A hazard is a potential source of harm. Substances, events, or circumstances can constitute hazards when their nature would allow them, even just theoretically, to cause damage to health, life, property, or any other interest of value. The probability of that harm being realized in a specific incident , combined with the magnitude of potential harm, make up its risk, a term often used synonymously in colloquial speech.
Hazards can be classified in several ways. They can be classified as natural, anthropogenic, technological, or any combination, therefore, such as in the case of the natural phenomenon of wildfire becoming more common due to human-made climate change or more harmful due to changes in building practices. A common theme across many forms of hazards in the presence of stored energy that, when released, can cause damage. The stored energy can occur in many forms: chemical, mechanical, thermal, radioactive, electrical, etc. Situations can also be hazardous, for example, confined or limited egress spaces, oxygen-depleted atmospheres, awkward positions, repetitive motions, low-hanging or protruding objects, etc. They may also be classified as health or safety hazards, by the populations that may be affected, and the severity of the associated risk. In most cases, a hazard may affect a range of targets and have little or no effect on others.
Identification of hazards assumes that the potential targets are defined, and is the first step in performing a risk assessment.