System-sensor A05-1003-002 Manuel d'utilisateur télécharger pdf (Page 10)

SYSTEM SENSOR

be mounted on the wall. Wall-mounted detectors should be

located not less than 4 inches nor more than 12 inches

from the ceiling to the top of the detector, and at least 4

inches (10 cm) from any corner wall junction. (See Figure

18.)

When air supply and/or air return ducts are present in a

room or space, the detector(s) should not be placed in the

path of the air flow supply or return duct (NFPA 72, 1999

Edition).

Smoke tests are helpful in determining proper placement.

Special attention should be given to smoke travel directions

and velocity, since either can affect detector performance.

Placement of detectors near air conditioning or incoming

air vents can also cause excessive accumulation of dust

and dirt on the detectors. This dirt can cause detectors to

malfunction and cause unwanted alarms. Detectors should

not be located closer than 3 feet from an air supply diffuser

or an air return vent.

Spot type detectors, in properly engineered systems, may

also be placed 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 from being transported

from the fire area to other parts of a building. (See Duct

Smoke Detector Applications Guide.)

Ceiling

Acceptable Here

Never Here

Top of Detector Acceptable Here

Side Wall

4 in. (10 cm)

Minimum

12 in. (30 cm)

Maximum

Note: Measurements shown are to the

closest edge of the detector.

Figure 18: Wall Mounted Detector – Placement

Where Not To Place Detectors

See Table A-2-3.6.1.2A in NFPA 72-1999.

One of the major causes of unwanted alarms is improper

placement of detectors. The best way to avoid unwanted

alarms is not to install detectors in environments that can

cause them to malfunction, or to install detectors specially

designed for those environments. Examples follow:

• Excessively Dusty or Dirty Areas

In excessively dusty or dirty areas consider using the

Filtrex

™

smoke detector. This detector incorporates a

microprocessor-controlled air intake fan and filter that

allows the unit to be installed in areas where ordinary

detectors cannot be used. Filtrex is an intelligent

smoke detector that removes airborne particles before

they reach the sensing chamber. It is ideal for textile

mills, dusty manufacturing facilities, paper mills, and

recycling centers. For more information see System

Sensor’s Filtrex

™

Applications Guide.

• Outdoors

Avoid using detectors outdoors, in open storage sheds,

or other open structures affected by dust, air currents,

or excessive humidity and temperature extremes.

• Wet or Excessively Humid Areas

Avoid damp, wet or excessively humid areas, or next

to bathrooms with showers.

• Elevator Lobbies

Do not place over ashtrays or where people will smoke

while waiting for the elevator.

•

Extreme Cold or Hot Environments

Avoid very cold or very hot environments, or unheat-

ed buildings or rooms where the temperature can fall

below or exceed the operating temperature range of

the detector. At temperatures above or below the oper-

ating range of the detector*, its internal components

may not function properly.

*Manufacturers’ specifications should list acceptable

temperatures in these ranges.

•

Areas with Combustion Particles

Avoid areas where particles of combustion are nor-

mally present, such as in kitchens or other areas with

ovens and burners; in garages, where particles of com-

bustion are present in vehicle exhausts. When a detec-

tor must be located in or adjacent to such an area, a

heat detector may be appropriate.

• Manufacturing Areas

Avoid manufacturing areas, battery rooms, or other

areas where substantial quantities of vapors, gases, or

fumes may be present. Strong vapors can make detec-

tors overly sensitive or less sensitive than normal. In

very large concentrations, gases heavier than air, such

as carbon dioxide, may make detectors more sensitive,

while gases lighter than air, such as helium, may make

them less sensitive. Aerosol particles may collect on

detector chamber surfaces and cause nuisance alarms.

• Fluorescent Light Fixtures

Avoid placement near fluorescent light fixtures.

Electrical noise generated by fluorescent light fixtures

may cause unwanted alarms. Install detectors at least

1 foot (0.3 m) away from such light fixtures.

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System-sensor A05-1003-002 Manuel d'utilisateur Page 10

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