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TV news crews, along with the curious, gather on a hillside in Point Richmond to photograph the the fire in an oil unit at the Chevron refinery in Richmond, Calif., Monday, Aug. 6, 2012. (D. Ross Cameron/Staff)

RICHMOND -- Chevron's top official at its local refinery said the company has identified "contributing factors" in the pipe failure that triggered a massive Aug. 6 blaze that shut down a crude unit and sent more than 15,000 people to area hospitals.

The pipe had a low silicon content, making it more susceptible to corrosion, refinery General Manager Nigel Hearne said Monday.

"We suspect the general thinning of the piping component," Hearne said, adding that the problem eluded Chevron's standard tests.

"It does not appear this information was fully understood and acted upon," he said, calling the thinning process "high temperature sulfidation corrosion."

During the news conference in a cafeteria on Chevron's Richmond property, Hearne also took on recent news reports and a local regulatory agency that has accused Chevron of intentionally flouting air quality regulations in recent years.

While not providing specifics, Hearne said Chevron had provided the San Francisco Chronicle with "additional details" not included in a recent report by the newspaper that revealed Chevron is the subject of a criminal investigation for failing to monitor pollutants released by one of its pipes. The probe by the U.S. Environmental Protection Agency focuses on emissions, or flaring, not recorded by air monitors as required by the Bay Area Air Quality Management District, resulting in $170,000 in fines.

"There is no reason that the company would have acted as the article suggests," said Hearne, adding that Chevron became aware of the EPA investigation a couple months ago.

Monday's news conference followed the report of the criminal investigation that has emboldened critics of the 245,000-barrel-per-day refinery. At a community meeting at the Richmond Memorial Auditorium on Monday night, Chevron spokeswoman Heather Kulp drew scattered heckles while delivering the same statements Hearne provided the press earlier in the day.

"As shocking as these new revelations are, I think most people think this is just the tip of the iceberg and there is a lot more shocking news to come," said Andres Soto, a local activist and founder of Communities for a Better Environment. "They have no credibility."

More than 150 residents turned out for the public meeting Monday night, which was hosted by federal, state and county agencies involved in the fire response and investigation. Cal/OSHA Chief Ellen Widess told the crowd that the fire at the Richmond refinery, Chevron's oldest, has exposed what may be a larger problem of thinning pipes passing through inspections. Widess said her agency has now expanded its investigation to Chevron's refinery in El Segundo and discovered "similar problems."

Also Monday, Assemblymember Nancy Skinner and state Sen. Loni Hancock, both Berkeley Democrats, called for a state hearing on steps government agencies are taking to prevent incidents like the Chevron fire.

Hearne said the purpose of the afternoon news conference was to highlight three main points: The company has identified "contributing factors" to the Aug. 6 blaze; safety is a core value; and the energy giant is continuing to cooperate with several federal, state and local agencies in their investigations.

Earlier Monday, an air quality district official said Chevron knowingly flouted regulations aimed at improving air quality.

"(Chevron) knew they were flaring, and they knew that unmonitored flaring was not legal," said Wayne Kino, an enforcement manager for the district.

Kino added, "certainly, upper management" was aware the refinery was using a 3-inch unmonitored pipe in violation of a 2005 air quality district rule intended to reduce flaring and emissions at Bay Area refineries.

Hearne denied any willful flouting of the law, contradicting statements in the press and by the air quality district.

"We did not recognize the need for a meter on this line and we advised (the air district) of this issue three years ago and remedied it then," Hearne said.

Hearne said Chevron officials alerted air quality control district inspectors "as soon as we knew the source of the unmetered flare."

"We need to find out why it was not identified," Hearne said, adding that emissions from the unmetered flare were so low that they "presented no public health risk."

Hearne said inspections of the pipe that failed and caused the fire were conducted as recently as June. The pipe is 200 feet long, Hearne said, and it was inspected for thickness at 19 locations.

"Unfortunately, we did not inspect a 5-foot length" of the pipe that failed in August, Hearne said.

U.S. Chemical Safety Board inspector Steve Cutchen said Monday night that internal Chevron procedure documents indicate that "every section (of the pipe)" should have been inspected."

Representatives from all the major agencies investigating the fire gave presentations Monday night, including Contra Costa Health Services, Contra Costa Sheriff's Office of Emergency Services, Environmental Protection Agency and Chevron.

Contact Robert Rogers at 510-262-2726 or rrogers@bayareanewsgroup.com. Follow at Twitter.com/roberthrogers.