LNG tankers routinely come in & out of Boston harbor, and I was a USCGAUX volunteer there for much of the 90’s ‘ early 2000’s. We would provide USCG escorts as they transited the harbor, as they have security zones for a mile or so in front of them. Our job was to shoo all the other boating traffic away from it well in advance.

After the 9/11 attacks there was a huge uproar from folks who were convinced one well aimed hand grenade would be enough to detonate one of these tankers with enough force to flatten downtown Boston. I recall the newspapers, local TV news, etc. all interviewing experts that said such an explosion was virtually impossible, and a burn-off like what happened here was the most likely outcome.

To become truly explosive, natural gas has to mix with an appropriate amount of oxygen, and for the LNG in a tanker to reach that state it would have to boil off a huge amount in such a way that the cloud of gas remains intact for a long time. You would need no winds at all for hours to reach that state, and then after that you would need an ignition source. When liquified natural gas ignites it is so condensed that it just burns.