1. Why Gas Companies Stop the Gas on Purpose After an Earthquake
Gas can cause fires or explosions if it leaks and comes near a fire. During an earthquake, pipes inside homes and under roads may be damaged. Therefore, gas companies follow a rule: if they feel strong shaking, they stop the gas first, before checking if there is damage. The Japan Gas Association explains this earthquake countermeasure through three pillars: equipment measures, emergency measures, and recovery measures [1]. There are two main places where the gas is stopped: inside the house and on the city side. We will look at these in order.
Note: If you cannot use gas after an earthquake, it is the result of this safety design, not an abnormality.
2. How the Microcomputer Meter in Your Home Shuts Off the Gas
Most household gas meters contain a safety device called a microcomputer meter. If it detects shaking equivalent to a seismic intensity of 5 or higher, it automatically stops the gas supply to the house [1]. It does not only activate during earthquakes. The red light may flash and the gas may stop if there is a continuous gas leak, if the gas pressure drops, or if appliances are used for a long time [3].
To reset it, you must turn off all gas appliances, press the reset button, and wait. During this time, the meter checks for gas leaks. The waiting time is about 3 minutes, but this varies by model. If you smell gas, you are instructed to contact the gas company instead of trying to reset it [3]. However, the home meter alone is not enough. If the pipes under the road are broken, the gas needs to be stopped before it even enters the house.
3. How District Governors and Blocks Shut Off Gas on the City Side
A district governor is a device that lowers gas delivered at medium pressure to the low pressure used in homes and offices. In the Tokyo Gas Network supply area, there are about 4,000 of these units, each equipped with a seismometer (SI sensor) [2]. If they detect shaking strong enough to damage gas pipes, that district governor automatically stops the gas supply. The low-pressure pipes are divided into many blocks, so the gas stops block by block. This makes it easier to stop only the dangerous areas without affecting regions that likely have no damage [2].
Another system is remote shut-off. Information from seismometers placed at a density of one per about 1 km² (about 0.4 square miles) is sent to a command center. From there, district governors in areas predicted to have fires or collapsed houses are stopped remotely [2]. Note that the number of units and blocks mentioned here is an example from Tokyo Gas; other companies have different numbers.
4. How Long Restoring Gas Took After the 1995 Great Hanshin-Awaji Earthquake
During the Great Hanshin-Awaji Earthquake in 1995, Osaka Gas reported that the supply stoppage exceeded 800,000 households, which was the largest scale in the country. Because preventing secondary disasters was the priority, it is said that recovery took about 3 months [4]. The number of households varies in records from about 840,000 to 860,000, so we stick to "exceeding 800,000 households."
Stopping the gas takes a moment, but restarting it requires finding and fixing broken spots, checking that there are no leaks in the pipes, and opening them up region by region. The Cabinet Office’s collection of lessons notes that propane gas was mostly recovered about 2 weeks after the quake, while city gas recovery was completed on April 11, except in some areas [5]. Based on this experience, measures to divide the shut-off range and earthquake-resistant pipes that are hard to break have been promoted. The next section covers the latter.
5. How Polyethylene Pipes Help Gas Pipes Resist Earthquakes
Polyethylene pipes combine strength with the ability to stretch well. The Japan Gas Association explains that gas leaks do not occur even when force is applied during an earthquake [1]. However, since this is an industry association explanation, it does not mean they "absolutely never leak." The earthquake resistance rate of the main low-pressure pipes was reported as 89.5% at the end of 2018. The national plan aims for 95% by the end of fiscal year 2030 [6]. Since it is not 100%, some areas still have old pipes. After the Great Hanshin-Awaji Earthquake, polyethylene pipes are said to have been widely used for newly built low-pressure pipes.
Note: The national "Gas Safety Enhancement Plan 2030" sets a target of 95% by the end of fiscal year 2030 [6].
6. What You Can Do Today: Find Your Home's Gas Meter
What you can do today: Find your home’s gas meter and confirm its location with your family. Do not touch it or press buttons. Just look to see where the reset button is.
What you can do when you go out: There may be marks or covers on the road that show the location of gas pipes. Do not open them; just look.
Talk with your family: It is reassuring to talk with your family about who will check the reset procedure if the gas stops and what to do if you smell gas. The Japan Gas Association and your local gas company’s pages also list how to respond during an earthquake [1][3].