Development of Safety Criteria for Potentially Flammable Discharges from Hydrogen Fuel Cell Vehicles

This paper describes the methodology for performing tests to measure the flammability limits for hydrogen (H2) in flowing gas discharges, and to quantify the hazard of ignition of flammable discharges from fuel cell vehicle (FCV) systems. Examples of results are provided for modified fuel cell car and bus systems. Also, a model is presented for determining the expected H2 accumulation due to an H2 leak inside a well-mixed enclosure, including the results of testing performed to validate this model.

These tests and models were developed as inputs to the SAE Recommended Practice for General Fuel Cell Vehicle Safety (J2578). The SAE Fuel Cell Vehicle Safety Working Group has published and is developing standards for FCVs and hydrogen vehicles. The SAE J2578 recommended practice addresses both electrical and fuel system hazards associated with integrating fuel cell systems into road vehicles, including the management of hazards associated with H2 storage and processing on-board the vehicle. The first version of SAE J2578 was released in December 2002; a key aspect of this standard was managing H2 hazards by ensuring that discharges from the vehicle remain nonflammable by staying below the traditionally-accepted lower flammability limit (LFL) for H2. An approach was also defined for assessing discharges for the hazard of H2 accumulation in the vehicle surroundings. The latest draft revision of J2578 allows for performance-based emission limits to avoid unnecessary design constraints; the testing described in this paper is included in the standard as the basis for performance-based emissions limits.