Are super-long escalators safe? Lessons learned from the Langham place escalator incident in Hong Kong

Abstract

Super-long escalators that are increasingly used in mega-cities take up a large number of passengers, and so their risk of sudden failure draws serious attention. As a case study, on 25 March 2017, an escalator with a 21 m elevation in Hong Kong’s Langham Place had its main drive chain suddenly snapped by metal fatigue, causing the escalator to reverse at an accelerating speed. A number of passengers were injured. In this paper, two issues will be discussed: (1) whether metal fatigue of the main drive chain can be detected with conventional protocols, and (2) what safety factor is needed to prevent metal fatigue. Analysis shows that initial fatigue cracks in escalator drive chains may not be easily detected with the commonly adopted maintenance protocol. Also, the time window from the emergence of clear signs of fatigue failure to the sudden snapping of the drive chain may be as short as weeks or even days, versus the common safety inspection intervals of six months. The safety factor to prevent metal fatigue of the drive chain should be at least 7, whereas lower values are allowed. The Hong Kong government has since then changed regulations and adopted additional measures to safeguard escalator failures against metal fatigue.