An engineer who gave a safety certificate to a shopping mall’s escalator just three months before it flipped into reverse and sent shoppers tumbling to the ground, injuring 18, has admitted he failed to check five components.
But Ma Siu-lun, 66, denied that those components included the escalator’s main drive chain and its broken drive chain device, whose combined malfunction caused the accident inside Langham Place, Mong Kok, on March 25 last year.
Kowloon City Court heard 120 people were going up the 45-metre escalator when it stopped suddenly and reversed at high speed, sending dozens tumbling down. Of the 18 hurt, three were sent to hospital.
An investigation by the Electrical and Mechanical Services Department found the escalator’s main drive chain was broken and its monitoring device had failed to stop the plunge.
On Tuesday, Ma admitted failing to ensure the thorough examination of five of the escalator’s pieces of equipment or machinery.
These included two sensors that stop the escalator if it goes too fast or in the wrong direction, and three switches that stop the escalator when loose items are stuck in the device.
But Ma pleaded not guilty to a second summons alleging that he failed to ensure the escalator was thoroughly examined – one specifically relating to the drive chain. The maximum penalty for each summons is six months in prison and a HK$100,000 fine.
Surveillance footage played in court captured Ma, who was employed by Otis Elevator Company (HK) at the time, doing twice-yearly checks on the company’s escalator, with two workers, from 7.18am to 7.40am on January 24 last year.
The court heard that Ma, a registered escalator engineer since 1988, issued a safety certificate on the same day, confirming the escalator and its associated equipment or machinery were in safe working order.
But prosecutors observed from the footage that the main drive chain had not been cleaned for the inspection and that the escalator was motionless most of the time.
They also accused Ma of examining only parts of the four-metre-long main drive chain and omitting to check whether its associated components were broken, fractured or deformed.
Their case was based on comments from department engineer Yiu Yung-ngai, who said 22 minutes was not long enough to examine the escalator thoroughly.
Yiu said a comprehensive inspection involved cleaning and measuring the main drive chain and testing the monitoring device.
His comments were supported by Lawrence Wu, a City University professor in engineering failure analysis, who added that workers should have checked for signs of metal fatigue, which could have been spotted with the naked eye once the chain was cleaned.
Independent expert Dr Eric Lim opined that the accident was caused by the combined effect of the main drive chain breaking down due to metal fatigue and the malfunctioning of its monitoring device.
The main drive chain was installed on August 31, 2009.
The trial continues before Magistrate Amy Chan Wai-mun on Wednesday.