Federal and state investigators say the section of natural gas pipeline that ruptured and exploded in a deadly fireball near San Francisco had been categorized as high risk because it ran through a highly populated area.

Documents obtained by The Associated Press showed that Pacific Gas & Electric submitted paperwork to regulators that said a section of the same gas line — about two and half miles from the blast — was within "the top 100 highest risk line sections" in the utility's service territory.

The federal Pipeline and Hazardous Materials Safety Administration classified the 30-inch diameter transmission line as a "high consequence area" requiring more stringent inspections called integrity assessments, agency spokeswoman Julia Valentine said.

Nationwide, only about 7 percent of gas lines have that classification, she said.

The official death toll from the blast was four Sunday, and San Mateo County Coroner Robert Foucrault said they're still trying to confirm whether more remains found are human and identify victims. Police have said five people are missing.

Police Chief Neil Telford had said Saturday that seven had died, but authorities said later it wasn't immediately clear if remains were from victims already accounted for.

Most of the residents whose homes suffered less damage will be allowed to go back starting at noon, City Manager Connie Jackson said Sunday. Nearly 40 homes were destroyed and seven severely damaged, while dozens of other homes suffered less severe damage in the fire that sped across 15 acres.

The cause of Thursday evening's and fire pipeline blast — which injured at least 60 people, some critically — is under investigation.

The section of pipeline also was given a high-risk classification by the state commission, which had conducted audits on that stretch, spokeswoman Terrie Prosper said. PG&E also had conducted leak surveys, evaluations and patrols on the gas line, she said.

PG&E did not immediately respond to a request for comment Saturday and referred questions related to the investigation to federal authorities.

Reams of data and records have been requested from PG&E, National Transportation Safety Board vice chairman Christopher Hart said at a Saturday evening briefing.

The segment of pipe that blew out onto the street was 28 feet long, the explosion sent that piece of pipe about 100 feet and the blast created a crater 167 feet long and 26 feet wide, he said.

An inspection of the severed pipe chunk revealed that it was made of several smaller sections that had been welded together and that a seam ran its length, Hart said.

The presence of the welds did not necessarily indicate the pipe had been repaired, he said. Asked whether a welded pipe was more susceptible to leaks or corrosion, Hart said: "Maybe, and maybe not."

One of the dead worked for the commission reviewing PG&E's investment plans to upgrade its natural gas lines, including another risky section of the same pipeline within miles of her home, a colleague confirmed.

Longtime California Public Utilities Commission analyst Jacqueline Greig and her 13-year-old daughter Janessa died in the massive blast, which left a crater near their house and laid waste to dozens of 1960s-era homes in the hills overlooking San Francisco Bay.

Jessica Morales, 20, was also killed in the explosion and fire. One other victim hasn't been identified.

Greig spent part of the summer evaluating PG&E's expansion plans and investment proposals to replace out-of-date pipes, co-worker Pearlie Sabino said.

Sabino and Greig were members of a small commission team that advocates for consumer and environmental protections pertaining to natural gas.

"It's just so shocking because she was one of the ones who was most closely involved with this kind of work," said Mike Florio, an attorney with a San Francisco-based utility reform advocacy group who worked with Greig. "Little did we know that pipe was near Jackie's own neighborhood."

Lt. Gov. Abel Maldonado, who is serving as acting governor while Gov. Arnold Schwarzenegger travels in Asia, directed the commission to perform integrity assessments of all pipeline segments in the area.

Maldonado also ordered further inspections and surveys for high consequence areas, including a detailed inspection of three transmission lines that run through San Mateo County.

PG&E workers have almost finished inspecting its three transmission lines that run through San Bruno and further south down the San Francisco peninsula, PG&E vice president Geisha Williams said.

Authorities were continuing to treat the site as a crime scene, Telford said.

"We don't know what caused this explosion. We have deaths," he said. "If there was any kind of criminal negligence or any kind of criminal activity, we need to maintain that crime scene."

Sonia Salinda's home was destroyed in the fire, but her husband, Ricardo, and 15-year-old son were able to escape. She said she wants to return to what's left of her home to find closure.

"I can't wait to see it, even though it's all destroyed, because I know that's where I am going to start again," she said.

When residents return to their homes on Sunday, PG&E representatives will accompany them to help restore pilot lights and make sure it is safe to turn power back on, Williams said.

"We know our customers are extremely nervous, and who wouldn't be given what's happened here?" she said.

On Saturday, PG&E also started giving out $1,000 gift cards, rental car and hotel vouchers to people displaced by the blast. Williams said the company also was prepared to compensate families with relatives killed or injured in the blast and provide long-term housing assistance to those who lost their homes.

"We will do everything we can to make you whole," she said.


Contributing to this report were video journalist Haven Daley in San Bruno and John S. Marshall and Sudhin Thanawala in San Francisco. Burke reported from Fresno, Calif.