Updated Friday, Feb. 8, 4:30 p.m.:
In a press conference on Friday afternoon, an NTSB official told reporters that the investigative team will be working on the timeline of events surrounding the incident. Tomorrow the team plans to conduct more interviews and visit the pipeline control center.
With the help of the FBI, the NTSB is working to secure a 3-4 foot length of the pipeline that may be sent to Washington, D.C. for testing.
Original Post Feb. 7: State and federal officials have launched an investigation into a fire sparked by a ruptured high-pressure gas line in San Francisco's Inner Richmond neighborhood Wednesday afternoon — an incident that featured a two-hour struggle by PG&E crews to shut off the flow of highly flammable natural gas.
Despite the spectacular nature of the blast and fire, no injuries were reported.
An unknown number of people were displaced from up to seven residential units because of the fire. PG&E said about 300 gas customers and 2,500 electric customers lost service because of the blaze.
J.D. Guidi, a PG&E spokesman, said electricity was restored to all of the affected customers early Thursday morning. PG&E crews were working to remove water left over from the firefight in order to introduce gas back into the area's system.
Speaking to reporters as the fire roared nearby, San Francisco Fire Chief Joanne Hayes-White said a construction crew installing underground fiber-optic equipment touched off the fire by hitting the natural gas line.
The incident involved a worker using an excavator to dig a trench, according to Frank Polizzi, a spokesman for California's Division of Occupational Safety and Health.
A Verizon spokeswoman confirmed Thursday morning that one of its contractors was working in the area of the blast.
"Yesterday's fire in San Francisco's Inner Richmond District is tragic for the people impacted by the incident and resulting power outage," said Heidi Flato, a company representative, in a statement.
"MasTec, a vendor contracted by Verizon, was working at that location yesterday. We understand that MasTec is cooperating with investigators as they determine the root cause of the incident. The fiber installation has been halted pending the outcome of the investigation by local authorities," Flato said.
A top executive for MasTec, an infrastructure construction company based in Florida, expressed concern about the incident and said the company was conducting its own probe of the explosion.
"We want to express our deep concern for those affected by the gas line rupture," said John Higgins, president of MasTec's Utility Services Group, in a statement.
MasTec has been the subject of three previous Cal/OSHA inspections and two citations, according to Polizzi.
One of those infractions included a serious citation involving an incident in Concord in 2015. MasTec and other companies were working on a site to demolish high voltage overhead power lines when an employee of another firm "suffered an electric shock" as he cut into a riser that housed a live power line, Polizzi said in an email Thursday.
Polizzi said Cal/OSHA launched an investigation into the incident on Thursday. MasTec and two of its subcontractors, Advanced Fiber Works and Kilford Engineering, are the subject of that probe.
In Wednesday's incident contractors had called to determine where the gas lines where in the area, and PG&E marked where the lines were, according to PG&E spokeswoman Andrea Menniti. However, that does not indicate whether PG&E correctly marked the lines. Marking errors have caused serious problems in the past, including an explosion that destroyed a home in Carmel in 2014.
The California Public Utilities Commission is also investigating the incident, commission spokeswoman Terrie Prosper said in an email Thursday morning.
The National Transportation Safety Board plans to send a team to the area to investigate as well.