Tuesday, April 15, 2008
There are other choices to make when planning your gas. Aside from the thorny issue of how much is enough, there is the strategy you use to supply that gas. Most gas management strategies view the dive team as a single entity and distribute the bail out gas amongst the team. They assume that an incident will affect one person only, leaving at least one (if not two) additional team members to assist. They also assume that the team will always be together so the gas is always available when needed. These are all assumptions that I am personally very uncomfortable with because I am having to place my life in the hands of another person. I guess it boils down to the fact that I simply do not believe that your buddy is someone you can trust your life to. Things happen on dives.
What if the team splits up and you now do not have all the planned bail out gas ? What if two divers are in trouble ? What if the divers are unable to get their stress under control and as a result that well laid plan is completely irrelevant and you are now in a situation where it does not matter how little you are breathing, your buddy is munching gas at a rate of knots ?
It is not that I am saying that I dive with unreliable people, I do not! But there are just some responsibilities you do not hand to people you love and respect. I do not want the people I dive with to have to live with the niggling doubt that they some how were responsible for my death. If for reasons beyond their control they were not where they were supposed to be and as a result I did not have the extra gas I planned on and I die, well that is not a burden I want to give people I care about. Things happen on dives. Things that are beyond an individual’s control. The only life I am responsible for underwater is my own. If I see someone in trouble I will still attempt to help, but I am not sure I would be willing to place my life on the line. Maybe I will, maybe I won’t. I don’t know, not until I am there. Is that uncertainty something you want to trust your life to ?
As a result, I believe that dive teams should plan dives as if each member of the team is diving solo. No diver should count on using his buddies gas to get out in an emergency (it is there, but not part of the plan). This is far safer and far more reliable an option, even if it does require more planning. Some may argue that it adds an element of complexity to the dive, after all if you have a three member team doing a deep penetration you now have to have three times the kit all of which has to be staged in the same place, creating clutter and possible problems when divers all try and get to their gas at the same time. My answer is perhaps, but those are predictable and therefore solve’able problems. You can change the process - each diver can stage in a slightly different place to avoid congestion. The worst thing that can happen is that one or two of the divers are late on their plan…alive but late. Not having the gas because your buddy never made it is a situation that is unsolve’able, especially underwater.
There are plenty of decisions like this in the world of extreme exploration and it is easy to get bogged down in which way is right and which wrong. There is no right and wrong way, only different sets of risks, different sets of probabilities. As a diver you need to understand all sids of the story and choose what fits you. If in doubt, there is one rule that makes decisions simple, find out which option will definitely kill you if you encounter it, and choose the other option, If you don’t’ like the other option, you should be choosing not to do the dive.
Wednesday, April 9, 2008
Easter 2004 and I found myself in the one situation no cave diver wants to be in, stuck at 152 meters, 10 minutes away from my nearest support diver and 15 minutes away from my staged gas. This was not supposed to happen! I was attempting to reach 160 meters in a narrow incline (well actually decline) shaft at Badgat. It had taken a 3 minute swim at 100 meters to get to the entrance and whilst narrow, the last descent was relatively simple – a quick in and out. My planning was (as always) a balance of practicality (there are only so many cylinders you can beg borrow or steal) and conservatism (I want as much air as possible to breathe). The problem was that all my planning had revolved around losing gas and then being able to head back to the safety of a support diver or staged gas. I had not planned to be trapped at depth having to rely only on what I had brought along to get me through. No wonder Sheck Exley had gas planning as his number two factor for surviving in a cave.
Sheck’s rule for gas management is most commonly referred to as the rule of thirds. Simply put, you use a third of your gas to get in, reserving a third to get back out and leaving a third for emergencies/ your buddy. The assumption is that you should use the same amount of gas (if not less) to get out and that if there is a problem, you will use gas at the same rate as your entry. These assumptions do not hold true all the time (which is always the problem with assumption) but as a guideline it is solid and gets divers thinking along the right lines – plan for the unknown.Do I use the thirds rule ? Yes, on every day, conventional dives (and there lies the risk… what dives conform to that definition ). But on a deep or extreme dive I use critical pressures to manage my gas requirements. For those of you who are unsure, the critical pressure is the number on your pressure gauge at which you must turn around. Put another way, the critical pressure tells you when you have reached that point where the gas that is left will get back to the surface and includes your ascent rate, travel time and any decompression obligation. It also includes that third reserve for emergencies. If you are doing a dive that uses staged gas to get you out, your critical pressure is that pressure that will get you to your next set of staged gases a opposed to the surface.Actually, as I write I realize that gas management is not as simple as using a flat rule of thirds. It is a complex three dimensional problem that includes parameters like the number of gases, how deep you can stage, what your decompression is, how fast you are going to ascend…. Let me explain.
My dive was to 221 meters. Now I know I can not carry my entire gas supply with me (well I could, but what is the point if I am in a cave and can stage), so I will carry enough gas to get me from a specific point (35 meters) to 221 meters and then back to a different point (my first decompression point and deepest staging point 130 meters). Going in is easy, I use my nitrox 36 until 35 m (yes, I run partial pressures of oxygen at 1.6 bar on open circuit). Then I swop over onto my bottom mix (I am going to avoid the discussion of which gas to swop onto, travel gas or bottom mix as that is an entirely different conversation). I know my gas consumption rate (I plan for 20litres per minute, I use around 12) and I know the time that I have allocated to get myself to 221 meters (13 minutes). This gives me the litres I need to get from 35 m to 221 m (at a conservative descent rate of 20 m/s) - namely 4900.The next step is to determine how I am going to carry that gas ? I physically can not manage twin 18’s so use twin 15’s with an assortment of side slungs. I like this approach because I protect my gas in nice neat and isolated containers where if something goes wrong with one, I still have others. At 250 bar, that means I can carry on my back 5600 litres BUT that gas has to also provide buoyancy for the whole dive so I can not plan to breathe my back mounts dry. I can however plan to swop onto a side slung at 35 meters and breathe that to 150 meters (a personal cut off point for managing stress and task loading).
That would mean that I have used approximately 1800 litres of gas from another source, which means I only need to get 3800 litres from my back mounts… to get there. Either way I do not have enough gas in my back mounts to get me there and back with a reserve. I know I need another side slung.Realistically I can not stage deeper than 130 meters (I do not have divers who can get that deep), so I will need enough gas to get back to 130 meters, which was 2500 litres. Each side sling manages 1800 litres of gas, so without a reserve, I need 2 and a half cylinders (I plan to be only able to get 1500 litres out of a cylinder). Translated this means that just to get from 35 meters to my first stage cylinder I need to carry a total of 7500 litres and that is without gas for buoyancy and a reserve. So, just to get there and back – if I were to breathe everything dry- would need a full twin set and two 10 litre side slungs. In order to feel safe I need my full exit gas in an isolated and protected reserve, i.e. 2500 litres which translates to at least one extra cylinder (total # of side slungs now required 3 or 1 to breathe in and two to get me out to my staged cylinders).
BUT I still have not accounted for the fact that I am not breathing my gas dry, so add another 1800 litres (an extra stage, total count is now 4 stage cylinders).
My gas consumption calculation requires that I have 7500 litres to breathe. I am planning on carrying 11250 litres which is a healthy extra 6300 litres over twin 15’s and four side slungs. Should I carry an extra stage ? Probably but that puts the descent at risk. Side slungs create drag and will slow me down. Am I happy with the risk ? Yes, because if I am coming out I have at least one if not two dedicated cylinders that I can use that I will not touch on the way down. I can also go straight to any number of staged cylinders as there is no swim required (I carry extra power inflator hoses and have independent bc’s inflated from independent sources to manage buoyancy risk).
Even if the calculations above indicate that in order to really be safe I should have an extra cylinder, my fail safe is my critical pressure. This will ensure that I leave with enough gas in my back mounts to get me out even though I have planned to use at least 3 extra cylinders (I build in a lot of fail safes). I know that if I am able to breathe my twin 15’s dry I will need 2500 litres to get to my staged gas (and that is at a conservative ascent rate, not an “oh my god things just when wrong, abort, abort, abort” ascent rate). That means I absolutely must turn my dive when my back mounts have 90 bar in them. Absolutely, because if I do not I absolutely do not have enough gas to live and will be doing my ascent on a wing and a prayer. Ad then there had better be a good reason why I pushed the limit so far because at that pressure in my back mounts I have no reserve and it is going to be real tight and real hard going to get to my staged gas.
My planned critical pressure is a more comfortable 140 bar. If I use gas at the planned rate (which is higher than my actual consumption) then I will get to my staged gas with 50 bar left in each 15 and three unused stages, oh and three stages that are full. Assume that something goes wrong with one stage, I still have two left. How much gas do I need to get to my staged gas at 130 meters, one cylinder. So to be in real trouble I would have to lose an entire back mount cylinder (I dive isolated manifold) and three side slungs. That scenario sounds highly unlikely but even if it does happen (gotta love Murphy), then I have one back mount and one side slung to get me back out. Those are odds I can live with.
Shew! Did you get all that ? It takes time to work out a proper gas management plan. It also takes an understanding of what the real, probably risks are. And there is a difference between a probable risk and a possible risk. I plan for probable risks because there is a good chance they will happen as opposed to possible risks which hardly ever happen. And then I work out what will happen if the unthinkable occurs… if I am happy with the risk, then I dive, if not I go back to the drawing board.Next week I will go into less extreme examples of gas management. Hopefully you have an understanding now of the importance I place on having enough gas, and how much thought goes into getting it right.
Tuesday, April 1, 2008
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!