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Author Topic: Why does pure CO2 kill you?  (Read 18466 times)

Offline krool1969

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Why does pure CO2 kill you?
« on: 02/11/2012 13:13:45 »
When I was a welder a very big deal was to weld in an enclosed space. All kinds of safety measures need to be taken. Even a completely brand new, virgin tank (that has never contained anything) can be really dangerous because the iron absorbs ALL the oxygen inside leaving just the nitrogen. (this can happen really quickly)
Even deadlier is an environment with pure carbon dioxide. In a pure nitrogen environment you take a breath you pass out but if someone can get you out in time, you should be okay. Pure CO2, one breath and you're stone dead. Why?


 

Offline RD

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Re: Why does pure CO2 kill you?
« Reply #1 on: 02/11/2012 15:37:29 »
Nitrogen is an asphyixiant gas : it's not toxic , it just does not contain oxygen, so causes suffocation.

Whereas carbon monoxide is toxic (poisonous) ...
Quote
[carbon monoxide] combines with hemoglobin to produce carboxyhemoglobin, which is ineffective for delivering oxygen to bodily tissues. Concentrations as low as 667 ppm may cause up to 50% of the body's hemoglobin to convert to carboxyhemoglobin. A level of 50% carboxyhemoglobin may result in seizure, coma, and fatality.
https://en.wikipedia.org/wiki/Carbon_monoxide#Toxicity
« Last Edit: 02/11/2012 15:42:23 by RD »
 

Offline Bored chemist

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Re: Why does pure CO2 kill you?
« Reply #2 on: 02/11/2012 18:13:30 »
Carbon monoxide is not the same as carbon dioxide.
Carbon dioxide and nitrogen both kill you by not being oxygen.
One breath of CO2 wouldn't do much harm, though it might make you cough a bit.
 

Offline CliffordK

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Re: Why does pure CO2 kill you?
« Reply #3 on: 02/11/2012 18:55:53 »
Your body, of course, has to get rid of CO2.  The higher the concentration of atmospheric CO2, the harder it is to do so.   CO2 does bind to hemoglobin, and while it is a different site than oxygen binds to the hemoglobin, it does reduce the oxygen carrying capacity of the blood.

The red blood cells also catalyze the dissolving of carbon dioxide in the blood, and the formation of carbonic acid.  The higher the CO2 concentration, the more acidic the blood.
 

Offline Bored chemist

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Re: Why does pure CO2 kill you?
« Reply #4 on: 03/11/2012 13:54:59 »
There's another factor. The body produces CO2 and it has a system for monitoring how much CO2 there is  in the blood. If that level is high, it increases the breathing rate to get rid of the excess.
In an atmosphere of pure CO2 that would tend to drive residual oxygen out of the body faster than an atmosphere of, for example,  nitrogen.
However there's another mechanism that's more likely to make a difference.
If the brain is deprived of oxygen you faint.
Normally, that's a good thing since it makes you lie down and that stops gravity draining blood + oxygen away from the brain.
However, if you are in a room with no oxygen and you faint then you are not in a position to save yourself.

The practical outcome of all this is that you should never enter a confined space unless you have tested the atmosphere and know for certain that there is enough oxygen.

In the UK, it's considered important enough to have its own law.
http://www.legislation.gov.uk/uksi/1997/1713/contents/made
 

Offline CliffordK

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Re: Why does pure CO2 kill you?
« Reply #5 on: 03/11/2012 22:12:48 »
How quickly does CO2 mix with air?  It is about 150% of the weight of O2 and N2, and thus if you introduce pure CO2 into a room, it could be more concentrated near the floor.  Thus, fainting might in fact be worse than if you could remain standing.
 

Offline Bored chemist

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Re: Why does pure CO2 kill you?
« Reply #6 on: 04/11/2012 11:29:38 »
Good point, it does "pool" and that's sometimes been a problem.
 

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Re: Why does pure CO2 kill you?
« Reply #6 on: 04/11/2012 11:29:38 »

 

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