Although the initial damage to elevators by a strong local earthquake is not often extensive, the displacement of counterweights from guides and wire ropes from pulleys can be hazardous and expensive if the elevators are permitted to continue operation. This problem can be eliminated by the addition of a simple seismic trigger, actuated at a preset vertical earthquake acceleration, to the elevator control system.

General Description
In practice, the EST-2 Elevator Seismic Trigger functions as a normally open switch until a significant earthquake occurs; this causes the EST-2 to transmit a switch closure to the elevators to continue to the next floor, allowing the occupants to leave, and automatically shuts down until an elevator mechanic has had the opportunity to examine the mechanical system and make any necessary repairs.

The EST-2 is typically preset at the factory for switch closure at 0.03g, but is field-adjustable between 0.025g and 0.25g with an FC-1 Field Calibrator (see Accessories). The switch remains closed as long as the vibration level exceeds the set point, plus an additional ten seconds after the acceleration falls below the set point. The EST-2 then automatically resets itself. Additional models include EST-2M and EST-2W, both with manual reset.