Risk can be defined as a chance of danger, damage, loss, injury, or any other undesired consequences. Most authors agree that risk involves 2 elements, possible consequences (impact) and associated uncertainty (probability of occurrence). The source of risk is known as hazard. So, hazard relates to the source of harm, while risk is the probability of the harm being experienced. Therefore, some authors defined risk as a combination of hazard and probability of hazard occurrence, where hazard is defined as the degree of harm to human beings, property, society or environment.