the "stroke mix'?

[PoorStudentDiver]

I have read a lot about the 80/20 mix, and was just curious why its a hot issue? I fugure that is just easier to carry 100% o2 but was wondering if there are anyother reasons. Havent found out why George Irvine hates it, i just know that he does.

"WKPP divers believe that 80/20 is a bad idea, and refer to it as "stroke mix".

[Dmitchell]

google -"bakers dozen" "george irvine" you'll find the answer.

[ljjames]

There has been a lot of randomness as to why different groups of divers used 80/20. When I started tech diving we did not have an O2 compatible booster pump. We used old low pressure steel 72's as deco bottles. If you have 3 O2 bottles in your banks (one almost empty, one mid range full, one mostly full) and a compressor capable of pumping 40% nitrox, it was easier to get a 'full fill' of 80/20 then it was to get a 'full fill' of 100%.

That was the primary reason we used it. it has nothing to do with 'safer' if you don't know how to hold stops, rough seas, oxygen PO2, etc. At the level of diving we were doing, 'holding a stop' was not an issue. We decompressed at 1.6. It came down to functional gas volume for your deco bottle. I had a pair of old 1800psi steel 40's that were wonderful because you were almost guaranteed a full deco bottle

GI3 and others turned it into a huge interweb battle that really had nothing to do with why (for at least our team) we were using 80/20. For what it's worth, I use 100% O2 now. Not necessarily because i think it's any better or 80/20 is worse, it's just about a million times easier to get a 100% O2 fill these days and there is never really any question of "do I have 80%, do I have 90%, do I have 95%? Having 100% is just 'easier'. You know your limit, there's no guess work, there are hopefully no differences in the team's gas (one having 80, one having 88 and not being able to go on deco at same depth). Why bother effing around with mixing?

If you've done your deco 'correctly' when all is said and done (talking about 200' and shallower dives here, I really don't think there is that much of a difference if you have 100% or 80% or 90% and you just went on any of them at 20' and did your alloted deco. Oh wait, two separate deco planners show only 3 min difference on a 200/20 with 50% at 70', and either 80/20 or 100% at 20'.

Anyhow, thats why we used it. and also why we don't use it now. its not because any person bashed us or convinced us otherwise, it just comes down to what made sense than and what makes sense now. Times and technology change, it's human to be stubborn, but it's better as a species to be adaptable

[vbcoachchris]

For the simplest answer:

At one time there was a mixing benefit. 80% could be made easily by trans-filling from a low pressure industrial oxygen cylinder to a Al cylinder and then topping with air.

Boosters are widely available today, so this is a non issue.

For me it comes down to this:

If you have an emergency what gas are you going to use to treat? Answer oxygen
If this is the case; why would I want 80% with me?

Scott

[ljjames]

FWIW, I have not seen a study showing a marked difference in 100% vs 80% for 'emergency' use. Either would be better than room air. A 100% O2 bottle is "the norm" because that is what is most readily available in the health care arena and on O2 kits with a demand regulator, oxygen mask/non-rebreather bag/ambu-bag set up. (again, super easy to fill if you have the ability to boost O2 or get from local gas fill company, no variations in mix).

Patients are very rarely getting '100% oxygen'.

If you look at most consumer Oxygen set ups available to the public, if is not the expensive DAN kit with their demand mask without a purge, it's either;

1) a mask that has no bag - just a mask with a tube (that has O2 flowing at a set liters per min) when you look closely you will see that the mask has one or both of the 'exhaust diaphragms' pulled out so that room air can get back in, the concentration of O2 available is about 35-40%.

2) The next type is recognizable by the reservoir bag and only one of the exhaust diaphragms removed, it is the "partial rebreather", meaning there is not a one way valve between the mask and bag that oxygen is flowing into at a set liters per minute, these can deliver oxygen at concentrations from 40-60%

3) A 'non-rebreather' mask, has a bag that fills with oxygen, but also has a one way valve between the mask and the bag, and diaphrams on the masks side vents. The mask is generally of a higher quality so you can get a much more secure seal than the previously mentioned two. With these, the patient is getting up to 90% oxygen breathing in from the bag and out the one way valves on the face mask. These are often considered 'medical professional grade' and generally prescription or for 'trained oxygen providers only. You will often see they have a special disclaimer on the bag or tag stating "this mask must be used with patient under constant supervision" as with both exhaust diaphragms in place and the one way valve to the bag, if the bottle runs out the patient who is likely already has 'issues' could suffocate. (d'oh!)

Knowing what kind of oxygen mask you have in your kit is good. If you've got a non-rebreather mask, be aware of not only its benefits but it's limitations (you can't just park a reduced consciousness but breathing victim on one side of the boat while you are trying to take care of his/her non-breathing buddy, in that case you'd pull out one of the exhaust diaphragms so they could get air, or have another person sitting and watching them (great if you have an excess of people)

Take the DAN O2 provider course, it's great! But it still doesn't make us medical professionals

Lynne, please correct any mistakes here about the delivery systems and O2 in general if I've made em! (thanks!)

Remember, the bottom line is "do no harm"

[PoorStudentDiver]

thanks for the wealth of information, laura james i have seen a few of your dive vids around, really cool stuff with way better music selection then most, thanks again

[vbcoachchris]

FWIW, I have not seen a study showing a marked difference in 100% vs 80% for 'emergency' use. Either would be better than room air. A 100% O2 bottle is "the norm" because that is what is most readily available in the health care arena and on O2 kits with a demand regulator, oxygen mask/non-rebreather bag/ambu-bag set up. (again, super easy to fill if you have the ability to boost O2 or get from local gas fill company, no variations in mix).

I am not a doctor and I do not play one on TV (I have stayed at a Holiday Inn Express).

You may very well be correct; however my common sense tells me that, if inert gas is my causing problems, I want to breathe less inert gas.

Scott

[Joshua Smith]

FWIW, I have not seen a study showing a marked difference in 100% vs 80% for 'emergency' use. Either would be better than room air. A 100% O2 bottle is "the norm" because that is what is most readily available in the health care arena and on O2 kits with a demand regulator, oxygen mask/non-rebreather bag/ambu-bag set up. (again, super easy to fill if you have the ability to boost O2 or get from local gas fill company, no variations in mix).

I am not a doctor and I do not play one on TV (I have stayed at a Holiday Inn Express).

You may very well be correct; however my common sense tells me that, if inert gas is my causing problems, I want to breathe less inert gas.

Scott

So, which rebreathers are you considering?

(Couldn't resist, sorry!)

[Grateful Diver]

When I was in Bonaire I inquired about doing a tech dive on the Windjammer. They told me the "standard" deco gases were EAN50 and EAN70. When I said I prefer to do my deco with EAN50 and oxygen the guy who was gonna be leading the dive said that using pure oxygen for deco was "too risky".

Turned out we couldn't get permission that week anyway, so it was a moot point.

... Bob (Grateful Diver)

[vbcoachchris]

FWIW, I have not seen a study showing a marked difference in 100% vs 80% for 'emergency' use. Either would be better than room air. A 100% O2 bottle is "the norm" because that is what is most readily available in the health care arena and on O2 kits with a demand regulator, oxygen mask/non-rebreather bag/ambu-bag set up. (again, super easy to fill if you have the ability to boost O2 or get from local gas fill company, no variations in mix).

I am not a doctor and I do not play one on TV (I have stayed at a Holiday Inn Express).

You may very well be correct; however my common sense tells me that, if inert gas is my causing problems, I want to breathe less inert gas.

Scott

So, which rebreathers are you considering?

(Couldn't resist, sorry!)

The RB80 of course

If I ever go CCR it would most likely be the sentential

Scott

[PoorStudentDiver]

RB80? is there anything that Halcyon makes that you wouldnt buy?? haha

[vbcoachchris]

Yes I would not buy Halcyon's
ccr wing
acb weight system
gaiter wraps
tank weight pockets
yellow smb's
life support raft
cold water spools
and I would never buy another Scout back up light, but I can't seem to bring myself replace the ones I already have(their my "binki's")

Scott

[Joshua Smith]

but I can't seem to bring myself replace the ones I already have(their my "binki's")

Scott

Oooo. "Binkies" are kind of like sacred cows, on this site. Mess with the binkie at your own peril.

[Sounder]

Oh, Scott's getting a new binky soon...

[vbcoachchris]

Oh, Scott's getting a new binky soon...

the X1 and it's not even made by Halcyon