Request for comments on article - mixed OC / CCR teams

[Gareth J]

Rebeathers and Scientific Dive Proceedings 2015/16: from what I’ve read, the most useful contribution was the gas density calculations, gradient factors, and for potential CCR students to seek instructors limited to teaching a maximum of 2 Rebreathers. The implied suggestion for a CCR diver to hand over his bailout bottle to an OC diver would be met with skepticism. CCR divers have a slower rate of ascent compared to OC divers, therefore, OC divers do not control the dive when diving mixed teams. I also got the impression the scientists were more interest in funding than anything else.

Can you explain this post?
It seems a bit jumbled.

1. Gas Density Calculations, and Gradient Factors Have been around since before CCR.
However, it is certainly true that since CCR more scientific papers appear to have been written.
The difference with CCR is that the gas delivery is at ambient, rather than at the interstage pressure. This would make little difference on the exhale, but some difference on the inhale. There is some talk that back mounted counter lungs increase the risk of IPO, due the requirement to 'draw' a breath from the lower pressure on the divers back compared with the same or higher pressure on the divers front with the different designs of counter lungs. Hence the increased interest in gas density. Although one of the issues with gas density on OC was the failure to fully exhale properly, and the issue of CO2 build up. So another issue relating to gas density.
We certainly discussed this at some length when I did my OC trimix certification way back in the 90's.

Gradient Factors are interesting. This has been going backwards and forwards for 20-30 years. The bubble model theories seem to have been debunked in more recent research. Both the deep stop philosophy and the bubble models are out of favour, against the preferred trend of get shallow, and have an extended stop in the shallower water.
In truth I liked the deep stop, because it gave me time on the gas switch back to the travel mix. I never really got into the bubble model approach, and would then ascend reasonably shallow from the deep stop.

2. CCR Tuition
To have more than two students with any instructor, especially on task/technical orientated diver training is foolhardy in the extreme. I can't believe any reputable technical instructor would do this, at least not without additional support divers. Even teaching entry Scuba, I prefer a maximum to two to one.
None of the CCR courses I have done have allowed for more than two students per instructor. I have seen groups with the primary instructor and a second instructor. Or an instructor doing shallow water skills with a number of already qualified CCR divers. (The same on tech courses, where there are a group of already qualified divers doing skills in 6m with an instructor). But certainly not on the deeper dives.

3. Handing off Gas
I don't understand this point. Most advanced CCR divers are taught and practice handing off gas. Especially on extremely dives where you are handling team bailout.
I certainly have no problem handing off gas at the end of a dive (if I have a working CCR). It really depends on the complexity of the dive. The feature Mike has written about is basic recreational OC/CCR dives, minimal decompression.
In that case, it is highly unlikely that the CCR diver has any decompression stops, or minimal stops. The controlling factor being the OC diver. In that case it is no big issue too had off the bailout. In that case, if there is a subsequent problem, you can bailout to BOV and make a direct ascent to the surface.
I seldom get the opportunity to dive with CCR divers at the moment, so most of the dives I do are with OC divers. Granted most are twinset, or, at worst, single + pony. But I carry case for either of us.

4. Who controls the dive.
Descent and Ascent are complex periods for CCR divers. So as Mike says, they tend to control the rate of ascent and descent. However, the controlling factor outside of this is always the OC diver. They have a limited amount of gas, and they are significantly more likely to have a decompression obligation than the CCR diver. So in both cases the OC diver controls depth, time and decompression stops.
Because of this, if I dive with an OC diver, I normally have one computer set to OC, and for the gas mix of my buddy. Then I have a rough idea of what their commitments are in terms of deco.


Personally, my big thing for OC buddies is :
1. Know where you are getting emergency gas from (stage), and how.
2. Know how to switch the CCR divers BOV to OC or close the mouth piece on a standard mouth piece.
3. Know how to inject DIL
4. Know how to dump the CL.

After that I'm on my own.

 

[Scuba Client]

CCRs have been around for more than a century. I’m specifically talking about 2 dive journals. I understand the WOB for CCR divers and how not being in trim affects it. Gas density is a non-issue for divers with good VO2 Max. There are divers who cannot walk up stairs without huffing and puffing. Professor Mitchell stated: if the US Navy had used the bubble model in a more conservative manner, it would be similar to the gas model. Perhaps you should read it for yourself. Gradient factors work. What you set it to is your belief: too shallow or too deep. I was agreeing with the journal that any Instructors who teach more than 2 particular CCRs should be avoided. You can’t be an expert on 10 CCRs. My point is that no CCR diver in their right mind is going to pass their bailout bottle to an OC, who could panic and shoot to the surface, next gas switch, or be caught in a current, leaving the CCR diver without bailout gas, should they need it at depth. They will hand over their regulator and stay with you until your next gas switch. Why don’t you write their dive plan on a slate, if you’re that concerned? CCR divers just ask what your TTS. Both CCR and OC set depth limits and ascent speed accordingly. The mixed team article was written for that specific reason. Some divers are ahead of their time. The others are still playing catch up.

 

[Gareth J]

CCRs have been around for more than a century. I’m specifically talking about 2 dive journals. I understand the WOB for CCR divers and how not being in trim affects it. Gas density is a non-issue for divers with good VO2 Max. There are divers who cannot walk up stairs without huffing and puffing. Professor Mitchell stated: if the US Navy had used the bubble model in a more conservative manner, it would be similar to the gas model. Perhaps you should read it for yourself. Gradient factors work. What you set it to is your belief: too shallow or too deep. I was agreeing with the journal that any Instructors who teach more than 2 particular CCRs should be avoided. You can’t be an expert on 10 CCRs. My point is that no CCR diver in their right mind is going to pass their bailout bottle to an OC, who could panic and shoot to the surface, next gas switch, or be caught in a current, leaving the CCR diver without bailout gas, should they need it at depth. They will hand over their regulator and stay with you until your next gas switch. Why don’t you write their dive plan on a slate, if you’re that concerned? CCR divers just ask what your TTS. Both CCR and OC set depth limits and ascent speed accordingly. The mixed team article was written for that specific reason. Some divers are ahead of their time. The others are still playing catch up.

It is quite difficult to respond to your post because it is a bit jumbled but I will try.

Before we start. I have been diving CCR since around 2004. Prior to that I was diving in OC/CCR teams as an OC diver.

When I was diving OC with CCR divers, we where predominantly doing mixed gas or ERD type dives. So each diver carried all their decompression gas, and were on twinsets, so in theory fully redundant. In addition, there was a stage at the bottom of the shot, a travel at 30m, and two or three cylinders of deco gas on the trapeze. But his was group diving so not really a surprise.

MOD1 has a simple rule, when in doubt bailout.
MOD2/3 has a rule, stay on the loop unless it is compromised.
MOD1 is simple recreational diving, max depth say 40m, deco no more than 30 minutes. So generally a single bailout cylinder.
MOD3 is deep trimix, you are carrying a bottom bailout (slightly hot), then one or two stages for decompression. It may well involve team bailout.

(Team Bailout) - you come off the loop you need one, two, or three other CCR divers to get you back to the surface because you require their OC gas as well as your own, unless you can pick it up on the shot/trapeze, or are happy that the drop cylinders will reach you.
Generally, you come off the loop onto your bottom bailout, signal the team and abandon the dive. Start the ascent, at 50% OC gas in the bottom mix you do a cylinder exchange with a team member, taking his full cylinder. He rotates to a team member with full OC cylinders and you rotate to the next team member with full cylinders. Continuing the ascent the next cylinder switch will probably be deco gas (yours). Then at 50% you hand it off and take on new gas, at 50% of that, you hand off and take on gas. Once you are shallow there are also sorts of potential exit plans, from richer deco gas being provided from the surface etc.​

The other option is to go SCR, where you flush the loop. Breath for five breaths, vent the last breath out of the loop, then top up again. i.e Gas extending. Although I can do this, and do on occasion do for practice, I do find it hard work.
Full bailout on a deep dive with long bottom times becomes complex. With the huge physiological issue that you are not self contained. i.e you are reliant on others.

Most of my dives over the last few years for me have been in the MOD1 limits. Predominantly, because I am diving with OC buddies. They generally are on twinsets, or have a pony. The depth is probably 40m max. Deco is unlikely to exceed 30 minutes. What I call recreational.
We really are having a bad day if he has a twinset failure and I have a CCR failure.
A gas failure for him means he takes the long hosed regulator off the bailout cylinder. Then we start the ascent. I have the option to hand off the stage totally to him/her at this point. If I do, I am now reliant on the CCR working perfectly, or the gas available in the onboard DIL cylinder and the BOV. Or SCR mode.
If I don't hand off the stage, I still have the added option of plugging the bailout cylinder back into the CCR, so that I can share the bailout cylinder.
Historically I carry bailout as a self contained unit so it can be handed off to a buddy if required. (i.e. MOD 3 team diving).

To your points
WOB
You are correct, Work of breathing, counterlung position and diver attitude in the water does effect this. There is actually a European Standard for CCR's which dictates the maximum WOB allowed for any unit sold in the EU (and the UK).
The original reason the AP had over the shoulder counter lungs was to get the WOB down. It took some time before they offered rear mounted C/L because with rear mounted counter lungs the WOB is going to be higher. Having them close to the divers body (i.e. minimal distance above the lung when the diver is horizontal) makes a huge difference.
As I said in my earlier post, there is some evidence to suggest high WOB promotes IPO.

decompression models
There are some good features on the DAN site from Professor Mitchell. Granted, I don't read as many as I used to. One of the more recent one seems to debunk a lot of the Bubble model approaches. From what I remember. On tests, it was found that there where more issues with models that had profiles that started deep getting progressively shallower (Bubble type models or GF 30/70 ), rather than approaches that skipped the deep stops and started shallower. i.e. against the historical approach. I could well be out of date on this.

Gradient Factors
These have proven to be very effective when used with Buhlmann tables.
The question is which set of figures are you using. From the Prof Mitchell article on DAN, he was suggesting bring the GF low up, i.e. making the first stop shallower.

Personally, all my computers use GF's.

Instructors and CCR's
I agree with you. Use an instructor who is diving the unit you wish to learn on.
In the same way you should use an instructor doing the type of diving he/she is teaching. There is a difference to course material and course dive on Trimix, over real life diving Trimix regularly.
I mis-interpreted your previous post and though you where talking about instructors with more than two students on advanced course.

Handing off Gas
90% of the diving I do is with people I know. As I previously said, recreational.
I have no problem handing off a stage to them if they need it. I know exactly where they will be, exactly where I will be, and exactly what we will be doing.
The amount of deco I have will be minimal in comparison to them. I will be staying with them to ensure they are OK, they will not be shooting anywhere.
Worst case, I would would flip the BOV, or go SCR. If we are already on the way up, no bother at all. The deco commitment for me is going to be minimal.

Monitoring the dive - dive plans
I am more than happy, in fact prefer to have a runtime when doing adventurous dives.
In recent history, most of the dives are recreational (as I have previously stated). So runtime is a bit overkill, and can be a bit restrictive.
Running one computer in OC mode, gives me a feel for my buddies dive. I do (used to do) exactly the same on OC one computer on my Nitrox mix, one on the buddies (in the early days few were using Nitrox).
I don't like surprises underwater. I like to plan for issues and manage them in advance. I don't want to get to a stop and swim through a buddies stop, or find we have an extra 30 minutes of deco to do, over and above what I expected. Especially if I am cold or want a pee.
I have enough computers, having one on OC is just easy and makes the dive relaxing. I don't have to keep asking questions throughout the dive. Once we get low on NDL, I can tap my computer to signal my buddy to check and confirm. Then as the deco time climbs, I can keep an eye on it and again signal for an update from my buddy on his TTS and first stop depth. Once we start the ascent I normally switch gas settings on the computer to wind down the deco faster. Letting my buddy run the deco schedule.


Having been diving CCR for some time now. There is one certainty, OC have no idea what is going on with CCR. Even those who have done courses, and dive with an CCR buddy. Quite frankly they are mostly in ignorance.
ANY change from the norm' freak's them out.

I can't honestly remember the last time I dived with a CCR diver. I am very familiar with diving with OC divers.
As a CCR diver, you plan for the worst.

If you have a link to the mixed team article I would be interested. Although, I have probably read it.

 

[Scuba Client]

It is quite difficult to respond to your post because it is a bit jumbled but I will try.

Before we start. I have been diving CCR since around 2004. Prior to that I was diving in OC/CCR teams as an OC diver.

When I was diving OC with CCR divers, we where predominantly doing mixed gas or ERD type dives. So each diver carried all their decompression gas, and were on twinsets, so in theory fully redundant. In addition, there was a stage at the bottom of the shot, a travel at 30m, and two or three cylinders of deco gas on the trapeze. But his was group diving so not really a surprise.

MOD1 has a simple rule, when in doubt bailout.
MOD2/3 has a rule, stay on the loop unless it is compromised.
MOD1 is simple recreational diving, max depth say 40m, deco no more than 30 minutes. So generally a single bailout cylinder.
MOD3 is deep trimix, you are carrying a bottom bailout (slightly hot), then one or two stages for decompression. It may well involve team bailout.

(Team Bailout) - you come off the loop you need one, two, or three other CCR divers to get you back to the surface because you require their OC gas as well as your own, unless you can pick it up on the shot/trapeze, or are happy that the drop cylinders will reach you.
Generally, you come off the loop onto your bottom bailout, signal the team and abandon the dive. Start the ascent, at 50% OC gas in the bottom mix you do a cylinder exchange with a team member, taking his full cylinder. He rotates to a team member with full OC cylinders and you rotate to the next team member with full cylinders. Continuing the ascent the next cylinder switch will probably be deco gas (yours). Then at 50% you hand it off and take on new gas, at 50% of that, you hand off and take on gas. Once you are shallow there are also sorts of potential exit plans, from richer deco gas being provided from the surface etc.​

The other option is to go SCR, where you flush the loop. Breath for five breaths, vent the last breath out of the loop, then top up again. i.e Gas extending. Although I can do this, and do on occasion do for practice, I do find it hard work.
Full bailout on a deep dive with long bottom times becomes complex. With the huge physiological issue that you are not self contained. i.e you are reliant on others.

Most of my dives over the last few years for me have been in the MOD1 limits. Predominantly, because I am diving with OC buddies. They generally are on twinsets, or have a pony. The depth is probably 40m max. Deco is unlikely to exceed 30 minutes. What I call recreational.
We really are having a bad day if he has a twinset failure and I have a CCR failure.
A gas failure for him means he takes the long hosed regulator off the bailout cylinder. Then we start the ascent. I have the option to hand off the stage totally to him/her at this point. If I do, I am now reliant on the CCR working perfectly, or the gas available in the onboard DIL cylinder and the BOV. Or SCR mode.
If I don't hand off the stage, I still have the added option of plugging the bailout cylinder back into the CCR, so that I can share the bailout cylinder.
Historically I carry bailout as a self contained unit so it can be handed off to a buddy if required. (i.e. MOD 3 team diving).

To your points
WOB
You are correct, Work of breathing, counterlung position and diver attitude in the water does effect this. There is actually a European Standard for CCR's which dictates the maximum WOB allowed for any unit sold in the EU (and the UK).
The original reason the AP had over the shoulder counter lungs was to get the WOB down. It took some time before they offered rear mounted C/L because with rear mounted counter lungs the WOB is going to be higher. Having them close to the divers body (i.e. minimal distance above the lung when the diver is horizontal) makes a huge difference.
As I said in my earlier post, there is some evidence to suggest high WOB promotes IPO.

decompression models
There are some good features on the DAN site from Professor Mitchell. Granted, I don't read as many as I used to. One of the more recent one seems to debunk a lot of the Bubble model approaches. From what I remember. On tests, it was found that there where more issues with models that had profiles that started deep getting progressively shallower (Bubble type models or GF 30/70 ), rather than approaches that skipped the deep stops and started shallower. i.e. against the historical approach. I could well be out of date on this.

Gradient Factors
These have proven to be very effective when used with Buhlmann tables.
The question is which set of figures are you using. From the Prof Mitchell article on DAN, he was suggesting bring the GF low up, i.e. making the first stop shallower.

Personally, all my computers use GF's.

Instructors and CCR's
I agree with you. Use an instructor who is diving the unit you wish to learn on.
In the same way you should use an instructor doing the type of diving he/she is teaching. There is a difference to course material and course dive on Trimix, over real life diving Trimix regularly.
I mis-interpreted your previous post and though you where talking about instructors with more than two students on advanced course.

Handing off Gas
90% of the diving I do is with people I know. As I previously said, recreational.
I have no problem handing off a stage to them if they need it. I know exactly where they will be, exactly where I will be, and exactly what we will be doing.
The amount of deco I have will be minimal in comparison to them. I will be staying with them to ensure they are OK, they will not be shooting anywhere.
Worst case, I would would flip the BOV, or go SCR. If we are already on the way up, no bother at all. The deco commitment for me is going to be minimal.

Monitoring the dive - dive plans
I am more than happy, in fact prefer to have a runtime when doing adventurous dives.
In recent history, most of the dives are recreational (as I have previously stated). So runtime is a bit overkill, and can be a bit restrictive.
Running one computer in OC mode, gives me a feel for my buddies dive. I do (used to do) exactly the same on OC one computer on my Nitrox mix, one on the buddies (in the early days few were using Nitrox).
I don't like surprises underwater. I like to plan for issues and manage them in advance. I don't want to get to a stop and swim through a buddies stop, or find we have an extra 30 minutes of deco to do, over and above what I expected. Especially if I am cold or want a pee.
I have enough computers, having one on OC is just easy and makes the dive relaxing. I don't have to keep asking questions throughout the dive. Once we get low on NDL, I can tap my computer to signal my buddy to check and confirm. Then as the deco time climbs, I can keep an eye on it and again signal for an update from my buddy on his TTS and first stop depth. Once we start the ascent I normally switch gas settings on the computer to wind down the deco faster. Letting my buddy run the deco schedule.


Having been diving CCR for some time now. There is one certainty, OC have no idea what is going on with CCR. Even those who have done courses, and dive with an CCR buddy. Quite frankly they are mostly in ignorance.
ANY change from the norm' freak's them out.

I can't honestly remember the last time I dived with a CCR diver. I am very familiar with diving with OC divers.
As a CCR diver, you plan for the worst.

If you have a link to the mixed team article I would be interested. Although, I have probably read it.

This is the only one I could find.

 

[Degenerate]

MOD1 has a simple rule, when in doubt bailout.

Is this agency specific?
Because I absolutely learned to deal with problems in order to stay on the loop in my MOD1 class.
Other guy in my class was handed a "rec" cert which specifically meant what you said basically, bail if anything happens and no deco or trimix.
Great and informative post!

 

[Gareth J]

Is this agency specific?
Because I absolutely learned to deal with problems in order to stay on the loop in my MOD1 class.
Other guy in my class was handed a "rec" cert which specifically meant what you said basically, bail if anything happens and no deco or trimix.
Great and informative post!

I have to be cautious here. It is almost 20 years since I did my course. At the time I am pretty certain that all of the agencies had the rule, if in doubt bailout.
I don't teach CCR courses, so can't comment on current course content. I would be interested to hear from anyone currently teaching CCR, if the mantra "if in doubt bailout" is still fundamental to entry level courses or not.

The big issue abut delaying bailing out is that the in a lot of cases on CCR, it becomes progressively harder and harder to get off the loop.
One of the reasons that BOV have become much more available, is that, in the event of a CO2 issue, paranoia and judgment impediments aside. The desire to take another breath is automatic, and it is almost (if not) impossible to suppress this desire to take another breath if you are suffering from CO2 issues. Hence the practice of getting off the loop early if you suspect you have an issue.

With MOD1, the depth and amount of decompression penalty incurred on a dive should not impede a relatively speedy return to the surface. So there should be little need to extend the available gas, or optimise the decompression schedule, unlike the situation when you are looking at MOD3 level dives.

 

[rddvet]

Is this agency specific?
Because I absolutely learned to deal with problems in order to stay on the loop in my MOD1 class.
Other guy in my class was handed a "rec" cert which specifically meant what you said basically, bail if anything happens and no deco or trimix.
Great and informative post!

i was taught both. The main focus was when in doubt bailout. But as we progressed through the course we were taught to figure out problems so that you can stay on the loop. Within reason. Obviously never delay bailing out. And if unsure, bailout, start problem solving, then go back on the loop of deemed safe. Not everyone is taught that because it can be risky. You could be wrong and get back on the loop and have big issues. For me, my ccr courses were focused on cave diving where being able to stay on the loop has many, many benefits. I try not to talk too much in specifics about when to bail out vs stay on the loop or when is a good choice to go back to the loop because the couple times I did disucss it I got hate mail from people who were only taught if anything is wrong youre only option is to bail out

 

[lermontov]

i was taught both. The main focus was when in doubt bailout. But as we progressed through the course we were taught to figure out problems so that you can stay on the loop. Within reason. Obviously never delay bailing out. And if unsure, bailout, start problem solving, then go back on the loop of deemed safe. Not everyone is taught that because it can be risky. You could be wrong and get back on the loop and have big issues. For me, my ccr courses were focused on cave diving where being able to stay on the loop has many, many benefits. I try not to talk too much in specifics about when to bail out vs stay on the loop or when is a good choice to go back to the loop because the couple times I did disucss it I got hate mail from people who were only taught if anything is wrong youre only option is to bail out

your unlikely to die by bailing out unless you've screwed up the gas plan, more chance the other way around

 

[rjack321]

i was taught both. The main focus was when in doubt bailout. But as we progressed through the course we were taught to figure out problems so that you can stay on the loop. Within reason. Obviously never delay bailing out. And if unsure, bailout, start problem solving, then go back on the loop of deemed safe. Not everyone is taught that because it can be risky. You could be wrong and get back on the loop and have big issues. For me, my ccr courses were focused on cave diving where being able to stay on the loop has many, many benefits. I try not to talk too much in specifics about when to bail out vs stay on the loop or when is a good choice to go back to the loop because the couple times I did disucss it I got hate mail from people who were only taught if anything is wrong youre only option is to bail out

How many people have actually died bailing?

I know a couple divers who bailed out but it was relatively late and they toxed within a few moments of bailing.
I know a few who bailed out not realizing that they were having a medical issue and died.

Don't know anyone who bailed and drowned due to lack of volume or inappropriate BOs. The Eagle's nest double fatality a few years ago had so much else going wrong after one of them ditched his JJ, its not possible to attribute that OOA to bailing

Everyone else died on the loop. Staying on the loop is not the savior you were taught it is.

 

[flymolo]

How many people have actually died bailing?

I know a couple divers who bailed out but it was relatively late and they toxed within a few moments of bailing.
I know a few who bailed out not realizing that they were having a medical issue and died.

Don't know anyone who bailed and drowned due to lack of volume or inappropriate BOs. The Eagle's nest double fatality a few years ago had so much else going wrong after one of them ditched his JJ, its not possible to attribute that OOA to bailing

Everyone else died on the loop. Staying on the loop is not the savior you were taught it is.

Wow, that's pretty intense. What would cause them to tox after BO? Something relating to hypercapnia?