Chemical Exposure: Employers need to ensure that the exposure level of the worker does not reach the maximum of their occupational exposure. Occupational Exposure Limits (UELs) are laid down for certain chemicals that are listed as extremely hazardous to human health; evidence exists for some of these substances to assess how much exposure will contribute to adverse health outcomes. The action limit helps to assess the maximum airborne concentration of hazardous or chemical agents that can be exposed to a worker for a period of time without adverse effects. Under Ontario's Occupational Health and Safety Act, there are over 3'50 chemical and hazardous substances under occupational exposure limits under the Control of Exposure to Biological or Chemical Agents {R.R.O. 1990, Regulation 833) and Designated Substances (Ontario regulations 490,109,} that are regularly reviewed and updated. Employers have a responsibility to take all reasonably appropriate steps to protect employees from exposure to a dangerous biological or chemical agent under such circumstances