Police say a tanker truck with nitrous oxide was being drained at Detox Environmental (on Bennett Road) on Thursday afternoon when a reaction occurred as it came in contact with another chemical.
The chemical activity resulted in a smoke release inside the building which escaped into the environment.
Police say about a dozen employees at Detox were evacuated, as were employees of a nearby forklift company.
Several Detox employees were injured after inhaling spilled chemicals and two were sent to Bowmanville Hospital, one with serious injuries.
A hazardous materials team is decontaminating the area and police have closed roads in the area as well as the off-ramp from Highway 401.
(The Canadian Press, CKPT)