RICHMOND -- Chevron Corp. has paid about $10 million and begun "corrective actions" in the aftermath of last summer's refinery fire, sparked when a corroded pipe leaked high-temperature gas oil, according to a report the energy giant filed with the Contra Costa County Health Services Department on Monday.

Among the changes made at the 245,000-barrels-per-day refinery are expanded testing to detect thinning pipes, new leak-response protocols and increasing employee training, according to the 11-page report.

The payouts result from 23,900 claims from affected residents, area hospitals and local government agencies. More than 15,000 people went to area hospitals in the hours and days after the Aug. 6 fire, which spewed a plume of black smoke that was visible for miles. Several workers also suffered minor injuries.

Chevron has not revealed how many total claims it received.

Chevron spokesman Sean Comey said Monday that most of the $10 million the company has paid "went to local hospitals for medical exams and treatment immediately following the incident."

Comey said the safety upgrades would address carbon steel piping with low-silicon content, which he said is susceptible to accelerated corrosion when exposed to "high-temperature sulfidation."

"This thinning was not readily detected by existing corrosion-monitoring locations on the pipe segment that failed," Comey wrote in an email. "To address this issue, the company has begun inspecting all components potentially susceptible to accelerated (high-temperature sulfidation) corrosion and will complete inspection of all such components in the No. 4 Crude Unit before restarting the unit. ... This inspection standard is being applied throughout our global manufacturing system."

Critics allege that Chevron operators failed at multiple levels leading up to the fire, including spotty testing of old pipes for strength and thickness and failing to promptly shut down the unit when it sprung a leak.

Asked whether the leak-response changes suggest that operators should have shut down the unit earlier on Aug. 6, Comey wrote, "We're enhancing leak response protocols to ensure appropriate process safety information is considered when evaluating leaks (and) reinforcing the authority that everyone has to issue immediate stop work authority and initiate a shutdown if conditions warrant."

Chevron critics on Monday were unmoved by Chevron's report, which Contra Costa Health Services requires as part of its Hazardous Materials Notification Policy.

"Chevron's profit motive is what drove them to operate this refinery to the point of structural failure," said Andres Soto of Communities for a Better Environment, a local watchdog group. "The risks posed to the workers and community remains unabated, and Chevron has a habitual pattern of lying to the community about operations."

Soto added that he is hopeful that independent investigations by the state Division of Occupational Safety and Health (Cal/OSHA) and the U.S. Chemical Safety Board will reveal more information about the fire and lead to fines and sanctions. Both agencies are expected to issue findings in the coming weeks.

Richmond passed an ordinance in November requiring that Chevron use the "best available technology" in rebuilding the crude unit, work that requires building permits from city staff.

Chevron also faces lawsuits headed by high-profile attorneys stemming from the fire. Tony Buzbee of the Buzbee Law Firm in Houston announced in November that he and John L. Burris of the Oakland-based Burris Law Firm are suing Chevron. The attorneys, who have more than 4,800 clients and two cases set for state court, allege that negligence led to the fire and delayed the emergency response.

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