SAN FRANCISCO—A gas pipeline that exploded in San Francisco’s Geary Boulevard neighborhood earlier this month shows evidence of being damaged by third-party excavators, the National Transport Safety Board indicated on Wednesday, February 27.

The 3-alarm fire occurred on February 6 when third-party excavators were installing fiber optic cables underneath Geary Boulevard. According to the report, a gas line was struck and ignited in less than 10 seconds. The five Kilford Engineering Inc. employees working during the incident were able to escape without injury because of “audible and visual cues” that indicated that a mini-excavator had struck the line, the report noted.

The contractors used a jackhammer to remove the top layer of concrete in order to install the fiber optic cables. After the concrete was cleared, the contractors used a mini-excavator with a bucket and hand shovel to remove the soil underneath.

Investigators indicated that the February 6 fire took more than two hours to extinguish, though crews from PG&E were on-site within 20 minutes. The agency will continue its investigation into whether Kilford Engineering was prepared and qualified to complete the excavation work.

There were no reports of injuries during the incident, but five structures were damaged during the process. Hundreds of customers and residents were without gas and others were displaced from their homes as a result of the fire.