Federal officials, utility workers, emergency response teams and nonprofit volunteer organizations descended on a normally quiet residential neighborhood in a San Francisco suburb Friday working their way deliberately through the rubble from a major natural gas transmission pipeline explosion and fire that destroyed dozens of homes, killed at least four residents and left more than 50 people injured, eight critically. Identifying the cause of the catastrophe, however, appeared to be out of reach until the water and power infrastructures in the immediate area were stabilized.

Pacific Gas and Electric Co. (PG&E) verified that a rupture three feet below ground in its 30-inch-diameter steel transmission pipeline caused the massive explosion and fire that tore through a residential neighborhood Thursday evening in San Bruno, CA, south of San Francisco near its international airport. At noon Friday, remnants of fire still burned in the undeveloped hills west of the residential area, and emergency officials said they still could not get close enough to the source of incident to identify a cause.

Officials said they were waiting for water crews and some of PG&E electrical workers to restore those two infrastructures in the area before investigators can get into areas they need to in order to begin pinpointing the incident’s cause. As of Friday afternoon, emergency response teams had gotten through about 75% of the seven-block residential area to inspect homes and look for other victims or injured residents.

PG&E and the California Public Utilities Commission (CPUC), fire officials and federal investigators were on the scene. National Transportation Safety Board (NTSB) investigators took the lead in searching for a cause, according to a PG&E spokesperson. PG&E clean-up crews circulated in the neighborhoods hit by blast to make the area safe, assess damage and restore service where possible, the spokesperson said.

PG&E deferred to the NTSB team Friday and during the day maintained its report from early in the morning that there were approximately 300 of its customers without natural gas service and up to 700 electricity customers in the area without service. At one point the utility said it shut off power to 5,800 customers in the area as a safety measure. The utility said the break on the transmission pipeline had been isolated, and flows were routed around the area.

Investors turned sour on PG&E’s stock as news of the tragedy grew. At closing the company’s share price had fallen more than 8%, or $4.03 as a record number of shareholders sold off their stock.

Company officials said they were focused on responding to the emergency and not concerned immediately about potential financial fallout.

“PG&E crews walked the neighborhood with fire officials this morning to make sure it is safe to restore power where possible,” the spokesperson said. “PG&E is also proactively surveying its gas transmission and distribution system to determine the extent of damage and ensure safety and begin restoration and repairs.”

The utility said it would “cooperate fully with the NTSB and all other federal, state and local agencies in the effort to identify the cause.”

Lt. Gov. Abel Maldonado, acting as governor with Arnold Schwarzenegger on a trade mission to China, commended emergency personnel for their quick response to the explosion and fire, vowing to have the state’s Emergency Management Agency “closely monitor” the situation. The CPUC spokesperson said one of the regulatory commission’s investigators was on the scene collecting evidence.

“During the next few days, we will work with local officials and federal agencies to gather all relevant information about the incident and obtain information from PG&E,” the CPUC spokesperson said. CPUC Executive Director Paul Clanon promised that his agency’s investigators “will get to the root cause of the explosion and fire.”

Local television news coverage showed the destroyed homes and flames reaching 60 feet in the air. Reports described the incident as a five-alarm fire located west of the two main north-south highways leading into Daly City, South San Francisco and ultimately San Francisco (Highways 280 and 101). The blast was in the general vicinity of Skyline Boulevard and San Bruno Avenue in San Bruno, which is in San Mateo County.

©Copyright 2010Intelligence Press Inc. All rights reserved. The preceding news reportmay not be republished or redistributed, in whole or in part, in anyform, without prior written consent of Intelligence Press, Inc.