Thescience of underwater diving includes those concepts which are useful for understanding theunderwater environment in whichdiving takes place, and its influence on the diver. It includes aspects ofphysics,physiology andoceanography. The practice ofscientific work while diving is known asScientific diving. These topics are covered to a greater or lesser extent indiver training programs, on the principle that understanding the concepts may allow the diver to avoid problems and deal with them more effectively when they cannot be avoided.
A basic understanding of the physics of the underwater environment is foundational to the understanding of the short and long term physiological effects on the diver, and the associated hazards of the diving environment and their consequences which are inherent to diving.
Diving physics are the aspects ofphysics which directly affect theunderwater diver and explain the effects that divers and their equipment are subject to underwater which differ from the normal human experience out of water.
These effects are mostly consequences of immersion in water;buoyancy, thehydrostatic pressure of depth, the effects of the pressure onbreathing gases and gas spaces in the diver and equipment, the inertial and viscous effects on diver movement, and the heat transfer effects. Other effects are the physical influences of the underwater environment on humansensory perception. An understanding of the physics are useful when considering the physiological effects of diving, thehazards and risks of diving, the working ofunderwater breathing apparatus,buoyancy control andbuoyant lifting.
Other foundational knowledge of physics for diving includes theproperties of gases andbreathing gas mixtures under variations ofabsolute pressure andtemperature, and thesolubility of gases in fluids.
The human physiology of underwater diving is thephysiological influences of the underwater environment on human divers, and adaptations to operating underwater, both duringbreath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes both the physiology of breath-hold diving in humans, and the range of physiological effects generally limited to human ambient pressure divers either freediving or usingunderwater breathing apparatus. Several factors affect the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety.[1]
Immersion affectsfluid balance,circulation andwork of breathing.[2][3] Exposure to cold water can result in the harmfulcold shock response,[4][5] the helpfuldiving reflex andexcessive loss of body heat.[6][7][8][9] Breath-hold duration is limited by oxygen reserves, and the risk ofhypoxic blackout, which has a high associated risk ofdrowning.[10][11][12]
Large or sudden changes in ambient pressure have the potential for injury known asbarotrauma.[1][13] Breathing under pressure involves several effects. Metabolically inactive gases are absorbed by the tissues and may have narcotic or other undesirable effects, and must be released slowly to avoid the formation of bubbles duringdecompression.[14] Metabolically active gases have a greater effect in proportion to their concentration, which is proportional to their partial pressure, which for contaminants is increased in proportion to absolute ambient pressure.[1]
Work of breathing is increased by increased density of the breathing gas, artifacts of the breathing apparatus, and hydrostatic pressure variations due to posture in the water. High work of breathing and large combinations of physiological and mechanicaldead space can lead tohypercapnia, which may induce apanic response.
The underwater environment also affects sensory input, which can impact on safety and the ability to function effectively at depth.[2]
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Other physiological effects become apparent at greater depths and where alternative breathing gas mixtures are used to mitigate some of these effects.Nitrogen narcosis occurs under high partial pressures of nitrogen, and helium is substituted to avoid or reduce this effect.High pressure nervous syndrome affects divers breathing helium mixes during rapid compression to high pressures,Compression arthralgia can also affect divers during rapid compression to high pressures. Long decompression times can be reduced by higher oxygen content of breathing gas, but this can expose the diver tooxygen toxicity effects, and changing from helium to nitrogen diluted gases during decompression can causeisobaric counterdiffusion problems. Toxicity of breathing gas contaminants is proportional to partial pressure, and a gas which may have no effect at the surface can be dangerously toxic at higher ambient pressure.
Hypoxia of ascent can affectfreedivers andrebreather divers, and in occasional circumstances scuba and surface-supplied divers, and can be a killer, as the diver can lose consciousness without warning and consequently drown or asphyxiate.
The ocean and aquatic environment is described byoceanography andlimnology. These are directly influenced by aspects ofgeology,weather andclimate. Theunderwater environment is inhabited byorganisms of great diversity, some of which may be hazardous to the diver, or affect the dive in some way.
Sufficient knowledge and a basic understanding of the expected environment for an intended dive allow the diver to predict the conditions which may reasonably be expected during the dive, and allow reasonable estimation ofhazards and associatedrisk, which allows effectivedive planning. There are a range ofenvironmental hazards which should be considered during dive planning.[1]
The other side of understanding of the environment by divers is the impact of diving activity on the environment. Theenvironmental impact of recreational diving on the popular tropical coral reef environment has been extensively studied, and there are known adverse effects due to poor diving skills and lack of environmental awareness, which can be addressed by training and education.[15][16] While commercial diving operations can also have significant environmental impact, they are less frequent, and where environmental impact is expected to be an issue it should be considered in the environmental impact study for the specific contract or project. Similarly, scientific diving environmental impact should be estimated during planning, and be subject to acceptance by the relevant ethics committee.
A basic understanding of the practical relevance of some environmental factors that influence diving operations is useful, such as:
