Diluent Switching why not?

rossh · 19th December 2006, 05:51

Quote: (Originally Posted by sabgia)

To all/any who have a potential contribution to this post, I ask

1) Is reduced deco obligation not reduced risk? (less CNS, OTU, and sooner to bed with wife/girlfriend/boyfriend).

Maybe, maybe not. There are situations where the planning tools and the reality of physiology diverge. The IBCD problem is a good example with these large flushes and associated big swings in ppInerts. The program can accomplish them easily, dropping a big chunk of deco off, but the body may not be able to keep up. This is why when DCS occurs here, it strikes hard. Hence you need to avoid this whole problem area.

Quote: (Originally Posted by sabgia)

2) Given the tried and proven OC

procedures for switching gas, is it not operationally feasible to do likewise on Rebreather (those of us with MGB)?

Granted the logistical complexity of all the bail out gas, but I won't go without adequate amounts and quality and a plan on how to use it.

3) Assuming you organize adequate bail-out, is there not a significant synergy in using it to flush your loop at appropriate levels even when you are not bailing out (assuming the profile and gas induces a safe time advantage).

The OC diver is limited in the ranges of mixes he can swap too, and the logistics of carrying that mix along. It is somewhat self regulating for most dives. Typically a OC diver needs to be on 100m+ type dives to get into these problems.

The CCR diver has a larger selection of inspired mixes possible, and with the typically larger dives carried out and increased deco obligation, he is subject to the problems of IBCD more frequently.

Regards

Gilles · 19th December 2006, 06:12

Quote: (Originally Posted by rossh)

Maybe, maybe not. There are situations where the planning tools and the reality of physiology diverge. The IBCD problem is a good example with these large flushes and associated big swings in ppInerts. The program can accomplish them easily, dropping a big chunk of deco off, but the body may not be able to keep up. This is why when DCS occurs here, it strikes hard. Hence you need to avoid this whole problem area.

Regards

Hi Ross;

What if the ppInerts swing is kept to a limited amount (like +0.5 ATA dPN2)? Aknowledged is the hazard of big swings in ppInert.

A week or so ago I watched a Discovery channel documentry of a 70m wreck dive in the Dardanelles (Turkey) using Hx 15/85. At some point in the decompression (depth not stated), the diver switched to Air, followed by a chamber session once on surface.

Quote: (Originally Posted by rossh)

Maybe, maybe not. There are situations where the planning tools and the reality of physiology diverge. The IBCD problem is a good example with these large flushes and associated big swings in ppInerts. The program can accomplish them easily, dropping a big chunk of deco off, but the body may not be able to keep up. This is why when DCS occurs here, it strikes hard. Hence you need to avoid this whole problem area.

Regards

Again, what if the flushes are sufficiently small (e.g. 0.5 ATA)?

It seems there are several instances of major flushes (I mean in the order of + 3-6 ATA ppN2), some with disastrous consequences.

There is a significant incentive in terms of decompression time, even when using very limited dPN2. The example I illustrated in the above keeps all ppInert changes to within 0.5 ATA.

G

dantheman · 19th December 2006, 22:46

Quote: (Originally Posted by rossh)

The CCR diver has a larger selection of inspired mixes possible, and with the typically larger dives carried out and increased deco obligation, he is subject to the problems of IBCD more frequently.

Ross,

While the first half of this sentence is true, I don't think many people would agree with the last clause.

IF the principal method of avoiding IBCD is to limit spikes in ppInert, then a rebreather is THE tool. It could have been made for this precise purpose.

If on CCR, you switch gasses without care, then you have simply taken on the (unnecessary) risks of OC deco.

I repeat my caveat that extreme exposures and (likely) HeOx will militate against this, but only somewhat.

On the other hand, if IBCD is really just a miscalibration of compartment 8 ...

--dan

Gilles · 20th December 2006, 08:14

I thought it would also be useful to illustrate the ppInert swings that the above illustrated deco time advantages are associated with.

The pN2 is the red line. Note that this is managed ppInert swinging.

rossh · 20th December 2006, 23:00

Quote: (Originally Posted by dantheman)

Ross,

While the first half of this sentence is true, I don't think many people would agree with the last clause.

--dan

Hmmm ....OK I'll change that then to read..

..he can be subjected to the problems of IBCD more frequently, if he chooses to use agressive Inert pp swings available to him.

Regards

19th December 2006, 05:51	#11 (permalink)
rossh Custom Title Allowed! Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Jul 2005 Location: Canada Posts: 106	Re: Diluent Switching why not? Quote: (Originally Posted by sabgia) To all/any who have a potential contribution to this post, I ask 1) Is reduced deco obligation not reduced risk? (less CNS, OTU, and sooner to bed with wife/girlfriend/boyfriend). Maybe, maybe not. There are situations where the planning tools and the reality of physiology diverge. The IBCD problem is a good example with these large flushes and associated big swings in ppInerts. The program can accomplish them easily, dropping a big chunk of deco off, but the body may not be able to keep up. This is why when DCS occurs here, it strikes hard. Hence you need to avoid this whole problem area. Quote: (Originally Posted by sabgia) 2) Given the tried and proven OC procedures for switching gas, is it not operationally feasible to do likewise on Rebreather (those of us with MGB)? Granted the logistical complexity of all the bail out gas, but I won't go without adequate amounts and quality and a plan on how to use it. 3) Assuming you organize adequate bail-out, is there not a significant synergy in using it to flush your loop at appropriate levels even when you are not bailing out (assuming the profile and gas induces a safe time advantage). The OC diver is limited in the ranges of mixes he can swap too, and the logistics of carrying that mix along. It is somewhat self regulating for most dives. Typically a OC diver needs to be on 100m+ type dives to get into these problems. The CCR diver has a larger selection of inspired mixes possible, and with the typically larger dives carried out and increased deco obligation, he is subject to the problems of IBCD more frequently. Regards __________________ Regards, Ross Hemingway V-Planner VPM-B Nitrox Trimix CCR Deco planning for Technical Divers www.v-planner.com Last edited by rossh : 19th December 2006 at 05:53.
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19th December 2006, 06:12	#12 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 762	Re: Diluent Switching why not? Quote: (Originally Posted by rossh) Maybe, maybe not. There are situations where the planning tools and the reality of physiology diverge. The IBCD problem is a good example with these large flushes and associated big swings in ppInerts. The program can accomplish them easily, dropping a big chunk of deco off, but the body may not be able to keep up. This is why when DCS occurs here, it strikes hard. Hence you need to avoid this whole problem area. Regards Hi Ross; What if the ppInerts swing is kept to a limited amount (like +0.5 ATA dPN2)? Aknowledged is the hazard of big swings in ppInert. A week or so ago I watched a Discovery channel documentry of a 70m wreck dive in the Dardanelles (Turkey) using Hx 15/85. At some point in the decompression (depth not stated), the diver switched to Air, followed by a chamber session once on surface. Quote: (Originally Posted by rossh) Maybe, maybe not. There are situations where the planning tools and the reality of physiology diverge. The IBCD problem is a good example with these large flushes and associated big swings in ppInerts. The program can accomplish them easily, dropping a big chunk of deco off, but the body may not be able to keep up. This is why when DCS occurs here, it strikes hard. Hence you need to avoid this whole problem area. Regards Again, what if the flushes are sufficiently small (e.g. 0.5 ATA)? It seems there are several instances of major flushes (I mean in the order of + 3-6 ATA ppN2), some with disastrous consequences. There is a significant incentive in terms of decompression time, even when using very limited dPN2. The example I illustrated in the above keeps all ppInert changes to within 0.5 ATA. G __________________ Gilles http://www.dirrebreather.com Last edited by Gilles : 20th December 2006 at 00:47.
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19th December 2006, 22:46	#13 (permalink)
dantheman Emoticonoclast Current Rebreather/s: Sport Kiss rEvo Other Rebreather/s: Classic Kiss rEvo Join Date: May 2005 Location: NorthEast USA Posts: 393	Re: Diluent Switching why not? Quote: (Originally Posted by rossh) The CCR diver has a larger selection of inspired mixes possible, and with the typically larger dives carried out and increased deco obligation, he is subject to the problems of IBCD more frequently. Ross, While the first half of this sentence is true, I don't think many people would agree with the last clause. IF the principal method of avoiding IBCD is to limit spikes in ppInert, then a rebreather is THE tool. It could have been made for this precise purpose. If on CCR, you switch gasses without care, then you have simply taken on the (unnecessary) risks of OC deco. I repeat my caveat that extreme exposures and (likely) HeOx will militate against this, but only somewhat. On the other hand, if IBCD is really just a miscalibration of compartment 8 ... --dan
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20th December 2006, 23:00	#15 (permalink)
rossh Custom Title Allowed! Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Jul 2005 Location: Canada Posts: 106	Re: Diluent Switching why not? Quote: (Originally Posted by dantheman) Ross, While the first half of this sentence is true, I don't think many people would agree with the last clause. --dan Hmmm ....OK I'll change that then to read.. ..he can be subjected to the problems of IBCD more frequently, if he chooses to use agressive Inert pp swings available to him. Regards __________________ Regards, Ross Hemingway V-Planner VPM-B Nitrox Trimix CCR Deco planning for Technical Divers www.v-planner.com
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