Most divers are worried about the hazardous effects of nitrogen, but for technical divers who go into the deeper reaches of the ocean, oxygen toxicity is more dangerous. Oddly enough, when the body is put into a higher-pressure environment, the very gas necessary to support life can become a dangerous, poisonous substance. To combat its effects, divers use a special gas mixture for deep diving.
While oxygen is the gas humans need to draw from the air for their metabolisms to function, absorbing too much of it into body tissues can be hazardous. This is called "oxygen toxicity, and is a particular threat to technical divers, or divers who go beyond the recreational limit of 138 feet. When your body is subjected to high pressures under water and is breathing compressed gas, it absorbs more of those gases. This greater absorption of nitrogen from the air can cause the condition known as "the bends," or decompression sickness, as well as an intoxicating effect called nitrogen narcosis. This is a hazard even for recreational divers who plumb relatively normal depths. Oxygen toxicity starts to become an issue at depths below 187 feet, but when it becomes a problem it is a very serious one indeed.
Central Nervous System Toxicity
The most common form of oxygen toxicity is CNS, or central nervous system toxicity. What happens is that elevated oxygen levels interfere with the functioning of the body's nervous symptoms. Symptoms include tunnel vision (which can be dangerously confused with nitrogen narcosis), nausea, ringing in the ears, twitching and other motor problems, and dizziness. A serious attack of CNS can cause seizures or loss of consciousness. The hazards posed by oxygen toxicity are obvious, since a bad attack can lead directly to drowning. However, even the symptoms are problematic, because anything that impacts judgment or motor skills on a technical dive greatly increases the risk of a potentially fatal accident.
Oxygen toxicity is addressed by reducing the amount of oxygen carried in the diver's air cylinder, thereby reducing the amount of oxygen absorbed while under high pressure. The problem is that regular air is made up mostly of nitrogen, and increasing the proportion of nitrogen in a diver's air greatly enhances potential problems with nitrogen narcosis and decompression sickness. Instead, a gas mixture called trimix is used. Trimix is made up mostly of helium. Helium is inert and does not react with anything in the body, and its low density has the added bonus of being easy to breathe under high pressure. Trimixtures of gas are adjusted to match the maximum depth of a proposed dive. An example is trimix 10-70, which is 10 percent oxygen, 70 percent helium and 20 percent nitrogen.
Article Written By Edwin Thomas
Edwin Thomas has been writing since 1997. His work has appeared in various online publications, including The Black Table, Proboxing-Fans and others. A travel blogger, editor and writer, Thomas has traveled from Argentina to Vietnam in pursuit of stories. He holds a Master of Arts in international affairs from American University.