A high-level, independent panel probing last year's deadly California pipeline explosion is urging deep reforms to fix ongoing problems at both the gas utility and the state commission responsible for its oversight.

At a meeting Thursday of the California Public Utilities Commission, panelists said the devastating blast in a San Francisco suburb resulted from a series of management and oversight weaknesses at Pacific Gas & Electric Co.

The utility commission not only lacked the resources to monitor the company's pipeline safety work, but it failed to pay attention to mounting concerns about PG&E's performance before the accident in a quiet San Bruno neighborhood, the panelists also found.

The panel did not explore the root cause of the explosion but suggested that, in its wake, major reorganizations were necessary at both PG&E and its regulator, which panelists deemed was understaffed and underspecialized.

"We seem to have drifted, both ourselves, this commission, and the ones we regulate, into a place of complacency," said the commission's president, Michael Peevey. "Just about everything you're recommending for this commission we will do our damndest to implement as soon as possible."

The Sept. 9 explosion killed eight people and sparked a fireball that torched 38 homes in the hills overlooking San Francisco Bay.

Regulators in October appointed the five-member panel led by University of California, Davis, chancellor emeritus Larry Vanderhoef to study and investigate the explosion and recommend actions for the utilities commission. Their guidance is not binding, but commission spokeswoman Terrie Prosper said the agency would likely address some of the recommendations in an ongoing proceeding.

Panelists also found that a city project to replace an aging sewer line in 2008 crossed the segment of pipe that burst last fall. Panelists said that work could have weakened that section of pipe and may have played a part in triggering the explosion.

"The panel believes third-party construction activity could have played a key role in transforming a fabrication flaw in the pipeline from a 'stable' to an 'unstable' threat, ultimately triggering the incident," the commission said in a statement released Thursday.

A top PG&E executive said the company welcomed the panel's report.

"We will move quickly to review the report's detailed findings and take further action to improve the safety, quality and performance of our gas system," said Lee Cox, interim chairman and CEO of PG&E Corp., the utility's parent company based in San Francisco.

Also on Thursday, the commission approved a proposal to require all California utilities to submit plans to pressure-test or replace any untested segments of their gas transmission lines — such as the pipe that exploded last fall.

But panelists scolded PG&E for the company's own safety and testing plan announced about a month after the accident, calling their Pipeline 2020 program "reactive."

"The document presented only addresses a strategy for system modernization and the installation of automated valves," the report said. "it does not express any vision for PG&E's gas transmission system of the future."


Garance Burke can be followed on Twitter at http://twitter.com/garanceburke.