Thursday, Oct. 18, was the Great Washington Shakeout earthquake drill. Sunday night, there were five reminder quakes up to 6.8 on the Richter scale off Vancouver Island. Here, in the Northwest, we are truly expecting the “Big One.”
The Cascadia Subduction Zone has the potential to be magnitude 9.2 or more. It will be 1,000 times more powerful than the Nisqually quake in 2001. Even the slipping and sliding of the infamous San Andreas Fault Line can only produce a magnitude 8.
Washington has no code requiring large residential propane tanks to be “earthquake strapped.” Experts say they are literally sitting on the ground waiting to roll around. Propane and spilled gasoline are heavier than air and do not dissipate into the atmosphere as natural gas does. The gas and fumes can form pools in depressions, along walls and buildings, by earth berms or even on the open ground when there is no wind to disperse them.
The Auburn code enforcement requires permission from the owner of a site that has features that are highly likely to contain these hazards to do a detailed survey to evaluate the risks. Anyone with hazardous atmosphere experience does not need a detailed survey to access the risks of a catastrophic event.
The last petroleum pooling tragedy I recall was the 1999 pipeline leak that killed three kids in Bellingham. A five-gallon propane explosion killed a family of five near Hood Canal last June. With propane tanks rolling around during the Cascadia, these risks are real. Since the city has chosen to place that ominous barrier to code enforcement, it is imperative all residents in the neighborhoods be aware and evacuate hazardous areas until the leak status can be determined.
The NOAA.org website shows a preferred evacuation radius for a 100-gallon tank to be 1,600 feet. It is 3,445 feet or over a half-mile for a 1,000 gallon tank. You can spot them on Google Maps. If they have an unobstructed area for a couple hundred feet downwind for the gas to dissipate to inert concentrations, they are relatively safe. Prevailing winds blowing toward any trap or obstruction are cause for concern.
– Bob Zimmerman