California regulators said today they will order Pacific Gas and Electric to survey all its natural gas lines in the state, after a massive gas line explosion in suburban San Francisco devastated a neighborhood and left at least four people dead.
As part of the order from the state's Public Utilities Commission, PG&E must run leak surveys on all natural gas lines, with priority given to higher pressure pipelines and to lines in areas of high population density.
The commission also plans to appoint an independent expert panel to help with its investigation.
News of the order came late today, after many residents of the San Bruno neighborhood were allowed to return to their homes for the first time since the blast Thursday.
Bruno City Manager Connie Jackson said during a morning news briefing that many residents in the area would be able to return home Sunday and stay in their homes.
Others whose were marked with yellow tags were only allowed to gather some clothes and belongings and leave.
The pipeline was known to be potentially dangerous. In a 2007 document, PG&E, which owns the line, said the pipeline, "ranks in the top 100 highest risk line sections," adding that the "risk of failure at this location is unacceptably high."
The document was part of a budget request to replace the line.
"This raises the question of what PG&E knew and when they knew it and whether better safety procedures could have avoided this horrible tragedy," said Mindy Spatt, of The Utilities Reform Network.
San Bruno's mayor said he was was unaware of the risk assessment.
"The whole thing is troubling to me," Mayor Jim Ruane said.
Investigators from the National Transportation Safety Board took measurements and pictures of pieces of the pipe that exploded, which is the focus of their investigation.
They plan to ship the damaged section of pipe to a lab in Washington for metallurgy tests to help determine whether sewer line work in the neighborhood could have been a factor in the explosion.
"That's one of the things the metallurgy examination will help ascertain, because we'll be able to determine was the failure in the pipeline due to fatigue or was it because of an impact in the case of construction," Christopher Hart of the NTSB said.
Police have officially said that five people are missing.
Authorities are attempting to confirm whether the remains they've discovered are human and then identify the victims, said San Bruno County Coroner Robert Foucrault.
State and local politicians vowed Saturday to get to the bottom of what caused the massive explosion and fire.
The explosion left more than 60 people injured and destroyed 37 of homes in the community, which is in the hills just south of San Francisco.
After touring the scene Saturday morning, Sen. Barbara Boxer said she would push for a federal investigation into what happened.
"We're going to push for robust inspections and action on these pipelines, particularly the ones that are close to residential homes," the Democrat said. "I am calling on all responsible parties -- PG&E and all the regulators, federal and state -- to outline a robust inspection system that begins right now."
Acting Gov. Abel Maldonado and Boxer said they planned to hold a news conference focusing on the recovery phase and how the federal, state and city governments will help those in need of assistance.
"The community of San Bruno needs answers. The people of California need answers," Maldonaldo said. "We need to know why this happened and we need to know how this happened."
The San Mateo County Coroner's Office released the names of three of the at least four people who were killed: Jacqueline Greig, 44, a California Public Utilities Commission employee; her 13-year-old daughter, Janessa Grieg; and 20-year-old Jessica Morales.
The name of the fourth victim has not yet been released, but Faye Wharton told ABC San Francisco station KGO-TV that the body of her 80-year-old grandmother was found in the ruins of her home, which is right next to the explosion.
Wharton told KGO-TV that she received word from authorities late Friday night. She said her two aunts and uncle, who were also in the house, made it out alive, but were severely burned.
Many residents were just sitting down to dinner Thursday when they heard the explosion and felt its force. At first, many thought a plane had gone down in the neighborhood, which is just a few miles from San Francisco International Airport.
"The house started shaking much more violently than it did in '89," during the Loma Prieta earthquake, said resident Rick Bruce.
"I was in the garage, the first thing I heard was a rumble, then all of the sudden a big explosion, like BOOM," said Larry Fioranelli, who lives a block from the center of the explosion. "The heat shot up the street and into the garage... It's like a movie when you see the A-bomb explosion... You felt the concussion."
The blast shot a fireball into the air that consumed several homes in an instant. Fire reached up to 100 feet high, witnesses said. The explosion left a 15-foot crater at its epicenter.
Temperatures from the fire were so extreme that as the first fire truck got to the scene, its windshield cracked and firemen saw paint bubbling up on cars, one fire official said.
"It was like, picture a hot air balloon of fire. That big and high," Fioranelli said. Though the Fioranellis' home was undamaged in the initial fireball, they do not know if the fire reached it after they evacuated.
As many as 100 people were evacuated from their homes, though only a few dozen needed shelter Thursday night, according to Red Cross officials.
One of the homes destroyed belonged to Ricardo Salinda. He and his young son Richard were in their house when the explosion rocked the neighborhood and a ball of fire lit up the sky.
"We tried to get out of the front door, but the heat was too much," Salinda said.
Salidna quickly led his son out the back of the home, with only his wallet in his pocket. The father and son didn't even have shoes on their feet.
Together, the Salindos climbed over the backyard fence to escape the heat, but not before the intense temperatures singed their skin. Ricardo suffered second degree burns on his leg and neck from the radiating temperatures, and son Richard now has burns on his arms.
With their home completely destroyed, Salindo, his wife and their son spent Thursday night in a hotel. On Friday, the father and son's arms and legs were bandaged in thick layers of white gauze, but they were still counting their blessings.
"If we'd stayed any longer in the house, we're dead," said Salinda. "We're lucky to be alive."
Officials Probing Cause of San Bruno Pipeline Explosion
Maldonado said Friday that the explosion was caused by a gas pipe rupture but added, "We don't know what caused [the rupture] or what happened."
"We will find out soon," he said.
The explosion occurred just after 6:15 p.m. Thursday in a residential area near highways 280 and 380 in San Bruno, just south of San Francisco. Thirty-eight structures were completely destroyed and another seven badly damaged.
"You've heard the numbers," San Bruno mayor Jim Ruane said Friday in a news conference. "Unfortunately, the numbers are going to get higher."
Local news reports said residents had attempted to alert Pacific Gas and Electric, the company that operates the pipelines, to the smell of gas days before the explosion.
"We have records that we are going back through right this minute to try and confirm what those phone calls looked like and when they occurred," PG&E president Chris Johns said Friday. Johns said that company policy was to immediately respond if someone calls in with a complaint about the smell of gas.
"We're really saddened and sorry about this tragedy," he said.
Officials from the National Transportation Safety Board are investigating the cause of the blast and will work with PG&E to determine exactly what happened.
"I want to make sure everybody knows that we are committed to do what's right and what's appropriate to help all the families and others who have been impacted by this tragedy," Johns said.
Johns said that no PG&E crews were working in the vicinity during the explosion, but he did not know about any other construction going on. The pipe that ruptured, Johns estimated, was 40 or 50 years old.
ABC News' Ariane Nalty, Neal Karlinsky and The Associated Press contributed to this report.