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NFPA-96 2011 Edition: Exhaust Duct Enclosure

Question asked by pglos on Jan 31, 2019

NFPA-96 2011 Edition: Exhaust Duct Enclosure Question

7.7.1 of NFPA-96 2011 discusses the requirement for grease ducts to be located in a continuous rated enclosure extending from the first penetrated fire separation through any concealed spaces, to or through the roof to maintain the integrity of the penetrated fire separation required by the applicable building code  (which is the Ontario Building Code in the province of Ontario, Canada)

 

7.7.5.1 of NFPA-96 2011 states;

Each duct system shall constitute an individual system serving only exhaust hoods in one fire zone on one floor.

7.7.5.2 of NFPA-96 2011 states;

Multiple ducts shall not be permitted in a single enclosure unless acceptable to the authority having jurisdiction.

 

I work for a municipal Building Department in Ontario, Canada reviewing mechanical systems for Building Permit purposes. I am aware that NFPA-96 compliant duct systems are required to be located in a rated enclosure per 7.7.1 of NFPA-96 2011 Edition. Sentence 7.7.5.1 limits a kitchen exhaust duct system to serve exhaust hoods located in one fire zone on one floor. Sentence 7.7.5.2 prohibits multiple ducts being combined within a single duct enclosure.

Question:

Is the intent of 7.7.5.2 to prevent multiple grease ducts serving multiple fire zones or multiple floors from being combined in a single duct enclosure?

OR

Is the intent of 7.7.5.2 to prevent a grease duct and any other duct (general exhaust, HVAC supply/return duct) from being combined in a single duct enclosure?

 

We have historically required a grease duct to be located in an enclosure dedicated to housing only the grease duct, however, realize that this interpretation may not be the intent of the referenced sentence. It would be greatly appreciated if you could share the intent of 7.7.5.2 as outlined above.

 

Regards,

 

P.M.G., P.Eng. Mechanical Plans Examiner

 

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