1-6
One of the major causes of nuisance alarms is improper placement of detectors/sensors.
The best way to avoid nuisance alarms is to not install detectors/sensors in environments that can
cause them to malfunction. See the table and examples provided below.
Table 1-1. Environmental Conditions that Influence Detector Response*
Detection
Protection
Air Velocity
>300 ft.
(91.4m)/min.
Atm. Pressure
3000 ft. (914m)
Above Sea Level
Humidity
>93% RH
Temp. <32°F (0C)
>100°F (38C)
Color of
Smoke
Ion X X X X O
Photo O O X X X
Beam O O X X O
Air Sampling O O X X O
* See Table A-5-3.6.1.1 in NFPA 72
X = May affect detector/sensor response
O = Generally does not affect detector/sensor response
DO NOT PLACE DETECTORS/SENSORS:
In excessively dusty or dirty areas, such as feed rooms, steel mills, etc. Dust and dirt can
accumulate on the detector/sensor’s sensing chamber and make it overly sensitive, or block
the air entrances to the sensing chamber and make the detector/sensor less sensitive to smoke.
Be especially careful to avoid areas where fumigants, fog or mist-producing materials, or
sweeping and cleaning compounds are used. These substances may cause nuisance alarms.
Outdoors, in stables, open storage sheds, or other open structures affected by dust,
air currents, or excessive humidity and temperature.
In damp or excessively humid areas, or next to bathrooms with showers. Water droplets
can accumulate inside the sensing chamber and make the detector/sensor overly sensitive.
A tremendous amount of humid air is produced during a hot shower. The moisture in this
humid air can enter the sensing chamber as water vapor, then cool and condense into droplets
that can cause a nuisance alarm.
In elevator lobbies over ashtrays or where people smoke while waiting for the elevator.
In very cold or very hot environments, or in unheated buildings or rooms where the
temperature can fall below or exceed the operating temperature range of the detector/sensor.
At temperatures below 32° F (0° C), ice crystals or condensation can appear inside the sensing
chamber and make it overly sensitive or cause a nuisance alarm. At temperatures above the
operating range of the detector/sensor greater than 120° F (49° C), its internal components
may not function properly.
In or near areas where combustion particles are normally present, such as in kitchens or other
areas with ovens and burners; in garages, where particles of combustion are present in vehicle
exhausts; within 15 feet (4.5 meters) of any type of furnace, hot water heater, or gas space
heater; or in welding shops or other types of work areas where some form of combustion is
used in the activity normally conducted in that area. When a detector must be located in or
adjacent to such an area, a fixed temperature heat detector may be appropriate.
Continued on next page
Where Not to Place Detectors and Sensors
Improper Locations
for Detectors
and Sensors
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