Vapors from peracetic acid, used to clean machinery at the Dannon plant, were released Monday.
Fire officials say two nearby construction workers and two police officers were treated for breathing problems. Authorities say a firefighter suffered heat exhaustion.
Dannon spokesman Michael Neuwirth says a diluted form of peracetic acid, stored in a tank, came in contact with an unknown organic substances and vapors escaped. Neuwirth says the reaction is under investigation.