A burst pipe probably caused the March 29 fire that injured a worker and seriously damaged the Evergreen Oil plant, fire officials said.
The pipe, which was 3 to 4 inches in diameter, was carrying de-gassed oil from a heat exchanger to a reactor vessel, said Holly Guier, Alameda County deputy fire marshal.
The oil that escaped then caught fire.
Guier said the investigation is still preliminary. It's not known yet what caused the pipe to break. She said it was possible the pipe, which was installed about 1990, had lost some of its inner wall thickness.
The fire damaged pipes, vessels, pumps, wiring and other equipment in both sections of the plant, said Bob Gwaltney, manager of Evergreen's Newark plant on Smith Avenue.
Gwaltney said the plant's other facilities, including wastewater treatment and hazardous waste treatment, are still operating.
However, the plant's refining process, which re-refines 13 million gallons of used oil every year, remains shut down. The plant, one of the largest of its kind on the West Coast, according to the company's website, is still accepting used oil from the public and is selling the unrefined, recycled oil as fuel.
Gwaltney said Evergreen is working with state regulators and city officials in the investigation.
"We are working to ensure that something of this nature never happens again," he said.
Officials said it will probably be months before the refining process at Evergreen is started up again.
The safety investigations need to be finished first. Then, Evergreen must obtain a permit from the city before it begins demolishing, repairing and replacing the damaged equipment.
Krisann Chasarik, a spokeswoman for Cal-OSHA, said it would be at least three months before her agency is finished with its investigation. She wouldn't comment on what problems, if any, Cal-OSHA had uncovered.
Alameda County Fire, the Alameda County Environmental Health Department and the city's building department are among the agencies involved in the investigation.
Newark City Manager John Becker said the city wants the plant to take advantage of this downtime to fix any problems that may exist.
Neighbors have complained about odors coming from the facility for years. The plant has been fined by state agencies on numerous occasions.
"We want to get to the bottom of this, so we don't have a repeat," said Becker.