If bus fueling is done outdoors on a separate fueling island, and FCEB bus maintenance is done in a separate detached building modified to meet NFPA-1 and NFPA-2 with relevant gas detection, flame detection, electrical, alarms, etc., is it OK if the FCEB passes inside the main diesel maintenance building for 10-15 minutes to go through the bus wash and then immediately exit the facility? Is the bus's H2 system a completely contained system?

Hydrogen gas storage and fuel cell systems are typically closed systems with a variety of monitoring and control functions to prevent leaks. Please check with the bus manufacturer and authority having jurisdiction to verify this is acceptable per their direction. However, a good safety practice would be to minimize the time spent indoors for these activities. Hydrogen vehicles maintained in a facility should be provided with separation/isolation and appropriate safety control systems. Further guidance can also be provided by the local Authority Having Jurisdiction with regard to local regulations.