San Bruno Explosion Aftermath

The interior of a destroyed car is shown in San Bruno, Calif., Tuesday, Sept. 14, 2010, where a pipeline exploded on Thursday.

Photos: California Gas Explosion

A thank-you sign is posted in front of a saved home about a block from destroyed homes in San Bruno, Calif., Tuesday, Sept. 14, 2010, where a pipeline exploded on Thursday. The tragic explosion of a gas pipeline has shed light on a problem usually kept underground: Communities have expanded over pipes built decades earlier when no one lived there. Utilities have been under pressure for years to better inspect and replace aging gas pipes, many of them laid years before sprawling communities were erected around them, that now are at risk of leaking or erupting.

Photos: California Gas Explosion

Construction workers walks by a destroyed home and a construction sign in San Bruno, Calif., Tuesday, Sept. 14, 2010 where a pipeline exploded on Thursday.

Photos: California Gas Explosion

A construction worker walks in the rubble of a destroyed home in San Bruno, Calif., Tuesday, Sept. 14, 2010, where a pipeline exploded on Thursday.

Photos: California Gas Explosion

Pacific Gas and Electric President Chris Johns, center, addresses questions during a news conference in response to a gas pipeline explosion in San Bruno, Calif., Monday, Sept. 13, 2010. Pacific Gas and Electric Vice President for Energy Delivery Geisha Williams, left, San Bruno Mayor Jim Ruane, second from left, and PG&E Chairman Peter Darbee, right, are also pictured.

Photos: California Gas Explosion

Residents aboard a school bus are given a tour of a burned down neighborhood damaged by a gas pipeline explosion in San Bruno, Calif., Monday, Sept. 13, 2010.

Photos: California Gas Explosion

Residents look ou the window of a school bus as they are given a tour on a burned down neighborhood damaged by a gas pipeline explosion in San Bruno, Calif., Monday, Sept. 13, 2010.

Photos: California Gas Explosion

Residents, bottom right, witness the raising of a U.S. flag at the site of a gas pipeline explosion in San Bruno, Calif., Monday, Sept. 13, 2010.

Photos: California Gas Explosion

A man walks past the remains of homes damaged from a fire caused by an explosion in a mostly residential area in San Bruno, Calif., Monday, Sept. 13, 2010. The explosion prompted California regulators to order the utility, Pacific Gas and Electric, to survey all its natural gas lines in the state in hopes of heading off another disaster. PG&E also announced it was establishing a $100 million fund for victims. 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.

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PG&E workers lower a gas pipeline into a box three days after a natural gas pipeline exploded into a deadly fireball in San Bruno, Calif., on Sunday, Sept. 12, 2010. Thursday's blast and fire destroyed nearly 50 homes and damaged dozens more. Four people were killed, four remain missing and at least 60 were injured.

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Counselor Regina Moreno, left, comforts area resident Karen Frechette shortly after Frechette returned to her home in a fire ravaged San Bruno, Calif., neighborhood on Sunday, Sept. 12, 2010. Police allowed some residents home for the first time since a gas line rupture Thursday night. Frechette's house escaped with minor damage.

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People line San Bruno Avenue to look at the fire ravaged area, three days after a natural gas pipeline exploded into a deadly fireball in San Bruno, Calif., on Sunday, Sept. 12, 2010.

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Harvey Devine and his wife, Alice, gather dust masks before being escorted back to their house as they gathered at Skyline College in San Bruno, Calif., Sunday, Sept. 12, 2010.

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Tina Villareal leans on Nelson Alvarado while waiting to return to her home in a fire-ravaged San Bruno, Calif., neighborhood on Sunday, Sept. 12, 2010. Thursday's blast and fire destroyed nearly 50 homes and damaged dozens more. Four people were killed, four remain missing and at least 60 were injured.

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Hundreds of San Bruno residents who were displaced by Thursday's natural gas pipeline explosion wait to be escorted back to their homes as they gathered at Skyline College in San Bruno, Calif., Sunday, Sept. 12, 2010.

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Hundreds of displaced San Bruno residents jammed a town hall meeting at St. Roberts Catholic Church in San Bruno, Calif., Saturday, Sept. 11, 2010. Thursday's blast and fire destroyed nearly 50 homes and damaged dozens more.

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Bob Vasquez, a volunteer and evacuee, helps with donation boxes at an evacuation center in San Bruno, Calif., Saturday, Sept. 11, 2010.

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Emergency workers walk through an area of burned homes in San Bruno, Calif., on Saturday, Sept. 11, 2010. On Thursday, a gas line rupture caused a deadly explosion that leveled dozens of homes.

Photos: California Gas Explosion

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A natural gas line, described by officials as the cause of a large explosion Thursday, Sept. 9, 2010, lies broken on a San Bruno, Calif., road on Saturday, Sept. 11. A rupture in the pipe caused an explosion that destroyed nearly 50 homes and damaged dozens more.

Photos: California Gas Explosion

A scorched Jeep sits among burned out homes in San Bruno, Calif., on Saturday, Sept. 11, 2010. A large explosion, caused by a gas line rupture, set the neighborhood ablaze Thursday night killing at least four people and leveling dozens of homes.

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Red tapes markes a burned home in San Bruno, Calif., on Saturday, Sept. 11, 2010. On Thursday, a gas line rupture caused a large explosion and fire destroyed nearly 50 homes and damaged dozens more.

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Dusk falls on a neighborhood damaged by a gas explosion in San Bruno, Calif., Friday, Sept. 10, 2010.

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A ruptured gas pipe that caused a massive explosion is shown beside a burned car in San Bruno, Calif., Friday, Sept. 10, 2010.

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An official walks past a charred car in a neighborhood damaged by a gas explosion in San Bruno, Calif., Friday, Sept. 10, 2010.

Photos: California Gas Explosion

An official walks through debris in a neighborhood damaged by a gas explosion in San Bruno, Calif., Friday, Sept. 10, 2010. The day after a gas line ruptured and a towering fireball roared through a suburban San Francisco neighborhood, officials were trying to determine what led to a blast that raised questions about the safety of similar lines that crisscross towns across America.

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Fireman walk past debris in a neighborhood damaged by a gas explosion in San Bruno, Calif., Friday, Sept. 10, 2010.

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Emergency workers walk through an area of burned homes in San Bruno, Calif., on Saturday, Sept. 11, 2010. On Thursday, a gas line rupture caused a large explosion that killed an undisclosed number of people and leveled dozens of homes.

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A burned car is shown in a neighborhood damaged by a gas explosion as power crews work to restore power in San Bruno, Calif., Friday, Sept. 10, 2010. The day after a gas line ruptured and a towering fireball roared through a suburban San Francisco neighborhood, killing several people, officials were trying to determine what led to a blast that raised questions about the safety of similar lines that crisscross towns across America.

Photos: California Gas Explosion