Diving disorders

Divers face specific physical and health risks due to venturing underwater and using high pressure breathing gases.

These risks are caused by :

Being unable to breath fresh air naturally whilst submerged and relying on limited breathing gas supplies and fallable breathing equipment:
- Drowning : being unable to inhale anything but water
- Secondary drowning : can occur hours after a near drowning
- Hypoxia : inhaling a breathing gas that contains insufficient oxygen to support normal activities or consciousness
- Anoxia : inhaling a breathing gas that contains no oxygen or being unable to inhale and breathing gas
- Salt water aspiration syndrome : the diver inhales a mist of sea water from a fault demand valve causing a reaction in the lungs
Barotrauma or pressure damage on descent:
- Tympanum damage (damage to the eardrum caused by failing to equalize pressure in the inner ear).
- Damage to the body's other air spaces, such as the paranasal sinuses
- Squeeze damage to tissues adjacent to equipment air spaces, such as the eyes inside the air space of the mask
Barotrauma or pressure damage on ascent:
- Pulmonary barotrauma - commonly known as "burst lung" by divers:
  - Pneumothorax - collapsed lung
  - Interstitial emphysema - gas trapped in the chest after lung barotrauma
  - Gas embolism - air or other gas bubbles in the blood stream
- Subcutaneous emphysema - gas under the skin tissue
- Damage to other air spaces, such as the facial sinuses or ears
Breathing gas at high pressure:
- Decompression sickness is caused by ascending too quickly to be able to eliminate excess nitrogen that had been adsorbed at depth
- Nitrogen narcosis is caused by using breathing gases that contain nitrogen at depth
- Oxygen toxicity is caused by using breathing gases that contain oxygen at depth
- HPNS, High Pressure Nervous Syndrome or Helium Tremors caused by using breathing gases that contain helium at depth
Impurities and poisons that may be present in breathing gas:
- Carbon monoxide poisoning is due to compressor maintenance errors or input of impure air to the compressor
- Carbon dioxide poisoning is due to incomplete elimination of carbon dioxide produced by the diver's own metabolism. This gas is normally safely exhaled to the environment and not re-inhaled in significant volumes.

Risk factors

Major deadly risk factors include:

Running out of breathing gas underwater, for reasons such as poor dive discipline, equipment failure or secondary factors such as getting trapped by nets, rocks or inside caves or inside wrecks
Losing control of buoyancy results is excessive vertical speed during descent and ascent causing barotrauma to air spaces within the body
Breath holding on ascent can cause barotrauma to the diver's lungs
Missing decompression stops or ascending faster than inert gases can be eliminated from the tissues can cause decompression sickness
Breathing poisnonous gases or contaminants present in a diving cylinder
Long exposure to cold water may cause hypothermia