On The Fly NDL & Deco calculations with the USN dive table data

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Posted by CalAbDiver on July 20, 2001 at 10:51:56:

If you are going to embrace the US Navy dive tables as your data set for Mike Kane's on-the-fly NDL calculations, it would be wise to make sure you are diving with EAN32 [Enriched Air Nitrox 32%]. The Navy tables are NOT real good for air dives.

My own explanation of why the Navy tables are not real good for air dives is because I believe the SEALS, HardHats, and Fleet Divers who worked on those dive table projects were so macho that they were in total denial about Type 1 DCS. So I veiw the Navy tables as where the borderline between Type 1 DCS (serious but endurable malaise) and Type 2 DCS (convulsions and muscle cramps requiring recompression) begins.

Global Underwater Explorers [GUE] is advancing the doctrine that air is not a good gas mix for any scuba diving, and that EAN32 should be used instead. I tend to agree with that, personally, and I have had all my scuba tanks O2 cleaned, and since then I have only been diving with nitrox. The depth limit for EAN32 is around 127 fsw, which almost coincides with the 130' "recreational" limit urged by the various scuba agencies [YMCA, NAUI, PADI, SSI, etc.] The 130' air limit is an N2 narcosis based limit, whereas the 127 fsw EAN32 limit is an O2 CNS toxicity based limit.

You are safer diving on EAN32 than on air. The tank fills cost twice as much, but it is worth it for your health. Thats what I do now, except my tank fills are always free because I D/M for a dive store.

Mike Kane did not mention "on-the-fly" decompression calculations, probably for obvious reasons. Let me give that to you. The general rule is this:

IF you exceed any NDL limit, THEN you have to "give back" each minute of excess exposure time at depth with a deco stop of at least the same lenght of time.

You would CONSTRUCT the deco stop in reverse order in your mind, from 10 fsw first, then 20 fsw if needed, then 30 fsw, etc.

You would FILL the deco stops with time in reverse order in your mind too. The 10 fsw stop gets filled first, up to 7 mins, then the 20 fsw stop gets filled next, up to 3 mins, then the 30 fsw stop gets filled third, up to 1 min, which all accounts for up to 11 mins of excess time at depth over the NDL limit. From then on, if you need more deco time than 11 mins, you double everything. So 1/3/7 becomes 2/6/14 or 3/9/21.

After constructing the deco stops in your mind, you execute them of course with the deepest stop occurring first.

Ultra-modern deco theory suggests egression in halves, rather than the Navy's 10,20,30,40,50 fsw model. So according to that, if you dove to 127 fsw, and stayed too long, then your egression model would be 1/2 of 127 = 63 fsw for the first stop, 1/2 of 63 = 31 fsw for the second stop, 1/2 of 31 = 15 fsw for the third and final stop. That makes more sense to me than the Navy's set-in-stone stops, personally.

I dont recommend staying longer underwater than the NDLs for the agency that trained you how to dive [YMCA, NAUI, PADI, SSI etc], but if you get hung up in a wreck, that is how I recommend you to egress, if you dont have decompression dive tables in your B/C pocket.

[Chris, since you prefer to dive without a B/C, you may want to have the dive tables tatoo-ed onto your hands, so you can pull off a gloves and read them there, buddy! Or if you dive like Mike Kane, without hood or gloves, then they are right in front of you all the time!]

I am looking forward to meeting SeaHunt-Mike in a few weeks when abalone season opens again, and we go ab freediving together at SeaRanch. His wife is not a cold water freediver, so she wont be buddy diving with him on their vacation. SeaHunt has lots of friends all over Northern and Southern California, and all he has to do is mention that he is coming to town, and divers drop everything to go scuba or freediving with him. That is my idea of ultimate buddy diving, when you dont let a friend of yours dive without a buddy, and you go with them to make sure they indeed have a good buddy to dive with.

I too want to express my appreciation to Mike Kane for his excellent contingency dive planning analyses. I thought I already knew everything there was to know about diving, til I read some of his posts. MHK, I still wish however that you would not throw down the gauntlet as much as you do. Its not nice. Everybody knows youre smart. Anybody who has met you thinks of you as a sheriff's dept recovery diver. Cave divers are different. I learned that 22 years ago. Even the Navy SEALs know that about cave divers, and even they respect cave divers.

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