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Jacques Cousteau referred to Nitrogen Narcosis as "Raptures of the Deep", most divers call it " the narcs". Here's all about it.
Introduction
It is generally described as being euphorically intoxicated. Any diver who has undergone a dry dive in a  recompression dive will recognise the euphoric properties of compressed nitrogen.
Nitrous oxide or "laughing gas" has been used as an anaesthetic in operating theatres and dentist surgeries for years. Its main purpose is to put the patient to sleep and relieve pain. Nitrogen Narcosis is like a mild dose of anaesthesia.
Nitrogen at higher partial pressures alters the electrical properties of cerebral cellular membranes, causing the anaesthetic effect we call nitrogen narcosis. Every 16m of depth is equivalent to one alcoholic drink. Thus, at 50m divers may experience alterations in reasoning, memory, response time, and other problems such as idea fixation, overconfidence, and calculation errors.
These effects are not unique to Nitrogen, many other gases are intoxicating if breathed under pressure including helium, neon and argon. Gases that easily dissolve in fat have the worst effect.
The Effects of Nitrogen Narcosis
It is a strange phenomenon and effects us all to a lessor or greater degree, it is often difficult to precisely predict it onset and its effect as it varies with each person and with each dive. If you dive below 30m you will become "narced", how that manifests itself, seems to be related to:
- Depth
- Personality and mood
- Body Mass Index (BMI) i.e., fat content
- Dive fitness
- Frequency of diving
- Mood
- Workload
- Anxiety and cold
- An elevated CO2 level
- Darkness
- Diver confidence
Just like drinking too much alcohol, some divers get over confident, some get boisterous, some aggressive and some giddy. The dangers arise through classic signs and symptoms such as:
- Thinking and responses significantly slow down
- Multitasking becomes difficult
- Loosing short term memory
- Lack of insight
- Faulty reasoning
- Calculation errors
- Idea fixations
- Increased anxiety, anger or euphoria
- Narrowing of a divers mental focus
Depth
Typically divers can become aware of its effects at about 30m although technically divers are effected as soon as they descend, and this can be borne out by some simple mathematics at 10 and 20m, you will be amazed at your slowness and the results. General research suggests that the more exposed a diver is to Nitrogen narcosis the less it affects them.
It is hard to predict what reactions a diver may have at a given depth and new divers are advised to build up experience at these depths slowly and carefully.
The Good News
It's not all bad news though, the effects of narcosis don't get worse with time, after about 2-3 minutes at a given depth the symptoms will remain constant, and amazingly, symptoms completely disappear as you ascend back to the 10-20m range. There is no long term or permanent damage either.
Avoidance
Given the symptoms outline above, there are a number of things divers can do to reduce the likelihood and impact of Nitrogen Narcosis.
Before the Dive
- Work up to depth - If necessary undertake training dives working up to the depth of the target dive. Bare in mind though, that research suggests that any "resistance" to narcosis, built up through training dives, is lost after a 7 day break.
It is also worth mentioning however that other researchers believe this apparent resistance to narcosis may not be a true physical adaptation. It's more likely that divers who routinely dive deep have developed ways to offset the mind-clouding effects of narcosis. As a result, they have less anxiety and more practice at performing certain tasks.
In any event it is good practice to develop deeper diving over several dives.
- Practice skills - Make them second nature so they will occur reactively and without thinking. This is particular relevant to emergency skills, e.g., jettisoning weight belts, switching air supplies, free flow drills.
- Plan the dive - Make sure all divers clearly understand the dive plan, the route, duration, depth etc. Plan for narcosis, e.g., if any diver is feeling narced, explore the top of the wreck as opposed to the sea bed. Make sure there is plan for safely aborting the dive if deemed necessary.
Prior to the Dive
- Be dive fit - Make sure all divers are sober, well hydrated, comfortably nourished and rested, prior to the dive.
- Avoid medication - There is evidence that some non prescription drugs can make narcosis worse., avoid them if at all possible. That said, avoiding sea sickness medication may be counter productive, as sea sickness can lead to dehydration, feeling unwell and a dangerous lack of concentration.
- Be warm - Ensure that suit leaks are fixed and that underclothing is adequate as the cold will make narcosis worse. Cold fingers coupled with a narced head can be dangerous.
- Be confident - Ensure all divers are well briefed and diving within their comfort zone. Anxiety is another exacerbating factor.
- Use a slate - Minimise any requirements for memory or calculations underwater, preplan everything and write it down clearly on a slate.
- Avoid task loading - Remember the KISS approach (Keep it Simple Stupid). Avoid any complicated equipments configurations, calculations and reduce new equipment to a minimum.
On the dive
- Avoid unnecessary depth - Wherever feasible. even a few meters can make a difference.
- Descend slowly - There is some evidence that fast descents increase narcosis.
- Routine checks - Agree that buddy and gauge/computer checks are to be frequent, i.e., every 2 or 3 minutes.
Narcosis Tests
There are a number of tests you can do underwater to assess yourself and your buddies degree of narcosis, two are listed below:
- Finger Test - Every few minutes, hold up a number of fingers to your buddy (say, three fingers). He has to respond with the same number plus one (four fingers). Note the time taken for the response and of course the accuracy.
- Mental test - Give your buddy a simple arithmetic test e.g., 36 x 36 and a slate and see how long it takes and how accurate they are.
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