STICK TO
DRINKING
BEER
Did you read about the diver who plunged to 156m on air and then shot back up to the surface in about a minute flat? John Bevan did, and he is distinctly unimpressed
Elsewhere in this issue you can read about the deep air diving exploits of Mark Andrews, exploits that I consider irresponsible. Not only is he endangering his life, but by boasting of breaking records he is attempting to win respectability for his "achievements" and so encouraging others to compete with him and endanger their lives as well.
I would draw attention to two aspects of deep air diving - oxygen toxicity and nitrogen narcosis. The first is something of an unknown quantity. To my knowledge, there has never been a reliable report of any incident of acute oxygen poisoning while breathing compressed air at great depth (to a maximum of 240m). Oxygen poisoning has been suggested as a contributory factor to some fatalities, but that's all.
The deepest scientific experiment with breathing oxygen at depth was, I understand, that carried out by Professor J B S Haldane in 1941. He breathed pure oxygen at 60m for 30 seconds and for the three-minute ascent (in a chamber) with no apparent ill effects due to the oxygen.
Here the exposure to the elevated O2 partial pressure was shorter than the normal delay in onset of oxygen toxicity symptoms, so the problem did not appear. When breathing air at great depth the anaesthetic effect of nitrogen narcosis possibly offers some protection.
However, the nature of acute oxygen poisoning is such that in short, extreme exposures the diver might surface in apparently good health but then pass out and convulse minutes later.
What of the effects of nitrogen? For many years, as a scientist working for the Ministry of Defence (Navy) Department, I studied the effects of nitrogen narcosis on divers. I carried out experiments with divers in chambers breathing air down to 91.5m, including computer analysis of their brain activity.
I also carried out dives breathing an oxygen-argon mixture with an equivalent air depth (from the point of view of narcosis) of 120m. I have been involved in many related experiments in chambers and in the sea, carrying out a whole gamut of psychometric tests.
>From this I developed a simple way of assessing the potential effect of nitrogen narcosis by comparison with drinking beer. My graph can help divers predict the likely level of narcosis they can expect to experience at a particular depth.
As with alcoholic intoxication, the only time we appreciate the effect of nitrogen is when our thought processes are tested with some form of mental challenge. Otherwise we can not only feel perfectly capable but have an exaggerated, false sense of well-being and security. This is why many divers sincerely believe that they are "not affected" by narcosis.
My graph is a personal assessment, but I challenge any responsible scientific organisation to carry out the experiments needed to produce an equivalent graph based on an objective study.
At the first main point on the graph, zero beer and zero depth, there is zero narcosis and zero alcoholic intoxication.
The second point is at 10 pints of beer and a depth of 120m in the sea. I chose this point because if I drank 10 pints of a certain brand of beer fairly quickly I would reach a point of alcoholic intoxication where I would be unable to think coherently or carry out the simplest mental task, and I have related this to the level of nitrogen narcosis I found on experiments at 120m in the chamber.
By connecting these points, it is a simple exercise to interpolate any point between the two. So for example, if I were to dive to 50m, I would expect to be affected to the same level as if I had drunk about four pints of beer.
I can also compare the effects of nitrogen narcosis directly with the known effects of alcoholic intoxication. At about 20m I will be cheerful and relaxed. At about 30m the risk of accidents will be four times greater than at 10m.
At about 60m I can become excitable and quarrelsome. I will have a 25 times greater risk of an accident than at 10m.
At about 70m, my sense of balance and orientation is significantly affected - dangerous in poor visibility or midwater. I will suffer memory loss and my vision will be adversely affected. At 120m I am close to blacking out and collapse.
For those who might claim they can breathe air deeper than 120m and still not be "indisposed", I have placed an alternative point at 150m, where breathing air would incapacitate the most macho.
Even then, the intermediate points show that intoxication/narcosis is significant at much shallower depths.
So what is our "kamikaze" diver Mark Andrews trying to do? He claims to dive regularly to more than 100m - to where he would have had the equivalent intoxication of more than eight pints of beer. Is this something to boast about? Clearly he is attempting to find out at which point he blacks out and collapses.
And well-known diving equipment manufacturers are sponsoring him!
Their money would be better spent on seeing how much beer Mr Andrews could drink before he fell over.
Appeared in DIVER - October 1999
