Diving hazards

Diving hazards are the agents or situations that pose a threat to the underwater diver or their equipment. 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 classes of 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 diving, divers can decrease the risks through effective procedures and appropriate equipment. The requisite skills are acquired by training and education, and honed by practice. Entry level recreational diving certification programmes highlight diving physiology, safe diving practices, and diving hazards, but do not provide the diver with sufficient practice to become truly adept. Professional diver training provides more practice, but continued experience and practice of essential skills is necessary to develop reliable response to contingencies.

Divers must avoid injuries caused by changes in pressure. The weight of the water column above the diver causes an increase in pressure in proportion to depth, in the same way that the weight of the column of atmospheric air above the surface causes a pressure of 101.3 kPa (14.7 pounds-force per square inch) at sea level. This variation of pressure with depth will cause compressible materials and gas filled spaces to tend to change volume, which can cause the surrounding material or tissues to be stressed, with the risk of injury if the stress gets too high. Pressure injuries are called barotrauma and can be quite painful or debilitating, even potentially fatal – in severe cases causing a ruptured lung, eardrum or damage to the sinuses. To avoid barotrauma, the diver equalises the pressure in all air spaces with the surrounding water pressure when changing depth. The middle ear and sinus are equalised using one or more of several techniques, which is referred to as clearing the ears.

The scuba mask (half-mask) is equalised during descent by periodically exhaling through the nose. During ascent it will automatically equalise by leaking excess air round the edges. A helmet or full face mask will automatically equalise as any pressure differential will either vent through the exhaust valve or open the demand valve and release breathing gas for into the low-pressure space. An insufficient gas supply for the descent rate can lead to helmet squeeze. This was more of a problem with manual air pumps, and often associated with a fall off the edge of a relatively high place by a diver in standard diving equipment with a lot of slack in the lifeline. Another barotrauma hazard is helmet squeeze caused by a shallow rupture of the surface-supplied breathing gas hose and simultaneous failure of the non-return valve at the helmet, which can cause a large pressure difference between the helmet interior and the rupture.

If a drysuit is worn, it must be equalised by inflation and deflation, much like a buoyancy compensator. Most dry suits are fitted with an auto-dump valve, which, if set correctly, and kept at the high point of the diver by good trim skills, will automatically release gas as it expands and retain a virtually constant volume during ascent. During descent the dry suit must be inflated manually unless sealed to the helmet.

Breathing high-pressure gas constitutes a hazard with associated risks of decompression sickness, nitrogen narcosis, oxygen toxicity and high-pressure nervous syndrome.

The prolonged exposure to breathing gases at high partial pressure will result in increased amounts of non-metabolic gases, usually nitrogen and/or helium, (referred to in this context as inert gases) dissolving in the bloodstream as it passes through the alveolar capillaries, and thence carried to the other tissues of the body, where they will accumulate until saturated. This saturation process has very little immediate effect on the diver. However, when the pressure is reduced during ascent, the amount of dissolved inert gas that can be held in stable solution in the tissues is reduced. This effect is described by Henry's Law.