SAN FRANCISCO -- PG&E officials told state regulators Friday that its natural gas pipelines are safe, despite its continuing failure to keep accurate records -- a problem that contributed to the fatal gas explosion in San Bruno three years ago.

The state Public Utilities Commission grilled PG&E officials about the utility's maintenance and performance records concerning three natural gas pipelines, including one in San Carlos. The newly revealed record-keeping flaws have sparked fresh questions about the safety of the gas system.

"In my opinion, these errors did not present a safety issue," M. Kirk Johnson, PG&E vice president of gas transmission maintenance and construction, told the hearing. "It is safe to operate these pipelines."

The hearing before a PUC administrative law judge was also attended by three PUC commissioners, as well as the agency's chief administrative law judge -- a rare event and a clear sign the PUC deems the matter serious. A PUC ruling on the flawed records is at least several weeks away.

"Are there other instances like this one out there? What does that say about the safety of the system?" PUC Commissioner Michael Florio said in an interview with this newspaper during a break in the hearings. "We have some comfort that we are not dealing with a ticking time bomb here. But we need to get to the bottom of whether there are other cases where something like this could present a problem."

Critics pilloried PG&E over why it waited from October 2012, when the record flaws first surfaced, until July 3 of this year to notify the PUC it had incorrect records regarding the maximum allowable pressure for the pipes.

"I don't understand why PG&E waited 10 months to tell the city of San Bruno that there were errors in the records," said Britt Strottman, an attorney for the city. "That should have raised a red flag. PG&E is not being forthcoming."

The disclosure comes at a delicate time for PG&E, which faces a possible $4 billion penalty by the PUC, including a fine of $300 million, as its punishment for causing the San Bruno explosion in September 2010 that killed eight people and devastated a neighborhood.

"These mistakes undermine PG&E's claim that they have righted the ship," said Thomas Long, legal director with The Utility Reform Network, a consumer group. "PG&E was worried this makes them look bad."

Human error was partly to blame for the new problems, Sumeet Singh, PG&E's senior director of asset knowledge management, testified.

"We did not turn a blind eye to the mistakes," Singh said. "The gas system records are reliable."

The utility has reviewed 3.8 million documents covering 3,750 miles of pipes and 500,000-plus pipeline components, Singh said.

"Our culture is find it and fix it. Find it before it finds you," Johnson said. "We have turned a corner. I believe the culture has changed significantly."

Contact George Avalos at 408-859-5167; follow him at Twitter.com/georgeavalos.