Understanding NFPA 96 Kitchen Exhaust

[IBechir]

Greetings

NFPA 96 states that kitchen exhaust ducts shall not pass through fire rated walls. Also NFPA 90A advises against using the same shaft enclosure for kitchen exhaust and other HVAC ducts. I want to understand the reasoning behind this.

My argument is against engineers that claim a kitchen exhaust duct is safe to pass through different fire zones and share shaft enclosure with other ducts because the duct has an intumescent coat applied. They argue that the NFPA requirements above are safety redundancies and that site coordination comes first especially if the coordination is tight/difficult.

I think that arguing against the code is not correct but these engineers are my seniors and I need to prove to them how dangerous it is.

Also will the above duct be safe if fire barrier duct wrap (such as

http://www.3m.com/us/bcsd/fire/stop/615ductwrap/index.html?WT.mc_id=

http://www.3m.com/ductwrap

) is used.

Much obliged for any information.

 

[stookeyfpe]

The reason that kitchen exhaust ducts are prohibited from passing through fire walls is:

1) You cannot provide a damper in a kitchen exhaust system due to the operating temperatures. Therefore, if the duct is compromised for whatever reason, a passage for fire extension from one side of the wall to the other is created.

2) I'm not sure what building code is in effect on your project. If the project is in the US, it is most likely subject to compliance with the International Building Code. A major concern for any through-penetration is that the penetration may pull down the fire wall in the event the structure collapses. If this project is subject compliance with the International Mechanical Code, it prohibits kitchen exhaust duct penetration of fire wall

3) From a practical standpoint, I've seen horizontal ducts on kitchen hood system and while they are allowed, they are a PITA (pain in the a$$) from a fire safety perspective because they are more difficult to clean. NFPA 96 has extensive ITM requirements, including established cleaning and inspection frequencies. Over the service life of the duct, if it begins to sag, ponding of proteins and oils will occur in the low point(s), and these are commonly missed by cleaning technicians.

Finally, site coordination is a pretty crappy basis for deciding that compliance with a nationally recognized standard for fire protection is not important. I sincerely doubt the jurisdiction would agree with this interpretation but I don't know the knowledge base of the enforcing jurisdiction.

 

[cdafd]

7.7.1 Duct Enclosures.

7.7.1.1 In all buildings where vertical fire barriers are penetrated, the ducts shall be enclosed in a continuous enclosure extending from the first penetrated fire barrier and any subsequent fire barriers or concealed spaces to or through the exterior, to maintain the fire resistance rating of the highest fire barrier penetrated.



7.7.1.2 In all buildings more than one story in height and in one-story buildings where the roof-ceiling assembly is required to have a fire resistance rating, the ducts shall be enclosed in a continuous enclosure extending from the lowest fire-rated ceiling or floor above the hood, through any concealed spaces, to or through the roof, to maintain the integrity of the fire separations required by the applicable building code provisions.



7.7.1.3 The enclosure shall be sealed around the duct at the point of penetration of the first fire-rated barrier after the hood, to maintain the fire resistance rating of the enclosure.



7.7.1.4 The enclosure shall be vented to the exterior of the building through weather-protected openings.



7.7.1.5 The continuous enclosure provisions shall not be required where a field-applied grease duct enclosure or a factory-built grease duct enclosure (see Section 4.3) is protected with a listed duct-through-penetration protection system equivalent to the fire resistance rating of the assembly being penetrated and where the materials are installed in accordance with the conditions of the listing and the manufacturer's instructions and are acceptable to the authority having jurisdiction.




7.7.2 Enclosure Fire Resistance Rating and Enclosure Clearance.

7.7.2.1 Fire Resistance Rating.

7.7.2.1.1 Buildings less than four stories in height shall have an enclosure with a fire resistance rating of not less than 1 hour.



7.7.2.1.2 Buildings four stories or more in height shall have an enclosure with a fire resistance rating of not less than 2 hours.





OR:::



7.1 General.

7.1.1 Ducts shall not pass through fire walls.



7.1.2* All ducts shall lead directly to the exterior of the building, so as not to unduly increase any fire hazard.



7.1.3 Duct systems shall not be interconnected with any other building ventilation or exhaust system.

 

[fireguy519345]

Stookey the FPE as usual gave very good information. The only thing I could add is concerning horizontal ducts. Not only are they difficult to clean, but normally the access panels for horizontal duct are not accessable themselves. If they are accessable, the way the panels are insulated, the insulation comes off, and gets thrown away. One brand of panel has a problem with the glue that holds the gasket in place. The glue deteriorates and allows the gasket to leak. We install

http://www.flamegard.com/products/su...ry/?category=4

Easy to install, the gasket withstands the temps and the grease.

If you see this

http://www.ductmate.com/product.aspx?id=13

access door with the red knobs, it is not listed for use in a grease duct. the gasket is foam rubber. These are often installed by HVAC contractors who do not know grease ducts. My solution, remove the panel, get the hose welded and install a new panel that is listed for the grease ducts.

Back to the access issue. During the inspection process, ask a couple of hood cleaners to come in and ask them if the panels are accessable. Remember, after the hoods & ducts are installed, someone will put cabinets, and other appliances in the kitchen that will make the access panels not accessable. J