SAN FRANCISCO (CBS SF) — If you look closely, there are still scars left over from the explosion of a ruptured natural gas line in San Francisco’s Inner Richmond neighborhood more than two years ago.

The blast rocked Geary Blvd. at Parker Ave. on the afternoon of Feb. 6, 2019. A two-story building on the corner – site of Hong Kong Lounge II restaurant and residences on the second floor – was extensively damaged by a giant orange fireball that sent diners running for their lives.

Sisters Cindy and Judy Chan were inside the restaurant celebrating Chinese New Year with their parents at the time, sitting right next to the fire when it erupted.

“I heard popping sounds. I thought it was fire crackers because it’s Chinese New Year,” Cindy Chan told KPIX 5 at the time. Within seconds, all they could see was a bright orange glow surrounding the restaurant.

Five buildings were damaged. There were no injuries.

After years of investigation, the National Transportation Safety Board issued its finding of blame on Tuesday.

Federal investigators determined the failure of Kilford Engineering Inc.’s excavation crew to follow safe excavation practices led to a backhoe striking a Pacific Gas & Electric Company 4-inch natural gas distribution pipeline, triggering the explosion.

“This accident shows there are rules and procedures in place to ensure safe excavation; however, in this case, the construction crew chose not to abide by them,” said Robert Hall, Director of the NTSB’s Office of Railroad, Pipeline and Hazardous Materials Investigations.

“Consequently, the crew conducted mechanical excavation too close to the pipeline without taking the proper precautions first to make sure the area was safe to execute the dig.”

The NTSB’s investigation also found that there was a 50-minute delay in identifying the locations of specific valves required to be closed to stop the flow of gas after the pipeline was damaged.

“Natural gas fires cannot be safely extinguished until the source is isolated, so the 50-minute delay extended the time the fire burned and increased the safety risk to the neighborhood,” the agency noted.

The NTSB’s report also found that during the post-accident response, the PG&E gas mechanic’s response to the scene was delayed by traffic.

The PG&E supervisor did ask for a police escort from a nearby police officer, but that request was denied.

The agency found that the escort request should have been made by PG&E headquarters to 911 dispatch. The lack of a police escort ultimately did not affect the timeliness of the fire being extinguished.