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+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).
+: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.
+ 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.
+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 [*]_.
+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/
+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