Santa Rosa PG&E gasline explosion

Political leaders are calling for PG&E to install on its gas lines automatic shut-off valves to prevent or mitigate future gas line disasters.

Sounds like a good idea. Here’s an interesting snippet from a report of the NTSB, the agency that is investigating the San Bruno gas explosion:

The Safety Board believes that had an EFV been installed . . .  the valve would have promptly closed . . . . This closure would have likely prevented the release of gas sufficient to form an explosive mixture . . .. Additionally, an EFV would have prevented the continued release of gas during the emergency response activities and endangerment to firefighters and other emergency personnel.

The NTSB’s recommendation makes good sense.  What’s most interesting, however. is that the NTSB’s recommendation wasn’t issued as a result of the San Bruno Fire.  Rather, it was issued after the Santa Rosa fire.  In 1992.

Why hasn’t NTSB’s recommendation been implemented in the 18 years since the last fatal gas explosion?

As I wrote here, the NTSB has no power to require PG&E to do anything.  It can only recommend.  And, of course, PG&E is free to ignore those recommendations.

Santa Rosa Gas Explosion Safety Recommendation


The google map below shows the spot where the pipeline exploded.  It also shows the asphalt patches placed on the street surface by a San Francisco firm (D’Arcy and Harty) after it completed sewer work in May 2008.

Before a contractor digs in the street, PG&E is supposed to mark on the street with spray paint the location of its gas lines so that the contractor can avoid them. Interestingly, those paint marks aren’t visible. Maybe they were worn away, or perhaps the contractor just paved over them after it finished the work.  Maybe the photo just isn’t of high enough resolution.  But certainly the situation brings back memories of the last underground gas explosion in the bay area —  the one on Spencer Avenue in Santa Rosa.

In the Santa Rosa explosion, PG&E failed to properly mark the location of its gas line. A contractor hit the line with a backhoe and damaged it. The line leaked months later. Residents smelled gas in the days leading to the blast, but nothing was done to find or repair the leak.  

One thing might be different here.  The contractor may have damaged the gas line not with a backhoe, as in Santa Rosa, but with the vibration resulting from its unique method of sewer line replacement.  According to the San Jose Mercury News

To avoid the disruption of digging trenches in the street, the contractor used a method called "pipe bursting." Crews pulled a large, cone-shaped device through the aging, 6-inch sewer pipes, shattering them, and replaced them by pulling a new, 10-inch, polyethylene sewer pipe in behind them. The technique can cause ground shaking and disruption of adjacent soil and rock.

Local residents report that there was certainly lots of shaking and pounding in connection with the D’Arcy and Harty project.

Of course, to a large extent, how the damage to the gas line was done isn’t nearly as relevant as why PG&E didn’t find and fix it.

San Bruno Excavation

Hearing about the San Bruno explosion brought back memories of another PG&E explosion that killed two, injured three others, and destroyed an apartment building in Santa Rosa.  In fact, the Wall Street Journal even mentioned that explosion in its article discussing the San Bruno blaze.

I spent 4 years prosecuting the case against PG&E on behalf of the families of those killed. Some of the lessons I learned from that case seem applicable here:

  • Gas leaking from the street will follow the path of least resistance. The path is typically through the airspace that exists around the pipes that lead into or under the nearby houses.
  • Natural gas has no odor. PG&E adds to the gas an odorant (called mercaptan) before distributing it. The sole purpose of the odorant is to help in detection of leaks.
  • The odorant is stripped from the gas when the gas passes through or along dirt. That means the odorant is effective of alerting people of a leak from an appliance such as a stove, but is much less effective at alerting people of a leak from the street.

If even one person reports to PG&E the smell of gas, or rotten eggs, or a smell like rotten food — however faint — PG&E must chase it down.  If the smell cannot be traced to an appliance, it’s potentially big trouble. A faint smell of gas can mean either a very small leak from an appliance or a huge leak that has passed through soil, been stripped of its odorant, and is permeating the neighborhood homes. 

In any case, locating and controlling leaks is PG&E’s responsibility.