. One is a mat of all metai construction available in various dimensions for use as a fuel fired radiant heater or alternately for oxidation of combustible materials in fume-air mixtures. The second type consists of ceramic or porcelain cohstruction arranged in various configurations for gas fuel or fume oxidation with catalyst media, including a variety of "Rare Earth" elements, platinum, or metallic salts. Both of these types arc classified as "fixed bed" catalysts since they arc normally held rigidly in place by clamps, cement, or other means. A third type consists of a bed of pellets or granules supported or retained between screens in essentially a fixed position, but with the individual members free to migrate within the bed.

AFTER-BURNER AND CATALYTIC COMBUSTION 86A-99

N O T E 3: Heating systems employing catalysts are finding wide appli- " cations for the conservation of oven fuel and for correction of organic ~nd enmh,l~tihle type Mr nnllutinn emis~ian.~. ,Rhine limitations must be recognized because of tl~eir inability to oxidize or consume silicones, chlorine compounds, and metallic vapors as from tin, mercury, and zinc. These elements and various inorgan!c particulates (dust) may retard or paralyze catalyst activity, thus suggesting specific maintenance requirements.," Consultation with qualified equipment manufacturers is recommended prior to installation and at periodic intervals during use to assure appropriate maintenance and reliable operation.

6-2.2 T h e usua l o v e n safety s t anda rds shall be a p p l i e d w i t h respect to loca t ion , p l a n a p p r o v a l , cons t ruc t ion , p ip ing, , safety cont ro l s , in ter locks a n d d a m p e r s , a n d re-use of ox id i zed exhaus t products .

6-2.3 E x h a u s t f r o m severa l ovens , kett les, or d rye r s shal l on ly be m a n i f o l d e d to a single ca ta ly t i c un i t w h e n a d o u b l e - j a c k e t e d , hea t ed m a n i f o l d is p r o v i d e d a n d w i t h o u t p r o v i s i o n for h e a t recovery to the o r ig ina l process.

6-2.4 A n excess t e m p e r a t u r e l imi t device , d o w n s t r e a m f r o m the ca t a lys t bed , shal l be a r r a n g e d to shu t d o w n the process bu rne r s , ma te r i a l h a n d l i n g e q u i p m e n t , a n d o p e r a t e e x h a u s t re l ief d a m p e r s to p r o v i d e m a x i m u m d i s c h a r g e to the ou t s ide at tmosphere. [ix spec ia l ins tances w h e r e an e x o t h e r m i c r eac t i on m a y o c c u r w i t h i n a process be ing served, f u r t h e r p r o t e c t i o n shall be. p r o v i d e d by a r r a n g i n g for c o m p l e t e d ivers ion of f umes f r o m the ca ta lys t sys tem w h e n t h e h i g h l im i t t e m p e r a t u r e con t ro l is a c t u a t e d .

6-2.5 C o n s i d e r a t i o n shall be g iven to m e a s u r e t he t e m p e r a - ture increase ( A T ) a n d the pressure d r o p (AP) across the ca ta lys t bed.

N O T E : Separate temperature• indicator controls may be used to arith- metically determine the AT. For example, an instrument measuring temperature on the upstream or entry side of the catalyst may be used to control fuel or electrical energy for preheating the fume stream, while a second controller measuring the downstream or catalyst exit temperature is employed as a limit device to actuate the fuel safety shut-off valve and fume diversion or exhaust relief dampers. The temperature difference (AT) indicated by these instruments will serve as a guide to the combustible energy release within the catalyst bed. A AT oi 500°F is usually a practical maximum for most fume destruction processes.

6-2.6 Suff ic ient exhaus t ven t i l a t i on shall be p r o v i d e d to m a i n - ta in vap0T-a i r -mix tu res b e l o w 5 0 p e r c e n t ( a u t o m a t i c s h u t d o w n point) of the L . E . L . ( u n d e r s t a n d i n g tha t a fixed, c o n t i n u o u s v a p o r c o n c e n t r a t i o n i nd i ca to r is ins ta l led a n d p r o p e r l y i n t e r l ocked w i t h fuel i n p u t a n d stock conveyor ) .

t ~


NOTE: Where the size of the installation may not require a continuous vapor concentration indicator, maximum vapor concentration in the exhaust shall not exceed 25 percent of the L. E. L.

6-2.7 Explosion relief of one square foot for each fifteen cubic feet of volume shall be provided for large catalytic units (above 64 cubic foot size) subject to excess energy release or fuel hazards.

NOTE: The access door can usually be used to provide all, or a portion, of this relief if equipped with explosion relief latches.

6-2.8 The p lant m a n a g e m e n t and the authori ty having jurisdiction shall r ecommend suitable time interval at which catalytic elements and related safety controls shall be tested for service re- l iabil i ty based on recommendat ions of the equ ipmen t manufacturer .

NOTE: Numerous arrangement~ for circulation of oxidized combustion products from the catalyst bed may be provided [see Figures 6-2. l(a) and (¢)]. Repeated cycling of such products through the oven heating zone and the catalyst bed [Figi~re 6-2.1(b)] is not recommended unless con- tlnuous supervision of the catalyst is provided by a combustible vapor concentration indicator or catalyst temperatures are maintained at sufficient levels to assure effective oxidation of major comhustible constituents by natural combustion means. This does not apply when heat recovery is provided by a single pass through the oven or through sealed heat exchanger surfaces as in a double manifold fume collection system or an appropriately designed heat exchanger [see Figure 6-2. l(c)].

INSPECTION AND MAINTENANCE 86A-101

Chapter 7 Inspection and Maintenance. (See Appendix F.)

7-1 Responsibility of the Manufacturer and User. The equ ipment manufac ture r shall impress upon the user the need for

• adequate operat ional checks and main tenance and shall issue complete and d e a r ma in tenance instructions. The final responsibility of establishing a main tenance program which ensures that the equ ipmen t is in proper working order shall rest with the user.

NOTE: An essential safety aid is an established maintenance program which ensures that the equipment is in proper working order.

7-2 Check List." (See A p p e n d i x F.) The user's operat ional and main tenance program shall include all listed procedures that are applicable to the oven. An operational ma in tenance check list shall be main ta ined and is essential to safe operat ion of the equipment .

NOTE: The user should review recommendations from the insurance underwriter, and the equipment supplier, and where applicable include these recommendations in the maintenance program.

7-3 C l e a n i n g . Foreign mater ia l , parts, and residue shall be removed from recirculat ion blowers, and exhaust blowers, burner and pilot ports, combust ion blower, ductwork and oven interior. Ductwork shall be checked for obstructions (i.e., improperly adjusted dampers).

7-4 Tension and Wear. Recirculat ion and exhaust system blowers that are V-bel t dr iven shall b e checked for proper belt tension and excessive belt wear.

7-5 Solvent Load ing . I t shal l be the user's responsibility to periodically check the type and a /nount of solvent enter ing the oven, to assure that the solvent loading does not exceed the capacity of the oven exhaust system.

O


Chapter 8 Fire Protection

8-1 Basic Fire Protection.

8-1.1 Ovens conta in ing or processing sufficient combust ible materials to sustain a fire, shall be equipped with automat ic sprinklers as required by the authori ty having jurisdiction. This shall include sprinklers in the exhaust ducts when necessary. Plans showing t he a r rangement of the sprinkler installation shall be submit ted to the authori ty having jurisdict ion for review and approval before the installation is started.

NOTE: The extent ,of protection required will depend-upon the construction and arrangement of the oven as ,well as the materials handled. Fixed protection should extend as far as necessary in the enclosure if combustible material is processed oi~ if trucks or racks used are combustible, or subject to loading with excess finishing material, also if an appreciable amount of flammable drippings, of finishing materials accumulates within the oven.

8-1.2 Dip tanks and dra inboards included in the oven enclosure shall be protected in accordance with NFPA 34-1974, Dip Tanks Containing Flammable or Combustible Liquids.

8-1.3 Automatic Sprinkler Systems.

8-1.3.1 Automat ic sprinkler installations shall conform to N F P A 13-1976, Installation of Sprinkler Systems.

NOTE 1: When oven temperatures are over 465°F or where flash fire conditions may exist, an open sprinkler system, supplied by an approved deluge valve equipped with a hand pull for manual operation, and controlled by heat actuated devices, is recommended within the oven; otherwise automatic sprinklers of proper rating may be used.

NOTE 2: When rapid temperature changes may be anticipated that will result in premature operation of rate-of-rise release equipment, fixed temperature controls should be used.

8-1.4 Water Spray Systems.

8-1.4.1 Water spray systems shall be fixed systems, automatic in operation and conforming to N F P A 15-1973, Water Spray Fixed Systems.

NOTE: Protection systems utilizing the application of water in finely divided form may be provided to protect oven enclosures.

8-1.4.2 Water spray systems shall be operated by deluge valves actuaiEed by either fixed temperature .or rate-of-rise equipment : as approved by the authori ty having jurisdiction. M a n u a l operat ion of the deluge, valve by hand-pul ls shall be provided in all eases.

FIRE PROTECTION 86A-103

8-1.4.3 Where fire in an oven may involve other equ ipmen t as may be the ease in " in l ine" coating or finishing operations,

shall be provided to protect the oven work openings. M a n u a l controls for these systems shall also be provided. Plans showing the a r rangement of such protection shall be submit ted to the authori ty having jur isdict ion before the installation is started.

8-2 Supplementary Fire Protection.

8-2.1 Plans showing the a r rangement of Supplementary protection shall be submit ted to the authori ty having jur isdict ion for review and approval before the installat ion is started.

NOTE: I f desired, permanently installed, supplementary protection of an approved type such as carbon dioxide, foam, dry chemical, etc., may be provided. Such protection is not a substitute for automatic sprinklers.

8-2.2 Carbon Dioxide Extinguishing Systems.

8-2.2.1 Carbon dioxide equ ipment shall be au tomat ic and shall be installed in accordance with N F P A 12-1973, Carbon Di- oxide Extinguishing Systems. M a n u a l control shall also be provided.

NOTE: These systems will provide good protection for ovens and dryers containing materials or deposits that would provide surface burning fires principally those involving flammable liquids.

"8-2.3 Foam Extinguishing Systems.

8-2.3.1 F o a m equ ipmen t shall be installed in accordance with N F P A 11-1976, Foam Extinguishing Systems.

NOTE: Foam protection can be a valuable supplement to the required automatic sprinkler protection in ovens which contain dip tanks and drip boards, and should be automatic.

8-2.4 Dry Chemical Systems.

8-2.4.1 D r y chemical extinguishing equ ipment as a sup- p lement to the required automat ic sprinkler protection shall be automat ic and shall be installed in accordance with N F P A 17- 1975, Dry Chemical Extinguishing Systems.

NOTE: These systems will provide good protection for ovens and dryers containing materials or deposits that would produce surface fires, principally those involving flammable liquids.

8-2.5 Steam Extinguishii~g Systems. NOTE: The use of steam in ovens and dryers is not generally recommended. However, where steam flooding is the only alternative, see Appendix B for details.

8 6 A - 1 0 4 O V E N S A N D F U R N A C E S

8-3 Por tab le Protec t ion E q u i p m e n t .

8-3.1 Ex t ingu i she r s . Approved portable extinguishing equip- men t shall be provided near the oven, oven heater, and related equipment , including dip tanks or other finishing processes op-

• erated i n conjunct ion with the oven. Such installations shall be in accordance with NFPA 10-1975, Portable Fire Extinguishers.

NOTE: Small hose with combination nozzles should be providedso that all parts of the oven structure can be reached by small hose streams.

8-3.2 M e a n s of Access. Doors or other effective means of access shall be provided in ovens and duct work so that portable extinguishers and hose streams may be used effectively in all parts of the equipment .

NOTE: Such access doors are also of great value for periodic cleaning and inspection.

8-4 M a i n t e n a n c e o f Fire Protec t ion E q u i p m e n t .

874.1 Inspec t ion . All fire protection equ ipmen t shall be inspected and main ta ined at regular intervals, in accordance with N F P A standards.

8-4.2 Records of inspection and tests shall be kept on forms prepared for this purpose and brought to the attention- of man- agement.

8-4.3 Test ing shall be done by responsible men famil iar with the" operat ion and maintef iance of this type of fire protection equipment .

8-4.4 Outlets . Sprinkler heads and outlets of other extinguishing equ ipment shall be kept clean and free of deposit under a regular inspection program.

A P P E N D I X A 8 6 A - 1 0 5

Appendix A

The Lower Limit of Flammability and the Autogenous Ignition Temperature of Certain

Common Solvent Vapors Encountered in Ovens Abstract of Underwriters Laboratories Inc., Bulletin of Research No. 43.

This Bulletin of R6search reports an investigation conducted by Under- writers Laboratories Inc., to determine the lower limit of flammability (upward propagation) and the autogenous ignition temperature of certain common solvent vapors encountered in industrial ovens. The solvents included acetone, iso-amyl acetate, benzene, normal butyl alcohol, cyclohexane, cyclohexanone, metapara cresol, ethyl alcohol, ethyl lactate,.gasoline, normal hexane, high solvency petroleum naphtha, methyl alcohol, methyl ethyl ketone, methyl lactate, No. 10 mineral spirits, toluene, turpentine and VM and P naphtha.

The lower limits of flammability of the solvent vapors in air at initial temperatures encountered in the operation of ovens were determined in a specially designed, electrically heated, closed explosion vessel of steel having a capacity of i cu. ft. (15~ in. high, 12 in. internal diameter). I t was equipped with an observation window, an externally driven mixing fan, and inlet and outlet valves. A transformer rated 15,000 v, 60 ma, 60 cycles for the secondary and having a 0.009 mfd. condenser connected across the secondary was used toproduce an electric discharge for ignition.

The lower limits of flammability of all. solvents included in this investigation were found to be lowered on increasing the initial ambient temperature, these changes in the lower limits being of such magnitude that they cannot be safely neglected in practical calculations of the amount of ventilation required to prevent formation of hazardous'concentrations of the vapors of the solvents in industrial ovens. The magnitude of the change in the lower limit with a given increase in initial temperature varied with the different solvents.

The autogenous ignition temperature (in air) of the solvent vapors was determined in combustion chambers of iron, stainless steel (AISI Type No. 302), copper, zinc, and yellow brass representing metals commonly used in oven construction Determinations in glass and quartz chambers were included for comparison. The autogenous ignition temperature of the solvents is influenced to some extent by catalytic or other reactions of the solvent vapor-air mixtures with the heated, metals or their oxides. Whether the ignition temperature of the solvent is increased or decreased (as compared with values obtained with glass or quartz combustion chambers) depends on the particular combination of solvent vapor and metals.

The ignition temperatures of solvents in metal chambers were higher , for the most part, than the ignition temperatures of the same solvents in glass or quartz chambers, but exceptions were found where the values obtained in the metal chambers were lower (i.e., butyl alcohol in eoppei and brass chambers). The autogenous ignition temperature of many sol~ents included in the investigation is within the range of temperatures encountered in industrial ovens and if conditions are such as to permit formation of flammable vapor-air mixtures in the oveh, autogenous ignition may occur.

Committee Note: I n calculating ° ventilation requirements for batch ovens operating between 250°F and 500 F, values for the lower flammable limit of the solvent determined at the operating temperature of the oven should be used when such data are available. However, when the data are obtainable only for room temperature, a correction factor is required. An averaged factor of 1.4 has been obtained from a graph of the experimental data plotted for a number of selected solvents over temperature ranges of 70 ° to 250°F (1.25) and 250 ° to 500°F (1.56).

8 6 A - 1 0 6 OVENS AND FURNACES

Append ix B

- Steam ~.xt lnguishing Systems

Steam extinguishes fires by the exclusion of air or the reduction of the oxygen content of the atmosphere in a manner similar to carbon dioxide or other inert gas. The use of s t e a m antedates other modern smothering systems.. I t is not a practical extinguishing agent except where a large steam suppl~ is continuously available. The possible personal injury hazard of burns should be considered in any steam extinguishing installation. A visible cloud of con- densed vapor, popularly described as steam, does not furnish any material protection.

While m a n y fires have been extinguished by steam, its use has often been unsuccessful due to lack of understanding of its limitations. Except for specialized applications, other types of smothering systems are preferred in modern practice. No complete s tandard covering steam smothering systems has been developed. '

One pound of saturated steam a t 212°F and normal atmospheric pressure l~s a volume of 26.75 cu. ft. A larger percentage of steam is required to

p r e v e n t combustion than in the case of other inert gases used for fire ex- t inguishment. Fires in substances which form glowing coals are difficult to extinguish with steam, owing to the lack of cooling effect. There are some types of fires for which steam is completely ineffective, such as fires involving ammonium ni t rate and similar oxidizing materials.

Steam smothering systems are permissible only when oven temperatures exceed 225°F and large supplies of s team are available a t all t imes when the oven m a y be in operation. Complete standards paralleling those for other extinguishing agents have not been developed for the use of steam as an extinguishing agent, and until this has been done, the use of this form of protec- t ion is not as dependable or the results as certain as those qualities of water, carbon dioxide, dry chemical or foam.

RELEASE DEVICES for steam smothering systems should be manual and controls should be arranged to close down oven outlets as far as practicable.

LIFE HAZARD. (a) Equipment should be so arranged as to qprevent operation of steam

valves while doors of box type ovens or access doo m or panels of conveyor ovens are open.

(b) A separate.out#ide steam manual shut-off valve should be provided for dosing off the steam supply during oven cleaning and shall be locked dosed whenever employees are in the oven.

(c) The main valve should be designed to open slowly as the release should first open a small bypass in order to allow t ime for employees in the vic ini ty to escape and also to protect the piping from severe water hammer. A s t e m t rap should be connected to the steam supply near the main valve to keep this line free of condensate.

i

S T E ~ OU:rLETS. If s team is used, then Steam outlets should be sufficiently large to supply 8 pounds of steam per minute for each 100 cubic feet of oven volume. They should preferably be located near t h e b o t t e m of the oven; bu t

• may be located a t the top, pointing downward if the oven is not over. 20 feet high. Steam jets should be directed a t dip tanks (in a manner to avoid dis- turbing the liquid surface) or other areas of special hazard.

A p p e n d i x C b e g i n s o n p a g e 8 6 A - 1 0 8 .

i MteRS JOB OR CONTRACT NO.

NAME & ADDRESS OF CUSTOMER (OWNER)

A p p e n d i x C Adapted f rom F o r m No. 69, Fac to ry M u t u a l Engineer ing Div is ion

TYPICAL OVEN DESIGN CHECK LIST FOR ACCEPTANCE sHE-T, o,,

P A R T A- PLANS I NAME & ADDRESS OF MANUFACTURER

DRAWINGS SUBMITTED, NOS,

I N S T A L L A T I O N

ERECTION & ADJUSTMENTS (SEE PART B) BY: OTHER (DESCRIB E)

[ ] MANUFACTURER [ ] CUSTOMER

CON- S T R U C T I O N

I IATED H E A T I N P U T

SAFETY VENTILATION AIR FLOW TESTS (SEE PART B) I OTHER (DESCRIBE) TO HE ~ O E A~ER r--7 I--7 I ERECTION BY: I I MAI~UFACTURER [..._J CUSTOMER, TYPE TYPE NO. OR OTHER INFORMATION [ ] HATCH [ ] CONTI]qUOGS

] SHEET-STEEL ON STEEL FRAME IF OTHER, DESCRIBE . NON-COMBUSTIBLE INSULATION

LENGTH (external) SIZE

BLDG, NO, OR NAME

NO. OF SETS

L O C A T I O N O F

E Q U I P M E N T

BTU/hr, [ ] FUEL OILNO.. GALS./hr [ ] ELECTRIC KW [ ] STEAM FEKS8. PetE

WIDTH (external) HEIGHT (external) " ft VOLUME (hltsrmd) cu. ft. OPERATING TKMP.

ft. ft. , BUILDING FLOOR CONSTRUCTION AND NO. OF FLOOR OR STORY

AIR SPACE ] OTHER (DESCRIBE) BETWEEN OVEN

I & WOOD FLOOR in. AIR SPACE OTHER |DESCRIBE~ BETIVEEN STACKS, DUCTS,

in. & WOOD BLDG. CONST.

O0 O',

I

O0

E X P L O S I O N V E N T I N G

AREA -

F U E L S H U T - O F F

F I R E P R O T E C T I O N

IN OVEN

F I R E P R O T E C T I O N

FOR D I P T A N K &

D R A I N B O A R D

T Y P E OF

W O R K

SOLVENTS EN- T E R I N G OVEN

D E S I G N E D

S A F E T Y

VENT1 LATION

OPEN END6 7 LO0gX ROOF pAN]tLfJ

MANUFACTURER A I q D ~ T O T A L AREA

ACCESSIBLE IN EVKNT OF FIRE

No

DN°~ D AOT°~TI°S~. [] OFRN~

ACCm~ DO~RS WITH ~ I , G S ~

vmrr Aftm~ INTERNAL VOLU Mle m

[ ] OTHERp DESCRIBE "~ r....~.S~pARATK I~XCKS 8 TIrMPERATURK ~

1 I I LIMIT SWITCH WITH MANUAL RESET "o

DRAWINGS SURMF'I'rED J ~ AUTO. CO I ~ DESCRI]N~ " I IDT~ • N o D , ~ •No

D,ES • N o D,Es DNOID_'ES •NO ONP~LUHEO, CONVE,OH MATERIALIMPREGNATED'COATED I.-.jABSOREENTcLoTH ] ~ F~pAPE R [--7 LITHOGRAPH VAR~L~H ' GRAVURE FOOD

[~] ELECT. COILS COATING [ ] PRESS [] PAIQNG METAL . ] DESCRIBE

[] oIPPED [ ] FL~-CO^THD [] SPRAVED [] OTHEH NAME OF SOLVENT USED I LENGTH OF BAKE T MAX. SOLVEMTMAX. SOLVENT FOR WHICH OVEN DESIGNED

-- ~ I ~ rain, ~ Gal/hr. PATCH GAL./batch ARRANGEMENT FILTERS ON FRESH AIR INTAKE

SEPARATE CENTRI- RECIR CULATING NATURAL OPENINGS

FRESH AIR ADMITTED INTO O P E ~ G WITH DAMPER ~[~HED DOES CONVEYO~ STOP AUTOMATICALLy ~ E T ~ EXHAUST OUTLET - - ~ y E H O V E N ' C F M REFERRED TO 70°F ON FAZLURE OF SAFETY EXHAUST FAN5

FAN MFR. SIZE, TYPE

D, . ~No ] CORES

OR MOLDS

--]NO ~ S ~ G N (BLADE TIPI

RADIAL BACKWARD FORWARD DIAM. TIP SPEED TIP INCLINED [ ] CURVED i~ ft. rain.

O0 O~

I CD ¢D

H E A T I N G

A R R A N G E -

M E N T '

M E T H O D O F L I G H T I N G O F F

M E T H O D O F

F I R I N G

M I X E R

T Y P E

INTERNAL DIRECT I~ED INTERNAL DIRECT FIRED EXTERNAL DHIECT EXTERNAL [] RECIRCULATING. [] FIRED RECIRCULATING [] INDIRECT FIRED LJ NON- RECIRCULATINO

(DESCRIBE) ] OTHEN / .

TYPE OF ELECTRIC HEATING ELEMENT8 AND LOCATION

NO. OF MAIN EURNERS- TNO. OF PILOT BURNERS

1 PC~TA]~LE

-~ ON-OFF ~ OUS ['YPE OF PILOT

[ ] CONTINUOUS [ ] INTERRUPTED

NO. MAIN BURNER I]~PINATORS -

]oAS

CAN DRIppINGS OFF WORK FALL ON HEATING ELEMENTS

~¥ES [] NO

~OIL [] GAS SPARK []I~N ~AUTO~ATIC - LIGHTED

]SEMI-AUTOMATIC- LIGHTED ~ MANUAL-LIGHTED

(DESCRIUE}

~ o~HEN ATMOSPHERIC HIGH LOW

~_~ IMSPIRATOR ~ PRES3URE ~PRESSURE

NO. pILOT ATMOSPHERIC ] INSPIRATON HIGH ~ PRESSURE LOW ~-~ PNESSURE N4SP~RATORS

[ ] OIL [ ] AIR (IS-3~ OZ. } ATOMIZING [ ] R06S OR DRY SYSTEM AIR ATOMIZING

INTERMITTENT

ZERO-GOVERNOR

ZERO-GOVERNOR

~ OTI~R OTHER TYPE MIXERS OR OIL BURNERS INCLUDING HII~TS (MFR. & TYPE1

] ~ ~ EX~Us'r ~D NE.CmC Z_ANS ~ ~ _ _ ~--~ coc~s CLO6ED ~ s.vFopp v ~ v ~ TioBY~s~ .RnT~-.,,,,..n~, I ~ ~P~LOT-FLA~.ZST^UL4~msu ~TNIAL-FOR-IGNY'flON PERIOD ~Oj~TEMP. I N T E N ~ {PROVED l~- x ~ ' r~*a/ 'JA~ AUTOMATICALLY LIMTrEEI FIRE INTERLOCK

A G A I N S T I ~ TM ~¢o s~c L ~ .o~ [--] NO ~mE~E~? S~OC~ No _ " | ~ ~MFR. AND TYPE NO. OF p. ]t~ ~ & TIMER [ C O M B U S T I O N AIR BLOWER CANNOT ~ CDMBUSTION SAFEGUARD PROVES

BE STARTED UNTIL END OF pILOT BEFORE MAIN SAFETY

E X P L O S I O N HEAT CUT.OPF AUTOMATICALLY. NEQUIR/NG MANUAL OPENAT]OII TO NESTORE,ON FAILURE OF O COMBUSTION AIR RECIRCULATING _~ [D GOMB~IUR [ ] ,AN

[ L.--.J PILOT IGNITES MAIN FLAME

SAFETY EXHAUST ' FUEL FLAME ~ FAN 1 ~ PRESSURE [ ] (combustion safeguard)

M A N U - m.

F A C T U R E R & T Y P E N O . I ] PRE~ UREs W r r cv , E S . . [Am-FLOWSWrrC~S .

P A R T A ACCEPTED ASsusatrrrKv []

S A F E T Y

V E N T I L A T I O N

CFMREF, TO 70°F

~ MANI)ATONY pURGE AFTER FLAME FAILURE - -- [ [ ] vE~ [ ] , ,o

MA/N SAFETY onUT-OFF VALVE L °S, IN. PILOT SAFETY SHUT-OFF VALVE ' ' IPS.

COMBUSTION SAFEGUARD

SUBJECT TO A~'~ANGJ~ INDICATED [ ] DATE

BY. FOR .

P A R T . R - M A N U F A C T U R E R ' S I N S t ~ E C T I O N ,~ T ~ T (completed installation)

MEASURED BY (SPECIFY) I MEASURED WITH FRESH AIR INLET I D p ~ [ ] o T e . I'EX"AUSTOOTLETDA"PERS~

"~MBM OL~E"P~I~ION i ~ S • N O B U R N E R S ' ~ Lmm'ED ~ S S [],~USTE. TR.P ~O~TNOL ' [ ] ~T [ ] ~ FONSTA~

LOW FLAME

S A F E T Y [ ] A ~ T E D [ ] TESTED FOR PROPER RESPONSE C O N T R O L S

I N S T R U C T I O N S l-"] CUSTOMBN'S OPESXTmt ~INTED OPENATmO t--.J INSTRUCTED [ ] INSTRUCTIONS LEFT [ ] APPLICATION FOR ACCEI~#J~CE

~reD ON CO~rFEOL pASTEL

SIGNATuREs MFES. FIELD REp~ - - I T E S T WITNESSED Ey ' DATE

- - J F O R CUSTOMER P A R T B A C C E P T E D suLr~c-r TO Amr ~oRs ~;CATED. DATE

B Y . ". '. F()N

P A R T C - F I E L D E X A M I N A T I O N O F C O M P L E T E D - . ~ ' I ' N S T A L L A T I O N - - -:

PART A ROD OR SCANNER ~K~ATION -~ ~JCHECK'ED PART N SAFETY CONTEOLB ' [ ] CHECKED ' [ ] TEbTED [ ] ASSURES PILOT IGNITES

• ~ MAIN FLAME ~TAL~ATION ACCEPTABLE ] 'DATE - -

j~

BY . . . . ~ I ... •

C~

J

A p p e n d i x D Adapted from Form No. 23, Factory Mutual Engineering Divls/on

TYPICAL FURNACE OESIGN CHECK LIST FOR ACCEPTANCE SHEEr I OF 2 MFRs. JOR OR CONTRACT NO. JDATE " ] I I ~ E X NO.

J AUTHORITY IIAVING Jt!RISDI('TION

I

PART A - PLANS ~AM~ OF CUSTOMER ( ~ e of owner)

ll)aB~(m.. &No.) ' {~TY STATS

IAME OF MAh'UFAC'I'UIII~

DRA~G~q ~JB~TT~D, ~ t r NO. OF SETS

INSTALLA"

TION

RATED HEAT INPUT

SIZE (scXTERNAL IN F'Y.)

LOCATION OF EOUIPMENT

TYPK

~ o ~ - m or

WIDTH [[~Hr OPERATJ~'G TEMP,

BLDG. lIO. Q~ NAM~ NO. OF FLO0~ OR.~T¢~

x'w

FU EL ACCmi,Z IN ~ OF IqRE :EPARATE EXCESS TEMPERATURE SHUT-OFF Yr~ [ ] m [--]i u ~ r s w r r c ~ s m ~ ° ' ' s e A T

, ° F

FIRE PROTECTION [ ] ~ [ ] ~mlU~I~sAU'rOMA'r/c [ ] ~ O P i ' N [ ] WATERAUTOMATIC~#oY [ ] . ~AUTOMATI(~I~DAM

OF OIL QUENCH [ ] l roTl i l ix . D ~

TANK HEAT TRKA'F/~O Idg'rAl~

TYPE OF [] ~ u s c l ~ ~:~MW~'-" a'rsmmm~l [ ] wrra ~ZC~L ~ AT~-~SP~RZ WORK i r o ~ m l ,

HEATING

ARRANGE.

MENT

METHOD OF LIGHTING OFIF

METHOD OF FIRING

F~R

Y~f-1 .o1-1

] D~II~I" l~Um

I "~E OF ZlJgb'~C I I ~ t ~ ~ ~ LOCA~OII

NO. OF ~ BglUfl[IU3 NOo OY ~ BUI~ I~8 %

MIXER GVI~

I I 1.0110 '

~ ~ DESCRBI (ILs'R. & Tl~Plll

D~ i f

' ' 9 M ,

P R O T E ~ T I O N

A G A I N S T

FUEL

E X P L O S I O N

P R O T E C T I O N

A G A I N S T

SPECIAL

TYPICAL FURNACE DESIGN CHECK LIST FOR ACCEPTANCE OPENINGS ~ ROOM :" : : = .~REET 3 OF l I • , =~ =

i t~O ~EL & ~Ur~siu~ U~qTIL: T l b ~ SKTT~;O • DOORS - ~i BURNER IF. M.) ~'~ MPAN8 P~OVIDED,FOR [] TIMED PREVE~TILATIQN B, ~'-~ W3~E OPRN [ ] C~C. CLOVIS, ~ CHECK OF b~ SA,ET,

m ~ o ~ - ~ R~^s,sm~u ~-~R=,o~ ~"~ ,~°I~l T~MP'~sE U~R~OC~r_]..~ ~ % v ~ c x ~ l O D ATJTOMA~(~ALLY L~TED ~UTOMATICALLy LIMITED

, m~c, ~'r ~ - oF M~.&T~E~O. OFF.~tCOC~A~DT~ COMB, AIR BLOWER CAMNOT BE COMB. SAFEGUARD PROVES PILOT

~ STARTED UNTIL E~ OF ~ BEFOREMA~N SAFE~'~ SHUT* pREVENT. (IF TfMER ~SED) 4--3 OFF VALVE OPENS

HEAT CTJT-OFF AUTOMATIC&LLY; RE~IIRIING MAI4U~ OPERATION TO RESt, ON F ~ q ~ OF

ROD 0'~ SCA~ER LOCATION INSURES MAI4DATOR-¥ PURGE A~ER FLAME FAILURE -----

• [--] yzs ~ - ~ . o - - " ~ T y Sntrr-OFFVA~VR ' " ' - x ~ ' ~ . p ~ s*F~'r~ SHUT'OFF#ALVR ' x~s. -'~-T ~

ATMOSPHERE FIRST TURNED 0-~ [ ~ HEATED WORK SECTION [ ~ COOL~O ~C'/'JON

1~ CooLn~o nctlo~q, BXPI.AIH ROW HAZARD A'~II~

TEMPERATURE OF TH~ ~CTION ~ ~ AT~P~RE INT~ITH ATM~SP~]~ TURNED ON ' F~RMACE TEMPERATURE CGNTROLLEI

l~ PRECA~TTONB WREN ~ ON *~m s ~ o OFF ~ T ~ O S P ~ n ~ o m [ ] ~uR~o [] wo xot~xo~ ~oua~ wmLz ~UR~ACS

L-~ F~ROR OUT" ATMOSPHERE EXPLOSIVE [~' LATTF.R CASE, 18 CHECK FOR

GAS NON-E~LOSIVE AT.SPHERE BY [] ANAL~VZ~R [] S ~ TE~T [] TIME-VOLUME [] ~E ffAMPLR It~JtASURE

HTROL~ER

O0

n TEM~ERATI~I~E, AT GIG~P~TOR.

I

[ . . . . B Y . . . . " ~ : II ~ I " i ~ ~ ~ __ ~ I " ~

, P A R T B - M A N U F A C T U R E R ' S I N S P E C T I O N &" T E S T (eompte~dtnMtntU~|

BURNE. RS . [ ] u a s " r ~

S A F E T Y ' ~ xmee-rm) CONTROLS

IMSTRUCT[ONS F-3 c'Ds.romm.s OPJmATCa U..I Ik~TRUCT~

t m e t ~qm~,&~n,. - . . . . S I G N A T U R E S

FAs, r e ACC~W'~ S~q~C~ ~O ~m~r c ~ n ~ m u ~ c ~

[ ] T ~ ' ~ ,,OR m o , ~ Rss~,sz.

I~.IRTE~ OP/~qA~ ~ APPIJCAT/~N lq3R A~PTANCR L_J J~B'rRuC'xIONS LEP~ ~ P O ~ ' g D ON CONTROL PANEL

I P A T ' S

L = . . . . . _]~lr" FOK

P A R T C - F I E L D E X A M I N A T I O N O]~ COMPLETEI~

. . . . . . . '

pAirr A ~ PABTB CHEC'IQCl} . L . . J C'HRCI~D

I .~'rALL*.'noN Acc~,'rAn~a~

L . . . . . . ~ I , I m ~ " ,

= ~ ~ n ON ~ LOCA~OX I I . ~ + m m e u . ~ t ' t ~ m r m .

£91,

7


Appendix E Availability of Publications Other than NFPA Standards Referenced in 86A

American National Standards Institute 1430 Broadway

New York, New York 10018

B31.1-1973, Power Piping, with Addenda

B93 Series

Y14.17-1966, Fluid Power Diagrams (Section 17)

Y32.10-1967, Graphic Symbols for Fluid Power Diagrams

Z50.1-1971, Safety Requirements for Bakery F~uipment

ZS0.1a-1973, Supplement to Z50.1-1971

American Society for Testing and Materials 1916 Race Street

Philadelphia, Pennsylvania 19103

D396 - - 1973, Specifications for Fuel Oils

Underwriters Laboratories Inc. 207 East Ohio Street

Chicago, Illinois 60611

Bulletin of Research No. 43

National.-Electrical Manufacturers Association 155 East 44th Strect

New York, NY 10017 T R 27-1971

APPENDIX F 8 6 A - 1 1 7

Appendix F

Suggested Operational and Maintenance Check List

Operational Check List. (a) Check burners for proper ignition and combustion characteristics.

(b) Check pilots or spark plugs, or both, for proper main burner ignition.

(c) Check for proper inlet air-gas ratios.

(d) Check for proper operating temperatures.

(c) Check sight drains or gauges, or both, for proper water flow and water temperature.

(f) Make sure atmospheric burners or pilots, or both, are protected from improper drafts, and adequate combustion air.

(g) Check for proper operation of ventilating equipment.

Regular Shift Check List. (a) Take necessary gas analyses; if automatic gas analyzers are used make

sure the manual and automatic readings coincide. Rccalibrate automatic gas analyzers.

(b) Standardize or balance instruments.

(c) Check hand valves, manual dampers, secondary air opcuings or adjustable bypasses, or both, for proper positions.

(d) Check blowers, compressors and pumps, for unusual bearing noise and shaft vibration; if V-Belt driven, check belt tension and belt fatigue.

(e) Lubricate as per manufactuz'cr's requirements.

Weekly Check L~t.

(a) Make sure flame and sensing devices arc in good condition, properly located and free of foreign deposits.

(b) Test thermocouples and lead wire for shorts and loose connections.

(c) Check setting and operation of lower temperature limit dcviec.

(d) Test visible or audible alarm systems, or both, for proper signals.

(e) Check ignition spark electrodes and check proper gap.

(f) Check all pressure switches for proper pressure settings.

(g) Check valve motors and coutrol valves or dampers for free, smooth action and adjustment.

Monthly "Check List. (a) Test interlock sequence of all safety equipment. Manually make each

interlock fall, noting that related equipment doses or stops as specified by the manufacturer.

(b) Test (Leak test) safety shutoff valves for tightness of closure.

(c) Te~t main fuel hand valves for operation.

&b


(d) Test pressure switch settings by checking switch movements against pressure settings and comparing with actual impulse pressure.

(e) inspect all deciaic~d switches a , d col,facts; . . . . . . . . . . . . . . . . .

(f) Test all amplifier and thermocouple fail-safe devices, making certain that the instrument drives in the proper direction.

(g) Clean the a i rblower filters.

(h) Glean water, gas compressor and pump strainers.

(i) Clean fire cheek screens and valve seats, and test for freedom of valve movement. /

(j) Inspect burners and pilots; clean if necessary.

(k) Check all orifice plates, air-gas mixers, flow indicators, meters, gages, a~nd pressure indicators; and clean or repair, if necessary.

(l) Check ignition cable and transformers.

(m) Test automatic or manual turn-down equipment.

(n) Check oven and furnace, interior, and ventilation, and duct work systems for cleanliness and restrictions.

(o) Test pressure relief valves, dean if necessary.

(p) Inspect air, water, fuel, and impulse piping for leaks.

Periodic Check List. "

The frequency of maintenance of the following will depend on the recommendations of the equipment manufacturer.

(a) Inspect radiant tubes, .and heat exchanger tubes for leakage, and repair if necessary.

(b)' Lubricate the instrumentation, valve motors, valves, blowers, com- • pressors, pumps, and other components.

(c) Test instrumentation, clean slidcwires, check amplifier tubes and battery.

(d) Teat flame safeguards units.

APPENDIX F 86A-119

Maintenance of Gas Equipment

g(1)as General . These recommendations a re prepared for maintenance of equipment. Speciai types of equipment command special attention. A

preventive maintenance program should be established and followed. This program should include adherence to the manufacturer 's recommendations. In this program a minimum maintenance schedule should include inspection and action on the recommendations given in the following paragraphs. An adequate supply of r e p ~ r parts should be maintained.

(2) Burners and Pilots. Burners and pilots*should be kept clean and in proper operating conditions. Burner refractory parts should be examined at frequent regular intervals to assure good condition.

(3) Flame Safeguard Equipment . When automatic flame safeguards a r e used, a complete shut-down and restart should be made at frequent intervals to check the components for proper operation.

(4) O t h e r Safeguard Equ ipment . Accessory safeguard equipment~ such as manual reset valves, with pressure or vacuum switches, high temperature limit switches, draft control, shut-off valves, air flow switches, door switches and gas valves, should be operated at frequent regular intervals to insure proper functioning. If inoperative, they should be repaired or replaced promptly.

When fire checks are installed in air-gas mixture piping, the pressure loss across .the fire checks should be measured a t regular intervals. When excessive pressure loss is found, screens should be removed and cleaned. Water type backfire checks should be inspected at frequent intervals and liquid level main- taincd.

(5) Safety Shut=off Valves, All safety shut-off valves should be checked for leakage and propcr ,operation at frequent regular intervals. A proccdurc for making tests of gas safety.shut-off valves is outlined as follows:

Recommended Leak Test Procedure for Safety Shut-off and Blocking Valves on Direct Gas Fired Oven,

(1) Safety Shut-off Valve Check.

(a) With oven in the resting position and main shut-off cock open.

(b) Place a tube on the downstl:eam side of the safety shut-off valve.

(c) Open V3 test cock.

(d) After immersing the tube into a glass of water, if more than 30 bubbles per minute appear, the valve is faulty.

(2) Blocking Valve.

(a) Start oven as normal to operating conditions (main burner on).

NOTE: For convenience purposea, the temperature controller may be set at a low temperature. -

(b) Place a tube on the downstream side of the blocking valve.

(c) Open V5 teat cock.

(d) Press and hold leak test button.

(c) Immerse the tube into a glass of water. If more than 30 bubbles appear, the valve.is.faulty.

This procedure is predicated on a piping diagram shown in Figure F-7-1 and a wiring diagram, F-7-2, entitled "Typical Safety Controls for a Direct Gas-flrdd Continuous Process Oven."


~ z u

<

c-=-fl I ; ~o ~ - - ~ 1 -7"

z x~.

- l ~ l u o,~ =_.

~ >~-'~ Z

~,~ =~ ,--[,

~u ~81 K 7

m

¢9z

~>

el

.E

"7 t~

APPENDIX F 8 6 A - 1 2 1

BLOWER BLOWER 8LI~NP R BLOWER BLOWE q RECI RCULATION EXHAUST CUMBUSTION AIR SEAL AIH ~¢~L CONVEYOR

~ C O N T R O L TRANSFORMER

H H H I_ I. . . . . . . ~ ; (~ - - . . . . r - - - - - - r . . . . . . . . i .

. . Pal ~ 2 M OL'S

4M 0 L'S

I OVER TEMPERATURE

r . . . . " - - • L , ~ , LIMIT P 1

I r , .-i OVE"TE"P: I I I I ! P- I . . . . . . . . . . . . . . . , .

L. . . . . . . , . I AF$1 AFS2 / 3M OL'$ RECIRC, EXHAUST l T . R ~ . . . . . . . ~ AIR FLOW AIR FLOW

. . . . . . . ~ COMB. * " AIR FLOW 6M OL'S

r - - - i / |" ~ | A PILOT VALV E CONVEYOR

I iGNITION i ~ . I TRANSFORMER i U I '~-.-,,-= I I " r 2 ~ - - I " I P-----FLAMe ~ I ' I I SAFEGUARD I I

~ , o I =" . . . . . I I G N ) T ~

I I ~ " L-- . 1

I ~ - i - . - ~ O , . . . . . . . .

SAFETY SHUT • OFF VALVE

I ~,;s . . . . . . . I

~ e v L E A K TEST eL~KtNGvENT vALVALVE:;~IIJ

Figure F-7-2 Typical Safety Controls for a Direct Gas-fired Continuous Process Oven.

" 4

86C-1 A M E N D M E N T S T O NI~PA,86C'

Part II,

Amendments to Standard for

Industrial Furnaces Using Special Processing Atmosphere

N F P A N o . 8 6 C - - 1 9 7 4

1. Revise 700- 7, Scope, to add a new paragraph (c) to read:

ic) Within the scope of this standard, a molten salt bath furnace. shall be any heated container that holds a melt or fusion composed of one or more relatively stable chemical salts which form a liquid- like medium into which metal work is immersed for various processes which include, but are not limited to, heat'treating, brazing, stripping, and descaling.

2. Revise 100-2, Definitions, to add a new paiagraph (d) to read:.

(d~ MOLTEN SALT BATH FURNACES are furnaces that employ, salts heated to tlae molten state. These do not include aqueous alkaline baths, hot brine, or other systemsutilizing salts in solutiofl.

3. Renumber existing paragraph (d) to (e) in 700-2.

d. Renumber Chapters 5 - 7 / a s Chapters 4-10.

5. Add a new Chapter 77, Molten Salt Bath Furnaces, as.follows:

CHAPTER 11. M O L T E N SALT BATH FURNACES:

ARTICLE 1100. GENERAL

1100-1. Scope. This chapter covers molten salt bath .furnaces, internal quench molten salt bath furnaces, and associated equipment. Molten salt bath furnaces will include any heated container that holds a melt or fusion of one or more relatively stable salts as a fluid medium into which metal. work is immersed.

1100-2. Responsibility. Molten salt bath furnaces shall be properly selected and operated for a specific process.

COM,MITTEE O N O V E N S A N D F U R N A C E S ' , 86C-2

(a) Responsibility for selection shall rest wi th the person or agency authorizing the equipment, and with the manufacturer ~up1J~yuJ ~ u t c ~ I U L ~ L .

(b) Responsibility for observing the operating instructions shall rest with the person or agency operating the equipment.

A RTICLE 1110~ L O C A T I O N AND COIqSTRUCTION

1110-1 Location. (a) A liberal area shall be allocated for the installation of each

salt bath furnace a n d t h e zone of operation shall be spaced-off immediately around the bath to prevent congestion and to prevent interference with normal operations.

(b) Every salt bath furnace shall be located either inside of a shallow cement lined pit or within a curbed area. ' I n either case, the p i t or curbed area shall be designed to contain the contents Of.the molten salt in the fmhaace.

(c) All salt.bath furnaces shall be' located so that the bath will not be exposed to leakage from overhead liquid conveying piping (service piping, steam.piping, sprinkler piping, oil piping, etc.), liquid entry through wall openings (windows, air intakes, etc.), or anticipated leakage or seepage through roofs or floors above. When it is not possible to protect against possible liquid leakage entering the salt bath because of location, then the salt bath shall be provided with a noncombustible hood that is designed and installed so that leakage into the molten salt is impossible.

(d) Where adjacent equipment (oil or water quench tanks, etc.) are located so that potential "splash over" could expose a molten salt bath, then the adjacent equipment shall be provided with deflecting baffles or guards to prevent the "splash over" from entering the salt bath.

1110-2. Construction. (a) All molten salt bath furnaces shall be constructed of non-

combustible materials.

(b) All molten salt bath furnaces shall be constructed of materials that are resistant t o the corrosive action of the chemical salts at the maximum design' operating temperature.

(c) The design of molten salt baths, and the materials selected for construction, shall minimize the possible effects of explosions, • fires, spattering and leakage, both as regards protection of property as well as safety to operating personnel.

(d)' All requirements.outlined in Chapter 2 (Location and Con- struction) shall also apply for the construction of salt bath furnaces.

86C-3 AMENDMENTS TO NFPA 8 6 C

A R T I C L E 1120. SALTS

1120-1. Gener~d.. For the purpose of this section, a salt shall be considered to be any chemical compound, or mixtures of compounds, that may be utilized to form a melt or fluid medium into which metal parts are immersed for processing. A list of commonly used salts and mixtures are contained in Appendix G.

1120-2. Storage and Handling. (a) All salts shall be stored in tightly covered' containers that

are designed to prevent the possible entrance of liquids or moisture (most salts are hygroscopic).

(b) All storage and shipping containers shall be prominently marked with the identification of the salt (or salt mixture) it contains, so that the possibility of accidentally mixing noncompatible salts will be minimized.

(c) The supply of nitrate salts shall be stored in a separated, fireproof and damp-free room or area that is away from heat, liquids and reactive chemicals. This room or area shall be secured against entry by unauthorized personnel at all times. Only the required amount of nitrate salt shall be removed from the storage room or area that is required for make-up or full bath charges. When nitrate salts have been transported to the furnace area, they shall be immediately added to the salt bath. Excess salt for later addition shall not be permitted in the furnace area.

(d) All furnace chargings (full charge or make-up) shall be from drums or metal containers. The use of fabric or paper sacks or bags shall be avoided.

A R T I C L E 1130. H E A T I N G SYSTEMS

1130-1. General. (a) For the purpose of this section, the term "salt bath furnace

heating system" shall include the heating source and all associated piping, electrodes, radiant tubes, and all other equipment or devices necessary to safely convey the heat to the bath that is required to create the salt melt or fusion.

(b) The heat source may be externally applied o r may be b y direct immersion of radiant tubes or electrical heating elements.

(c) All of the requirements outlined in Chapter 3 (Heating Systems) and Chapter 4 (Safety Control Equipment ) will apply.

COMMITTEE ON OVENS AND F U R N A C E S 86C-4

1130-2. Gas and Oil Heating Systems.

(a) The design of a salt bath furnace shall never permit direct flame impingement upon the wall of the salt container.

(b) Whenever burner immersion tubes or radiant tubes are used, the design shall prevent any products of combustion from entering the salt bath.

(c) All immersion or radiant tubes shall be fabricated of materials that are resistant to the corrosive action of the salt, or salt • mixture, being used.

(d) All immersion tubes shall be designed so that the tube outlet is above the salt level and the inlet shall be below the salt bath level. The burner shall be sealed fit tube entry to prevent salt leakage outside of the bath upon tube failure.

(e) The design of a molten salt bath furnace shall eliminate (or minimize) the potential build up of sludge and foreign materials that can result in "hot spots" bn imriaersion tubes.

(f) For control equipment requirements, see Article 1150.

1130-3. Electrical Heating Systems.

(a) Whenever immersed or submerged electrodes are used, the design shall prevent tile possibility of stray current leakage (which could result in electrolytic corrosion and subsequent perforation of the wall of the salt container) and the electrodes shall be fixed or restrained to prevent possible arcing to the salt bath container Or metal work in process.

(b) When internal resistance heating elements are used, they shall be fabricated of materials that are resistant to the corrosive action of the salt and the salt bath shall be designed to prevent sludge build-up on the element that can result in damage from "hot-spots."

(c) Whenever immersed or submerged electrodes or internal resistance heating elements are used,, they shall be positioned in the bath so that all heat transfer surfaces will be below the salt level at all times.

(d) For control equipment requirements, see Article 1150.

, ,4

\

86C-5 AMENDMENTS TO NFPA 8 6 6

A R T I C L E 1140. V E N T I L A T I O N

1140-1. Hoods. In order to remove, and appropriately control, the emission of heat and toxic (or otherwise deleterious) fumes, molten salt bath furnaces shall be provided with vented hoods that are constructed of noncombustible materials which are resistant to the max imum design temperature of the salt bath a n d the corrosive action of the salt being used.

1140-2. Exhaust. (a) Salt ba th furnace hoods shall be provided with exhaust

ductwork and a blower (mounted external to the hood) for the continuous evacuation of fumes and heat.

(b) When required for the reduction of pollution by exhaust emissions, an air washer, chemical scrubber or fume destructor

• shall be installed that will-perform the required altering of the exhaust without reducing the exhaust system effectiveness.

A R T I C L E 1150. SAFETY C O N T R O L E Q U I P M E N T

1150-1. General .

(a) A molten salt bath furnace shall be equipped with control instrumentation and interlock systems that provide protection against the various and known types of potential equipment malfunction.

(b) Gas and oil fired salt bath furnaces shall be provided with controls as specified in Chapter 4 of this standard. In addition,

a n approved flame supervisory device shall be provided for each burner which shall be interlocked to shut off the fuel supply to the affected burner and activate the alarms.

(c) All salt bath furnaces shall be provided with a temperature control instrument that will maintain the set temperature of the furnace. The temperature control instrument shall be of the "fail safe" type. Any failure of the instrument or failure of the circuit to the temperature sensing device shall immediately drive the instrument upscale and automatically open the safety contacts or shunt trip. This shall shut down the furnace and activ~ite the alarms.

(d) An excess temperature control instrument shall be provided, which shall have its own temperature sensing element, and shall be interlocked to shut off the heating system and activate t h e a l a r m s when an excess" temperature condition is detected.

COMMITTEE ON OVENS AND FURNACES 8 6 C - - 6

(e) All immersion-type temperature sensing elements or devices shall be resistant to damage from the maximum design temperature

(f) When a salt bath is operating in a temperature range close -to the melting point of the metal work in process, or when nitrate, salts are being used, it is recommended that a second over-tempera-

' ture control instrument be provided. As possible alternates, a preset timer which limits the "on" time of the heating system may be used or the original instrument may be of a "fail safe" design.

(g) When nitrate salts are being used '(regardless of the type of heating system) a "heat •rate" controller should be installed to prevent a too rapid heat-up, thus preventing localized overheating and ignition of the salt.

(h) All electrical wiring and control cabinets and cubicles shall conform to the requirements of NFPA 70-1978, National_ Electrical Code.

(i) Each salt bath furnace shall be provided with audible and visual alarms. These alarms shall be interlocked with the operating and safety control instrumentation so that the alarms will be activated upon instrument "failures or instrument detected mal- functions.

1150-2. Electrlcally Heated Salt Bath Furnaces. (a) A step-switch power transformer shall be used to provide a

simple and positive control of the heating load. W h e n the salt bath furnace is idled over long periods, left unattended or when not operating, the lower voltage taps should be used.

~(b) A transformer switch interlock shall be provided and shall be interlocked to disengage the operating contactor. This Will prokect against the h a z a r d of changing secondary voltage taps

-under load, (c) Whenever transforr~ers are forced-air cooled, a transformer

air flow switch shall be provided. This air flow switch shall be interlocked to open the safety control contactor or actuate the shunt trip in the event of loss of air flow.

(d) Whenever water cooled furnace electrodes are used, safety control instrumentation shall be provided to detect failure of the cooling-water system and shall be interlocked to open the safety control system contactor or actuate the shunt trip. This instrumentation may be a waterflow switch or a thermal detector on the drain side, or both.

- (e) The current input shall be constantly measured by ammeters and voltmeters, with constant visual read out. These instruments shall read out amperes and voltage for each phase.

, , L

86C-7 AMENDMENTS TO NFPA 86C

A R T I C L E 1160. INTERNAL Q U E N C H I N G SALT BATHS

1160-1. G e n e r a l . Whenever a salt bath is utilized as an internal quenching tank in an internal quench furnace, then all requirements in Chapter 10 shall apply, in addition to the requirements outlined in this chapter. ~-

1160-2. Low Temperature Salt Bath Quench Tanks. Salt bath q.uench tanks (350 ° F to 750 ° F), that utilize sodium and/or potassium nitrates and nitrites and operate with a combustible furnace atmosphere above all, or part, of the salt bath surface, shall be designed to :

(a) Control the interface between the atmosphere and the salt surface to prevent carbon precipitation onto the salt surface, and

(b) Provide adequate circulation of the salt to prevent localized overheating of the salt where it is exposed to furnace temperatures.

NOTE 1 : Carbon concentration on the salt surface can cause localized overheating when hot material in process enters the salt quench from the furnace.

NOTE 2. A typical arrangement is shown in Appendix H.

1160-3. High Temperature Salt Bath Quench Tanks. Salt bath quench tanks that operate between 700°F and 1300° F shall utilize salts, or salt mixtures, that are chemically and physically stable at operating temperatures and are nonreactive to furnace atmospheres.

A R T I C L E 1170. HAZARDS OF SALT "BATHS

1170-1. Genera l . ' The hazards that are inherent in the operation of molten salt bath furnaces can result in explosions or fires, or both. These explosions and fires can occur inside the salt bath furnace or may occur external to the furnace. Basic causes can be chemical or physical reactions and may occur in combination.

Since molten salts have high heating potential, low viscosities, and relative!y little surface tension, even minor physical disturbances to the molten salt bath can result in spattering or ejection of the molten salt out of the furnace cofitainer. This ejection can become violent when liquids (water, oil, etc.) or reactive materials are allowed to penetrate the surface of the salt bath.

COMMITTEE ON OVENS AND F u R N A c E s 8 6 C - 8

Nitrate salts can produce violent explosions because of chemical chain reactions when the nitrate salt is overheated. Overheating can occur because of a malfunction of the heating system controls, from a floating or i 'hung-up" work load, or from an operator processing error.

While this standard deals primarily with the protection and conservation of property, salt bath explosions (chemical or physical) can be expected to involve injury to personnel. As a result, it is recommended that all aspects of personnel safety be thoroughly investigated.

1170-2. Operator Precautions.

(a) Each molten salt bath operator shall be thoroughly trained, as specified in Chapter 1, Section 100-5. Only trained, qualified operators shall be permitted to operate or service molten salt bath furnaces.

(b) Each molten salt bath installation shall be furnished with a prominently displayed wall chart, which shall be supplied by the manufacturer. These charts shall contain all of the instructions and information specified in Chapter 1, Section 100-5, paragraphs (d) and (e). In addition, a clearly visible, and conspicuous, sign shall be posted at each salt bath furnace. This sign shall state which s a l t - or salt mixtures - - are to be used, and what the maximum design operating temperature is.

(c) A complete operation and service manual shall be available at each salt bath furnace.

(d) Since emergency procedures are not utilized on a day-to- day basis, all emergency procedures shall be reviewed with the operators on a regularly scheduled basis.

(e) Because of the potential for spattering of the molten salts, it is recommended that consideration be given to the provision of heat resistant clothing, safety glasses or goggles, full face shields, heat resistant gloves, safety shoes, and all other personnel protection recommended by the equipment manufacturer, user standards, industrial safety standards, and local, state or federal requirements.

1170-3. Miscellaneous Precautions.

(a) All fixtures, tools, baskets, parts, etc., that are-to be immersed in a molten salt bath must be thoroughly dry before immersion.

- s6c -~ AMENDMENTS TO NFPA 866

(1~) If a crust forms on the surface of a molten salt ba th because of salt freezing, no at tempt shall be ma_de to phy.qieally hrenk the crust while the furnace is in operation. Instead, the temperature of the bath shall be gradual ly raised unti l the crust melts. Care must be taken so that the bath temperature does not exceed the m a x i m u m design operat ing temperature at any time. ' .

(c) All salt bath furnace covers shall be in the closed position whenever the furnace is not in use or is being idled over prolonged periods.

(d ) All public fire depar tment and p lant emergency organiza- tions that will respond to fires and explosions within the p lan t shall be made familiar with the na ture of the chemical salts being used, t h e location and operat ion of each molten salt ba th furnace, and the extinguishing and control methods that can be safely employed.

COMMITTEE ON OVENS AND FURN.~CES 86C-10

6. Add a new Appendix G; as follows:

A P P E N D I X G.

MELTING POINTS OF C O M M O N CHEMICAL SALTS

Salt

BariiJm Chloride

Barium Fluoride

Boric Oxide (Anhydride)

Calcium Chloride

"Calcium Fluoride

Calcium Oxide

Lithium Chloride

Lithium Nitrate

Magnesium Fluoride

Magnesium Oxide .

Potassium Carbonate

Potassium Chloride

Potassium Cyanide

Potassium Fluoride

Potassium Hydroxide

Potassium Nitrate

Potassium "Nitrite

Sodium Carbonate

Sodium Chloride

Sodium Cyanide

Sodium Fluoride

Sodium Hydroxide

Sodium Metaborate

Sodium Nitrate

Sodium Nitrite

Sodium Tetrahorate

Strontium Chloride

o F o C

1764 963

2336 1280

1071 578

1422 773

2480 1360

4662 2575

i135 613

491 255

2545 1397

5072 2802

1636 892

"1429 777

1174 635

1616 880

716 380

631 333

567 297

1564 852

1479 805

i047 564

1796 980

605 319

1771 967

586 308

520 271

1366 742 ~

1603 - 873

8 6 C - 11 AMENDMENTS TO NFPA 86C

MELTING POINTS OF COMMON SALT MIXTURES

(Lowest Constant Melting Point Given)

(Proportions given are percentages by weight.)

Mixture and Proportion OF °C

Lithium Nitrate 23.3, Sodium Nitrate 16.3, Potassium Nitrate 60.4 250 121

Potassium Hydroxide 80, Potassium Nitrate 15, Potassium Carbonate 5 280 138

Potassium Nitrate 53, Sodium Nitrate 7, Sodium Nitrite 40 285 141

Potassium Nitrate 56, Nitrite 44 ~ 295 146

Potassium Nitrate 51.3, Sodium Nitrate 48.7 426 219

Sodium Nitrate 50, Sodium Nitrite 50 430 221 ,

Sodium Hydroxide 90, Sodium Nitrate 8, Sodium Car- bonate 2 560 294

Lithium Chloride 45, Potassium Chloride 55 666 353

Barium Chloride 31, Calcium Chloride 48, Sodium Chlor- ide 21 806 430

Calcium Chloride 66.5, Potassium Chloride 5.2, Sodium Chloride 28.3 939 504

Calcium Chloride 67, Sodium Chloride 33 941 505

Potassium Chloride 35, Sodium Chloride 35, Lithium Chloride 25, Sodium Fluoride 5 960 516

Potassium Chloride 40, Sodium Chloride 35, Lithium Chloride 20, Sodium Fluoride 5 990 533

Barium Chloride 48.1, Potassium Chloride 30.7, Sodium Chloride 21.2 1026 555

Sodium Chloride 27, Strontium Chloride 73 1049 565

Potassium Chloride 50, Sodium Carbonate 50 1085 585

Barium Chloride 35.7, Calcium Chloride 50,7, Strontium Chloride 13.6 1110 599

Barium Chloride 50.3, Calcium Chloride 49.7 1112. 600

Potassium Chloride, 61, Potassium Fluoride 39 1121 605

Sodium Carbonate 56.3, Sodium Chloride 43.7 1177 637

Calcium Chloride 81, Potassium Chloride 19 1184 640

Barium Chloride 70.3, Sodium Chloride 29.7 1209 654

Potassium Chloride 56, Sodium Chloride 44 1220 660

Sodium Chloride 72.6, Sodium Fluoride 27.4 1247 675

Barium Fluoride 70, Calcium Fluoride 15, Magnesium Fluoride 15 1454 790

Barium Chloride 83, Barium Fluoride 17 1551 845

Calcium Fluoride 48, Magnesium Fluoride 52 1738 949

COMMITTEE ON OVENS AND FURNACES 86C-12

7. Add a new Appendix H (a figure showing Typical Arrangement to Prevent Salt Overheating and Carbon Precipitation)as follows:

APPENDIX H.

~~ WORK ENTRY

EDUCTOR

ENDO. GAS

V---] ALT COR

SALT LEVEL

I

/

/ SA LT CIRCULATING

PUMP •

Typical arrangement to prevent salt Overheating and carbon precipitation

".4

report of committee on ovens and furnaces · the report of the committee on ovens and furnaces is...

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