In an earthquake, the
shaking of a building 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 businesses have several
potential exits for escape from a fire.
the Possibility of Gas Leaks
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. This is particularly true for restaurants
or other businesses with large numbers of appliances using natural gas.
a minimum, both you, and your employees, should know how to turn off the
natural gas supply to your business. Make sure that there is an appropriate
wrench easily accessible. Because the natural gas utility (such as PG&E)
will be the one to relight the pilot of any appliances, make sure that you
(or your employees) turn off the gas only if they smell gas.
||Diagram courtesy of the
Calfiornia Seismic Safety Commission
Answer - ShutOff Valves
One of the most common
ways of protecting your business 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. Businesses should work with the property owner
and should consider their individual needs and use the tables select their
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
Shutoff Option Costs
valve & wrench
|Excess flow valve
|Excess flow valve
||There are significant
differences in the operaton of the various devices listed.
||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
do not include a survey of the gas system that can cost over $200.
costs may occur if substantial modifications of plumbing are necessary.
costs may occur if substantial modifications to attach the valve to
the building are necessary.
||Costs for hybrid systems
depend on the number and type of components installed.
costs can be incurred for hybrid systems that require installation
of wiring to connect multiple sensing units.
Shutoff Valve and Wrench
have installed manual shutoff valves near gas meters allowing owners
with proper wrenches to shutoff gas in emergencies
shaking in a building that is above a design level of shaking and
automatically shuts off gas.
gas flows that are above a design shutoff flow rate and automatically
shuts off gas.
the presence of natural gas in the air and triggers an alarm.
variety of modular devices that could include a main control unit,
shake sensors, excess flow sensors, methane detectors, and alarms.
gas services already have valves installed. Guidance for occupants
is currently provided in many public information documents like the
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.
only in cases when excess gas flows downstream of the device. Someone
does not need to be present to ensure shutoff.
occupants when detectable gas concentrations are present they reach
hazardous levels, allowing time for shutoff and evacuation.
are modular and can be customized for desired applications. Each module
has benefits associated with specific action.
effective if someone is present, knows the valve location, has access
to the valve, and has a wrench suitable to close the valve.
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.
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.
needs to be present to respond to the alarm. Alarm may trigger for
other flammable vapors in addition to natural gas.
module has drawbacks associated with specific actions.
|The two tables
above are courtesy of California Seismic
Safety Commission (The Homeowner's Guide to Earthquake Safety).
Commision - The
Homeowner's Guide to Earthquake Safety
Commision - Improving
Natural Gas Safety in Earthquakes
of the State Architect - Earthquake
(Describes the State of California Gas Shut-Off Valve Certification Program)
California Gas Company - Earthquake
for an Earthquake