Earthquake Shut-Off Valves
When most people think of earthquakes they think of glass breaking, bridges tumbling, houses collapsing, but most people don't think of fires. Fact during the 1994 earthquake there were 110 fires leading to 6.1% of the deaths, and 7.7% of the hospitalizations caused by the disaster.
During an earthquake, it is very likely that a gas pipe will crack or obtain damage. Natural gas can be harmful to inhale leading to health concerns, but more concerning is its ability to catch fire. An earthquake valve is designed to be installed in regions where earthquakes are more likely, such as California. It is usually installed between the gas meter and the house. The way they work is much simpler than you would imagine. There is a ball that is sitting on a pedestal over the flow pipe, when the valve shakes it knocks the ball off the pedestal blocking the flow.
There are several types of valves but most can be reset by pulling a chain or turning a screw, however, it's recommended to have a plumber present when resetting it after an earthquake to ensure there are no leaks.
The downside to having one is that if something bangs into the gas pipe, such as a garbage can, or even kids playing, it can trip the mechanism. This not only shuts off the gas to your house, but you will have to relight all your pilots. Thankfully most new appliances are moving away from pilots, but new water heater tanks still have them. To reduce the chance of this happening, you can install bollards, or fencing around the device.
When buying a house in some cities, the seller is required to bring the house up to certain standards. Los Angeles for example requires smoke and carbon monoxide detectors, Water Conservation Devices, and Seismic Gas Shut-Off Valves to name a few. (here is a link to the LADBS website https://www.ladbs.org/services/getting-started/requirements-when-selling) So it may be the seller's responsibility to install earthquake shut-off valves. You can consult your agent who will know about these requirements.
Some common mistakes I’ve seen in the installation of these include mounting it upside down or I’ve even seen it installed backward allowing the flow in the wrong direction. I’ve also seen it installed after the gas line branches in another direction, causing some gas lines to bypass the device.
Because this requires handling a live gas line, I’d recommend getting a qualified plumber. It's not worth doing it yourself.
In conclusion, an earthquake shut-off valve turns the gas supply off to your house if it senses movement. They are recommended in areas where earthquakes are more likely, and should be installed by a qualified plumber.