Under specific circumstances, health risk can be a probability of injury, disease, or even death. All exposures to chemicals carry some degree of health risk. Health risks may be expressed in quantitative terms, taking values from one to zero. The outputs of health risk assessment are necessary for informed regulatory decisions regarding worker exposures, plant emissions and effluents, ambient air and water exposures, chemical residues in foods, waste disposal sites, consumer products, and naturally occurring contaminants. The health hazard identification step in health risk assessment involves collecting, organizing, and evaluating toxicity data on the types of health injury or disease that may be produced by the chemicals and on the conditions of exposure under which injury or disease is produced. Generally, the assumption that all forms of toxicity observed in animal studies will also be observed in human is a prudent one and has been accepted for public health policy.