The WITS University says all the students who experienced breathing problems last night in a dining hall in Parktown have fully recovered.
The University says a preliminary investigation into the incident in the Highfield dining hall indicates that a suction fan has failed.
Spokesperson Shirona Patel says no gas leak was found.
Yesterday, emergency services workers examined at least 160 people at the scene and at least 60 were admitted to hospital after they allegedly fled the building due to a gas leak.
The 55 students who were admitted to hospital were all discharged.