Gas Alarm System (Figure 1-17). The gas alarm system consists of a main control unit (cabinet assembly) and
two remote detector assemblies. The main control unit is wall-mounted on the roadside and connects electrically to the
two detector assemblies. The system operates on 110V, 60Hz, single-phase power. The main control unit supplies 5.5
Vdc to the detectors. The alarm is calibrated for propane and has a setting of 20 to 40 percent of the lower explosive limit
(ell) of gasoline. An indicating meter in the control unit shows the concentration being monitored and adjustable dual-
level alarm circuits are triggered whenever a concentration exceeds the ell. The alarm alerts personnel of combustible
mixtures that could cause explosions or fires, and it automatically activates the air purge system.
Figure 1-17. Gas Alarm System