In fact a natural gas outage of 300 households is an extremely rare event. This area's natural gas system is vulnerable to earthquake damage, third party damage and landslide damage. Earthquake damage could include a catastrophic systems failure in which ground movement causes a pipeline to sever allowing gas to escape. Puget Sound Energy is less concerned with gas escaping in wild settings, where life and property are not threatened. This is because natural gas is lighter than air and will quickly dissipate, minimizing risks.
Gas escaping into buildings or heavily populated areas is a bigger concern.
The current infrastructure does include control valves for shutting down pipelines in the event of such problems. The city of Seattle's natural gas system is more vulnerable to ground shaking than other parts of King County. This is because Seattle has a low pressure system made of cast iron which does not do as well in earthquakes. The marina that caught fire after the Loma Prieta earthquake had this type of system. Puget Sound Energy is in the process of replacing this sys tem with one that handles ground shaking more effectively.