Nitrogen narcosis: Most divers have experienced this phenomenon to some degree. The effects of nitrogen at elevated partial pressures much above 4.0 ATA, the equivalent of 130 fsw, can produce varying symptoms from mild “fuzziness” to near incapacitation and collapse. Forget about nonsense like “Martini’s Law”; narcosis is entirely subjective and will induce different reactions in each individual. Compressed air is a viable breathing media for most experienced divers, if trained properly, down to around 200 fsw. But it is vital that initial forays beyond traditional sport depths be under the supervision of a professional technical instructor who is capable of recognizing your impairment and helping you understand those limitations.
Continued exposure to a regular regime of deep diving has a certain adaptive effect whereby narcosis is lessened in many individuals. However, a small segment of the diving population will hit a finite physiological wall at some depth and they should never venture deeper. Elevated partial pressures of carbon dioxide (CO2) will increase the onset and severity of impairment. Narcosis is a factor on every deep dive. Develop a thorough understanding of this effect and plan accordingly.
Oxygen toxicity: Probably more misconceptions have been centered around central nervous system (CNS) toxicity (known as the “Paul Bert effect”) than any other diving hazard. Realistically the threat of a CNS hit is very low on compressed air dives above 200 fsw. This depth produces approximately 1.5 ATA of O2 with an allowable exposure of two hours on a single dive. This is, of course, less than the recommended maximum of 1.6 ATA of O2 for working divers and provides a huge cushion of time since it would be difficult for a diver to physically carry enough breathing supply in open circuit scuba to reach the two hour limit.
Most errors in dive planning occur when the diver fails to account for the total “dose” of oxygen. This means counting the bottom depth exposure and the decompression time for a total. A diver breathing pure oxygen at 20 feet during his decompression is at 1.6 ATA of O2. In some dive profiles a higher oxygen dose is received during decompression than during the bottom depth phase of the dive. Like narcosis, elevated CO2 is a triggering mechanism. Other common mistakes include rigorous tracking of “whole body” or pulmonary oxygen toxicity (known as the “Lorraine Smith effect”). This is unnecessary since dives planned within CNS limits will never approach a threshold of vulnerability for pulmonary problems.
All deep divers should familiarize themselves with allowable exposure times and never run times to the limit. Risks from exceeding limits or for idiosyncratic reactions to lower exposures include convulsions that could drown the diver. Be sure to balance both the working dive at depth with the decompression if oxygen or nitrox is used.
Decompression sickness: Arguably there is no hard data to suggest that deeper diving presents any higher statistical incidence of DCS than longer, shallow dives. In fact, most DCS hits occur between 60-90 foot depth exposures. However, deeper diving usually involves planned decompression and most divers have not been adequately trained in technique and procedures in mainstream sport classes. The added discipline of ascent rates and maintaining precise depths during stops is an acquired skill for most people. And with the addition of strong currents and the burden of handling heavier equipment rigs, it is advisable to seek every hedge against risk.
Plan for extra reserves in decompression gas supplies and employ pure oxygen or 80/20 nitrox for its increased efficiency in outgassing absorbed nitrogen. Adopt diving habits that limit hard work and swimming. And learn to recognize DCS signs and symptoms in both yourself and your dive team. Carry emergency oxygen deliverable by demand mask or regulator on the boat and don’t hesitate to use it.
There’s no big mystery about DCS and sooner or later you or someone you dive with may experience “the bends”. You can do everything within decompression model limits and even with an extra dose of conservatism still fall victim. That’s the breaks, there’s no shame in it. What’s bloody stupid is not reporting symptoms or seeking treatment. If you approach deeper diving with the proper respect and due diligence for the decompression, you are probably at no more risk than any diver.
Stress: The unexpected circumstance in an unfamiliar environment can rattle anybody. Add a component of depth where narcosis or breathing resistance can be a factor and stress levels can skyrocket. In deeper diving, we are usually task-loaded to a higher degree than the guy doodling around on a shallow reef. Keeping track of time, depth and remaining air supply while managing a set of doubles and an extra deco cylinder doesn’t allow a whole lot of attention to be paid to other outside stimuli like the ball of monofiliment line that snags you or an unstoppable second stage free-flow at 175 feet.
Keep cool, stay in control and follow contingency protocols taught in training. Most accidents in deep diving can ultimately be traced back to panic induced by stress. If you have known heebie-jeebies such as claustrophobia, don’t decide to take up penetration wreck diving at 160 feet. Better than anyone, you can assess potential problem areas in your individual psyche. Then have the common sense to avoid those situations.
Another common stress disorder is invoked by simply overloading yourself with more gear than you can comfortably handle and swim with. I’ve seen divers ready to collapse from the weight of their equipment package before they’ve even gotten in the water. Common sense goes a long way. And it’s cheap. Use plenty of it.
Marine life and Mother Nature: In other situations if you encounter some nasty creature you can simply decide to make a dignified exit. But if you’re staring down the face of an aggressive shark with another 45 minutes of decompression obligation… well, your options get a bit more limited. That’s what buddies are for: so sharks can eat them first.
Seriously, almost any marine life threat can be dealt with by a dive team if they keep cool. Sharks are notoriously over-rated in their actual menace to divers and even the most curious can be discouraged with a solid reaction such as poke in the nose. More insidious are dangers from stinging organisms such as sea wasps or Portuguese Man-of-War. These are most likely to be found in the shallow decompression depths where many divers tend to be inattentive during long boring hangs. Pay attention, have at least one team member actively watching the area to alert the team to hazards.
And never forget that Mother Nature has a bit of whimsy that seems to delight in throwing in unexpected currents that blow divers off wrecks and cause them to miss their anchor lines. Or the violent thunderstorm that appears from a clear summer sky while you’re on the bottom and your support boat drifts away. Be prepared for contingencies with lift bags to do drifting decompression under, deployable safety sausages on lines that you can run up to the surface while drifting underneath, flares or flashers for night signaling, and self-contained decompression gases. And always have a low pressure sonic Dive-Alert ready to blast when you surface.
He who prepares and anticipates his adversary, whether narcosis or the great white shark, will handle the situation well. And likewise, he who hesitates… is lunch!
54 Stonetree Rd.
Arrowsic, ME 04530