"Service Restoration Time for Major Earthquakes"

Northridge 120,000 12 days
Loma Prieta 156,355 9 days
Whittier 20,600 10 days
*Does not include customers affected by the additional time needed
to reconstruct gas distribution facilities or structures

Also:
"The risk of a gas-related fire in residential
structures following earthquakes is generally
very low because of the numerous conditions
necessary for gas ignition (see, for example,
Williamson and Groner, 2000).
The ignition of leaking gas requires an ignitable
mixture of gas and oxygen between the
approximate range of lower (5%) and upper
(15%) explosive limits and an ignition source.
This can occur in the presence of a pilot light or
when a light switch is turned on or off. For
natural gas that is lighter than air and tends to
disperse, the rate of gas leakage capable of
igniting is related to the air exchange rate in the
area of the leak. The likelihood of ignition is
higher in conditions where poor air mixing
allows formation of pockets of higher
concentrations of gas.

. . . . Post-earthquake restoration of gas service by
non-qualified personnel increases the potential
risk of injury or death from the accumulation
and ignition of unidentified gas leaks and carbon
monoxide in damaged gas appliance vents.
Lengthy service interruptions may lead to nonqualified
personnel re-establishing service
without taking the necessary precautions."

From the California Seismic Safety Commission's "Improving Natural Gas Safety in Earthquakes." Link below.

Mike Williams

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