Cave diver pulled to surface barely alive - Eagle's Nest

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09-30-2005 08:12 AM
Gary

Quote:

Originally Posted by Angie Reim

So why would 21/60 vs. 21/40 be a bad thing? More HE is not going to hurt you is it?

Well one problem is that I had a fill to 2400 instead of 3500 in my HP120s - so if I arrived at the site with that my dive was screwed.

If I were actually to dive with that on my expected profile the difference in the mix would only require some longer deep stops and an extra 6 minutes of deco so that I'd likely manage on the original schedule without getting bent. Fortunately Helium is very forgiving that way and even if mybottom time extended out from 40 to 60 minutes the additional deco required by V-planner would only be 10 extra minutes (compared to the gas I planned for).

So while it could end up getting me bent I would probably get by OK or with only a minor bend whenI might have otherwise expecte to be OK. Luckily though we figured it out while gearing up at the next shop and figured out what happened and topped off the mix - otherwise I would have ended up sitting out the dive (not having enough gas to do the planned dive or having any deco tables printed for the gas I ended up with and no way to guess how much difference it would have made.)
09-30-2005 08:13 AM
Genesis

The additional Helium changes the deco significantly but is otherwise a non-event. Nothing wrong with lots of He, other than the impact on the deco schedule.

Being off a couple of percent is not a big deal on Helium, but off by 20% would force recalculation of the decompression schedule - it'd be off significantly.
09-30-2005 08:37 AM
Simon Richards

Quote:

Originally Posted by Gary

If you are mixing normoxic trimix your O2 is going to be 21% regardless of how much Helium is added.

Is this right? Surely more He means less O2 and vice versa?
09-30-2005 08:49 AM
Genesis

Quote:

Originally Posted by Simon Richards

Quote:

Originally Posted by Gary

If you are mixing normoxic trimix your O2 is going to be 21% regardless of how much Helium is added.

Is this right? Surely more He means less O2 and vice versa?

No. You add the He and O2, then top it off.... (usually with either air or EANx32)
09-30-2005 09:14 AM
wingman

Quote:

Originally Posted by Simon Richards

Quote:

Originally Posted by Gary

If you are mixing normoxic trimix your O2 is going to be 21% regardless of how much Helium is added.

Is this right? Surely more He means less O2 and vice versa?

I think he is speaking of the outcome...the final numbers of a normoxic mix should 21% O2 regardless of how much helium/nitrogen there is in the mix. Bill
09-30-2005 10:44 AM
Simon Richards

Quote:

Originally Posted by wingman

Quote:

Originally Posted by Simon Richards

Quote:

Originally Posted by Gary

If you are mixing normoxic trimix your O2 is going to be 21% regardless of how much Helium is added.

Is this right? Surely more He means less O2 and vice versa?

I think he is speaking of the outcome...the final numbers of a normoxic mix should 21% O2 regardless of how much helium/nitrogen there is in the mix. Bill

Agreed it _should_ be, as that's just the definition of a normoxic mix. I'm just concerned that the implication is that if you aim for a normoxic mix you will always get a normoxic mix - that's generally not the case (unless you are using a 21/X premix and topping with air I suppose).
09-30-2005 01:42 PM
Gary

Quote:

Originally Posted by Genesis

No. You add the He and O2, then top it off.... (usually with either air or EANx32)

Right - you generally add O2 and He (or sometime He and then O2). If the final mix is planed for around 21% then the He and O2 added will be in proportion to create 21% heilox when they are added - then you top with air. No matter how much air you add the percentage of O2 will remain 21% because that's the % O2 you started with and that's the % O2 you're adding. The only difference is in the Nitrogen you are adding in the air will shift the ballance of the remainder of the mix from Helium to Helium & Nitrogen.

This would be the standard way to partial pressure mix the Trimix. If you are starting with or topping with a 10/50 premix of He and the ballance with Nitrox this wouldn't be the case. :wink:
09-30-2005 02:55 PM
Simon Richards

Quote:

Originally Posted by Gary

Quote:

Originally Posted by Genesis

No. You add the He and O2, then top it off.... (usually with either air or EANx32)

Right - you generally add O2 and He (or sometime He and then O2). If the final mix is planed for around 21% then the He and O2 added will be in proportion to create 21% heilox when they are added - then you top with air. No matter how much air you add the percentage of O2 will remain 21% because that's the % O2 you started with and that's the % O2 you're adding. The only difference is in the Nitrogen you are adding in the air will shift the ballance of the remainder of the mix from Helium to Helium & Nitrogen.

This would be the standard way to partial pressure mix the Trimix. If you are starting with or topping with a 10/50 premix of He and the ballance with Nitrox this wouldn't be the case. :wink:

OK with all that, but what you actually said was: "If you are mixing normoxic trimix your O2 is going to be 21% regardless of how much _Helium_ is added." - if you had said "regardless how much _air_ is added" then I would agree. I'm not trying to be picky, just trying to get to the bottom of what you said.

Cheers,

Simon
09-30-2005 05:35 PM
Gary

You are right, more clearly it should have read:

If you are mixing normoxic trimix your O2 is going to be 21% thoughout the top off regardless of the % of Helium in the final mix.
10-05-2005 08:21 AM
Arnold Mesiser

http://www.sptimes.com/2005/10/02/He..._urged_f.shtml

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