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Commercial Kitchen hood #197065 11/07/10 12:59 AM
Joined: Aug 2006
Posts: 356
Niko Offline OP
I was asked to wire a commercial kitchen hood that is tied to the extinguisher. But before hooking it up i need to learn the operation, the code behind, what needs to turn ON/OFF when the lever is pulled.
Can anyone please tell me the basic operation or refer me to a site that i can learn from?


Be kind to your neighbor, he knows where you live

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Re: Commercial Kitchen hood [Re: Niko] #197068 11/07/10 02:36 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Online Content
Basically, when the fire supression system is activated, the MUA (make-up-air) (supply air) (intake air) MUST be put in an "OFF" state, and the exhaust fan MUST be "ON".

Additionally, any electrical cooking equipment under the hood must be de-energized upon activation of the fire supression system. All the gas appliances are shut down via a gas valve.

Control is thru the dry contacts on the fire supression controller and the contactors for the MUA and exhaust, ad shunt trip for electrical cooking appliances under the hood.

Code requirements are within NFPA. It's best to check with your local Fire AHJ as he/she can provide code in effect in your area.

Re: Commercial Kitchen hood [Re: HotLine1] #197073 11/07/10 04:50 PM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
I disagree completely with the requirements as you explained them.

NFPA 96 is as close as you're going to get as a 'standard,' ant it does not say what you claim.

NFPA 96 does NOT require the exhause fan to operate, be shut down, or any other action for the exhaust fan.

NFPA 96 only required fresh air supplied directly to the hood to be shut down - there is no requirement for the general fresh air supply for the room to be shut down.

It's simply amazing what NFPA 96 actually says, as opposed to what various installers, fire marshals, etc. seem to think it says.

There's simply no excuse for not reading it. The proper title is: NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations

Otherwise, it is required that all sources of ignition under the footprint of the hood be extinguished. This, of course, means that the lights, receptacles, etc., be killed.

It ALSO means that the gas be shut off. If the equipment uses standing pilot lights, you will also have to instal a solenoid-operated interlock to prevent the gas valve from re-opening until you are actually ready to light the pilots; simply resetting the contactor won't be enough.

Another thread on this forum has drawn attention to the few inspectors out there who object to installing your contactor in a simple 'pull can,' as opposed to using a 'control panel' with a hinged door.

There is also an alarm requirement. If there is no central-station monitored system, you will have to instal a bell that rings when the system is activated.

Keep in mind that the inspection will be by the fire marshal, rather than the usual building inspector.

Re: Commercial Kitchen hood [Re: renosteinke] #197076 11/07/10 09:55 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Online Content

You state: "I disagree completely with the requirements as you explained them."

And your comments of disagrement seem to apply only to the exhaust fan operation in a fire supression activation. The other items, you seem to agree with what I said, with additional embelishments. Note that I used three (3) terms for what I usually only call Make Up Air, none of which are intended to mean the 'general fresh air supply to the room'.

As I do not have any NFPA Fire Codes at my desk now, I will check the statement regarding the exhaust fan operation Monday at the office. In the event that I have provided mis-information, I will post a correction.

Last edited by HotLine1; 11/07/10 10:59 PM. Reason: correct word 'is' to 'in'.

Re: Commercial Kitchen hood [Re: HotLine1] #197078 11/07/10 10:42 PM
Joined: Aug 2007
Posts: 853
leland Offline
NFPA 17A Wet Chemical systems.

Yes make up air must shut down. All electricity and gas/fuel shall be shut off.

As far as the exhaust shutting down... you will be hard pressed to get a solid answer.

I may have mis-spoke.

I'm looking and nothing yet.

Last edited by leland; 11/07/10 10:51 PM.
Re: Commercial Kitchen hood [Re: leland] #197087 11/08/10 09:35 AM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
The issue of the 'make up' air hit a button with me, because the NFPA codes are quire explicit, yet the 'common understanding' is quite different. This continues, even though NFPA 96 is pretty clear.

Clear, that is, only if you have seen hoods that had their own make-up air supplied to them. Since most hoods do not have this dedicated air supply, but draw from the kitchen in general, it is common for the kitchen air to be shut down. As I read NFPA 96, though, it's not actually required to do so.

This is more than just hair-splitting. When there is an "open" kitchen, as is often seen with the "mongolian grills' set in the eating area of restaurants (rather than back in the kitchen), there is no single unit that can be described as serving the hood; shut down one and the others will readily supply the air. While that air might 'feed the fire,' it will also help ensure that the occupants can escape.

Another detail sometimes asserted is that the exhaust fan must operate when the unit trips. Again, NFPA 96 goes to the extreme of explaining, in the text of the code itself, that there is no need for the fan to operate if all the cooking equipment has been shut off.

Re: Commercial Kitchen hood [Re: renosteinke] #197094 11/08/10 03:04 PM
Joined: Aug 2006
Posts: 356
Niko Offline OP
Thank you guys for the explanation.

So, if i understand this correctly, once the pull station is activated, the alarm (fire bell) goes ON, any source of ignition (power, gas) turns OFF, the make up air turns OFF and the exhaust may stay ON.

I will call the AHJ to see what they need.

Be kind to your neighbor, he knows where you live

Re: Commercial Kitchen hood [Re: Niko] #197096 11/08/10 03:30 PM
Joined: May 2005
Posts: 984
ghost307 Offline
I was always told that you need to kill any sources of ignition, any fuel sources, and get the smoke out of the space as much as possible while the Fire Department is on its way to you.

But you're absolutely on the right path...check with the AHJ to find out exactly what they want to see.
Now much point in doing it twice if you don't need to.

Re: Commercial Kitchen hood [Re: ghost307] #197110 11/09/10 09:30 AM
Joined: Apr 2002
Posts: 7,233
HotLine1 Online Content
From NFPA 17A:
2-4.3 Shutoff Devices.

2-4.3.1 Exception No. 2

Exaust fans and dampers are not required to be shut down upon system activation as the systems have been tested under both zero- and high-velocity flow conditions.

Although this does not say the exhaust must be on, it has been interperted as the exhaust must be 'on' during a supression activation.

based on this, I have to correct my initial reply above to restate from that the exhaust fan MUST be "ON", and restate that it CAN be "ON"

That all said, it has been common accepted practice that the exhaust is "ON" during activation of supression. Some opinions are to remove smoke/fumes, and expel same to the exterior.

Last edited by HotLine1; 11/09/10 10:07 PM. Reason: corrected error in sentence

Re: Commercial Kitchen hood [Re: HotLine1] #197113 11/09/10 03:58 PM
Joined: Jun 2004
Posts: 1,273
Tesla Offline
I once buried a man-week on an ANSUL system.

It was incorrectly engineered for Safeway.

First of a kind, and the boys made a number of errors.

Anyhow, the lesson is: try and get a control panel designed for ANSUL - -factory built.

I forget the name, but at least one outfit is making them.

NO WAY can you build your own for less, adjusted for your personal learning curve.


And now, their mistakes:

24V control circuit unable to supply enough power to contactors -- especially notable for MUA blower at the roof.

Hence, an auxiliary XFMR and relay were tacked on.

Improper fusing -- original design placed fuses on the return path of one phase hot-to-neutral circuits. Obviously, this is a hazard since in overload there is a 50:50 chance that the return side fuse will blow first. Non-electricians will then have an outstanding opportunity to electrocute themselves doping out why things don't work. ( On a ladder, back against the grid, hanging on to bare metal studs while poking around in the dark: sweet)


To complete the picture, this control can had a complicated push-button (with interlocks) control for chef use.

But that's not all: I had a trooper who balanced his meth with Mary Jane. He became upset and decided to get even with the Man. So he took enough care and effort to cross wire a fist full of circuits feeding the hood blowers. Come power-up they'd be toast.

Unfortunately, anyone that obvious is too obvious. So I sent him on far away business -- pulling in home runs -- and personally corrected his 'craft.' Come power-up he stood aghast as EVERYTHING worked perfectly the first time. ( Even the General Foreman was stunned, he told me he'd never seen THAT happen before.)

Naturally, I congratulated bozo on his outstanding work!

Come break-time he fired up Mary like he was Chong: right in front of the GC Superintendent! The smoke was so staggering you couldn't see in!

Say, goodbye!

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