An extensive debate on the safety of allowing tractor-trailer vehicles to carry liquefied natural gas (LNG) on highways and through cities currently is raging. LNG is a very unstable substance. It can ignite on contact with oxygen alone on some occasions, and even if this is not the case there are often plenty of sparks, smoke and small fires to help ignite the substance in a major semi-truck accident.
This has lead to a number of regulations proposing “safe” routes for the transport of such goods. But some debate participants say these routes are nowhere near safe enough. European standards, for example, require much greater distance between LNG transport routes and hospitals or schools than current American standards.
The danger comes from multiple sources. The first is the LNG itself. Cooled to an incredibly low temperature, LNG is so cold that direct exposure from a spill usually kills on contact. Further, if the LNG ignites, the consequences could be extreme. It will burn as a pool fire, which is to say that while the liquid itself will not burn, the vapor that results will. Then as the vapor burns, it evaporates and consumes more of the fuel, creating a flame that has to burn itself out; in fact, standard firefighting practice advises waiting it out rather than trying to suppress it.
The extreme heat from an LNG fire often will burn people right through their cars, and from a considerable distance away. Second-degree burns occur within 30 seconds at any reasonable distance.
Advocates of LNG transport point to the extremely good safety record of LNG transport for the past 50 years, indicating there has only been one accident thus far in which the gas vaporized, and in that case no one was injured. They make an appeal that people should consider the probability, rather than focus on the consequences alone.