page_title: Scuba diving
section_title: Hazards
hierarchical_section_title: Scuba diving / Safety / Hazards
caption_attribution_description: Español: Buceo en cenotes English: Diving in cenote
context_page_description: Scuba diving is a mode of underwater diving where the diver uses a self-contained underwater breathing apparatus, which is completely independent of surface supply, to breathe underwater. Scuba divers carry their own source of breathing gas, usually compressed air, allowing them greater independence and freedom of movement than surface-supplied divers, and longer underwater endurance than breath-hold divers. Although the use of compressed air is common, a mixture of air and oxygen called enriched air or nitrox has become popular due to its benefit of reduced nitrogen intake during long or repetitive dives. Open circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver through a regulator. They may include additional cylinders for range extension, decompression gas or emergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration.
context_section_description: Divers operate in an environment for which the human body is not well suited. They face special physical and health risks when they go underwater or use high pressure breathing gas. The consequences 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.
  The presence of a combination of several hazards simultaneously is common in diving, and the effect is generally increased risk to the diver, particularly where the occurrence of an incident due to one hazard triggers other hazards with a resulting cascade of incidents. Many diving fatalities are the result of a cascade of incidents overwhelming the diver, who should be able to manage any single reasonably foreseeable incident. Although there are many dangers involved in scuba diving, divers can decrease the risks through proper procedures and appropriate equipment. The requisite skills are acquired by training and education, and honed by practice. Open-water certification programmes highlight diving physiology, safe diving practices, and diving hazards, but do not provide the diver with sufficient practice to become truly adept.
  Scuba divers by definition carry their breathing gas supply with them during the dive, and this limited quantity must get them back to the surface safely. Pre-dive planning of appropriate gas supply for the intended dive profile lets the diver allow for sufficient breathing gas for the planned dive and contingencies. They are not connected to a surface control point by an umbilical, such as surface-supplied divers use, and the freedom of movement that this allows, also allows the diver to penetrate overhead environments in ice diving, cave diving and wreck diving to the extent that the diver may lose their way and be unable to find the way out. This problem is exacerbated by the limited breathing gas supply, which gives a limited amount of time before the diver will drown if unable to surface. The standard procedure for managing this risk is to lay a continuous guide line from open water, which allows the diver to be sure of the route to the surface.
  Most scuba diving, particularly recreational scuba, uses a breathing gas supply mouthpiece which is gripped by the diver's teeth, and which can be dislodged relatively easily by impact. This is generally easily rectified unless the diver is incapacitated, and the associated skills are part of entry-level training. The problem becomes severe and immediately life-threatening if the diver loses both consciousness and the mouthpiece.  Rebreather mouthpieces which are open when out of the mouth may let in water which can flood the loop, making them unable to deliver breathing gas, and will lose buoyancy as the gas escapes, thus putting the diver in a situation of two simultaneous life-threatening problems. Skills to manage this situation are a necessary part of training for the specific configuration. Full-face masks reduce these risks and are generally preferred for professional scuba diving, but can make emergency gas sharing diff
caption: Scuba diving in a cave
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