Figure 24. Overhead lighting fixture and ballast that must be relocated. Photo from Gladstein, Neandross & Associates, NREL 44678 Figure 26. A typical electric door motor. Photo from Gladstein, Neandross & Associates, NREL 44680 26) because of the possibility that sparks may be gener ated by the electric motors. If gas is detected, the electric door motors will be activated to open the doors. For this reason, depending on the type of motors, the accompa nying proximity switches, and the physical location of Other electrical appliances and equipment within the hazardous zone must also be removed or relocated. Figure 25 displays a typical rotary fan that, although not located within 18 in.
of the ceiling, would be determined as a potential ignition source because of the possibility that sparks may be generated within the drive motor. The rotary fan would be classified as a potential ignition source because rising released gas could encounter the fan before reaching the ceiling-mounted gas detectors. In some cases, the AHJ may require that all such fixtures be removed completely to avoid this hazard. Figure 27. A typical overhead crane. Photo from Gladstein, Neandross & Associates, NREL 44681 the openers, AHJs may require electric door motors to be upgraded or replaced with explosion-proof equip ment.
Doors that are not activated during a gas detection event do not need to be replaced with explosion-proof equipment. Similarly, overhead cranes (Figure 27) should be shunt-tripped to prevent activation of their electric motors in the event of a gas release. Shunt tripping, which is further discussed in Section 3.5, Gas Detection, Alarm, and Control Systems, involves an interface between the methane detection controls and the circuits within the facility electrical panel. When methane is detected, selected circuits can be instantaneously deactivated. Figure 25. An overhead rotary fan that presents a potential ignition source.
Photo from Gladstein, Neandross & Associates, NREL 44679 Electric door motors, commonly found on main bay doors, are also a potential ignition source even when they are not located within the hazardous zone (Figure COMPRESSED NATURAL GAS VEHICLE MAINTENANCE FACILITY MODIFICATION HANDBOOK 18