108.409—Location and spacing of tubing in pneumatic fire detection system.
(a)
All tubing in a pneumatic fire detection system must be on the overhead or within 300 millimeters (12 inches) of the overhead on a bulkhead in a location where—
(2)
Beams or girders extending below the ceiling or other obstructions do not detract from the effectiveness of the tubing; and
(b)
If tubing in a tubing circuit is installed in an enclosed space, at least 5% of the tubing in the circuit must be exposed in the space, except that at least 7.6 meters (25 feet) of tubing must always be exposed in the space.
(c)
A pneumatic fire detection system must be set to activate after approximately a 22°C. (40°F.) per minute increase in temperature at the center of the circuit in the system.