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       I realize the title of this page, ďThings That ChangeĒ is very broad and probably grossly inaccurate. Obviously, Iím not about to attempt to embark on a discussion about everything that changes.  On this page, I will discuss a few key things that change when you enter the underwater environment.  Those few key things are vision, sound, exposure, and pressure.

         Vision. The first thing youíll notice about vision if you stick your head underwater and look around is that it is severely degraded. Your eyes arenít designed to work underwater.  Theyíre designed to work in air.  Scuba divers wear a mask to create an air pocket so that their eyes can function properly.  Unfortunately, this doesnít work perfectly. When light passes from the water into the air pocket of the mask, it bends and alters the image. Things underwater look 33% larger and 25% closer. Is that really a problem?  No. Not really, but that shark you saw that was THIS big, well . . . .
         A second issue involving vision underwater is color.  Water absorbs light, starting with the longer, lower energy wave lengths.  As you go deeper, you lose the color. The acronym ROY G BIV (Red Orange Yellow Green Blue Indigo Violet) describes the order in which you lose the colors. Take a flashlight with you even in the daytime to restore the absorbed wavelengths and bring back the color.
         Sound. One of the most obvious effects being underwater has on sound is that you canít talk.  Depending on who youíre diving with, this may or may not be a disadvantage. However, some communication is necessary.  Unless you have some kind of underwater communications system, you will rely on hand signals to get the message across.
         Sound moves faster through water than it does through air.  In fact, it moves 4X faster.  Everything sounds much closer and the sound is omnidirectional.  Normally, you can tell what direction a sound came from because the sound waves hit one ear a fraction of a second before the other and your brain converts that difference into a direction. Underwater, the 4X faster sound waves hit both ears simultaneously.  You canít tell what direction it came from.
         Exposure.   When I talk about exposure here, it is important to point out that Iím not talking about anything that might get you thrown in jail. Iím talking primarily about temperature and aquatic wounds and stings. Temperature first. Water absorbs heat from your body 25X faster than air. This means that even warm water will start to feel cold, especially if youíre doing multiple repetitive dives day after day.  Itís important to stay warm and keep your core temperature up. To do this, youíll need some kind of thermal protection. This protection can come in the form of wetsuits or drysuits and if necessary, hoods and gloves.
         There are creatures underwater, such as jellyfish and fire coral, that can sting. These stings are protein based.  All you need to protect yourself from these protein based stings is something to keep the proteins from contacting your skin. A wetsuit, drysuit, or diveskin will do the trick. A diveskin, which is a Lycra suit, is adequate protection from protein based stings, but it offers no thermal protection.  What about protection from things with teeth like barracuda and sharks?  Well, you could wear a chain mail suit, but your best protection is simply to not harass things with teeth.
         Pressure. As you go deeper, you subject your body to more and more pressure. For every 33 feet of sea water or 34 feet of freshwater, you apply an additional atmosphere of pressure (14.7 psi) to your body.  This pressure squeezes and compresses all flexible air spaces (Boyleís Law).  Some of those air spaces include the inner ear, lungs, scuba mask, BCD, and wetsuit or drysuit. If not compensated for, the squeezing of these air spaces can cause pain or increasingly negative buoyancy as you go deeper. The important things to know about scuba and pressure fall under Gas Laws (primarily Boyleís Law) and Diving Maladies.  For this section, Iíll keep it simple and say that the compression of these air spaces must be equalized or compensated for. The ears can be cleared by holding your nose and gently blowing, moving your jaw, or swallowing.  Failing to equalize the ears can result in pain and possibly damage to the ear drum.  Clear the mask by exhaling through your nose. If you donít equalize the mask, you get a nasty bruise where the mask skirt contacts your face.  This is actually less painful than it is embarrassing.  Compression of the BCD and wetsuit/drysuit causes a loss of buoyancy. To compensate, add air to the BCD.