10. chapter - 10 ventilation and heat control

8/19/2019 10. CHAPTER - 10 Ventilation and Heat Control

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CHAPTER - 10

Ventilation and Heat Control

1 Purpose & Efects o Ventilationand Heat Control1.1 Purpose o Ventilation & Heatcontrol1.2 Efects o Good and BadVentilation

2 Statutory Provisions3 ndian Standards! "#er$al Environ$ent and its

%easure$ents !.1 "e$perature %easure$ent !.2 Hu$idity %easure$ent

!.3 'ir %ove$ent and Content%easure$ent

( P#ysiolo)y o Heat *e)ulation (.1 Heat Stress and "#er$o

*e)ulation(.2 "#er$al +i$its or Co$ort and

E,ciency (.3 Heat and Cold Stress & t#eir

ndices(.! Healt# and Saety Pro-le$s in

Hot & Cold Environ$ent (.( Control o Heat Stress

General Considerations .1 /e0nitions.2 'ir *euire$ent .3 Control Criteria.! So$e /esi)n actors

"ypes o Ventilation .1 Classi0cation o Ventilation

Syste$s.2 4atural Ventilation

/ilution & *ooed Ventilation.3 %ec#anical Ventilation

Buildin) Ventilation 5E6#aust7 Plenu$7 Co$pound7

*oo7 and Co$ort Ventilation

Process Ventilation 5/ilution7 +ocal E6#aust and

E$er)ency Ventilation.! 'ir /istri-ution.( 'ir Conditionin). Ventilation or Special

8perations9 Control o Heat E6posures

9.1 Control at Source :solation orSe)re)ation;

9.2 nsulation9.3 Su-stitution9.! +ocal E6#aust Ventilation9.( Control o *adiant Heat

9. +ocal *elie 9. Personal Protective Euip$ent

< "estin) and %aintenance oVentilation Syste$s

1= >or?ed E6a$ples

1 PURPOSE OFVENTILATION AND HEATCONTROL

Why is good ventilation necessary? This basic question is replied with shortexplanation in part 2.1.5 of Chapter!.

1.1 Puro!e o" Ventilation and HeatControl #

The need or purpose of ventilation andheat control are su""arised here asfollows #

1. $ir is life and fresh air is the %rst needfor survival of living creatures.$bsence of air brings death within a

few "inutes. &ife without breathing isnot possible and the clean air isneeded for the whole life for breathingand functioning of hu"an body.

Therefore good ventilation givingsu'cient fresh air is the per"anentrequire"ent.

2. (u"an body cannot tolerate excessivete"perature. (eat stresses producedby high heat exposures cause adversee)ects on health and safety of wor*people. Therefore environ"ental

te"perature control is also

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THEME


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per"anently needed for wellfunctioning of hu"an body. +entilationhelps in re"oving excessivete"perature.

,. (eavy physical wor* or heavy wor*load causes heat stress and strain andincrease "etabolic heat- body

te"perature- sweating- heart rate etc. To "aintain control/ bodyte"perature- ventilation is necessary.0ee art 5.1.

. Carbon dioxide is continuouslyexhausted by all hu"an beings. 3uch"ore conta"inants are added by"anufacturing processes to pollute air.

Therefore cleaning of air and supply of fresh air with su'cient oxygen are alsonecessary. This is possible by goodventilation and pollution controltechniques only.

5. Where due to weather or at"osphericconditions or process para"eters-excessive te"perature is unbearableor unco"fortable- air conditioning orrefrigeration syste"s are alsonecessary. Conversely where airheating is necessary as in case of excessive cold cli"ate- it "ust beprovided.

4. asic functions of ventilation are to a/

"aintain the oxygen content of the airand to prevent C62 concentrationsfro" rising b/ prevent or re"oval of body odours c/ prevent har"fulconcentration of aerosols and airborneconta"inants and d/ "aintainreasonable conditions of ther"al li"itsfor co"fort and e'ciency which resultin decreased heat stress- increasedproductivity- reduced accident rateshot conditions induce unsafe acts/and adverse health e)ects interaction

with other ha7ards/- higher level of 8obsatisfaction- reduced absenteeis"-i"proved attitudes- reduced downti"efor hot vessels and co"pliance of required standards.

!. While designing industrial buildingscare "ust be ta*en to provide goodventilation for dilution of inside air toprevent vitiation by causes- such asbody odours- to re"ove processreleased conta"inants and heat

exposures to "aintain satisfactoryther"al environ"ents- to "aintain

heat balance of body and to preventacute disco"fort and in8ury to thehealth of the wor*ers. 9f naturalventilation is not su'cient for thesepurposes- "echanical ventilation-cooling syste" or other techniques"ust be e"ployed to achieve

satisfactory results.:. $s explained in subsequent part 5.1 ;

5.2 of this Chapter- the basic need forventilation is to "aintain the bodyheat balance equation by controllingair and surrounding te"perature-hu"idity and air velocity. Thereforesupply- well distribution and"aintenance of fresh air throughoutthe factory are ut"ost necessary to"aintain co"fortable wor*ingconditions as expected by sections 1,to 15 of our


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lectric %ttings for ventilation syste"in @a""able>explosive area should be@a"eproof and of the approved type.

1. Ee%t! o" /ood and adVentilation #

fu"e>gas generating processes.

Ne9 rule 1 prescribes or$ 4o.3or @or? environ$ent $onitorin). =ule4:E for ovens and dryers and new

schedules 2-11-1!-1-25 and 24 u>r 1D2

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E


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of an airwater "ixture. The direct dialhygro"eters are also available.

$ whirling hygro"eter sling psychro"eter/ is used to assess the a"bient airte"perature and hu"idity. The dry andwet bulb asse"bly is rotated at 4D rp"till the readings beco"e steady. The

reading of the dry bulb gives the a"bientte"perature while drop between dry andwet bulb te"perature is an indication of relative hu"idity by using a psycho"etricchart.

4.3 Air :o$e&ent andContent :ea!ure&ent #

s. "#e Cu ane&o&eter

consists of four he"ispherical cupscarried on the ends of four radial ar"spivoted so as to rotate in a hori7ontalplane. The speed of rotation is indicatedon a dial graduated to read air velocityfro" 1 to 2D ">s. +elocities under D., ">sare "easured by "eans of a&i%roane&o&eter or ele%tri%alt*er&al ane&o&eter.

;ata t*er&o&eter designed by&eonard (ill in 11 "easures the cooling

power of the air to cool s*in surface- apower that is "easured in ter"s of drybulb te"perature- the radiation and therate of air "ove"ent. The *atather"o"eter is an alcohol- liquid inglass ther"o"eter with a large bulb andan upper reservoir. There are two "ar*son the ste". 9t is cheap but fragile anduseful for low air velocities below D.25">s 5D fp"/. The bulb is war"ed by awar" water so that the alcohol %lls up thewhole ther"o"eter up to D DC/. The

ther"o"eter is then carefully dried and

placed at the sa"pling point. The coolingti"e is "easured by a stopwatch. Thenair velocity is calculated by using thevalues of cooling ti"e- air te"peratureand instru"ent factor.

0winging van ane"o"eter- (ot wireane"o"eter ane"other" air "eter/-

$lnor ther"oane"o"eter- 3echanicalane"o"eter- Ther"istor eadane"o"eter- (eated ther"ocoupleane"o"eter and =otating vaneane"o"eter of cloc* type or electronicdirectreading type are also used inindustrial hygiene to "easure the airvelocity.

Pre!!ure tue! are used to"easure both pressure total and static/and velocity of the air in air ducts. Thedyna"ic velocity/ pressure is deter"inedas the di)erence between the total andthe static pressures. The air velocity in airducts can be "easured with a Pressure#ead device static and pilot tubeconnected with di)erential pressure Hgauge/.

Indi%ation tue or /a! dete%tiontue is used to "easure contents of airconta"inants such as toxic vapours andgases vi7. Cl2- C6- 062- I62- (,- ethanoletc. $ co""on type is her"etically

sealed glass tube about to ! "" wideand 1DD "" long containing a %llercrushed silica gel- glass or porcelaincru"bs/ treated with solutions of variousreagents. The tube is *ept into inti"atecontact of the air to be analysed. ypu"pstro*es air sa"ple is drawn in. Theconcentration of the i"purity can be readon a scale by a length or rate of changein colour of the %ller "aterial that hasco"pleted reaction.

Air urit, can be "easured by air or

gas analysers of various designs. Birecttechniques of gas analysis!e%tro&etr,7 electricalche"ical andoptical "ethods per"it auto"atic andcontinuous air analysis. 9n air !a&lin'&et*od the sa"ples collected by airsa"pler pu"ps- are analysed in alaboratory to get accurate "easure"ent.

Indoor air +ualit, "onitors aredirect reading instru"ents for gaseoussa"pling.

Du!t %ontent! in the wor*roo" aredeter"ined by passing a "easured

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quantity of air through %lters during aparticular ti"e and calculating the dust"ass collected. 3ethods to "easurecharacter and si7e of dust particles arealso available.

vapour "ay bepresent. $verage velocity "easured/"ultiplied by the area of the openinggives the $olu&e s. 9f air @owpressure I>"2 or a/ is *nown-considering air density dJ1.2 *g>", for

"ost ventilation situations- the airvelocity + ">s/ is given by

22P 1V or P dV

d 2= =

ilot static tubes are thin and can beeasily inserted into ducting. 'll velocity $eters s#ould -e placed parallel to t#eair strea$ and cali-rated ro$ ti$e toti$e.

ressure di)erence in air can be"easured by a &ano&eter or U-tue'au'e! %lled with water or para'n.Biaphrag" pressure gauges are alsoavailable.

$ir @ow patterns can be detected by!&o=e tue! which produce a plu"e of

s"o*e when air is pu)ed through the".


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Clothing a)ects the heat stress.Cotton clothing is "ost co"fortable as itsoon absorbs sweating and dissipatesheat. 0ynthetic clothing- though loo*sgood- adds to sweating and increasesheat stress.

Heat Stre!! of any given wor*environ"ent is considered as theco"bination of both cli"atic and noncli"atic factors leading to heat gain bythe body by convection and radiationand>or li"iting heat dissipation fro" thebody.

Cli&ati% "a%tor! are # airte"perature- hu"idity- radiantte"perature and air "ove"ent.

Non-%li&ati% (er!onal) "a%tor!are # "etabolic wor*load degree of physical wor*/- clothing- age- sex- bodybuild- accli"atisation- physical %tnessand ethnic di)erences.

Heat Strain is the physiological orpathological change response/ resultingfro" heat stress vi7. rise in bodyte"perature- sweating- heart rate etc.

The severity of strain depends onprevailing stress- age- physical %tness-degree of accli"atisation and dehydrationof the wor*er. When the strain beco"es

excessive- disco"fort or distress is felt.$ccli"atisation helps to tolerate heatstress.

Heat alan%e E+uation #

( J 3 M C M B M = H

Where( J $"ount of heat gain or loss by

the tissues of the body. 9f the body

"aintains ther"al equilibriu" 0 J D3 J 3etabolic heat production. 9t

depends on the rate of "etabolis". J vaporative heat loss. 9t partly

depends on the sweating rate andpartly on the cli"atic conditions-especially watervapour tension andhu"idity.

C J Convective heat gain or lossNdepends

B J Conductive heat gain or loss N

on the

= J =adiant heat gain or loss Ncli"aticN condition

J (eat expanded in physical exertionH J (eat loss due to respiration- exertion-

urination etc.

$ hot environ"ent will increase heatgains by radiation- convection orconduction. (u"idity retards heat lossfro" the body by evaporation. The bodywill atte"pt to balance any heat gain byperspiring to increase cooling byevaporation. 9f the loss of heat does notbalance the gain- the body will su)er.

The rate of "etabolis" for asedentary i.e. seated adult is about 1DDOcal>hr but it increases in heavy wor* upto 1DDD Ocal>hr. (eat balance equationsuggests the factors deter"ining heatstress as air te"perature- air velocity-hu"idity- te"perature of surroundings-degree of activity and clothing worn.

Therefore it should be the basic ai"of any ventilating syste" to

1. Oeep the air te"perature in the roo"low enough to dissipate body heat byconvection.

2. revent excessive hu"idity to help

body heat loss by evaporation and,. =egulate the air "ove"ent to help

body heat loss by rapid evaporation.

:etaoli% *eat rodu%tion # 9t isthe a"ount of heat produced in the bodyby way of "etabolis" which variesdepending upon the level of activity.

A%ti$it, Heat rodu%tion;%al>*r

asal condition 4D&ight physical wor* 21D3oderately heavy 21D,15

physical wor*(eavy physicalwor*

,15

Con$e%ti$e *eat 'ain or lo!! #ody gains or looses heat by convectiondepending upon the gradient between thes*in and air te"perature. 9t is "odi%ed byair "ove"ent.


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calculate the heat exchange byconvection.

( J D.5 + tsta/

Where ( J a"ount of heat loss>gain inOcal>"2 of body surface area>hr-

+ J air speed in ft>"in-

ts J s*in te"p. inDC and

ta J air te"p inDC.

Radiant *eat 'ain or lo!! #Bepending upon the level of radiant

te"perature tr/ of the surrounding

environ"ent over that of the s*in

te"perature ts/ the body will gain or lose

heat by radiation. The following equation

represents heat exchange by radiation.

(r Ocal>"2>hr/ J 5.! ts A tr /

E$aorati$e *eat lo!! # 0weatproduced on to the surface of the s*inevaporates- when the vapour pressure onthe s*in is higher than the vapourpressure of the surrounding environ"ent.$ir "ove"ent enhances evaporative heatloss. y using the following equation- the

heat loss due to evaporation can bewor*ed out.

(e J 1. + D.,! s a/

Where

(e J evaporative heat loss in Ocal>"2>hr-

+ J air speed in ft>"in-

s J vapour pressure of the s*in and

a J vapour pressure of the air.

Fa%tor! ae%tin' *eat-alan%e o" t*eod, #

Heat-rodu%tion is increased byco"bination of carbohydrates- fats andproteins. The factors are # asal heatproduction 3=/ speci%c dyna"ic actionof food 0B$/- (igher 3=- Hnconscioustensing of "uscles- shivering andexercise.

Heat lo!! is increased by convection-radiation ; evaporation. The factors are #asal heat loss- increased air "ove"ent-increased radiating surface- increasedinsensible vaporisation- increased s*incirculation- sweating- panting anddecreased clothing.

5. T*er&al Li&it! "orCo&"ort and E?%ien%, #

T*e ee%t o" at&o!*eri%%ondition i.e. te"perature- ventilation-hu"idity- radiant heat- greenhouse e)ectsee art 4.5 of Chapter2/ etc.- uponwor*erLs e'ciency or susceptibility toaccident is di'cult to predict- because- itvaries with person to person and one

co"fortable condition "ay beunco"fortable for others. 3uch variationfro" the body te"perature ,!DC :.4D


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Ee%ti$eTe&.

DC D<1 0afe tolerable li"it for

a/ &ight wor* ,2 :.4b/ 3oderate wor* 2.5 :5.1c/ (eavy wor* 2 :.2

2 revention of steepfall in production

2:. :

,


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at core body/ te"perature of ,.5DCnor"al oral te"p. ,!DC/. $t about D.4DC1D5D


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in hot environ"ents. 9ts deter"inationis si"ple and requires less expensiveequip"ent.9t is necessary to deter"ine theaverage exposure of a person over along period of ti"e when WET varied.$ ti"eweighted average is given by #

$verage WET J

xposures should not exceed thevalues given in the following chart #

5D

12D

5

11D

D WET D


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has the drawbac* that cu"berso"eno"ogra"s are required which isnot always practical.

(6) Cold Stre!! and @ind C*ill Inde(@CI)# 9t refers to the coldenviron"ent and uses only dry bulb

te"perature and air velocity butta*es into account the cooling e)ectof the wind.

9n cold countries whereenviron"ental te"perature goes belowDC- cold stress hypother"ia orfrostbite/ is also possible. ody core/te"perature rectal ,!.4DC- 6ral ,!DC/should not fall below ,5DC 5DT or WET inour control progra""es.

Heat E6posure "#res#old +i$it Values :S'; and Boldin) Hatc# Heat Stress nde6 :HS; are other indices.

5.4Healt* and Sa"et,Prole&! in Hot and ColdEn$iron&ent #

5.4.1. Hot En$iron&ent#

Types of *ealt* di!order! causedby exposures to high heat are asunder #

1. 0*in disorders pric*ly heat "iliariarubra/- s*in cancer rodent ulcer/.

2. 0yste"ic disorders heat stro*ehyperpyrexia/- heat exhaustioncirculatory de%ciency- heatsyncope/- heat cra"p sweatingde%ciency/- water de%ciency- salt

de%ciency.,. sychoneurotic disorders "ild

chronic heat fatigue- acute loss of e"otional control.

T*e!e di!order! %an %au!e"ollo9in' ee%t! -

1. (eat or sun stro*e due to excessiverise in core body/ te"peratureresulting fro" failure of ther"oregulatory "echanis".

2. (eat xhaustion due to loss of body@uid with salt/ in sweating.

,. (eat or "uscle cra"ps due toprofuse sweating and salt loss-drin*ing "uch water and failure toreplace bodyLs salt loss.

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4.


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"ini"ise heat stresses. 3ethods of engineering control and personnel"anage"ent are given below #

5.5.1 :et*od! o" En'ineerin'Control! #

=efer heat balance equation in part5.1. Then to control the e)ects of para"eters 3- C- = ; followingcontrol "easures are necessary #

To redu%e *eat o" &etaoli!&i.e. 'ain , : - =educe level of physical activity by sharing wor* loadwith others or by using "echanical"eans. 0chedule cooler periods forwor*. 9ncrease rest periods.

To redu%e *i'* air te&erature

i.e. 'ain , C 5 9nsulate hotequip"ent. rovide canopies with fansover hot equip"ent to drive away hotair. 9"prove general and localisedventilation over personnel. rovideexhaust ventilation- local cooling-evaporative cooling- refrigeration-isolation- substitution- relocation andredesign as per need. Hse ventilatedsuits against excessive heat.

To redu%e radiationte&erature i.e. 'ain , R 5

9nsulate hot equip"ent. Hse re@ectiveor absorptive shielding between theheat source and "an. aint the surfaceof hot equip"ent or shield or clothe itby using white colour for short wave of solar radiation and alu"iniu" colour forinfra red radiation. Wear protectiveclothing of re@ective surface of polished"etal or paint or ventilated suits.9nterpose line of sight barrier. Coverexposed parts of the body. Hse fans to"ove air and exhaust ventilation.

To redu%e *i'* *u&idit,(re!tri%tion on lo!! , E) 5 reventstea" lea*s. 9"prove generalventilation. $pply dehu"idi%cation incon%ned spaces. Hse ventilated suitsfor high hu"idity. Becrease hu"idityand increase air speed.

5.5. :et*od! o" Per!onnel:ana'e&ent(Ad&ini!trati$e eort!)#

1. rovide a"ple supplies of cool wateror @avoured drin*s.

2. rovide extra salt where required.,. nsure lightweight- loose %tting

clothing. 9n conditions with noradiant heat load- use as littleclothing as possible. With high

radiant heat loads- clothing shouldcover s*inV where possible- clothingshould be of cotton and white.

. nsure quic*est develop"ent of accli"atisation. &ac* of salt- lac* of water or poor physical conditionretards accli"atisation.

5. Where possible do not e"ploy "enin hot conditions if they are # obese-su)ering fro" any cardiovasculardisease- su)ering fro" or recoveringfro" febrile illness- over 5 years of age- physically un%t and su)eringfro" any s*in disease or if they failto sweat properly.

4. Where possible- arrange for "enwho are to wor* in hot surroundingsto spend their %rst two wee*swor*ing in cool surroundings in the"orning and in the heat in theafternoon. This will helpaccli"atisation/

!. $nalyse wor*ing situations for

esti"ation of heat load throughvarious channels. $pply physical"ethods to control ha7ardV if necessary a"plify by control of wor*and rest routine.

:. =est periods should be ta*en in coolsurroundings. 3en "ay e)ectivelyKcool o)L even when they continue towor* in cool conditions.

. 9n extre"e conditions "an "ay #wear ventilated suits- be precooledby i""ersion in cool water and be

cooled down by spraying the" withcool water.

1D. Train in %rstaid for heat strainsy"pto"s.

11. ree"ploy"ent and periodic"edical exa"inations for properplace"ent of individuals consideringtheir age- sex and physical %tnessand

12. 6bservation of individualphysiological responses to heat and

to change their 8ob or place if necessary.

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0ee part :. of Chapter2 forwor*load and heat exposure li"its.

A%%li&ati!ation is an i"portantfactor for a wor*er to wor* for a longperiod in hot environ"ent.$ccli"atisation "eans the habit by

which a person adapts hi"self to livingand wor*ing in a hot and hu"idat"osphere. t is $aniested as areduction in t#e #eart rate and internal-ody te$perature at t#e e6pense o increased s@eatin).

The factors a)ecting physiology of accli"atisation are 1/ rocess of ther"al regulation 2/ Cardiac outputand heart rate ,/ 0weating.

0weating starts when the s*inte"perature exceeds ,, DC. There areso"e 25 lacs sweat glands in a body of !D *g "an. Buring the period of accli"atisation- the sweating rate "ayrise fro" 1.5 lit>h to ,.5 lit>h. The"aintenance of a body te"perature ,!DC is achieved by constant ad8ust"entof the process of ther"ogenesis andther"olysis. $n accli"atised personshould not lose "ore than 1 lit>h andthe rectal te"perature should notexceed ,: DC.

The following factors helpaccli"atisation to high te"peratures #

1. ersons having less than 5D *g bodyweight- "ore than 5 years of ageand "axi"u" oxygen consu"ptionless than 2.5 lit>"in should not beselected. 25-DDD of an inch/.

Aero!ol# $n asse"blage of s"allparticles- solid or liquid- suspended inair. The dia"eter of the particles "ayvary fro" 1DD "icrons down to D.D1"icron or less- e.g.- dust- fog- s"o*e.

:i!t!# 0"all droplets of "aterialsthose are ordinarily liquid at nor"alte"perature and pressure.

Vaor# The gaseous for" of substances which are nor"ally in thesolid or liquid state and which can bechanged to these states either byincreasing the pressure or decreasingthe te"perature.

Du!t# 0"all solid particles createdby the brea*ing up of larger particles byprocesses li*e crushing- grinding-drilling- explosions- etc. Bust particlesalready in existence in a "ixture of "aterials "ay escape into the air

through such operations- as shoveling-conveying- screening- sweeping- etc.

Fu&e!# 0"all- solid particlesfor"ed by the condensation of vaporsof solid "aterials.

/a!e!#


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electrostatic precipitators and charcoal%lters./

Co&"ort one $verage/# Therange of e)ective te"peratures overwhich the "a8ority 5DF or "ore/ of adults feel co"fortable.

Du!t Colle%tor# $n air cleaning

device to re"ove heavy particulateloadings fro" exhaust syste"s beforedischarge to outdoors. Hsual range#loadings D.DD, grains per cubic foot andhigher.

Entr, Lo!!# &oss in pressurecaused by air @owing into a duct orhood inches (2D/.

Hood# $ shaped inlet designed tocapture conta"inated air and conduct itinto the exhaust duct syste".

Cature Velo%it,# $ir velocity atany point in front of the exhaust hoodnecessary to overco"e opposing aircurrents and to capture theconta"inated air at that point bycausing it to @ow into the exhaust hood.

:ano&eter# $n instru"ent for"easuring pressureV essentially a Htube partially %lled with a liquid- usuallywater- "ercury or a light oil- soconstructed that the a"ount of displace"ent of the liquid indicates the

pressure being exerted on theinstru"ent.

:ini&u& De!i'n Du%t Velo%it,#3ini"u" air velocity required to "ovethe particulates in the air strea"- fp".

Plenu ressure equali7ingcha"ber.

Natural Ventilation# 0upply of outside air into a building throughwindows or other openings due to windoutside and convection e)ects arisingfro" te"perature or pressure

di)erences or both/ between insideand outside of the building.

/eneral Ventilation# 0upply of outside air either by positive ventilationor by in%ltration into the building.

Po!iti$e Ventilation# 0upply of outside air by "echanical device- suchas a fan.

Dilution Ventilation# 0upply of outside air to reduce the airborne

conta"inants in the building. 9t "ay bedue to natural or "echanicalventilation.

E*au!t o" Air# =e"oval of airfro" a building and its disposal outsideby "echanical device such as a fan.

:e%*ani%al Ventilation# 0upply of

outside air either by positive ventilationor by exhaust of air causing reductionof pressure inside/- or by theirco"bination.

Lo%al E*au!t Ventilation#+entilation e)ected by exhaust of airthrough an exhaust appliance- such ashood with or without fan located asclosely as possible to the origin of conta"inants so as to capturee)ectively the conta"inants andconvey the" through ducts to a safepoint of discharge e.g. dust collector-scrubber- @are etc./.

Dr, ul Te&erature# Thete"perature of the air read on ather"o"eter- placed in such a way asto avoid errors due to radiation.

@et ul Te&erature# Thesteady te"perature %nally given by ather"o"eter having its bulb coveredwith gau7e or "uslin "oistened with

distilled water and placed in an airstrea" of not less than .5 ">s.

Hu&idit, A!olute# The weight of water vapour per unit volu"e- lb>ft, org>c",.Hu&idit, Relati$e# The ratio of the

actual partial pressure of the watervapour in a space to the saturationpressure of pure water at the sa"ete"perature.Hu&idi%ation# The process

whereby the absolute hu"idity of the

air in a building is "aintained at ahigher level than that of outside air orat a level higher than that which wouldprevail naturally.

Due Point# When the te"peratureof a saturated space is reduced- "ore"oisture will condense than evaporateuntil equilibriu" is again reached. Thete"perature at which saturation occursand condensation begins is the duepoint or saturation te"perature.

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Sra,-*ead S,!te $ syste" of ato"ising water so as to introduce the"oisture directly into a building.

:a=e U Air# 6utside air suppliedinto a building to replace the airre"oved.

Air C*an'e er Hour# =atio of the

outside air volu"e allowed into a roo"in one hour to the roo" volu"e.

6. Air Re+uire&ent #

efore studying the types of ventilation- it will be useful to *nowabout the required air co"position andair "ove"ent. 9t is given table 1D.2 #

Tale 10. # $ir Co"positionercentage +olu"e/Co&one

ntOutdoo

r airDr,

Indoorair 0DC RH

50

Eired air36 DC

RH 100

6xygen 2D.! 2D.4 14Carbondioxide

D.D, D.D4

Watervapour

D.DD 1.25 5

9nertgasesIitrogen-$rgonetc./

!.DD !:.DD !5

1DD.DD 1DD.DD 1DD

Thus ventilation is necessary for notallowing the air co"ponents to reachtheir expiry li"its.

$ person wor*ing hard- breaths

about D litres of air per "inute-consu"es about 2 litres of oxygen andexhales about 1.! litres of carbondioxide. $ sleeping person consu"esonly about 1>1D of this a"ount. $ir"ove"ent below D.D!5 ">s givesfeeling of stagnation and above D. ">sa perceptible draft. 9ts co"fortablerange is D.1 to D., ">s.


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of heat or conta"inant to prevent theirescape in surrounding.

Air %leanin' de$i%e! are used tore"ove conta"inants fro" the air orgas strea". They are available in awide range of varieties. Their selectioncriteria are #

1. article si7e and concentration of conta"inant.

2. Characteristics of the air or gasstrea".,. Characteristics of the conta"inant.. Begree of collection required- and5. 3ethod of disposal.

The equip"ent wor*s on followingprinciples #

1. Eravity forces.2. Centrifugal forces.,. lectrostatic forces.. 0crubbing- and5. 9"pactiation.

quip"ent available are of thetypes # 0ettling cha"bers- Eravitytraps- =otoclone- Cyclone separator-3ulticyclones- Wet cyclone-


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1. Wet bulb te"perature in a wor*roo"should not exceed ,D DCther"o"eter ht 1.5 "t/.

2. $ir "ove"ent should not be lessthan ,D ">"in.

,. Bry and wet bulb te"peratureshould be as under

Dr, ulTe& (0C)

@et ulTe& (0C)

,D to , 2,5 to , 2:.5D to 2:5 to 2!.5

. +entilating openings B- W ; +/ in awor*roo" should be "ore than 15Fof the @oor area and so located as to

a)ord a continued supply of fresh airat wor*ersL level.5. uantity of fresh air supply by

"echanical "eans should be sixti"es the wor*roo" volu"e ",/ perhour. 9t should be evenly distributedin the wor*roo".

4. 9n su""er when te"peratureexceeds ,5 DC and hu"idity "orethan 5DF per"issible in thewor*roo"- desert coolers or centralair washing plant can be suggested

by the 9nspector.!. $bove li"its are not applicable

where arti%cial hu"idi%cation 0ec.15 of the s/ for localexhaust ventilation for conta"inantscontrol are given in Table, of 90#,1D,.

The rate of air @ow in the duct or grilleshall be within 1DF of the a"ountrequired and variation of air @owthrough %lters and grilles shall notexceed M 2DF of the "ean value.

The dry and wet bulb te"peraturesshall be "aintained as per the schedulegiven by the h>"2 of

@oor area have been found satisfactory.Where the desired te"peratures andhu"idity cannot be obtained by "ereventilation- air conditioning "ay beresorted to as per 90#45 and 44D.

7 T2PES OF VENTILATION

7.1 Cla!!i%ation o" Ventilation S,!te&! #


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a/ =efrigerationb/ (eatingc/ (u"idity Control or

vaporative Cooling

The details of these varieties of

ventilation and calculation "ethodsoccupy "uch space. Their design is aspecialised 8ob for ventilatingengineers. (ere they are explained inbrief as follows.

7. Natural Ventilation #

Iatural ventilation is inducedbecause of two reasons 1/ outsidewind pressure i.e. wind action and 2/

te"perature di)erence of the air insideand outside the roo" i.e. chi"neye)ect. There is a positive pressure onwindward side and negative pressureon leeward side. y providing adequateopenings in these pressure areas-natural ventilation can be achieved.

The rate of ventilation by natural"eans through windows or otheropenings depends on direction andvelocity of wind outside- solar radiation-si7e and disposition of opening wind

action/- convection currents arisingfro" te"perature or vapour pressuredi)erence or both/ between inside andoutside the roo" and the di)erence of height between the outlet and inletopenings stac* e)ect/. They are of twotypes as under

(1) Dilution or Cro!! Ventilation #9nlet openings should be located on thewindward side at a low level and outletopenings should be located on theleeward side near to the top so thatinco"ing air strea" is passed over theoccupants. Ereatest @ow per unit areaopening is obtained by using inlet andoutlet openings of nearly equal areas.Hnder the "in- $ J cross sectional area of theventilator in "2- ( J height of the

ventilator above the inlets in "- t i and

tD are the inside and outsidete"peratures in DC and + J wind

velocity in *"ph.

9n roofed ventilation- naturalventilation is caused by chi"neystac*/ e)ect due to te"peraturedi)erence. This e)ect is counteractedby wind blows straight against roof openings. y suitable design of pitchedroof- sawtooth roof or "onitor roof thisinterference can be reduced.

Co9l t,e Roo" Ventilation #


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roofed ventilation. The perfor"ance of roof cowls depends on te"peraturedi)erence between inside and outsideair- velocity of inco"ing wind- crosssectional area of the ventilator and itsheight above air inlet.


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ventilation with the advantage of betterair distribution over the entire area of alarge building. y supplying propervolu"es of air at suitable velocities atthe required areas through duct and byextracting the air in the return duct andrecirculating this air after proper

cleaning and "ixing it with cool freshair- good results can be obtained. 9t ispreferable to provide slight excess of exhaust if there are ad8oining occupiedspaces and a slight excess of supply if there are no such spaces. Hnitexhausters can be used to "atch withunit ventilators exteriors and locatedalong the outside wall.

(4) :e%*ani%al Roo" Ventilation # 9tis used for aug"enting naturalventilation in buildings with large widthQ,D "/ or where the heat load is veryheavy. xhaust fans exercise very littlein@uence beyond a velocity contour atabout 15 ">"in which is a shortdistance fro" the fan. The volu"e of airrequired in re"oval of sensible heatgained in Ocal>hr/ can be calculatedfro" the for"ula

J

where is the volu"e of air in ",>hr-and allowable te"perature rise J 9nletopening te"p. 6utside te"p.- is givenby following approxi"ate %gures.

Roo" ele$ation in&t

Ri!e in 0C

4 , to .5 .5 to 4.512 4.5 to 11

These values are at roof exit andnot the @oor te"peratures. The"axi"u" allowable te"perature risefor an air strea" as it leaves the grillsand reaches the wor*ing level is 1.! to2.: DC 5 D


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3echanical ventilation is also e"ployedfor conta"inants control as follows #

(1) Dilution or For%ed Ventilation #9t is helpful in reducing conta"inantconcentration in wor* area to controlhealth and %re ha7ards. This is useful to

control less toxic vapours such as fro"organic solvents. 9t is not useful tocontrol fu"es- dusts and conta"inantsof high toxicity T&+ less than 1DD pp"/and high quantity or concentration. 9t isalso not useful where pollutants arereleased inter"ittently. The a"ount of air required for dilution can becalculated fro" the following for"ula #

$ir required for dilution in ",>*g of evaporation or generation of gas

J

Where < is a factor of safety forhealth ha7ard varying fro" , to 1D anddepending on the toxicity- evolutionrate of conta"inant and e)ectivenessof the ventilation.

The for"ula for control of %reha7ard is as follows#

$ir required for dilution in ",>*g of @a""able gas.

J

Where < is a factor of safety for %reha7ard varying fro" to 12 dependingupon the percentage of && &ower

xplosive &i"it/ and C is a constantwhich is 1 for te"peratures up to 121DC and D.! for te"peratures above 121DC.

Ior"ally this "ethod is adoptedwhere it is i"possible to %t an extractorto the wor* point. (ourly air changes ina wor* roo" are for dilution purpose. 9tshould be 4 ti"es the roo" volu"e perhour.

The air @ow volu"e to be provided

should ta*e into account 1/ the volu"eof the pollutants released 2/ the

concentration per"itted in thewor*place and ,/ a factor of safetywhich allows for the layout of the roo"-the air@ow patterns created by theventilation syste"- the toxicity of thepollutant and the steadiness of itsrelease.

() Lo%al E*au!t or Etra%tVentilation # 9t is applied at therelease points of conta"inants dust-gas- fu"es- particles etc./ to reducetheir concentration in the wor*roo"below T&+s. 0uch points shall beenclosed except where access isnecessary for the process- but in thatcase- the exhaust appliance shallcon%ne the conta"inants as "uch aspossible.

The volu"e of air required iscalculated fro" the area of openingsand the capture velocity su'cient toprevent outward escape"ent. The si7esof the ducts shall be calculated fro"the volu"e of air required and ductvelocities necessary to convey theconta"inants with "ini"u" staticresistance.

Capture velocities "ay vary fro"D.25 to 1D ">s proportionately

increasing with the conta"inantsvelocity as given in Table1D.,. The testreport for dust>fu"e extraction syste"shall be in for" Io. 24$ under theEu8arat


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avoided. Cleaning and trapping gatesshall be provided. Eenerally theconveying velocity "ay be fro" 1D to25 ">s depending upon the type of conta"inant and balancing of equal@ow rate of air.

Types of aircleaners- dust

separators or collectors are settlingcha"bers- cyclones- dry dyna"icprecipitators- scrubbers- wet collectors-electrostatic precipitators- fabric %ltersand air cleaners for gases and vapours.

The fan selection depends upon airvolu"e and static pressure required. $guide for selection of collectors is givenas Table1: in Chapter,2.

oints to be considered whilede!i'nin' a *ood are#

1. nclose the operation as "uch aspossible. (ood should be as near aspossible to the source of generation.Boubling the distance requireapproxi"ately four ti"es the airvolu"e.

2. (ood should be so located as to *eepthe @ow of conta"inants away fro"the wor*er.

,. (ood should be so placed as to ta*eadvantage of initial velocity and

direction of the throw of theconta"inant.


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9n !u!titution safe substituteshould be found for a toxic "aterial.

9n !e're'ation the ha7ardousprocess and persons are *ept away by"eans of suitable partition orincreasing their distance.

En%lo!ure prevents conta"inant of

surrounding by physical separation of toxic "aterial or process by enclosingthe".

@et &et*od uses water spray toprevent dust escape into at"osphere.9n

Du!t !ure!!ion "ethod 8et orspray is applied to cutting tool- chisel-grinder- saw etc. to wet the surface fordust suppression.

Du!t re$ention includes both-wet "ethod and dust suppression"ethod. Hsing paste instead of powder-dipping in water- oil or other suspensionare useful for gases- dusts and clothing.roper personal protective equip"entshould be utilised as the last controlagainst conta"inants.

7.4 Air Di!triution #

9n any type of ventilation- proper airdistribution is "ost i"portant. $ir

should be distributed evenly withoutdead air poc*ets or undue drafts of high inlet velocities. The si7e anddistribution of windows- inlet and outletopenings- ducts- fans- air inlet grillsshould be properly located consideringorientation- prevailing winds andbuilding and process layout. Ior"allyair "ove"ent below 4D ">"in withoutob8ectionable draughts should beprovided in the vicinity of wor*ers forbetter co"fort. (igh air "ove"ent "aybe required for heavy "anual wor*. $blast of air up to ,DD ">"in "ay bedirected at the wor*ers wor*ing in highte"perature and high hu"idity- forvelocity cooling.

7.5 Air Conditionin' #

y air conditioning $C/ nor"allypeople "ean Kair coolingL but it is notnecessarily so. 9n a very cold country-

roo" air heating to "aintain

co"fortable te"perature/ is also airconditioning. 9ts pri"e purpose is to*eep air in a condition %o&"ortale to"an.

$ir conditioning "eans conditioningthe air for "aintaining speci%cconditions of te"perature- hu"idity- air

circulation and dust level inside anenclosed space or roo". The conditionsto be "aintained are dictated by theneed for which the space is intendedfor.

When air conditioning is designedfor hu"an beings- it is called %o&"ort%onditionin' as it *eeps into accountthe regulated @ow of air- itste"perature- hu"idity and cleanliness"ost favourable- bearable andco"fortable to "en. ut when it isdesigned to preserve things at lowte"perature- it is called re"ri'eration.

Why co"fort air conditioning isrequired ? ecause of physiology of heat regulation in hu"an body only.Bue to "etabolis" the bodyte"perature is "aintained at ,!DC:.4D


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unifor" to create a feeling of co"fort.


27/33

overhead canopy hood- general roo"ventilation etc.

Sra, oot*! for spraying paint-ena"el- bleaching- gla7ing- weldingetc.- require deeper spray booth orbaSes of non@a""able "aterials.

Foundrie! need dust control in

sha*e out and cleaning roo"s wherewet "ethod "ay be suitable. 9n a"echanised foundry tight enclosinghood and side hood on the sha*e outgate are useful. 0and conveying andreconditioning equip"ent should beco"pletely enclosed and ventilationshould be provided at dust producingspots.

/rindin' u?n' and oli!*in'oeration! need local exhaustsyste"s. (oods on grinding and cuttingwheel for local exhaust with anad8ustable tongue to peel o) the dustcarried around the wheel in the airstrea" set up by the wheelLs rotation-are desirable. Iot "ore than 25F of thewheel should be exposed. +elocity inbranch ducts and "ain duct "ay be G5DD and ,5DD fp" respectively. 0winggrinder should be housed in a booth.ortable hand grinding can be done in abooth or on a table with downdraft

ventilation.@ood9or=in' "achinery need

exhaust ventilation. Cyclone arrester isused to collect scrap.

Ca!t-iron &a%*inin' needs hooddesign according to the "achine tool.0"all local hoods with face velocitiesDD to 2DDD fp" "ay be suitable.

0i"ilarly local hoods of specialdesign are needed for oil "eltingfurnaces- petrol engines etc.

8 CONTROL OF HEATEPOSURES

Control of heat stress is explainedin foregoing part 5.5.


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9f possible the hot process shouldbe substituted by localised or "oree'ciently controlled "ethod of heating.


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2. 0urrounding the wor*er with arelatively cool at"osphere by adirect supply of air introduced at thewor*ing level or over a s"all area of the plant.

,. Birecting a high velocity air strea"at the wor*er when the air is capable

of absorbing heat i.e. either its drybulb te"perature is reasonably lowerthan the body te"perature or itshu"idity is low enough to allowevaporation of sweat.

. Eive a cup of cool palatable drin*ingwater at 2D to ,D "inutes.

5. Eive training about heat stress andstrain and their control "easures.

4. ncourage consu"ption of saltyfoods if "edically not restricted.

!. er"it self li"itation of heatexposures and frequent restintervals.

8.7 Per!onal Prote%ti$eE+ui&ent

9n certain operations- such as glassdrawing- blowing or ena"elling- "etal"elting furnace etc.- the wor*ers "aybe required to wor* within reach of hotob8ects which "ay be at te"perature of

:DD DC 1!2 D


30/33

$ir cleaning equip"ent or collectorsuch as Du!t %olle%tor or De-du!tin'%*a&er to precipitate suspendeddust- %,%lone a dust extractorwherein dust is separated fro" thecyclonically rotating dusted air bycentrifugal force- a' lter (*ou!e) to

separate air depositing the %ne dustparticles on outside of the canvas- Oillter! for %ne cleaning of the air inwhich dust concentration are up to 1D2D "g>",- Paer lter! to clean theplenu" air fro" the %ne dust andEle%tri%al re%iitator! to attract andcollect airborne dust particles in electric%eld are also equally i"portant for"aintenance purpose.

9ndustrial ventilation is- thus- aco"plex installation which requiress*illed and specially trained personnelfor proper operation and "aintenance.$ "aintenance boo* or register shouldbe *ept with each ventilation unit.9nstructions for startup- shutdown-"aintenance- repair- operatingpara"eters- nature of trouble and itseli"ination and trial runs should berecorded in the register. While testing aventilation syste"- the fans should bechec*ed for its e'ciency- pressure and

speed. Hnguarded "oving parts shouldnot be touched.

9ndian 0tandards useful forelectrical safety are !,2 and for %resafety 144.

ersonal protective equip"ent suchas special clothing- goggles- safetyshoes- gloves- hard hats- aprons- earprotection- respiratory or lungprotection including various dust %ltersand gas "as*s- barrier crea"s anddetergents should be chec*ed before

use- well "aintained and *ept e)ective.$ll ventilating equip"ent should be

chec*ed periodically- bearings andvarious "oving parts should belubricated and all "etal parts and aircleaning devices including %lters shouldbe chec*ed regularly for dustdeposition- cho*ing- corrosion andprotected by anticorrosion paint.

"in. This @ow "ay fall downbecause of wear and tear- lac* of lubrication- corrosion- cho*ing of air%lters- ducting etc. Testing of air @owcan reveal this fact and suggest thenecessary replace"ent or"aintenance.

The volu"e of inlet air outside airby positive ventilation/ is given by

J *$+

where $ J $rea of inta*e opening of duct in "2 and + J $verage velocity of

air in ">"in- "easured by a calibratedKane"o"eterL- velocity "eter and pivottube. Coe'cient K*L varies fro" D.5 toD.4 when air openings face wind andD.25 to D.,5 when openings are atangle.

The volu"e of exhaust air can alsobe "easured by the sa"e for"ula and"anner.

+entilation due to convectione)ects arising fro" te"peraturedi)erence between inside and outside

is given by

( )0t-it"7AQ =

where and $ as stated earlier- h Jvertical distance between inlets andoutlets in ""- ti J te"perature of indoor air at the outlet in DC and to Jte"perature of outdoor air in DC.

30


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+ariation of air @ow through %ltersor grills/ should not be "ore than ±2DF of the "ean value.

Turbulent air @ow at the wor*ing7one can be "easured by Oatather"o"eter- heated ther"o

ane"o"eter or properly calibratedther"ocouple ane"o"eter.

10. @OR;ED EA:PLES

Eer%i!e

1. Elain State :ention ordi!%u!! #-

1. The purpose or ob8ective of ventilation and heat control.

2. 0tatutory provisions regardingventilation.

,. ara"eters of ther"al

environ"ent and "ethods of their "easure"ent.

. Bi)erent factors a)ecting heatstress and "easures to controlthe".

5. (eat balance equation andfactors a)ecting it.

4. )ects of hot and hu"idenviron"ent on safety ande'ciency.

!. The concept of WET and its

usefulness.:. )ects of cold stress- factorsincreasing it and factorsdecreasing it.

. (ealth disorders in hotenviron"ent.

1D. 0afety proble"s due toincreased te"perature.

11. ngineering controls to reducee)ects of para"eters of (eatbalance equation.

12. 3ethods of personal

"anage"ent ad"inistrativee)orts/ to control heat stress.

1,.


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11. redicted


33/33

Re"eren%e and Re%o&&ended Readin' #

1. Code of ractice for 9ndustrial+entilation- 90#,1D,.

2. Training 3aterial- T3 ; 5- 9&6-ang*o*.

,. ncyclopaedia of 6ccupational (ealthand 0afety- 9&6- Eeneva.

. 6ccupational (ealth and 0afety in3anufacturing 9ndustries- 3 O oltev-3ir ublishers- 3oscow.

5. sychology for usiness and 9ndustry-(erbert 3oore- 3cEraw(ill.

4. ollution Control in rocess 9ndustries- Tata 3cEraw(ill- Belhi11DDD2.

!. 9ndustrial +entilation 3anual of =eco""ended ractice- $"ericanConference of Eovern"ental9ndustrial (ygienists- $EE9(- 1D1roadway- Cincinnati- 6hio 52D2.

:. lant and rocess +entilation- (e"eonW.C.&.- 9ndustrial ress- 2DD- 3adison

$ve.- Iew Por*.. Besign of 9ndustrial xhaust 0yste"-

$lden Xohn &.- 9ndustrial ress- Iew Por*.

1D. (eating- +entilating and $irConditioning

10. chapter - 10 ventilation and heat control

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