So, if CO2 really does sink below oxygen...

...wouldn't the CO2 in the atmosphere float to the ground and we'd all suffocate?

In a completely inert atmosphere and if there were a source crankling out a huge volume of pure CO2 then yes.

Concentration, miscibility (if you can really describe gases as miscible), and convection currents.

Think of the high school chemistry adage "Like, dissolves like". As a crude example consider ethanol and water, ethanol is less than dense than water but you don't get a layer of ethanol floating on top of your vodka, no matter how long you let it sit.

The difference is that stuff moves on the surface of the earth... there are temperature differences and weather that keep the air circulating... trees & plants inhale CO2 and exhale oxygen...

If you find any of these conditions in your keg, I suggest you not drink it.

Think of it this way: if alcohol is really lighter than water, shouldn't it float to the top of a beer and make the first few sips really strong?

Nope. It's a homogenous solution...much like the atmosphere.

EDIT: Crap. Rushis beat me to the analogy.

Here's a list of occasions where CO2 flows resulted in fatalities.

There's a recent case where CO2 evolving from a lake-bed killed a bunch of people, but I can't find the reference.

In all cases (like your first brew), insufficient mixing.

The lake bed was methane not co2.. just so you know. Lake Kivu, in Africa.

CO2 is a trace gas being only 0.038% of the atmosphere. CO2 is toxic in higher concentrations: 1% (10,000 ppm) will make some people feel drowsy. Concentrations of 7% to 10% cause dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.

CO2 is heavier than "air", (which is nitrogen and oxygen, mostly). In fact, oxygen is heavier than nitrogen.

Brownian motion, random movement of molecules, will mix the gasses eventually. The atmosphere is full of convective currents, (WIND), so it mixes much faster.

If you fill a carboy with CO2 and let it sit open to the atmosphere, however, the CO2 WILL diffuse out into the air, and after a little while the composition of gas inside the carboy will be the same as the composition of gas outside the carboy. We say "blankets of CO2" and "CO2 is heavier than air" because, in sufficiently short timescales, they stay distinct. This is why we have airlocks on carboys, however, because once the rate of CO2 production inside the carboy slows, O2 and N2 will start to mix back in to the headspace.

Getting . . . sleepy. Can't keep my eyes open.

I must be in a pocket of co2 concentration. Or could it be from reading Shorty's explanation.

david_42 said:

Here's a list of occasions where CO2 flows resulted in fatalities.

There's a recent case where CO2 evolving from a lake-bed killed a bunch of people, but I can't find the reference.

In all cases (like your first brew), insufficient mixing.

Click to expand...

I saw a thing on this, kewl how the brewery near the lake was harvesting teh CO2 for brewery use.

In at least older breweries someone needs to get in the fermenting vessel to clean after the beer has been racked off. IIRC, if they get in too soon, the blanket of CO2 will not have dissipated, and they could pass out/die.

dontman said:

Getting . . . sleepy. Can't keep my eyes open.

I must be in a pocket of co2 concentration. Or could it be from reading Shorty's explanation.

Click to expand...

<----Chemist/Chemical Engineer. I'm a hit at parties.

shortyjacobs said:

<----Chemist/Chemical Engineer. I'm a hit at parties.

Click to expand...

LOL!

BioBeing said:

In at least older breweries someone needs to get in the fermenting vessel to clean after the beer has been racked off. IIRC, if they get in too soon, the blanket of CO2 will not have dissipated, and they could pass out/die.

Click to expand...

Older breweries, and TONS of brew pubs and craft breweries. Completely hands free CIP systems are really something that only the big boys have. That said, I have in fact crawled into the tank too early and gotten quite the head rush from too much CO2 still in there, it is VERY important to make sure you let it air out before climbing in.

My boss told me a story about the brewery he worked at as a kid in Germany. Some guys showed up one morning to find a pair of rubber boots hanging out of a tank. Turns out one of the brewers had gotten there extra early to get a jump start on things and tried to climb in and clean the tank before all the gas was gone and it killed him before anyone else got to work, the rubber boots were attached to his legs as he was laying in tank. For that reason, we have to wait a while and let someone else know that we are about to get into a tank, that way they can check on us if we've been in there for a while, make sure we're still kickin.

RyanK2 said:

The lake bed was methane not co2.. just so you know. Lake Kivu, in Africa.

Click to expand...

its actually mostly CO2
"in Lake Kivu's case, methane and carbon dioxide due to lake water interaction with a volcano. The amount of methane is estimated to be 65 cubic kilometers, along with 256 cubic kilometers of carbon dioxide.'"
kivu

david_42 said:

Here's a list of occasions where CO2 flows resulted in fatalities.

There's a recent case where CO2 evolving from a lake-bed killed a bunch of people, but I can't find the reference.

In all cases (like your first brew), insufficient mixing.

Click to expand...

In 1986, a tremendous explosion of CO2 from the lake Nyos, West of Cameroon, killed more than 1700 people and livestock up to 25 km away. The dissolved CO2 is seeping from springs beneath the lake and is trapped in deep water by the high hydrostatic pressure. If the CO2 saturation level is reached, bubbles appear and draw a rich mixture of gas and water up. An avalanche process is triggered which results in an explosive over-turn of the whole lake. Since 1990 a French team has carried out a series of tests in an attempt to release the gas slowly through vertical pipes

Nyos

like others have said without the movement of the air it would eventually settle out

springer said:

In 1986, a tremendous explosion of CO2 from the lake Nyos, West of Cameroon, killed more than 1700 people and livestock up to 25 km away. The dissolved CO2 is seeping from springs beneath the lake and is trapped in deep water by the high hydrostatic pressure. If the CO2 saturation level is reached, bubbles appear and draw a rich mixture of gas and water up. An avalanche process is triggered which results in an explosive over-turn of the whole lake. Since 1990 a French team has carried out a series of tests in an attempt to release the gas slowly through vertical pipes

Nyos

Click to expand...

that's the one I saw.

RyanK2 said:

The lake bed was methane not co2.. just so you know. Lake Kivu, in Africa.

Click to expand...

Lake beds do contain CO2 which if the lake does not "turn over" i.e. if the layers are stagnent can build up. After build up a lake that turns over, particularly in a valley will release this CO2 forcing out the Oxygen out killing all animal life. The CO2 generally will dispate in a matter of hours or a few day. Methane CH4 can also build up like at Lake Kivu however methane floats very well so suffication is unlikely. however it is combustable leading to a nother potential risk.

Article: http://www.nature.com/news/2010/100823/full/4661033a.html