Where Not To Place Detectors And Sensors; Incorrect Locations For Detectors And Sensors - Simplex 4098 Manual

Smoke tests help determine the correct placement of detectors and sensors. Observe the smoke travel directions and velocity, as these
factors can affect detector and sensor performance.
Placement of a detector or sensor near air conditioning or incoming air vents can cause excessive accumulations of dust and dirt on
the detector or sensor. This dirt can cause the detector or sensor to malfunction and cause nuisance alarms. Do not locate detectors or
sensors closer than 3 feet, or 0.9 meters from an air supply diffuser.
Spot type detectors or sensors in correctly engineered systems, can also be installed in return air ducts, or in approved duct detector
housings designed for this application. Although duct detectors are not a substitute for open area detectors, they can provide an effective
method of initiating building control functions to prevent smoke being transported from the fire area to other parts of a building.
2.3

Where not to place detectors and sensors

2.3.1

Incorrect locations for detectors and sensors

Installing detectors or sensors in an incorrect location is a major cause of nuisance alarms. To avoid nuisance alarms do not install
detectors or sensors in environments that can cause them to malfunction. See the following table and examples:
Detection Air velocity >300 ft.
protection
(91.4 m) / min.
Photo O
Beam O
Air Sampling O
*See Table A-5-3.6.1.1 in NFPA 72
X = May affect detector or sensor responses
O = Generally does not affect detector or sensor responses
Do not install detectors or sensors in the following areas:
• In excessively dusty or dirty areas, such as feed rooms, steel mills, etc. Dust and dirt can accumulate on the detector or sensor's
sensing chamber and make it overly sensitive, or block the air entrances to the sensing chamber and make the detector or 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 can 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 or sensor overly sensitive. A large 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 causing 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 or sensor. At temperatures below 32°F, or 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 or sensor greater than 120°F, or 49°C, its internal components may not function correctly.
• 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, or 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
page 7
Figure 2: Detector placement - air supply or return ducts
Table 1: Environmental conditions that influence detector response*
Atm. pressure
3000 ft. (914 m)
above sea level
O
O
O
4098 Detectors, Sensors, and Bases Application Manual
Humidity Temp. <32°F (0°C)
>100°F (38°C)
>93% RH
X X
X X
X X
Color of smoke
X
O
O
574-709 Rev. AP