What advantages or dis-advantages does Heliox have vs. Trimix.? (the Cost differences aside)
Heliox Vs. Trimix
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Same thing different O2 percentages. Heliox normally has an elevated O2 percentage >21% as if it were a nitrox. Trimix is more generic and can have any O2 percentage including <21% or greater then 21%
ajduplessis
Contributor
Heliox generally refers to 21% O2 and 79% helium (helium and oxygen = heliox), no nitrogen in the mix, but I could be wrong.
Trimix are any combination of 3 gasses (helium, O2 and nitrogen) depending on depth.
Trimix are any combination of 3 gasses (helium, O2 and nitrogen) depending on depth.
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Kiwi303
Contributor
This is not from a Tech diver, just a curious guy who reads a lot... but you asked disadvantages of Heliox and Trimix...
As I understand it, the very small size of the helium molecule relative to the Nitrogen and Oxygen, which are both much further up the periodic table, provides it's own challenges regarding deco obligations.
Being so small it diffuses through the tissues much more rapidly than nitrogen does, and als comes out of saturation and bubbles more readily. So Ascents are much more a matter of controlling speeds and keeping within the ascent speeds plotted for the dive, and in an emergency there is a much shorter period on a crash surface to chamber ride in which the gasses bubble out and serious/irreversable damage can occur.
On the other hand, it is far less narcotic (not non-narcotic) than Nitrogen. Trimix is to Heilox as Nitrox is to Air. The percentage of Nitrogen means there is a lesser percentage of Heilum, so offgassing through the breathing is faster, same as breathing 100% O2 is sometimes used to offgas nitrogen loadings.
I'll be glad to be corrected by true Tech and Tri/Heilox divers... Always glad to learn
As I understand it, the very small size of the helium molecule relative to the Nitrogen and Oxygen, which are both much further up the periodic table, provides it's own challenges regarding deco obligations.
Being so small it diffuses through the tissues much more rapidly than nitrogen does, and als comes out of saturation and bubbles more readily. So Ascents are much more a matter of controlling speeds and keeping within the ascent speeds plotted for the dive, and in an emergency there is a much shorter period on a crash surface to chamber ride in which the gasses bubble out and serious/irreversable damage can occur.
On the other hand, it is far less narcotic (not non-narcotic) than Nitrogen. Trimix is to Heilox as Nitrox is to Air. The percentage of Nitrogen means there is a lesser percentage of Heilum, so offgassing through the breathing is faster, same as breathing 100% O2 is sometimes used to offgas nitrogen loadings.
I'll be glad to be corrected by true Tech and Tri/Heilox divers... Always glad to learn
Ozgarr
Registered
Yeah, so Heliox is mainly for commerical and military diving because the complete absence of nitrogen (and nitrogen narcosis) is required for delicate tasks (diffusing mines, etc.)
Heliox is not commonly used in recreation sectors first because it's expensive, and most people are willing to endure a Equivalent Narcotic depth of about 30/40m to avoid the extra $$$
Secondly, Helium is a rapidly diffusing gas and results in longer decompression requirements at relatively shallow depths than trimix (because of faster tissue halftimes with helium). In long 'Saturation' dives, there is faster decompression with Helium, as the contrary is true, and Helium off-gases faster than Nitrogen (as Kiwi said). Great post BTW, I'm also a non-tech diver who likes to read.
And finally, there is the risk of High Pressure Neurological Syndrome which kicks in past hundred metres.
...Hope that helps, Oscar
Heliox is not commonly used in recreation sectors first because it's expensive, and most people are willing to endure a Equivalent Narcotic depth of about 30/40m to avoid the extra $$$
Secondly, Helium is a rapidly diffusing gas and results in longer decompression requirements at relatively shallow depths than trimix (because of faster tissue halftimes with helium). In long 'Saturation' dives, there is faster decompression with Helium, as the contrary is true, and Helium off-gases faster than Nitrogen (as Kiwi said). Great post BTW, I'm also a non-tech diver who likes to read.
And finally, there is the risk of High Pressure Neurological Syndrome which kicks in past hundred metres.
...Hope that helps, Oscar
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OP
alright so in a rebreather (where the additional Helium cost would be negligible) application there is no benefit to using Heliox as a diluent Vs. Trimix for saturation diving as it would actually increase the deco requirement vs. an "equivalent" trimix.
that's interesting, anyone happen to have some good sources i can read up more on trimix and heliox diving?
More curiosity at this point but I will eventually swap out my Air Dil for the trimix variety in the near future.
that's interesting, anyone happen to have some good sources i can read up more on trimix and heliox diving?
More curiosity at this point but I will eventually swap out my Air Dil for the trimix variety in the near future.
Ozgarr's comments are correct but neglected the thermal conductivity factor, which is third in line behind cost and tissue permeability. Unless you are in very warm water and durations are short, it is very difficult to prevent hyperthermia. Remember around 50% of your total heat loss is through respiration. Air or Argon in a drysuit is critical on any Helium mix, but doesnt help the other half of the heat loss equation.
The only reason saturation divers can work is the 2½ gallons/minute of 110° water pumped into their suits. Breathing gas heaters are usually added ~600 by necessity. This list shows thermal conductivity as a multiple of air.
1.0 Air (gas)
0.7 Argon (gas)
5.9 Helium (gas)
1.0 Nitrogen
1.0 Oxygen
24.2 Water
HPNS is rarely a problem for military and commercial divers until well below 100 meters/328. By that point most are in saturation systems where descent rates are very slow to avoid the symptoms. Sixty feet per hour or less is common on deeper sats. HPNS tremors are only one of the reasons for the slow descent. Cartilage compression in joints is so painful that divers rapidly pressed to say 600 can barely work anyway like 24 years old to an arthritic 92 in 10 minutes.
Luckily, I was never blown down that fast but my younger brother was for an emergency repair at ~600. He said he could barely climb into the bell.
This must be regional difference. I have never heard of a Heliox premix for diving at or above 21% O2 in the millions of cubic feet I have seen delivered for military and commercial diving operations. The vast majority was ~1-3%. The majority of tri-mix I have seen is around 17% O2 and below. I was taught that oxygen levels in Heliox, Nitrox, or Trimix were anything intentionally blended above 0% and below 100% O2. Enhanced Nitrox or EAN of course has oxygen levels above 21%.
The only reason saturation divers can work is the 2½ gallons/minute of 110° water pumped into their suits. Breathing gas heaters are usually added ~600 by necessity. This list shows thermal conductivity as a multiple of air.
1.0 Air (gas)
0.7 Argon (gas)
5.9 Helium (gas)
1.0 Nitrogen
1.0 Oxygen
24.2 Water
HPNS is rarely a problem for military and commercial divers until well below 100 meters/328. By that point most are in saturation systems where descent rates are very slow to avoid the symptoms. Sixty feet per hour or less is common on deeper sats. HPNS tremors are only one of the reasons for the slow descent. Cartilage compression in joints is so painful that divers rapidly pressed to say 600 can barely work anyway like 24 years old to an arthritic 92 in 10 minutes.
Luckily, I was never blown down that fast but my younger brother was for an emergency repair at ~600. He said he could barely climb into the bell.
This must be regional difference. I have never heard of a Heliox premix for diving at or above 21% O2 in the millions of cubic feet I have seen delivered for military and commercial diving operations. The vast majority was ~1-3%. The majority of tri-mix I have seen is around 17% O2 and below. I was taught that oxygen levels in Heliox, Nitrox, or Trimix were anything intentionally blended above 0% and below 100% O2. Enhanced Nitrox or EAN of course has oxygen levels above 21%.
Well I thought the US Navy considered heliox any mix of helium and O2 and the term is used that way in commercial diving. But recreationally NAUI and others here in the States consider heliox any trimix with >normoxic levels of O2. Things like 26/17, 25/25, and 30/30 are all considered "heliox" here (althought the term is not common).
Trimix being the more generic term for any combo of O2/He/N2
w ripley
Contributor
Gilldiver
Contributor
Heliox is an easier gas to manage as there is no nitrogen to balance with the helium and oxygen.
For a surface supplied or saturation Heliox system all the tenders need to do is monitor two gasses, O2 and CO2 and not worry about the He. For a Tri-mix system the tenders also have to watch all four gasses.
Or
Heliox worry about O2 and CO2%
Trimix worry about O2, CO2%, N2, and H2%
For a surface supplied or saturation Heliox system all the tenders need to do is monitor two gasses, O2 and CO2 and not worry about the He. For a Tri-mix system the tenders also have to watch all four gasses.
Or
Heliox worry about O2 and CO2%
Trimix worry about O2, CO2%, N2, and H2%
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