Ships bringing liquefied natural gas from the Middle East pass regularly through Boston Harbor. Experts say there’s little chance of an LNG tanker going up in a fireball. Then why are city officials so worried? Should you be?
LNG ships carry four to six tanks. If about half of a single 6.6-million-gallon tank spilled from a 54-square-foot hole and the vapors ignited, the fire would “cause significant damage to structures, equipment, and machinery” within a 1,280-foot radius and leave second-degree burns on people more than three-quarters of a mile away, according to Sandia’s study, which measured impact on open water. In a city, variables such as buildings would affect the fire’s path and intensity. Sandia’s worst-case scenario measured the result of LNG spilling simultaneously from three tanks, which “would set structures aflame out to 2,067 feet and burn people as far as [1.3 miles] away,” says study coauthor Mike Hightower. Sandia is now studying scenarios in which tanks are breached successively. Results are expected this summer.
1. LNG immediately begins to evaporate when it spills. A vapor cloud forms and grows, and you hope there’s no spark. Even with a spark, only the cloud’s edges, where 5 to 15 percent of the air is LNG, can ignite. Yet if that part catches fire, the whole thing burns.
2. In an attack, a spark would probably be present as the LNG began to spill, so a fire would start right away. Because the LNG hits the water faster than it all can evaporate, it would form a pool on top of the water. As more spilled, the pool — and the fire — would grow.
3. The LNG would continue feeding the blaze (imagine the fire being attached to the pool) until all the fuel evaporated and burned off, which could take anywhere from three to forty minutes. By then, anything within reach could have ignited and set off other fires.