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