The Emergency Services Agency said firefighters were called to the campus early Friday afternoon "following reports of a strong smell of gas".
An update an hour later simply said they had "located the source of the smell" and allowed people back in the building after conducting atmospheric testing.
The library revealed on Facebook the source of the trouble: a durian.
Durian is a fruit most common in south-east Asia and known for its incredibly bad smell. It's banned in some places, such as Singapore's subway system.
Staff said the offending fruit was removed from the building in a sealed bag after being found near an air vent on level B.
They said while food was allowed in parts of the library "it's not appropriate student conduct if they did it on purpose, and lack of common sense if they didn't".