SCUBA Diving Injuries: Barotrauma & Dysbarism
This is a review series on injuries and emergencies that can occur SCUBA diving.
We have to remind ourselves that we do not belong under the water, breathing compressed air out of a tank on our backs. To do so requires fitness, training, and a trust in the technology that allows us to breath underwater.
Mechanism of Injury of Barotrauma:
Breathing a Gas Under Pressure
Pre-dive on the Surface = Environmental Exposure
Descent Injuries – Increasing Pressure = Compression Injuries or Squeeze Injuries
Bottom Time = Saturation Injuries
Ascent – Decreasing Pressure = Decompression Injuries
Post-dive on the Surface = Environmental Exposure
In the Ocean = Hazardous Marine Life
THE GAS LAWS That All Divers Must Know:
The volume of a gas varies inversely with the pressure.
Increase the pressure = decrease the volume (squeeze)
Decrease the pressure = increase the volume (expand)
The volume of a gas varies with temperature.
Cold gas = less volume, Warm gas = more volume
GENERAL GAS LAW:
Pressure 1 x Volume 1 = Pressure 2 x Volume 2
Temperature 1 Temperature 2
Law of partial pressures: P = Pp1 + Pp2 + Pp3 ….
Total pressure (P) = sum of all the partial pressures (Pp), nitrogen + oxygen + …
As pressure increases the amount of gas dissolved into the body increases.
Bottom time = saturation of gas in tissues.
ATMOSPHERIC ABSOLUTE (ATA):
The atmospheric pressure at sea level is 1 ATA =:
14.7 psi (pounds per square inch)
29.9 inmg (inches of mercury)
760 mmhg (millimeters of mercury) or Torr
1033 g/cm2 (grams per centimeter squared)
1013.3 mbar (millibars)
10.08 msw (meters of sea water)
33 fsw (feet of sea water)
34 ffw (feet of fresh water)
Every 33 feet of sea water adds 1 ATA…so at 100′ you are at 4 ATA.
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