Safety is of paramount importance in the design of hydrogen-powered vehicles. Inherent safety is an important design consideration in modern engineering safety practice. Through inherent safety, systems are designed to be safe without extensive protective systems. Quantified risk assessment can play a valuable role in optimizing the safety features of the on-board hydrogen system. Protective safety systems can sometimes fail to function and quantification can help to indicate where redundant systems may be required as well as how often they must be functionally checked. The size of flammable zones from some types of open air leaks can provide guidance for the design of vehicle systems.