Not true. LNG, Liquified Natural Gas won't even burn. It has to be vaporized first.
LNG is at -260°F, so when it leaks out and is exposed to outside air, it quickly warms up, becomes a vapor and can be ignited.
But before the methane vapor will ignite, it has to be mixed with air down to 15% concentration. By the time you get to a mixture that 85% air, the methane is so light it has risen up away from any leaking vessel on the ground. If it gets below 5% concentration, it can not be ignited either.
Because of these physical properties, it is very safe. However, a vessel that has been unloaded, is going to be full of vapor, not LNG. That is the more dangerous condition.
Is LNG flammable? / Is LNG explosive?
http://www.energy.ca.gov/lng/faq.html#900
Thank you for the info. I just remember years go people worrying about LNG tankers being blown up by terrorists in Boston harbor, etc.