Many of you on this forum have firefighting experience. On rooftop air handlers with direct exhaust who decides what the unit does when the fire alarm goes off? Is it specific to the city or building?

Is it best to have the air handler exhaust smoke until the fire department cuts power? Would it depend on the estimated time to evacuate the building? Say run the exhaust for 45 minutes if it takes 30 minutes to evacuate the building? These are the same questions I am asking our customer but I would like to see the different applications and their effects that people have seen in real world applications.

I also know there are so many variables involved that it becomes complicated. From my Navy firefighting days I remember ventilating the compartment with a hatch, then someone opens a hatch on the other side and it creates a blow torch effect.

I would appreciate hearing your views on this application.

If it is only exhaust, then it would depend on whether smoke control is required by the mechanical code. If smoke control is not required, then there is no requirement to shut down an exhaust only fan .

Based on my experiences in NJ

The BOCA Code calls for a duct mounted smoke detector to shut down an air handler for any unit 5-Tons Nominal and over.

Rad:
Are you talking about kitchen exhaust hoods? or HVAC equipment??

Kitch exhaust hoods, exhaust "on", MUA 'OFF' for fire activation

John

I asked the same question because we have two offices. One the HVAC shuts down on fire alarm the other it does not.
One building has two floors the other is single floor. I was told HVAC only needs to shut down on two story or up buildings. This is in Ontario Canada.

NJ_Grad,
I believe that New Jersey statewide goes by the 2003 International Mechanical Code. Smoke control systems are handled by Section 513, which is a special animal regarding when it goes on or off.
Section 606 is where duct detectors are required, which identify return or common supply and return locations requiring shutdown. There is no mention of exhaust.

This is where the engineer / archetect earns his pay. The question of "to vent or not to vent" is decided in conjunction with other parts of the system.

While kitchen hoods always get shut down, I have seen major public buildings where a fire alarm will both close fire doors AND turn on major exhaust fans.

Ron,
Understood

With Mechanical it really breaks down to using the correct terminology.

I read "Rooftop Air Handlers" as a Packaged Rooftop Unit (RTU), it didn't sound like he was reffering to a smoke control system.

Just depends on what rad74ss was refering to.

thanks on the specifics though

John,
Many times the exhaust hood stays on to pull the extinguishing agent up the duct.
Don

This is an HVAC air handler with a split condensing unit. The fire alarm turns of the heater and/or the supply air blower. There are two exhaust fans blowing out horizontally on the left and right sides of the return air stack.

The whole unit can be disabled by a remote signal and of course disconnecting main power. It is currently set up to stop the supply blower and vent smoke with the exhaust fans until the unit is disabled. The customer has not responded yet on what they require and if their fire system can disable the unit if the fire is directly in the zone the air handler supplies.

Thanks, Don: I stand corrected.

My experience of hoods and the like is that if the flames are vented straight up, it will close an in-tumescent barrier, by virtue of a temperature rated fusible wire link.
These are also used at corners of ducting.

There was a mistake in the write up and the controls are by a third party.

They said that their building code requires venting smoke with the exhaust fans with fusible links in the return air fire dampers so that if it gets too hot it shuts the damper and a differential pressure switch cuts out the exhaust fans after that.

Fire suppression systems used in commercial kitchen hoods are UL listed to operate w/the exhaust fans on or off. Leaving the exhaust fan on helps to distribute the suppression chemical throught the hood and duct. This also helps to move the combustion gases out of the fire area, improving visiblity for the responding fire department. The intake or make-up air is to shut down.

There is an IBC requirement to shut down air handling ducts moving 2000 CFM or more. This requirement may be modified by the type of occupancy, building construction and the whim of the building inspector.

Fireguy

Fireguy is correctm as far as the way we do it here. Every fire-suppression system we've wired in has the same parameters:

The exhaust must run, regardless of the switch's position, and the intake must not run, regardless of the switch position.

I figured out a way to do it using ony one of the two microswitches ours come with, requiring only three conductors between boxes.

Larry, could I trouble you for a diagram of your wiring? Most electricians have trouble leaving the exhaust on and shutting down the intake. I am often asked how to wire the contactors and I know just enough about wiring to hurt myself. Hey, are those wires supposed to spark like that?
Thank you in advance.
fireman@eoni.com