SAN FRANCISCO -- Under increasing public scrutiny for their role in overseeing PG&E, state regulators approved a plan Thursday for an independent investigation of the San Bruno natural gas pipeline explosion that killed seven people and destroyed 37 homes.

The California Public Utilities Commission voted 4-0 to appoint a panel of experts to probe the Sept. 9 blast, and to examine whether there are larger, systemic problems at the utility or the CPUC.

"We have to look at every facet of the factors that led up to this accident -- in particular, not be afraid to look in the mirror," said Commissioner Nancy Ryan.

Besides looking at whether PG&E could have done anything to avoid the blast and fire, the investigation will try to determine whether the commission failed to protect the public. Commissioner Timothy Simon said that includes looking for gaps or shortcomings in regulation of the utility.

The National Transportation Safety Board launched an investigation immediately after the explosion, but its final report is not expected for 18 months. Simon said that even as the CPUC works with federal investigators, the commission can begin immediately answering other questions raised by the disaster.

The commission ordered PG&E to pay the costs of the investigation and is pushing the company to cover the expense with money from shareholders, not ratepayers. PG&E could not be reached for comment Thursday.

"We expect PG&E to cooperate fully with this commission's staff and the panel during this investigation," said commission President Michael Peevey. "To this date they have shown every indication of a willingness to do so."

The panel -- which will have three to five members, to be chosen by Peevey in the next 60 days -- won't have the power to assign blame or levy punishment. Instead, it will deliver recommendations to the commission on possible regulatory improvements.

Assemblyman Jerry Hill, D-San Mateo, urged the commission to determine whether PG&E actually performed repairs and maintenance it has claimed were needed as justification for past rate increases. He noted that the line that blew up in San Bruno wasn't on the "top 100" list of highest-risk pipeline segments the utility had slated for repair or monitoring.

"Our residents deserve to know whether our utilities are being regulated adequately," Hill said, questioning what steps the CPUC is taking to inspect natural gas pipelines.

Mark Toney, head of The Utilities Reform Network, a watchdog group, said after the meeting that the panel won't be effective if it is mostly made up of industry executives and experts.

"It has to include people who are critical," Toney said.

As the meeting played out in San Francisco, crews in San Bruno began their first day of carrying away the charred remains of homes. County environmental division head Dean Peterson said the work clearing away three homes was nearly completed Thursday.

So far, asbestos and other contaminants in ash at the site haven't shown up on air quality tests, he said. Crews are slated to resume work at 8 a.m. today.

Just around the corner from the work, Jerry Guernsey was pulling off his white protective suit after sifting through the ashes at his home on Concord Way. After loading a few charred items into his car, he said he had to go lock his house. For Guernsey, that meant pulling closed the chain-link fence in front of the ruins.

Meanwhile, at a congressional hearing in Washington, federal regulators and lawmakers vowed to step up government oversight of the nation's 2.5 million miles of pipelines. A series of oil and gas leaks around the country in recent months has commanded the attention of government officials.

"Some of these pipelines seem nearly as fossilized as the fuel they transport," Rep. Edward Markey, D-Mass., said at a House Energy and Commerce subcommittee hearing on the San Bruno explosion as well as incidents in Michigan, Utah and other states. "It is critical that we unearth the causes of these accidents and hold the responsible parties fully responsible. Just as important, we must re-examine and strengthen our laws to ensure that accidents like these do not happen again."

Cynthia Quarterman, administrator of the Pipeline and Hazardous Materials Safety Administration, vowed at the hearing that her agency "will use its full enforcement authority" to force operators to meet safety standards and will press for "the most stringent oversight feasible." She said the agency is considering an industrywide "leak-detection standard" with which all pipeline owners would have to comply; such standards are now decided by individual companies, she said.

Quarterman's boss, Transportation Secretary Ray LaHood, last week proposed legislation to increase pipeline oversight by adding inspectors and increasing fines. Building on his proposal, California's two Democratic senators, Dianne Feinstein and Barbara Boxer, introduced a bill to double the number of pipeline inspectors to 200 and require pipeline operators to deploy electronic valves that can automatically shut off gas in a fire. It took workers almost two hours to shut off manual valves after the San Bruno explosion.

Their bill would also require pipeline owners to use small robotic devices known as "smart pigs" to inspect the insides of pipelines for signs of corrosion. The San Bruno pipeline could not accept pigs. And it would direct inspectors to make a higher priority of older pipelines in seismic areas.

Other legislation pending in the House would require pipeline operators to report leaks within one hour or face increased fines.

Oil and gas companies are pushing back against proposals for expansive new rules, saying regulators already have the authority they need and the government's focus should be on preventing pipeline accidents caused by excavation, the most common culprit. The NTSB is investigating a 2008 sewer line project in the area of the San Bruno explosion. The technique the company used can cause ground shaking and disruption of adjacent soil and rock.

"It would be premature to suggest that any recent incident means current safety regulations need to be changed," Andrew Black, president and CEO of the Association of Oil Pipe Lines, testified at the hearing. "Existing laws and regulations cover the major causes of (oil and gas) releases; we may find that these incidents do not reveal any gaps."

Bay Area News Group staff writer Mike Zapler contributed to this report. Contact Joshua Melvin 650-348-4335.