Residents returned Sunday to the ruined hillsides of their suburban San Francisco neighborhood, three days after a natural gas pipeline exploded into a deadly fireball.
A nearby segment of the line was due to be replaced, the utility responsible said, because it ran through a heavily urbanized area and the risk of failure was "unacceptably high." That 30-inch diameter pipe about two and a half miles north was installed in 1948, and was slated to be swapped for new 24-inch pipe.
But investigators still don't know what caused the blast Thursday night, and even as dozens of people returned to their scorched homes — accompanied by gas workers to help restore pilot lights and make sure it is safe to turn power back on — officials tried to confirm just how many people died.
The remains of at least four people have been found, and authorities have said five people are missing and at least 60 injured, some critically.
San Mateo County Coroner Robert Foucrault said they're still trying to confirm whether some of the remains they found are human and identify victims.
Streets were crowded Sunday with Pacific Gas and Electric cars and trucks, and representatives were handing out gift certificates for grocery stores. Nearly 50 homes were destroyed and seven severely damaged in the blast, while dozens of other homes suffered less severe damage in the fire that sped across 15 acres.
Pat and Roger Haro and their dog, "Rosie," have been living in a hotel room since Thursday after fleeing their home with the clothes they were wearing, dog food, water and an iPad.
When they returned, their home was marked with a green tag — indicating less damage than others with yellow or red tags — and their electricity was still off.
"Once I saw the house was still there then I felt a whole lot better," Pat Haro said. "I think we'll be a tighter community."
A few blocks away, houses have collapsed into black and white debris on ground, with a smell like charcoal in the air. All that remain standing is a row of brick chimneys, while across the street, some homes are undamaged.
Meanwhile, local and federal officials are probing the cause of the explosion that blew a segment of pipe 28 feet long onto the street some 100 feet away, creating a crater 167 feet long and 26 feet wide.
PG&E submitted paperwork to regulators for ongoing gas rate proceedings that said a nearby section of the same gas line a few miles away was within "the top 100 highest risk line sections" in the utility's service territory, the documents show.
The company also considered the portion that ruptured to be a "high consequence area" requiring more stringent inspections called integrity assessments, federal Pipeline and Hazardous Materials Safety Administration spokeswoman Julia Valentine said.
Nationwide, only about 7 percent of gas lines have that classification, she said.
PG&E spokesman Andrew Souvall said the company had planned to replace the piece of the gas line mentioned in the documents as a part of its broader proposal to upgrade infrastructure that the commission began considering last year.
Souvall did not immediately say whether records showed any complaints from San Bruno residents in the days leading up the blast, or when the section that ruptured had last been inspected. But he said the segment farther north was checked for leaks on September 10 and none were found.
"We take action on a daily basis to repair our equipment as needed," he said. "PG&E takes a proactive approach toward the maintenance of our gas lines and we're constantly monitoring our system."
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, but a federal safety official said that did not necessarily indicate the pipe had been repaired.
Asked whether a welded pipe was more susceptible to leaks or corrosion, National Transportation Safety Board vice chairman Christopher Hart said: "Maybe, and maybe not."
At a church service at the St. Roberts Catholic Church on Sunday morning, the Rev. Vincent Ring conducted a prayer for the people who died, as well as a prayer for the victims who have not been identified.
"We turn to God and we ask for mercy upon all our brothers who are hurtling so badly, whose lives have changed so drastically and whose help is so badly need from us," Ring said.
Contributing to this report were Associated Press video journalist Haven Daley and writer Lisa Leff in San Bruno and John S. Marshall and Sudhin Thanawala in San Francisco. Burke reported from Fresno, Calif.