I remember when I guy in Whitefish MT parked his LPG fueled truck in his garage, and it leaked. when the propane gas reached the pilot light on the water heater, the garage exploded, along with the house. It broke windows several blocks away.
As for Natural Gas, if you had it in a tank, it was CNG. If it wasn't compressed, it would not flow out of the tank. LNG., however, is an entirely different thing. I don't know if Liquified Natural Gas has ever been used as a motor fuel.
I googled it, but the site wouldn't load. Apparently, it has been or can be used as motor fuel.