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Attention: Fred Garth

This is the kind of article you need to be publishing in Deep Tech; 
something useful and thought provoking. Instead we get things like 
"Favorite Regulators of the Rich and Foolish Running PO2s of 3.0". I need 
THAT about as much as a companion piece on "An In Depth Look at 
Snorkels".

Chuck

G. Irvine wrote:
> 
> Common Gas Diving Topics
> 
>  We need to look at some topics in gas diving that are being misapplied
> due to misunderstanding, and then used to justify deep air diving.
> 
>  #1 - "air tables" are wrong. We all learned some simple things first,
> like PADI tables, and then Navy tables. PADI tables are Navy
> no-decompression tables. Navy tables are nonsense - they bend you by not
> doing the deep stops and then treat you by extending the shallow stops.
> 
>  #2 - Gas tables are more correct: unlike the more arcane Haldanean
> models in the air tables, gas tables were mostly developed using
> Bulhmann's theories which started deco deeper, but not deep enough.
> 
>   #3 - In real life, stops start deep, helium is your friend, it makes
> you fell better after the dive and keeps you from narcosis, it is EASIER
> to decompress from.
> 
>    The result is that people were first taught to believe that gas needs
> deeper deco than air, when in fact air needs deeper deco than is in the
> "air" tables.
> 
>    The term "decompress from gas on an air table" is an oxymoron - there
> is no "correct" "air" table as we know it, the gas tables are what is
> needed for air.
> 
>     Having said that, let's look at a diving situation:
> 
>   I want to do the "Doria", but my captain, Janet Beiser, has to limit
> my gear baggage since there are others on the boat. I can be a dope and
> dive air ( if Janet would let me), or a convolute and put air in my back
> tanks and take gas stages, losing redundency in an emergency, and being
> forced to air at the worst posible time ( like what happened in the
> death of Rob Parker), or sharing air with an out of gas divier, who is
> now hammered , scared, and on my long hose, or I can make the exact mix
> for one dive and then blow it into oblivion with air, or,
> 
>                      I can "Do It Right":
> 
>    I can lose the abject fear of helium and low oxygen mixtures, and
> make up two sets of doubles with high helium, like 50%, and low oxygen ,
> like 14 percent, and take stages of the exact mix for the depth ,
> probably something like 18/33, and some stages of 50/50 and my oxygen
> bottle.
> 
>   I dive the stages and try to save the backgas, but let's say I want to
> use the backgas. I can blow it back three times and still be ok on the
> oxygen, and probably pretty good on the helium, but what happens to the
> deco?
> 
>   My first dive for 25 minutes is problably a good hour of deco, my
> second with the diluted mix is more like 52, and the third more like 45
> ( relatively 60,50,40 or padded ratios like that). In other words, for a
> few extra minutes in the water, I get to do it safely. I then do the
> same with my other set, and/or my stages were dived first, and then I do
> a couple of back gas dives . I keep the dives to reasonable bottom
> times, and end up making the deco gas last longer, and as the deco gas
> gets diluted or lower, the deco using the higher oxygen "reblows" is
> getting shorter and shorter anyway, assuming I am giving myself a decent
> interval between dives. Most of the deco time is on oxygen anyway.
> 
>    POINT here: mixes that are too low in oxygen and too high in helium
> are not a bad thing - this is ok. The opposite is not. The former means
> a tad more deco, the later means a lot more risk.
> 
>   For a shallower dive, lets say 130-160, I can take my doubles with
> something like a 16/40 and blow that up a couple of times for back gas
> diving in that range with the boat's compressor. The deco pickup over a
> higher oxygen mix is not enough to warrant the air, especially at the
> more insideous depths, like 150, that have enough impairment to cause an
> accident, but not enough to "ring your bell" and make you aware of the
> impairment.
> 
>   Keep in mind I am talking about trips where you have limited gear
> space and want to maximize your gas .
> 
>   Technical diving is fun, but it is geting a bad name due to the
> accidents.AAAThe accidnets are due to impairment from nacosis. The
> accidents need to stop. I repeatedly do dives that were not even thought
> possible by my original dive partner , Bill Gavin, and I do them safely,
> and I do them all the time, and they are fun to do. If I can do 300 for
> three hours and then go out to dinner with my pals, then you can dive
> the Doria or anything else without the self-imposed risk. I know what I
> am talking about  -  learn this stuff right and stop the nonsense.
> 
>   If you need information to keep yourselves alive, ask me or any of the
> WKPP guys, and examine your own misconceptions - there is no such thing
> as an "air table", and the real risk is death. - G
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