A Few Things Your Sport Diving Instructor May Not Have Told You About Deeper Diving
by Larry "Harris" Taylor, Ph.D.
There is an incredible fascination with diving on intact shipwrecks. In the quest for this thrill of diving unmolested wrecks, some divers in the Great Lakes are diving on compressed air in the vicinity of 200 ffw or deeper. A few of these "sport divers" have taken years to develop skills, technique and equipment that allow them to survive these penetrations into that deep, dark, cold and silent world that lies beneath the sport diving limit of 100 - 130 Feet. A few are truly highly skilled diving adventurers. Some would call them pioneers. Others would call them something less dignified. It is true that some walk with a noticeable limp, stand a little funny (numbness in the legs), have difficulty remembering things or seem to have somehow slowed their thinking and speech processes. None-the-less, many of these diving adventurers have seen splendors that not many will ever know. Other diving "adventurers" have found unique pains and death.
Divers new to our sport often do not realize that the successful deep diver has generally taken a decade or more to develop the necessary skills, equipment and technique to survive consistently this deeper diving. Make no mistake; some of these divers are highly skilled and physically fit. That exceptional proficiency, however, was not acquired in only a few days or even years. Although most are self-taught, many of these deep divers were trained when diving courses were longer and discussions on diving physics and physiology was more extensive. Thus, they have had access to information often missing in today's shorter curriculum ... material that is essential to make informed risk/benefit assessments. There are distinct physiological problems associated with deep diving. Since divers do not breathe water, the physiological impairments caused by deep diving can be (and have been) life threatening. Sport "deep diving" courses are simply insufficient training for diving to depths "below the limits." Divers compelled to dive below 100 feet should consider commercial or military dive training - depths below 100 feet are beyond the realm of sport diving...Sport diving equipment and techniques no longer are adequate! In addition, the training agencies will not, for a variety of reasons, address the question of training, at this time, for diving below 100-130 feet.
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DECOMPRESSION SICKNESS: The risk of permanent tissue injury increases with depth. Many sport divers have been given the impression that "the bends" is a benign disease. That simply is not true. The bends can kill, but most often it cripples. The DAN numbers show more than 500 divers a year now require chamber treatment. After 3 months post treatment, 13% of those treated still show some residual impairment. Severe sport diver bends hits most often show spinal cord involvement. This means that anything "South" of the lesion will be impaired. The spinal cord mediated functions most often tainted are walking, urinating, defecating, and sexual response. So, if you like to walk without a cane or wheelchair, go to the bathroom unassisted or to have sex, it is worth your while to develop some understanding of decompression sickness and its prevention. (A recent national survey reported in Skin Diver magazine noted that approximately 60% of those in the sport diving community surveyed could not recognize the symptoms of the bends and almost every survey of divers done recently suggests that more than 50% of sport divers cannot plan dives using decompression tables.)
A real danger of decompression sickness is that it is often a progressive disease; it may continue to get worse until treated. In North America the time from onset of recognizable symptoms to chamber treatment is often more than 12 hours. It is this delay that can be so devastating. It is believed that the longer the delay between onset of severe symptoms and treatment, the less the chance for total recovery. During the delay the bubbles formed continue to impair or destroy body functions. The key to successful recovery from the bends is immediate recognition of symptoms and the prompt administration of the highest possible concentration of O2 (preferably by demand mask). Medical consultation/treatment should always be sought. Not recognizing or ignoring the symptoms may allow the disease to do more damage. Although there are anecdotal stories of acute relief of decompression sickness symptoms without medical treatment, there is a lingering question of the potential for long-term damage even though immediate clinical signs were absent or simply went away.
The problems linked to decompression sickness can primarily be called "bubble trouble." Whenever bubbles form, they obstruct normal body function. This may prevent normal exchange of nutrients and oxygen and allows waste products to accumulate. This can, over time, create destruction of body cells. Medical evidence is beginning to accumulate that suggests there may be gradual deterioration of nervous system tissue upon repeated exposure to deep diving. It is believed that this damage can occur without ever showing gross clinical signs (i.e. joint pain, etc.) classically associated with decompression sickness hits. Although still far from complete, early studies seem to imply that there is a marked deterioration in short-term memory and reasoning skills in commercial divers aged 24-39. Autopsy studies of three deep divers who died of non-diving related causes indicated that there was a marked degradation of spinal cord tissue. It is believed that the spinal cord lesions were created from diving. Although controversial, there is some evidence that deep diving can block retinal blood flow and create vision problems due to a damaged retina. Additional studies measuring blood chemistry and urine of divers imply that the liver, as well, may be damaged in divers diving as shallow as 30 meters (98 feet).
The body is a remarkable biochemical machine with much redundancy. It can sustain some tissue damage that can be compensated for by this redundancy. However, repeated exposure to tissue-damaging conditions will ultimately result in loss of function.
Bottom line: The DAN numbers suggest that diving below 80 fsw is a significant risk factor for sport divers (more than 70% of DAN treatments involved sport dives to depths below 80 fsw). The deeper and more often this deep diving occurs, the more the risk for long-term neurological damage. It is not possible to predict the type and severity of this physiological impairment.
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There are other problems that could result from the practice of breathing pure O2 at depth (during decompression stops?). There are some medical authorities who consider 100% O2 at elevated pressures a cellular toxin. Breathing pure O2 at elevated pressures for extended times can induce abnormalities in the red blood cells that carry O2 to the body. High O2 concentrations can constrict blood vessels in the eye and lead to visual problems. In addition, high O2 can create a mild hearing loss that may appear hours after the dive and take a day or so to disappear. High p O2 has also been proposed as contributing to dysbaric osteonecrosis ("bone death"- usually seen in deep diving commercial divers; this malady may eventually require surgery to replace bone joints with artificial devices.)
Bottom line: The potential for grand mal seizure and subsequent death caused by oxygen toxicity makes diving below 180 fsw in sport diving equipment on compressed air an extremely high risk activity. Below 200 fsw many diving authorities believe that oxygen toxicity poses a greater risk to the diver on compressed air than nitrogen narcosis.
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