Heliox ccr controller

[Decodiver]

I did say that the other bit on the loop (ie you) would not be happy if you had to breath it and I personally wouldn't do it, but many many folks do dive hypoxic mixtures on their rebreathers every day, 10/50 and 5/70 are quite common

I would quite happily do it but would make sure that my bailout was not conencted to the Helium tank (which my system is rigged to be able to do)

We do have Inspiration folks who dive Heliox only and they seem to survive fine

Ok,

I read here quite often but do not post all that much.

Madmole I can tell you that to put pure Helium in as diluent is utter rubbish!!

Scenario 1:

Diver at surface with ADV fitted to Inspiration exhales all gas from lungs and counterlungs in order to sink. Diver takes breath below surface activates ADV and inspires pure Helium. Diver dies.

Scenario 2:

Diver loses all O2 at depth (for whatever reason), he can no longer use his inboard diluent to go SCR. He must ascend OC from the point at which he loses his O2. On expedition diving this could entail problems of not being able to return to the shot and staged gases.

I teach both entry level and mixed gas Inspiration courses. There is no valid reason whatsoever to put pure Helium in as diluent and anyone who recommends this should seriously consider what they ACTUALLY know about CCR diving.

The ability to go SCR is a fundamental part of entry level and advanced mixed gas rebreather diving. Bail-out is a seperate issue. I frequently dive the unit to great depth and teach its use in that environment.

The use of a HeliAir or Heliox should never be confused with the unit mixing its own gas. The Inspiration does not do this!!

It is only a fixed PPO2 unit with a dynamic FO2.

Maths and physiology tell us that bail-out on inboard diluent can be made even if the diluent is hypoxic. However, proper contingency planning, carrying and staging of bail-out and the fundamental principle of being able to go SCR on the unit are extremely important.

There, I've said my bit.

best regards

Dave Cooper

 

[BigJetDriver]

Ok,

Madmole I can tell you that to put pure Helium in as diluent is utter rubbish!!

I teach both entry level and mixed gas Inspiration courses. There is no valid reason whatsoever to put pure Helium in as diluent. The use of a HeliAir or Heliox should never be confused with the unit mixing its own gas. The Inspiration does not do this!!

It is only a fixed PPO2 unit with a dynamic FO2.

Dave Cooper

Dave, et al,

Well said. These are all good points to make.

For those not too familiar with the discussion, we do not speak here of a mix that is hypoxic at some point in the water column, either trimix or heliox, but of a diluent cylinder filled with a pure inert gas.

For various tactical reasons, largely involving the attack of the known Scuba Terrorist, al Murphy, having onboard gas available for injection into the system that is inert at all ambient pressures is just NOT good planning.

Sorry, Mole, but that's the TRUFF--- !!!

 

[scubahubby]

Hey scubahubby,

How about posts a picture for viewing??? I be grateful

Sorry, but I have to respect Phil's wishes regarding publicity until the device is officially available. Otherwise I would gladly put up some pictures and provide what details I have.

- Ozzy

 

[madmole]

I'm not advocating it and I cant personally see any reason for doing it but as long as you planned it properly it is doable and HAS been done by at least one person (not me I hasten to add). ie it is more than theoretically possible. It is also done daily by commercial divers

NOTE TO ALL THIS IS A THEORETICAL CONVERSATION BY TRAINED STUNT REBREATHER DIVERS. DO NOT ATTEMPT THIS AT HOME

As I said above, you would need to make sure that your bailout is breathable and plan this. you cannot just swap the dil over and jump in

THERE IS ABSOLUTELY NO DIFFERENCE in being at the surface or shallow with pure Helium diluent and hypoxic trimix (A very common practice). Neither will support life at that depth on their own (in a rebreather however O2 is being added to the mix to make it breathable)

Scenario 1:
Diver at surface with ADV fitted to Inspiration exhales all gas from lungs and counterlungs in order to sink. Diver takes breath below surface activates ADV and inspires pure Helium (or 5/70). Diver dies. True for both Pure Helium and hypoxic trimix. Not so true in reality as the CCR will be frantically injecting O2 to make the mix breathable

Scenario 2:
Diver loses all O2 at depth (for whatever reason), he can no longer use his inboard diluent to go SCR. He must ascend OC from the point at which he loses his O2. On expedition diving this could entail problems of not being able to return to the shot and staged gases. Diver just swaps to his planned breathable OC bailout. If he is stupid enough to be an alpinist and is not carrying enough/any OC bailout to do this he deserves everything he is going to get

The diluents main job in a rebreather is to be able to LOWER the PO2, its use as a bailout gas and SCR source is secondary and a bonus of the design of most RB's. If you use an onboard diluent that is not usable as a bailout then you MUST plan an alternative

Personally I do not consider the use of SCR mode the main backup mechanism of my RB as I can think of quite a few failure mechanisms that will prevent its use, its a bonus if I can use it. OC bailout should always be planned. If you are relying on SCR mode to bail from a deep dive and NOT carrying enough OC bailout then I will reserve a space for you on my fatalities list now. A hypoxic diluent of any sort cannot be used in SCR mode to the surface anyway, even Air is barely able to do this, the PO2 just drops to much while shallow (you basically need to vent each breath in the shallows for air to maintain >0.2 PO2)

######

OK after I wrote the above I talked to Dave Thompson about this who confirmed it HAS been done by Stuart Clough. However there are several problems with mixing. Apparently pure Helium does not like to mix with O2 and the loop needs to ensure the O2 is thoroughly mixed before it gets to the diver or else he is likely to get a breath of pure He or O2. Apparently cutting the He with about 2% or so of O2 gets round this (something like a detergent effect to allow mixing easier it sounds like).

Lyndon has been using Heliox in his Inspiration lately with doppler monitoring and has been noticing a more rapid onset of bubbles post dive (max within 30 mins of surface v the normal max of 1-1.5 hours), but much more rapid degassing

Also having no N2 in the gas increases your susceptability to HPNS. Richard Pyle having reported onset at 80-90m with heliox dil v 130m when using trimix diluent

 

[Decodiver]

Madmole,

I'm replying as best I can to you here. Your words as replied are in bold italics and mine are normal font:


THERE IS ABSOLUTELY NO DIFFERENCE in being at the surface or shallow with pure Helium diluent and hypoxic trimix (A very common practice). Neither will support life at that depth on their own (in a rebreather however O2 is being added to the mix to make it breathable)

There is a very marked difference, hypoxic gas at least contains an amount of O2. Helium does not. As we move through the water column that gas becomes breathable. Even a small percentage of O2 for a small amount of time can support life. Helium never does whether at the surface or 4 metres or ever.

Scenario 1:
Diver at surface with ADV fitted to Inspiration exhales all gas from lungs and counterlungs in order to sink. Diver takes breath below surface activates ADV and inspires pure Helium (or 5/70). Diver dies. True for both Pure Helium and hypoxic trimix. Not so true in reality as the CCR will be frantically injecting O2 to make the mix breathable

This is not true. It will only frantically try and raise the O2 if you exhale. If you empty your lungs and inhale pure Helium, whether at the surface on a rebrether or your sofa at home you will fall unconscious almost immediately. The Inspiration will not be able to inject O2 quick enough to keep you alive.

Scenario 2:
Diver loses all O2 at depth (for whatever reason), he can no longer use his inboard diluent to go SCR. He must ascend OC from the point at which he loses his O2. On expedition diving this could entail problems of not being able to return to the shot and staged gases. Diver just swaps to his planned breathable OC bailout. If he is stupid enough to be an alpinist and is not carrying enough/any OC bailout to do this he deserves everything he is going to get

The very nature of the diving that some of us do means we can never carry ENOUGH Bail-out to return to the surface straightaway. We carry bail-out but may chose an optimum trimix that will allow us to return to further staged tanks on the shot and then ascend OC. This may be by way of SCR and OC as a last resort. The use of a trimix which will give you a PPO2 of 1 bar at your target depth will mean that you will not compromise your decompression massively. I side-sling two 5 litres down to 100 metres and two 10 litres after that. We then stage variuos tanks on the shot and I have a twin 10 litres on a 25 metre drop line.

Personally I do not consider the use of SCR mode the main backup mechanism of my RB as I can think of quite a few failure mechanisms that will prevent its use, its a bonus if I can use it. OC bailout should always be planned. If you are relying on SCR mode to bail from a deep dive and NOT carrying enough OC bailout then I will reserve a space for you on my fatalities list now. A hypoxic diluent of any sort cannot be used in SCR mode to the surface anyway, even Air is barely able to do this, the PO2 just drops to much while shallow (you basically need to vent each breath in the shallows for air to maintain >0.2 PO2)

I'll deal with these issues in order.

It is less likely well advanced into a dive to suffer loop flood problems, this should happen soon after immersion. Catastrophic loss of O2 and or complete electronics failure could happen at any time. SCR allows you to return to the shot and or staged gases. SCR should be used before OC to return to the shot and then due to the difficulties of ascending whilst performing the skill an OC ascent should be made until 6 metres where the unit can be run as an O2 rebreather without electronics (for those able to perform this skill)

If you are relying on SCR mode to bail from a deep dive and NOT carrying enough OC bailout then I will reserve a space for you on my fatalities list now.

This is where I am interested to know how you have the arrogance to feel qualified to judge whether I or any other person will end up on your fatality list?

You said:

A hypoxic diluent of any sort cannot be used in SCR mode to the surface anyway, even Air is barely able to do this, the PO2 just drops to much while shallow (you basically need to vent each breath in the shallows for air to maintain >0.2 PO2)

That is why the properly trained mixed gas rebreather diver would use the unit as an O2 rebreather at 6 metres (assuming he has not lost his inboard O2 and it is just his electronics that have failed.) I personally have a spare isolated 3 litre of O2 on the side of the unit.

This leads me to the following question:

Have you actually completed a mixed gas ticket for the Inspiration and if so to which level?

If so I am amazed that you see OC as your main way out of problems.

How many hours do you have on your rebreather?

There are hundreds of divers worldwide using the Inspiration to depths where they cannot physically carry enough bail-out. Why are they not all dead?

I have in excess of 400 hours on Military Rebreathers (not including Inspiration hours) and never, ever carried bail-out. I was taught to stay on the unit and solve the problem. I do carry bail-out now.

You talk about Lyndon using Heliox, I know of many more people using Heliox to various depths with the unit. Heliox decompression is going to change the face of deep gas rebreather diving and I applaud the guys pushing the envelope.

You have styled yourself as:

A man on a mission to stop the misinformation spread about rebreathers

You know early on in this thread you said there was no difference to putting pure Helium in the diluent cylinder, you qualified it as being the same as hypoxic heliox or trimix. You know, that is just so wrong and that is why I've answered this as I see.

Best regards

Dave

P.S. I may not be able to answer to further posts on this thread for a couple of days as I have a guy travelling over from Switzerland to do an Inspiration course.

 

[caveseeker7]

For those of you intrested in the subject, "Staying on the loop" and CCR bailout modes, including unmonitored SCR (when all sensors fail), is being discussed at http://www.diveoz.com.au/discussion_forums/FORUM.asp?FORUM_ID=8
after being hotly debated in the Prism thread there.

Using pure He or any other pure inert gas as diluent is nonsense, though.