Explosive situation in Pittsburg resolved after 16 hours

Three things happened Wednesday night between approximately 6 and 8 p.m. in Pittsburg, California: A grass fire broke out. A PG&E power line fell. An underground, 8-foot-deep, 10 by 12 vault that serves a 12-inch, high pressure, Chevron gas main erupted into flames.

It is not known if the fallen power line started the grass fire or the fire caused the power line to fall. What is known is that thousands of residents were evacuated from their homes for 16 hours.

The hot-vault fire, spewing flames, had the potential to damage the gas main with an explosive effect.

First crews had to stop the gas flow.

"We were able to take that 12-inch natural gas pipeline, bleed the natural gas out of that in a controlled manner, in a safe manner, taking it from 480 PSI down to 25 PSI," said Contra Costa Direct District Chief Terrence Carey.

Then, nitrogen was injected into the pipeline to remove all flammables from the pipeline and the vault.

Once that was complete, we took Chevron personnel and our fire personnel down to the scene. We went into the scene into the vault," said Chief Carey.

Once they entered vault, which had badly damaged cover doors and a see-through grate, they found the likely source of the fire in the vault.

"In the vault, you had the 12-inch line running through there and then you has these small feeder lines, which I don't know what the proper professional term is from Chevron, a 3/8th inch line and that's where the breach occurred, which was that gas was exposed, that gas was on fire and our concern was it was impinging on the larger line," said Carey.

The only way to more speedily depressurize the pipe was to vent the huge amount natural gas into the atmosphere so the gas could more safety dissipate.