'Deco-on-the-Fly'

[Mr T.]

Might I ask one you DIR chappies to explain further how this is done and the circumstances under which it might be deployed? Davey Willo ran it passed me briefly the other day after his Tech-1 Course and it sounded very much worth a board-viewing.

Take it away chaps.

[Juz]

I'd be interested in knowing more too - the talk at the dive show didn't help at all.

Juz

[Pierre Farrugia]

Hello,

I think you lost a lot of threads about this ! We asked this question a couple of times before and the answer was DO THE COURSE ! Hope you will be more convincing as I am very interesed in this subject.

[Crisspy Fiver]

I would one day like to do the course but feel that I dont have any were near the amount of experience necessary at this stage of my dive career. Im sure there is also people who smoke and are not able to do the course who would like to know the theory at least.

This is what at this stage i would be personally interested in, the theory.

Take care

Jamie

[Fraser]

You'll be lucky guys. Aside from any other issues I strongly doubt that a GUE trained diver will post potentially dangerous information on an open forum. You REALLY need to learn from an instructor and none of us are qualified to explain it.

Also you would need to do two courses (and a lot of hard work between) - this stuff isn't covered on Fundamentals.

Cheers,

Fraser.

[Mark Chase]

Originally Posted by Fraser

You'll be lucky guys. Aside from any other issues I strongly doubt that a GUE trained diver will post potentially dangerous information on an open forum. You REALLY need to learn from an instructor and none of us are qualified to explain it.

Also you would need to do two courses (and a lot of hard work between) - this stuff isn't covered on Fundamentals.

Cheers,

Fraser.

Hmmmmmm... Doesn’t that kind of defeat he object of it then? If its complex, difficult and potentially dangerous how can any one be expected to cope with doing it in a high stress situation during a dive?

Fact is it sounds pretty simple. I am sure I have made a some errors so don’t try this at home but just to give you a basic idea its something like this...

Bottom time is limited to 30mins regardless of depth up to a max depth (60m I think for teck 1) Deco is calculated on a single deco mix of 50%. First stop is 80% of average dive depth. 21m stop is always 5min to open the 02 window on the 50% mix. Remaining stops are calculated for the 3m stop based on a percentage of the depth of the deepest stop. The remaining deep stops are a percentage of the 3m stop, which is then spread over the stops between 21 and the surface working backwards from 6m in 3m increments. The 5min ascent to the surface is included in the decompression schedule. If you start planning 30min dives at varoius depths you will see that there is a loose relationship between the depth and the length of deco.

Putting this information on the net is no more dangerous than selling someone a set of BSAC 88 tables. The only reason the DIR boys don’t tell the story in detail is to keep up the vale of mystery. Any one who attempts any sort of deco schedule without a basic understanding of deco in asking for trouble. The DIR system is no different.

As far as I am aware, the more serious DIR deco dives with multiple deco gas tanks are planned on computers like every one else does and then they are modified to smooth out the deco curve. DIR /GUE even do their own Decoplanner decompression soft where. The DIR boys play games like ignoring the He in the back gas and deco mixes or inputting 25% when they are running a much higher helium content but they haven’t had the confidence to incorporate their belief in the off gassing of He into the actual program its self.



ATB

Mark Chase

[Crisspy Fiver]

Thanks Mark,

Also I love the way we can now read the reply through the email notification. This is great, means my boss cant catch me any more.

Im going to have a detailed look and if there are any questions will ask...

Thanks

Take care

Jamie

[Mark Chase]

Actualy I just found my old notes on deco from GI3

Here you go:

In determining where to start your decompression, the logic is very simple: you want to let gas escape from the tissues prior to bubbling. Once it bubbles, it will not escape. Rising up rapidly from depth is a good way to trap gas in tissues by forming bubbles which will then grow when you are higher in the water column. On the other hand, gas that bubbles into the blood is generally trapped by the lungs, but those with any kind of pulmonary or cardiac shunt are at risk if this occurs. If it occurs to fast, and or the bubbles grow too large, they can block the effective lung function and will damage the capillary beds of the lungs. From depth, you want to remove gas in solution form.

The best way to do this is to begin your decompression stops at 80% of your profile in atmospheres rounded up. For a ten atmosphere dive, the first stop is 8 atmospheres, or about 240 feet. At the same time, the traveling time between 300 and 240 should be at 30 feet per minute max, so it should take you two minutes to get to 240.

There is a fine line between getting rid of gas and adding gas at this end of the deco. All you are trying to do is buy time to get the gas coming out in solution, and there is a point of diminishing returns for stops in the lower end of the deco range. The maximum deep stop is 5 minutes, the minimum is 20 seconds ( 30 FPM ascent). The best way to assure your ascent is at the correct speed is to physically stop every ten feet. That will get you your 20 seconds per ten feet. The range of bottom times that determine the length of the deep stops is 0-150 minutes. For 0, you still have the 30 foot rate, for 150 minutes you max out at 5 minutes per stop. Anything beyond this is effective saturation and the maximum applies.

These deep stops are equally divided at all depths up to 65 percent of the profile. At that point you begin lengthening the stops. Between 65% and 45%, the steps slightly lengthen, but max out at 10 minutes. Between 45% and 35%, the max is 20 minutes, between 35 and 25%, the max is 30 minutes, subject to certain parameters.

Going back to the deepest stop, if you switched gases, and 80% is where you need to switch gases on a long dive, you are maximizing the effect. If you use a helium based gas you further improve the results. Air is unacceptable as a deco gas as it causes damage that can not be fixed by decompressing, and further complicates the decompression due to the body's immune response to damage and the stress of rigid red cells jamming through small capillaries.

When you approach a gas change, you should be coming off of back gas. For the first deep switch, this is obviously the case. Having been on a low ppo2 operating gas, you can afford to spike the ppo2 with a deco gas, whereas yo do not dare do that without breaking to back gas first. You do not use a full 1.6 ppo2 fro any part of deep decompression. The risk is too high. You don't want an oxygen reaction at depth as you will not have any chance of recovering from this, or surfacing and going back down. Be smart and rely on helium and gradient more than ppo2 for these steps. Clearly, a 1.4 or less is preferred for deep stops max, whereas shallower you can do the full 1.6 because you are able to break to a lower effective ppo2 shallow by using back gas. Some people stage a full face mask starting at these stops. JJ does this.

It takes a solid two minutes for gas to make its first pass through the body when you switch. The switch step should be the longest of the series that uses one gas. You are getting the best oxygen window for that gas at this point, and you just came from a low ppo2, and the gradient is not that severe. As you move up, the steps do not need to be longer on the same gas. In fact, you are best served to do your last step before gas switch on back gas and to make it the shortest of the steps. Here you are relying on gradient and the toggle effect.

The toggling effect is simply alternating between higher and lower ppo2s in order to prevent the onset of lung tissue damage, swelling, adding of protective layers, and constriction of the blood vessels. The reduced ppo2, especially the closer it gets to normoxic, will prevent and reverse these effects (other than the damage if it is already done). Using the gradient at this juncture is the best way to rid gas.

As you get up into the shallower areas prior to going to oxygen, you should take a full back gas break - what I call a "cleanup break". For instance, on a sat dive to 300, I will do 20-30 minutes on back gas at 50 feet. Cleanup breaks are effectively being done on long dives prior to gas switch if you do your last step on a gas by going back to the backgas.

In the 40-30 foot range from a deep dive with a long deco, it is unnecessary to extend the 40 and 30 foot stops at all. In fact these one can be sharply reduced if you have no shunts. You are better served by bubbling the gas into the blood stream sat these depths, a far more efficient and rapid way to get rid of it. Bubbles trapped here can be fixed by going back down slightly, but doing it just right means that will not happen to a well-perfused diver For instance, on a sat dive to 300 that would call for 120-140 minutes at 40 feet on any deco program, I do 20 minutes and then move up.

Following each oxygen stint, you must break to back gas. If you were breathing oxygen dry, as in a habitat or trough, you must do a ten minute break before going back into the water. The ascent rate from your oxygen stop to the surface is one foot per minute for a long dive, a scaled down version of that for a short dive. The greatest case of bubbling off-gassing occurs in the move from 10 or 20 feet to the surface. You want that to occur under some pressure and to be controlled by the slow ascent, so that when you are up, you will not get the sudden rush of bubbles that could shunt or cause other problems.

For shorter dives, the deco gases are added from the top down. In other words, your shortest dive might have just oxygen as the only different deco gas. A longer dive of the same profile may add the 50% gas. Still longer times would add the 35% gas and so forth. You weigh the advantage of the gas to the problem of carrying it. The effective shortening of the deco is not in play here because a shorter dive hits the minimum deco rules, so yo have to do the time anyway. Longer dives demand the extra gases to stay efficient. Toggling and alternating are key to decompression. There is no way you can beat this by maintaining a high ppo2.

GI3

ATB

Mark Chase

[Mark Chase]

And here is the other one:

By GI3

Decompression is a not linear event: twice the bottom time does not mean twice the deco, and half the bottom time does not mean half the deco. This is fairly intuitive, but for you Marines, the fact is that the fastest movement of gas occurs where there is the greatest differential. When you first go from one ATA to two for instance, there is a fast on gas rush, but as you stay there a while it slows down since the gradient factor powering the movement is lessening, like charging a battery.
On gassing is easy - you do not blow gas into the tissues in bubble form by on gassing. Off gassing is more tricky, as you want to prevent bubble formation in the tissues at all depths, and in the blood deep. Off gassing in bubble form into the blood is extremely efficient time wise and allows faster decompressions that avoid building in one tissue while eliminating in another, but this is for non shunt people only. Unfortunately for the shunts, the greatest incidence of bubbling into the venous blood occurs after you get out of the water.

It takes a certain amount of time to circulate the blood, maybe about two minutes, and it can take as much as five to get gas in solution to begin to come out of solution in bubble form in the tissues or into the blood in response to a reduction in pressure. Most of the short on/offs are handled well by the body in terms of outright pain or obvious symptoms, but they may cause the body's immune system to respond to the insult that is actually occurring, and uneven off gassing from sensitive tendon attachment points and live bone surfaces as well as certain dense muscle may not be able to accommodate the super short cycles. Tissues that are hard to on gas are not as much of an issue on minimum deco, only on longer exposures.

We have found that the short schedules under 30 minutes are inaccurate predictors. What we do is set a shape for the deco as if it were a longer dive, complete with starting the stops at 80% of the profile in ATA's, and merely go to a minimum reading for each stop. The minimum deep stop is 20 seconds at each ten feet, which is effectively 30 feet per minute plus the moving time. The max for these is five minutes for saturation ( or anything within 85% of technical saturation, which I assume to occur at 150 minutes bottom time ).The stops indicated by the shape of the deco curve higher up need to be done to a minimum number, like 1 minute for the deeper ones and then more when the gas switches come in. Give the gas a chance to work, then go back to the curve with the 1-2 or 3 minute stops. As you get higher up, the fact that you did the deeper part more meticulously will allow some abbreviation in the shallower steps.

In any of these decompressions, do your calculation and then discard the ten foot stop completely from the figures - throw it and its time out completely - that is total bullshit. Then ask yourself how much time do I need at 20. The answer is, enough to make it work if I did the deeper steps correctly. Two minutes on oxygen is not doing anything, ten is more like it. However, what you want to do is incorporate a slow ascent rate into the last 20 feet of the dive, so what was the 20 foot stop should be eased up from 20-6 in a steady motion after you have sat at 20 and allowed a full circulation of the blood and the effects of the pressure change and the gas to begin to work and a relative time based on you real bottom time where the total of the 20 plus ascent to surface is at least equal to your bottom time, again assuming you have done the other steps correctly. Do not waste a bunch of pyramided time at steps where there is little partial pressure advantage, use the gradient more in these cases, again assuming you have conscientiously done the lower steps.

Don't be in any big hurry to get up from the bottom, and do not be in any big hurry to get up from 30 feet to the surface. These two areas need careful attention.

I think that if you discard the 10 foot silliness in any program and the unnecessary time, then put some of that time back into the correct shape and strategy, you will not only prevent the out right DCS, you will prevent the sub clinical DCS and the immune responses.

If you execute deco correctly and are in good shape and have no preconditions, you should be clean and ready for anything 30 minutes after you get out of the water. You can tell if you have not done what I am saying here, you will not feel so good. It will be subtle, but if you want to test it, try going for a run. If you are immediately short of breath, you blew the deco. If you can rock, you did it right. If you get bent trying this, then tough luck, blame JJ. In reality, you will feel a little sluggish and heavy just putting your gear away if you did an inadequate deco.

Now, if there are questions that can help with the understanding, bring them on. If anyone wants to argue with me, save your breath and be ready to show me your logbook, and don't bother with the IANTD, TDI, PADI, DAN or any other form of nonsense that is floating around out there. Nobody understands this like I do, and nobody can execute it like I do, and nobody has done it this way for as long as I have, not even my own team. I know for a fact that this is not only correct, it is correct beyond a shadow of a doubt. I remember getting Exley to get out of the water with me at Wakulla one time on my schedule. That was easy to do with him because he responded very well to peer pressure - I could get him to do anything I dreamed up. He spent the next four hours in the lobby of the Lodge getting FSU to Doppler him over and over just waiting for the big bends hit - never happened. That was nine years ago. We have really perfected it now.


ATB

Mark Chase

[adam]

Hi all,

Very briefly, I would like to disassociate DIR from what Mark has said in his first post above-none of it has anything whatsoever to do with DIR "on the fly" deco. Bottom time is unlimited, depth as well-and it is really very simple. I understand how to do it so it must be! However, the information must be used in the context in which it is intended. This cannot be done in a forum or newsgroup-and it would be wrong for me or anyone else (who actually knows what it is about) to attempt to do so.

What you have in Marks first post is a collection of what he thinks it is, not what it is at all! For information-the Britannic 99 trips dives were all planned "on the fly", and as I have already stated on another post, Mark's insistance that because Decoplanner is a GUE product it must therefore be a DIR item-without using it in a DIR context/mind set, where we modify and change profiles to suit conditions, individual physiologies etc. is proof that he really doesn't understand it or DIR very well at all!

Maybe not so briefly!

Adam