A man accepted a free ticket from a stranger before arriving at an Adelaide hospital with burning hands and laboured breathing linked with exposure to an 'unknown substance'.
The man arrived at the Lyell McEwin Hospital at about 1.45am on Tuesday with "burning hands and laboured breathing", the Metropolitan Fire Service says.
Staff who dealt with the man soon reported having similar symptoms, leading emergency service crews to block off a section of the hospital as a precaution.
Both the man and the staff were decontaminated and have since recovered, while all parts of the hospital are now open and running as normal.
Hazardous materials experts performed tests on the man's belongings but could not determine what he had been exposed to.
Police say the man was approached by a stranger outside the Elizabeth Shopping Centre and offered a free ticket, which he accepted, less than an hour before arriving at the hospital.
The man who offered the ticket is described as being Caucasian, aged in his late 30's, with a tall and slim build and medium-length black hair.
Premier Jay Weatherill told reporters on Tuesday the incident was "worrying" but praised the quick work of emergency crews.
"It is pleasing to see that the emergency service protocols around incidents of this sort were immediately put into place to try to protect the patient and also the associated staff and also the rest of the hospital," he said.