Safe Harbor?

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.

  • Robert

    Skikda, Algeria, had a catastrophic LNG accident in 2004, that killed 26 workers and injured 74.

  • Robert

    LNG storage tanks contain vapor (called “boil off”) at the top, above the liquid. It does not require pouring onto land or water to vaporize — it simply needs a slight rise in heat.

    The statement about a lit cigarette and LNG vapor flammability give a false impression of safety. Liquid gasoline will not burn until it vaporizes, either.

    LNG vapor is 3.7% more flammable than gasoline vapor. Methane (LNG) has a fuel-to-air flammability range of 5% to 15% (a 10% range), while gasoline has a flammability range of 1.4% to 7.6% (a 6.2% range). Neither will burn or explode outside those ranges.

    The Federal Government has defined LNG ship Hazard Zones that extend 2.2-miles from the ship. The hazards within those zones include cryogenic burns, asphyxiation, fire, thermal-radiation burns, and explosion.