Partial Pressure in Diving Breathing Gases
In recreational diving and professional diving the richness of individual component gases of breathing gases is expressed by partial pressure.
Using diving terms, partial pressure is calculated as:
- partial pressure = (total absolute pressure) × (volume fraction of gas component)
For the component gas "i":
- ppi = P × Fi
For example, at 50 metres (165 feet), the total absolute pressure is 6 bar (600 kPa) (i.e., 1 bar of atmospheric pressure + 5 bar of water pressure) and the partial pressures of the main components of air, oxygen 21% by volume and nitrogen 79% by volume are:
- ppN2 = 6 bar × 0.79 = 4.7 bar absolute
- ppO2 = 6 bar × 0.21 = 1.3 bar absolute
| where: | |
| ppi | = partial pressure of gas component i = in the terms used in this article |
|---|---|
| P | = total pressure = in the terms used in this article |
| Fi | = volume fraction of gas component i = mole fraction, in the terms used in this article |
| ppN2 | = partial pressure of nitrogen = in the terms used in this article |
| ppO2 | = partial pressure of oxygen = in the terms used in this article |
The minimum safe lower limit for the partial pressures of oxygen in a gas mixture is 0.16 bar (16 kPa) absolute. Hypoxia and sudden unconsciousness becomes a problem with an oxygen partial pressure of less than 0.16 bar absolute. 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 determines the maximum operating depth of a gas mixture.
Nitrogen 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 is 4.5 bar absolute, based on an equivalent narcotic depth of 35 metres (115 ft).
Read more about this topic: Partial Pressure
Famous quotes containing the words partial, pressure, diving, breathing and/or gases:
“The one-eyed man will be King in the country of the blind only if he arrives there in full possession of his partial faculties—that is, providing he is perfectly aware of the precise nature of sight and does not confuse it with second sight ... nor with madness.”
—Angela Carter (1940–1992)
“He who is of a calm and happy nature will hardly feel the pressure of age, but to him who is of an opposite disposition youth and age are equally a burden.”
—Plato (c. 427–347 B.C.)
“A worm is as good a traveler as a grasshopper or a cricket, and a much wiser settler. With all their activity these do not hop away from drought nor forward to summer. We do not avoid evil by fleeing before it, but by rising above or diving below its plane; as the worm escapes drought and frost by boring a few inches deeper.”
—Henry David Thoreau (1817–1862)
“Mark the babe
Not long accustomed to this breathing world;
One that hath barely learned to shape a smile,
Though yet irrational of soul, to grasp
With tiny finger—to let fall a tear;
And, as the heavy cloud of sleep dissolves,
To stretch his limbs, bemocking, as might seem,
The outward functions of intelligent man.”
—William Wordsworth (1770–1850)
“The bird is not in its ounces and inches, but in its relations to Nature; and the skin or skeleton you show me, is no more a heron, than a heap of ashes or a bottle of gases into which his body has been reduced, is Dante or Washington.”
—Ralph Waldo Emerson (1803–1882)