This may be more of an NFPA question but here goes. A rehab facility has an Ansul fire supression system in the kitchen exhaust hood. When the system activates, normal electrical power to the kitchen is automatically cut off. This includes power to the exhaust hood. The rep from the fire supression company says the exhaust hood should be wired to the emergency backup panel so that it will continue to exhaust smoke during a fire.
18.104.22.168 A hood exhaust fan(s) shall continue to operate after the extinguishing system has been activated unless fan shutdown is required by a listed component of the ventilation system or by the design of the extinguishing system.
A careful reading of NFPA 96 is quite clear on two commonly misrepresented points.
First, "make up air" is specifically described as air supplied specifically to the hood, from within the hood assembly. NFPA 96 does NOT call for shutting down the general air supply to the kitchen, or shutting down the general air conditioning. Doing so is not forbidden - but it's not required.
Second, NFPA 96 is quite blunt that the exhaust fan need not operate if the cooking units and hood are "off." The fan need operate only when the equipment is operating.
hem and haw and engineer all you want, but your 'design ideas' may not be what the code actually calls for.
It was always Explained to me is that the MAU must shut down so it does not feed fresh air to the Fire , But Exhaust maintains running because of the Grease up in the exhaust Duct well get The fire stopping chemical.
The problems arise when there is no fresh air piped directly to the hood. I routinely see the 'hood guys' hanging their tissues on every air supply in sight, expecting them to be shut down. In some instances the kitchen is connected to the dining area with a pass-through, bar-like opening, and the fresh air comes from that other room. I wanted to stress that the only make up air that is required to be shut down is the air supplied directly to the hood, and not these indirect supplies.
Likewise, I have witnessed tests where the hood guys expected the exhaust fan to start up when they tripped the unit, even when everything was shut down. Again, NFPA 96 specifically explains that this is not required.
I suppose I ought to add two other 'refinements,' details that apply only in some cases: 1) If there is no alarm system, you need to mount some manner of alarm (bell, strobe, etc.) that will sound off if the unit trips; and, 2) If the cooking equipment uses 'old fashioned' pilot lights, you need a gas shut-off that has to be manually reset, rather than one that automatically resets when you reset the unit.
I've done these hoods in a few different jurisdictions, alongside several different hood guys, and ... this is the part that annoys me ... I have yet to encounter either a hood guy or a fire marshal who has ever actually held NFPA 96 in their hands. They know 'all about' the requirements, but have never read them. Ah, the look of wonder and amazement when I produce my copy ...
The other thing that annoys me is when I hear 'it's a pre-packaged unit, all you need to do is bring power to it.' Yea, right. Invariably I end up doing a lot more than just that.
A final note: At least once I've encountered a hood guy who did not want to pass inspection. No, his 'game' involved charging for each visit .... so, if he could give me non-functioning equipment and incomplete/erroneous instructions that would allow him to charge for another test, all the better! All I can say is that he picked the wrong guy to annoy.
Just an FYI on this subject. About 10 days ago, a resturant renovation inspection, I was checking the hood. I noticed that there were 'registers' (HVAC vents) cut into the front face of the hood, and they had little 'streamers' to indicate air-flow. For a few minutes, I thought 'HVAC' for the kitchen. I asked that the exhaust fan be 'on' & he flipped a switch. I said 'turn on MUA, he walked out of site. Came back & said 'it's on'. I said 'turn it off', he walked away, the air stopped. Ah, so did the 'registers'.
I said, where is the switch.....he walked over to the HVAC T'stat!!! They tapped the HVAC duct for the MUA!
There was a severe language issue; my Cantoneese is very limited!
Red sticker, there was a lot of issues in addition to the above.