San Francisco natural gas pipeline puncture, USA. 25th August 1981

Accident summary

A 16 inch natural gas pipeline, located in California (USA), which conveys gas entrained with oil containing polychlorinated biphenyl (PCB) was damaged by third party activity.

An excavation subcontractor using a drill punctured the gas pipeline. The hole allowed the gas to escape in an upward direction, which was then carried towards nearby buildings. The gas did not ignite and was naturally dispersed. However, there was a fall out of the PCB-oil as a mist, which contaminated an eight square block area of the city's financial district. This initiated the evacuation of approximately 30,000 individuals.

Failings in technical measures

The probable cause of the incident was failure of the principle contractor to comply fully with the terms of the excavation permit, which required the verification of local underground facilities. The subcontractor was aware of the presence of a gas main, but did not know its precise location.
Permit to Work Systems: location of hazardous substances
Contributing to the duration of the gas leak was failure of the pipeline operator to locate an emergency valve due to inadequate documentation.
Emergency Response / Spill Control: emergency operating procedures/training
When one of the emergency isolation valves had been identified, its physical accessibility was restricted because the valve had been paved over. Another isolation valve failed to close because of inadequate maintenance/testing procedures. Also, some operators were unaware how to operate particular isolation valves)
Emergency Response / Spill Control: emergency operating procedures/training
Maintenance Procedures: maintenance systems
Isolation: remote and manual isolation

References

'Natural Gas Pipeline Puncture, San Francisco, California', National Transportation Safety Board, 1981.