7.2.5: Utility Lines

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Overview

One of the greatest dangers in an earthquake is fire. Fire caused much of the loss of life and property in the 1906 San Francisco Earthquake and the 1995 Kobe Earthquake, and large fires destroyed property in the Marina District of San Francisco after the 1989 Loma Prieta Earthquake. The problem is natural gas.

If gas connections are rigid, they are likely to shear during an earthquake, releasing gas that needs only a spark to start a fire. Gas connections should be flexible. After an earthquake, you must shut off the main gas supply to the house (Figure 11-7). Learn where the gas supply line is and ensure that the shut-off valve is not stuck in place by turning it one-eighth turn (one-quarter turn is the closed position). Your gas company will sell (or give) you an inexpensive wrench (illustrated in Figure 11-7) that should be kept permanently near the valve. Tell all members of the family where the wrench is and how to use it. In the event of a major earthquake, shutting off the gas is a top priority. You won’t have time to rummage around a heavily damaged house looking for a wrench.

For $400 to $600, you can have an automatic shutoff valve installed on the gas line. This valve, located between the gas meter and the house, is activated by earthquake shaking, which knocks a ball or cylinder off a perch inside the valve into a seat, thereby shutting off the gas. Consider an automatic shutoff valve if you are away from home a lot and are not likely to be around to shut off your gas after an earthquake. A disadvantage of the automatic shutoff valve is that you wouldn’t be able to tell easily if you had a gas leak in your house after the valve had shut off the gas. If you’re confident that you don’t have a gas leak, you should know how to reset the valve yourself, because after a major earthquake, weeks might go by before the gas company or a plumber could get to your house and reset the valve for you. Remember that when the valve is reset, you must immediately relight all the pilot lights on your appliances.

All gas lines and water pipes should be supported at least every four feet. Earthquake vibrations can be strongly exaggerated in an unsupported pipe in your basement or crawl space. If pipes are not supported, strap them to floor joists or to walls.

If liquefaction occurs, underground utility lines might be severed, even if your house is anchored below the liquefying layer and doesn’t fail. Underground gas lines failed due to liquefaction in the Marina District of San Francisco, triggering many fires.

A generator can supply emergency power, but this should be installed by a licensed contractor. The generator should be installed in a well-ventilated place outside the home or garage, and fuel should be stored according to fire regulations. A generator installed in a closed place in the house could lead to carbon monoxide poisoning.