YD Scuba Diving Forums banner

1 - 20 of 22 Posts

·
The Artist formerly known as 'John Duncan'
Joined
·
364 Posts
Discussion Starter · #1 ·
Imported post

<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 "poor mans trimix" 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
 

·
Registered
Joined
·
2,839 Posts
Imported post

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

·
Registered
Joined
·
64 Posts
Imported post

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
 

·
The Artist formerly known as 'John Duncan'
Joined
·
364 Posts
Discussion Starter · #4 ·
Imported post

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

·
Registered
Joined
·
5,736 Posts
Imported post

[b said:
Quote[/b] (JohnDuncan @ Mar. 11 2004,13:34)]Heli-air is defined as "Helium mixed with Air" not "Helium mixed with O2 and Air" 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
 

·
Registered
Joined
·
2,839 Posts
Imported post

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

·
Membership Cancelled
Joined
·
980 Posts
Imported post

[b said:
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 "poor mans trimix" 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.  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.  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.  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
 

·
The Artist formerly known as 'John Duncan'
Joined
·
364 Posts
Discussion Starter · #8 ·
Imported post

[b said:
Quote[/b] (Juz @ Mar. 11 2004,13:49)]
[b said:
Quote[/b] (JohnDuncan @ Mar. 11 2004,13:34)]Heli-air is defined as "Helium mixed with Air" not "Helium mixed with O2 and Air" that is Trimix as far as I know(?)
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.
 

·
Registered
Joined
·
64 Posts
Imported post

[b said:
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
 

·
Shipwrecked & Comatose, drinking fresh mango juice
Joined
·
2,614 Posts
Imported post

<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 "with a normal level of oxygen", i.e. 21%:
[b said:
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. "Normoxic Trimix" 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
 

·
The Artist formerly known as 'John Duncan'
Joined
·
364 Posts
Discussion Starter · #11 ·
Imported post

[b said:
Quote[/b] (aclivity @ Mar. 11 2004,18:08)]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 "with a normal level of oxygen", i.e. 21%:
<font color='#F52887'>Normoxic means Life sustaining at the surface (AFAIUI)
and trimix is expressed thus O2/He/N2.
 

·
The Artist formerly known as 'John Duncan'
Joined
·
364 Posts
Discussion Starter · #12 ·
Imported post

[b said:
Quote[/b] (Alan57 @ Mar. 11 2004,17:04)]
[b said:
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
<font color='#F52887'>Thank you for your answer as to advantages. and thanks too for the disadvantages, that was all I was looking for. I was questioning the high END in my original post, but thank you for pointing out my original point back to me.
 

·
The Artist formerly known as 'John Duncan'
Joined
·
364 Posts
Discussion Starter · #14 ·
Imported post

<font color='#F52887'>I think that Normoxic Trimix covers O2 content down to 16%, that is the mixes that you train for when you do Entry level Trimix training (life sustaining at the surface) But technically, Trimix is HYPOXIC at the surface, NORMOXIC as you descend and finally becomes HYPEROXIC at the depth limits of the gas mix you use.
 

·
Registered
Joined
·
313 Posts
Imported post

<font color='#0000FF'>
[b said:
Quote[/b] (aclivity @ Mar. 11 2004,18:08)]So, if Heliair is Helium mixed with air, it can't be normoxic?
The way I see it, if anything below 20.9%O2 is hypoxic then all heli-air will be hypoxic.

Once you add another gass to the mix, the percentage of O2 in the mix will drop, as will the % N2, the HE will go up.

Is that what u mean Aclivity?

Stu.
 

·
Registered
Joined
·
313 Posts
Imported post

<font color='#0000FF'>
[b said:
Quote[/b] (JohnDuncan @ Mar. 11 2004,18:44)]I think that Normoxic Trimix covers O2 content down to 16%, that is the mixes that you train for when you do Entry level Trimix training (life sustaining at the surface) But technically, Trimix is HYPOXIC at the surface, NORMOXIC as you descend and finally becomes HYPEROXIC at the depth limits of the gas mix you use.
Surely a 21/30/49 mix wouldnt be hypoxic John?

Only benefits would be END however, wouldnt be a deep gas.

Stu.
 

·
The Artist formerly known as 'John Duncan'
Joined
·
364 Posts
Discussion Starter · #17 ·
Imported post

<font color='#F52887'>I think that I should keep my mouth shut, and not ask too many questions. 21% would be normoxic, anything below it would be Hypoxic. I think most Trimix diving seems to be done with a percentage of O2 lees than 21%. this mix of low O2 and He in the mix give a gas suitable for deeper diving. I do not know about a lot of this, that is why I am asking questions. I am hoping to do my Entry Trimix later in the year.
 

·
Registered
Joined
·
676 Posts
Imported post

<font color='#810541'>TDI entry level Trimix- you can use down to 18% o2 which is still life sustaining at the surface which is more than can be said for the atmosphere in my bedroom after beer and curry.
 

·
Shipwrecked & Comatose, drinking fresh mango juice
Joined
·
2,614 Posts
Imported post

[b said:
Quote[/b] (PressurE @ Mar. 11 2004,19:57)]
[b said:
Quote[/b] (aclivity @ Mar. 11 2004,18:08)]So, if Heliair is Helium mixed with air, it can't be normoxic?
The way I see it, if anything below 20.9%O2 is hypoxic then all heli-air will be hypoxic.

Once you add another gass to the mix, the percentage of O2 in the mix will drop, as will the % N2, the HE will go up.

Is that what u mean Aclivity?

Stu.
<font color='#810541'>exactly!

(also want to do more training but need to do nitrox first and get some more diving experience rather than theory!)

Andy
 
1 - 20 of 22 Posts
Top