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James-S
12-01-2015, 02:01 PM
I may have misunderstood but the general impression that I get is that people think breathing helium, certainly on open circuit, will make you lose heat faster than if you were breathing nitrox/oxygen. I assume that this is because of the association with getting cold if you put helium in your drysuit, but when you actually think about the physics this can't be the case. I'm only talking about breathing it here, not putting it in your suit, just to be clear. Before I ramble on explaining why, is this already accepted knowledge to everyone or am I actually picking up on a general misconception?

GLOC
12-01-2015, 02:06 PM
I don't think people are saying breathing helium will make you colder than breathing any other compressed gas. Can you point to specific examples?

Regards

James-S
12-01-2015, 02:11 PM
I don't think people are saying breathing helium will make you colder than breathing any other compressed gas. Can you point to specific examples?

Regards

No I don't think I can, but I have definitely heard people say things that suggested it in the past, and then I've just accepted it until now I've actually thought about it. I must be in the minority then. Nothing to see here people, apart from a small personal epiphany.

OutOfTest
12-01-2015, 02:22 PM
To my brain it would make sense for breathing helium to make you colder as it will transfer the heat out your lungs faster and then get breathed out.

So if this isn't the case Id be interested to hear the reason? Not that I don't believe you, I'm sure you're much more knowledgable than I.


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GLOC
12-01-2015, 02:25 PM
Whether it transfers heat faster (or slower) than air is probably true, whether you as a diver can tell the difference is a different question.

Regards

Allan Carr
12-01-2015, 02:27 PM
Interesting link on the subject

http://www.nitroxdiver.com/Library/coldreg.html

johnkendall
12-01-2015, 02:28 PM
I may have misunderstood but the general impression that I get is that people think breathing helium, certainly on open circuit, will make you lose heat faster than if you were breathing nitrox/oxygen. I assume that this is because of the association with getting cold if you put helium in your drysuit, but when you actually think about the physics this can't be the case. I'm only talking about breathing it here, not putting it in your suit, just to be clear. Before I ramble on explaining why, is this already accepted knowledge to everyone or am I actually picking up on a general misconception?

Helium has a thermal conductivity about 6 times higher than air, so it can conduct heat out of the body faster. This seems to match my practical experience too.

HTH
John

notdeadyet
12-01-2015, 02:32 PM
The biggest loss of heat from the lungs is evaporation.

For conduction to transfer heat then it has to go somewhere. Where will it go in your lungs?

I would have thought denser gases would be better at transferring heat from your lungs. It's no different to a heat pump circuit. Lungs are the heat source, breathing gas is the carrier fluid. It has to store energy to get it to the cold outside like the liquid in the pipes.

What are you studying again?

Wilbo
12-01-2015, 02:33 PM
from Wikipedia:

Helium is the second least reactive noble gas (http://en.wikipedia.org/wiki/Noble_gas), after neon (http://en.wikipedia.org/wiki/Neon), and thus the second least reactive of all elements.[40] (http://en.wikipedia.org/wiki/Helium#cite_note-40) It is inert (http://en.wikipedia.org/wiki/Inert) and monatomic (http://en.wikipedia.org/wiki/Monatomic)in all standard conditions. Because of helium's relatively low molar (atomic) mass, its thermal conductivity (http://en.wikipedia.org/wiki/Thermal_conductivity), specific heat (http://en.wikipedia.org/wiki/Specific_heat), and sound speed (http://en.wikipedia.org/wiki/Speed_of_sound) in the gas phase are all greater than any other gas except hydrogen (http://en.wikipedia.org/wiki/Hydrogen). For similar reasons, and also due to the small size of helium atoms, helium's diffusion (http://en.wikipedia.org/wiki/Diffusion) rate through solids is three times that of air and around 65% that of hydrogen.[8] (http://en.wikipedia.org/wiki/Helium#cite_note-enc-8)

From this I read Helium (within a breathing gas) as being a reason for losing heat quicker..

James-S
12-01-2015, 02:42 PM
Helium has a thermal conductivity about 6 times higher than air, so it can conduct heat out of the body faster. This seems to match my practical experience too.

HTH
John

How does the heat conduction out of the body happen? Helium makes you cold in your drysuit because heat is conducted from your body to the water via the gas, and helium is a better thermal conductor so that process happens faster than with air. The same process doesn't happen with breathing gas though, because when you inhale the gas, there can be no conduction from inside to outside of the body via the gas you're breathing. The only heat loss happens when you exhale and you lose the energy that it took to heat the gas you had in your lungs. Helium has a lower specific heat capacity than nitrogen (by about 1/3), so less energy will be used in heating the gas to body temperature. The heating process with happen faster with helium that with air because of the higher thermal conductivity, but as I believe exhaled air is generally at body temperature anyway, no more energy will be spent heating helium over air (in fact less as just explained), and the rate of conductivity would actually be irrelevant.

The only thing that I can think of that would make this wrong is if exhaled breath is normally colder than body temperature. Specifically, if the difference between inhaled and exhaled gas temperature is <70% of the difference between inhaled gas and body temperature.

Also a paper I found on Rubicon, I've only read the abstract though so I don't know if it's actually any inconsistencies: http://archive.rubicon-foundation.org/xmlui/handle/123456789/5819

Foggy
12-01-2015, 02:52 PM
from Wikipedia:

Helium is the second least reactive noble gas (http://en.wikipedia.org/wiki/Noble_gas), after neon (http://en.wikipedia.org/wiki/Neon), and thus the second least reactive of all elements.[40] (http://en.wikipedia.org/wiki/Helium#cite_note-40) It is inert (http://en.wikipedia.org/wiki/Inert) and monatomic (http://en.wikipedia.org/wiki/Monatomic)in all standard conditions. Because of helium's relatively low molar (atomic) mass, its thermal conductivity (http://en.wikipedia.org/wiki/Thermal_conductivity), specific heat (http://en.wikipedia.org/wiki/Specific_heat), and sound speed (http://en.wikipedia.org/wiki/Speed_of_sound) in the gas phase are all greater than any other gas except hydrogen (http://en.wikipedia.org/wiki/Hydrogen). For similar reasons, and also due to the small size of helium atoms, helium's diffusion (http://en.wikipedia.org/wiki/Diffusion) rate through solids is three times that of air and around 65% that of hydrogen.[8] (http://en.wikipedia.org/wiki/Helium#cite_note-enc-8)

From this I read Helium (within a breathing gas) as being a reason for losing heat quicker..




Q=MCpDT
where Q = heat transferred
M = mass of gas
Cp = Specific heat of gas
DT = temp difference

Also 1 mole of gas occupies 22 cubic meters (or thereabouts); or for a given volume a gas of lower atomic mass will have a lower actual mass.

So air has a lower Cp and higher mass (per lungful) than helium - possibly little difference

Assuming the body (lungs) are at the same temp, then what temp is the incoming gas - well that depends on its latent heat of expansion (assuming that the source is at a higher pressure than the lungs)

The short answer is its going to make a marginal difference and as Gareth said I wonder if a diver can tell (have to do double blind tests etc to avoid physcological influences, and a big study group to avoid physiological ones..)

:)

James-S
12-01-2015, 02:54 PM
If I'm right then the difference will be marginal, except it will be marginally warmer. And for very long dives in very cold water that marginal difference would probably be handy to take advantage of.

nickb
12-01-2015, 02:56 PM
It's all good on CCR - just saying ;)

MikeF
12-01-2015, 02:59 PM
and cheaper

notdeadyet
12-01-2015, 03:01 PM
And tastes nicer.

And prevents erectile dysfunction.

And gives you super powers.

stuart_m
12-01-2015, 03:14 PM
First your 100m on OC thread now this. Are you bored James? ;)

OutOfTest
12-01-2015, 03:15 PM
So to put it in lay mans terms for myself...

You think it would make you colder as it conducts better. So it conducts the heat in your lungs, but because it retains less heat when you breath it out, you aren't losing as much warmth and you're warmer?


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James-S
12-01-2015, 03:15 PM
First your 100m on OC thread now this. Are you bored James? ;)

Well it's either this or learn quantum mechanics...

Ron MacRae
12-01-2015, 03:21 PM
Well it's either this or learn quantum mechanics...

For pity's sake don't do that.

Particles in a box, or not, was bad enough. I got to inverse effective mass tensors and lost the will to live.............

stuart_m
12-01-2015, 03:21 PM
Well it's either this or learn quantum mechanics...

:rofl: thought as much. For me it's either this or finish my b4$t4rd dissertation,

James-S
12-01-2015, 03:25 PM
So to put it in lay mans terms for myself...

You think it would make you colder as it conducts better. So it conducts the heat in your lungs, but because it retains less heat when you breath it out, you aren't losing as much warmth and you're warmer?


Sent from my iPhone using Tapatalk

Yep pretty much. Helium holds less heat when it's "full" than nitrogen does, so less heat is taken from your body to "fill" the gas with heat at body temperature. Helium being a better conductor means it will balance any difference in temperature between two surfaces that it is in contact with quicker than nitrogen, but when the only surface that it's in contact with is your lungs, there is no where for the heat to be transferred to, so the fast conductivity is irrelevant. This is of course different when it's in your drysuit, as the helium is on contact with both you and your drysuit, which is in turn in contact with the water, so the heat is conducted from your skin, to your drysuit, then into the water.

James-S
12-01-2015, 03:26 PM
:rofl: thought as much. For me it's either this or finish my b4$t4rd dissertation,

Still?? Honestly, how hard can it be...

James-S
12-01-2015, 03:27 PM
For pity's sake don't do that.

Particles in a box, or not, was bad enough. I got to inverse effective mass tensors and lost the will to live.............

Unfortunately it's compulsory this year. Not having gone to the lectures before Christmas didn't really help :/

Baron015
12-01-2015, 03:28 PM
Well it's either this or learn quantum mechanics...

QM can't be learned, it's just a probability distribution of whether you know it on observation.

graham_hk
12-01-2015, 03:49 PM
Yep pretty much. Helium holds less heat when it's "full" than nitrogen does, so less heat is taken from your body to "fill" the gas with heat at body temperature. Helium being a better conductor means it will balance any difference in temperature between two surfaces that it is in contact with quicker than nitrogen, but when the only surface that it's in contact with is your lungs, there is no where for the heat to be transferred to, so the fast conductivity is irrelevant. This is of course different when it's in your drysuit, as the helium is on contact with both you and your drysuit, which is in turn in contact with the water, so the heat is conducted from your skin, to your drysuit, then into the water.

Amount and rate are two different things - you are over thinking this ... for sure you feel colder breathing Helium that nitrox as JK said.

stuart_m
12-01-2015, 03:50 PM
Still?? Honestly, how hard can it be...

You forget I'll be seeing you soon young man!

nigel hewitt
12-01-2015, 04:07 PM
Being away from home so I don't have the old rubber book to hand and I can't be bothered to google for specific heats BY VOLUME (not mass).
I wouldn't know if OC helium makes you colder because I'm not stupid enough to breathe it OC.

What is surprising is that is that you don't notice how cold any OC gas is. Dropping from 10 bar to 1 bar drops the temperature at least 100C which is why regulators are susceptible to icing and the makers like nice chunky water-warmed metal bits where it happens.

hippytyre
12-01-2015, 04:21 PM
20. COLDER BREATHING HELIUM?
There is much discussion whether you get colder breathing helium than breathing air. 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. So there.


From here: http://scuba-doc.com/myths.html

GLOC
12-01-2015, 04:22 PM
https://cognitasresearch.wordpress.com/2014/05/27/how-low-can-you-go-temperature/ for an article on how easy regulators ice up and the (obvious) implications when diving in the cold.

Regards

ebt
12-01-2015, 04:26 PM
I must admit I've always been of the opinion that breathing helium is probably colder, but it probably pales into noise when you remember the gas you inhale is bloody freezing from its recent expansion/pressure reduction.

Anyway its a moot point, breathing helium OC just demonstrates poor judgement. One thing thats sure, when you bail off the loop and put the old OC stuff in your mouth, its a shocking temperature difference ;)

ps. until you see proper calcs with real numbers, its all just opinion....

taz
12-01-2015, 05:30 PM
.

Doesn't the specific heat content of the gas come into play?

He specific heat is 5.19 if pressure is constant and
N2 specific heat is 1.04 if pressure is constant.

That equals about 1.2 calories used in heat to warm up He by 1 degC
if you warm the gas up by 10 degC then it will be 12 cals (per Kg).

N2 is about 0.2 calories for the same amount per degC so 10 degC
would require 2 calories (per Kg).

As a crude back of the fag packet calculation He absorbs about
5 times more energy to heat it than N2?

Remember don't confuse heat with temperature.
Some products move a hugh amount of heat energy with little temperature difference
compared to others and its the energy that does the work.

taz

.

James-S
12-01-2015, 05:37 PM
.

Doesn't the specific heat content of the gas come into play?

He specific heat is 5.19 if pressure is constant and
N2 specific heat is 1.04 if pressure is constant.

That equals about 1.2 calories used in heat to warm up He by 1 degC
if you warm the gas up by 10 degC then it will be 12 cals (per Kg).

N2 is about 0.2 calories for the same amount per degC so 10 degC
would require 2 calories (per Kg).

As a crude back of the fag packet calculation He absorbs about
5 times more energy to heat it than N2?

Remember don't confuse heat with temperature.
Some products move a hugh amount of heat energy with little temperature difference
compared to others and its the energy that does the work.

taz

.

Per unit mass yes, but per mole is what matters in this case, as there is 1/7 the mass of helium in a given volume as there is nitrogen in the same volume at the same pressure.

James-S
12-01-2015, 05:39 PM
I'd imagine that the perception of helium being colder is due to the rate of conduction, in that the moment that you inhale it, it momentarily takes heat from your lungs much faster, it's just that it also stops sooner.

ebt
12-01-2015, 05:45 PM
I'd imagine you've got too much time on your hands and if you really want the answer you should run the numbers ;)

graham_hk
12-01-2015, 05:45 PM
I'd imagine that the perception of helium being colder is due to the rate of conduction, in that the moment that you inhale it, it momentarily takes heat from your lungs much faster, it's just that it also stops sooner.

But does it stop before you breath out?

James-S
12-01-2015, 05:48 PM
But does it stop before you breath out?

Well exactly, that's the key question, everything else is scientifically guaranteed as far as I can tell, that's the only possible place I can see it coming unstuck. A Google of the temperature of exhaled air seems to say that it is body temperature, and therefore has stopped. However, whether this is technically true or if it's "not far off" is a different question. Any ideas of how to accurately measure the temperature of my breath?

James-S
12-01-2015, 05:50 PM
I'd imagine you've got too much time on your hands and if you really want the answer you should run the numbers ;)

The only numbers that would be useful running are what temperature the gas in your lungs will be after x seconds of being inside you. Everything else is a case of greater than or less than and the absolute values aren't relevant.

nigel hewitt
12-01-2015, 08:14 PM
The only numbers that would be useful running are what temperature the gas in your lungs will be after x seconds of being inside you. Everything else is a case of greater than or less than and the absolute values aren't relevant.
Given the tiny size of an alveoli and the enormous area for heat exchange I would expect the temperature to normalise before you have finished the inhale.

Steve Clark
12-01-2015, 08:40 PM
Is it as simple as temperature of the gas you breathe in? (Rather than worrying about the exhale transfer).

On OC, the temperature of the helium reaching your second stage is probably lower due to the gas characteristics during expansion. Compressing helium uses more energy than air. Common sense would say it gets colder when it expands. Plus it has lower specific heat capacity and will cool more in the expansion.

My thermo is rusty. Something like that.....

Steve

gobfish1
12-01-2015, 08:59 PM
Well exactly, that's the key question, everything else is scientifically guaranteed as far as I can tell, that's the only possible place I can see it coming unstuck. A Google of the temperature of exhaled air seems to say that it is body temperature, and therefore has stopped. However, whether this is technically true or if it's "not far off" is a different question. Any ideas of how to accurately measure the temperature of my breath?

Yes call round and breath on my bell end and ill tell you the temperature , may take a few go,s tho :rofl:

jeff1955
12-01-2015, 10:43 PM
Yes call round and breath on my bell end and ill tell you the temperature , may take a few go,s tho :rofl:

And thus doth science advance....

Tens
12-01-2015, 11:14 PM
And thus doth science advance....

On the knees of giants.

Capt Morgan
13-01-2015, 12:28 AM
How about the helium absorbed in your system,
would it cause you to get colder ?

graham_hk
13-01-2015, 08:12 AM
How about the helium absorbed in your system,
would it cause you to get colder ?

I have just heard in a presentation by Doolette that helium is absorbed by the body at the same rate as nitrogen (as I recall diffusion is almost instantaneous so the differences predicted by Graham's law don't come into play).

James-S
14-01-2015, 12:52 PM
I have just heard in a presentation by Doolette that helium is absorbed by the body at the same rate as nitrogen (as I recall diffusion is almost instantaneous so the differences predicted by Graham's law don't come into play).

Really? That's interesting... Any published papers on the topic he referenced?

graham_hk
14-01-2015, 01:45 PM
Yes there are - I have them written down somewhere

nigel hewitt
14-01-2015, 03:17 PM
...(as I recall diffusion is almost instantaneous so the differences predicted by Graham's law don't come into play).
Since we have 70 to 100 square meters of alveoli ready to exchange, the distances are decimals of a millimetre and the volumes fractions of a litre it is all going to be over pretty quickly. Most of the 'fast compartment' delay is a result of the blood circulating so to get the net gas tension in the blood up takes time to get the exposure. The slower compartments feed from the blood and can be several further steps removed which is why they are slower and this is where Graham's law begins to bite.

Bühlmann's compartment times are faster for Helium factoring by 2.65 which is √7 which is the ratio of the molecular weights of nitrogen to helium so effectively using Graham's law.

graham_hk
14-01-2015, 04:17 PM
Since we have 70 to 100 square meters of alveoli ready to exchange, the distances are decimals of a millimetre and the volumes fractions of a litre it is all going to be over pretty quickly. Most of the 'fast compartment' delay is a result of the blood circulating so to get the net gas tension in the blood up takes time to get the exposure. The slower compartments feed from the blood and can be several further steps removed which is why they are slower and this is where Graham's law begins to bite.

Bühlmann's compartment times are faster for Helium factoring by 2.65 which is √7 which is the ratio of the molecular weights of nitrogen to helium so effectively using Graham's law.

Tell you what Nigel - why don't you argue with Doolette and the data. Which showed that Helium was not infact in or offgassed faster than Nitrogen. I will provide references if I can find my notes from talk. There is only one tissue in body which is diffusion limited which is inner ear.

Classic case of physiology over ruling physics.

jturner
14-01-2015, 04:18 PM
I think the reason it seems that breathing He OC makes you feel colder is actually due to the rapid evaporation of money from your wallet and also the dramatic thinning associated with this caused by not being able to afford to eat anymore.
But I may have just made that up!

simon mitchell
09-02-2015, 06:22 PM
Really? That's interesting... Any published papers on the topic he referenced?

Yes, here.....

http://www.ncbi.nlm.nih.gov/pubmed/25525213

Simon M

PeterL
09-02-2015, 06:39 PM
Yes, here.....

http://www.ncbi.nlm.nih.gov/pubmed/25525213

Simon M

Wow, that Doolette guy really gets around.....

So in short there is no apparent reason to pad deco for high HE mixes based on controlling compartments and no reason to accept higher END's to reduce deco? Would love to read the full text to know more about method and environment.

gobfish1
09-02-2015, 07:20 PM
Wow, that Doolette guy really gets around.....

So in short there is no apparent reason to pad deco for high HE mixes based on controlling compartments and no reason to accept higher END's to reduce deco? Would love to read the full text to know more about method and environment.

wow you got a lot more than i did From the link , i just go hot or cold HE or N2

huwporter
10-02-2015, 03:23 AM
Yes, here.....

http://www.ncbi.nlm.nih.gov/pubmed/25525213

I personally think this info is potentially more earthshaking than even the deep stops debate for decompression practice.

Simon, since the full article is subscription only, can you say if it elaborates on the "multi-exponential" kinetics that are the best fit to the data? Is there a substantive difference to the exponential decays that (e.g.) Buhlmann currently assumes for each compartment?

If the real-world half-times for Nitrogen and Helium are substantially similar for all or most compartments, is it still supported that these gasses be treated independently in terms of on-and-off gassing? (i.e. if you have tissues loaded with He and switch to a N2 mix, would you still be expected to off-gas the helium and on-gas the Nitrogen based solely on the independent gradients for each gas?)

Can these results be used to determine whether the current assumed time constants (in Buhlmann) for Nitrogen or those for Helium are 'more correct' - or is that not possible from the data? (- Just that they are substantially the same?) (Edit - thinking about it this is likely impossible, as compartments are theoretical constructs anyway.)

Thanks for any info,
Huw

nigel hewitt
10-02-2015, 09:59 AM
If the real-world half-times for Nitrogen and Helium are substantially similar for all or most compartments...
This one worries me.
We helicoptered off a diver with a rapid ascent and a friend of mine picked him up from the chamber.
The doctors there stated the opinion "thank goodness he didn't do that on helium"
I assumed that was personal experience of sorting out divers with similar profiles.
Hence my attachment to the idea that you gas on more helium faster.

Personally I thought he did do the rapid ascent because he wasn't on helium but that's another story.

Steve Clark
10-02-2015, 11:39 AM
Very simplistically, I've always worked on the principle that helium goes in (and out) 3 times as fast as nitrogen. You can kinda treat them both the same if you are doing normal ascents. If you do a fast ascent, you have a greater helium load with a potential to do damage. Once the dives are long enough that compartments begin to saturate both are equally bad.

Rough analogy of driving a car. If you drive a car that accelerates and decelerates slowly, you don't really get going very fast and it's not so bad if you hit something. If you drive a fast car, you can accelerate very quickly and hitting something is more dangerous.

(I'm not a deco nerd - pull it apart if you like)

Steve

HelmGuy
10-02-2015, 11:50 AM
..I've always worked on the principle that helium goes in (and out) 3 times as fast as nitrogen.

What's what I and I guess most people have assumed but maybe this research is showing this could be a false assumption.

nigel hewitt
10-02-2015, 12:32 PM
What's what I and I guess most people have assumed but maybe this research is showing this could be a false assumption.
I would guess that what these tests are showing is that transfer into blood is virtually instant but as blood circulates it looks like it is slow at effecting the total blood volume.
This short circuits the fastest compartment where the bulk of the gas resides.
Once the gas is inside it is defusing through tissues so Graham's law will be the driving force.
Perhaps what we need are additional faster compartments...
or a better model of blood as a compartment where some blood does a quick trip to the heart muscle and back in seconds while some heads off for your cold constricted feet.
I'm not sure this would change the model ascent timings much.

johnkendall
10-02-2015, 03:06 PM
Very simplistically, I've always worked on the principle that helium goes in (and out) 3 times as fast as nitrogen. You can kinda treat them both the same if you are doing normal ascents. If you do a fast ascent, you have a greater helium load with a potential to do damage. Once the dives are long enough that compartments begin to saturate both are equally bad.

Rough analogy of driving a car. If you drive a car that accelerates and decelerates slowly, you don't really get going very fast and it's not so bad if you hit something. If you drive a fast car, you can accelerate very quickly and hitting something is more dangerous.

(I'm not a deco nerd - pull it apart if you like)

Steve

The new research indicates that Helium and Nitrogen on-gas at a similar rate for any given compartment (apart from the inner ear).

HTH
John

huwporter
10-02-2015, 06:21 PM
This one worries me.
We helicoptered off a diver with a rapid ascent and a friend of mine picked him up from the chamber.
The doctors there stated the opinion "thank goodness he didn't do that on helium"
I assumed that was personal experience of sorting out divers with similar profiles.
Hence my attachment to the idea that you gas on more helium faster.

It could still be the case that uncontrolled ascents are worse on helium even if you don't on gas helium faster, if helium is more easily provoked into forming (troublesome) bubbles on ascent?

Cheers,
Huw

Tim Digger
17-03-2015, 09:52 AM
OK been mulling this one over and need to make the following point. Although with the exception of the Inner Ear most tissues of the body are perfusion limited with respect to on gassing the solubility of Nitrogen and Helium in water at 37deg C are radically different 0.015 and 0.0014 respectively. Thus for the same number of molecules being supplied to a tissue at the same partial pressure by blood perfusion (both Nitrogen and Helium behave as Ideal Gases in this respect so same number of molecules needed to reach same partial pressure), the tissue will become saturated/equilibrated about 10 times faster with helium than with nitrogen as fewer molecules are needed in the solution to produce a given partial pressure.

Where is the flaw in my thinking?
Would like the full text of Doolettes article though, if anyone has it, this may just be a case where physics and physiology colide and the results are not as one might expect.

johnkendall
19-03-2015, 06:33 AM
Here is the link: http://m.jap.physiology.org/content/118/5/586

huwporter
19-03-2015, 09:44 AM
Here is the link: http://m.jap.physiology.org/content/118/5/586

Only the abstract is available for free?

Cheers,
Huw

GLOC
19-03-2015, 10:47 AM
Looks like it. Same as many high end journals unfortunately.

Regards

MadUKDiver
19-03-2015, 01:01 PM
Full text here (http://jap.physiology.org/content/118/5/586)

GLOC
19-03-2015, 02:08 PM
Nope. Says full text, but you need to subscribe to get it.

Regards

MadUKDiver
19-03-2015, 02:27 PM
Nope. Says full text, but you need to subscribe to get it.

Regards

Their page must be flaky as I got full text first time I visited, now all I get is Abstract and Glossary. Lucky I saved it as PDF on my first visit!

Richie
19-03-2015, 04:27 PM
Bit beyond my A level zoology 😄


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Logun
19-03-2015, 04:49 PM
I may just so happen to have access via my uni library. ;)