Children die playing with scuba gear left in pool - Jensen Beach, Florida

[Biotech Diver]

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I deleted

 

[DandyDon]

Plus the rest truly is no one else's business. People need to let the families grieve

That's covered here: PLEASE READ FIRST: Special Forum Rules

 

[Storker]

heavier gas will stay at the bottom for some time

Yes, for "some time". Because diffusion is slow, particularly in pressurised containers where the gas viscosity is higher, so it may well take a while before Nature has eliminated the concentration difference she abhors.

However, a mixture will not stratify unless perhaps in extreme gravitational or centrifugal fields (see e.g. centrifugal separation of uranium isotopes).

EDIT: This may be enlightening for those who missed chem 101:

 

[Biotech Diver]

Yes, for "some time". Because diffusion is slow, particularly in pressurised containers where the gas viscosity is higher, so it may well take a while before Nature has eliminated the concentration difference she abhors.

However, a mixture will not stratify unless perhaps in extreme gravitational or centrifugal fields (see e.g. centrifugal separation of uranium isotopes).

EDIT: This may be enlightening for those who missed chem 101:

Great video. As the video demonstrates the lighter Nitrogen Dioxide gas diffuses much more quickly than the heavier Bromine. This means the Helium gas in a scuba tank will diffuse even quicker in than the NO2. I think this pretty much settled the debate in my opinion.

 

[kelemvor]

Helium diffuses into air at a rate of 0.697cm2/s at 1ata. Adjust that for ~218ata (3200psi) and you'll have the answer. I suspect @Biotech Diver is right.

 

[jadairiii]

Yes, for "some time". Because diffusion is slow, particularly in pressurised containers where the gas viscosity is higher, so it may well take a while before Nature has eliminated the concentration difference she abhors.

However, a mixture will not stratify unless perhaps in extreme gravitational or centrifugal fields (see e.g. centrifugal separation of uranium isotopes).

EDIT: This may be enlightening for those who missed chem 101:

And yet, people will still believe the helium in their Trimix tanks will "naturally" separate if left unmolested......just like their Paul Newman's Italian Dressing.......keep rolling those tanks!

 

[yle]

Regarding gas separation by gravity, please read this article:
https://www.researchgate.net/profile/Sathish-Dhandapani/post/Is_gas_gas_gravity_separation_possible_What_conditions_and_restrictions_are_needed/attachment/59d640b679197b807799cdd9/AS:431900461408257@1479984502567/download/FULLTEXT01.pdf
As you will see, separation of gases by gravity actually occurs, and can even be exploited industrially. It is more evident when the two gases have very different molecular mass. Hence in air nitrogen and oxygen do not separate significantly, as their molecular mass are very close (28 and 32 kg/kmol respectively). But when one of the two gases is much lighter (helium has a molecular mass of just 4 kg/kmol), then the separation occurs quite significantly, given enough time and lack of mechanical mixing.
And I can endorse it by first hand experience: when young, I served my military service, for one year, in 1984, in the fire brigade (instead of serving as a soldier). During training we were given an anti-gas mask, which in reality has just an active carbon filter, and we had to cross a large building saturated with a mixture of toxic gases.
As Oxygen is the heavier, it tends to stay close to the floor, whilst toxic gases such as CO, being lighter, stratify at higher elevation.

You claim that nitrogen and oxygen do not separate significantly, because their molecular masses, at 28 and 32, respectively, are similar.

But then you claim that CO and oxygen do separate significantly... even though their molecular masses are 28 and 32, respectively.

As a scientific claim, this is interesting.

 

[CT-Rich]

Undiffusing gasses seems very unlikely at room temperature. Molecules will simply have too much kinetic energy to settle out by molecular mass. The only exception MIGHT be Helium because it is so much lighter than the other gasses. In a pressurized cylinder at room temperature, and in a gas column less than 3’ tall and being moved around by kids, it is extremely unlikely.

 

[Angelo Farina]

You claim that nitrogen and oxygen do not separate significantly, because their molecular masses, at 28 and 32, respectively, are similar.

But then you claim that CO and oxygen do separate significantly... even though their molecular masses are 28 and 32, respectively.

As a scientific claim, this is interesting.

That's not a scientific claim, it is the training I received as a firefighter... Which possibly has very little scientific significance!

 

[DandyDon]

But then you claim that CO and oxygen do separate significantly... even though their molecular masses are 28 and 32, respectively.

That's not a scientific claim, it is the training I received as a firefighter... Which possibly has very little scientific significance!

I suspect that your firefighter training taught you how to operate safely in the possible presence of the gas, like wearing a breathing kit similar to scuba. CO is slightly lighter than air so might tend to accumulate more close to the ceiling, but the difference is neglibable. It'd be found throughout the room.