| The
Problem |
|
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. |
|
Diagram courtesy of the Calfiornia Seismic
Safety Commission |
| One
Answer - ShutOff 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 shutoff devices at time of sale or when significant renovations are
being undertaken.
|
| Gas
Shutoff Option Costs |
|
Device
1
|
Hardware
Cost
|
Installation
Cost 2
|
| Restrain Individual
Gas Appliance |
$15-$50 |
$0-$100 |
| Manual Shutoff
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 |
| Methane Detector |
$25-$75 |
$0 |
| Hybrid system |
$150-over $5006 |
$100-over $5007 |
| Notes: |
| 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
Shutoff Comparisons |
|
Consideration
|
Manual
Shutoff 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 courtesy of California Seismic
Safety Commission (report on Improving Natural Gas Safety in Earthquakes). |
| Other
Resources: |
 |
Seismic Safety
Commision - The
Homeowner's Guide to Earthquake Safety |
|
Seismic Safety
Commision - Improving
Natural Gas Safety in Earthquakes |
 |
Division
of the State Architect - Earthquake
Valves
(Describes the State of California Gas Shut-Off Valve Certification Program)
|
|
Southern
California Gas Company - Earthquake
Information |
|
PG&E
- Preparing
for an Earthquake |
