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

[rjack321]

In the fire fighting context CO is rising and near the ceiling because its the byproduct of combustion. The higher temps of the combustion products are overwhelming the slight molecular mass differences.

I'm not sure the relevance to this accident since the cylinder was filled with 100% helium and unanalyzed and unmarked. There was nothing to separate.

 

[Angelo Farina]

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.

We were trained to use both an air tank (without any need of staying close to the ground) and a simple full face mask with anti-smoke filter. The need of staying close to the ground was just when using the latter.
We were told that the filter was good against smoke, but not against CO or other gases.
About stratification, it must be understood that the products of combustion tend to stratificate close to the ceiling because they are less dense. But this is only marginally due to their lower molecular mass, the lower density is mostly caused by the high temperature.
However I remember that the stratification was clearly visible: around 50 cm above the floor there was an evident thermocline.
Below there was fresh air, quite breathable.
Above the thermocline there was smoke with very limited visibility and higher temperature.
I do not think that this can happen inside a tank, where the gas is substantially isothermal.
And of course in this sad accident there was pure helium, so we are going OT. Sorry for that...

 

[DandyDon]

About stratification, it must be understood that the products of combustion tend to stratificate close to the ceiling because they are less dense. But this is only marginally due to their lower molecular mass, the lower density is mostly caused by the high temperature.

Right, the CO produced in a house fire would be higher because it was warmer, not so much because it's lighter than air. You would understand this more than most as you have actually trained and worked in fires while most of us would prefer to get out and stay out of the way.

However I remember that the stratification was clearly visible: around 50 cm above the floor there was an evident thermocline.
Below there was fresh air, quite breathable.

I guess that's why we're warned to escape a burning building by crawling.

 

[PBcatfish]

For those who don't want to read 25 pages to find out what happened, take a look at post #56 on page 6. It appears that the kids got a tank of HE rather than a tank of air.