box or generated in normal operation of an unprotected electric motor is cause for concern. Additionally, unsealed conduits may also provide a means of gas migration from one portion of the facility to another. Before modifying a maintenance facility to service CNG fuel vehicles, the existing design must be taken into consideration so that each of the safety risks is mitigated. NFPA 30A states that in major repair garages, the area within 18 in. of the ceiling is considered a hazardous zone and is designated as Class I, Division 2.
Within these areas, all electrical wiring, conduits, junction boxes, and electrical appliances must be either explosion proof or relocated outside the hazard zone. In general, it is less expensive to eliminate or relocate non-compliant electrical fixtures than to replace them with more costly explosion-proof units. The NFPA 30A Class I, Division 2 designation does not apply for minor repair garages. However, it is best practice to also eliminate credible sparking risks in minor repair garages. Figure 22. Relocating multiple conduits, such as those shown here, would be costly and complex. Photo from Gladstein, Neandross & Associates, NREL 44676 non-sparking.
Examples may include loudspeaker and security camera wiring; wiring used for data transmis sion; alarms; and wiring used for similar applications (Figure 23). However, the AHJ must approve the low- voltage wiring; otherwise, it may be considered hazard ous and subject to Class I, Division 2 requirements. In the hazardous zone within 18 in. of the ceiling, all electrical wiring, conduits, junction boxes, and electrical appliances must be either explosion proof or relocated outside the zone. For lighting fixtures to comply with Class I, Division 2 requirements, they must be either classified as explo sion-proof or moved to a location that is more than 18 in. from the ceiling.
All components (e.g., fixtures, bulbs, ballasts, transformers, etc.) must be relocated outside of the hazardous zone (Figure 24). In general, lowering the fixtures and components is the most common and cost-effective approach for compliance. It is important to note that NFPA 30A does provide an exception to the Class I, Division 2 designation. NFPA 30A states that if the structure has an effective continu ous ventilation rate of at least 4 ACH, the area within 18 inches of the ceiling is not considered a hazardous zone. This exception is covered in Section 3.2, Ventilation.
For maintenance facilities where providing continuous ventilation is deemed impractical, the following provides solutions for many commonly encountered conditions. In some cases, the number of conduits or junction boxes located in the hazardous zone is large enough that relo cating each of them is unreasonable because of the cost or complexity (Figure 22). Class I, Division 2 compliance can be obtained if conduits or junction boxes are pro vided with seal-offs that create a physical barrier that pre vents gases from traveling freely through the conduit as well as the migration of methane into the conduits. The use of seal-offs in lieu of relocation must be approved by the AHJ.
According to NFPA 30A, low-voltage wiring and containing conduits may be exempt from the Class I, Division 2 requirements if they are determined to be Figure 23. Low-voltage wiring and devices. Photo from Gladstein, Neandross & Associates, NREL 44677 SEPTEMBER 2017 17