Fire Protection Strategy for Compressed Hydrogen-powered Vehicles

Virtually all major automotive companies are currently developing hydrogen-powered vehicles. The vast majority of them employ compressed hydrogen tanks and components as a means of storing the fuel onboard. Compressed hydrogen vehicle fuel systems are designed in the same way as compressed natural gas vehicles (NGV), i.e. the high pressure (up to 70 MPa) fuel is always contained within the system under all conditions, with the exception of vehicular fire. In the event of a vehicle fire the fuel system is protected using a non-reclosing thermally activated pressure relief device (PRD) which safely vents the contents. Hydrogen fuel system PRDs are presently qualified to the performance requirements specified in draft hydrogen standards such ANSI/CSA HPRD 1 and EIHP Rev. 12b. They are also qualified with individual fuel tank designs in accordance with the engulfing bonfire requirements in various published/draft tank standards such as CSA B51 Part 2, JARI S001, SAE TIR J2579, ANSI/CSA HGV 2, ISO DIS 15869.2 and EIHP Rev. 12b. Since 2000 there have been over 20 documented NGV tank failures in service, 11 of which have been attributed to vehicle fires. This paper will examine whether currently proposed hydrogen performance standards and installation requirements offer suitable fuel system protection in the event of vehicular fires. A number of alternative fire protection strategies will be discussed including: i. The requirement of an engulfing and/or localized fire test for individual tanks, fuel systems and complete vehicles; ii. The advantages/disadvantages of point source-, surface area- and/or fuse-based PRDs; iii. The use of thermal insulating coatings/blankets for fire protection, resulting in the NON-venting of the fuel; iv. The specification of appropriate fuel system installation requirements to mitigate the effect of vehicular fires.