Editing Partial pressure (section)

==In diving breathing gases==
In [[underwater diving]] the physiological effects of individual component gases of [[breathing gas]]es are a function of partial pressure.<ref name="NOAA Diving Manual 1979" > {{cite book |title=NOAA Diving Manual, Diving for Science and Technology |author=NOAA Diving Program (U.S.) |edition=2nd |editor-first=James W. |editor-last=Miller |date=December 1979 |publisher=US Department of Commerce: National Oceanic and Atmospheric Administration, Office of Ocean Engineering |location=Silver Spring, Maryland |isbn= }}</ref>

Using diving terms, partial pressure is calculated as:
:'''partial pressure = (total absolute pressure) × (volume fraction of gas component)'''<ref name="NOAA Diving Manual 1979" />

For the component gas "i":
:'''p<sub>i</sub> = P × F<sub>i</sub>'''<ref name="NOAA Diving Manual 1979" />

For example, at {{convert|50|m|ft|0}} underwater, the total absolute pressure is {{convert|6|bar|kPa|abbr=on}} (i.e., 1 bar of [[atmospheric pressure]] + 5 bar of water pressure) and the partial pressures of the main components of [[Earth's atmosphere|air]], [[oxygen]] 21% by volume and [[nitrogen]] approximately 79% by volume are:
:'''pN<sub>2</sub>''' = 6 bar × 0.79 = 4.7 bar absolute
:'''pO<sub>2</sub>''' = 6 bar × 0.21 = 1.3 bar absolute

{| border="0" cellpadding="2"
|-
|align=right|where:
|&nbsp;
|-
!align=right|p<sub>i</sub>  
|align=left|= partial pressure of gas component i &nbsp;= <math>P_{\mathrm{i}}</math> in the terms used in this article
|-
!align=right|P
|align=left|= total pressure = <math>P</math> in the terms used in this article
|-
!align=right|F<sub>i</sub> 
|align=left|= volume fraction of gas component i &nbsp;= &nbsp;mole fraction, <math>x_{\mathrm{i}}</math>, in the terms used in this article
|-
!align=right|pN<sub>2</sub>
|align=left|= partial pressure of nitrogen&nbsp; = <math>P_\mathrm{N_2}</math> in the terms used in this article
|-
!align=right|pO<sub>2</sub> 
|align=left|= partial pressure of oxygen&nbsp; = <math>P_\mathrm{O_2}</math> in the terms used in this article
|}

The minimum safe lower limit for the partial pressures of oxygen in a breathing gas mixture for diving is {{convert|0.16|bar|kPa}}<!-- (The correct figure is <= 9.5 KPa or .095 bars. People living in Colorado have a partial pressure of oxygen of only 13.9 KPa. Working on a proper citation) This is recommendations for breathing gases for underwater diving, see section header. Please make sure your reference is relevant to this application. Divers are not usually acclimatised to high altitute, may have to exert themselves somewhat, and if they lose consciousness underwater they tend to drown.--> absolute. [[Hypoxia (medical)|Hypoxia]] and sudden unconsciousness can become a problem with an oxygen partial pressure of less than 0.16 bar absolute.<ref name="Sawatzky 2008">{{cite book |last=Sawatzky |first=David |editor-last=Mount |editor-first=Tom|editor2-last=Dituri |editor2-first=Joseph |title=Exploration and Mixed Gas Diving Encyclopedia |edition=1st |date=August 2008 |publisher=International Association of Nitrox Divers |location=Miami Shores, Florida |isbn=978-0-915539-10-9|pages=41–50|chapter=3: Oxygen and its affect on the diver }}</ref>   [[Oxygen toxicity]], involving convulsions, becomes a problem when oxygen partial pressure is too high.  The [[NOAA]] Diving Manual recommends a maximum single exposure of 45 minutes at 1.6 bar absolute, of 120 minutes at 1.5 bar absolute, of 150 minutes at 1.4 bar absolute, of 180 minutes at 1.3 bar absolute and of 210 minutes at 1.2 bar absolute. Oxygen toxicity becomes a risk when these oxygen partial pressures and exposures are exceeded. The partial pressure of oxygen also determines the [[maximum operating depth]] of a gas mixture.<ref name="NOAA Diving Manual 1979" />

[[Nitrogen narcosis|Narcosis]] is a problem when breathing gases at high pressure. Typically, the maximum total partial pressure of narcotic gases used when planning for [[technical diving]] may be around 4.5&nbsp;bar absolute, based on an [[equivalent narcotic depth]] of {{convert|35|m|ft}}.

The effect of a toxic contaminant such as [[carbon monoxide]] in breathing gas is also related to the partial pressure when breathed. A mixture which may be relatively safe at the surface could be dangerously toxic at the maximum depth of a dive, or a tolerable level of [[carbon dioxide]] in the breathing loop of a [[diving rebreather]] may become intolerable within seconds during descent when the partial pressure rapidly increases, and could lead to panic or incapacitation of the diver.<ref name="NOAA Diving Manual 1979" />