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{{short description| Aspects of physics which affect the underwater diver }}
'''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 diving|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 (disambiguation)|buoyancy control]]<!-- disambiguation page intended --> and [[Diver trim|trim]], and the [[List of diving hazards and precautions|hazards and risks of diving]].

Changes in density of breathing gas affect the ability of the diver to breathe effectively, and variations in partial pressure of breathing gas constituents have profound effects on the health and ability to function underwater of the diver.

== Aspects of physics with particular relevance to diving ==
[[File:Buoyancy corr.svg|thumb|upright=2]]
The main [[laws of physics]] that describe the influence of the [[underwater diving]] environment on the diver and [[diving equipment]] include:

===Buoyancy===
[[Archimedes' principle]] ([[Buoyancy]]) - Ignoring the minor effect of surface tension, an object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.  Thus, when in water, the weight of the volume of water displaced as compared to the weight of the diver's body and the diver's equipment, determine whether the diver floats or sinks.<ref name=acott /><ref name=buoyancy /> Buoyancy control, and being able to maintain [[neutral buoyancy]] in particular, is an important safety skill. The diver needs to understand buoyancy to effectively and safely operate [[drysuit]]s, [[buoyancy compensator (diving)|buoyancy compensators]], [[diving weighting system]]s and [[lifting bag]]s.<ref name="NOAA Diving Manual 2001"  />

===Pressure===
The concept of [[pressure]] as force distributed over area, the transmission of pressure through hard and soft tissues and physiological gas spaces, and the variation of pressure with immersed depth are central to the understanding of the [[physiology of diving]], particularly the [[physiology of decompression]] and of [[barotrauma]].<ref name="US Navy Diving Manual 2016" />

There are several regions of the body which have a characteristic pressure range relative to the external ambient pressure.{{efn|These include blood pressure, intraocular pressure, and intrapulmonary pressure changes during breathing}} These are usually measured relative to the atmospheric gas environment, where variation with vertical position is insignificant due to low density of the surrounding gas having a negligible effect on external pressure variation. The pressure distribution therefore varies significantly with height in the body due to hydrostatic pressure variations in the body tissues, which are similar in density to water.<ref name="lumenlearning" >{{cite web|url=https://courses.lumenlearning.com/suny-physics/chapter/11-9-pressures-in-the-body/ |title=Pressures in the Body |website= courses.lumenlearning.com|access-date=2 November 2025 }}</ref><ref name="fiveable" >{{cite web |url=https://fiveable.me/intro-college-physics/unit-11/9-pressures-body/study-guide/a9iVz0DcdyOqNo2E |title=11.9 Pressures in the Body – College Physics I – Introduction. |website=Fiveable |date=18 June 2024 |access-date=2 November 2025 }}</ref> Consequently the internal pressures in the body will vary with changes in posture,<ref name="Yartsef 2023" >{{cite web |url=https://derangedphysiology.com/main/cicm-primary-exam/cardiovascular-system/Chapter-501/physiological-response-changes-posture |title=Physiological response to changes in posture |first=Alex |last=Yartsev |date=18 December 2023 |website=derangedphysiology.com |access-date=16 November 2025 }}</ref> and with immersion depth in a denser fluid, such as water, following [[Pascal's law]].<ref name="Weenink and Wingelaar 2021" >{{cite journal |last1=Weenink |first1=R.P. |last2=Wingelaar |first2=T.T. |title=The Circulatory Effects of Increased Hydrostatic Pressure Due to Immersion and Submersion |journal=Front Physiol. |date=July 2021 |volume=19 |issue=12 |article-number=699493 |doi=10.3389/fphys.2021.699493 |doi-access=free |pmid=34349668 |pmc=8326965 }}</ref> In air, the hydrostatic pressure of body fluids is supported by the tensile strength and elasticity of the containing tissues. Fully immersed in water the hydrostatic pressure is almost completely balanced by the hydtostatic pressure of the water, and in partial immersion, the hydrostatic support imbalance is a function of the height of the emersed portion. Pressure needed to circulate blood through the vascular system is additional to static pressure.<ref name="Nishiyama et al 2022" >{{cite journal |first1=Akira |last1=Nishiyama |first2=Kento |last2=Kitada |first3=Miwa |last3=Suzuki |title=Blood pressure adaptation in vertebrates: comparative biology |journal=Kidney International |volume=102 |issue=2 |date=2022 |pages=242-247 |issn=0085-2538 |doi=10.1016/j.kint.2022.03.032 |url=https://www.sciencedirect.com/science/article/pii/S0085253822004343 }}</ref>

The [[absolute pressure]] on an [[ambient pressure diver]] is the sum of the local [[atmospheric pressure]] and [[hydrostatic pressure]].<ref name=pressure /><ref name="CMAS-ISA 3-star" /> Hydrostatic pressure is the component of [[ambient pressure]] due to the [[weight]] of the water column above the depth, and is commonly described in terms of [[Metre sea water|metres or feet of sea water]].<ref name="US Navy Diving Manual 2016" /> 

The ambient pressure of the water is transmitted to the diver by direct contact with the skin and indirect contact through the divers suit and soft equipment. The soft tissues are incompressible and the pressure is transferred through them to any gas spaces. Since gases are compressible they will be compressed until the pressure is balanced. In the case of a breath-hold diver the lungs and upper airways must reduce in volume to compress their gaseous contents to balance the pressure in the walls of the gas spaces. If the spaces are not sufficiently compliant, fluids will accumulate in the adjacent tissues, which may be damaged, resulting in oedema and possibly internal haemorrhage. When the diver has an ambient pressure breathing gas supply, ambient pressure gas can flow in to fill the gas space without a forced volume reduction. This inflow of ambient pressure gas is known a pressure equalisation. A similar effect occurs in external gas spaces in contact with the skin or isolated from the body.<ref name="NOAA Physiology" />

The [[partial pressure]]s of the component gases in a breathing gas mixture control the rate of diffusion into and out of the blood in the lungs, and their concentration in the arterial blood, and the concentration of blood gases affects their physiological effects in the body tissues. Partial pressure calculations are used in [[Gas blending for scuba diving|breathing gas blending]] and analysis<ref name="CMAS gas blender" />

A class of [[diving hazards]] commonly referred to as [[Delta-P (hazard)|delta-P hazards]] are caused by a pressure difference other than variation of ambient pressure with depth. This pressure difference causes flow that may entrain the diver and carry them to places where injury could occur, such as the intake to a [[marine thruster]] or a [[sluice gate]].<ref name="CADC" />

===Gas property changes===
[[Gas]] equations of state, which may be expressed in combination as the [[Combined gas law]], or the [[Ideal gas law]] within the range of pressures normally encountered by divers, or as the traditionally expressed gas laws relating the relationships between two properties when the others are held constant, are used to calculate variations of pressure, volume and temperature, such as: [[Boyle's law]], which describes the change in volume with a change in pressure at a constant temperature.<ref name=acott/> For example, the volume of gas in a non-rigid container (such as a diver's [[lungs]] or buoyancy compensation device), decreases as external pressure increases while the diver descends in the water. Likewise, the volume of gas in such non-rigid containers increases on the ascent. Changes in the volume of gases in the diver and the diver's equipment affect buoyancy. This creates a [[positive feedback]] loop on both ascent and descent. The quantity of open circuit gas breathed by a diver increases with pressure and depth.<ref name="CMAS-ISA 3-star" /> [[Charles's law]], which describes the change in volume with a change in temperature at a fixed pressure, [[Gay-Lussac's Law#Pressure-temperature law|Gay-Lussac's second law]], which describes the change of pressure with a change of temperature for a fixed volume, (originally described by [[Guillaume Amontons]], and sometimes called Amontons's law). This explains why a diver who enters cold water with a warm diving cylinder, for instance after a recent quick fill, finds the gas pressure of the cylinder drops by an unexpectedly large amount during the early part of the dive as the gas in the cylinder cools.<ref name="Amontons'law" /><ref name="NOAA Diving Manual 2001"  />

In mixtures of [[breathing gas]]es the concentration of the individual components of the gas mix is proportional to their [[partial pressure]]s and [[volumetric gas fraction]].<ref name=acott/> Gas fraction is constant for the components of a mixture, but partial pressure changes in proportion to changes in the total pressure. Partial pressure is a useful measure for expressing limits for avoiding [[nitrogen narcosis]] and [[oxygen toxicity]].<ref name="CMAS-ISA 3-star" /> [[Dalton's law]] describes the combination of partial pressures to form the total pressure of the mixture.<ref name=acott/> 

Gases are [[compressibility|highly compressible]] but [[liquids]] are almost incompressible. Gas spaces in the diver's body and gas held in flexible equipment contract as the diver descends and expand as the diver ascends.<ref name=compression /><ref name="CMAS-ISA 3-star" /> When constrained from free expansion and contraction, gases will exert unbalanced pressure on the walls of their containment, which can cause damage or injury known as barotraum if excessive.<ref name="Bennett and Elliott 2003" />

===Solubility of gases and diffusion===
{{further|decompression theory}}
[[Henry's law]] describes how as pressure increases the quantity of gas that can be dissolved in the [[biological tissue|tissues]] of the body increases.<ref name=henrys /> This effect is involved in [[nitrogen narcosis]], [[oxygen toxicity]] and [[decompression sickness]].<ref name="CMAS-ISA 3-star" />

[[Concentration]] of gases dissolved in the body tissues affects a number of physiological processed and is influenced by [[diffusion]] rates, [[solubility]] of the components of the [[breathing gas]] in the tissues of the body and pressure. Given sufficient time under a specific pressure, tissues will saturate with the gases, and no more will be absorbed until the pressure increases. When the pressure decreases faster than the dissolved gas can be eliminated, the concentration rises and [[supersaturation]] occurs, and pre-existing bubble nuclei may grow. Bubble formation and growth in [[decompression sickness]] is affected by [[surface tension]] of the bubbles, as well as pressure changes and supersaturation.<ref name="NOAA Diving Manual 2001" /><ref name="US Navy Diving Manual 2016" />

===Density effects===
The [[density]] of the breathing gas is proportional to absolute pressure, and affects the [[breathing performance of regulators]] and the [[work of breathing]], which affect the capacity of the diver to work, and in extreme cases, to breathe. Density of the water, the diver's body, and equipment, determines the diver's [[apparent weight]] in water, and therefore their [[buoyancy]], and influences the use of buoyant equipment.<ref name=density /> Density and the force of [[gravity]] are the factors in the generation of hydrostatic pressure. Divers use high density materials such as [[lead]] for [[diving weighting system]]s and low density materials such as [[Density of air|air]] in [[Buoyancy compensator (diving)|buoyancy compensators]] and [[lifting bag]]s.<ref name="CMAS-ISA 3-star" />

===Viscosity effects===
The absolute (dynamic) [[viscosity]] of water is higher (order of 100 times) than that of air.<ref name="Dougherty and Franzini 1877" /> This increases the drag on an object moving through water, and more effort is required for propulsion in water than air relative to the speed of movement. Viscosity also affects the work of breathing.<ref name="Mitchell" />

===Surface tension===
{{main|surface tension}}
Surface tension is a factor in the formation, growth, and elimination of gas bubbles in a liquid, and as such, relevant to [[bubble mechanics]] aspects of [[decompression theory]].

===Heat balance===
{{main|Thermal balance of the underwater diver}}
[[Thermal conductivity]] of water is higher than that of air.<ref name=thermal /> As water conducts heat 20 times more than air, and has a much higher thermal capacity, [[heat transfer]] from a diver's body to water is faster than to air, and to avoid excessive heat loss leading to [[hypothermia]], thermal insulation in the form of diving suits, or active heating is used. Gases used in diving have very different thermal conductivities; [[Heliox]], and to a lesser extent, [[Trimix (breathing gas)|trimix]], conducts heat faster than air because of the helium content, and [[argon]] conducts heat slower than air, so technical divers breathing gases containing helium may inflate their dry suits with argon.<ref name=IEEE2008 /><ref name=argon /> Some thermal conductivity values at 25&nbsp;°C and sea level atmospheric pressure: argon: 16&nbsp;mW/m/K; air: 26&nbsp;mW/m/K; neoprene: 50&nbsp;mW/m/K; wool felt: 70&nbsp;mW/m/K; helium: 142&nbsp;mW/m/K; water: 600&nbsp;mW/m/K.<ref name=thermal />

===Underwater vision===
[[File:NOAA Deep Light diagram3.jpg|thumb|upright=2|Comparison of penetration of light of different wavelengths in the open ocean and coastal waters]]
[[Underwater vision]] is affected by the [[refractive index]] of water, which is similar to that of the [[cornea]] of the [[human eye|eye]], and which is about 30% greater than air. [[Snell's law]] describes the angle of refraction relative to the angle of incidence.<ref name=snells /> This similarity in refractive index is the reason a diver cannot see clearly underwater without a [[diving mask]] with an internal airspace.<ref name="NOAA Diving Manual 2001"  /> [[Absorption (electromagnetic radiation)|Absorption of light]] depends on wavelength, this causes loss of [[colour]] underwater.<ref name=Luria /><ref name=light /> The red end of the [[spectrum of light]] is absorbed over a short distance, and is lost even in shallow water.<ref name=Luria/> Divers use artificial light underwater to reveal these absorbed colours. In deeper water no light from the surface penetrates, and artificial lighting is necessary to see at all.<ref name="CMAS-ISA 3-star" /> Underwater vision is also affected by [[turbidity]], which causes scattering, and dissolved materials which absorb light.<ref name="Luria and Kinney" />

===Underwater acoustics===
[[Underwater acoustics]] affect the ability of the diver to hear through the hood of the diving suit or the helmet, and the ability to judge the direction of a source of sound.<ref name="Phys org" />

== Environmental physical phenomena of interest to divers ==
[[File:THERMOCLINE.png|thumb|upright=1.2|Graph showing a tropical ocean thermocline (depth vs. temperature)]]
The physical phenomena found in large bodies of water that may have a practical influence on divers include:
* Effects of [[weather]] such as [[wind]], which causes [[Wind wave|waves]], and changes of [[temperature]] and atmospheric pressure on and in the water. Even moderately high winds can prevent diving because of the increased risk of becoming lost at sea or injured. Low water temperatures make it necessary for divers to wear diving suits and can cause problems such as freezing of [[diving regulator]]s.<ref name="NOAA Diving Manual 2001"  /><ref name="CMAS-ISA 3-star" />
* [[Halocline]]s, or strong, vertical [[salinity]] gradients. For instance, where fresh water enters the sea, the fresh water floats over the denser saline water and may not mix immediately. Sometimes visual effects, such as shimmering and reflection, occur at the boundary between the layers, because the refractive indices differ.<ref name="NOAA Diving Manual 2001"  />
* [[Ocean currents]] can transport water over thousands of kilometres, and may bring water with different temperature and salinity into a region. Some ocean currents have a huge effect on local climate, for instance the warm water of the [[North Atlantic drift]] moderates the climate of the north west coast of Europe. The speed of water movement can affect dive planning and safety.<ref name="NOAA Diving Manual 2001"  /><ref name="CMAS-ISA 3-star" />
* [[Thermocline]]s, or sudden changes in temperature. Where the air temperature is higher than the water temperature, shallow water may be warmed by the air and the sunlight but deeper water remains cold resulting in a lowering of temperature as the diver descends. This temperature change may be concentrated over a small vertical interval, when it is called a ''thermocline''.<ref name="NOAA Diving Manual 2001"  /><ref name="CMAS-ISA 3-star" />
* Where cold, fresh water enters a warmer sea the fresh water may float over the denser saline water, so the temperature rises as the diver descends.<ref name="NOAA Diving Manual 2001"  /> 
* In lakes exposed to geothermal activity, the temperature of the deeper water may be warmer than the surface water. This will usually lead to convection currents.<ref name="NOAA Diving Manual 2001"  />
* Water at near-freezing temperatures is less dense than slightly warmer water - maximum density of water is at about 4&nbsp;°C - so when near freezing, water may be slightly warmer at depth than at the surface.<ref name="NOAA Diving Manual 2001"  />
* [[Tides|Tidal]] currents and changes in sea level caused by [[Gravity|gravitational]] forces and the [[Earth's rotation]]. Some dive sites can only be dived safely at [[slack water]] when the tidal cycle reverses and the current slows. Strong currents can cause problems for divers. Buoyancy control can be difficult when a strong current meets a vertical surface. Divers consume more breathing gas when swimming against currents. Divers on the surface can be separated from their boat cover by currents. On the other hand, [[drift diving]] is only possible when there is a reasonable current.<ref name="NOAA Diving Manual 2001"  /><ref name="CMAS-ISA 3-star" />

==See also==
*{{annotated link|Ambient pressure}}
*{{annotated link|Atmospheric pressure}}
*{{annotated link|Buoyancy}}
*{{annotated link|Pressure}}

==Notes==
{{notelist}}

==References==
{{Reflist|refs=

<ref name=acott>{{cite journal |last=Acott |first=C. |title=The diving "Law-ers": A brief resume of their lives. |journal=South Pacific Underwater Medicine Society Journal |volume=29 |year=1999 |issn=0813-1988 |oclc=16986801 }}</ref>

<ref name="Amontons'law">{{cite web |url=http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/gaslaws3.html#amonton |title=Amonton's Law |publisher=Purdue University |access-date=8 July 2008 }}</ref>

<ref name=argon>{{cite web |first=Eric |last=Maiken |title=Why Argon |url=http://www.decompression.org/maiken/Why_Argon.htm |website=www.decompression.org |access-date=11 April 2011}}</ref>

<ref name="Bennett and Elliott 2003" >{{cite book |title=Bennett and Elliott's physiology and medicine of diving |edition=5th Rev |editor1-last=Brubakk |editor1-first=A.O. |editor2-last=Neuman |editor2-first=T.S. |year=2003 |publisher=Saunders |location=United States |isbn=978-0-7020-2571-6 |last=Neuman |first=T.S. |chapter=Arterial gas embolism and pulmonary barotrauma |pages=558–61}}</ref>

<ref name=buoyancy>{{cite web |first=Larry "Harris" |last=Taylor |title=Practical Buoyancy Control |url=http://www-personal.umich.edu/~lpt/practical.htm |publisher=University of Michigan  |access-date=10 October 2008 }}</ref>

<ref name="CADC" >{{cite book |url=http://www.cadc.ca/downloads/DeltaPHazards_CADC.pdf |title=Guideline for Diving Operations at dams and other work sites where Delta P hazards may exist |publisher=Canadian Association of Diving Contractors |date=17 October 2011 }}</ref>

<ref name="CMAS-ISA 3-star">{{cite book|last=Scully|first=Reg|title=CMAS-ISA Three Star Diver Theoretical Manual|edition=1st|date=April 2013|publisher=CMAS-Instructors South Africa|location=Pretoria|isbn=978-0-620-57025-1}}</ref>

<ref name="CMAS gas blender">{{cite web |url=http://www.cmas.org/sitemap/trimix-gas-blender-training-programme |title=Trimix Gas Blender Training Programme |last=<!-- not specified --> |year=2012 |work=CMAS Training standards |publisher=World Underwater Federation (CMAS) |access-date=3 July 2016 |archive-date=7 August 2016 |archive-url=https://web.archive.org/web/20160807184229/http://www.cmas.org/sitemap/trimix-gas-blender-training-programme |url-status=live }}</ref>

<ref name=compression>{{cite web |title=Compressibility and Ideal Gas Approximations |url=http://www.shodor.org/unchem/advanced/gas/compress.html |publisher=UNC-Chapel Hill  |access-date=2008-10-10}}</ref>

<ref name=density>{{cite web |title=Density and the Diver |url=http://www.deep-six.com/page69.htm |publisher=Diving with Deep-Six  |access-date=10 October 2008 }}</ref>

<ref name="Dougherty and Franzini 1877">{{cite book |last1=Dougherty |first1=R.L.|last2=Franzini |first2=J.B. |title=Fluid Mechanics with Engineering Applications |edition=7th |year=1977 |publisher=McGraw-Hill |location=Kogakusha |isbn=978-0-07-085144-3 }}</ref>

<ref name=IEEE2008>{{cite journal |last1=Nuckols |first1=M.L. |last2=Giblo |first2=J |last3=Wood-Putnam |first3=J.L. |title=Thermal Characteristics of Diving Garments When Using Argon as a Suit Inflation Gas. |journal=Proceedings of the Oceans 08 MTS/IEEE Quebec, Canada Meeting |publisher=MTS/IEEE |date=September 15–18, 2008 }}</ref>

<ref name=henrys>{{cite web |title=Henry's Law |url=http://cancerweb.ncl.ac.uk/cgi-bin/omd?Henry%27s+law |archive-url=https://archive.today/20070813174048/http://cancerweb.ncl.ac.uk/cgi-bin/omd?Henry's+law |archive-date=August 13, 2007 |publisher=Online Medical Dictionary |access-date=10 October 2008 }}</ref>

<ref name=light>{{cite journal |title=Why is Water Blue |journal=J. Chem. Educ. |date=1993 |volume=70 |issue=8 |page=612 |doi=10.1021/ed070p612 |bibcode=1993JChEd..70..612B |url=http://www.dartmouth.edu/~etrnsfer/water.htm |via=Dartmouth College |access-date=10 October 2008 |last1=Braun |first1=Charles L. |last2=Smirnov |first2=Sergei N. |archive-date=25 May 2019 |archive-url=https://web.archive.org/web/20190525162353/http://www.dartmouth.edu/~etrnsfer/water.htm |url-access=subscription }}</ref>

<ref name=Luria>{{cite journal |last1=Luria |first1=S.M. |last2=Kinney |first2=J.A. |title=Underwater vision |journal=Science |volume=167 |issue=3924 |pages=1454–61 |date=March 1970 |pmid=5415277 |doi= 10.1126/science.167.3924.1454|bibcode=1970Sci...167.1454L }}</ref>

<ref name="Luria and Kinney" >{{cite journal |last1=Luria |first1=S. M. |last2=Kinney |first2=J. A.|title=Linear polarizing filters and underwater vision |journal=Undersea Biomedical Research |volume=1 |issue=4 |pages=371–8 |date=December 1974 |pmid=4469103 }}</ref>

<ref name="Mitchell" >{{cite web |title=Respiratory failure in technical diving |url=https://www.youtube.com/watch?v=QBajM3xmOtc |website=www.youtube.com |publisher=DAN Southern Africa |last=Mitchell |first=Simon |date=2015 |access-date=6 October 2021 |archive-date=9 October 2021 |archive-url=https://web.archive.org/web/20211009210228/https://www.youtube.com/watch?v=QBajM3xmOtc&feature=youtu.be |url-status=live }}</ref>

<ref name="NOAA Diving Manual 2001" >{{cite book |title=NOAA Diving Manual, Diving for Science and Technology |author=NOAA Diving Program (U.S.) |edition=4th |editor-first=James T. |editor-last=Joiner |date=28 Feb 2001 |publisher=National Oceanic and Atmospheric Administration, Office of Oceanic and Atmospheric Research, National Undersea Research Program |location=Silver Spring, Maryland |isbn=978-0-941332-70-5 |ref={{sfnRef|NOAA Diving Manual|2001}} |url-access=registration |url=https://archive.org/details/noaadivingmanual00noaa }} CD-ROM prepared and distributed by the National Technical Information Service (NTIS)in partnership with NOAA and Best Publishing Company</ref>

<ref name="NOAA Physiology" >{{cite book|url=https://www.ehs.ucsb.edu/sites/default/files/docs/dbs/physio.pdf |title=NOAA Diving Manual |chapter=3: Diving Physiology |publisher= Best Publishing Company |via=www.ehs.ucsb.edu }}</ref> 

<ref name="Phys org" >{{cite web|url=https://phys.org/news/2024-06-scientists-puzzle-underwater.html |title=Scientists solve the puzzle of directional hearing underwater |website=phys.org |access-date=26 November 2024 |date=21 June 2024 |author=Charité }}</ref>

<ref name=pressure>{{cite web |title=Pressure |url=http://library.thinkquest.org/28170/32.html |publisher=Oracle ThinkQuest |access-date=10 October 2008 |archive-url=https://web.archive.org/web/20081012193020/http://library.thinkquest.org/28170/32.html |archive-date=12 October 2008 }}</ref>

<ref name=snells>{{cite web |title=Snell's Law |url=http://scienceworld.wolfram.com/physics/SnellsLaw.html |publisher=scienceworld.wolfram  |access-date=10 October 2008 }}</ref>

<ref name=thermal>{{cite web |title=Thermal Conductivity of some common Materials |url=http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html |publisher=The Engineering Toolbax  |access-date=10 October 2008 }}</ref>

 <ref name="US Navy Diving Manual 2016">{{cite book|last=US Navy|title=U.S. Navy Diving Manual Revision 7 SS521-AG-PRO-010 0910-LP-115-1921|url=https://www.navsea.navy.mil/Portals/103/Documents/SUPSALV/Diving/US%20DIVING%20MANUAL_REV7.pdf?ver=2016-12-14-135043-757|date=1 December 2016|publisher=US Naval Sea Systems Command|location=Washington, DC.|ref={{harvid|US Navy Diving Manual|2016}}}}</ref> 
 
}}

{{Branches of physics}}
{{Underwater diving|scidiv}}
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