By Thomas K. Pendergast
A more detailed account explaining how a two-story column of fire blasted up from a Pacific Gas and Electric (PG&E) gas line at the corner of Geary Boulevard and Parker Avenue in February of 2019 was released last month by the National Transportation and Safety Board (NTSB).
Although reaching the same conclusion as the preliminary report – that an excavator from a third-party engineering firm hired to put fiber-optic cable in the ground caused the explosion when it disturbed a pipeline connection – the new report also offers recommendations for dealing with such disasters in the future to avoid repeating this event, which took two-and-a-half hours to cut off the gas and put out the fire.
According to the new report, the Feb. 6 incident started about 1:07 p.m. when a third-party contractor for a Verizon Wireless project, Kilford Engineering Inc., hit a 2-inch PG&E natural gas main where it connected to a 4-inch main, rupturing the pipe and igniting the gas.
The fire torched the building on the northwest corner, including the dim sum restaurant Hong Kong Lounge II and at least two residential units on the second floor above it. The fire also damaged the building next door to the point where it is still uninhabitable. There were no injuries. The estimated cost of the damages to nearby buildings and the pipeline system exceeded $10 million.
The San Francisco Fire Department was dispatched and arrived on scene at 1:12 p.m. to contain the fire. Fire and police department personnel evacuated about 100 people in the immediate area and PG&E shut off natural gas service to 328 customers.
At 3:36 p.m., the damaged pipelines and branch connection were isolated, and the fire department extinguished the fire two minutes later.
“The National Transportation Safety Board determines that the probable cause of the Feb. 6, 2019, release of natural gas from the Pacific Gas & Electric Company distribution pipeline and the subsequent fire was the failure of the Kilford Engineering Inc. operator and spotter to follow safe excavation practices within the tolerance zone, which resulted in the mini excavator trenching bucket attachment impacting the pipeline’s branch connection,” according to the latest report.
“Kilford did not follow the best practices for digging around utilities,” said Robert Hall, the NTSB director for their Office of Railroad, Pipeline and Hazardous Materials Investigations. “You’re supposed to hand dig, within I believe in California it’s 18 inches, and they weren’t doing that. And they ruptured the pipe.
“They shouldn’t have been doing mechanical digging. They should have been digging by hand, or there’s a technique called vacuum excavation where literally they use a big vacuum truck to suck up the dirt. That would have been an acceptable method,” Hall said.
The report states that the job foreman, while using a mini excavator, relied on a spotter to help locate utilities. The spotter determines the depth of underground utilities because of the limited view from inside the excavator.
They had previously located the 4-inch gas pipeline and the 2-inch gas pipeline at 48 inches deep, although they only exposed a portion of each pipeline and did not expose the branch connection where the two pipelines met. The operator stated that he was digging at least 2 to 3 feet from the 2-inch gas pipeline that had been exposed along Parker Avenue and was likely higher than the 2-inch gas pipeline; he was about 4 feet from where the spotter exposed the 4-inch pipeline along Geary Boulevard. The spotter reported that he could not see either of the gas pipelines (he never saw the yellow plastic pipelines) in the trench, although he could see an electrical conduit and a metal line. He also stated that the mini excavator bucket was about 2 feet south of where the gas pipeline was.
The operator also reported that he decided to dig to 30 inches, even though the scope of work called for 36-inch trench depth. The spotter reported that the trench was only 24 to 30 inches deep where the mini excavator was working at the intersection.
As the operator continued to remove dirt with the excavator, the gas started to escape; he did not notice an impact or scraping before the gas release. Once the release began, the spotter immediately climbed out of the trench and ran north, away from the release site. The operator got out of the excavator as the spotter exited the trench. As the operator was returning to the excavator to retrieve his phone, the gas ignited.
The fire brought oncoming traffic to a halt and PG&E officials had a hard time getting to the scene through the ensuing traffic jam, so they requested police escorts from a nearby police officer but were denied because the officer he asked “did not believe that escorts were a service the SFPD offered” according to the report.
The PG&E “911 Notification Process” stated Gas Distribution Control Center (GDCC) personnel should request assistance from 911 dispatch if PG&E personnel are delayed due to traffic, yet the GDCC did not make such a request although they were aware of the delays.
“We felt that if they had a formal document outlining the process by which they could get a police escort for the gas responders to get to the scene, that that would be helpful in securing the leak,” Hall said.
“On the day of the incident, our crews arrived on site within 20 minutes of the initial notification and worked diligently and safely to shut off gas to the immediate area,” said PG&E spokesman Jason King. “PG&E is collaborating with the San Francisco Department of Emergency Management (SFDEM) to establish an agreement on providing a coordinated response to enable crews to arrive more rapidly at the scene of a pipeline accident. Discussions are ongoing, and a meeting with SFDEM is scheduled for September.”
An initial excavation of a 4-inch polyethylene pipeline on Parker Avenue was completed by 2:34 p.m., while a second crew on site began work at 1:50 p.m. to excavate the 6-inch steel pipeline in the center of Geary Boulevard where a 12-inch steel pipeline interconnected with the 6-inch steel pipeline.
After the excavation of the 6-inch steel pipeline was already underway, three PG&E locators determined that excavation would not isolate the segment, so it was abandoned. Another excavation of the 12-inch pipeline was started closer to the fire.
The fire was extinguished at 3:38 p.m.
“We did find that PG&E needed improvement in their planning for isolation in that the geospatial location should be on the valve plan,” Hall said. “You could use a cell phone then with latitude and longitude to direct you to the exact location of the valves you needed to close.”
“PG&E has already incorporated the use of a Gas Distribution Geographic Information System (GDGIS) layer with detailed location information for the field crews in creating isolation plans for gas dig-ins,” King said. “PG&E also has a project underway to integrate our Emergency Shutdown Zone (ESZ) information into GDGIS. Integrating our ESZ information into GDGIS will improve our ability to provide detailed location information for valve isolation plans requiring the use of a full ESZ or multiple ESZs. PG&E currently anticipates completing the data integration project around the first quarter of 2022.
A spokesperson for Kilford Engineering declined to provide a comment for this article.