============ SCUBA Diving ============ --------------------------------------------- Self Contained Underwater Breathing Apparatus --------------------------------------------- SCUBA stands for "Self-Contained Underwater Breathing Apparatus". One of the primary organization regulating recreational SCUBA diving is PADI (the Professional Association of Diving Instructors). Equipment --------- :BCD: The buoyancy control device is basically an inflatable live vest that you can inflate using the regulator (or by mouth) to control your buoyancy. Your buoyancy changes as you use up air (tank gets lighter for same volume displaced), inhale/exhale, swim in water of different temperature or salinity, or change depth: increased pressure compresses any flexible air pockets, including the BCD itself, neoprene foam, or a dry-suit. Most BCDs have their own pressure hoses coming from the first stage regulator that supply air. Sometimes there is only one vent valve, which has to be at the highest orientation or air will not vent out of the bladders. :Tank: Most tanks are made of steel or aluminum and can store compressed air of up to 3000psi. They are stored at pressure to prevent moisture from leaking in. There is a valve built into the tank itself that usually gets taken apart and repaired every two years. Tanks can last for decades even with heavy use; they are pressure tested for fatigue and leaks. :Regulator: The first-stage regulator is connected to the tank and steps the pressure down to about 250psi above the surrounding/ambient pressure. Hoses carry air at this mid-level pressure to the second stage regulator/mouthpiece, which steps the pressure down to about what is in your lungs. Depending on the regulator they can be stiff (you have to suck a bit to get air, but then it rushes in with force) or very natural feeling (air comes very smoothly on inhalation and doesn't press into your lungs). :Alternate: These days almost everybody carries a second regulator mouthpiece for emergencies. These are always on and ready to breath from, but usually stiffer so they don't free-flow as often. :Dive Computer: A dive computer monitors time and depth to give you an accurate picture of how much excess nitrogen is in a diver's bloodstream. By continuously integrating they usually "give more time at depth" than hand calculations using tables (which err towards safety). :Dry Suit: A dry suit is a sealed and air tight, keeping the diver's skin dry. Extra insulation is needed to give warmth underneath. Some dry suits are made of compressed neoprene. A dry suit has to be constantly adjusted with tank air just like the BCD to maintain inflation and buoyancy. :Wet Suit: Wet suits work on the principle of holding water against the skin: a diver's body warms this water and stays cozy as long as water flow is restricted enough. Even little bit too much flow through wrist or ankle openings can be very cold. Depths ------ A PADI Open Water Diving course gives a recommended limit of 20m/60ft. A "deep dive adventure course" gives a recommended limit of 30m/100ft, and additional experience gives a limit of 40m/130ft. With careful decompression stops and enriched compressed air (higher oxygen content) it's possible to reach depths of hundreds of meters. Sometimes commercial divers will dive for many hours using surface supplied air, then live at the surface in a compression chamber overnight between dives to stay at the same pressure [*]_. History ------- I'm pretty sure `Jacques Cousteau`_ invented the aqualung, which is the basis for modern diving, but I'll have to check. .. _Jacques Cousteau: /k/jacquescousteau/ Flying ------ After a regular no-decompression dive, wait at least 12 hours before flying (or going to high altitude, eg over 300m). .. [*] Need a citation, heard this word of mouth