Sgt. Stephen Jones, a state police spokesman, said an internal alarm at the Rainbow Center in Pittsgrove Township went off at about 2:40 p.m. Thursday, alerting staff to the contaminant.
They noticed a mist coming out of the vents, so about 110 people - 64 residents plus staff - were soon evacuated.
The residents were being cared for at four area hospitals. They were expected to return to the building by Friday morning.