The blaze occurred when a pipe mysteriously ruptured Thursday evening, setting off thousand-foot-high (300-meter-high) fireballs and resulting flames that killed at least six in the suburb south of San Francisco as of Friday morning, the Associated Press reported.
"It looked like hell on Earth," resident Bob Pellegrini told the AP of the San Bruno explosion. "I have never seen a ball of fire that huge."
Some people in the neighborhood had been complaining of a natural gas odor before the San Bruno explosion. Those reports are now under investigation, Pacific Gas and Electric Company officials told the Los Angeles Times.
Photograph by Paul Sakuma, AP
Charred Hulks in San Bruno
At times 300 feet (90 meters) tall, the San Bruno fire gathered strength as it leaped from home to home, leaving more than 50 in total ruin and reducing parked cars to burned-out hulks (pictured Friday).
The gas pipeline explosion that set off the fires also released a boom "so loud, it could have been a nuclear explosion," resident Ed Hornung told the San Francisco Chronicle.
Where houses once stood, smoke shrouds singed trees and telephone poles in the aftermath of the San Bruno explosion, caused by a massive gas-line accident in the San Francisco, California, suburb late Thursday.
Four firefighters who suffered from smoke inhalation are among the 50 people so far hospitalized due to the San Bruno fire, according to the Los Angeles Times on Friday morning.
Also on Friday morning, Pacific Gas and Electric Company announced that it had identified a damaged 30-inch-wide (76-centimeter-wide) steel pipeline at the site of the San Bruno fire, though the cause of the explosion isn't yet clear, the Associated Press reported.
A firefighting plane dumps retardant onto the San Bruno fire, which engulfed several northern California blocks on September 9.
Though the gas flow was stopped and the fire mostly contained by late Thursday, extinguishing street gas-line fires is notoriously tough, according to the San Francisco Chronicle. Until the source of the gas is found, the pressure of the fuel and volatility of the escaping gas creates flames too forceful for firefighters to tackle.
Firefighters work to contain the massive San Bruno fire (pictured Thursday evening).
Many people fled their homes and are still unaccounted for, but at least a hundred are safe in evacuation centers, the San Francisco Chronicle reported. About 700 Pacific Gas and Electric Company customers were without electricity as of early Friday morning, according to the Associated Press.
"Say a special prayer for those people," San Bruno mayor Jim Ruane told the Chronicle. "This is going to be a long haul for the city."
Late Thursday firefighters wade at the edge of the crater left by the San Bruno explosion earlier that evening. Now filled with water from fire hoses, the roughly 15-foot-deep (4.6-meter-deep) hole is about 30 feet (9 meters) long and 20 feet (6 meters) wide, according to San Francisco's KGO TV news.
Though the San Bruno fire's source is still a subject of investigation, most gas pipeline accidents are due to digging projects, Nicor Gas executive Rocco D'Alessandro said during testimony at a June U.S. Senate hearing on pipeline safety. Speaking on behalf of the American Gas Association, D'Allessandro argued for the reauthorization of current federal pipeline-safety laws.
Some critics, though, argue that the laws don't do enough to protect the 70 million U.S. households that rely on gas pipelines for heat. For example, Carl Weimer, executive director of the nonprofit Pipeline Safety Trust, argues for rules limiting how close homes can be to pipelines.