79%Helium - 21% O2 blending? Why not?

[grahamsp]

I know this is off topic but relevant to breathing helium, as long as you don't use it to inflate your suit, it doesn't cool the body anymore than breathing air.

dive safe!---brando

Don't think this is right. It's been a while but from memory, diving heliox is cold, cold, cold. The cause is helium's thermal conductivity, which is significantly greater than that of air. Any physicists out there who can confirm or deny?

 

[wedivebc]

err really? my understanding is that it does, through the lungs.

A rebreather doesnt have anything to do with your suit either, but it keeps you significantly warmer because you are breathing gas warmed by the chemical reaction of scrubber material.

You wouldnt want to use helium for suit inflation, it is a contentious subject, but Isobaric counterdifusion "could" potentially cause this problem. Personally I have never heard a confirmed example of this.

What does ICD have to do with how cold you feel?
As a person who dives helium mixes with a rebreather I can honestly say I have found little difference in the effect of my breathing mix on how cold I feel. And I dive in some pretty cold water. I am not really even sure I feel any warmer on a rebreather dive than OC. Just my observation.

 

[Mako Mark]

What does ICD have to do with how cold you feel? .

nothing, just that it was another reason not to put it in your suit.

I personally have noticed a diference with rebreathers, but maybe it was just in my head. I guess it is hard to quantify, it was just what I felt.

 

[California Diver]

when diving a helium mix your body is cooler and thats why you fill your drysuit with argon while diving trimix or any helium based gas because it insulates much better than air.

 

[BCS]

Don't think this is right. It's been a while but from memory, diving heliox is cold, cold, cold. The cause is helium's thermal conductivity, which is significantly greater than that of air. Any physicists out there who can confirm or deny?

I used to think so too...but don;t take my word for it...here's something form Dr. Jolie Bookspan.
"Helium has greater thermal conductivity than air. Undeniably, you lose more heat when surrounded by helium than by air, because heat conductance is the major factor in skin heat loss. Therefore helium is not used in dry suits. However, respiratory heat loss depends on heat capacity, and not at all on conductance. The thermal capacity of helium per gram is higher than that of air. However, there are fewer grams of helium for the same volume breathed because it is far less dense, making thermal capacity less compared to the same volume of air. Less heat would be lost breathing helium, so it should not chill you to breathe, as commonly thought. In a helmet or full face mask, your face may feel cool, making it hard to separate out the lesser loss through breathing.
Depth affects gas density, and so, heat loss through the breathing medium, and to be more confusing, you also need to account for interactions of respiratory heat loss through convection and evaporation. With helium you may also be more aware of the cold that is so common in diving, than when dulled by narcosis while breathing non-helium mixes. Remember too, it is generally not feasible to breathe air at depths where helium is used, so hard to compare in actual use. The short answer seems to be that breathing mixtures of helium at depths encountered by technical divers does not seem to result in greater cooling than breathing air. Helium feels colder to your skin than air, but it carries away less heat when you breathe it."
I was taught back in the 80's when I was in a commercial diving academy that heat loss was greater when breathing helium. But after a bit of research learned that is not exactly correct. Just like argon does not insulate us better because it is "denser". Here's a link to someone who can explain that a lot better than I can...http://www.decompression.org/maiken/Why_Argon.htm
like I said earlier, a bit off topic but beneficial knowledge nonetheless.

dive safe!---brando

 

[lamont]

Don't think this is right. It's been a while but from memory, diving heliox is cold, cold, cold. The cause is helium's thermal conductivity, which is significantly greater than that of air. Any physicists out there who can confirm or deny?

In the case of breathing, its probably heat capacity more than conductivity which is important. I'm guessing all three breathing gases probably are exhaled at a similar temperature.

 

[lamont]

In the case of breathing, its probably heat capacity more than conductivity which is important. I'm guessing all three breathing gases probably are exhaled at a similar temperature.

Following up to myself after poking my nose in a few of my old physics textbooks....

Helium is a monatomic gas, while nitrogen and oxygen are diatomic gases. That means that when you pump thermal energy into nitrogen or oxygen some of that energy goes into rotational and vibrational states of the diatomic molecule rather than into kinetic energy. That means that nitrogen and oxygen have higher heat capacities. The numbers are close to 20 J/mol-K (He) and 30 J/mol-K (O2, N2). That means that if your lungs heat the same volume of the gases (and same # moles) to the same temperature that the Helium will actually carry off less heat when you exhale. Since Helium has a higher thermal conductivity than N2 + O2 it might be exhaled hotter, but you still need to make it have a delta-T of 150% of the deltaT of O2/N2 to make the total thermal energy come out the same. As an example, if the temperature of the inspired gas is 45 degrees, the same amount of heat will be needed to warm He to 97.5 as it will take to warm O2/N2 to 80 degrees.

I'm with brando on this one. Breathing helium isn't likely to be any cooler, while helium in the drysuit is gonna be chilly...

 

[WarmWaterDiver]

Bravo Lamont!

 

[padiscubapro]

I used to think so too...but don;t take my word for it...here's something form Dr. Jolie Bookspan.
"Helium has greater thermal conductivity than air. Undeniably, you lose more heat when surrounded by helium than by air, because heat conductance is the major factor in skin heat loss. Therefore helium is not used in dry suits. However, respiratory heat loss depends on heat capacity, and not at all on conductance. The thermal capacity of helium per gram is higher than that of air. However, there are fewer grams of helium for the same volume breathed because it is far less dense, making thermal capacity less compared to the same volume of air. Less heat would be lost breathing helium, so it should not chill you to breathe, as commonly thought. In a helmet or full face mask, your face may feel cool, making it hard to separate out the lesser loss through breathing.
Depth affects gas density, and so, heat loss through the breathing medium, and to be more confusing, you also need to account for interactions of respiratory heat loss through convection and evaporation. With helium you may also be more aware of the cold that is so common in diving, than when dulled by narcosis while breathing non-helium mixes. Remember too, it is generally not feasible to breathe air at depths where helium is used, so hard to compare in actual use. The short answer seems to be that breathing mixtures of helium at depths encountered by technical divers does not seem to result in greater cooling than breathing air. Helium feels colder to your skin than air, but it carries away less heat when you breathe it."
I was taught back in the 80's when I was in a commercial diving academy that heat loss was greater when breathing helium. But after a bit of research learned that is not exactly correct. Just like argon does not insulate us better because it is "denser". Here's a link to someone who can explain that a lot better than I can...http://www.decompression.org/maiken/Why_Argon.htm
like I said earlier, a bit off topic but beneficial knowledge nonetheless.

dive safe!---brando

wow,
sound like what we have been teaching at ANDI for many years.. When we have instructors doing xovers from other agencies they usually get this wrong...

Most have been taught that breathing helium means greater heat loss.. Nice to see someone else teaches it correctly..

They incorrectly assume that since they will be colderfrom using Helium for their dry suits breathing it would do the same..

 

[archman]

Helium is a monatomic gas, while nitrogen and oxygen are diatomic gases. That means that when you pump thermal energy into nitrogen or oxygen some of that energy goes into rotational and vibrational states of the diatomic molecule rather than into kinetic energy. That means that nitrogen and oxygen have higher heat capacities. The numbers are close to 20 J/mol-K (He) and 30 J/mol-K (O2, N2). That means that if your lungs heat the same volume of the gases (and same # moles) to the same temperature that the Helium will actually carry off less heat when you exhale. Since Helium has a higher thermal conductivity than N2 + O2 it might be exhaled hotter, but you still need to make it have a delta-T of 150% of the deltaT of O2/N2 to make the total thermal energy come out the same. As an example, if the temperature of the inspired gas is 45 degrees, the same amount of heat will be needed to warm He to 97.5 as it will take to warm O2/N2 to 80 degrees.

Ow. I stopped reading after the first sentence. I'll just agree with you... got a D in physics the second time I took it.