Abstract: The safety of onboard hydrogen systems is one of the core technical indicators of fuel cell vehicles (FCVs), and its safety guarantee is an important prerequisite for the large scale of commercialization of FCVs. Focusing on the safety of the onboard hydrogen system, this paper introduces the composition of the onboard hydrogen system and analyzes the failure modes and causes of the onboard hydrogen system and its components. This paper summarizes the failure consequences of the onboard hydrogen system and discusses the urgent need for the improvement in the fire safety of FCVs at this stage. The analysis shows that the potential failure modes and causes of onboard hydrogen systems mainly include sealing, vibration fatigue, mechanical shock, collision, rapid hydrogen charging and discharging fatigue, thermal damage, and control system function failure, and the main consequence of failure is hydrogen leakage. In extreme scenarios, "hydrogen leakage+confined / semi-confined space+ignition source" will cause fire or even explosion, which will seriously threaten the safety of public life and property. Therefore, it is recommended to improve the safety level of onboard hydrogen systems from many aspects, such as optimizing safety design and verification, improving hydrogen leakage monitoring and gas source control technology, carrying out quantitative evaluation of failure disaster hazards, and strengthening fire prevention and control technology.

Key words: fuel cell vehicles, onboard hydrogen systems, failure modes, failure causes, hydrogen safety