exhaust hood presentation1 (2)

7/29/2019 Exhaust Hood Presentation1 (2)

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NFPA 96 and Building Code Requirements

for Commercial Kitchen Hood Systems

Presentation for the Sevier County Fire Code and

Building Code Officials

Presented by Roger Griffith, PE

Griffith Engineering, Jefferson City, TN

April 21, 2004


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Course Outline

Problem Areas

General Requirements

Hoods Exhaust Ducts

Fans

Fire Suppression System

Code Changes NFPA 96

International Mechanical Code (IMC)


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GENERAL REQUIREMENTS

Where are commercial hoods required?

NFPA 96: Cooking equipment used in processes

producing smoke and grease-laden vapors shallbe equipped with

NFPA 96 A-1-1 intended to includeresidential cooking equipment where used forpurposes other than residential family use

SMC gives exceptions for domestic equipmentinstalled in dwelling units and ovens do not heatfood above 2120F.


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Clearances

18 inches to combustible material

3 inches to limited-combustible material

0 inches to noncombustible material


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Exceptions

When the hood is listed for lesser clearances

If the combustible materialis protected asfollows:

28 gage sheet metal spaced out 1 inch onnoncombustible spacers 9 inch clearance tocombustible material

22 gage sheet metal on 1 inch mineral wool bats orceramic fiber blanket reinforced with wire mesh or

equivalent spaced out 1 inch on noncombustible spacers 3 inch clearance to combustible material

Reduced clearance to limited-combustible materials tozero clearance where protected by noncombustiblematerials or materials listed for the purpose of reducingclearance, and acceptable to the AHJ.


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9 inch clearance reduction


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3 inch clearance reduction


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Clearances


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Clearances


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Duct Clearances

Protection methods for ducts to reduceclearances shall be applied to the

combustible or limited-combustibleconstruction, not to the duct itself.

Exception: Field applied grease duct

enclosures and factory-built grease ductenclosures


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Field Applied Protection


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Duct Enclosures

Field applied grease duct enclosure: Alisted system evaluated for reduced

clearances and as an alternative to aduct with its fire-rated enclosure.

Factory-built grease duct enclosure: Alisted factorybuilt grease ductenclosure system evaluated forreduced clearances to combustiblesand as an alternative to a duct with its

fire-rated enclosure.


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EXHAUST HOODS

Type 1: Hoods designed for greaseexhaust applications

Type 2: Hoods designed for heatand steam removal and othernongrease applications. (NFPA 96does not cover)

NFPA 96: 2-1, 1998 Edition


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Exhaust Hoods

Hoods shall be constructed of 18 gagesteel or 20 gage stainless.

All seams, joints, and penetrations ofthe hood enclosure that direct andcapture grease-laden vapors and

exhaust gases shall have a liquidtightcontinuous weld external weld.


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Hood Integrity


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Exhaust Hood

Hoods must be sized and configured toprovide for the capture and removal of

grease-laden vapors. Size:

Configuration:

Backshelf/Proximity Hoods

Short-Circuit Hoods Face Discharge Makeup Hoods

Exhaust Only Hoods w/Supply Plenums



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Short Circuit Hoods

Hood performance is principallydependent upon net exhaust.

Net exhaust = Total exhaustinternal makeup

Large airflows are required highfirst cost & operating cost.


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Backshelf Hood


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Face Discharge Makeup

Hood Originally designed

for non-air-

conditionedkitchens

Makeup airbecomes load to

kitchen HVAC


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Exhaust Only Hood Cross

Section


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Exhaust OnlyHood w/Supply

Plenum


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Hood w/Supply Plenums


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Fire Dampers at Hoods

Fire dampers are installed in supply airconnections where they penetrate the

hood. Fire dampers are not installed in

exhaust ducts.

Fire dampers are not required insupply plenums that are isolated fromthe continuously welded shell.


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Filters and Baffles

They are required!

They must be 18 inches from cooking

surface. (Hoods above char-broilers must be4 ft above the cooking surface).

Filters must be installed at an angle of notless than 45 degrees

Filters must be easily accessible andremovable for cleaning.

NFPA 96: Ch.3, 1998 Edition


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EXHAUST DUCTS

Ducts can not pass through fire wallsor fire partitions.

Ducts cannot have dips or traps.

Clearances must be maintained.

Ducts must be 16 gage steel or 18

gage stainless.

Seams and joints shall have liquidtight external welds.


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Openings in Exhaust Ducts

Location At changes of direction For damper cleaning and inspection At both sides of inline fans

Construction On horizontal ducts20x20; if size is not possible, provide

openings large enough for cleaning every 12 feet. Access openings shall be of the same material and thickness

as the duct. Access panels shall have a gasket or sealant that is rated for

15000

F and shall be grease tight. Enclosure openings are required to reach access panels.They shall be protected by approved self-closing firedoors.



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Exhaust Ducts Exterior

Fasteners cannot penetrate duct walls.

Ducts must be painted or be

constructed of stainless steel.


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Exhaust Ducts Interior

Enclosures must be provided forbuildings more than one story, and

when penetrating a rated floor /ceilingassembly.

Enclosure shall be sealed around the

duct at the bottom.Exception: Field applied or factory

applied grease duct enclosures.NFPA 96: 4-7, 1998 Edition


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Clearances at Enclosures

18 to combustible construction 6 to noncombustible or limited-combustible

construction Clearances may be reduced with field

applied or factory applied grease ductenclosures.

Multiple ducts are not permitted in a single

enclosure

(SMC only requires 6 clearance)


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Rooftop Terminations

Maintain 10 feet clearance to adjacentbuildings, property lines, and air

intakes, or locate exhaust 3 feet aboveair intakes.

Ductwork must extend 18 above

roof.


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Fans

Fans must be listed for commercialcooking equipment.

Rooftop Fans Rooftop fans must be hinged.

Exhaust outlet must be 40 inches above

roof. Termination must have a grease trap.

Safe access must be provided to the fan

for inspection and cleaning


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Fans

Wall Termination Fans

Wall must be noncombustible

Maintain a minimum of 10 feet clearance fromoutlet to adjacent buildings, property lines,grade level, combustible construction, electricalequipment, air intakes or operable windows.

Air intakes or operable windows above exhaustshall be 10 feet plus 0.25 feet for each 1 degreefrom horizontal.


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Airflow

Air flow has traditionally been 1500 ft/minminimum. This is changing with the newer

codes. Air volumes should be of sufficient level to

capture and remove grease-laden cookingvapors.

Makeup air shall prevent negative pressuresfrom exceeding 0.02 wc in the cookingarea.


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Fire Suppression Systems

Automatic fireextinguishing

systems must be inaccordance with

NFPA 12 - CO2 NFPA 13 Wet

NFPA 17 DryChemical

NFPA 17A WetChemical


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Ansul System


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Pyrochem System


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Exhaust fans must continue to operate after theextinguishing system has been activated. Fans donot have to be started upon activation of the

extinguishing system. Makeup air supplied internally to the hood must be

shut off when fire suppression system activates.

All sources of fuel and electric power that produceheat to all equipment requiring protection by that

system shall automatically shut off upon activationof any extinguishing system.


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A means of manual activation must be provided inthe path of egress. (SMC requires it to be from 10-20 feet of hood.)

An audible alarm or visible indicator shall beprovided.

If fire alarm system is installed in building, it shallbe activated.

If electric power is required to operate the firesuppression system, it shall have a backup powersupply or all sources of fuel shall automatically shutoff when the system is inoperable.

Portable fire extinguishers


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Fire Suppression System

Inspection and Servicing Systems are required to be inspected every 6

months by properly trained and qualified

persons.All devices, actuators, detectors, andcomponents shall be checked for properoperation.

Fusible links and automatic sprinkler heads shall

be replaced at least annually, or morefrequently. If required, certificates of inspection and

maintenance shall be forwarded to the AHJ.


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Cleaning and Inspection

The entire system shall be inspected byproperly trained and certified personnel. Quarterly high volume operations (24 hour,

charbroiling) Semi-annually moderate volume

Annually low-volume (churches)

During inspection if the system is found to

be contaminated with grease, the entiresystem shall be cleaned by properly trainedand certified personnel.


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Cleaning and Inspection

Hoods, ducts, fans, etc. shall becleaned as needed to prevent them

from becoming heavily contaminatedwith grease.


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Code Updates

NFPA 96

International Mechanical Code


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Revisions to NFPA 96

Minimum Air Velocity through a greaseduct

1,500 ft/min (1998 edition) 1,200 ft/min (2001 edition)

500 ft/min (Errata 96-01-01 to 2001

edition in January 2002


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NFPA 96 2001

Protection shall be provided on thewall down to the floor or to

noncombustible material. Horizontal duct support systems shall

be designed for weight of duct plus800 lbs. at any point.

Penetrations to ducts and hoods shallbe listed.


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NFPA 96 2001

A minimum of 5 feet horizontalclearance from fan to combustible

material.


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NFPA 2004 under review

Chapter 15, Down Draft ApplianceVentilation Systems

A new section requiring a 20 x 20 openingfor personal entry for duct cleaning

A requirement for factory-built ductenclosures and duct-wrapped grease duct

systems to be listed in accordance with UL2221, Tests of Fire Resistive Duct Enclosure

Assemblies.


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International MechanicalCode

2000 Code

Performance Test

Net Exhaust 2003 Code

Capture and Containment Test

Net Exhaust


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Capture and ContainmentTest

Adjust and verify all exhaust and makeupairflows.

Operate equipment at cooking conditions

Verify capture and containment with smokepuffers

Verify pressurization, and adjust if

necessary Building positive to outdoors, kitchen negative todining


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Capture and ContainmentTest

exhaust hood presentation1 (2)

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