Science of underwater diving

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The science of underwater diving includes those concepts which are useful for understanding the underwater environment in which diving takes place, and its influence on the diver. It includes aspects of physics, physiology and oceanography. The practice of scientific work while diving is known as Scientific diving. These topics are covered to a greater or lesser extent in diver 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.

Contents

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.

Physics

Diving physics are the aspects of physics which directly affect the underwater diver and which 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, the hydrostatic pressure of depth, the effects of the pressure on breathing 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 human sensory perception. An understanding of the physics is useful when considering the physiological effects of diving, the hazards and risks of diving, the working of underwater breathing apparatus, buoyancy control and buoyant lifting.

Other foundational knowledge of physics for diving includes the properties of gases and breathing gas mixtures under variations of absolute pressure and temperature, and the solubility of gases in fluids.

Physiology

The human physiology of underwater diving is the physiological influences of the underwater environment on human divers, and adaptations to operating underwater, both during breath-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 using underwater 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 affects fluid balance, circulation and work of breathing. [2] [3] Exposure to cold water can result in the harmful cold shock response, [4] [5] the helpful diving reflex and excessive loss of body heat. [6] [7] [8] [9] Breath-hold duration is limited by oxygen reserves, and the risk of hypoxic blackout, which has a high associated risk of drowning. [10] [11] [12]

Large or sudden changes in ambient pressure have the potential for injury known as barotrauma. [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 during decompression. [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 mechanical dead space can lead to hypercapnia, which may induce a panic response.

The underwater environment also affects sensory input, which can impact on safety and the ability to function effectively at depth. [2]

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 to oxygen toxicity effects, and changing from helium to nitrogen diluted gases during decompression can cause isobaric 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 affect freedivers and rebreather 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.

Environment

The ocean and aquatic environment is described by oceanography and limnology. These are directly influenced by aspects of geology, weather and climate. The underwater environment is inhabited by organisms 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 of hazards and associated risk, which allows effective dive planning. There are a range of environmental 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. The environmental 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:

Related Research Articles

<span class="mw-page-title-main">Ice diving</span> Underwater diving under ice

Ice diving is a type of penetration diving where the dive takes place under ice. Because diving under ice places the diver in an overhead environment typically with only a single entry/exit point, it requires special procedures and equipment. Ice diving is done for purposes of recreation, scientific research, public safety and other professional or commercial reasons.

<span class="mw-page-title-main">Underwater environment</span> Aquatic or submarine environment

An underwater environment is a environment of, and immersed in, liquid water in a natural or artificial feature, such as an ocean, sea, lake, pond, reservoir, river, canal, or aquifer. Some characteristics of the underwater environment are universal, but many depend on the local situation.

Diving physics, or the physics of underwater diving is the basic aspects of physics which describe the effects of the underwater environment on the underwater diver and their equipment, and the effects of blending, compressing, and storing breathing gas mixtures, and supplying them for use at ambient pressure. These effects are mostly consequences of immersion in water, the hydrostatic pressure of depth and the effects of pressure and temperature on breathing gases. An understanding of the physics behind is useful when considering the physiological effects of diving, breathing gas planning and management, diver buoyancy control and trim, and the hazards and risks of diving.

<span class="mw-page-title-main">Saturation diving</span> Diving decompression technique

Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working at great depths must undergo by only decompressing divers once at the end of the diving operation, which may last days to weeks, having them remain under pressure for the whole period. A diver breathing pressurized gas accumulates dissolved inert gas used in the breathing mixture to dilute the oxygen to a non-toxic level in the tissues, which can cause potentially fatal decompression sickness if permitted to come out of solution within the body tissues; hence, returning to the surface safely requires lengthy decompression so that the inert gases can be eliminated via the lungs. Once the dissolved gases in a diver's tissues reach the saturation point, however, decompression time does not increase with further exposure, as no more inert gas is accumulated.

Dysbarism refers to medical conditions resulting from changes in ambient pressure. Various activities are associated with pressure changes. Underwater diving is the most frequently cited example, but pressure changes also affect people who work in other pressurized environments, and people who move between different altitudes.

<span class="mw-page-title-main">Diving medicine</span> Diagnosis, treatment and prevention of disorders caused by underwater diving

Diving medicine, also called undersea and hyperbaric medicine (UHB), is the diagnosis, treatment and prevention of conditions caused by humans entering the undersea environment. It includes the effects on the body of pressure on gases, the diagnosis and treatment of conditions caused by marine hazards and how relationships of a diver's fitness to dive affect a diver's safety. Diving medical practitioners are also expected to be competent in the examination of divers and potential divers to determine fitness to dive.

<span class="mw-page-title-main">Scuba diving</span> Swimming underwater, breathing gas carried by the diver

Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.

Diving disorders, or 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 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.

<span class="mw-page-title-main">Underwater diving</span> Descending below the surface of the water to interact with the environment

Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving, an ambiguous term with several possible meanings, depending on context. Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well-adapted to the environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done.

<span class="mw-page-title-main">Breathing performance of regulators</span> Capacity of breathing regulators to function as specified

The breathing performance of regulators is a measure of the ability of a breathing gas regulator to meet the demands placed on it at varying ambient pressures and temperatures, and under varying breathing loads, for the range of breathing gases it may be expected to deliver. Performance is an important factor in design and selection of breathing regulators for any application, but particularly for underwater diving, as the range of ambient operating pressures and temperatures, and variety of breathing gases is broader in this application. A diving regulator is a device that reduces the high pressure in a diving cylinder or surface supply hose to the same pressure as the diver's surroundings. It is desirable that breathing from a regulator requires low effort even when supplying large amounts of breathing gas as this is commonly the limiting factor for underwater exertion, and can be critical during diving emergencies. It is also preferable that the gas is delivered smoothly without any sudden changes in resistance while inhaling or exhaling, and that the regulator does not lock up and either fail to supply gas or free-flow. Although these factors may be judged subjectively, it is convenient to have standards by which the many different types and manufactures of regulators may be objectively compared.

<span class="mw-page-title-main">Underwater breathing apparatus</span> Equipment which provides breathing gas to an underwater diver

Underwater breathing apparatus is equipment which allows the user to breathe underwater. The three major categories of ambient pressure underwater breathing apparatus are:

<span class="mw-page-title-main">Scuba gas planning</span> Estimation of breathing gas mixtures and quantities required for a planned dive profile

Scuba gas planning is the aspect of dive planning and of gas management which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive. It may assume that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.

<span class="mw-page-title-main">Diver training</span> Processes to develop the skills and knowledge to dive safely underwater

Diver training is the set of processes through which a person learns the necessary and desirable skills to safely dive underwater within the scope of the diver training standard relevant to the specific training programme. Most diver training follows procedures and schedules laid down in the associated training standard, in a formal training programme, and includes relevant foundational knowledge of the underlying theory, including some basic physics, physiology and environmental information, practical skills training in the selection and safe use of the associated equipment in the specified underwater environment, and assessment of the required skills and knowledge deemed necessary by the certification agency to allow the newly certified diver to dive within the specified range of conditions at an acceptable level of risk. Recognition of prior learning is allowed in some training standards.

Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing.

<span class="mw-page-title-main">Physiology of decompression</span> The physiological basis for decompression theory and practice

The physiology of decompression is the aspect of physiology which is affected by exposure to large changes in ambient pressure. It involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs, or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again.

Human physiology of underwater diving is the physiological influences of the underwater environment on the human diver, and adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes the range of physiological effects generally limited to human ambient pressure divers either freediving or using underwater breathing apparatus. Several factors influence 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.

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.

<span class="mw-page-title-main">Outline of underwater diving</span> List of articles related to underwater diving grouped by topical relevance

The following outline is provided as an overview of and topical guide to underwater diving:

References

  1. 1 2 3 4 US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. 2006. Archived from the original on 2 May 2008. Retrieved 26 May 2008.
  2. 1 2 Pendergast, D. R.; Lundgren, C. E. G. (1 January 2009). "The underwater environment: cardiopulmonary, thermal, and energetic demands". Journal of Applied Physiology. 106 (1): 276–283. doi:10.1152/japplphysiol.90984.2008. ISSN   1522-1601. PMID   19036887. S2CID   2600072.
  3. ↑ Kollias, James; Van Derveer, Dena; Dorchak, Karen J.; Greenleaf, John E. (February 1976). "Physiologic responses to water immersion in man: A compendium of research" (PDF). Nasa Technical Memorandum X-3308. Washington, DC: National Aeronautics And Space Administration. Retrieved 12 October 2016.
  4. ↑ Staff. "4 Phases of Cold Water Immersion". Beyond Cold Water Bootcamp. Canadian Safe Boating Council. Archived from the original on 17 February 2019. Retrieved 8 November 2013.
  5. ↑ "Exercise in the Cold: Part II - A physiological trip through cold water exposure". The science of sport. www.sportsscientists.com. 29 January 2008. Archived from the original on 24 May 2010. Retrieved 24 April 2010.
  6. ↑ Lindholm, Peter; Lundgren, Claes EG (1 January 2009). "The physiology and pathophysiology of human breath-hold diving". Journal of Applied Physiology. 106 (1): 284–292. doi:10.1152/japplphysiol.90991.2008. PMID   18974367. S2CID   6379788.
  7. ↑ Panneton, W. Michael (2013). "The Mammalian Diving Response: An Enigmatic Reflex to Preserve Life?". Physiology. 28 (5): 284–297. doi:10.1152/physiol.00020.2013. PMC   3768097 . PMID   23997188.
  8. ↑ Sterba, J.A. (1990). "Field Management of Accidental Hypothermia during Diving". US Navy Experimental Diving Unit Technical Report. NEDU-1-90. Archived from the original on December 6, 2008. Retrieved 11 June 2008.{{cite journal}}: CS1 maint: unfit URL (link)
  9. ↑ Cheung, S.S.; Montie, D.L.; White, M.D.; Behm, D. (September 2003). "Changes in manual dexterity following short-term hand and forearm immersion in 10 degrees C water". Aviat Space Environ Med. 74 (9): 990–3. PMID   14503680 . Retrieved 11 June 2008.
  10. ↑ Pearn, John H.; Franklin, Richard C.; Peden, Amy E. (2015). "Hypoxic Blackout: Diagnosis, Risks, and Prevention". International Journal of Aquatic Research and Education. 9 (3): 342–347. doi: 10.25035/ijare.09.03.09 .
  11. ↑ Edmonds, C. (1968). "Shallow Water Blackout". Royal Australian Navy, School of Underwater Medicine. RANSUM-8-68. Archived from the original on April 15, 2013. Retrieved 21 July 2008.{{cite journal}}: CS1 maint: unfit URL (link)
  12. ↑ Lindholm, P.; Pollock, N. W.; Lundgren, C. E. G., eds. (2006). Breath-hold diving. Proceedings of the Undersea and Hyperbaric Medical Society/Divers Alert Network 2006 June 20–21 Workshop. Durham, NC: Divers Alert Network. ISBN   978-1-930536-36-4. Archived from the original on October 7, 2008. Retrieved 21 July 2008.{{cite book}}: CS1 maint: unfit URL (link)
  13. ↑ Brubakk, A. O.; Neuman, T. S. (2003). Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. United States: Saunders Ltd. p. 800. ISBN   0-7020-2571-2.
  14. ↑ Bauer, Ralph W.; Way, Robert O. (1970). "Relative narcotic potencies of hydrogen, helium, nitrogen, and their mixtures".
  15. ↑ Johansen, Kelsey (2013). "Education and training". In Musa, Ghazali; Dimmock, Kay (eds.). Scuba Diving Tourism: Contemporary Geographies of Leisure, Tourism and Mobility. Routledge. ISBN   9781136324949.
  16. ↑ Hammerton, Zan (2014). SCUBA-diver impacts and management strategies for subtropical marine protected areas (Thesis). Southern Cross University.
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