Hazard
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, 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 and 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. Characteristics. Environmental hazards include long term environmental deterioration such as acidification of soils and build-up of atmospheric carbon dioxide to communal and involuntary social hazards such as crime and terrorism to voluntary and personal hazards such as drug abuse and mountain climbing. Environmental hazards usually have defined or common characteristics including their tendency to be rapid onset events meaning they occur  with a short warning time, they have a clear source of origin which is easily identified, the impact will be swift and losses suffered quickly during or shortly after the onset of the event, risk of exposure is usually involuntary due to location or proximity of people to the hazard and the "disaster occurs with an intensity and scale that justifies an emergency response". Hazards may be grouped according to their characteristics. These factors are related to geophysical events, which are not process specific: Natural hazards may be defined as "extreme events that originate in the biosphere, hydrosphere, lithosphere or  atmosphere" or "a potential threat to humans and their welfare" which include earthquake, landslide, hurricane and tsunamis. Technological and man-made hazards include explosions, the release of toxic materials, episodes of severe contamination, structural collapses, and transportation, construction and manufacturing accidents etc. A distinction can also be made between rapid-onset natural hazards, technological hazards, and social hazards, which are described as being of sudden occurrence and relatively short duration, and the consequences of longer-term environmental degradation such as desertification and drought. 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 and that it is otherwise merely an event of interest. In this sense, the environmental conditions we may consider hostile or hazardous can be seen as neutral in that it is our perception, human location and actions which identify resources and hazards within the range of natural events. 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 ). Smith states that natural hazards are best seen in an ecological framework to distinguish between natural events as natural hazards. He says, "natural hazards, therefore, result from the conflict of geophysical processes with people and they lie at the interface what has been called the natural events system and the human interface system." He says that "this interpretation of natural hazards gives humans a central role. Firstly through location, because it is only when people and their possessions get in the way of natural processes that hazard exists." A natural hazard can be considered as a geophysical event when it  occurs in extremes and a human factor is involved that may present a risk. In this context, we can see that there may be an acceptable variation of magnitude which can vary from the estimated normal or average range with upper and lower limits or thresholds. In these extremes, the natural occurrence may become an event that presents a risk to the environment or people. Smith says "most social and economic activities are geared to some expectation of the 'average' conditions. As long as the variation of the environmental element remains fairly close to this expected performance, insignificant damage occurs  and the element will be perceived as beneficial. However, when the variability exceeds some threshold beyond the normal band of tolerance, the same variable starts to impose a stress on society and become a hazard." Thus, above-average wind speeds resulting in a tropical depression or hurricane according to intensity measures on the Saffir–Simpson scale will provide an extreme natural event that may be considered a hazard. Classification. Hazards can be classified as different types in several ways. One of these ways is by specifying the origin of the hazard. One key concept in identifying a hazard is 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. Another class of hazard does not involve the release of stored energy, but the presence of hazardous situations. Examples include confined or limited egress spaces, oxygen-depleted atmospheres, awkward positions, repetitive motions, low-hanging or protruding objects, etc. Hazards may also be classified as natural, anthropogenic, or technological. They may also be classified as health or safety hazards and 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. Based on origin. "…to reduce through concerted international action, especially in developing countries, the loss of life, property damage, and social and economic disruption caused by natural disasters, such as earthquakes, wind-storms, tsunamis, floods, landslides, volcanic eruptions, wildfire, grasshopper and locust infestations, drought and desertification and other calamities of natural origin." Disasters. Disaster can be defined as a serious disruption, occurring over a relatively short time, of the functioning of a community or  a society involving widespread human, material, economic, societal or environmental loss and impacts, which exceeds the ability of the affected community or society to cope using its own resources. Disaster can manifest in various forms, threatening those people or environments specifically vulnerable. Such impacts include loss of property, death, injury, trauma or post-traumatic stress disorder. Disaster can take various forms, including hurricane, volcano, tsunami, earthquake, drought, famine, plague, disease, rail crash, car crash, tornado, deforestation, flooding, toxic release, and spills (oil, chemicals). These can affect people and the environment on the local regional level, national level or international level  (Wisner et al., unknown) where the international community becomes involved with aid donation, governments give money to support affected countries' economies with disaster response and post-disaster reconstruction. A disaster hazard is an extreme geophysical event that is capable of causing a disaster. 'Extreme' in this case means a substantial variation in either the positive or the negative direction from the normal trend; flood disasters can result from exceptionally high precipitation and river discharge, and drought is caused by exceptionally low values. The fundamental determinants of hazard and the risk of such hazards occurring is timing, location, magnitude and frequency . For example, magnitudes of earthquakes are measured on the Richter scale from 1 to 10, whereby each increment of 1 indicates a tenfold increase in severity. The magnitude-frequency rule states that over a significant period of time many small events and a few large ones will occur. Hurricanes and typhoons on the other hand occur between 5 degrees and 25 degrees north and south of the equator, tending to be seasonal phenomena that are thus largely recurrent in time and predictable in location due to the specific climate variables necessary for their formation. Major disaster, as it is usually  assessed on quantitative criteria of death and damage, was defined by Sheehan and Hewitt (1969), having to conform to the following criteria: This definition includes indirect losses of life caused after the initial onset of the disaster such as secondary effects of, e.g., cholera or dysentery. This definition is still commonly used but has the limitations of number of deaths, injuries, and damage (in $). UNDRO (1984) defined a disaster in a more qualitative fashion as: an event, concentrated in time and space, in which a community undergoes severe danger and incurs such losses to its members and physical appurtenances  that the social structure is disrupted and the fulfilment of all or some of the essential functions of the society is prevented. As with other definitions of disaster, this definition not only encompasses the social aspect of disaster impact and stresses potentially caused but also focuses on losses, implying the need for emergency response as an aspect of the disaster. It does not, however, set out quantitative thresholds or scales for damage, death, or injury, respectively. Status of a hazard. Hazards are sometimes classified into three modes or statuses: Risk. The terms "hazard" and "risk" are often used interchangeably. However , in terms of risk assessment, these are two very distinct terms. A hazard is an agent that can cause harm or damage to humans, property, or the environment. Risk is the probability that exposure to a hazard will lead to a negative consequence, or more simply, a hazard poses no risk if there is no exposure to that hazard. Risk can be defined as the likelihood or probability of a given hazard of a given level causing a particular level of loss of damage. The elements of risk are populations, communities, the built environment, the natural environment, economic activities and  services which are under threat of disaster in a given area. The total risk according to UNDRO 1982 is the "sum of predictable deaths, injuries, destruction, damage, disruption, and costs of repair and mitigation caused by a disaster of a particular level in a given area or areas". David Alexander distinguishes between risk and vulnerability, saying that "vulnerability refers to the potential for casualty, destruction, damage, disruption or other forms of loss in a particular element: risk combines this with the probable level of loss to be expected from a predictable magnitude of hazard (which can be considered as the  manifestation of the agent that produces the loss)." Since hazards have varying degrees of severity, the more intense or severe the hazard, the greater vulnerability there will be since the potential for damage and destruction is increased for the severity of the hazard. Ben Wisner argues that risk or disaster is "a compound function of the natural hazard and the number of people, characterised by their varying degrees of vulnerability to that specific hazard, who occupy the space and time of exposure to the hazard event." (Wisner, et al., 1994). Another definition of risk is "the probable frequency and probable  magnitude of future losses". This definition also focuses on the probability of future loss whereby the degree of vulnerability to hazard represents the level of risk on a particular population or environment. The threats posed by a hazard are: Marking of hazards. Hazard symbols or warning symbols are easily recognizable symbols designed to warn about hazardous materials, locations, or objects. The use of hazard symbols is often regulated by law and directed by standards organizations. Hazard symbols may appear with different colours, backgrounds, borders and supplemental information to specify the type of hazard and the level of threat (for example , toxicity classes). Warning symbols are used in many places in place of or in addition to written warnings as they are quickly recognized (faster than reading a written warning) and more universally understood, as the same symbol can be recognized as having the same meaning to speakers of different languages.