The NTSB also said PG&E exploited the lack of monitoring by regulators, who mistakenly placed "blind trust" in the utility.
The report made on Aug. 30 concluded that poor pipeline welds went undetected because of a lack of inspections by the company and inadequate monitoring by state and federal regulators. The utility also lacked a workable emergency response plan that board members said could have helped to prevent the devastation in the city of San Bruno.
"This represents a failure of the entire system - a system of checks and balances that should have prevented this disaster," said Robert L. Sumwalt, an NTSB board member. "The seam weld may have been the technical reason, but this was an organizational accident."