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Should the HVAC System be Shut Down on Alarm?

The NFPA indicates that if smoke is detected in the ductwork near a fire damper, the damper should close. The same with an air handler. The fire marshal, though, may have more requirements, like any fire alarm in the building shuts down all dampers and fans.

Should the HVAC System be Shut Down on Alarm?


Greetings Douglas,

I've been told that the HVAC system in a building is supposed to shut down when a fire alarm is triggered, (on the idea that smoke and heat won't be distributed throughout the facility, but confined as much as possible to the area of origin). Is that correct or not, and what are your thoughts on this idea?

Thank you, CN

A fire alarm system detects fire and sounds the alarm. Also, because fire can be detected, often the fire alarm system takes action like closing fire doors, unlocking some doors, shutting down dampers and HVAC fans, etc.

The fire alarm system, though, is a life safety system; the fire alarm system takes action because, when there's a fire, people's lives are in danger.

Smoke from a campfire is not like smoke inside a burning building. Smoke from a campfire is from burning wood; smoke from a burning building is from burning wood, and from burning plastics, burning resins, burning PVCs, other burning chemicals, etc. If people breathe a few breaths of smoke from a campfire, most of time, they will cough for a short while and their lungs will be irritated for a short while; if people breathe a few breaths of smoke from a burning building, most of time they will be in danger of collapse, hospitalization, and possibly death.

Smoke is a huge danger. Smoke inside of burning buildings kills many more people than the flame inside of burning buildings.

The idea behind the fire alarm system shutting down the HAVC in case of fire is that the fire alarm shutting-down the fans will save lives. When a fire is detected, rather than allowing the whole building to fill smoke, the fire alarm system closes the fire doors, closes the fire dampers in the ductwork, and shuts down the air circulating fans.

This isn't really an issue of what the rules or codes say, though, this is an issue of life safety.

Douglas Krantz

Further Question

Mr. Krantz

That helps, somewhat. I guess what I'd like to know is - is it code (i.e. mandated) that the fire alarm system MUST shut down the dampers and turn off the HVAC fans when an alarm is triggered? (At present, yes, we do have three fire-rated doors which close. I check those, and in fact I always know if something was wrong during the night, because when I come in the morning, all my smoke doors are closed).

I've seen annual checks of the smoke detectors before, but I have never actually seen an inspector check to see if the dampers did indeed close, or if the HVAC fans did indeed shut off. (Perhaps there's a way to know this from observations which I simply don't know about, but each time I ask someone (at the three facilities I've worked at) I'm given the standard, pat answer, "I don't have time for these silly questions", or "The system is working just fine and is doing what it's supposed to do!". Yet. I've sometimes gotten the impression that shutting down dampers isn't something the person was even familiar with!

Since I am NOT a certified or even formally trained fire systems technician, I have no legitimate way of challenging the person's response, except to take their word for it. I just want my facility to be as safe as it can be, and I think part of that is to make sure to "Dot the "i's" and cross the "T's".

Thank you, CN

NFPA Code versus the Law

It's important to understand the difference between the publication "NFPA Code" and the law. The NFPA Code is a publication produced by the National Fire Protection Associating, a non-profit publishing house. As such, the NFPA 72 Code is a suggestion or recommendation on the minimum standards for a fire alarm system. A Law or Mandate is totally up to the government. Usually governments say "We will use the NFPA Code" as our law. That's where a mandate comes from, not the NFPA.

Somewhere in the NFPA Code, the Code does say to use the air duct smoke detector that is next to the damper to shut the damper, and the Code does say to use the air duct smoke detector at the air handling unit to shut down the fan. More stringent may be the building owners, the insurance company, the building's architect or design engineer, these Authorities Having Jurisdiction (AHJ) may want more devices to shut down the dampers and fans.

I've seen a lot of fire marshals say that anytime there is a fire alarm, all the dampers and all fans shut down. Sometimes, they'll even watch the dampers and fans to make sure they shut down on alarm. To me, that sounds like a good idea. Keep in mind that the fire marshal is the representative of the government, what the fire marshal says, goes.

These AHJs make the decisions on what is to be done with the dampers and fans. If the AHJs, including fire marshals, building inspectors, architectural engineers, insurance representatives, etc. don't enforce the shutdowns, it usually won't be done.

See Just Who Is the Authority Having Jurisdiction (AHJ)? for more information on just who is the AHJ.

Unfortunately, for you, it's probably the building owners that are the ones that decide to make improvements to the fire alarm system, or not. The fire marshal really has to deal with a grandfathered building; for the fire marshal to require changes, the building owners would have to pay.

The testing isn't that expensive, but still, someone has to be convinced because testing the dampers and fans can take 5% to 50% longer to test, and that does cost money. Only a few building owners are willing to pay the extra inspection costs.

Douglas Krantz
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

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