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About the photo (above):
Cindy LaRosa on the surface before diving the wooden tug Alice G in Little Tug Harbor, Tobermory, Ontario. This wreck lies in 15'-25' (5-8 m) of water in the Georgian Bay of Lake Huron. This was a Lake Erie Wreck Divers (LEWD) trip on September 14, 2002. Photo by Greg Ondus.

The vast majority of scuba diving involves what is termed "recreational diving." This is the most basic form of diving, and all divers are introduced and trained to this level. It involves a single tank of air (not oxygen as many erroneously state). One regulator is attached to the tank's valve. Two hoses are attached to this regulator. One leads to the diver's mouth for breathing, and the other is stowed for emergencies involving sharing air with another diver.

Most new divers are limited to depths of about 40-60 feet (12-18 m) for safety reasons. More advanced and experienced divers may regularly go to depths up to 100-130 feet (30-40 m), but this is considered the practical limit of recreational scuba diving. This is due to several factors.

• First, the amount of available dive time on the bottom begins to decrease to just a few minutes beyond these depths. Staying longer would risk “the bends,” or decompression sickness. Bends are caused by nitrogen building up in the body's tissues due to the higher pressure of depth. The deeper a diver goes, the faster this critical amount of nitrogen builds up. The diver cannot then go straight to the surface but must instead go up in small timed steps before finally reaching the surface. This is called decompression, and it is considered an unsafe practice since any problem underwater does not allow immediately going to the surface.

 

• Second, the amount of air held in the typical scuba tank starts to become too little beyond these depths. The regulator automatically compensates for the increased pressure of depth, and every 33 feet (10 m) of water increases the ambient pressure by one atmosphere. This means that at 33 feet, every breath is like taking two breaths on the surface. At 66 feet (20 m), it is like taking three breaths on the surface. By the time 130 feet (40 m) is reached, every breath is equivalent to taking five breaths on the surface. Obviously, this greatly increases the amount of air used, making the overall air supply available in the tank insufficient.

 

• Third, beyond 100 feet (30 m) the nitrogen in the air starts to become narcotic. Jacques Cousteau called this “the rapture of the deep.” Nitrogen under pressure starts to cause the brain to become impaired and the diver to feel as if he/she were intoxicated. This greatly affects the ability of the diver to safely monitor the amount of air or bottom time remaining and to resolve unexpected difficulties like equipment failure or entanglements. Ultimately, divers at extreme depth under the influence of nitrogen narcosis have been known to just sit on the bottom unable to move or respond to any stimulus until they run out of air and drown. Narcosis can be made worse by cold, decreased visibility, and decreased light, all of which are found at greater depths.

Despite all of these dangers, the modern sport of diving is incredibly safe. The estimated rate of bends is roughly one in 5,000 dives — far more than most divers ever see in their lifetime of diving. Fatalities are very rare and are most common in very new (inexperienced) or very experienced (careless and/or overconfident) divers.

There are many wonders to behold at recreational depths, especially in terms of fish life, coral, and other beautiful sights, and many divers never find the need to explore beyond these limits.