I'm not sure what it takes to blow up an LNG tanker. In fact, not sure it blows up, implodes, explodes, condenses or combusts. Any experts out there?
What happened to the one off the coast of Virginia last winter? Or was it just a fire on board?
For max effect (and this is no secret,by the way) you need to ring the cryo tank with explosives to heat it up as it is being released (a necklace?), then ignite it before it vaporizes and mixes with the atmosphere too much. For the most damage to occur, the flame needs to blow outward along an already expanding wave front of gas and not consume it before it reaches its max diameter.
It is the security implications of handling LNG that concern US security officials. Specialists calculate that a terrorist attack on a LNG tanker would have the explosive force equivalent of a small nuclear explosion.
http://www.janes.com/security/international_security/news/jtsm/jtsm040706_1_n.shtml
First the container must be punctured/ruptured to release the LNG. The LNG will rapidly go to a gas form. If it encounters a flame/ignition source where there is adequate oxygen to support combustion, it will ignite explosively. One review suggests that it would be like one of our fuel-air explosive bombs with the force like a small nuke.