Metro Rail Tunnel Fire Ruled Accidental : Report: A metal-cutting torch, not arson, probably was to blame. The Fire Department confirms results of earlier probe.

Fire officials have concluded that a $2.2-million underground blaze that gutted an unfinished section of the Metro Rail last summer was accidental, probably caused by a metal-cutting torch or hot chunk of metal that scorched the subway tunnel’s wooden supports and ignited a plastic lining.

In a 100-page report released Tuesday, an investigator for the Los Angeles Fire Department ruled out arson. He theorized that the wood supports smoldered for as long as eight hours before igniting the plastic.

Deputy Fire Chief Davis R. Parsons, the city’s fire marshal, said the burning lining produced a fire that took almost no time to become a major conflagration.

“Once it starts to burn it begins to drip very rapidly, and once it drips and pools it’s just like gasoline,” he said. “. . . Then we have a fire that really begins to rip.”

The investigation, which included an examination of soil samples and a look at the electrical system in the subway tunnel, ruled out methane gas as a factor.

To a large extent, the Fire Department’s conclusion confirmed the results of an earlier probe commissioned by the Los Angeles County Transportation Commission, which oversees Metro Rail.

That report, issued in September, was conducted by the Rail Construction Corp., a subsidiary of the transportation board. Ed McSpedon, president of the corporation, said its investigation focused on why the fire spread so quickly, rather than its cause.

“We’re pleased that the Fire Department has come to exactly the same conclusion that we had,” McSpedon said Tuesday. “The most important thing for us was that they came to a conclusion that methane gas played absolutely no part in this fire.”

The July 13 blaze destroyed a 750-foot stretch of tunnel beneath the Hollywood Freeway in downtown Los Angeles, leading to closure of part of the freeway for three days. It was a major setback for construction of the first 4.4-mile phase of the $1.4-billion project, which is running millions of dollars over budget and months behind schedule.

McSpedon, whose agency took control of the project shortly before the fire, said that construction crews now are required to employ safer methods, including additional fire watches and the use of concrete supports instead of wood.

“We’ve changed the whole design of these tunnels so that there is nothing left to burn,” McSpedon said.

McSpedon acknowledged that there were “a lot of weaknesses” in the contractor’s construction methods that may have contributed to the fire. But he was reluctant to lay blame on the firm, Tutor-Saliba-Perini.

“We have not determined that there was anything intentional or anything unreasonably negligent involved in this,” he said.

The president of the firm, Ronald Tutor, said he is not persuaded by the Fire Department’s conclusions. He believes that the fire was set, possibly by a transient.

“What’s the difference?” he asked. “It’s a tragedy. It’s part of the things that happen in a big construction project. There certainly isn’t any negligence on anybody’s part.”

The Fire Department investigation included a sophisticated analysis by the National Institute of Standards and Technology, a division of the U.S. Department of Commerce. The Fire Department requested the study to confirm its theory about the burning wood and plastic lining.

During the course of the probe, arson investigator Tom Campuzano discovered that the Fire Department had extinguished two previous subway tunnel fires, both involving cutting torch operations.

And those, he wrote in his report, were not the only such fires.

“In the numerous conversations with the mine and construction workers on the site, I was told that fires caused by cutting torch operations happened all the time and were extinguished by the workers themselves.”

The report said that two workers who were installing the plastic lining on July 12, the day before the fire, told investigators that they had used cutting torches to cut steel hooks off the large steel rings that form the body of the tunnel. The hooks are used to hang utility lines, but once the tunnel construction is finished they must be removed in a process known as “smoothing.” Afterward, the plastic lining is installed.

The workmen finished hanging about 200 feet of lining at 6 p.m. on July 12. By that time, investigators theorized, the wood was already smoldering, although the workmen did not know it.

Several hours later, investigators wrote, a workman walked through the tunnel. “He stated that he smelled something and thought that it was unusually hot in the tunnel,” the report said. “He even went to the trouble of feeling the walls but did not detect anything. He again walked through the tunnel at (11:30 p.m.) and detected an unusual stench.”

At 2 a.m., a wall of flames was discovered by six workers who had been in an adjacent tunnel.