Runaway trolley knocks over two shoppers on travelator at Sheng Siong

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 yesterday, 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 has empty carton boxes on it, knocks her over.

A staff member is seen running after the trolley, but fails to stop it before it knocks over another person at the bottom of the travelator.

Another employee presses 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 Sheng Siong spokesman said the incident happened at its outlet in 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 are of utmost importance to us," said the spokesman.

"We will learn from the incident and take necessary measures to prevent them."

Sheng Siong declined to comment on how the footage was leaked.

As to how the trolley rolled freely down the travelator, Associate Professor Zhou Kun from Nanyang Technological University's School of Mechanical and Aerospace Engineering said that when a carton was repositioned on the trolley, a momentum was induced, causing it to move to the escalator.

Typically, the grooves on the escalator increase friction. Some trolley wheels also have a magnetic design that helps lock the trolley on a travelator.

"It is apparent that the friction force between the escalator and the trolley wheels was insufficient to resist the motion of the trolley," he said, adding that a moving trolley with a heavy load may also overcome these resisting forces.

In a similar incident in 2013, a 60-year-old woman in Shanghai was crushed to death by a fully loaded trolley that had rolled down a travelator, after another shopper lost his grip on it in a mall.