WASHINGTON – A terror attack on a tanker delivering liquefied natural gas at a U.S. port could set off a fire so hot it would burn skin and damage buildings nearly a mile away, government scientists say in a report expected to influence where new multibillion-dollar terminals will be built.

The report from a government nuclear weapons lab, a 160-page unclassified version of which was obtained Monday by The Associated Press, characterizes an LNG tanker spill from a terror attack as a low probability. If successful, however, it would become “a high consequence event” that could produce massive injuries and property damage, the report said.

The yearlong study by scientists at Sandia National Laboratory, a premier federal research facility, provides the most detailed analysis to date of the potential public safety impact of a terrorist attack on an LNG transport tanker.

While the report does not recommend prohibiting tankers from carrying LNG through heavily populated areas, it says those shipments should occur only after “the most rigorous deterrent measures” are in place to reduce the probability of an attack.

The tankers, each of which carries up to 30 million gallons of LNG, arrive every few days at four U.S. terminals: one on Boston’s outskirts, another in Maryland and two on the gulf coast. All are expanding as regulators weigh the merits of putting more than three dozen more such facilities at U.S. ports, many in urban areas.

In its minus 260 degrees liquid state, LNG cannot explode and is not flammable. If a missile or explosive should tear a hole in a tanker or a storage tank, however, the escaping liquid would be transformed instantaneously into a gas and probably would ignite in a massive fire.

The Sandia report said terrorists, using readily available weapons and technology, could blast a 10-foot hole into the side of an LNG tanker.

The assessment evaluates a range of scenarios that would result in release of millions of gallons of LNG from a transport tanker. The scenarios include a takeover of a vessel by an insider or hijacker, external attacks using explosives-laden boats, triggered explosions or rocket-propelled grenades or missiles.

Under some circumstances an attack could produce cascading damage that could result in failure of as many as three of a ship’s five LNG cargo tanks, which would increase the fire’s intensity and lengthen its duration.

Detailed discussions of specific threats were included only in the classified version of the report, but the unclassified version examined the general impact such an attack and LNG fire on water would have to people within a mile of the spill.

“We are not recommending that there be any kind of ‘no ship zone,”‘ said Mark Maddox, a deputy assistant secretary at the Energy Department, which commissioned the study. “What we’ve learned is that we can significantly reduce the likelihood of a terrorist attack occurring with security planning and mitigation.”

Even with many details left out of the unclassified version, the report describes a harrowing potential for disaster if a terror attack were to succeed in releasing millions of gallons of LNG from a double-hulled vessel that typically carries more than 30 million gallons of the frosty liquid fuel.

The Sandia scientists identified “several credible” terror scenarios that the report said would result in at least one – possibly as many as three – of a tanker’s five cargo tanks being breached. That would ignite a pool of fire to spread several hundred yards in all directions, the report said.

While “the most significant impacts to public health” and the most severe destruction of buildings would be within a 550-yard radius of the fire, heat that could burn the skin and damage houses could extend to nearly a mile away.

The government study also confirmed the possibility raised earlier this year by some scientists that a breach of a cargo tank could cause a cascading of structural breakdowns in adjacent tanks and result in a larger release of LNG and a more intense and longer-lasting fire. Such a cascading event “cannot be ruled out especially for large spills,” said the report.

The study found that the foam insulation used on many LNG tankers is likely to decompose under intense heat from a fire, resulting in a heat transfer that “could lead to rupture or collapse” of adjacent tanks, adding to the cascading effect.

Concern about the foam was raised earlier this year by Jerry Havens, a chemical engineer at the University of Arkansas in letters to both the Department of Homeland Security and Rep. Ed Markey, D-Mass.

Homeland Security officials initially claimed tanks did not use foam insulation, only to acknowledge later that, in fact, the material was widely used.

While generally discounting the likelihood of an explosion, the report said in a large release LNG would flow into ship cavities and with the optimal mixture of fuel and oxygen, an explosion could not be discounted. That would result in more fuel being released onto the water.