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The dictionary definitions do not correspond entirely with what epidemiologists or professionals in the field of Occupational and Environmental Health would understand these terms to mean. Hazard is not deemed to be synonymous with risk although it can be an important determinant of risk. Although risk may be related to a chance event and expressed as a probability, there is much more to it than that. Probability is not an entirely haphazard one of course but relates to a number of factors which will be discussed further.
However in Occupational and Environmental Epidemiology, we prefer to define these two words as follows:
Hazard is the potential to cause harm; risk on the other hand is the likelihood of harm (in defined circumstances, and usually qualified by some statement of the severity of the harm).
The relationship between hazard and risk must be treated very cautiously. If all other factors are equal - especially the exposures and the people subject to them, then the risk is proportional to the hazard. However all other factors are very rarely equal.
Examples:Consider the following examples:
1. Potassium Dichromate is a highly toxic carcinogenic chemical. It is used in some techniques to analyse exhaled breath for alcohol content. However for this purpose it is sealed in a tube, and does not become airborne when air is drawn over it. Therefore although it is a highly hazardous substance, its use as described, does not present any risk to the subject.
2. Flour would not be considered by many to be a hazardous substance. A jar of it on a shelf would not have a skull and crossbones depicted on it together with other hazard warnings, as might have been the case for a bottle of potassium dichromate However, if a baker was exposed over a period of time to airborne flour dust and/or dust by skin contact, he/she could develop dermatitis (an inflammation of the skin), conjunctivitis (inflammation of the eyes), rhinitis (inflammation of the nose) and even asthma - an inflammatory disease of the lungs which can cause a great deal of distress and may even by life threatening.
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