Rob Kidd, operations and marketing general manager of Duncan New Zealand Ltd, confirmed the incident had been due to an adverse chemical reaction involving a small amount of cleaning product.
The reaction occurred on Tuesday morning in one of the anterooms of the Puddle Alley facility, he said.
"A very small amount of chemical was involved and reacted, creating some gas."
Fire and Emergency New Zealand staff checked the air in the rooms was safe and a precautionary washdown of the area was undertaken.
"Our first priority is the safety of our people so they will remain our main priority at this point in time."
A Fenz spokeswoman said they were called to the spill at the Duncan South facility about 10.25am. Two fire appliances responded, one from Lookout Point and one from Mosgiel.
A spokeswoman from St John said three ambulances also responded and 16 patients were assessed at the scene.
Three of those patients were then transported to Dunedin Hospital, two with minor health problems and one in a moderate condition, she said.
The facility was about 100m from the road and close to AgResearch’s Invermay campus.
