CBS News correspondent Priya David Clemens reports there are four confirmed deaths, including a 44-year-old woman and her 8th grade daughter.
Relatives of an 81-year-old woman who lived near the epicenter of the blast believe she also perished in this disaster; they're just awaiting confirmation from dental records.
At least 50 people were hurt, with seven sustaining critical injuries in the explosion Thursday evening that left a giant crater and laid waste to dozens of 1960s-era homes in the hills overlooking San Francisco Bay.
The city will hold a Saturday town hall meeting at a local church.
Federal authorities are probing the natural gas pipeline and how it was maintained as they investigate the thunderous line explosion and raging inferno that devastated this suburban San Francisco neighborhood.
The eruption also raised questions about the safety of similar lines that crisscross towns across America.
"It looks like a moonscape in some areas," Fire Chief Dennis Haag said Friday.
The utility that operates the 30-inch diameter line said it was trying to find out what caused the steel gas pipe to rupture and ignite. Federal pipeline safety inspectors were also on the scene Friday afternoon.
"It was just an amazing scene of destruction," National Transportation Safety Board vice chairman Christopher Hart said.
The closest fire station was just two blocks from the neighborhood. But at 1,200ºF, the fire was so hot it cracked the windshield of the first fire truck as it approached.
Once on scene, a new problem developed: The explosion had knocked out the underground water lines, so each fire truck was limited to the 500 gallons on board. Water had to be pumped from hydrants 2 miles away.
When asked by CBS News how long the water problems may have delayed extinguishing the fire, State Fire and Rescue Chief Kim Zagaris said, "I'm willing to bet you we're talking hours."
With the smoke clearing, the fire's devastation is thrown into stark relief. Tires are melted on burnt-out cars.
At an evacuation center, residents anxiously awaited word on the fate of their homes.
Others, like Freddy Tobar and his wife Nora, thought about the house they lost. He saw flames shooting up outside his window and then through his home. He grabbed his chihuahua and ran outside, getting second degree burns on his arms and the side of his face.
The couple saw the house burning to the ground on the news, and returned Friday to find it completely destroyed.
"We have to start from zero again. When you start remembering it gets too sad," Nora Tobar said.
"But the most important thing is that we're alive," she said.
Some residents said they smelled gas in the neighborhood over the past several weeks. The utility said it was checking its records for the complaints, but added that none of its crews were at work on the line Thursday.
State Assemblyman Jerry Hill, who represents San Bruno and surrounding cities, said he has heard multiple reports from constituents who had alerted PG&E of gas odors in the neighborhood before the disaster.
The residents "deserve to know if PG&E used the correct procedures in the days and weeks leading up to this disaster," Hill said.
PG&E President Chris Johns said the company has heard the reports of a gas odor in the area before the blast.
"Right now, we haven't got confirmation about that, but we have records that we are going back right this minute to try to confirm what exactly those phone calls look like and when they occurred, and we will report back as soon as we know something," he said.
By mid-afternoon Friday, the utility could not confirm the residents' reports of gas odors, but said it was "looking into it."
Federal investigators will analyze the pipeline's condition, along with its maintenance history, pressure levels and the safeguards put in place to prevent pressure from building up, Hart said. The NTSB will also look at the training and experience of the people who operated the pipeline and screen them for alcohol and drugs.
Compared to the tens of thousands of miles of gas pipelines across the country, accidents are relatively rare.
In 2009, there were 163 significant accidents involving natural gas pipelines, killing 10 people and injuring 59.
Transmission lines like the one that burst in San Bruno deliver natural gas from its source to distribution lines, which then carry it into neighborhoods before branching off into homes.
Over the past two decades, federal officials tallied 2,840 significant gas pipeline accidents nationwide - including 992 in which someone was killed or required hospitalization, according to the Pipeline and Hazardous Materials Safety Administration.
Those accidents killed 323 people and injured 1,372.
Experts say the nation's 296,000 miles of onshore natural-gas lines routinely suffer breakdowns and failures.
More than 60 percent of the lines are 40 years old or older and almost half were installed in the 1950s and 1960s, according to a recent analysis by the Pipeline Safety Trust, a nonprofit advocacy group based in Bellingham, Wash.
Most of the older pipelines lack anticorrosion coatings that are prevalent in the industry today, said Carl Weimer, executive director of the trust, which was set up following a 1999 explosion that killed three people in Bellingham.
"The industry always says that if you take care of pipelines, they'll last forever," Weimer said. "But what we see over and over again is companies are not doing that and corrosion and other factors are causing failures."
And once a high-pressure pipeline fails, he added, anything can trigger a deadly blast. A cigarette or rocks smashing as high-pressure gas shoots by. Even someone answering a cell phone can cause a spark, because it is battery-powered, Weimer said.
The damaged section of pipe was isolated and gas flow to the area was stopped. Haag said PG&E crews were still not able to access the site of the ruptured line Friday because it was covered with water.
This is not the first time a deadly explosion occurred on a PG&E gas line. The utility has had 19 significant pipeline incidents since 2002, but there was only one fatality, according to records provided by the trust.
In 2008, the state regulators inspected a leaky PG&E pipeline in the Sacramento suburb of Rancho Cordova that had been repaired, and found that the company wasn't properly training its workers to recognize potentially dangerous leaks.
PG&E agreed to update its safety training, and a deadline was set for Dec. 31, 2008.
On Christmas Eve, the pipeline exploded, killing a 72-year-old man and injuring five others.
An NTSB's final report on the blast concluded that PG&E used a wrong pipe to repair the gas line two years before and that residents had reported a gas smell before the explosion.
In response to the findings, the company said it had taken "extraordinary measures" to ensure a blast like that wouldn't happen again.
PG&E has not returned calls seeking a response to its history.
Four firefighters suffered minor smoke inhalation injuries and were treated and released, Haag said.
Haag said crews walked through the neighborhood Friday morning and revised the damage estimate to 38 structures destroyed and seven significantly damaged. Dozens of other homes suffered less severe damage in the fire, which burned 15 acres.
Haag said Friday afternoon a quarter of the homes were still too hot to search. He said he didn't know of anyone confirmed missing, though officials were still waiting for all residents to check in.
Shares of PG&E Corp. fell sharply Friday. PG&E shares closed down $4.03, or about 8 percent, at $44.21 during the regular session. The drop slashed $1.57 billion from the company's market capitalization, based on its 390.75 million shares outstanding at July 29.
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