Escalator Comb Impact at a Transit Station
You are called to a 40 ft rise, 30-degree escalator at a busy Maryland transit station during the morning rush. The inspector on duty reports that three comb teeth are broken, the step-to-skirt gap at one location measures 5 mm, and the comb impact device did not trip when tested with a gauge. The escalator is still running, and the station manager wants you to replace the broken comb segment and “keep it moving” because the adjacent escalator is already out of service. You notice a small piece of metal trapped between the step and the skirt panel near the damaged comb. Passengers are using the unit.
1. What immediate actions must you take, and why is replacing only the comb segment unacceptable?
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The first action is to stop and secure the escalator: remove it from passenger service, place barricades at both ends, lock out the drive, and notify the station manager and supervisor. The broken comb teeth, the 5 mm step-to-skirt gap, the failed comb impact device, and the trapped metal are a cluster of hazards, not a cosmetic defect. Replacing only the comb segment would leave the cause unaddressed. The 5 mm gap exceeds the 4.8 mm (3/16 in) maximum allowed between the step and skirt panel at that point, and a gap that large can allow objects or clothing to be caught. The comb impact device is a safety device intended to stop the escalator if something is trapped at the comb; if it did not trip on test, it must be repaired and retested before return to service. The trapped metal must be removed and the step, skirt panel, and comb alignment inspected for damage. Returning the unit to service after a cosmetic comb replacement would expose passengers to the same trapping hazard and would not meet the maintenance and safety obligations of the mechanic.
2. What root-cause checks and component inspections should be completed before the escalator is returned to service?
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The mechanic should inspect the full comb and skirt area, not just the damaged spot. Check comb tooth alignment and mesh with the step cleats, skirt panel fasteners and clearances at multiple points along the curve, step tread deflection, and the condition of the step chain and guide rollers. Look for the source of the trapped metal: a broken fastener, a damaged skirt panel, a worn step guide, or debris from the station. Verify that the comb impact device trips with the test gauge and that the escalator stops as designed. Test the handrail speed and synchronization, the brake, the emergency stop buttons at both landings, and the skirt guard switches if provided. Check the step-to-skirt clearance after any panel adjustment and confirm it is within the code maximum at every point. The unit should remain out of service until the comb, skirt, step, and impact device are repaired and the tests are documented. The station manager’s desire to keep the unit moving does not override the safety defect.
3. What documentation and return-to-service criteria should you apply?
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Document the initial condition with measurements, photographs, and the failed impact test; record the lockout and barricade time; and note who authorized the shutdown. After repair, record the replacement parts, the corrected skirt clearance at each measured point, the comb mesh adjustment, and the results of the impact-device test, brake test, handrail-speed check, and emergency-stop test. Return to service only when the comb is intact, the step-to-skirt gap is within the 4.8 mm maximum, the impact device trips and stops the escalator, the trapped object and its cause are removed, and no step or skirt damage remains. A second person should verify the tests. Notify the station manager in writing that the unit is back in service and state any remaining follow-up, such as monitoring a worn step or ordering a skirt panel. If the AHJ requires notification for the repair, make that notification before or as the unit returns to service.