Tuesday, April 1, 2008

Cave Skills Part 2 - Too Deep (Helium vs Air)

Interestingly Sheck Exley named the third greatest risk to a cave diver’s life as going too deep. This was the only explanation that could be found for a number of deaths where a continuous guideline and sufficient gas had been implemented. The magic number even back then was 40 meters but that is often (and especially in technical circles) ascribed to be too shallow – a number reserved more for the sport masses than the technical diving elite.

Every agency these days limits air dives to 40 meters. The technical agency’s still accommodate deep air diving with courses still available, but here the trend is toward mixed gas diving rather than the more macho (and dare I say it, old fashioned) deep air dive. There is some physiological support for the number 40 – it appears to be the depth at which deep water black out is experienced. Deep water black out is not a phenomenon we here much about these days even though it is not uncommon and has been deemed to be the cause of a number of ‘inexplicable’ diving deaths. Victims literally drown. To an observer they appear to be asleep with their eyes open and are immobile butt breathing. On examining their dives it is often found that these divers were on their deepest dive to date and that there was a significant jump between their previous deepest dive and the one on which the deep water black out was experienced. The most frightening aspect of a deep water black out is that divers who do survive do not recall any unusual symptoms prior to blacking out, which means that you as a diver never know about it!

So is 40 meters the dividing line between deep and too deep ? And is the 40 meter limit something that is reserved only for the non-technically trained ? The interesting thing about 40 meters is that it is the depth at which most divers (if not all) experience a narcotic effect that is strong enough to affect their control and ability underwater. This tends to give them a healthy respect for narcosis and at least introduce an element of caution should they decide to break their training and go deeper on their own (which is not something I sanction, but seems to be an unfortunate fact of life).
The problem with the 40 meter limit is its practicality. Inland dive sites like Wondergat and Badgat extend deeper than 40 meters as do the more interesting ocean dives and wrecks. However the ability to dive these sites within the air depth limit is restricted with the majority of dive sites and operators falling into the not ‘technical’ friendly category and either not providing helium filling facilities or actually accommodating the extra kit that a helium dive requires (twin sets and stage cylinders). This means that divers have to fill at home (Gauteng has two full time helium mixing stations with full boosting facilities) and sees many divers having to dedicate a set to a single helium dive and using an alternative set for normal air/ nitrox build up dives.
Diving legal has another set of complications, that of the expense of diving helium. Helium diving normally requires a twin set (or at least a H-valve and extra dv), decompression gas (read extra cylinder (s) and dv’s) and a helium enabled computer. All for an extra 10 or 15 meters of depth. Now compare that to a deep air dive where you use the kit you have do not need decompression gas or a new computer. The cost saving is sizeable in rand terms.

The expense of diving helium is not restricted to the cost of the extra gear, the big cost is the price of helium. It is an expensive gas made even more so with shop mark up’s. Not many shops believe in the principle of volume to offset a lower price (we most definitely do) and helium prices in the range of 45c a litre mean that a standard 20:30 fill (20% oxygen, 30 % helium which will allow you to dive within the ‘limits’ to 60 meters) will set you back around R750 (for twin 12’s – excludes oxygen and other filling costs that might apply).

If you have been able to extend your finances to proper helium kit the chances are still good that you can not dedicate a set to holding helium so at the end of your 45 minute dive you have no choice but to dump two thirds of your mix. Now compare that to R80 for the equivalent in an air fill (not to mention the fact that you do not need extra kit) and there is no wonder divers are still using air for most of their diving.

So should the air limit be extended to accommodate practicality ? I mean we all know that divers do not obey the 40 meter limit so surely if we should acknowledge reality and safely train divers to do what they are already doing, dive deep on air ?

There are a number of problems with this not the least of which is the number of times the ‘normal’ diver dives. I am a deep air diver (my personal limit is 60 meters) and for most of my open circuit career have dived sub 50 meters quite comfortably on air. But, I practice diving deep and if I am planning something that requires a 55 meter or 60 meter air depth, I build up to it… slowly. Deep air diving is not something you do once every three months. You do not simply throw your kit on and hop into the water. It requires discipline to dive deep on air. It also requires serious attention to your dive plan and in particular gas management. I know that if I build up slowly I can function at high narcotic depths. I know that I can build up narcotic adaption. But I also know that narcosis is deceptive. When I am diving sub 50 meters I pay a whole lot more attention than I normally would because I know that one of the effects of narcisis is that lovely “everything is just fine” feeling when in fact it is not. There are some dives where I get to 50 odd meters and feel totally crap so I turn around. I listen to what my body is telling me.

The problem with narcotic adaptation is that it can not be proved by science. Physiologically there is no adaptation and the effect you experience is actually psychological which means that the dangers of diving narced still exist, you just are more used to coping through the fog. It is important as a reader that you understand that whilst I understand why people dive deep air and I have and do dive deep air, it is not my preferred choice. I also avoid high narcotic depths when I have task loading or something complicated to perform (like navigating the jungle gym at Badgat). When I dive deep air I do it for a reason - in order to dive sub 150 meters I have to use gas mixes with a high narcotic depth ( (it is practically impossible to do it on a 40 meter EAD) which means I have to be able to function, think and problem solve under that stress. In order to do that I have to practice being exposed and I do so relentlessly. Now that I have moved onto my rebreather I have easy and cheap access to Helium I rarely dive with a narcotic depth deeper than 35 meters and as a result my diving is way more fun (ok, it could also be the fact that I am on a machine which is quiet and enables me to stay longer ). But not diving high EAD’s is going to be a problem when I want to go deep again because I am finding I am way more susceptible to narcosis than I used to be. If I want to go back to 200 meters (or deeper), I am going to have to rebuild that narcotic tolerance that was almost a decade in the making.
So is 40 meters the magic number ? Narcosis is debilitating of that there is no doubt.. The effects are also highly personal and there are few divers out there who have the physiological predisposition to manage it and manage it well (thanks to the very nature of narcosis there are a lot of divers out there who think they do though).

As a cave diver the situation is complicated by the fact that in a cave you have to retain control. You have to be able to dive without silting, you have to remember to lay a line that will get you out. You have to be able to think and reason and process underwater. It is not the same as diving where the surface is just above you. The gap between being safe and being dead is much smaller, there are more things that can go wrong. Here being narced is the difference between coming back or not.
Perhaps 40 meters is a good number. We have to draw the line somewhere! It is also the number that has been universally accepted so perhaps the question is not whether or not too deep is deeper than 40 meters, but rather whether or not you wish to bet your life on the fact that you can beat narcosis when it counts ?

Dives are more enjoyable when you are not narced. You are safer which means you are not a threat to your buddies when you are not narced, all valid reasons to subscribe to the teachings of the dead. Even more important is the fact that as a diver your life is worth more than the investment in trimix gear and fills. If you get it wrong there are seldom do over’s. Dead is dead!
The fact that diving deep on air is too easy and too accepted by the community at large is not a valid reason to choose to dive deep on air. As a cave diver we all have a choice - to contribute positively to our community and so build one that is responsible and safe or to promote practices that have been proven to be unsafe and kill divers. It is our responsibility to eradicate the misconception that diving deep on air is the kewl thing to do. It is our responsibility to create divers who can make informed choices based on fact and not ego!