Is anybody else convinced that narcosis starts shallower than most people think? I have been to almost 150' without a problem but I'm pretty sure that I don't think as clearly at 50' as I do at the surface. The only times I've felt really narced was from CO2 at less than 100'.
Nitrogen narcosis begins when you leave the surface. It doesn't become significantly debilitating until you reach a depth of 30m/100ft to 40m/130ft.
What confuses people are the signs and symptoms of narcosis. Often these signs and symptoms are incorrectly educated - being focused only on sensations associated with intoxication. These symptoms present in only a very small number of narcosis events, which leads many divers to believe that they aren't experiencing narcosis on their deeper dives.
In fact, nitrogen narcosis is a form of anesthesia, not intoxication. Many of those effects/symptoms are not noticeable to the individual diver. If accompanying divers are equally narc'd, those signs will not be apparent to them either.
The easiest way to appreciate the more insidious effects of narcosis would be to assume you lose IQ. Put simply, you get more stupid as ppN2 rises. As it gets more severe, you lose cognition, memory function and, eventually at extreme depth, you lose consciousness.
Losing IQ... losing intelligence... as depth increases is rarely identifiable by the individual or the (equally compromised) divers around them. You get stupid... you stop processing information... and you're entirely unaware of it.
CO2 narcosis presents slightly differently. Often it is, what divers call, 'Dark Nark'... feelings of anxiety or panic. CO2 narcosis, I believe, is what often presents after a fast descent because any CO2 retention occurring during water entry etc results in a ppCO2 'spike' on rapid pressurization. It hits you as soon as you get deep. I've seen it in action a few times.
Nitrogen narcosis takes longer to present. A
study has shown that mental debilitation from nitrogen narcosis occurs progressively over the bottom time.... it 'creeps' up. It is also suggest that it's effect can persist even after ascent.
In the (distant) past I completed some very extreme deep air dives - circa 260-300ft (80-90m). I didn't feel 'intoxicated' on any of those dives and all of the requirements for complex technical dives were achieved without drama. Nonetheless, it required immense mental focus and was reliant on all of the dive skills, procedures and habits being completely ingrained and instinctive. In short, the dives were performed unconsciously, not by intelligence and problem solving.
Interestingly, most of those dives involved considerable post-dive amnesia... it's hard to remember what happened at depth. A team of 8 experienced technical divers using air needed a week to identify and survey a wreck - a task that could be completed in day if using trimix.
Needless to say, those dives were successful as a result of completely ingrained diving competencies, in divers who had thousands of hours practice and practical experience at a high level. However, if anything unexpected had occurred that was beyond the scope of ingrained skill and procedural response, I remain absolutely convinced that achieving a safe resolution would be far from guaranteed. That is why I would never do very deep air dives any more.
To summarize, people who deny they are influenced by narcosis are either in denial, or simply ignorant of how narcosis actually effects them. They are searching for symptoms that only represent a 'tip of the iceberg' in respect to their actual mental impairment. Where those limited symptoms don't present, they incorrectly believe that narcosis is not present.
I learned a lot about narcosis from my history of deep air diving. I also learned a great deal when I switched to making trimix dives. In particular, through two incidents that allowed a direct comparison between compromised and uncompromised mental ability:
1. Diving trimix on a 36m/120ft wreck that I had previously dove for years on air or nitrox. I was shocked at how 'clearly' I could understand the wreck layout when clear-headed on trimix. Despite hundreds of dives on that wreck using air/nitrox, I really hadn't managed to 'put the pieces together' with any significant level of granularity. I had never felt narc'd diving the wreck - but a single dive on trimix demonstrated to me exactly how little information had been absorbed from my eyes to my brain.
2. Diving trimix with an experienced technical diver who was diving air. I dove a 55m/180ft wreck on trimix and was able to observe significant mental impairment in the air diver; a divers who is at a very elite level of technical diving and whom I respect immensely. I'd never noticed any impairment previously, when we had both dived air to those depths. However, once I was uncompromised by narcosis, it was very easy to recognize the severe impairment in my buddy's cognition and faculties.
I take narcosis very seriously nowadays. Yes, it's possible to compensate for narcosis by having
very ingrained dive skills and procedures. But there's no way to compensate for narcosis if unexpected or unforeseen events occur that require solutions beyond your ingrain competencies. The more narc'd you are, the less likely you are to resolve your situation safely.
Don't kid yourself that you don't suffer impairment at depth/high ppN2 folks....
