commercial kitchen hoods

[cselectric]

Of late, we've found ourselves in a bit of a debae at work, I was hoping to enlist some of the vast brainpower here to clear things up.

What we have is, in my mind anway, a non-typical hood installation. I'm used to commercial hoods having both an exhaust and a make up air unit servicing them. When the rip cord is pulled on the dry chem fire system, it initiates a shunt trip(s) that dump the cb's for the underhood power and the make up air unit.

We have recently wired several fast food stores (Arby's) that use a small hood over the fryers, serviced by an exhaust fan but not a make up air unit. Per engineering spec. our shunt trips must shut down the underhood electical (of course) and the RTU's for the entire building. Obviously, we will follow the engineering spec. unless it is a code violation in some way. The question is; is this purely an engineers wishes or is it a code requirement? Being none of us have worked on a hood set up this small, none of us know for sure. So far we've had one fire marshall tell us it is absolutely required (though it's not required to shut down the RTU's if a make up air unit is present?) We've also had another fire marshall (different jurisdiction) that was a bit confused by the install, but not opposed to it per se. Finally, we had a third fire marshall that approved the installation, but indicated that he was a bit worried about it, in that shutting down all of the HVAC systems and leaving the hood exhaust running would suck a large amount of the air out of the room, thus creating a potetntial for a backdraft fire if a door were opened.

So, is this a requirement? Is this a code violation? What code(s) specific addresses this type of install?

 

[joe tedesco]

Re: commercial kitchen hoods

See NFPA 96, Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations
2001 Edition

Committee Scope: This Committee shall have primary responsibility for documents on fire safety in the design, installation, and use of exhaust systems (including hoods, grease removal devices, exhaust ducts, dampers, air-moving devices; and auxiliary equipment) for the removal of products of combustion, heat, grease, and vapors from cooking equipment, including the application of associated fire extinguishing systems.

1.1 Scope.
1.1.1* This standard shall provide the minimum fire safety requirements (preventative and operative) related to the design, installation, operation, inspection, and maintenance of all public and private cooking operations.
1.1.2 This standard shall apply to residential cooking equipment used for commercial cooking operations.
1.1.3 This standard shall not apply to cooking equipment located in a single dwelling unit.
1.1.4* This standard shall not apply to facilities where all of the following are met:
(1) Only residential equipment is being used.
(2) Fire extinguishers located in all kitchen areas in accordance with NFPA 10, Standard for Portable Fire Extinguishers.
(3) Facility is not an assembly occupancy.
(4) Subject to the approval of the authority having jurisdiction.

Joe Tedesco
Disclaimers: www.joetedesco.com

 

[websparky]

Re: commercial kitchen hoods

Dry Chemical Systems.

2002 NFPA 17
6.2.2 Leakage and Ventilation. The leakage of dry chemical from the protected space shall be minimized because the effectiveness of the flooding system depends on obtaining an extinguishing concentration of dry chemical.

Usually, everything in the protected area that moves air, needs to be shut down.

However, only licensed designers and the AHJ can deside what is involved.

 

[cselectric]

Re: commercial kitchen hoods

Joe, Sparky, thanks for the input. Those were the codes I was looking for. I somehow knew there was NFPA documentation directly related to this environment, but I was unsure as to which codes covered it and where I might obtain them. I do appreciate the guidance.

Sparky, I have seen the NFPA 17 documentaion in the past (though couldn't remember which book it came from.) The question that arises is "what exactly defines the hood area?" As you stated, the AHJ and design engineers will have final say on that. Unfortunately, there seems to be a great deal of variance in the opinions of those experts. This apperas to be one of those issues where the exact design and requirement will be subject to change from jurisdiction to jurisdiction and engineer to engineer. Leaving the correct answer to our debate as "RFI the engineering firm and consult the AHJ before install."

 

[websparky]

Re: commercial kitchen hoods

cselectric,

Typically here in my area, we consult with the AHJ prior to the actual install and get his blessing. We do not want the liability for deciding if something will perform properly!
In some cases, the AHJ is not aware of any approved drawings and may demand such or demand the pre-engineered system's manufacturers installation requirements. He doesn't want to make the wrong decission either!

From my limited knowledge of the dry system, the area directly beneath and above the nozzles coverage pattern is what is most critical.

 

[cselectric]

Re: commercial kitchen hoods

Originally posted by websparky:
cselectric,

From my limited knowledge of the dry system, the area directly beneath and above the nozzles coverage pattern is what is most critical.

That's always been my understanding, based on how I've seen commercial hoods spec'd. and inspected in the past. This particular spec. is the first time I've seen a requirement for the environmental air system to be shut down, but it's also the first time I've seen a hood without a make up air unit. Under those circumstances I could just run with the engineering spec. and call it good. But my curiosity and desire to learn kick into high gear and the questions begin to formulate in my mind. My boss tends to act in a similar way, so you can imagine the conversations and data searches that ensue. Which is a good thing, especially since I haven't worked a restaurant in 4 or 5 years and am, frankly, a bit rusty on the subject.

 

[hbendillo]

Re: commercial kitchen hoods

Do these small systems have a fire suppression system? Do we always shut down the exhaust fan in a conventional system or just the make-up air fan? If no suppression system is involved, why do we need to shunt-trip the power?

 

[jerryb]

Re: commercial kitchen hoods

I don't want to try and quote chapter and verse for all the regulations but basically if it is a commercial kitchen and they need a class 1, fire rated hood then there must be a suppression system. If the suppression system is activated then all cooking equipment is to be shut-down that is located under that hood (gas and/or electric). Also, if the suppression system is activated the make-up air is to be shut-down so as to stop feeding fresh air to the fire. But the exhaust fan is supposed to continue to run. The reason is two fold, first exhaust the fumes from the kitchen and hood area. Second, the exhaust fan will help pull some of the dry chemical up into the hood and ductwork to help extinguish any fire that might be in the duct.

What I have described is the standard control installation for hood manufacturer's such as Captive Aire and Halton Hoods.

Hope this helps

 

[delfa]

Re: commercial kitchen hoods

Jerry I've wired a few large hood systems in the last couple of years and your description is exactly the way we wired them. Ansol system pulled, hits micro switch for shunt trip, all power and gas under hood turns off, make up air off, hoods stay on.....

 

[hurk27]

Re: commercial kitchen hoods

That is strange as I just did a hood and the manufacture had us wire the exhaust fan so it will shut off when the ansel system is discharging and when it is empty the exhaust fans restart to remove the smoke. he told us that the reasone is the exhaust fans in some of the newer hoods will suck the dry chem right out it and then the flames too. so they now have two sets of contacts in the control box on top of the ansel tanks that have to control relays to shut down everything under the hood and the other set controls the exhaust fan. of course this might be just this manufacture but it makes sense.

 

[hurk27]

Re: commercial kitchen hoods

After re-reading all the post I think this should be clarified as it seems we all have different opinions as weather or not the exhaust should be shut down Web sparky Posted. NFPA 17 6.2.2 which seems to say that it should be shut down. and I have witness a restaurant that burnt down because of this very reason as the flames went up the exhaust pipe and caught the sub roof on fire, the dry-chem didn't even get to the steak broiler that was on fire as there also was no evidence of any dry-chem on it. and people outside complained of the dry-chem coming down on them while the fire was going on. this meant that it was being sucked up and out of the building as it was all over what was left of the roof. This is what happened to rosewood restaurant in Portage, In. This was about 12 years ago. Glen might remember it as he's not to far away.