Three prison officers at the Otago Corrections Facility are off work, recovering from an incident thought to have involved some form of chemical contamination inside two cells earlier this week.
But exactly what caused the staff to feel unwell was still a mystery, facility manager Jack Harrison said.
Two of the officers were conducting a routine search in a low-security unit cell about 11am on Monday and the third entered a neighbouring cell shortly after.
All three became unwell, complaining of sore throats, nausea, headaches and blurred vision.
The officers were immediately taken to the prison's health centre and later transferred to Dunedin Hospital's accident and emergency department, where they were monitored for several hours before being discharged later that day.
All three have since seen their own Gps. It is understood they will return to work next week.
Both cells have been isolated and the prisoners relocated to another unit on the Milburn site.
No-one else in the unit, including the two prisoners from the two cells, was affected or had displayed any similar symptoms over the past five days, he said.
Police were called to examine the scene, and swabs taken from both cells have been sent to Environmental Science and Research for analysis.
Those results were expected back next week, Mr Harrison said.
While the incident could have been triggered by the mixing of cleaning fluids, that was unlikely because the prison had not changed its operating procedures for cleaning, he said.
