The U.S. Department of Homeland Security has been forced to acknowledge that point as local and state officials grapple with concerns about the potential fire dangers posed by LNG tanker ships.

However, in its letter to a Massachusetts congressman last month, the department also asserted that a foam fire is "highly unlikely" due to the ships' double hulls and protective steel that covers the insulation.

Coast Guard officials supported that argument yesterday and also said that the polyurethane foam used on some tanker ships is quite different from and less flammable than the foam that helped spread the deadly blaze at The Station nightclub last year.

"We feel very comfortable with the safety and security measures we have in place," said a Coast Guard spokeswoman, Jolie Shifflet. "We'll do everything that we need to do. We're not looking at changing the design standards for LNG tankers."

U.S. Rep. Edward J. Markey had sought clarification on the matter because of concerns about the potential for a catastrophic fire being fueled by spilled LNG in the aftermath of a terrorist attack on a tanker ship.

The possibility for such an event, however unlikely, is also on the minds of officials in Fall River and Providence, where developers have proposed LNG port facilities similar to the Everett terminal in Markey's district.

Under certain conditions, a large spill of liquefied natural gas is capable of turning a small flame into a huge blaze and burning people up to a mile away, according to a report commissioned by the Federal Energy Regulatory Commission last spring.

That study is based on a spill involving just one of the five tanks on the typical tanker, which carries about 30 million gallons of LNG.

But since last February, a University of Arkansas professor, the same expert who authored the government's methods for assessing such incidents, has warned that such a fire could be far bigger.

The professor, Jerry Havens, argues that the initial fire could melt the foam insulation around the ship's other LNG tanks.

This would warm up the LNG inside the tank, causing it to vaporize, to turn from a liquid into a gas. This could greatly increase pressure on the tank's walls, he says.

LNG tanks have emergency valve systems for releasing gas into the atmosphere if a tank should fail to keep the cargo cool enough to prevent vaporization.

But Havens said he believes the systems aren't capable of relieving the levels of pressure that can build up if too much insulation burns away or melts.

"The tanks might be subject to rupture," he said.

Federal officials seem to be more optimistic, however.

Pamela J. Turner, the homeland security official who responded to Markey's questions on the subject, said the government sought feedback from the manufacturers of LNG tankers.

The response was that the tanks should be able "to withstand the expected fire load ... without over-pressuring the containment system," Turner wrote in a lengthy letter to Markey on Sept. 13.

The Coast Guard regards "the breach of an LNG cargo tank to be unacceptable" and has "implemented the most rigorous safety and security measures possible to prevent this from occurring," Turner wrote.

The Journal obtained a copy of the letter from the Coast Guard yesterday.

The letter corrects some erroneous information that the department had supplied to Markey on Aug. 30.

At that time, the department had asserted that foam polystyrene was not used on LNG carriers.

Turner also notes that scientists at Sandia National Laboratory are investigating the survivability of cargo tanks after the loss of insulation to a fire.

So far, the tanks have proven solid and impervious to fire under various simulations, according to Coast Guard Commander Bruce Graham.

Graham, an LNG specialist, also said the valve systems on LNG tanks can function effectively without any insulation to keep the contents sufficiently cool.

"That was one of the few things that did come out of our Sandia testing so far," said Graham.

Graham also explained the difference between the particular type polyurethane foam sometimes used to protect LNG tanks and the notorious type that played into the deaths of 100 people at The Station last year.

The highly flammable foam at the nightclub caught fire during a pyrotechnics display.

The tight, dense construction of foam for insulating LNG makes it less flammable, Graham said.

"There's no question," said Graham, "that by making any of these substances good insulators also leads them to be somewhat poor in the flammability range. But not so poor as the stuff you're going to use for soundproofing."