fraction of carbon dioxide in the atmosphere from burning fossil fuels and other sources. The concentration of water vapor in the air (humidity) also varies widely around the earth. The major components of air are often simplified as 4/5 (80%) nitrogen and 1/5 (20%) oxygen. Other special gas mixtures are sometimes used in diving, especially in technical diving and commercial diving. Nitrox, also called enriched air nitrox (EAN) or oxygen enriched air (OEA), is a blend of oxygen with air. Adding oxygen to air has the advantage of reducing the percentage of nitrogen in the breathing gas, but there are certain trade-offs because of the increased oxygen level. Nitrox is increasingly popular in recreational diving for those with special training in its use and limitations. The benefits and limitations of nitrox are addressed in more detail in other chapters. Nitrogen Nitrogen (N2) is the most plentiful component of air. It is a colorless, odorless, and tasteless gas. Although nitrogen is present in the constituent compounds of all organisms, only a few organisms are able to assimilate nitrogen. For us nitrogen is a metabolically inert gas. We cannot use it physiologically. Instead we must rely on the food we eat to obtain needed nitrogen compounds. In respiration, nitrogen is essentially a diluent for the oxygen in the air. Although it is metabolically inert, breathing nitrogen at increased pressures has potential problems for divers. These problems include nitrogen narcosis and decompression sickness, which are discussed in detail in the physiology and decompression chapters of this book. Oxygen Oxygen (O2) is also a colorless, odorless, and tasteless gas. It is our life-support gas, the gas we extract from air in respiration and use in metabolism to generate heat and energy. Although gaseous oxygen is only 21% of the atmosphere, oxygen is one of the most abundant elements on earth. About 90% of water by weight is oxygen, and almost 50% of the earth’s crust is oxygen occurring in various compounds. Oxygen itself does not burn, but it supports combustion. The ease and rapidity with which it reacts with other materials make it hazardous to handle, and special precautions must be taken when handling oxygen or gas mixtures that are high in oxygen concentration. For instance, petroleum lubricants will flash in the presence of pure oxygen. Nitrox handling facilities and divers whose equipment will be exposed to gas mixtures that are higher than 40% oxygen must be careful to use oxygen clean equipment with oxygen compatible components. Although it does not impact the compressed air diver who remains within the generally accepted recreational depth limit of 40 meters (130 feet), breathing high partial pressures of oxygen can lead to oxygen toxicity, including convulsions and loss of consciousness. Preventing oxygen toxicity is a concern that is specifically addressed in nitrox courses and technical diver training courses. Carbon Dioxide Carbon dioxide (CO2) is colorless and, in low concentrations, odorless and tasteless. It reacts readily with water to form carbonic acid, which gives it a distinctly sharp, acidic smell and taste in higher concentrations. It does not support combustion, and for that reason it is widely used in fire extinguishers. Carbon dioxide is the by-product of our respiration. It is produced in metabolism when our body combines the oxygen we have breathed in with carbon to produce energy. We eliminate the carbon dioxide in our exhaled breath. The level of carbon dioxide in our body controls the stimulus to breathe. As with oxygen, too high a level of carbon dioxide in the body can be toxic. Atmospheric carbon dioxide is used by chlorophyll-containing plants to produce their food through the process of photosynthesis. Carbon Monoxide Carbon monoxide (CO) is also a colorless, odorless, and tasteless gas. It is highly poisonous, combining with the hemoglobin in our red blood cells in preference NAUI Master Scuba Diver 70 Diving Physics
20047TC
To see the actual publication please follow the link above