"Cal-OSHA would benefit from greater process safety staffing with expanded technical qualifications," Tillema wrote.
Chevron had performed internal reviews of its pipe system, which resulted in a 2009 memo calling for a comprehensive inspection to ensure the pipes weren't corroding to dangerous levels.
"This (recommendation) was not implemented by the Chevron Richmond Refinery, and neither Contra Costa (County inspectors) nor Cal-OSHA was aware of this memo," Tillema wrote.
Chevron did not return a request for comment.
Erika Monterroza, a spokeswoman for Cal-OSHA said the agency is reviewing the board's findings.
"As for this incident, we issued 25 citations, 23 of them for serious and willful violations with penalties of nearly $1 million, demonstrating that we take our enforcement obligations seriously," Monterroza said.
Cal-OSHA on Friday approved Chevron's request to restart production in the crude unit destroyed in the fire.
Chevron has said it plans to resume operations by the end of June.