Seismic valves automatically shut off natural gas service during an earthquake to prevent gas leaks and potential fires or explosions. They are mandatory in some regions and can be installed in the pipeline leading to a facility. Overflow sensors and methane detectors are also used as precautions. Gas appliances should be docked and gas meters have manual shutoff valves.
A seismic valve automatically shuts off natural gas service to a home or business when an earthquake occurs at or above a level that could damage the equipment. These valves could prevent fires or explosions from gas leaks after an earthquake and allow for faster restoration of service once the danger has passed. In some regions prone to frequent seismic activity, a seismic valve is mandatory before insurance companies issue policies. Seismic valves are typically installed in the pipe that leads from the gas company’s pipeline to a facility.
When the earth moves, the movement can damage gas main lines or lines connected to gas appliances. If a leak occurs, an electric spark or open flame could ignite the natural gas, resulting in an explosion or fire. One study found that more than half of all fires after an earthquake came from natural gas leaks.
A seismic valve detects the movement of the ground, which activates a closing device. An advantage of a seismic valve includes the ability to prevent gas leaks into a hollow structure. Disadvantages include automatically shutting off gas flow when there is no damage to the gas lines and no leaks. Aftershocks could also cause a seismic valve to go out of service after it has reset, creating the need to repeatedly reset the valve.
Overflow sensors also work to shut off gas service during an earthquake. They work by shutting off the gas when the flow rises above a certain level. These devices are ineffective for slow leaks that do not activate a shutoff mechanism. Overflow sensors can be installed on the main line entering a building or on each gas appliance.
Some residents who live in earthquake-prone areas install methane detectors as a precaution against gas leaks. An alarm on this device goes off when methane gas permeates the air, allowing the occupants time to shut off the gas and evacuate. However, someone must be available to listen for the alarm and shut off the gas lines when these alarms sound. Methane detectors could also set off an alarm for other vapors in the air.
During an earthquake, gas appliances could tip over or shift, rupturing the rigid connections that supply fuel. In some cases, walls collapse and land on gas lines or meters, causing damage that could start a fire. Mobile homes usually fall off their jacks if they are not properly secured and anchored, rupturing the gas lines leading into the residence. The hoses could prevent a gas leak during seismic activity.
Gas company experts recommend docking all gas appliances, including water heaters. If the heater is on a raised platform, it can move during an earthquake if the platform is unstable. Most gas meters have manual shutoff valves designed to shut off the flow of gas with a simple wrench.
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