In an earthquake, the shaking of a home or apartment can cause damage to gas piping and appliances. This damage can result in releases of natural gas that can lead to fires or even explosions. Structural weaknesses, the absence of appliance anchors, seismic activity, and a lack of flexible pipe connections can all contribute to a greater possibility of natural gas leaks. This problem is so prevalent that natural gas contributes to one of every four fires after an earthquake.
A primary concern when dealing with natural gas leaks and ensuing fires is the protection of property, rather than personal safety, because most homes have several potential exits for escape from a fire.
Reduce the Possibility of Gas Leaks
An effective way of REDUCING many natural gas leaks in the first place is to make sure that your water heater and any other appliances using natural gas are properly anchored and have flexible pipe connections.
The Simple Solution
At a minimum, know how to turn off the natural gas supply to your home. Make sure that you have an appropriate wrench easily accessible. You may also want to join a neighborhood preparedness group or make arrangements with your neighbors so that they can turn off your gas if you are not home and if they smell gas.
Warning: You should NOT turn off your gas unless you smell gas. The gas should only be turned back on by your gas company
One Answer – Shut-off Valves
One of the most common ways of protecting your home from gas leaks is by installing some sort of shut-off valve. These include Earthquake Actuated Valves, Excess Flow Valves, Methane Detectors, Hybrid Systems, and Manual shut-off valves. Each may have its advantages and disadvantages and these are compared in the following tables. Homeowners should consider their individual needs and use the tables select their best personal option.
Note: Earthquake Actuated Valves and Excess Flow Valves should be certified by the State Architect. Some installations may require building permits (consult your local jurisdiction). Some juridictions have adopted ordinances requiring gas shut-off devices at time of sale or when significant renovations are being undertaken.
|Gas Shut-off Option Costs|
Installation Cost (2)
|Restrain Individual Gas Appliance||$15-$50||$0-$100|
|Manual Shut-off valve & wrench||$5-$20||$0|
|Earthquake actuated valve||$100-$300||$100-over $300 (3,4,5)|
|Excess flow valve at meter||$20-$100||$100-over $300 (3,4)|
|Excess flow valve at appliance||$5-$15||$0-$100|
|Hybrid system||$150-over $500 (6)||$100-over $500 (7)|
1. There are significant differences in the operaton of the various devices listed.
2. All costs are approximate and do not include permit and inspections fees that may range from $25 to over $100 depending upon the local jurisdiction. Installations that can be performed by the building owner are assumed to have no cost.
3. Installation costs do not include a survey of the gas system that can cost over $200.
4. Higher installation costs may occur if substantial modifications of plumbing are necessary.
5. Higher installation costs may occur if substantial modifications to attach the valve to the building are necessary.
6. Costs for hybrid systems depend on the number and type of components installed.
7. Higher installation costs can be incurred for hybrid systems that require installation of wiring to connect multiple sensing units.
|Gas Shut-off Comparisons|
|Consideration||Manual Shut-off Valve and Wrench||Earthquake Actuated Valve||Excess Flow Valve||Methane Detector||Hybrid System|
|Basis of Operation||Utilities have installed manual shutoff valves near gas meters allowing owners with proper wrenches to shutoff gas in emergencies.||Senses shaking in a building that is above a design level of shaking and automatically shuts off gas.||Senses gas flows that are above a design shutoff flow rate and automatically shuts off gas.||Senses the presence of natural gas in the air and triggers an alarm.||A variety of modular devices that could include a main control unit, shake sensors, excess flow sensors, methane detectors, and alarms.|
|Benefits||All gas services already have valves installed. Guidance for occupants is currently provided in many public information documents like the phone book.||Actuates only in cases when building shaking may be sufficient to cause damage to the gas system. Someone does not need to be present to ensure shutoff.||Actuates only in cases when excess gas flows downstream of the device. Someone does not need to be present to ensure shutoff.||Alerts occupants when detectable gas concentrations are present they reach hazardous levels, allowing time for shutoff and evacuation.||Systems are modular and can be customized for desired applications. Each module has benefits associated with specific action.|
|Potential Drawbacks||Only effective if someone is present, knows the valve location, has access to the valve, and has a wrench suitable to close the valve.||Can actuate even if damage and hazards do not exist. Aftershocks can cause the device to actuate after service has been restored. May actuate from shaking not related to earthquakes.||Will not shut off gas if leakage is below the design shutoff flow rate, even if a slow leak exists. May not activate if the occupant changes gas systems downstream without modifying the device.||Someone needs to be present to respond to the alarm. Alarm may trigger for other flammable vapors in addition to natural gas.||Each module has drawbacks associated with specific actions.|
The two tables above are from Improving Natural Gas Safety in Earthquakes, California Seismic Safety Commission