Figure 2 (left). Structural members passing through a wall present a potential path of migration. Figure 3 (middle). Gaps between walls and the corrugated ceiling panels present a potential path of migration. Figure 4 (right). Wall penetrations properly sealed to prevent migration. Photos courtesy of Gladstein, Neandross & Associates, NREL 44897, 44898, and 44896 barriers, pressurizing adjacent areas, and sealing gaps in the structure to prevent migration into unprotected areas. signage should also be used to ensure that the door is not propped open. Doors should not be fitted with louvers or other means of ventilation that may create paths of migration.
Examples of potential paths of migration resulting from the structural characteristics of a facility are shown in Figures 1–3. These potential paths of migration can be eliminated by installing sealing material around the wall penetrations and at the ceiling level, as shown in Figure 4. Figure 7 shows a vehicle parts room adjacent to a main tenance area that is serviced with a pass-through win dow—a potential path of migration to an unprotected area.
This hazard can be eliminated by permanently sealing the window, adopting strict operating protocols to ensure it is only open during active use, or installing a pressurizing fan in the parts room to prevent the inward flow of gas from the maintenance area. Figure 5 shows an open passage to an adjacent non- maintenance area through which gas migration could occur. The two areas must be isolated to prevent migra tion between the two rooms. Stairways accessing an upper level could accentuate the upward gas flow (Figure 6). In these cases, the potential path of migration should be intercepted by isolating the two levels to prevent natural gas from entering an unprotected area.
One method for isolating two areas is to install a self-closing door between them. The door must be fitted with a self-closing mechanism to keep it closed except when in use. Operating protocols and Ventilation Ventilation of a CNG vehicle maintenance facility is one key area of concern that is addressed by the applicable codes. Proper ventilation can be achieved by mechanical means (powered fans) or by convection to provide air flow. However, it is rare that convection alone can provide sufficient or predictable air flow. There are several reasons Figure 5 (left). A potential path of migration created by an open passageway. Figure 6 (middle, right).
Examples of stairways to upper levels that are potential paths of migration. Photos courtesy of Gladstein, Neandross & Associates, NREL 44899, 44900, 44901 COMPRESSED NATURAL GAS VEHICLE MAINTENANCE FACILITY MODIFICATION HANDBOOK 10