"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.
White House Program Cuts Up to $1k off Monthly Payments! (3.05% APR)