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============
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