normoxic/Hypoxic diffrences

[To_Narced]

Hey Guys,

Just wondering if anyone could explain to me what he diffrence between normoxic and hypoxic is. My buddys are tech divers and I often hear them use these terms but I jave never grasped there full meaning. Thanks to anyone who could help.

 

[Xman]

Normoxic is a gas mix with the same level of oxygen as found in air, (normal level of oxygen).
Hypoxic is a gas mix with a lower level of oxygen than found in air.
Enriched air Nitrox is hyperoxic- it has a greater level of oxygen than found in normal air.
Normoxic Trimix is used to reduce the END diving within air limits. It has 21%oxygen, but some of the nitrogen is replaced with helium to reduce narcosis at depth.
Hypoxic Trimix is used to dive deeper than safely possible on Normoxic mixes. It ordinarily requires the use of different gas mixes for the shallower portions of the dive, and is used to keep the maximum partial pressure of oxygen within acceptable limits to avoid oxygen toxicity and overexposure.

 

[Mako Mark]

what he said,

Normoxic can be used to 190-220 ft, where the partial pressure of O2 in air would not nessicarily be a serious problem, but the narcotic effect of the nitrogen is seen to be too great.

Hypoxic mixes (less than 21% O2) used for deeper diving, here some general guidelines:

16% oxygen is roughly equivalent to the percentage in your exhaled breath, so you can theoretically breathe this all the way to the surface and or decompress on it in the event you lost your deco gasses.

less than about (between) 9-12% oxygen and you would pass out if you tried to breathe it at the surface, so requre the use of a travel gas, but could not decompress on you bottom mix in the event of lost deco gas.

Until the mid 90's, it was seen as perfectly acceptable to dive to the depths of 190-200 ft on air. The trend since then is that while the risk of oxygen toxicity is acceptable at those depths, the effects of Narcosis are not acceptable on air, so helium is introduced to reduce the levels of narcosis.

 

[DA Aquamaster]

Just to round off the vocabulary lesson we should add that Hyperoxic mixes involve O2 percentages above the normal 21%.

 

[Xman]

Just to round off the vocabulary lesson we should add that Hyperoxic mixes involve O2 percentages above the normal 21%.

Yup, thats kinda what I was getting at when I said "Enriched air Nitrox is hyperoxic- it has a greater level of oxygen than found in normal air." in my above post.

In anything Hypo means less than normal, Hyper means greater than normal (and in this case "normoxic" becomes self explanatory)

 

[Stirling]

Hey Guys,
Just wondering if anyone could explain to me what he diffrence between normoxic and hypoxic is. My buddys are tech divers and I often hear them use these terms but I jave never grasped there full meaning. Thanks to anyone who could help.

Summarizing:

Norm = "standard" (hence the word "normal"), and so "normoxic" is a gas with 21% oxygen, because that is the percentage of oxygen found in air. Air is normoxic; but so is any blend of gases (e.g., helium, nitrogen, and oxygen) if the oxygen is 21% of the total.

Hypo = "under," "beneath," or "less than," and so "hypoxic" refers to a gas with less than 21% oxygen.

Hyper = "above" or "greater than," and so "hyperoxic" describes a gas with more than 21% oxygen. That is generally going to be a mix of nitrogen and oxygen only (as in air), with an elevated oxygen level, which is referred to as "enriched air" or "nitrox" - the acronym "EANx" for enriched air describes a blend of nitrogen and oxygen, with the percentage of oxygen in the mix indicated - e.g., EANx28 or EANx32.

This page includes a discussion of the reasons why you might prefer a mix with higher or lower percentages (and thus partial pressures) of nitrogen or oxygen - to manage the variable risks of narcosis, DCS, and oxygen toxicity at different depths and partial pressures. If all you have in the mix is oxygen and nitrogen, you can't have the percentage of nitrogen and oxygen *both* go up or down at the same time - the total has to be 100% - so helium is one of the inert gases that can be added to a mix to give you additional options for adjusting the percentages of nitrogen and oxygen. Helium presents some of its own issues.

Whether a particular blend is "better" or "worse" than another depends upon the depth and the time it is going to be used. Just a little bit of reading will demonstrate why special training and careful planning are required to dive with specially mixed gases.
http://njscuba.net/gear/trng_06_tech.html

 

[wedivebc]

OK got it, so what's the difference between trimix, triox, and helitrox?

 

[diverbrian]

what he said,

Normoxic can be used to 190-220 ft, where the partial pressure of O2 in air would not nessicarily be a serious problem, but the narcotic effect of the nitrogen is seen to be too great.

Hypoxic mixes (less than 21% O2) used for deeper diving, here some general guidelines:

16% oxygen is roughly equivalent to the percentage in your exhaled breath, so you can theoretically breathe this all the way to the surface and or decompress on it in the event you lost your deco gasses.

less than about (between) 9-12% oxygen and you would pass out if you tried to breathe it at the surface, so requre the use of a travel gas, but could not decompress on you bottom mix in the event of lost deco gas.

Until the mid 90's, it was seen as perfectly acceptable to dive to the depths of 190-200 ft on air. The trend since then is that while the risk of oxygen toxicity is acceptable at those depths, the effects of Narcosis are not acceptable on air, so helium is introduced to reduce the levels of narcosis.

190 ft.? Once I get the card done so that I can get fills, I don't plan on doing anything below the 130 ish range without helium in that mix. That limit becomes more shallow if I plan to do any serious work.

 

[lamont]

OK got it, so what's the difference between trimix, triox, and helitrox?

I believe trimix is any mix containing O2, He and N2. Triox is hyperoxic trimix (30/30) and helitrox is pure He/O2 (50/50). Heliair is a mix of helium an air (hypoxic trimix).

 

[wedivebc]

I believe trimix is any mix containing O2, He and N2. Triox is hyperoxic trimix (30/30) and helitrox is pure He/O2 (50/50). Heliair is a mix of helium an air (hypoxic trimix).

Actually your naming convention is even more confusing. 30/30 is called triox and contains 30% oxygen and 30% helium but 50/50 contains 50% O2 and 50% helium? If I wanted a heliox mixture containing 15% 02 and the renainder HE how would I designate that?
BTW helitrox is not the same as heliox.
And I forgot about heliair, yeah yet another name for a gas commonly used in the dive industry.