Technicians gave the all clear on Friday afternoon after examining the chemistry laboratory where it was thought an experiment with arsenic-containing compounds used to make World War I poison gas.
Although 97 students and staff - and five fire fighters - had gone to hospital complaining of nausea, headaches and some started vomiting, no-one had been poisoned. The only clue that remained was that many said the 'poisonous gas' had smelled of garlic.
The entire building was evacuated after the alarm was raised on Friday morning.
The university spokeswoman said students had been doing basic chemical experiments at the time of the incident although no one had yet pinpointed what had caused the leak. Officials said they had launched a full investigation.