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When Air Becomes Poisoness
The air that we breathe at sea level contains 21% oxygen at a pressure of 0.21 bar. The human body needs this oxygen to perform vital chemical reactions to produce energy and thereby sustain life. In the consumption of this oxygen, highly poisonous oxygen radicals are produced that are contained and disposed of by normal body processes and are therefore essentially harmless. The challenge lies when as divers we breathe this same air under increased ambient pressure underwater. The deeper we go underwater, the greater this partial pressure or concentration of oxygen becomes which places an increased burden on the 'waste disposal' capabilities of the body. If this ability is exceeded, the oxygen radicals act like pool acid to destroy normal body tissues and disturb vital chemical reactions. This phenomenon is called Oxygen Toxicity or OxTox.
What kind of problems can oxygen toxicity cause?
The lungs and the brain are the two target organs of major concern when it comes to oxygen toxicity. Toxicity of the lungs has been compared to developing a bad case of the flu and the damage is seldom permanent in sport diving cases. This type of toxicity can be very serious however in saturation divers in the oil fields of the North Sea or during extensive treatment for decompression sickness in a hyperbaric chamber.
Toxicity of the brain (CNS toxicity) is the big daddy of oxygen toxicity. This can actually occur while diving and result in Grand Mal seizures or convulsions underwater. The seizure in itself is not life threatening nor does it cause permanent damage, but loss of a regulator mouthpiece and drowning certainly is. The most common symptoms are flashing lights in front of the eyes, ringing in the ears, tunnel vision, twitching of the lips, confusion and vertigo. The good news is that convulsions are rare, the bad news is that there may not always be the warning of the symptoms mentioned above.
Oxygen Toxicity is a concentration-duration phenomenon: that is, a diver would need to be exposed to high concentrations of oxygen for specific periods of time to be adversely affected. To put all of this information into perspective, a diver using normal air need mainly be aware of decompression sickness as oxygen toxicity may only occur at approximately 66 metres after 45 minutes! (This time can be reduced by previous exposure, exercise, cold, drugs etc.) Nitrox divers may have longer dive times or possibly safer dive profiles than their air diving counterparts, however, they need to be well trained to avoid oxygen toxicity by not diving too deep on their oxygen enriched air. i.e. A diver using a 40% nitrox mix should not go deeper than 25 metres (PADI standards).
The fascinating topic of oxygen toxicity has many intriguing twists and turns and makes for excellent reading while doing a NITROX course which is without doubt, the best avenue to become a more informed and safer diver.
- Article By - Dr Bradley Wagemaker
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