OOSC, Part II, Item 7. Fuel Systems - LNG Fuel Systems

Recently this publication of yours (Appendix A, North American Uniform out-of ¦service-criteria) was forwarded to us by one of our customers. There is a lot of confusion on the fuel system section for vehicles that use LNG fuel systems. Under the LNG section there are three criteria used to put a vehicle out of service. a) A cloud of water vapor coming from any component of the fuel system. b) Any leak detected by a methane detection meter. c) Dripping liquid that boils or vaporizes in the air. While a) and c) would both indicate large leaks that need immediate attention b) is quite ambiguous. Since most methane detectors measure levels in parts per million in air they are sensitive to leaks that pose no hazard whatsoever to the vehicle or persons in it. It seems that this provision should be replaced with one that states a leak size as opposed to an overly sensitive leak detection method. As the engineering manager for the worlds largest manufacturer of LNG vehicle tanks I deal with this type of question quite often. Here is a link to our Vehicle Tank Operations Manual it should give you a good deal of insight on LNG vehicle tanks. Pg 15 and 16 deal specifically with the subject of leaks. To summarize I think you should include audible leaks in this criteria. Audible leaks are quite large and always flammable in air. However, leaks below 25 cc/min are not flammable in air and pose little more than an economic nuisance to the vehicle owner. We recommend that leaks less than 25 cc/minute be fixed during a scheduled maintenance interval on the vehicle. Leaks less than ® cc/minute can be ignored completely. They are so small that the people inside of the vehicle are giving off more methane than the leak. The easy way to identify these extremely tiny leaks is with bubble test solutions. Leaks larger than ® cc/minute bubble up at the site of the leak. Leaks of the 1/2 cc/minute size form a chain of tiny (pinhead size) bubbles that flow away from the leak.

Currently creating a lot of confusion and waste of time and effort chasing non¦-hazardous leaks on LNG vehicle systems. It also gives the false perception that gaseous leaks are more hazardous than liquid fuel leaks due to the lack of parity with gas or diesel requirements.

Define a leak criteria for LNG fuel systems that is similar to the one for liquid fuel systems taking into account the actual hazard presented by the size of leak encountered.