Hazard

A hazard is a potential source of harm. Substances, events, or circumstances can constitute hazards when their nature would potentially allow them 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. This term is often used synonymously in colloquial speech.

Hazards can be classified in several ways which are not mutually exclusive. They can be classified by causing actor (for example, natural or anthropogenic), by physical nature (e.g. biological or chemical) or by type of damage (e.g., health hazard or environmental hazard). Examples of natural disasters with highly harmful impacts on a society are floods, droughts, earthquakes, tropical cyclones, lightning strikes, volcanic activity and wildfires. Technological and anthropogenic hazards include, for example, structural collapses, transport accidents, accidental or intentional explosions, and release of toxic materials.

The term climate hazard is used in the context of climate change. These are hazards that stem from climate-related events and can be associated with global warming, such as wildfires, floods, droughts, sea level rise. Climate hazards can combine with other hazards and result in compound event losses (see also loss and damage). For example, the climate hazard of heat can combine with the hazard of poor air quality. Or the climate hazard flooding can combine with poor water quality.

In physics terms, common theme across many forms of hazards is the presence of energy that can cause damage, as it can happen with chemical energy, mechanical energy or thermal energy. This damage can affect different valuable interests, and the severity of the associated risk varies.

A hazard is defined as "the potential occurrence of a natural or human-induced physical event or trend that may cause loss of life, injury, or other health impacts, as well as damage and loss to property, infrastructure, livelihoods, service provision, ecosystems and environmental resources."

A hazard only exists if there is a pathway to exposure. As an example, the center of the Earth consists of molten material at very high temperatures which would be a severe hazard if contact was made with the core. However, there is no feasible way of making contact with the core, therefore the center of the Earth currently poses no hazard.

The frequency and severity of hazards are important aspects for risk management. Hazards may also be assessed in relation to the impact that they have.

In defining hazard Keith Smith argues that what may be defined as the hazard is only a hazard if there is the presence of humans to make it a hazard. In this regard, human sensitivity to environmental hazards is a combination of both physical exposure (natural and/or technological events at a location related to their statistical variability) and human vulnerability (about social and economic tolerance of the same location).