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11.5.2 Atmosphere Pressure Changes


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Flying and Diving

Diving before flight increases the risk of Decompression Sickness. If compressed air is used under pressure, the body's store of nitrogen is increased. As an ascent is made, nitrogen comes out of solution - thus causing Decompression Sickness. Do not fly within 24 hours of SCUBA diving.

Decompression Sickness

Decompression sickness is caused by inert gases, mainly nitrogen, coming out of solution into the body's tissues due to exposure to reduced atmospheric pressure. When breathing air at sea level, the body is normally saturated with nitrogen.

When the ambient pressure is reduced by increasing altitude, the body becomes super-saturated with nitrogen. Some of this nitrogen can come out of solution as bubbles in joints, the skin or the chest. Depending on the location, and the extent of bubble formation, the symptoms can vary.

The common names for Decompression Sickness and the location in the body are listed below:

  • Bends: Painful joints such as the knees or elbows.
  • Creeps: Itching in the skin that may be accompanied by a rash.
  • Chokes: Pain in the chest with a dry hacking cough.
  • Nervous System Effects: Possible paralysis and a loss of vision.
  • Staggers: Loss of balance which is similar to the actions of a drunk.
  • Collapse: Unconsciousness, death may occur.

Certain conditions make decompression sickness more likely:

  • Altitude: Cabin altitudes greater than 18 000 ft. Above 25 000 feet the chances of suffering from decompression sickness are greatly increased.
  • Duration: The longer a person is at altitude the more likely the chance of decompression sickness.
  • Age: Age seems to affect the onset.
  • Weight: Obese and overweight people are more susceptible.
  • Diving: Diving allows the body to "super saturate" with Nitrogen. An increased altitude allows this Nitrogen to come out of solution.
  • Rate of Climb: The faster the rate of climb the faster the onset.
  • Exercise: The parts of the body that are most used in exercise are those that are most susceptible.
  • Other Factors: Fatigue, Alcohol, Hypoxia and cold.

Re-exposure Flying within 24 hours of suffering from Decompression Sickness will increase a pilot's susceptibility of contracting the problem again. 48 hours should be the minimum time allowed to elapse before flying again.

Treatment of Decompression Sickness

Decompression sickness can be avoided by preoxygenation (breathing 100% Oxygen before flight) and then breathing 100% Oxygen during flight. This saturation of the body with Oxygen reduces the Nitrogen saturation and reduces risk of Decompression Sickness.

If Decompression Sickness does occur:

  • Descend immediately.
  • Land as soon as possible.
  • Use 100% Oxygen.
  • Keep the patient warm.
  • Recompression in a hyperbaric chamber may be required after landing.
  • Do not rub affected parts.

Decompression Sickness can occur as low as 6000 ft after diving. Modem passenger jets are pressurised to altitudes between 6,000 to 8,000 feet.

A recompression chamber is a hyperbaric treatment chamber used to treat divers suffering from certain diving disorders such as decompression sickness.

They are used either as compression or decompression chambers for divers or for medical treatment, to speed up the healing of wounds, amongst other things. They come in a variety of interesting forms, from hyperbaric lifeboats to miniature portable fold-up or telescopic versions for helicopter rescue of divers.