LNG stands for liquified natural gas. It's a cryogenic (super-cooled to -275 degrees or so) natural gas. It's super-cooled to turn it into a liquid for transportation and storage purposes (takes up a lot less space, that way). While there may be attempted terrorist activities at one of the conventions, the scenarios played out here are pretty speculative. It sounds like Boston will be a nightmare during the convention, and the confusion created by the security measures would, IMHO, be one of the best tools for the terrorists.
I'd watch support staff at the convention center like a hawk. There's an old saying, "You can go anywhere in the world with a maintenance uniform, a handtruck and a clipboard."