ABSTRACT
Air is a mixture of gases, mainly oxygen (21%) and nitrogen (78%). The other 1% of air is made up of several other gases, such as carbon dioxide (CO2), argon, krypton, and neon. In any mixture of gases, the individual gases do not chemically combine with each other. Air underwater obeys the same laws as air in the atmosphere. Hyperventilation causes some central nervous system changes as well. Practiced to excess, it causes decreased cerebral blood flow, dizziness, and muscle cramping in the arms and legs. Pressure changes in the free diver’s descent/ascent cycle conspire to rob the diver of oxygen as he or she nears the surface by the mechanism of partial pressures. Most recreational divers have been certified to dive to a depth around 138 feet. The reason that 138 feet is the limit without further training is that the increase in the partial pressure of nitrogen can cause an intoxication similar to that experienced with alcohol.
