EKPP Ressel (August 2003)

[Andy Phillips]

Originally Posted by [b

Quote[/b] ]Regarding the supposed he bend. So you don't think that an increase in pn2 was to blame? Moving from 17/40 to 32% nitrox at 39 mtrs is quite a jump IMHO. 2.3 pn2 to 3.4 pn2. How can you ever know exactly which gas is causing the bend? Sounds like the usual helium is devil gas story.

Nobody on this thread is making any sad remarks about He, the particular diver Mark is talking about is very, very experienced, he has had the misfortune to be bent on N2 as well as He. If he say's it was an He bend, then it was an He bend.
Inspired gas? not certain what you mean, I have seen this word used a couple of times when people talk about gas / decompression and it seems misleading, so I went to a dictionary, and,
Inspired = To draw in (air) by inhaling, I guess the implication is a gas is drawn into a tissue, but how that helps with off gassing is beyond me. I can only assume I am missing something.

What you are really talking about is diffusion and counter diffusion, in other words the absorbtion of and the release of a gas. The theory is that high gradients, i.e. going from a gas with a high percentage of He to a gas with no He creates too big a gradient and can create it's own problem. There is some empirical data to back this up, with people who have done very big / deep dives suffering convulsions even though they were inside CNS limits. In terms of N2, we are not refering to the same thing, although the idea behind having He in your first deco gas would appear to offer two or three benefits,
1) To reduce the He gradient
2) reduce the PPN2 and thus reduce the on-gassing of N2 into the faster tissues. (in the case of some of the profiles Michael and his crowd are doing this is a mute point)
3) (for me this is the debateable point) Any He on-gassed will be off-gassed faster because it is a faster gas, therefore you can get out of the water faster. I am yet to be convinced by this arguament.

d8bus, whilst I agree, not knowing what your minimum deco commitment is / could be, is daft, the problem is, how do you actually know what your minimum deco is. OK, I carry a bailout profile based on decoplanner's fastest solution, but short of continually shortening my deco until I get a type-1, I will never actually know what my minimum time for a given depth / bottom time is. I will have to live with this, and continue to do what I do, which works for me.

Tricky innit.

Andrew

[adam]

Hi guys,

Great debate. As I understand it:

Helium is a smaller lighter molecule, which is 2.65 times less soluble then Nitrogen (Bunsen co-efficient). Hence Helium is absorbed significantly faster than Nitrogen (due to it's mobility), but more critically, releases at least 2.65 times faster. Note this 2.65 refers to solubility, not mobility (which will be the same for both on and off gassing). Thus using He, in combination with deep stops, should actually allow for significantly shorter deco than conventional air/nitrox.

Buhlman, by the way, ignored the difference in solubility and only took into affect mobility.

As I se it, Decoplanner, and any other computer generated profile, only represents the computer models best guess. Most are padded to limit liability.

Mark, you harp on about Decoplanner being a GUE product. The DIR approach is to use it's results to generate an outline idea, but to understand the deco process and modify it's results to suit the individual. A crucial part of DIR is not to be reliant on any specific technlogy, but rather to ensure that skill, knowledge and experience are used. These issues are covered in all GUE courses, and it is important not to use the "Decoplanner is a GUE product and it's results are therefor DIR" arguement as you are using the software out of it's DIR context.

Just my thoughts!

Adam

[Pierre Farrugia]

<font color='#0000FF'>Hello all DIR divers here,

Can someone expalins to me how you actually plan a trimix deco dive, does not have to be complicated! Last year we ran a similar thread and this was mentioned many times , many time by WL, I am in no way criticizing DIR but would like to understand this thing better. So after you plan which gas to use, which I think should be standard for a given depth, then you use a programme to cut tabels? Use a formula WL mentioned which I wish to know how it works? or an other method?

EG. Me I find best mix for diving conditions and depth. Run proplanner and then check if my twinset and deco cylinders would last safely, if yed then it is my profile. Then I run decoplanner and check for big difference and then compare with buddy. Mix and dive!

Regards

Pierre

[Bob Cooper]

Originally Posted by [b

Quote[/b] (Pierre Farrugia @ April 22 2004,19:46)]

Originally Posted by [b

Quote[/b] ]Can someone expalins to me how you actually plan a trimix deco dive

I just do the deco I did last time......for a similar depth and time!

That may not be too helpful to you though...........

I have a set of tables I made up, which is basically what decoplanner spews out for GF 20/100. I have a 30m table, a 40m table, a 50m table and so on. &nbsp;What we do is compare notes on the boat and modify the &quot;standard&quot; tables depending on the expected profile, conditions and, most important how we &quot;feel&quot;. &nbsp;Add some here, take some off there etc. I just modify my tables in pencil and rarely have to look at them.

One important thing is the use of standard gasses. &nbsp;I'm diving Sunday and don't even need to discuss gas choice, we just turn up with the same gas. Once the gas is sorted, the rest is easy.

That's how I do it anyway.

Bob

[Bob Cooper]

Originally Posted by [b

Quote[/b] (adam @ April 22 2004,18:18)]

Originally Posted by [b

Quote[/b] ]Mark, you harp on about Decoplanner being a GUE product. The DIR approach is to use it's results to generate an outline idea, but to understand the deco process and modify it's results to suit the individual. A crucial part of DIR is not to be reliant on any specific technlogy, but rather to ensure that skill, knowledge and experience are used. These issues are covered in all GUE courses, and it is important not to use the &quot;Decoplanner is a GUE product and it's results are therefor DIR&quot; arguement as you are using the software out of it's DIR context.

Well said Adam!

My sentiments exactly.

[Mark]

Originally Posted by [b

Quote[/b] (Bob Cooper @ April 22 2004,20:14)]

Well said Adam!

My sentiments exactly.

<font color='#000080'>And mine.

[Pierre Farrugia]

<font color='#0000FF'>Hello,

Is this a poll &nbsp;

Thanks Bob for your replay, yu gave me best explained answer yet on that topic, as at least like this you have something to start with. When you say you modify the profile yourself, what exactly you do? Why you cannot only use deco planner? Why you think you know better than deco planner, no offence intended? Also why you cannot adj. profile from deco planner playing with GF?

Also do you have a rule when you use 1 deco mix or not?

Thanks again,just keep in mind that here in Malta there are no DIR divers I know of, so here is my only knowledge on this subject.

[Bob Cooper]

Originally Posted by [b

Quote[/b] (Pierre Farrugia @ April 23 2004,14:43)]

Originally Posted by [b

Quote[/b] ]When you say you modify the profile yourself, what exactly you do? Why you cannot only use deco planner? Why you think you know better than deco planner, no offence intended? Also why you cannot adj. profile from deco planner playing with GF?

Decoplanner (and other Buhlman based progs.) doesn't undersand helium, doesn't understand the O2 window and doesn't make allowances for conditions, fitness etc. &nbsp;Read Adam's excellent post about use of decoplanner.

We tend to use decoplanner or tables to get the &quot;total deco&quot; and then shape that deco. according to certain &quot;rules&quot;. &nbsp;The Tech 1 boys (WL, Mark Emery etc.) have a better idea of what those &quot;rules&quot; are as they have recently done courses. &nbsp;I covered Tech1/2 theory in Florida a couple of years ago and I must admit to being a bit out-of-date on the current thinking!

Anyway, here's are some examples - a typical profile from decoplanner for a single deco gas dive, will give you a pause at 21m. &nbsp;We extend this to -say- 5mins to make good use of the O2 window when we get on the 50%. &nbsp;We look at the time on the shallow stops and move some of that time to the intermediate stops. &nbsp;If the final stop is -say- 15mins, we might make that 10mins and do a slow (5min) ascent from 6m. &nbsp;It depends on many factors. &nbsp;The Tech 1 boys will be along soon to give the current thinking on these things, I'm sure.

Regarding the &quot;1 deco gas or two&quot; choice. I often carry the O2 as a &quot;get out of jail free card&quot;. &nbsp;By that I mean as an insurance against having some difficulty with the 50%. &nbsp;The gas choice is also dependent on bottom time of course and depth. &nbsp;Anything deeper than approx 55m would normally be a two deco gas dive for me, depending on the bottom time. We are talking about dives with helium here, not nitrox where O2 is added first (like in a cave dive). Also, remember the old saying that you need to &quot;weigh the advantage of carrying the gas against the disadvantage of not carrying it&quot; (or something like that anyway), stages can be a real PITA on some dives and it's often better to leave them behind and adjust the dive accordingly. Remember also that you might want to carry the 2nd deco gas just to get used to carrying two stages for &quot;bigger&quot; dives later in the year.

Best way to learn all this is to take a Tech 1 class of course!

[Pierre Farrugia]

<font color='#0000FF'>Hello Bob,

Very good reply to my questions and this answers a lot! In my case normally I use 60% and 32%, and you may ask why, the 32%gas? many time it's more a bail out if I loose my 60%.

This year I will try to experiment with 50%, 80% and 100%. If it ws possible I will dive without stages but then for carrying less you will have to stay a lot more!

Doing tech 1 for me is not a vible option, first of all I am not DIR, equipent is not DIR and have to travel abroad to do it. But hearing other people views, can make you learn new things.

WL and Mark, it's your time to replay and add to Bob's replay and maybe refresh your knowledge with us.

Where I can find &nbsp; Read Adam's excellent post about use of decoplanner.


Thanks

Pierre

Originally Posted by [b

Quote[/b] ]

[bang-on]

Originally Posted by [b

Quote[/b] (Bob Cooper @ April 23 2004,16:12)]

Decoplanner (and other Buhlman based progs.) doesn't undersand helium, doesn't understand the O2 window and doesn't make allowances for conditions, fitness etc.  Read Adam's excellent post about use of decoplanner.

We tend to use decoplanner or tables to get the &quot;total deco&quot; and then shape that deco. according to certain &quot;rules&quot;.  The Tech 1 boys (WL, Mark Emery etc.) have a better idea of what those &quot;rules&quot; are as they have recently done courses.  I covered Tech1/2 theory in Florida a couple of years ago and I must admit to being a bit out-of-date on the current thinking!

Anyway, here's are some examples - a typical profile from decoplanner for a single deco gas dive, will give you a pause at 21m.  We extend this to -say- 5mins to make good use of the O2 window when we get on the 50%.  We look at the time on the shallow stops and move some of that time to the intermediate stops.  If the final stop is -say- 15mins, we might make that 10mins and do a slow (5min) ascent from 6m.  It depends on many factors.  The Tech 1 boys will be along soon to give the current thinking on these things, I'm sure.

Regarding the &quot;1 deco gas or two&quot; choice. I often carry the O2 as a &quot;get out of jail free card&quot;.  By that I mean as an insurance against having some difficulty with the 50%.  The gas choice is also dependent on bottom time of course and depth.  Anything deeper than approx 55m would normally be a two deco gas dive for me, depending on the bottom time. We are talking about dives with helium here, not nitrox where O2 is added first (like in a cave dive). Also, remember the old saying that you need to &quot;weigh the advantage of carrying the gas against the disadvantage of not carrying it&quot; (or something like that anyway), stages can be a real PITA on some dives and it's often better to leave them behind and adjust the dive accordingly. Remember also that you might want to carry the 2nd deco gas just to get used to carrying two stages for &quot;bigger&quot; dives later in the year.

Best way to learn all this is to take a Tech 1 class of course!

<font color='#0000FF'>bob,
read your post a couple of times and still makes no sense,if you take a total deco time and alter the stop depths and times you will alter the total deco.
if you cut 5 mins off your final deco stop and do a slow ascent from 6 mtrs to the surface!!!
i could understand if you did a slow ascent from 6 mtr to the surface after your deco has cleared as an additional safety margin.
maybe you could clarify or get someone who understands what your trying to say to explain the 'rules'.
i think you will agree when talking about deco it is important to be accurate with the reasons for changing stops and times.

cheers
barrie