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Early Warning (cont'd)

With ESS systems, there are discrete output alarm signals for both early-warning (low level, advisory) AND a separate high-level (shutdown) alarm is generated when strong motion exceeds the user's preset thresholds. The high-level output can be used to shutoff the flow of combustible or toxic gases, isolate water tanks to conserve water and more. Any process can be automatically controlled at the onset of strong motion shaking.

Also, of import is the fact that a broadcast alarm signal does not take into account site specific issues such as local geology, soil conditions, fault geometry, fault orientation or structure fragility. Why shut down your operations just because a broadcast signal declares a M6 earthquake? If the event is 30 miles away and the strongest motion is generally directed away from your facility, it may not produce excessive shaking at your site.  If your location is on bedrock, the shaking is often less damaging than the shaking on, say, a deep alluvial plain. Therefore, most commercial & industrial facilities are better served by shutting down ONLY if there is excessive ground shaking at their specific location.  Earthquakes in NorthridgeSan Jose, TorranceEureka, & Seattle are examples of the benefit of a site specific response.  Newer MSC Master Seismic Controller units are designed to accept the future government broadcast EEW alarm as an optional 'ENABLE' signal for the high level seismic shutdown alarm

The ESS Apollo Guardian Seismic Switches & MSC Guardian Seismic Monitors include an audio module with a user-recordable alarm broadcast message and user-adjustable peak ground acceleration (PGA) setpoints. Upon exceedance of the user's PGA settings, the pre-recorded message is broadcast over the user's PA system. Wireless PA systems are also supported.

Alternatively, if the end-user only requires normally open or normally closed alarm relay contacts to change state when peak acceleration exceeds a pre-set threshold, the Saturn S-001 Seismic switch will do the job. The Saturn is available in horizontal (standard) or vertical mount. Note: vertical mount should be carefully considered as there is the potential for pre-mature actuation from the resonant response of the wall 'amplifying' the input energy.  It is preferable to mount the instrument on an inertial mass such as a tank ringwall, building foundation or isolated (freefield) concrete housekeeping pad.

In some cases, just a few seconds of warning could make a difference. Imagine operating a forklift in an aisle lined with cases of liquid filled glass bottles. BC Liquors in Vancouver, BC protects warehouse & distribution personnel with an 'Earthquake, Duck , Cover, Hold' announcement upon p-wave detection. Other installed applications for 'Duck, Cover, Hold' annunciation have included schools, parking structures, semi-conductor fabrication plants and office buildings.

For more information on earthquake early warning visit:
http://www.eew.caltech.edu/education/earlywarningfaq.html
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