Dawn Johnson of San Antonio is a veteran insurance and financial services executive. A former member of the executive council of USAA, Dawn Johnson spends some of her free time scuba diving.
Scuba tanks are what hold divers’ air reserves while underwater, allowing them to swim with fish for extended periods of time. They are made from a variety of materials, including aluminum and steel. An average scuba tank holds a standard 80 cubic feet of air, compressed to 3,000 pounds per square inch. It can last a diver anywhere from 45 to 60 minutes at an average depth of 40 feet.
Contrary to popular belief, the tanks are not filled with pure oxygen. Rather, they contain a mixture of oxygen, nitrogen, argon, carbon dioxide, helium, and neon, which are prevalent in the Earth’s atmosphere. Nitrogen is the majority at 78 percent, oxygen comes in second at 21 percent, and the remainder is a mixture of other gases.
There are tanks with hybrid mixtures used by professional divers who intend on staying longer underwater or to compensate for the high pressure at depth. A good example is a nitrox cylinder, which has a higher concentration of oxygen, up to 40 percent, allowing more oxygen into the bloodstream.