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

[fsardone]

That is a thought I had no considered. Wouldn't they start floating after they warmed to room temperature?
They did not.

depends a day old baloon stops floating due to the fact that helium escapes … being so thin, and in a mix this would be even less apparent helium would effuse faster than nitrogen and oxygen ….

 

[lowviz]

...//... The first 5 balloons floated, the next few wouldn't float. They were all the same balloons, the only difference was the order in which they were filled. Wound up being kind of a neat experiment. Given enough time, they will actually separate back out.

The gasses are infinitely soluble in each other and this is why they will never separate back out to initial fill conditions:

• Entropy is also associated with the tendency toward disorder in a closed system.

 

[yle]

The gasses are infinitely soluble in each other and this is why they will never separate back out to initial fill conditions:

Yeah, kind of hard to get around that second law of thermo. But there will always be people that insist they can.

While I know this to be correct in theory, I have seen it not hold water with my own eyes. Used an AL80 of 18/45 bailout that had been sitting in the garage for multiple years untouched. Started using it to fill balloons for my friends daughter's birthday party. The first 5 balloons floated, the next few wouldn't float. They were all the same balloons, the only difference was the order in which they were filled. Wound up being kind of a neat experiment. Given enough time, they will actually separate back out.

You're onto something here... a simple experiment: exactly what you describe here, but then analyze the gas in each balloon immediately after they are filled. Not good for the party, of course, but great for science and our curiosity.

 

[Angelo Farina]

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. Hence we had to crawl through the building for crossing it safely. Guys who did not bear staying on the floor for 20 minutes crawling slowly, and who did stand up and run away, were often seeing collapsing after breathing the toxic CO, and then they had to be treated with pure oxygen or even in the hyperbaric chamber. After the second failed attempt, the guy was expelled by the fire brigade and sent back to normal military service. I managed to pass through the toxic gas building at the first attempt, luckily, and with no harm...

 

[DandyDon]

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. Hence we had to crawl through the building for crossing it safely. Guys who did not bear staying on the floor for 20 minutes crawling slowly, and who did stand up and run away, were often seeing collapsing after breathing the toxic CO, and then they had to be treated with pure oxygen or even in the hyperbaric chamber. After the second failed attempt, the guy was expelled by the fire brigade and sent back to normal military service. I managed to pass through the toxic gas building at the first attempt, luckily, and with no harm...

I'm having difficulties accepting that as presented. They lied to me about some things in the Marines as well, but maybe there is just more to that story. Sources vary but are similar enough in stating "CO has a molar mass of 28.0, and air has an average molar mass of 28.8. The difference is so slight that CO is found to evenly distribute itself indoors." I can guess that something else was in play there. Maybe it was how that CO was being generated so that it initially rose with smoke above the air in the room?

 

[Angelo Farina]

I'm having difficulties accepting that as presented. They lied to me about some things in the Marines as well, but maybe there is just more to that story. Sources vary but are similar enough in stating "CO has a molar mass of 28.0, and air has an average molar mass of 28.8. The difference is so slight that CO is found to evenly distribute itself indoors." I can guess that something else was in play there. Maybe it was how that CO was being generated so that it initially rose with smoke above the air in the room?

It is true the the density of a gas does not depend only on the molecular mass, but also on its temperature. CO, being a product of combustion, is hot, hence lighter. However in that room there was an evident thermocline, the air was "clean" in the lower 40 cm close to the ground, and full of smoke above. So yes, the presence of a thermocline indicates that the temperature was also playing a big role in toxic gas stratification.

 

[Storker]

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

Care to provide a summary? Or at least the DOI so we can see if the paper has been accepted in a reputable journal? Researchgate is great for accessing papers which aren't published open access, but only if the final version has been properly peer-reviewed for a decent journal.

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.

I'd like to see some numbers here. Mixing due to Brownian motion and the fact that Nature abhors a concentration difference (I.e. entropy) versus density differences. Methinks that the former might be more significant than the latter.

 

[DandyDon]

Hence we had to crawl through the building for crossing it safely. Guys who did not bear staying on the floor for 20 minutes crawling slowly, and who did stand up and run away, were often seeing collapsing after breathing the toxic CO, and then they had to be treated with pure oxygen or even in the hyperbaric chamber.

As an old story went in the U.S.Marines, several decades ago they trained infantry to crawl under live machine gunfire until one day one crawled into a rattlesnake, jumped up, and got shot. By the time I got there in 1967, they had done away with the live fire and had us crawl under threat of being kicked by roving instructors.

It is true the the density of a gas does not depend only on the molecular mass, but also on its temperature. CO, being a product of combustion, is hot, hence lighter. However in that room there was an evident thermocline, the air was "clean" in the lower 40 cm close to the ground, and full of smoke above. So yes, the presence of a thermocline indicates that the temperature was also playing a big role in toxic gas stratification.

I can't imagine that delicate thermocline surviving at 40 cm/16 inches off of the floor with trainees crawling under it for long. Maybe so, but when the first one failed and stood up, I would imagine the barrier was broken and gases readily mixed. I am guessing that you only heard of such happening and were not inside when such actually happened so your experiences are based on what you were told, perhaps?

 

[Biotech Diver]

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. Hence we had to crawl through the building for crossing it safely. Guys who did not bear staying on the floor for 20 minutes crawling slowly, and who did stand up and run away, were often seeing collapsing after breathing the toxic CO, and then they had to be treated with pure oxygen or even in the hyperbaric chamber. After the second failed attempt, the guy was expelled by the fire brigade and sent back to normal military service. I managed to pass through the toxic gas building at the first attempt, luckily, and with no harm...

In all practicality the heavier gas molecules do not stratify and settle to the bottom of a container. The concentration of gases in the Earth’s atmosphere does not really change all the way up to the edge of space. If heavier gas molecules stratified, the surface of the earth would have an atmosphere of almost pure radon.

An explanation of why you can breathe while crawling on the floor in a room with a fire is that as the combustion occurs, heat is produced and the air rises while drawing in fresh air at the floor from the surrounding areas. If the room was sealed off the concentration of oxygen and CO would be equal, from top to bottom, almost instantly.

 

[wgw04024]

So is this about all we're going to hear about this accident?