accumulations of natural gas which may be subject to ignition sources. Figure 13 shows a ceiling configuration that could accumulate concentrations of natural gas. Because the “pockets” do not contain heaters, electrical wiring, or appliances, there is no ignition source and it is not necessary to ventilate each “pocket.” Some maintenance facilities have bay doors equipped with stops that maintain a gap (typically around 12 inches), providing a permanent ventilation space between the bottom of the door and the ground when fully “closed.” If this type of configuration presents a security concern, a mesh or a grate can be installed at the bottom of the door as shown in Figure 14. Figure 15.
In-wall louver that provides make-up air flow. Photo courtesy of Gladstein, Neandross & Associates, NREL 44706 Figure 13. Ceiling configuration with “pockets. ” Photo courtesy of Gladstein, Neandross & Associates, NREL 44704 Make-up air for the ventilation system may be derived from a number of sources. In warm climates, makeup air may be supplied through open bay doors. In cool climates or in hot climates where cooling is provided, a continuous ducted ventilation system may be employed. In the case of ducted systems, the bay doors may be opened by the gas detection system interlock to provide additional makeup air flow and additional paths of personnel egress.
It is not necessary to open all of the bay doors in a multi-bay maintenance facility, only a suf ficient number to provide the required makeup air flow. In-wall louvers (Figure 15) can also be employed to provide a portion of the makeup air flow. Generally, they are not able to provide the sufficient make-up air volume or flow direction to meet the codes and regulations on their own. Powered side wall fans (Figure 16) may also be used to provide the requisite air flow. Figure 14. Security mesh in overhead doors. Photo courtesy of Gladstein, Neandross & Associates, NREL 44705 Figure 16. Powered sidewall fan that provides make-up air flow.
Photo from Gladstein, Neandross & Associates, NREL 44707 COMPRESSED NATURAL GAS VEHICLE MAINTENANCE FACILITY MODIFICATION HANDBOOK 14