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YD's Caribbean Outpost
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Greetings all.

I wonder if anyone can point me in the right direction. I had a discussion with one of my colleagues recently about the benefits/disadvantages of staying on a % of Helium when changing to a deco gas. Example: doing a 200 foot dive on 19/40, and then changing to 36% when appropriate, compared to another possibility of changing to something like 50/20....(again, when the depths are safe). Going on to a richer deco gas (e.g. 80% or whatever) again when appropriate.

The conversation was interesting, but I couldn't come to any conclusions about the benefits or disadvantages of staying on Helium, albeit in small quantities to reduce the gradient change from a deep dive through to a deco profile.

I work for a dive centre, so cost is not an issue for any mixes, but for my own personal education, I would appreciate any thoughts on the topic, both benefits, disadvantages, current opinions etc.

Thanks in advance - I genuinely would like to hear people's thoughts.

Steve
 

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Reading...

I would start with Yount's chapter on page 90 and work my way out from there...

Isobaric Inert Gas Counterdiffusion.
Lambertsen et. al. 1979
RRR ID: 4337
 

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A short fat well off crap cave diver. Likes wrecks
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The above is prety heavy going

Take a look at this:

Decompression myths and mistakes

My2p The nitrogen spike is the primary issue on deco. Even the GUE boys are gas switching from 18/45 to 50%. A lot of the thing about putting Helium in the deco mix is more to do with making the damed stages float so they can rig them all on the left.

Personally on OC I had 3 deco gases. 21/35 32% and 80% I never had any issues using these mixes and switching for what ever back gas. Then again I am jo average tecy diver not a 120m monster dive freak so I haven't pushed it.

When i switched to CCR I dived helium in the mix all the way from the bottom out of the water. I felt absolutely awful doing this.. Now i run pure 02 for at least the last 20mins of deco and I feel fine again after the dive.

This proves nothing but its my personal experience and the same experience shared by my buddy at that time.

ATB

Mark Chase
 

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The above is prety heavy going

Take a look at this:

Decompression myths and mistakes

My2p The nitrogen spike is the primary issue on deco. Even the GUE boys are gas switching from 18/45 to 50%. A lot of the thing about putting Helium in the deco mix is more to do with making the damed stages float so they can rig them all on the left.

ATB

Mark Chase

I would have to agree with this the primary reason behind the He in deco mix is to eliminate the Nitrogen spike, but thats if you believe ICD and i have spoken to a few that think it's just myth.

I would say that i don't think the reason GUE put He in the tins is to make them float :), it's more to do with the set deco profiles they use and the curve it produces gas curve as well!

Its no good having a good deco curve only to have the gas curve go up and down on gas switches like a whores draws on pay day!

the reading that mark has links to is very good but you need to make your own judgement as this is all theory V Planner only works for me on +2 conservatism which is what i set the VR3 to.

I do use V planner for indications of Nitrogen spikes when looking at dives and adjust gases accordingly, but i use optimum gas for the depth and not just standard gases

Graham
 

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I would say that i don't think the reason GUE put He in the tins is to make them float :), it's more to do with the set deco profiles they use and the curve it produces gas curve as well!

Graham


Check out DIRX on threads about using stages. Loads of referance in there to putting helium in the tank to trim it out.


ATB

Mark Chase
 

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Good post Graham.

It is an interesting question.

I've been trying to find out a little more about the TBG algorithm used in the Decoceck calcs which checks for this.

The software didn't like it when I scheduled a switch from 35/25 to 50 per cent. The addition of 10 per cent helium made it happy but can't say I'm convinced of the need on short exposure dives.

I've switched from 15/55 to 50 per cent on ocean dives without issue but these were not that lengthy so would be cautious to say that it was proof of anything. All standard deco gasses below 21 contain helium for various reasons, trimming out tanks is not a driving factor.
 

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Check out DIRX on threads about using stages. Loads of referance in there to putting helium in the tank to trim it out.


ATB

Mark Chase

If i get caught there i turn to stone and the PC bursts in to flames :D

Graham
 

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Good post Graham.

All standard deco gasses below 21 contain helium for various reasons, trimming out tanks is not a driving factor.

I was referring to the idea of putting Helium in the 50% tank (21m tank)to help trim it out when it had to have more than 160 bar in it.


After a chat with Mark at the dive show a few years ago I started running 32/30 for deep deco mix. But it only lasted a few dives as i went CCR shortly after.

I don't see the old idea of going back gas and on to 32% as being dangerous but i do agree it was probably putting unnecessary stress on the profile. The Nitrogen is controling the over all deco time not the helium, so as long as the final gas has no helium in it i dont see a problem.


ATB

Mark Chase
 

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The He in the 21m stage does help in float a bit more but this has nothing to do with why the Helium.

The addition of the gas was based on how a group (WKPP) felt post dive , and specifically Jarrod Jablonski.

To tell the story properly and so get a sense of some perspective, I will have to go back and start with a bit of history.

Back in the mid-nineties the group were using a range of gases including, some deeper mixes, but also Air, Nitrox and O2 for deco. After some of the longer dives 20 odd hours they had a number of post dive symptoms - remember all the deco schedules were experimental - there is nothing in the public domain that handles this and the commercial boys use chambers and many days to deco.

So effectively we are looking at almost a SAT dive - the post dive syptoms that were experienced were as follows (this excludes any real bends)

Significant post dive fatigue, very much Flu like syptoms, especially the day after.
Chest tightness and dry throat etc, due to lungs being fried due to long exposures on O2 (20 minutes on 5 minutes off) for many hours.

The deco tables being used were based on some stuff that Bill Hamilton produced, which were then used and modified over time. But they included deep stops, but at the time were probably more orientated towards Buhlmann rather than the bubble models.

JJ did not like the way he felt after doing the long dives, so started experimenting with changing gases. The first gas to go was Air, due to a variety of reasons. Firstly narcosis, but much more importantly nitrogen is a difficult to decompress from effectively due to its lipid solubility (affinity for the fat)

After removing the air, and increasing the HE content of most of the dive gase/deco gases (same deco) there was a significant imrovement in well being post dive, however still with Pulmonary problems due to the O2.

JJ then started experimenting with He in the 36m and 21m stages, and again noticed by then a complete lack of flu like syptoms, but still pulmonary.

They started cutting the time on O2 gradually and eventually arrived at 12 mins on O2 and then 6 minutes off - with the deco clock still running. This left them with no pulmonary problems at all.

Thet then started reducing the overall O2 time, and found that they could do significantly less with no adverse effects.

Obviously these are very unusual dives and in no way the norm, however all of us can learn from their experiences.

In summary Nitrogen is nasty and best avoided as much as possible. He is good for us as its inert (non narcotic) and is much easier to decompress from. Prolonged O2 exposure even with air breaks has to be managed and 20 minutes on 5 minutes off is not enough to stop the lungs getting fried. Despite the increases in Helium and the significant times involved there have been no instances of ICD (Isobaric Counter Diffusion).


Andy
 

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The He in the 21m stage does help in float a bit more but this has nothing to do with why the Helium.

The addition of the gas was based on how a group (WKPP) felt post dive , and specifically Jarrod Jablonski.

To tell the story properly and so get a sense of some perspective, I will have to go back and start with a bit of history.

Back in the mid-nineties the group were using a range of gases including, some deeper mixes, but also Air, Nitrox and O2 for deco. After some of the longer dives 20 odd hours they had a number of post dive symptoms - remember all the deco schedules were experimental - there is nothing in the public domain that handles this and the commercial boys use chambers and many days to deco.

So effectively we are looking at almost a SAT dive - the post dive syptoms that were experienced were as follows (this excludes any real bends)

Significant post dive fatigue, very much Flu like syptoms, especially the day after.
Chest tightness and dry throat etc, due to lungs being fried due to long exposures on O2 (20 minutes on 5 minutes off) for many hours.

The deco tables being used were based on some stuff that Bill Hamilton produced, which were then used and modified over time. But they included deep stops, but at the time were probably more orientated towards Buhlmann rather than the bubble models.

JJ did not like the way he felt after doing the long dives, so started experimenting with changing gases. The first gas to go was Air, due to a variety of reasons. Firstly narcosis, but much more importantly nitrogen is a difficult to decompress from effectively due to its lipid solubility (affinity for the fat)

After removing the air, and increasing the HE content of most of the dive gase/deco gases (same deco) there was a significant imrovement in well being post dive, however still with Pulmonary problems due to the O2.

JJ then started experimenting with He in the 36m and 21m stages, and again noticed by then a complete lack of flu like syptoms, but still pulmonary.

They started cutting the time on O2 gradually and eventually arrived at 12 mins on O2 and then 6 minutes off - with the deco clock still running. This left them with no pulmonary problems at all.

Thet then started reducing the overall O2 time, and found that they could do significantly less with no adverse effects.

Obviously these are very unusual dives and in no way the norm, however all of us can learn from their experiences.

In summary Nitrogen is nasty and best avoided as much as possible. He is good for us as its inert (non narcotic) and is much easier to decompress from. Prolonged O2 exposure even with air breaks has to be managed and 20 minutes on 5 minutes off is not enough to stop the lungs getting fried. Despite the increases in Helium and the significant times involved there have been no instances of ICD (Isobaric Counter Diffusion).


Andy
so not wanting to argue but do you base your whole decompression theory on these couple of divers playing with how they feel? or is there more to this with medical references and survey reports on effects.

i saw a post once that said there is no such thing as a undeserved bend after the research i have done I'm inclined to believe it, new studies into pure O2 in English waters are in there infancy, but the initial reports don't look that good, factors like cold water elevated stress levels etc all play a part regardless of how small.

and alveoli shunts are being looked at more closely now than ever before. the problem we have here is and i quote "very little study material I.E. patients" because the use of pure O2 as the last gas is used by a small minority, however rebreather divers are starting to show with the same problems due to the use of 100% in the final part of the dive

Graham
 

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so not wanting to argue but do you base your whole decompression theory on these couple of divers playing with how they feel? or is there more to this with medical references and survey reports on effects.

i saw a post once that said there is no such thing as a undeserved bend after the research i have done I'm inclined to believe it, new studies into pure O2 in English waters are in there infancy, but the initial reports don't look that good, factors like cold water elevated stress levels etc all play a part regardless of how small.

and alveoli shunts are being looked at more closely now than ever before. the problem we have here is and i quote "very little study material I.E. patients" because the use of pure O2 as the last gas is used by a small minority, however rebreather divers are starting to show with the same problems due to the use of 100% in the final part of the dive

Graham
Once you get beyond recreational limits in diving there is very little statistically to base any of our decisions upon.

As has already has been stated by many what works works, especially if it works for you. We really do not understand that much about deco, and significantly less about the O2 tox mechanism and exactly why it happens. We not not really understand narcosis etc

I think that if you are diving to 80+ meters for over 6 hours, plus the associated deco, and have dramatically reduced the decompression time, flying in the face of convention, then yes we have something to learn from their experiences . I am not pretending that our shorter bottom times come anywhere near some of this stuff, but they are a subset without question.

As for the use of O2 for deco, it has gone on for many years. Personally I am unaware of any tox incident that occured at 6m that could be attributed directly to breathing O2. Most have occured due to incorrect gas switches or breathing to high a PPO2 throughout the dive. Afterall what is the greatest risk in diving toxing and drowning or getting bent.

Andy
 

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.. however rebreather divers are starting to show with the same problems due to the use of 100% in the final part of the dive

Graham
Hi

Rebreathers have a higher co2 content to manage too, and as you know co2 does not help when it comes to oxygen problems, and in the little I have read of this shunt thingy, co2 is significant.

I would be interesting to hear of any cases where rebreather divers have suffered from shunts due to flushing the loop with o2, especially on short wreck dives.

Andy
 

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just curious what plan would you chose if you had to

plan A



plan B



Graham
 

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A short fat well off crap cave diver. Likes wrecks
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Hi

Rebreathers have a higher co2 content to manage too, and as you know co2 does not help when it comes to oxygen problems, and in the little I have read of this shunt thingy, co2 is significant.

I would be interesting to hear of any cases where rebreather divers have suffered from shunts due to flushing the loop with o2, especially on short wreck dives.

Andy


The total co2 flow through a functonal Inspiration scubber is zero. I nominate the Inspiration scrubber as an example as there is technical referance for this.

Co2 issues exist in OC as they do in CCR. The co2 is due to the dead air space in the void imidiatly in front of the mouthpiece on the regulator or mouthpiece on each system. A CCR that is letting C02 through has a fault or the scrubber is exausted.

ATB

Mark Chase
 

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A short fat well off crap cave diver. Likes wrecks
Joined
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15,343 Posts
The He in the 21m stage does help in float a bit more but this has nothing to do with why the Helium.

The addition of the gas was based on how a group (WKPP) felt post dive , and specifically Jarrod Jablonski.

To tell the story properly and so get a sense of some perspective, I will have to go back and start with a bit of history.

Back in the mid-nineties the group were using a range of gases including, some deeper mixes, but also Air, Nitrox and O2 for deco. After some of the longer dives 20 odd hours they had a number of post dive symptoms - remember all the deco schedules were experimental - there is nothing in the public domain that handles this and the commercial boys use chambers and many days to deco.

So effectively we are looking at almost a SAT dive - the post dive syptoms that were experienced were as follows (this excludes any real bends)

Significant post dive fatigue, very much Flu like syptoms, especially the day after.
Chest tightness and dry throat etc, due to lungs being fried due to long exposures on O2 (20 minutes on 5 minutes off) for many hours.

The deco tables being used were based on some stuff that Bill Hamilton produced, which were then used and modified over time. But they included deep stops, but at the time were probably more orientated towards Buhlmann rather than the bubble models.

JJ did not like the way he felt after doing the long dives, so started experimenting with changing gases. The first gas to go was Air, due to a variety of reasons. Firstly narcosis, but much more importantly nitrogen is a difficult to decompress from effectively due to its lipid solubility (affinity for the fat)

After removing the air, and increasing the HE content of most of the dive gase/deco gases (same deco) there was a significant imrovement in well being post dive, however still with Pulmonary problems due to the O2.

JJ then started experimenting with He in the 36m and 21m stages, and again noticed by then a complete lack of flu like syptoms, but still pulmonary.

They started cutting the time on O2 gradually and eventually arrived at 12 mins on O2 and then 6 minutes off - with the deco clock still running. This left them with no pulmonary problems at all.

Thet then started reducing the overall O2 time, and found that they could do significantly less with no adverse effects.

Obviously these are very unusual dives and in no way the norm, however all of us can learn from their experiences.

In summary Nitrogen is nasty and best avoided as much as possible. He is good for us as its inert (non narcotic) and is much easier to decompress from. Prolonged O2 exposure even with air breaks has to be managed and 20 minutes on 5 minutes off is not enough to stop the lungs getting fried. Despite the increases in Helium and the significant times involved there have been no instances of ICD (Isobaric Counter Diffusion).


Andy


Before any one gets too over excited about this....


Fact is GUE don't specify helium in their standard gas list for the 21m 50% bottle.

People use it to help trim out the tanks.

The use of Helium in the 50% bottle and the burning of the lungs are two separate issues. The ONLY way to stop burning the lungs is to reduce CNS exposure or to reduce the level of 02.

I am fully supportive of the research from the WKPP in this area. Using pure 02 over long decos causes mucus to build up on the lungs. This mucus is there to protect the lungs from the 02.

The use of air breaks on rich helium mixes and low 02 gives the lungs a rest , slows the production of mucus and allowed the 02 to carry on the process of off gassing it would otherwise be prevented from doing by the mucus.

All good stiff but not particularly relevant to the helium except for the fact HE is easy to breath.

If Andy would like to comment on my statement it is as follows.

99% of us don't do dives where its an issue. QED the ONLY reason for 99% of us to put Helium in the 50% bottle is to trim out the tank.

With regard to the Nitrogen spike? If your doing a dive where the gas switch from back gas to 50% causes a significant spike then you should have a third deco gas. GUE say 35/25






ATB

Mark Chase
 
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Co2 issues exist in OC as they do in CCR. The co2 is due to the dead air space in the void imidiatly in front of the mouthpiece on the regulator or mouthpiece on each system. A CCR that is letting C02 through has a fault or the scrubber is exausted.

ATB

Mark Chase

Yes, and the dead space present in a rebreather loop is larger than that on an OC reg, as on a rebreather the deadspace is surely the space between the one way valves in the loop.

I'm not sure that it makes any difference anyway, but was investigating why rebreather divers where suddenly suffering from something that OC divers have been doing for years with no significant numbers suffering this complaint on short exposures.

Andy
 
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