Two workers were sprayed by sulfuric acid at Tesoro Corp's Golden Eagle refinery in Martinez, California, on Monday, the second such incident in less than a month, according to state regulators.
A Tesoro spokeswoman, however, would not identify the chemical which the two contract workers were exposed to while carrying out maintenance on a unit at the Martinez refinery.
"The contractors were doing maintenance, with full protective safety equipment worn," Tesoro spokeswoman Tina Barbee said in a statement. "They were decontaminated in a shower and have been transported to a local medical facility."
Lacey Friedman, a Contra Costa County hazardous materials specialist, said in a telephone interview that one of the workers has been released while the second remains in a hospital under observation.
An initial description of the accident released by the Contra Costa County Hazardous Materials Program said one of the workers was "saturated" by the acid.
On February 12, an alkylation unit involved in gasoline production was shut at the 166,000-barrel-per-day Martinez refinery after a sulfuric acid release injured two workers.
Tesoro told the Contra Costa County Hazardous Materials Program on Monday that the latest two workers were sprayed with the acid while working on the alkylation unit, Friedman said.
"We believe it was the same unit, but a different process area from the sampling area," Friedman said.
A spokesman for the California Division of Occupational Safety and Health (Cal/OSHA), which is investigating the earlier accident, said the agency was told the workers on Monday were sprayed by sulfuric acid from the alkylation unit.
"We've issued an order to preserve the site of the incident," Cal/OSHA spokesman Peter Melton said.
That order does not prevent Tesoro from operating the unit, he added.
In the February 12 accident, two workers were testing material produced by the alkylation unit in a sampling area. The alkylation unit uses sulfuric acid to convert refining byproducts into octane-boosting gasoline blending components.
The workers who were sprayed with acid were treated at a hospital, then sent home to recover. That accident triggered a dispute between the U.S. Chemical Safety Board (CSB) and Tesoro, in which the company temporarily blocked board investigators from the refinery.
In a letter to Tesoro about the dispute, board members wrote that Martinez refinery workers told the board that being sprayed with acid was a common occurrence and that they lacked face shields and protective clothing for tests on the alkylation unit.
On Monday, the CSB said an investigator was expected to be in Martinez by Monday night to look into the latest incident.
A board spokeswoman said in a statement that refinery managers worked with board investigators last week, though some key documents including a recent survey of safety culture had not been provided.
"One eye-opening document that the team did obtain is a Tesoro engineering calculation estimating that 84,000 pounds of sulfuric acid were released in the February 12 incident - hardly the minor release that Tesoro has been describing to the public," said the CSB's Hillary Cohen in a statement.
Tesoro's Barbee said Monday's accident "is believed to be unrelated to the chemical release that occurred on February 12."
The company has said that after the earlier accident the refinery followed industry standards for safety and had reviewed safety procedures with employees, including the use of protective equipment.
The February accident is still being investigated by Cal/OSHA, which will begin a separate probe of Monday's incident, Melton said.
Each investigation must be completed within six months of the date of the accident.
Under federal law, the board works to determine the causes of U.S. chemical plant accidents. It has no regulatory or law enforcement authority.
The CSB is still completing a report on a deadly 2010 explosion at Tesoro's refinery in Anacortes, Washington. Seven refinery workers died of injuries sustained in the accident.
(Reporting by Koustav Samanta in Bangalore and Erwin Seba in Houston; Editing by Richard Chang and Richard Pullin)