A passenger terminal at Melbourne airport was evacuated on Monday after dozens of people were taken ill following a suspected chemical leak.
Most of those affected were Virgin Blue security and airline staff
At least 45 people were hospitalised suffering nausea, vomiting and respiratory problems.
Hundreds of others were evacuated from the Virgin Blue domestic terminal where the leak is thought to have occurred.
Domestic flights were severely delayed, before the terminal was re-opened on Monday evening.
Most of those who fell ill were security and airline staff, according to airport officials.
By mid-afternoon the majority had been released from hospital, but the terminal was closed for several hours while emergency services looked for the source of the leak.
Melbourne Airport spokeswoman Brooke Lord said: "Initially... there was immediate testing done of the air quality and the air conditioning systems, and nothing was identified through that that could have caused the problem.
"But as we got further reports of people feeling unwell, as a precaution, the aviation rescue and firefighting [crews] working on site decided to evacuate the terminal," she told the Australian news agency AAP.