Her sister and brother-in-law had gone into the 7-Eleven store at a Shell station to pay for petrol, while Ms Lim and her sister's two children waited in the car.
When the couple did not exit after a while, Ms Lim, a 40-year-old clerk, found it odd.
She declined to give her full name.
Her mobile phone then went off.
It was Ms Lim's sister, and she was telling her how she and her husband were trapped as the automatic sliding doors at the 7-Eleven would not open.
The incident happened at the Shell petrol station at Peirce Reservoir on Upper Thompson Road last Sunday at about 11.45am.
Other than Ms Lim's elder sister and brother-in-law, three 7-Eleven employees were also trapped in the store for about an hour.
They were later freed by a contractor who repaired the doors, reported Chinese evening daily Lianhe Wanbao.
Ms Lim said: "My sister sounded panicky, and asked me to try opening the doors from the outside.
"I got out of the car and found that the store's doors were shut."
An employee slid a key under the door to Ms Lim and asked her to try inserting it into the keyhole outside.
But Ms Lim was still unable to open the door, so she called the Singapore Civil Defence Force (SCDF) for help.
An SCDF spokesman said an ambulance, a Red Rhino and a fire engine were sent to the scene.
But he added that their assistance was not required, as 7-Eleven employees had contacted their contractor for help.
The contractor repaired the lock at the bottom of the doors and opened them.
He also fixed the lock near the ceiling.
It took about 15 minutes for the doors to be functional again.
Ms Lim told Wanbao: "There's only one exit. In case of emergency, how are customers and employees supposed to escape?"
When TNP visited the store on Monday, the employees declined to comment.
This is an isolated incident and investigations are ongoing, said 7-Eleven and Shell in a joint statement on Monday.
The statement added: "We have offered our sincerest apologies to the affected customers. Rest assured that we will take all the necessary steps to prevent any future recurrence."
This article was first published on Dec 03, 2014.
Get The New Paper for more stories.