Drifting elevator cab trips passenger
January 17, 2019
Regulated industry sector: Elevating devices - Elevator
Qty injuries: 0
Injury description: None
Injury rating: None
Damage description: The rubber washer inside the machine brake plunger assembly disintegrated.
Damage rating: Minor
Incident rating: Minor
As the passenger was entering the elevator, the elevator cab began to drift up which caused the passenger to trip into the elevator.
Site, system and components
Traction elevators use machine brakes to ensure the elevator does not move when passengers are entering and exiting the elevator. The brakes use a plunger system to engage/disengage brake pads. A rubber washer is installed on one end of the plunger to reduce the impact of the plunger against its housing.
Elevator and hoistway sills are metal tracks that guide the bottom of the elevator and hoistway doors. They also act as part of the floor as you enter and exit elevators.
When an elevator is at a landing and the doors are fully open, the elevator sill must be substantially flush with the hoistway sill and remain flush until the elevator doors are fully closed. During this time the machine brake is set ensuring no movement of the elevator.
After the elevator doors opened, with the car and hall sill substantially flush, the brake plunger caused a delay in the brakes engagement. The elevator started to drift up approximately 4” before the brakes were fully engaged and the elevator stopped.
Facts and evidence
· Video obtained from the building security camera captured the incident.
· Safety Officer arrived on-site and mechanic had started repair job. Brake plunger assembly was already disassembled.
· Mechanic stated they were not aware the repair was due to an incident so they did not wait for a Safety Officer prior to starting the repair job.
· Mechanic stated the disintegrated rubber washer had been replaced during a brake upgrade that occurred in the last 12 months.
· Brake upgrade was performed by mechanics with proper training (photo 1)
· Disintegrated rubber washer left contaminants in the plunger housing (photo 3 and 4)
· No clear evidence for what caused the rubber washer to disintegrate.
Causes and contributing factors
It is likely that the rubber washer disintegrated inside the brake plunger assembly. It is possible the rubber washer was not installed correctly causing abnormal stress on the washer resulting in the washer disintegrating. It is probable pieces of the disintegrated washer impeded the plunger, causing a delay in the brake engaging.
Photo 1 Training sign off sheet for the 340 machine brake upgrade
Photo 2 Machine brake assembly with a new rubber washer
Photo 3 Machine brake assembly with rubber washer disintegrated to small pieces
Photo 4 Brake brass sleeve with remnants of the rubber washer