All of these persons need to understand the basic safety concepts listed below. Hazard is any set of circumstances that may cause harm. Hazards may be mechanical, biological, chemical, thermal, or of some other type. Hazards can be ranked in order of the severity or degree of damage they can cause. For example, the consequences of a tractor rollover can be very severe.
Risk is the probability of occurrence.
In other words, risk is the chance that a given hazard will occur and that a worker might be exposed to it. Some hazards, while severe, have a low risk associated with them because the probability of occurrence is very low. For example, the chances that a worker will be exposed to a hazardous chemical are fairly low if the worker is wearing proper protective clothing. Other hazards, while not so severe, may have a higher degree of risk because incidents may occur more frequently. Exposure occurs when a part of your body comes into contact with a hazard or a hazardous environment.