Heli-air

[JohnD]

<font color='#F52887'>I am trying to find out what are the advantages of using Heli-air. I know that it is sometimes known as &quot;poor mans trimix&quot; but are there advantages and disadvantages. The END for the normoxic mixes are still quite high e.g. 16/24/60 at 60m is 43m END and at 70m it is 51m END

[Dominic]

Apparently a 50/50 Helium/Air mix is popular amongst rebreather divers...

[Alan57]

I think you mean 10/50 O2/He ( actually for the pedants 10/52 or 10.5/50) which I use for all my dives. I can mix it with just air and He (no separate O2 so no bangs or expensive cleaning). Just fill to half the working pressure with He top of with air). Other Heleair mixes are just other proportions.
The problem for OC is that the 10% O2 is not life sustaining at shallow depth. Fortunately the Inspiration I use ensures it is safe and optimised for deco.
Hope this helps.
Alan

[JohnD]

<font color='#F52887'>no, I mean 16/24/60 and I said that I was talking about Normoxic mixes. Heli-air is defined as &quot;Helium mixed with Air&quot; not &quot;Helium mixed with O2 and Air&quot; that is Trimix as far as I know(?)

[Juz]

Originally Posted by [b

Quote[/b] (JohnDuncan @ Mar. 11 2004,13:34)]Heli-air is defined as &quot;Helium mixed with Air&quot; not &quot;Helium mixed with O2 and Air&quot; that is Trimix as far as I know(?)

<font color='#32CD32'>But surely Helium mixed with Air will end with a gas containing Helium, Oxygen, Nitrogen and minor trace gasses.

Juz

[Dominic]

Better tell the EU we'll be needing yet another valve design to distinguish between Heliair and Trimix then

[Duncan Price]

Originally Posted by [b

Quote[/b] (JohnDuncan @ Mar. 11 2004,11:21)]I am trying to find out what are the advantages of using Heli-air. I know that it is sometimes known as &quot;poor mans trimix&quot; but are there advantages and disadvantages. The END for the normoxic mixes are still quite high e.g. 16/24/60 at 60m is 43m END and at 70m it is 51m END

<font color='#8D38C9'>I have used it - particularly for line laying and surveying in caves below 40 m. &nbsp;I prefer at least 30% He or more otherwise there is not much narcosis benefit but even a little can help.

The advantages are:

0. I don't have a trimix (or even nitrox) ticket.
1. Its cheap - I use Helium at work...
2. Easy to make.
3. Easy to analyse (and re-analyse if you top it off with air).

The disadvantage is that anything pokier that Helair 17:20 is potentially hypoxic on the surface. &nbsp;However I've got travel/deco gas to breathe and even if I did dive from the surface on a light O2 mix then I'm quickly going to be at a depth where the ppO2 has risen. &nbsp;When you get to around 60-70 m you need a mix that would be hypoxic on the surface anyway.

10:50 is a popular diluent.

Duncan

[JohnD]

Originally Posted by [b

Quote[/b] (Juz @ Mar. 11 2004,13:49)]

But surely Helium mixed with Air will end with a gas containing Helium, Oxygen, Nitrogen and minor trace gasses.

Juz

<font color='#F52887'>OK, you pedant. what I am saying is that you put He into your cylinder then top up with Air. In trimix you use He, O2 (or EANx) and air.
If you want to be really anal you could say that we are breathing Trimix effectively because those gasses exist in (differing quantities) in the air that we breathe.

[Alan57]

Originally Posted by [b

Quote[/b] (JohnDuncan @ Mar. 11 2004,11:21)]I am trying to find out what are the advantages of using Heli-air.

My post answered you question about advantages.

Another advantage is that the helair mix can be topped off as the ratio of O2 to N is fixed in air and so the He can be calculated.

The big disadvantage of normoxic helair is that the END will not be shallow for OC at the depths you mention. Unless of course you add O2 which upsets the variables in para two above and negates the comments made in my first post

[aclivity]

<font color='#810541'>Excuse me if I am being a numpty .... I've always been of the understanding that the ratios (e.g. 16/24/60) are expressed in the order O2/H2/N2?

Is that correct?

If so ... plunging on ... the mix specified above is NOT normoxic as (AFAIUI) normoxic means &quot;with a normal level of oxygen&quot;, i.e. 21%:

Originally Posted by [b

Quote[/b] ]Trimix is comprised of three (tri) gases; nitrogen, oxygen and either helium, neon or hydrogen. The third gas is nearly always helium as neon is expensive and hydrogen somewhat unstable. &quot;Normoxic Trimix&quot; is a breathing mix with no less then 21% oxygen and no more then 25-30% helium

(I found this definition on divermag article)

So, if Heliair is Helium mixed with air, it can't be normoxic?

(again, apologies if I am being a numpty, I am not Trimix or any kind of gas blending trained but I am an avid reader, and I read up on Heliair after it was mentioned in either The Last Dive or Deep Descent)

Andy