Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Nobody's Confidant on 20/09/2007 17:52:58
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So pure oxygen is highly reactive right? So why do smokers with bad lungs carry around tanks with them full of the stuff to breathe in? Isn't that dangerous?
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Most things used for medical purposes are dangerous.
Pure O2 can be dangerous, but not extremely so. Many industries use extensive amounts of O2, and it is even used by sportsmen (mountain climbers and divers). Accidents do happen, but they are rare.
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It was dangerous next door at my sisters house, My brother in law is a truck driver and quite and eperienced good welder who keeps several large tanks of oxygen for welding. They had an apartment over the garage area where his big rig was stored. They were gone camping and the tenant dropped a cigarette in the carpet before going out for the evening and it smoldered and caught the place on fire it burned the place down and you would not believe the explosions when the oxygen tanks went off! It shot them hundreds of feet into the air exploding with very loud explosions one after another part of one oxygen tank flew over our house and into the woods on the side of out property! It was crazy and so very scary and dangerous. Especially in a fire!
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Divers don't use pure O2, they use a mix with helium. When mixed with an inert gas, be it helium (divers) or nitrogen (the air), oxygen is no more dangerous than air.
On the other hand, you do get treatments like this
http://news.bbc.co.uk/1/hi/health/medical_notes/g-i/980118.stm
Basically the big risk with oxygen is that things just get a load more flammable. People, for example. But in the absence of a source of ignition that's not too much of an issue.
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So pure oxygen is highly reactive right? So why do smokers with bad lungs carry around tanks with them full of the stuff to breathe in? Isn't that dangerous?
You are talking about molecular or atomic oxygen?
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Karen, these explosions were not caused by the fact that the tanks contained oxygen, they would have occurred with any gas. What happens is that the temperature rise due to the fire results in a pressure rise in the container. At 300°C (about 570°F) the pressure would be doubled (roughly). But next the oxygen escaped from the container is bound to intensify the fire.
But you can have gas containers with nitrogen exploding in a fire.
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I did not know that I always thought that it was the oxygen itself that caused the loud explosion, but what your saying is that it was really the built up pressure in the tank from the heating up of the oxygen? Does Oxygen expand when heated??
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All gasses expand, at about the same rate. At constant volume, the pressure is proportional to the absolute temperature (°Kelvin).
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I did not know that I always thought that it was the oxygen itself that caused the loud explosion, but what your saying is that it was really the built up pressure in the tank from the heating up of the oxygen? Does Oxygen expand when heated??
There are two separate issues.
The first is to do with pressurise gas tanks - any gas.
The other problem is that oxygen itself will easily cause things to ignite (not explode). This is less of a problem, and causes fewer accidents, than the problems with the gas being pressurised, but it did cause problems with a fatal fire in Apollo 1.
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Well these tanks exploded and shot pieces everywhere! Is there more in an oxyacetylene tank then oxygen??
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When astronauts are in their space suits what they breath in is pure oxygen.
No harm done and designed to give them plenty of available oxygen.
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Um, an oxyacetylene tank will actually be two tanks. One is filled with oxygen. It'll be at high pressure, it'll go off with a hell of a bang, and it'll increase the proportion of oxygen near the fire for a bit, which will make it burn faster until it disipates/gets used up.
The acetylene is actually the big deal here, I think. Acetylene is highly flammable, burns really hot, and just for added amusement value, I believe you can get more acetylene into a tank by dissolving it in some solvent (I forget what) than you could as a compressed/liquified gas at the same pressure. So when the cylinder blows off, the flammable gas is released, expands hugely, makes itself a lot hotter (which means it expands more) result is a huge mess.
So yeah, I doubt if the oxygen cylinders were really the big deal there (unless I guess one went off right at the same time as the acetylene).
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Acetylene tanks are even more dangerous than oxygen or nitrogen tanks. Acetylene is unstable anyway and will explode when heated. The explosion will have flung bits of the tank about. Acetylene is stored in solution (usually in acetone) held in place on an innert substrate because it's too unstable on its own. Pure acetylene isn't usually used above about 9PSI pressure for this reason.
Oxygen is toxic if breathed at much more than the normal concentration in air.On the other hand if your lungs have been damaged by smoking then the only way they will transfer enough oxygen to your blood is if you breath a higher concentration than normal. The moral of this is don't smoke.
Atsronauts do breathe pure oxygen but usually at low pressure (about 1/5 times normal atmospheric). This means that they suits are less cumbersome (these guys aare walking about inside an inflated baloon) and also that there's less weight to take up into space.
The actual number of oxygen molecules in a lungfull is the same as normal air so the toxicity doesn't come into effect.
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When astronauts are in their space suits what they breath in is pure oxygen.
No harm done and designed to give them plenty of available oxygen.
The problem is not with humans breathing oxygen (it happens all the time in ICUs). The problem is inflammable substances in a pure oxygen environment.
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Let me make this as clear as I can.
Pure oxygen is toxic at normal pressures.
Generally, humans breathing pure oxygen for any length of time is a problem.
The astronauts get by because they are at low pressure.
It's only used in ICU for people who cannot otherwise get enough oxygen.
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When astronauts are in their space suits what they breath in is pure oxygen.
No harm done and designed to give them plenty of available oxygen.
Astronauts like divers under normal conditions breath normal air not pure oxygen , the only time either breath pure oxygen is to rid their bodies of nitrogen .
With astronausts i believe its before a space walk and with divers after a deep dive. Their are also many other mixture of gases which divers can breath like Nitrox(N2O2),Heliox(HeO2),Trimix (HeN2O2)etc
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Let me make this as clear as I can.
Pure oxygen is toxic at normal pressures.
Generally, humans breathing pure oxygen for any length of time is a problem.
The astronauts get by because they are at low pressure.
How come? Does Oxygen's high reactivity damage cells or something? (and maybe when the pressure is lower then the rate of reaction is lower too so it's less dangerous?)
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"Does Oxygen's high reactivity damage cells or something?"
Essentially, yes.
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Let me make this as clear as I can.
Pure oxygen is toxic at normal pressures.
Generally, humans breathing pure oxygen for any length of time is a problem.
The astronauts get by because they are at low pressure.
How come? Does Oxygen's high reactivity damage cells or something? (and maybe when the pressure is lower then the rate of reaction is lower too so it's less dangerous?)
Yes, oxygen forms free radicals that damage tissues and DNA. Higher blood concentrations of oxygen facilitate the formation of more free radicals, which means more damage to tissues.
But, as Bored chemist has pointed out, the pressure of inspired oxygen is the key. This governs how much oxygen in the inhaled mix will be absorbed by the blood and hence end up in the tissues. Breathing a high concentration of oxygen at sea level will result in a much greater oxygen load than breathing the same concentration of oxygen at the top of Everest. And if your lungs are stuffed, then you need a much higher alveolar concentration to drive the gas into the blood stream to achieve arterial oxygen levels approaching those yielded by a normal pair of lungs.
Chris
Chris
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When astronauts are in their space suits what they breath in is pure oxygen.
No harm done and designed to give them plenty of available oxygen.
Astronauts like divers under normal conditions breath normal air not pure oxygen , the only time either breath pure oxygen is to rid their bodies of nitrogen .
With astronausts i believe its before a space walk and with divers after a deep dive. Their are also many other mixture of gases which divers can breath like Nitrox(N2O2),Heliox(HeO2),Trimix (HeN2O2)etc
The NASA astronauts when outside their suits in the shuttle etc breath in a mixture of oxygen but when preparing for spacewalks they have to breath in pure oxygen to get rid of the nitrogen. They have to do this as while they are in their space suits they breath in pure oxygen, but as mentioned at a different atmospheric pressure.
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Yes, oxygen forms free radicals that damage tissues and DNA.
Isn't there a way to limit the oxygen free radicals; maybe if the oxgen was prepared inside and never exposed to sunlight (and therefore UV light) then free radicals will never form? Or are there other ways which the free radicals form? (cosmic rays maybe?)
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Elemental oxygen is naturally a free radical. It doesn't exist any other way.
Dick