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HVAC Shutdown by Fire Alarm System

HVAC Shutdown by Fire Alarm System

HVAC Shutdown by Fire Alarm System

Does anyone know if the Uniform Codes (UBC, UFC, UMC, etc) or NFPA 72 requires shutdown of all HVAC systems bringing outside air into an area on activation of the alarm system, either by the sprinkler flow switch or an area smoke detector? We have a large open office area (cubicles) served by a dozen rooftop air conditioning units.

Our fire alarm contractor insists that the code requires shutdown of all the HVAC units on activation of the building fire alarm.

Comments please. Thanks

RE: HVAC Shutdown by Fire Alarm System


The contractor is confused. If your design is based on the Uniform Mechanical Code, shutdown of the respective air handler is only required if the unit has a discharge rate of 2000 CFM or greater.

NFPA 72 (2002 ed) allows the use of area smoke detection. However, its less expensive to use duct smoke detectors. These devices are listed for installation in the supply side of the air handler unit. If you already have area smoke detection, you may use it to shutdown the air handlers provided that detectors are provided throughout. This can create significant maintenance costs.

If one uses a duct smoke detector, it only needs to shutdown the air handler unit it is connected to.

Also, NFPA 72 only requires that the activation of the duct smoke detector to transmit a supervisory signal - it does not need to activate audible or visual alarm notification devices.

On a separate note, your post indicates that you have an office building that is sprinklered. If your applicable code is the Uniform Fire Code I am not aware of a fire alarm system requirement for a B occupancy unless its a highrise. Even then, smoke detection is not required in offices unless one is seeking increased exit travel distance.

RE: HVAC Shutdown by Fire Alarm System

It is required under the International Mechanical Code (I'm looking at 2003) which was partially derived from BOCA, and is also based on the principles within NFPA 90A (I'm looking at 1999).  A common method is to have return air duct-mounted smoke detectors which are interlocked with the respective air handler fans (one per air handler).  These are normally connected to a central fire alarm system anyway for annunciation purposes.

In the case of air systems where "all portions of the building served by the air distribution system are protected by area smoke detectors connected to a fire alarm system" you don't need duct-mounted ones, but "upon activation, the smoke detectors shall shut down the air distribution system".  There are other exceptions and limitations within the code(s) depending on the size of the fans (2,000 CFM), whether there is a "smoke control system", etc.

In general, however, the concept is to keep that "outside air" from feeding a fire.  It depends, but I believe you'll find the Contractor is correct in this case.

Good luck

RE: HVAC Shutdown by Fire Alarm System

I think in most cases you would have to shut down all of the units anytime a fire alarm initiating device is activated.  There are exceptions but you really need to carefully research them before taking action.  Factors may include how the system is designed, occupancy type, etc.  Generally if the building has a fire alarm system even duct detectors must be connected to the fire alarm system and set off the notification appliances.  The only exception is usually when you have an occupancy that allows you to use a pre-signal system.

RE: HVAC Shutdown by Fire Alarm System

Consider the actual situation instead of some general rule.  The considerations include the detector locations, the space application and the system design issues and more.  For example, perhaps you need to shutdown the HVAC for an equipment room for confirmed smoke or fire in that room.  In the HVAC equipment room, that might shutdown the entire HVAC system.  This might be very different for an occupied area where the exhaust fans could remove the smoke.

Is the detector on the supply fan inlet or supply ducting?  Is the detector in the room?
Is there free ventilation between rooms or open areas?
Are the rooms sealed with fire doors?

Is this an office building, a hospital or an ocean going vessel?

Generally, if the detection initiates a suppression system such as FM-200, CO2 etc. then shutdown the fans and dampers to contain the suppression agent.  I think that this is covered within old NFPA standards for computer rooms.  You might not expect the old mainframe based standards to apply to a server room.  Also, expect standards for a computer room to differ from standards for a hospital or a night club.  ...


RE: HVAC Shutdown by Fire Alarm System

I think that it is NFPA-90A that you want ..... (but I might be wrong ....) and there is a requirement for shutdown of all systems above a certain flowrate (15,000 CFM I think) into any single smoke zone AND which are in a space covered by the reqmts of NFPA-90A (ie NFPA-90A doesn't necessarily aply to all buildings ...)

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