August 25, 1993
Circular Letter E-93-1
T0: Elevator Companies, Elevator Inspectors and other Concerned Parties
SUBJECT: Hoistway Door Interlock Control Relays
Recently in San Diego while making yearly elevator inspections for the operating permits, inspectors found two elevators that would run with the hoistway doors open. The elevators were removed from service. It's hard to think of a more dangerous condition than an elevator running with the hoistway doors open.
The elevators were using two Guardian relays for the hoistway door interlock protection circuit. Residual magnetism had built up over time and the relays were being held in the closed position. The springs used to open the relays were of the compression type with the relays mounted horizontally in the controller. The elevators were approximately 10 years old.
One must question the design of fastening relays horizontally that are intended to prevent the elevator from operating with the hoistway doors open. Any malfunction of the relay to operate in the intended manner will allow an extremely dangerous condition.
Those elevators having Guardian relays for door interlock protection shall have the relays replaced. The new relays may be Guardian or other brand relays. The relays shall be designed for the intended use, arranged so a failure will allow the relay to open.
It is fortunate no one has been injured or worse because of this potential unsafe condition. Elevator companies aware of this condition must make the replacement as soon as possible. If the elevator owner will not have the change made, .please notify the local Elevator Unit Office and the appropriate steps will be taken.
VV. E. McTiernan
Principal Safety Engineer
DOSH - Elevator, Tramway and Amusement Ride Unit