Escalator Defects Before Station Opening
At a busy subway station, you are assigned to a 15-year-old escalator with a 5.5 m rise, 1,000 mm step width, and a 0.5 m/s rated speed. During a routine maintenance visit at 06:30, before the station opens, you observe: the right handrail moves noticeably slower than the steps; two adjacent comb teeth are missing at the lower landing; the skirt panel on the left side has a 5 mm gap at the step; and the step demarcation strips on four steps are worn through. The station manager says the escalator was “running fine” yesterday and asks if it can open at 07:00. You have a tachometer, a feeler gauge, and a copy of the maintenance manual. The escalator is the only accessible route between the platform and the concourse for passengers with strollers; the elevator is out of service for a planned modernization.
1. Prioritize the four defects and state which, if any, require removal from service before opening. Explain your reasoning.
Read the worked answer
The missing comb teeth are the highest priority. The comb plate is the transition point where shoes, clothing, and small items can be caught; missing teeth create an open gap and are a direct entrapment hazard. The 5 mm skirt gap is next: the skirt panel must limit the clearance to the step to prevent shoes or clothing from being drawn in, and a 5 mm gap is likely outside the code tolerance. The slow right handrail is also a stability hazard: if the handrail moves slower than the steps beyond the permitted tolerance, a passenger holding it can be pulled backward. The worn demarcation strips are a visual and trip hazard but are lower priority than the three mechanical defects. Because at least three defects affect entrapment or passenger stability, the escalator should not be opened. The fact that the elevator is out of service does not justify operating an unsafe escalator; the manager must arrange an alternate accessible route, staff assistance, or a shuttle, and the escalator must be tagged out until repairs and re-tests are complete.
2. How would you measure and diagnose the handrail speed problem?
Read the worked answer
I would use the tachometer to measure the step speed at a marked step and the handrail speed at the same side over the same interval, then compare the two readings with the manufacturer’s tolerance and the applicable CSA B44 requirement. The handrail should not be slower than the steps beyond the permitted tolerance; if it is, the unit is not acceptable for passenger service. Mechanically, a slow handrail usually points to a slipping handrail drive wheel, inadequate handrail tension, worn drive rollers, a binding handrail guide, or a handrail that has stretched. I would inspect the drive station, clean or replace the drive wheel if glazed or worn, check the tensioning device, and verify that the handrail runs freely through the guides. After adjustment or repair I would re-measure both speeds and record the results before returning the escalator to service.