Scuba divers carry a supply of compressed air in tanks on their backs. Refillable, pressurized tanks have come a long way since their 19th century beginnings, allowing divers to make longer and deeper dives. Scuba certification courses train divers to use tanks safely.
History
Auguste Denayrousse and Benoit Rouquayrol developed the first compressed air tank in 1865, according to MarineBio.org. Because this early tank could carry air only at the low pressures of 250 to 350 psi, it relied on a surface-supplied source of air. Yves Le Prieur invented a higher-pressure tank in 1933. His tank could hold air at 1,500 psi, allowing divers to carry a larger supply. In 1942, Jacques-Yves Cousteau and Emile Gagnan made a leap toward modern scuba tanks with the invention of a self-contained tank and regulator known as the Aqua Lung. In the 21st century, scuba divers fill tanks with air at pressures up to 3,500 psi, allowing for much longer dives.
Tank Parts
Scuba tanks have two basic parts, including a steel or aluminum canister and a control valve fitted over the top. A knob on the tank's valve controls a piston inside the valve. By turning the knob, you can move the piston into the open position to allow air to flow out of the tank, or into the closed position to prevent air from flowing out of the tank. Scuba divers breathe the air in a tank through a regulator. Most regulators have four hoses, including one connected to the buoyancy compensator device, one connected to a pressure gauge for monitoring the tank's air, one connected to a primary mouthpiece and one connected to a secondary mouthpiece. The regulator's first stage connects to the tank's valve and forms an airtight seal with the valve's O-ring. Once attached to the tank, the regulator will supply air to the diver only when she inhales through the mouthpiece.
Breathing Gases
Divers breathe a variety of gas mixtures. Recreational open water divers typically breathe compressed air, which contains the same mixture of 21 percent oxygen, 78 percent nitrogen and trace inert gases that we breathe in daily life. Divers with specialized training breathe other mixtures, including nitrox, trimix, heliair and heliox. Nitrox, also known as enriched air, contains less nitrogen and more oxygen than normal air, allowing divers to make longer and deeper dives with less unsafe buildup of nitrogen in the body's tissues. This mix's higher quantity of oxygen puts divers at increased risk of oxygen toxicity, however. Trimix contains some helium, a gas that does not become toxic at depths.
Labels
A tank's labels provide important information about its contents and recent inspections. Tanks filled with any type of gas other than basic compressed air must have labels that clearly indicate the tank's contents. Tanks filled with nitrox must have a large green and yellow sticker that reads, "Enriched Air Nitrox." Tanks filled with trimix must have a label indicating what percentage of oxygen and what percentage of helium the tank's mixture contains. All tanks must have a label indicating the most recent visual inspection and the most recent hydrostatic test. Tanks must undergo visual inspection once a year and hydrostatic testing once every five years.
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