Wednesday, October 1, 2008

Diving Deep on Air

Last weekend a young sport instructor (who only recently completed her Advanced Nitrox course), deemed herself fit to take an even less experienced diver (open water 2 I believe, so what, 20 dives ?) to the back of the cave at Wondergat. This is a cavern dive to 52 meters. It looks easy. First you descend 35 or so meters to the cave grid. Then you head off on one of the permanent lines, down a fairly sleep slope that slowly levels out as you enter the gloom of the cavern. If the vis is good you can see the whole cavern mouth from the back. Normally the vis is trashed thanks to inexperienced sport divers speeding in on short bottom times (to avoid decompression) and with inadequate buoyancy skills.

This is not the first time that this instructor has done this. Last time a complaint was lodged with her agency (nothing happened) and she was talked to by experienced technical instructors so I can only conclude that she sees nothing wrong with her actions and deems herself to be a superior diver that can manage any situation at any depth with any number of following divers. This is interesting because one of the fatalities from the back of the cave was a highly experienced national instructor who took open water 2’s to the back of the cave and paid for it not only with his life but also the life of one of his students (the student was on a single cylinder and ran out of air at the back of the cave. The instructor was on twins. They both ran out of air before reaching the mouth of the cave).

The thing about Wondergat is that it is deceptive. Going in is easy thanks to the slope which means that there is little effort involved. Going out is a swim thanks to that slope. This means divers are having to work, which increases gas consumption… all of which is a recipe for disaster. Especially if the divers are sport divers with marginal buoyancy (yes, pretty much every diver we get thinks they have buoyancy control but turns out when they have to do the standard technical drills they do not), sport equipment (one cylinder, one first stage, no back up gas, no decent lights) and no gas planning. Oh yes, and no experience or build up to mitigate narcoris.

I have a number issues with this dive. Firstly let me point out that this lady is not the only instructor doing this. She was just silly enough to brag about it on the net, so she gets to be the lesson.

My first is the arrogance of instructors who think that they are capable of dealing with the situation just because they are instructors. That is the kind of attitude that has killed people in the past and will kill people in the future. It is called ego and it seems that women are not immune to it. An instructors does not give you immunity or god like powers (and this applies to highly qualified, experienced technical instructors as well).

The second is the blind naivette of the student who believed her and followed her (see my blog on trusting experienced divers). As a diver you need to take responsibility for your own safety and not just trust divers who seem to know better. The odds are they do not! And you pay the price, often with your life.

Lastly, I am annoyed and concerned with the blasé attitude of sport divers and instructors who simply DO NOT KNOW how restricted their world is and break the rules without bothering to find out how. Now I guess that last statement could be deemed to be contradictory. After all, I am stating that I do not condone breaking of the rules (divers should not dive outside of the depth they are trained to) and then I say if you are going to break them at least know how ? Training is one way to learn how to break the rules. It is there to teach you what you do not know and how to to safely extend your limits. It is not the only way to learn however it is the safest.

I should at this point say that there is a reason PADI does not have courses that take you deep…depth changes the rules significantly. Sport diving teaches you to dive on a single cylinder with no decompression. It does not teach proper dive planning, proper gas management, proper buoyancy control and any appropriate risk assessment or management that will allow you to undertake a deep dive safely. Why ?Because that is not what sport diving is about. Sport diving is about the path of least resistance. It is about the least amount of knowledge that will get the most people divin, safely enough to avoid legal action (perhaps a bit cynical, but not so far from the truth). That is why technical dive training exists.

So, why is the back of the cave so different ? And how would a technically trained diver do things differently ?

The first hurdle to get over is the anti-air brigade. It has become kewl to diss air and recommend Trimix. Yes, air is bad and yes, you should be diving Trimix. The problem is Trimix is not always available and when it is, it is ludicrously expensive (think R600 for a dive). Based on these two facts alone, air is NOT going to go away easily. Add to that the fact that air is easy to come by never mind easy to breathe and there is no real hard limit to stop a diver from just going deeper and deeper. Now throw in the handy dive computer and any limits a sport diver used to have disappear entirely. They don’t have to think! They don’t have to know anything about decompression. All they need is a full cylinder and a dive computer and they can go anywhere for as long as they like…… or so they think.

If you are going to dive air you need to understand the characteristics of air and the risks entailed so that you can actively PLAN for these. In a nut shell dive planning firstly identifies what risks are unique to the dive you are doing. Then it allows you to consciously determine if you can avoid these and if not, how you are going to manage them. All dive planning amounts to ensuring you have enough gas to breathe for the whole dive (and never touch your reserve), you have enough light to see by, you have the mental ability to think and that you can manage any probable situation underwater.

For the back of the cave the list has things like:
- Narcosis, it is 50m
- It is dark, and gloomy so if you lose the line you are lost
- It is dark and gloomy, so your narcs is going to be higher as you are going to be more stressed
- It is at least 5 minutes (that is optimistic) from the surface, probably more so what happens if you have a dv failure, or blow an o-ring ?
- It is going to take at least 5 minutes to get there, which means you have descended at speed, which means your narcosis is going to be way worse.

Lets look at narcosis first!
Now every diver thinks they know about narcosis. But what do they know ? That it starts at 30 meters ? What divers tend to be unaware of is that the increase in narcosis with depth is not linear but rather exponential. Narcosis at 50 meters plus is very, very different to that at 30 or even 40 meters. To give you an example - as an instructor with Wits Underwater club I regularly had over confident open water 2 divers who (because they had been trained at 30 meters) had NO respect for narcosis simply because they had never really experienced it ( 30 meters is the start of narcosis so the effects are hard to notice). I learnt quickly that talking about narcosis had not effect. The only time these divers got respect for how bad they are at thinking and ‘doing’ at depth was when they were deliberately taken on a dive designed to narc them out (that would be a fast descent to 35, 40 meters). Then and only then did some (not all ) of them realise how debilitating narcosis really is, which is the point at which they started to take it seriously.

The next thing you learn is that there is no cure for narcosis. If you dive deep enough on nitrogen you will always experience narcosis (adding helium only extends that limit, it does not cure narcosis ). To get rid of narcosis you have to reduce the partial pressure of the nitrogen in your mix, which practically means ascending. Acclimitisation makes a difference. In fact, divers who regularly dive deep air spend inordinate amounts of time training for deep air and acclimatising.

Now the concept of acclimitisation is in itself controversial. I am a deep air diver, so my experience is that if you build up for depth your ability to manage task loading (think and do) is greatly improved. In fact, if I have not dived deep for a while my first deep dive will be a nightmare. I am totally narced, so I spend as little time as possible there and get shallow as fast as I can. The next dive is normally better. My approach to managing high levels of narcosis is to slowly build up to them. What do I mean ? Well if I was to move from 30 meters to 50 meters I would spend a weekend just doing 30 meter dives -. 3 on the Saturday (all with decompression because it is time at depth that gives you acclimitisation) and then a 30 and 40 meter on the Sunday. The next weekend (not more than 2 weeks later) I would then do 4 40 meter dives. Only then would I deem myself to be fit to do a 50 meter dive (and then only if the dive is within 2 weeks of the build up sequence). On the actual weekend I would do a 30 and a 40 m on the Saturday followed by the big dive first thing on Sunday. Oh, and I would have had no alcohol for the entire build up sequence and be avoiding things like caffeine and coke.

There are two other aspects a technical diver would look at, having the right equipment and being 100% familiar with that equipment. Being familiar with equipment means being able to lay your hand on a dv or a cylinder or a fin or a knife within seconds of thinking you need it… without spending valuable seconds searching for it. It takes effort and lots of practice to build up that kind of unthinking familiarity with your equipment.

Which brings us to equipment. From our dive planning we know that this dive is at least 10 minutes, if not 15 minutes long which means gas is going to be a concern. It is also deep, so you are going to be using more gas than on your normal 20 meter dive. You are also going to have to swim, are going to be narced and it is dark and guaranteed as a sport diver that means you have insufficient light (last Time I heard this dive done with one torch between 4 divers), so you are going to be stressed. As a technical diver you know what your gas consumption rate is so you can work out for a 15 minute bottom time (that means leaving the surface, getting to the back to the cave and leaving on 15 minutes) exactly how much gas you are going to need.

You are also not working on a standard 50 bar reserve rate, but on critical pressures (which is a whole blog on its own). In a nutshell your critical pressure is the number on your spg at which you must turn around. If you turn around when your gas content gets to that pressure you have enough gas to get you to the surface and still have 50 bar left. This is completely different to the sport divers who turn around on 50 bar without knowing if 50 bar is enough to get them to the surface. The assumption is it is and in most cases that is true, because they are diving within very tight limits. Another difference is that leaving on 50 bar means you are still using gas to get to the surface and are planning on reaching the surface with 20 bar. We plan to reach the surface still with all our reserve…totally untouched. If you are not using critical pressures (which requires conscious dive planning), you should be using at the very least the rule of thirds, i.e. you breathe a third of your gas mix into the cave and when that is gone REGARDLESS OF WHETHER YOU HAVE REACHED THE BACK OR NOT, you turn around and come back out.\

There is a good chance that calculating your actual gas requirements will indicate that this dive is NOT feasible on a single cylinder. In any event, as a technical diver you always have at least two cylinders with you. There is a very good reason for this and it is called redundancy. The last place you want to lose your entire gas supply is at 52 meters. Now every good sport diver just shrugs and says, my buddy is right next to me…except he is stressed and sitting at 80 bar, so now you have to get two divers all the way out of the cave on 80 bar ? Not a situation I would rate my chances in. Sport rigs also have only one pillar valve, which means if you blow an 0-ring or have a problem with a first stage you lose BOTH dv’s, the octo as well. Not a situation I would like to be in at 52 m with only a novice buddy to look to for assistance.

At the very least on a dive like this every diver should have access to staged gas. They should be carrying it with them or have placed it at the grave stones and then the cave grid and still they should have something with them.

This is the abbreviated version of a dive to the back of the cave. It does not even touch on decompression, just the basics of making sure you are not narced out of your tree and have enough gas to get yourself and a buddy all the way back out again. There is simply no way I could put into a single blog all the information you would need to be able to do this dive safely…which is why we have technical training. It is also why I will strongly berate divers who do this kind of thing. If you take only one thing away from this, let it be this…. It is never what you know that kills you, it is what you did not know…and what you did not plan for…..oh and sport diving is highly, highly restricted and limited.

1 comment:

car6006 said...


First of all I have enjoyed reading this article. Up to now I have no idea who you are and from what I read, you know what you are talking about.

I am not going into much about my own experiences, therefore all I have to say about this article is that it's very, very useful, educating and a reality check.

Thanks and you should post more often.

best regards