Deep Diving By Linda Gettmann

Earthlings are adapted to living in an air environment with an ambient air pressure of about one atmosphere. When we dive into the depths, we are forcing our bodies and senses to adjust to a totally new set of environmental factors, some with detrimental consequences.
Experienced divers learn to compensate for these changes which are magnified by each 33 feet in depth (= one atmosphere) from the surface. A mask restricts divers' vision, as does murky water, and objects appear larger and closer than they actually are due to the water column magnification. Hearing and balance are affected by pressure changes to the ears and the sound of your own breathing through the regulator. Lack of smell and taste result in further sensory depravation. A diver's unfamiliarity with the underwater environment may cause psychological changes, especially at greater depths.

Risks in sport diving beyond 100-130 feet include the increased susceptibility for DCS, nitrogen narcosis, stress reactions including anxiety and panic, vertigo, negative buoyancy, breathing resistance through the regulator, increased air consumption, hypothermia, and high carbon dioxide and nitrogen levels. In addition, the deeper dives increase risk for a rapid ascent and resulting air embolism injuries.

How can you avoid or minimize these risks? Short of not diving, there are prudent actions every diver should take including:
1. Choose conservative no-decompression limits.
2. Reduce bottom time to compensate for risk factors and increase surface interval time.
3. Ascend slowly, 30 feet per minute.
4. Avoid multiple ascents, bounce profiles.
5. Do a 3-5 minute safety stop at 15 feet at the end of every dive.
6. Avoid dives deeper than 100 feet.
7. Avoid excessively long dives at depth.
8. Take a day off during multi-day repetitive diving.
9. Ensure gauges and computers are working properly.
10.Dive to the deepest depth early in the dive and gradually work shallower during the dive.

Nitrogen narcosis may affect divers at relatively shallow depths, however its manifestations at depth have been compared to the effects of alcohol, drugs, and the early stages of general anesthesia. Brain functions such as memory, concentration, reasoning, and judgment are the first affected by narcosis. A sense of euphoria or anxiety may be experienced, leading to errors in judgment. At depths beyond 165 feet, serious impairment, hallucinations, and unconsciousness may occur. Susceptibility to narcosis varies among individuals and from dive to dive and many divers do not realize they are affected ("narc'd").

Safe diving beyond 100 feet requires considerable diving experience and an awareness of the ever-increasing risk of narcosis and its affect on a diver's judgment and performance. It also requires a diver to be in good physical condition as well as mentally stable and alert. Deeper diving requires a far greater level of knowledge, skill, equipment, and preparation than is required for shallower dives. Only divers who possess the required attributes should attempt such dives. Dive deep safely and be prepared:
* Thoroughly plan and prepare for the dive.
* Ensure that the boat is suitable for the conditions and is adequately equipped and staffed.
* Only dive in conditions that are safe. Avoid diving deep in currents and poor visibility.
* Ensure that all divers have enough experience, are confident, and fit to dive.
* Enforce the buddy system.
* Plan on doing an extra safety stop and avoid doing dives involving mandatory decompression stops.

There is no substitute for knowledge and planning. Dive only to your personal comfort and training limits and resist going deeper just because some or most of the group think that is the way to enjoy a dive. Most of the colorful coral growth and fish life is found above 60 feet, so that's where most of us spend most of our dive time. In those instances where a shipwreck or other reason to dive below 100 feet exists, make sure you and the divemaster have a clear plan and have the capabilities to handle a potential emergency situation at depth. Your life may depend on it.