Photo: Santiago Mejia, The Chronicle
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It took more than two hours to shut off the gas at the site of a large fire in the Inner Richmond, which authorities say was caused by a gas pipeline breach. The length of time the fire burned left many wondering why it took so long to stop the flow of gas.
The blaze started near the intersection of Geary Blvd. and Parker Ave. at approximately 1:18 p.m. It burned in front of the restaurant Hong Kong Lounge II, which was damaged along with the units above the restaurant. The flames were extinguished around 3:38 p.m.
San Francisco Fire Chief Joanne Hayes-White said the entire perimeter was evacuated and no injuries were reported. As the fire burned, she said firefighters could not get the blaze under control “until PG&E manages the gas.”
PG&E spokesperson Paul Dougherty would not immediately comment on the process for shutting down the gas pipeline.
“Every situation is different,” he said.
In 2010, it took between 60 and 90 minutes to shut off the gas after the deadly PG&E gas line explosion in San Bruno. San Bruno Fire Chief Dennis Haag cited a complex shutoff system as the reason for the delay.
Lacking further information from PG&E, one can only speculate as to why the gas flowed for more than two hours at the Inner Richmond fire, said Captain James Colburn with the Alameda County Fire Department.
“There are a variety of reasons for why the gas would still on,” Colburn said. “It could be a problem with the shut-off valve, or the operator might not be able to reach the valve.” He also said factors such as the diameter of the pipe, as well as the distance between isolation valves, affects the shut-off time.
The Pipeline and Hazardous Materials Safety Administration said in a statement it was “gathering information and evaluating the situation in San Francisco, California.”
“Based on that information, the agency will determine whether or not to deploy investigators to assist California state officials at the site of the incident,” the statement continued.
A 2011 paper by the American Gas Association said the amount of time for a section of pipeline to depressurize is determined by the speed with which the block valves are closed. Some valves must be shut down manually by an operator, others automatically close after sensing a change in pressure, and some are operated by remote control from a central operating center.
“Depending on these physical parameters, a pipeline may take a considerable amount of time to reach 0 psig (depressurize) after the valves are closed,” the paper said. It estimated the process could take anywhere from “tens of minutes to several hours.”
Between 2011 and 2016, PG&E crews installed 235 automatic and remote-controlled valves within its jurisdiction, it said in a press release. The automatic valves are installed where transmission pipelines cross major fault lines, the utility said. It was not immediately known if the valves controlling the flow of gas at the site of the Inner Richmond fire were automatic, remote-controlled or manually operated.
“Workers doing fiber optic work might have breached the gas line,” Hayes-White said, discussing the circumstances surrounding the start of the fire.
“I’m told there were eight workers in that vicinity, all were accounted for,” she said. “We have medical personnel on scene. We have not had to use them at this time.”
SFMTA tweeted that the 38 Geary was being re-routed due to the fire. Muni riders should expect delays.
About 3,000 PG&E customers in the area were without power as of 3 p.m. A reunification site for those affected by the fire has been set up at Mel’s Drive-In at 3355 Geary Boulevard, across the street from Hong Kong Lounge II, according to SFFD.
Dianne de Guzman contributed to this report.
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This post was originally posted at https://www.sfgate.com/bayarea/article/fire-inner-richmond-gas-shut-off-long-time-how-13595728.php.