D296/D297 Series Application Guide 7
6.3 Environmental Considerations
6.3.1 Outdoor
Beam smoke detectors are inappropriate for outdoor applications. Environmental conditions such as temperature extremes, bright
sunlight, rain, freezing rain, snow, sleet, fog and dew can interfere with the proper operation of the detector. Outdoor conditions also
make smoke behavior impossible to predict.
6.3.2 Indoor
Avoid sources of heat and air movement:
• Don’t mount the detectors where hot or cold air can blow directly into the beam path.
• Heating, ventilating, air conditioning systems and ceiling fans can cause smoke to be blown away from the projected beam.
Smoke must accumulate in the projected beam to be detected.
• Heaters mounted close to the projected beam path can cause the beam to be distorted.
Avoid sources of bright light:
• Sunlight. Avoid pointing the receiver directly at the rising or setting sun. If you are installing the unit where sunlight can’t be
avoided, mount the receiver slightly higher than the transmitter and aimed down towards the transmitter. This should reduce the
problem by causing the receiver to look below the horizon.
•Bright Lights. Although bright lights are generally not a problem, exposed bulbs of high pressure sodium, mercury vapor and
metal halide should not be placed in close proximity to the receiver. Bare fluorescent lights may pose a problem in long hallways
where a series of lights run perpendicular to the beam.
6.4 Mounting
Section 5.7.3.4.8
of
NFPA 72
®
, National Fire Alarm Code
®
(2002 Edition)
states: "The light path of projected beam-type detectors
shall be kept clear of opaque obstacles at all times."
Section A.5.7.3.4.8
of
NFPA 72
®
, National Fire Alarm Code
®
(2002 Edition)
states: "Where the light path of a projected beam-type
detector is abruptly interrupted or obscured, the unit should not intiiate an alarm. It should give a trouble signal after verification of
blockage."
Because beam smoke detectors are line-of-sight devices which go into trouble on sudden and total loss of signal, care must be
taken that all obstacles be kept clear of the beam path at all times.
This requirement could make the use of beam smoke detectors impractical in factory applications where overhead cranes and hoists
are present and in warehouses where high fork lifts may block the beam. This factor should also be considered in occupied areas
where normal ceiling heights exist.
Beam smoke detectors depend on the measurement of the projected beam to sense smoke. Therefore, shifts in the alignment of the
beam due to movement of the transmitter or receiver can cause trouble or alarm conditions.
• Always select a stable mounting surface. The walls and attached girders of steel-sided buildings (especially those walls facing the
sun) may be very unstable throughout the day. A roof support girder may provide better support in this case.
• Never mount the units to a suspended support such as a pipe or length of wood supported at only one end.
• Never use mirrors to extend the beam around corners.
• Never mount behind clear glass or plastic covers other than those supplied by Bosch with the detectors.
• When mounting in high ceiling areas such as atriums, several mounting levels should be considered to account for stratification
due to ceiling height or low energy fires.
Multiple
Level
Mounting