Why are experienced divers getting killed and injured lately?

[lamont]

Ok, here is what I read: helium has poorer thermal properties than air. It is smaller molecularly so more of it is absorbed making the decompression stops, offgasing, longer. Trimix has 02 at 17%/18%, helium 50%, nitrogen the remainder. It was seen as a "warmer blend"

Helium is a lighter, less dense gas than nitrogen. Argon is added to a mix because of the poor themal properties of helium. ergo, I would think, you feel colder on your hang times with a higher mix of helium, which is why they added the denser gas, argon.

All I can tell from that is that you are confused.

Helium in breathing gas may actually carry away less heat with each exhale due to its lower heat capacity (the heat needed to heat the helium up to body temperature in your lungs will actually be less than the heat required to heat up O2 or N2).

Helium in your drysuit will be super chilly because it has higher thermal conductivity.

Argon is used in drysuit gas because it is a big, fat, slow atom that has a lower thermal conductivity than He, N2 or O2, while still being inert and all that.

Argon is not used in breathing gases because it is incredibly narcotic.

Helium is used in breathing gases because it is not narcotic.

And the relative quickness of ongassing/offgassing of Helium and the length of decostops on He is debatable.

 

[pilot fish]

I'm not sure what they were trying to say. All sorts of different mixes are used depending on the depth. As we go deeper we need to get rig of more O2 because it's toxic and we need to get rid of more N2 because it's narcotic. Helium is used to replace everything that we need to get rid of. That allows us to control both the PPO2 (MOD) and the PPN2 (END). We've dived some mixes with pretty high helium content in some pretty cold water and there isn't a problem

I think argon has been experimented with as a decompression gas and, I don't know, maybe there's some commercial diving application for it. Otherwise in recreational technical diving we don't breath it because it's very narcotic. However, some divers do use it as a dry suit inflation gas.

I'm not sure what they were saying either. These exotic mixes are all new to me and I have never used them, so I defer to you.

 

[pilot fish]

All I can tell from that is that you are confused.

Helium in breathing gas may actually carry away less heat with each exhale due to its lower heat capacity (the heat needed to heat the helium up to body temperature in your lungs will actually be less than the heat required to heat up O2 or N2).

Helium in your drysuit will be super chilly because it has higher thermal conductivity.

Argon is used in drysuit gas because it is a big, fat, slow atom that has a lower thermal conductivity than He, N2 or O2, while still being inert and all that.

Argon is not used in breathing gases because it is incredibly narcotic.

Helium is used in breathing gases because it is not narcotic.

And the relative quickness of ongassing/offgassing of Helium and the length of decostops on He is debatable.

Yes, I'm sure I am confused. I think one thing that most people agree on is that helium has pooer thermal properties than air. I don't dive these mixes, doubt I ever will, so it's moot for me.

 

[lamont]

Yes, I'm sure I am confused. I think one thing that most people agree on is that helium has pooer thermal properties than air.

but then most people are incorrect.

it has 'worse' (in the sense of carrying away more heat) thermal conductivity, but 'better' (in the sense of carrying away less heat) heat capacity.

 

[MikeFerrara]

MNaybe we're making it sound more complicated than it is.

Should I try again?

As we go deeper we need to have less oxygen and less nitrogen. The O2 makes you do the funky chicken and the nitrogen makes you loopy enough to enjoy doing it. The only way get rid of O2 and N2 is to replace it with something and that's where helium comes in.

 

[lamont]

s/helium makes you loopy/nitrogen makes you loopy/

 

[lamont]

another way of looking at this are that helium atoms are an incredibly fast bucket brigade and can carry a lot away very fast when they're operating that way, but the buckets are individually very small.

so, when they're your drysuit gas, the helium bucket brigade takes away a lot of heat. but when you breathe in helium the atoms have very small buckets which get completely filled up and then entirely exhaled (while O2 and N2 have bigger buckets, but they do a much slower bucket brigade).

 

[MikeFerrara]

s/helium makes you loopy/nitrogen makes you loopy/

ooops. I fixed it. that wasn't any way to get some one unconfused was it?

 

[pilot fish]

In short, more complex dives are being done now, with the introduction of new breathing gases, and deeper depths. Add to that the growing population of diving and you get an increase in accidents. It seems inevitable that divers will push the limits and some will have accidents.

 

[texdiveguy]

Can someone recap the previous 67 pages,,,,I missed out---