NTSB to investigate why it took 2 hours to stop 3-alarm San Francisco gas fire

NTSB addresses the media in San Francisco. 

SAN FRANCISCO (BCN) The National Transportation Safety Board has begun its investigation into a pipeline rupture that caused an explosion and three-alarm fire in San Francisco's Lone Mountain neighborhood Wednesday, according to an NTSB spokeswoman.

Speaking Friday near Geary Boulevard and Parker Avenue, the scene of the rupture and blaze, NTSB Board Member Jennifer Homendy said investigators have already been briefed by both PG&E and the California Public Utilities Commission and have inspected the valves used to shut off the gas.

Now, she said, investigators will be looking at a timeline of Wednesday's events to determine how long it took to shut off the gas and what actions were taken before and after the rupture.

They're also going to secure three or four feet of the ruptured 4-inch pipe and may send it to a lab for further analysis, she said.

The FBI is assisting with the investigation, Homendy said, but she stressed, "There is not a criminal investigation. The FBI is here to help us document evidence; helping secure the 3 to 4-foot section of the pipeline."

Additionally, she said, "What we wanted to look at here is has PG&E followed up with past NTSB recommendations, and that is part of what we'll be looking at for part of this investigation."

Investigators will also be speaking with the third-party contractors and subcontractors involved in the rupture.

The 1 p.m. Wednesday rupture began when the contractors working on fiber optics struck the gas pipe, causing the breach and subsequent explosion and fire, PG&E officials said.

Flames shot in the air for more than two hours before crews stopped the flow of gas at 3:36 p.m.

People in the area were evacuated and no injuries were reported. Two buildings were left with major structural damage and three others with extensive water damage, according to police and fire officials.

Three hundred PG&E customers were left without gas and 2,500 lost power. Those customers have since had service restored.

According to PG&E, the contractors had called 811 to check for any utilities underneath the area before they started digging. PG&E crews then sent a locator to the scene on Jan. 28 and made markings in the area.

PG&E said is also conducting an investigation and a reason for the breach. 

The NTSB may provide an update on their investigation on Saturday, Homendy said.