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Breakdown with Mark Irons: Gas valves are important safety equipment

Submitted by on 1, March 17, 2011 – 12:01 am2 Comments
Seismic valves are important safety equipment.

The objective of this series of articles is to break down the basic elements of construction and remodeling for lay persons and homeowners. The series started with permits and the plan review process because those are such fundamental steps for planning and cost estimating.

I would like to proceed through each of the trades, discussing them as analogous to systems of the body: Structural foundation and frame are like bones, plumbing and mechanical are like the circulatory or digestive system and lungs. The exterior systems of weatherization are literally the skin of the building, and like human skin help regulate internal climate and respiration. The electrical system is like the life force that animates the body, and the era of high tech gives us the potential for the brain, with communications systems or even “smart homes.” I’ll start with plumbing.

Because natural gas utilities are the most important when it comes to cost, conservation and safety, I’ll cover additional plumbing-related issues at another time. Today, I’d like to discuss public safety and disaster preparedness.

Having just passed the six month anniversary of the San Bruno natural gas disaster, the local media is ablaze with new facts about that incident, including possible bad welds, bad records, and recently, the electrical failure to monitoring equipment at a distribution station, leaving employees unable to verify or effectively regulate line pressures.

For anyone living in Alameda in April 1994, the San Bruno incident brings back memories of our own gas pressure spike. At the time, PG&E was in the process of retrofitting individual home meters with high pressure regulators so that eventually the mains could run at higher pressures. A large regulator on the gas distribution system failed, causing local gas pressures to spike. Without high pressure regulators on home meters, the normal household pressure of about two pounds per square inch ( p.s.i.) increased multiple times, causing open pilot flames to leap in height, starting some 30 fires and badly damaging or destroying 10 structures. 

In 1992 I retrofitted a seismic gas valve downstream from my meter, meant to automatically turn off our gas in case of earthquake. Back then, concern about failure to properly re-light pilots in the case a seismic valve was accidentally tripped caused PG&E to discourage them entirely. (In 18 years our valve has never been accidentally tripped.)

That said, pressure spikes are less of a concern for Alameda: PG&E’s maps indicate only one large transmission line like the one that ruptured in San Bruno entering the Island near the Tubes, which reduces to local distribution mains under Alameda streets. But because of the inevitable odds for a serious seismic event, any homeowner would be wise to invest in a seismic gas valve, costing about $150 plus installation. This is critical if you have utilities with open pilot flames, to reduce the threat of post-quake fires.

City code now requires seismic valves be installed when homes are sold, similar to sewer lines which must be tested for leaks. The valves are also required to be installed any time any gas utility work is performed, or on remodeling projects with values over $50,000. Concern about open pilot lights has also declined with the introduction of electronic  ignition on new gas utilities.


  • Roger Smart says:

    Thanks Mark for the timely reminder of how this simple shutoff device can markedly increase post earth quake safety. I think people often forget that broken gas lines can be a major source of property damage after the quake has come and gone.
    I was struck by the images of extensive fire damage in Japan after the quake and tsunami. In a major quake it’s extremely unlikely that
    there will be fire dept. services available to douse a house fire. This makes it doubly important to do the simple and affordable things, like an automatic gas shutoff valve, to lessen the chance of fire before a quake happens.

  • JA says:

    Can you recommend companies that do the installation? About how much should it cost?

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