Bolding mine. Who is “we” in this assertion ? I am having a conversation with @engineer_comp_geek - Since when has SD changed into “we” versus “others” ? Is there a internal group, I’m not aware of ?
See above . It was asserted that CO2 pools in low lying areas - This is what I am responding to.
Perhaps you can learn from the demonstration that firefighters use all inert gases equally. There is no preference for CO2 because it settles in low areas and smothers out liquid fuels which may be sitting in low areas too.
Here is a similar experiment with a person pouring out Helium to put out a fire. Again, nothing to do with density
From the kinetic theory of gases, the velocity of CO2 molecule versus that of a Oxygen molecule in air is inv proportional to square root of the Mol weight.
So compared to Oxygen molecules in air, the CO2 molecules are moving at 85% of their speed, or compared to N2 molecules - they are moving at 80% of their speed.
Again, to emphasize, CO2 in pits accumulates because the source of the leak is in the pits - it does not flow down into pits without diffusing in air.
Argon has the same mol weight as CO2 - it does not accumulate in low spots either.
In this virtual space, you and @engineer_comp_geek are not the only people present. “People chatting around a table in a bar” is a decent model for the interaction here. When I say “we”, I’m not using the royal “we.”
The settling/creeping tendency of a plume of CO2 is certainly not something to be relied upon in a firefighting situation. For starters, the violent expulsion of CO2 from an extinguisher immediately contributes to turbulent atmospheric mixing. Ambient wind/HVAC convection can also help with mixing. At the same, ambient wind/convection can’t be relied upon to serendipitously move bulk quantities of CO2 to where you want it. If you see a fire, you blast it directly with CO2, you don’t hope your overspray from 20 feet away drifts over to it.
They did not pour out helium; the helium was confined in a flask, and the match was inserted into the flask. To the extent that helium was coming out of the flask, it was almost certainly pouring up through the top half of the neck, with air entering the flask via the bottom half of the neck. If you did the same demo with a flask of CO2, I definitely would expect it to pour from the bottom half of the neck; you should be able to extinguish the match simply by holding it near the flask opening, without having to actually insert it in the flask as they did in this demo.
Nice try. I am not buying it. 
Please provide a cite for “settling/creeping tendency of a plume of CO2”
They did - watch it again.
See my cite upthread re: the Lake Nyos disaster.
Watching it again:
1:22, flask is full of helium, stopper is removed.
1:23, lit match is inserted into the neck of the flask, where already-present helium promptly extinguishes the flame.
How/when is any kind of pouring action demonstrated in this video?
Do not go by wikipedia. Here is a peer reviewed Journal publication of the Lake Nyos disaser.
The initial velocity of the gas jet should have been 28 m/s, the volume of pure CO2 0.6 km3 and the gas release should occur in a very short time (a few minutes).
This a forced diffusion system with lots of factors playing into it like wind direction.
The system - @engineer_comp_geek and I were talking about was CO2 settling in low pits in a brewery.
The helium has not collected at the top of the beaker but the flame goes out right near the entrance to the flask.
You didn’t include the link, so I went out and found it. I’m not sure why you’re quoting that part of the abstract. The relevant part would seem to be the first few sentences:
In order to explain the origin of the Lake Nyos Disaster, a three-dimensional model for carbon dioxide flow has been calculated. The boundary conditions were based on the field observations. Calculations show that CO2 tends to flow down slope by gravity and velocity tends to increase on steep slopes. The results of calculation are in good agreements with the effects observed in the field.
In other words, their work supports my contention that bodies of CO2 gas will flow under the influence of gravity. A large release or continuous source of CO2 need not be in a pit in order for CO2 to flow across the floor in a way analogous to water, eventually finding low spots.
? The helium hasn’t “collected” anywhere. The flask was completely filled with helium before the stopper was placed. The flame doesn’t go out until the match is inserted into the flask. Claiming this demonstrates pouring of helium gas is like dropping a match into a beaker of water and claiming that that demonstrates pouring of water onto the flame.
No it doesn’t. What it supports is my original assertion that " Low spots that have CO2 leaks will accumulate CO2. CO2 will not flow under buoyancy differential and collect in low spots.
It also proves that your wikipedia link was wrong.
What part of “CO2 tends to flow down slope by gravity” (from your cite) are you interpreting to mean “CO2 will not flow under buoyancy differential”?
This was the original statement, I posted about. And my link contained a link to a published paper that said -
A very common opinion among cavers (and not only
cavers, see (Al-Azmi, 2008)) is that dense gases tend to
accumulate in depressions, and especially, at the bottom of
caves. It is widely accepted that CO2 accumulates at the
> bottom of shafts; this concept has been infrequently
> discussed, but often repeated from paper to paper. In this
> paper we show that this concept is in fact false and may be
regarded as an underground legend (James, 2003; Cigna,
2008).
This publication can be found here : https://caves.org/pub/journal/PDF/v71/cave-71-01-100.pdf
As far as I am concerned, this is my final post. I believe, my assertion is adequately backed up by citation from peer reviewed literature. Yes, it is true that NIOSH and OSHA also have done the mistake of saying that "dense gases tend to accumulate in depressions" but this is a myth that just keeps getting perpetuated.
The wildly feared problem that denser than air gases released underground or in a confined space will stay there may be a myth - I have no idea - but I’m certainly never going to test the hypothesis. If someone who’s an experienced caver or engineer tells me not to do something, I’m definitely not going to go against their advice.
We weren’t sure how seriously to take it, but at one stage as teenagers we actually popped a bag over our heads each (very briefly) to prove to ourselves it wasn’t that dangerous.
