Detector Positioning - FFE Fireray 50RU Technical Bulletin

3. Detector Positioning.

An infrared signal is projected out of the transmitter optics (see Fig 3) to the reflector placed at the
opposite end of the detection zone. The signal is reflected back to the receiver where it is analysed for
fire and Trouble.
It is important that the Fireray 50/100RU Detector is positioned correctly to minimise the detection time.
Experiments have shown that smoke from a fire does not rise directly upwards, but fans out or
mushrooms due to air currents and heat layering effects. A fire condition occurs when the infrared beam
is obscured by a preset limit. The time to signal a fire condition depends on the location of the Detector
within the premises, the volume of smoke produced, construction of the roof, and ventilation
arrangements.
The maximum lateral distance either side of the beam is found to be typically 30 feet for satisfactory
detection under flat ceilings, providing a total area coverage of 19,800 square feet (60 feet X 330 feet).
Single Beam Multiple Beams
19 ↔ 24 In
60 Ft
19 In ↔ 30 Ft 19 In ↔ 30 Ft
60 Ft
Smoke layering may be overcome by mounting the beam Detector at different heights, which will project
the infra-red beam below the heat layer and into the smoke layer. Multiple beams at different heights
may therefore be required.
Detection time will be longer in a building with a peaked roof if a fire occurs at the fringes of the protected
area. If in doubt, prove operation by smoke tests.
The ideal location and spacing of the Detector is critical in a properly installed and operating fire alarm
system. It is recommended that the detectors be located and spaced in accordance with the National Fire
Protection Association (NFPA) Standard 72 "The National Fire Code". No liability will be accepted for
applications not conforming to NFPA regulations.
The recommended installation height is approximately 19 to 24 inches below the ceiling. However, in all
installations the National Fire Standards for that country/state must be consulted.
Because of the reflecting properties of the beam, all objects must be kept a minimum of 19 inches away
from the centre of the beam path down the entire beam length. If highly reflective surfaces are close to
the beam, then greater clearances should be applied.
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