Placement of sensors
This section explains how to determine the number of sensors are needed, and where to place them. By following the
guidelines listed in the NFPA 72, base the number and location of sensors on an engineering survey of the area to be
protected.
Factors to consider:
Contents to be protected
Type of construction and use of structure
Human occupancy
Burning characteristics of contents
Space involved
Height of ceiling
Surface condition of ceiling
Total area
Air movement (stratification)
Vent location (velocities and dilution
Deflections and obstructions
Sensor Location:
One smoke sensor covers 450 to 900 square feet
One heat sensor covers up to 2500 square feet
Consider local conditions and codes along with engineering evaluations to determine the proper spacing and
specification
WARNING: Heat sensors are not life safety devices. Smoke sensors are recommended where life safety is a factor
Examples:
1.
You may use 30' spacing on smooth ceilings for smoke sensors
2.
You may use 70' spacing on smooth ceilings for heat sensors
3.
Beams or other obstructions extending more than 18" below the ceiling reduce the effective range of the sensors. Such
obstruction should designate a new separation point and be considered a border for a new section.
4.
Beams or other obstructions extending more than 8" but less than 18" require reduced spacing at the perpendicular of
the obstructions.
NOTE: For information on differing styles of construction consult the NFPA handbook, section 72.
WARNING: Do not install Hochiki smoke sensors in the following areas:
Closer than 4" to any side wall
Where forced ventilation can dilute the smoke from a fire
In known areas of combustion such as kitchens or furnace rooms
Testing
Photoelectric/Heat/Multi-Criteria Sensors:
For a smoke sensor to operate efficiently, the combustion products must enter the outer chamber. Air flow, stratification,
velocity, stagnation, and migration all affect the efficiency and accuracy of the sensor. Use a air flow meter to determine the
movement of the air within a structure. Field testing equipment is available from Hochiki America for testing the function of the
sensors. Consult local codes and ordinances for maintenance requirements. Hochiki America Corporation recommends a
bi-annual functional testing and visual inspection. See the Tester section in this Technical Bulletin and the control panel
manual for additional information.
JULY 2016
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