SINGAPORE - A runaway trolley at a Sheng Siong outlet in Sembawang knocked over two shoppers on a travelator in February this year.
In closed-circuit television (CCTV) footage leaked on various social media platforms on Tuesday (April 20), a staff member at the supermarket can be seen unloading boxes near the top platform of a downward-moving travelator.
The trolley is left unattended as the staff member pushes a carton away. It begins rolling down the travelator behind a woman.
The trolley, which also has empty cartons on it, picks up speed and knocks her over.
A staff member is then seen chasing after the trolley, but fails to catch it before another person at the bottom of the travelator is knocked over.
Another employee pushes the emergency stop button at the top of the travelator.
The CCTV footage time stamp shows that the incident happened at about 3.50pm on Feb 25.
Responding to queries from The Straits Times, a spokesman for Sheng Siong said the incident happened at its outlet at Block 105 Canberra Street.
ST understands that no ambulance was called to the scene.
"Our store personnel had immediately apologised and extended assistance to the two customers. The health and safety of our customers is of utmost importance to us.
"We will learn from the incident and take necessary measures to prevent such incidents," said the spokesman.
As to how the trolley was able to roll freely down on the travelator, Associate Professor Zhou Kun from the Nanyang Technological University's School of Mechanical and Aerospace Engineering told ST that this was due to insufficient friction force.
When shown clips of the footage, Prof Zhou said: “When a carton box was placed at the side of the trolley closer to the escalator, a momentum was induced to the trolley along the incline, causing it to travel to the escalator.
“It is apparent that the friction force between the escalator and the trolley wheels was insufficient to resist the motion of the trolley caused by the gravitational force. Thus, the trolley started to accelerate down the escalator, resulting in the accident.”
Some shopping trolleys have wheels that lock onto the ridges on travelators.
In a similar incident, a 60-year-old woman in Shanghai was crushed to death in 2013 by a fully loaded trolley that had rolled down a travelator, after another shopper lost his grip on it in a shopping mall.