Case study: Reducing the impact of nuisance alarms
By using the correct type of programming, smoke detectors initiated a supervisory signal instead of nuisance alarms
In certain parts of the world, it is customary to install automatic smoke detection in above ceiling spaces when the height of the space exceeds 32 inches. Where this criterion was applied to a large health care facility, more than 15,000 smoke detectors were installed in the building.
Shortly after occupancy of the facility, the nuisance alarm rate at this facility was averaging in excess of one fire alarm system activation per day. The causes of the nuisance alarms were identified as well as whether it was a detector above or below the ceiling.
It was quickly determined that the nuisance alarm rate could be reduced significantly if the smoke detectors were not installed above the ceiling.
In an attempt to reduce the nuisance alarm, one approach considered was to eliminate the smoke detectors installed above the ceiling. While the project was to have been designed and constructed to comply with U.S. codes, the authority having jurisdiction took the position that the smoke detectors were required in the space above the ceiling membrane. It was determined that this approach could be costly and disruptive if the facility was told that the detectors had to be removed if they were not being properly inspected, tested and maintained.
A less costly and disruptive approach was to have the above-ceiling smoke detectors reprogrammed to initiate a supervisory signal instead of an alarm signal. Clearly this change in the design of the fire alarm system required approval by the AHJ. Instead of explicitly asking to make the change, the fire protection engineer approached the AHJ with some questions:
- If an above-ceiling smoke detector identifies a smoke condition, should the facility staff implement the emergency plan and begin to relocate patients?
- If the answer to the first question is “no,” what is the desired response to a smoke condition above the ceiling?
The AHJ responded that the facility was not required to implement the emergency plan, but rather a fire alarm technician was to investigate the source of the alarm signal and determine what, if any, action should be taken. After receiving the response, the fire protection engineer asked the AHJ if the above-ceiling smoke detectors could be reprogrammed to initiate a supervisory signal — the AHJ agreed that a supervisory signal was acceptable.
The reprogramming of the above ceiling smoke detectors was far less expensive and disruptive than removing the detectors. Admittedly, reprogramming the smoke detectors did not eliminate the nuisance alarm issue. It did, however, reduce the impact of the nuisance alarms.
Also, when a technician responded to investigate the source of the condition detected, the technician was then able to identify the appropriate corrective action for that specific detector to reduce the nuisance alarm rate at the facility.