If you maintain fire alarm systems, you have encountered false alarms. If you look around in a panic and find nothing, reset the fire alarm control unit and leave the building, you will likely experience additional false alarms from that system later on. I know many of you are nodding your heads in agreement. I also know this scenario is true from my years of experience investigating false alarms and fire scenes.
A real-life example
I was staying at a well-known hotel when a fire alarm occurred at 3 a.m. I quickly got dressed and began to evacuate the building.
As I was leaving my room, I encountered a hotel employee running up the stairs. He told me it was a false alarm but, not trusting someone who was not a firefighter, I continued to evacuate. When I got to the lobby, the fire department captain confirmed there was no fire. The alarm had been caused by someone smoking in the hallway. I returned to my room thinking, smoking at 3 a.m.?
The following morning at 2 a.m., there was another alarm. I again got dressed and began to evacuate. I saw the same employee from the day before and, again, he told me it was a false alarm. This time I believed him. Later that morning after breakfast, I asked to speak with the facility engineer.
The engineer and I discussed the false alarms. He told me both alarms, according to the fire department, were attributed to someone smoking in the hallway. I advised him that this was unlikely given the current UL standard’s tests for smoke detector listing, and I asked if both alarms came from the same device. He answered affirmatively. I advised him to maintain a stock of 2–4 spare new smoke detectors and, after any alarm from a smoke detector, to assume the detector was defective or dirty and immediately change it out. Before I left, I called a representative of the factory, and he said my suggestion made good sense.
Best practices
All of the above is to suggest that if you are a system maintainer, you should advise all your clients to maintain a stock so you can change out any detector that false alarms. This will ensure they will not get a second alarm from the same device.
If most of the fire alarm systems you maintain are from the same manufacturer, make sure each of your trucks have a stock of new ones. Analyzing false alarms takes some experience, so train your techs on what to look for and to not accept glib answers from firefighters who want to leave quickly once they discover there is no fire.
The National Fire Alarm and Signaling Code is clear. Section 17.7.1.7 states, “The selection and placement of smoke detectors shall take into account both the performance characteristics of the detector and the areas into which the detectors are to be installed to prevent nuisance and unintentional alarms or improper operation after installation.”
Unless you installed the system, you should always advise your technicians to review where the detector is installed to ensure it meets the code’s requirements. Never assume the previous installer did it correctly. Also, don’t think that because the fire department accepted the system that every smoke detector was installed properly.
The technician should investigate thoroughly and be aware of potential causes of false alarms. For example, is the owner performing any renovations that could have filled the smoke detector with dust? Have new fluorescent lights been installed in the area near the alarmed detector?
The code also requires the smoke detector location be based on an evaluation of potential ambient sources of smoke, moisture, dust or fumes, and electrical or mechanical influences, to minimize nuisance alarms.
Common causes of false alarms are listed in Annex A of NFPA 72-2025. Table A.17.7.1.10(a) lists common sources of aerosols and particulate matter moisture that can set off a smoke detector:
- Moisture: humid outside air, humidifiers, live steam, showers, slop sink, team tables, water spray
- Combustion products and fumes: chemical fumes; cleaning fluids; cooking equipment; curing; cutting, welding, and brazing; dryers; exhaust hoods; fireplaces; machining; ovens; paint spray
- Atmospheric contaminants: corrosive atmospheres; dust or lint; excessive tobacco smoke; heat treating; linen and bedding handling; pneumatic transport; sawing, drilling, and grinding; textile and agricultural processing
- Engine exhaust: diesel trucks and locomotives, engines not vented to the outside, gasoline forklift trucks
- Heating elements with abnormal conditions: dust accumulations, improper exhaust, incomplete combustion.”
This list is not exhaustive, but reading the Annex A material associated with the false alarm issue will help you and your technicians better understand the possible causes of false smoke detector activations.
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About The Author
MOORE, PE, is a licensed professional fire protection engineer, and located in Jamestown, R.I. He is the editor of five editions of the National Fire Alarm Code Handbook. He authored, “Designing Mass Notification Systems – A Pathway to Effective Communications.” He is a principal member of the NFPA 72 Correlating Committee and former chair, now principal member, of the Emergency Communications System Technical Committee. He can be reached at [email protected].
