02e39f42_stem_Risks_of_Alternative_Fuel__Background
[Hazard --Event] Vehicle fire --from fuelsystem leaksdue tocomponentfailure. [Consequences] Fires from liquid fuels are limitedby the relatively slowevaporation of the fuel. Forgaseous fuels, this limitationdoes not exist and large firescan develop quickly. [Knowledge] An example of componentfailure is the PRD failuresobserved in CNG transit buses. An early review of natural gasvehicle safety concerns is givenin. . "Natural Gas Fuel Tanks for Automobiles: Safety Problems," F.A. Jennings and W.R. Studhalter, ASMEpaper 71-PVP-62, May 1971. [Background] 
The use of compressed natural gas fuelinvolves materials and components which havenot been generally used on motor vehicles. And new component designs may not provereliable. An example, is the number (at least50) of Mirada PRD. A pressure relief device (PRD) is connected to a compressed gas cylinder to relieve excess pressure. PRDsmay act from excess pressure through the use of a burst disk, or from excessive temperature, through theuse of a fusible plug. Most PRDs used on CNG vehicles incorporate both types of protection. failures observed intransit bus fleets in 1993-1994. Each of thesefailures resulted in a major fuel release.
Clean Air Program -- Assesment of the Safety, Health, Environmental and System Risks of Alternative Fuel
Background