The cause of the San Bruno pipeline disaster remains unsolved. But scores of pipeline disasters are avoided every day thanks to a program called Underground Service Alert, "USA" or "DigAlert" for short.
DigAlert did not yet exist in June 1976 when a construction crew in Culver City was excavating the median strip of Venice Boulevard. The crew did not know that just feet below the ground lay a petroleum pipeline, the fuel inside pressured to 550 psi.
Suddenly, the smell of petroleum and gas filled the air. The excavator had struck and broken the pipeline. The volatile fuel sprayed into the atmosphere and vaporized. A crewmember tried to warn passers-by and nearby shopkeepers to move away.
Then came the enormous explosion, followed by waves of fireballs.
The disaster killed nine people and severely burned 14 more. Nearly an entire block of Venice Boulevard was leveled.
Out of the ashes came a commitment to prevent such disasters. The answer was a program to make sure anyone digging knows what's below before starting.
Underground Service Alert was established as a consortium of the major utilities and local governments. It maintains detailed maps of the locations of all underground utility lines.
To get the locations pinpointed on the ground for any particular project, all the contractor needs to do is call 8-1-1 and open a ticket.
DigAlert inputs the location into a computer program that determines which utilities have lines at that location. Then DigAlert notifies those utilities, which send out technicians to the project site to determine the exact locations, and spray paint them on the ground above.
Fees from the utilities cover the costs of the program. For the caller, it's absolutely free.
Even if you're not involved in construction, chances are you've seen the "USA" painted on the ground at a site where there will be digging.
The oft-repeated message is that 8-1-1 needs to be called if you're digging a trench or just planting a jacaranda on your curb strip.
The only way DigAlert fails is when excavators fail to call. Pipelines still get broken in excavation accidents, but the risk is nowhere nears as high as it was prior to Culver City's 1976 disaster.