RICHMOND (CBS SF) – Corrosion that damaged a steel pipe led to a disastrous fire at Chevron’s Richmond refinery last August, oil company officials confirmed in a report released Friday.

The investigation report was submitted to Contra Costa Health Services on the Aug. 6 refinery fire that sent a toxic plume of smoke into the air and some 15,000 people to hospitals complaining of breathing problems.

READ MORE: Fourth Stimulus Check: Is Another Relief Payment Coming?

In the report, Chevron representatives said that damage to the crude oil pipe was not appropriately documented after inspections in 2002 and 2011.

The oil giant’s report, based on findings from Chevron technical experts and members of the United Steelworkers Union, also lays out a list of corrective actions to prevent future leaks from occurring and to improve safety procedures.

“We have identified what went wrong and are taking steps to prevent a similar incident in the future,” Nigel Hearne, the refinery’s general manager, said in a statement.

“The causes of the incident were multi-faceted,” Hearne said. The refinery’s management and our entire workforce are implementing actions to address the issues underlying the August incident and as part of our commitment to continuous improvement.

Hearne said Chevron will improve its inspection procedures and is inspecting every pipe in the facility.

READ MORE: Unique Twist To Pandemic Shutdown Of Long-Establish Santa Clara Restaurant

The report’s conclusions echo some of the findings of prior investigations into the refinery fire conducted by the California Division of Occupational Safety and Health (Cal/OSHA) and the U.S. Chemical Safety and Hazard Investigation Board, or CSB.

A report issued by the federal and state agencies in February stated that severe corrosion was found on the pipe that leaked oil, sparking the catastrophic fire last August.

Last week, representatives from Cal/OSHA and the CSB attended a legislative hearing in Richmond during which Contra Costa County officials said they plan to conduct an extensive audit of the refinery.

The CSB will hold a public meeting in Richmond next Friday to release findings from its ongoing investigation into the refinery fire and safety recommendations.

Andres Soto of Communities for a Better Environment questioned the timing of the report.

“This report is smoke and mirrors as a PR strategy in advance of the Chemical Safety Board hearing which is taking place next week. The staff is going to be making recommendations that will impact the entire industry of refining across the nation,” Soto said.

In January, Cal/OSHA fined Chevron $963,200, the agency’s largest fine and the maximum legally allowed, for 25 alleged worker safety violations that occurred before, during and after the pipeline rupture.

Chevron has said it will appeal some of the citations.

MORE NEWS: Hunting Mountain Lion Videotaped On San Carlos Home Backyard Security Camera

(Copyright 2013 by CBS San Francisco and Bay City News Service. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)