Since natural gas rises, the concentration is not likely to reach its flammable range anywhere other than near the release point, unless you are in an enclosed space.If the tank is punctured you will see frost appear and hear the gas release.Despite being stored as a liquid there is very little chance of it leaving the tank in that state.It vaporizes so quickly it will exit as a gas at a low pressure and rise.Any visible vapor cloud is condensed moisture from the air.The edge of that cloud falls within its flammable range.