of diving incidents range from merely annoying to rapidly fatal, and the result often depends on the equipment, skill, response and fitness of the diver and diving team. The hazards include the aquatic environment, the use of breathing equipment in an underwater environment, exposure to a pressurised environment and pressure changes, particularly pressure changes during descent and ascent, and breathing gases at high ambient pressure. Diving equipment other than breathing apparatus is usually reliable, but has been known to fail, and loss of buoyancy control or thermal protection can be a major burden which may lead to more serious problems. There are also hazards of the specific diving environment, and hazards related to access to and egress from the water, which vary from place to place, and may also vary with time. Hazards inherent in the diver include pre-existing physiological and psychological conditions and the personal behaviour and competence of the individual. For those pursuing other activities while diving, there are additional hazards of task loading, of the dive task and of special equipment associated with the task. Professional divers may be exposed to a wider range of hazards, some of which are inherent in the equipment used to reduce the risk of other hazards. Saturation diving is intended to reduce a relatively high risk of decompression sickness, but introduces other health and safety hazards of living at a high ambient pressure for extended periods, and transfer between pressurised spaces. Failure of a saturation system can be catastrophic and fatal to the occupants and bystanders. Such failures are seldom engineering failures, they are more often ergonomic design and operation failures, and usually systems are corrected after analysis of such failures. Occupational hazard types can also be classified as biological, chemical, physical, and psychosocial hazards. Consequences Diving related medical conditions, are conditions associated with underwater diving, and include both conditions unique to underwater diving, and those that also occur during other activities. This second group further divides into conditions caused by exposure to ambient pressures significantly different from surface atmospheric pressure, and a range of conditions caused by general environment and equipment associated with diving activities. Disorders particularly associated with diving include those caused by variations in ambient pressure, such as barotraumas of descent and ascent, decompression sickness and those caused by exposure to elevated ambient pressure, such as some types of gas toxicity and excessive work of breathing. There are