The fire happened in a control room at Block B of the campus just before 9 am, Lum, SIM's director of brand, marketing and Communications, said.
Investigations showed that it was due to a short-circuited portable air cooler, CNA said.
When TODAY reached SIMs Block A campus at 11 am, students were seen sitting at the building's lobby.
Several said they were allowed back into the building 15 minutes after the evacuation announcement, adding that their classes were cancelled for the rest of the day.
She was in the middle of her psychology module test when the fire alarm went off in the block B building, Goh said.
We didnt think much about it until about 9.20 to 9.30 am, she said, because we were all focused on the exam and nobody was panicking.
About five minutes after the alarm, there was an announcement that there would be an investigation. It told us not to panic, but that it was also not a drill. A second announcement followed, with faculty staff and students eventually evacuating to the atrium near the entrance of the school.
There is a class test of Introductory Psychology that ended about the same time the evacuation was made, Mr Lum said.
He said we have made arrangements for students to re-sit the test if they wish to do so.
TODAY's attempt to enter the basement of the building, the stairs that led to the car park were cordoned off and there was a pungent smell of smoke lingering in the air.
This article has been updated with information provided by SIM, including clarification of the location of the fire and a clarification that students were not sitting for an examination.