OK I am full of crap on this subject. It may have been an ammo ship that went up in the northeast. I know methane used to work in the coal mines. Also knew that the ratio had to be reached to explode it. But with the correct ignition source are you saying it can not ignite? First explosion releases the gas, delayed second explosion ignites the gas after the air fuel ratio is reached. Not possible?
Methane, refrigerated down to a liquid at -260°F will not ignite.
The vapors that come off it are pure methane gas and will ignite when diluted sufficiently with air, but has 47% the density of air so it rises up and away rather quickly.
Natural Gas needs to be contained to create a explosive pressure wave. Unconstrained, it burns and burns rapidly, but it is not an explosion.
LNG SAFETY MYTHS and LEGENDS
http://www.netl.doe.gov/publications/proceedings/02/ngt/Quillen.pdf
Another point to consider:
LNG has 88% the energy per gallon compared to propane.
LNG has 64% the energy per gallon compared to gasoline.
LNG has 58% the energy per gallon compared to diesel.
If all the others are okay for ship transport into the harbor, why is the one with the least amount of energy, and won’t even burn, a concern?
If you are willing to spend 10 minutes, the video at the link below does a great job of explaining why LNG is a relatively safe method of transporting energy.
http://www.freeportlng.com/safety_information.asp
The video includes putting out a cigarette in the LNG and drinking a glass of water after pouring LNG on top.