According to the California Seismic Safety Commission, a gas leak is the cause, or a contributing factor, of one in every four post-earthquake house fires. Therefore, it is important to both make sure that natural gas pipelines leading to your home have flexible pipe connections and are well-anchored, and to know how to shut off the natural gas supply altogether.
Manual Shutoff Valve
All natural gas meters are equipped with a manual shutoff valve, located near the utility-owned meter on the outside of the building. A 12-to-15 inch adjustable pipe or Crecent-type wrench is necessary to shut off the gas using these valves. To shut off the gas, locate the valve and rotate it a quarter-turn in either direction. The gas is off when the handle is perpendicular to the pipe. After the gas is shut off manually, only utility personnel and plumbers can restore service.
Earthquake Actuated Valve
State-approved automatic shutoff devices can be installed on the pipeline between the building and the gas meter. One such device is the earthquake actuated valve, which shuts off the gas flow automatically when it senses a certain amount of shaking. These are handy because no one needs to be present and paying attention for the gas to be shut off. However, they can activate due to shaking that has nothing to do with an earthquake, or during aftershocks after gas service has been restored.
Excess Flow Valve
Like an earthquake actuated valve, an excess flow valve works without a human presence. It automatically shuts off gas when it senses that the flow of gas into the building is faster and more plentiful than ordinary. However, these can be ineffective in the case of a very slow leak. There are two main types of excess flow valves: non-bypass valves (or EFVNBs), which form a gas-tight seal and must be reset manually after the leak is stopped; and bypass valves (EFVBs), which allow a small amount of gas to pass through and automatically reset when the flow is no longer excessive.
Modular hybrid systems, which may feature a Rube-Goldberg-like chain of automatic shutoff valves, methane detectors, alarms and sensors are also available. These are highly customizable and come with all the benefits of the different types of valve that compose them. Unfortunately, they also include the drawbacks of the different types of valves. For example, an earthquake actuated valve with a connected alarm may go off due to non-earthquake shaking and cause an unneeded evacuation. On the other hand, a methane detector attached to an earthquake actuated valve may prevent the gas from being shut off by non-earthquake shaking.