Before I start I'll admit what many of you already know which is that I have little use for this magazine. After having a dive shop for a couple of years I got rid of it and wouldn't sell it. Now, I don't ask for it and sure don't pay for it but they just keep sending it to me.
Yesterday the May issue came. I skimmed through it during a commercial last night and my eye was caught by an article titled "Is Deep Air Diving Safe?" by Michael Ange
BTW, I put this post here rather than the technical section because the magazine is a recreational diving magazine and is read by recreational divers so I wanted to address my comments to recreational divers.
I'm not going to comment on how deep I am willing to use air or what I think your maximum depth on air should be. I must, however, comment on a couple of points made by the author that sent my BS meter streight through the roof.
The article...
He starts by stating a case for deep air based on it's good safety record. I won't spend much time here other than to say that there is plenty of reading out there to the contrary but it's a wast of time to talk about it without getting into specific depths. I will say that if air was so great we sure wouldn't mess with the cost and trouble of other gasses.
Next I have to address his comments on trimix. For those who don't know...trimix is a mixture of oxygen, nitrogen and helium. The helium is used primarily to displace some of the nitrogen (reducing narcosis) and oxygen (limiting oxygen exposure). At sufficiently high partial pressures and or periods of time oxygen becomes toxic.
ok, on to what Michael Ange said...I quote
I call BS in that a travel gas isnt needed unless diving a hypoxic mix (Not enough O2 to keep you alive near the surface. This is only an issue using mixes designed for very deep dives. Even then, not always.
He goes on...
First off, even deep air divers often use nitrox and or oxygen to accelerate and improve the efficiency of decompression. By the same token you could use a single gas on a trimix dive also. BTW thats exactly whats done in classes like the GUE recreational triox, the IANTD recreational trimix and the NAUI class whos name I dont remember.
When he refers to fatal gas switches hes talking about mistakenly breathing a gas too deep or too shallow for its oxygen content causing oxygen toxicity or hypoxia respectively with the former being the more common mistake.
There have been lots of technical diving accidents due to improper gas switches but multiple gasses are necessitated by the amount of required decompression and not by the choice of the main diving gas. The same risk exists for the deep-air diver because there will most likely be more than one gas used for a dive of any significant depth or time.
More importantly breathing the wrong gas at the wrong depth is easily avoided by proper tank marking, correct gas switch procedures and sensible equipment configurations. We could write a book about just this one point but if you look at some of the instances of divers dying due to breathing the wrong gas youll see that often their procedures and their equipment were a total mess. I know thats a little vague but I want to limit the length of the post. We can sure go into more detail later if you want.
He goes on to say that
Helium isnt new at this point and we could say the same. It hasnt been in use as long but it has certainly been used with far greater success. The current deep sport diving records were set using helium and the world record cave penetrations have been set using helium. Divers are going deeper, longer with less narcosis and feeling better afterwards than ever before and all using helium! Again we could write a book here so please comment and well go into it more.
The other main point I have to comment on is what he has to say about gas management. I quote
Again I call total BS and I cant believe that they put this trash in print. The rule of thirds originated in cave diving and the idea is to have twice the gas reserved for exit as you should need. That gas can be used to cover yourself for delays or gas loss or it can be used to get a buddy out in a worst case situation where the buddy suffers a total gas loss at maximum penetration. I will admit that if the diver is hosed and all narced on deep-air he is more likely to need it himself.
Also one-third is not reserved for ascent and decompression. This is a completely false statement. The idea is to have twice the gas needed to get back to the surface or the first gas switch. If part of that will be significant ascent or decompression time then a straight thirds calculation on the total supply isnt good enough. In other words youll need to turn the dive before one-third the total gas is used if getting back to the entry point is critical. I believe the only one mistaken here is Michael Ange.
Read the article for yourself. The author contradicts himself on several points and provides no references at all.
For a quick list of references Id refer you to Basic Cave Diving a Blueprint for survival by Sheck Exley, the IANTD Technical Diver Encyclopedia (and all the study references it contains), the NACD cave diving text The Art of Safe Cave Diving and the NSS cave diving manual. Ill add a fourth set of agency texts and also recommend the GUE fundamentals, tech and cave texts.
Some books Id recommend to get a feel for the history of some of this stuff would be Caverns Measureless to Man by Sheck Exley and the Cave Divers by...Burgess?...I dont remember but Ill look it up if any one needs it.
I have to get to work but I asked my wife to email a link to this thread to Rodales and invite them to comment.
Yesterday the May issue came. I skimmed through it during a commercial last night and my eye was caught by an article titled "Is Deep Air Diving Safe?" by Michael Ange
BTW, I put this post here rather than the technical section because the magazine is a recreational diving magazine and is read by recreational divers so I wanted to address my comments to recreational divers.
I'm not going to comment on how deep I am willing to use air or what I think your maximum depth on air should be. I must, however, comment on a couple of points made by the author that sent my BS meter streight through the roof.
The article...
He starts by stating a case for deep air based on it's good safety record. I won't spend much time here other than to say that there is plenty of reading out there to the contrary but it's a wast of time to talk about it without getting into specific depths. I will say that if air was so great we sure wouldn't mess with the cost and trouble of other gasses.
Next I have to address his comments on trimix. For those who don't know...trimix is a mixture of oxygen, nitrogen and helium. The helium is used primarily to displace some of the nitrogen (reducing narcosis) and oxygen (limiting oxygen exposure). At sufficiently high partial pressures and or periods of time oxygen becomes toxic.
ok, on to what Michael Ange said...I quote
I call BS in that a travel gas isnt needed unless diving a hypoxic mix (Not enough O2 to keep you alive near the surface. This is only an issue using mixes designed for very deep dives. Even then, not always.
He goes on...
First off, even deep air divers often use nitrox and or oxygen to accelerate and improve the efficiency of decompression. By the same token you could use a single gas on a trimix dive also. BTW thats exactly whats done in classes like the GUE recreational triox, the IANTD recreational trimix and the NAUI class whos name I dont remember.
When he refers to fatal gas switches hes talking about mistakenly breathing a gas too deep or too shallow for its oxygen content causing oxygen toxicity or hypoxia respectively with the former being the more common mistake.
There have been lots of technical diving accidents due to improper gas switches but multiple gasses are necessitated by the amount of required decompression and not by the choice of the main diving gas. The same risk exists for the deep-air diver because there will most likely be more than one gas used for a dive of any significant depth or time.
More importantly breathing the wrong gas at the wrong depth is easily avoided by proper tank marking, correct gas switch procedures and sensible equipment configurations. We could write a book about just this one point but if you look at some of the instances of divers dying due to breathing the wrong gas youll see that often their procedures and their equipment were a total mess. I know thats a little vague but I want to limit the length of the post. We can sure go into more detail later if you want.
He goes on to say that
Helium isnt new at this point and we could say the same. It hasnt been in use as long but it has certainly been used with far greater success. The current deep sport diving records were set using helium and the world record cave penetrations have been set using helium. Divers are going deeper, longer with less narcosis and feeling better afterwards than ever before and all using helium! Again we could write a book here so please comment and well go into it more.
The other main point I have to comment on is what he has to say about gas management. I quote
Again I call total BS and I cant believe that they put this trash in print. The rule of thirds originated in cave diving and the idea is to have twice the gas reserved for exit as you should need. That gas can be used to cover yourself for delays or gas loss or it can be used to get a buddy out in a worst case situation where the buddy suffers a total gas loss at maximum penetration. I will admit that if the diver is hosed and all narced on deep-air he is more likely to need it himself.
Also one-third is not reserved for ascent and decompression. This is a completely false statement. The idea is to have twice the gas needed to get back to the surface or the first gas switch. If part of that will be significant ascent or decompression time then a straight thirds calculation on the total supply isnt good enough. In other words youll need to turn the dive before one-third the total gas is used if getting back to the entry point is critical. I believe the only one mistaken here is Michael Ange.
Read the article for yourself. The author contradicts himself on several points and provides no references at all.
For a quick list of references Id refer you to Basic Cave Diving a Blueprint for survival by Sheck Exley, the IANTD Technical Diver Encyclopedia (and all the study references it contains), the NACD cave diving text The Art of Safe Cave Diving and the NSS cave diving manual. Ill add a fourth set of agency texts and also recommend the GUE fundamentals, tech and cave texts.
Some books Id recommend to get a feel for the history of some of this stuff would be Caverns Measureless to Man by Sheck Exley and the Cave Divers by...Burgess?...I dont remember but Ill look it up if any one needs it.
I have to get to work but I asked my wife to email a link to this thread to Rodales and invite them to comment.
throne--it has some nice pics of some future dive sites!
