Terrorism Ruled Out In Texas Blast

Federal Officials Examine History Of Accidents During Refinery Maintenance

(CBS/AP)  FBI agents have ruled out terrorism, but federal regulators estimate it will take them months to determine what caused an oil refinery explosion that killed 15 and injured more than 100.

Investigators from two agencies, the Occupational Safety and Health Administration and the U.S. Chemical Safety and Hazard Investigation Board, arrived Thursday at the 1,200-acre BP plant to start sorting through the debris.

Also Thursday, an FBI spokesman in Houston dismissed a statement posted on an Islamic Web site claiming responsibility for the blast. He said there was no indication of foul play.

Wednesday's blast came during a maintenance period in an area that boosts the octane level of gasoline. An explosion happened during a maintenance period the same time last year, but no one was injured.

"History has shown that many of these kinds of accidents tend to happen before, during or after a maintenance turnaround," said Angela Blair, lead investigator for the Chemical Safety Board.

CBS News Correspondent Lee Cowan describes the scene of the blast as leaving a crater so deep that it looked as if the nation's third largest refinery had been struck by a meteor.

"First I heard a little small explosion, five seconds later, you hear a big explosion knocked everybody's hard hat off and people are falling down, and the next thing you know people are running and I'm just trying to run with everybody else," said Tory Scott who works at the plant.

About 1,100 employees and 2,200 contract workers were on site when the explosion took place, shortly before 1:30 p.m. Those killed were all contract workers. It was not immediately known who employed four, but 11 worked for J.E. Merit Constructors Inc., a subsidiary of Jacobs Engineering Group Inc. in Pasadena, Calif.

Jacobs CEO Noel Watson said Jacobs was not performing any work on the unit that exploded, but "a number of our employees were meeting in a staff office trailer about 150 yards from that unit."

Refineries throughout the United States commonly use contract employees during so-called turnaround periods, when routine maintenance is completed, she said. Most refineries operate around the clock for 18 months to five years before taking equipment down for repairs, Blair said.

"It's clear that we have a lot of work to do in the coming days to make sure we understand exactly what happened, and we're going to do that," BP America President Ross Pillari said. "We are going to put all of our resources into it."