Marine CNG
In the mid-80's, a number of boat builders (like Sabre) used CNG precisely because it is lighter than air and thus does not settle in a bilge ready to explode when a source of ignition appears. However, so the story goes, tanks are more expensive than for propoane and the propane equipment manufacturers managed to lobby through expensie and supposedly unnecessary requirements on the use of CNG such that boat builders went back to the cheaper and supposedly more dangerous propane. For whatever reason, CNG never really caught on and as a result, it is not widely available, thus further contributing to its lack of popularity. It is pretty expesnive to convert a CNG stove to propane, so most folks who have CNG hang onto it if they're near one of the few suppliers. Perhaps CNG will come back because its the same fuel now being used on many urban bus systems and natural gas cars. Unfortunately, the converter needed to fill your marine CNG tank at a bus garage costs as much as a few year's worth of propane.
