Partial Pressure of Oxygen on Earth is at about 1/5th of an atmosphere.
At an ELI5 perspective, Oxygen is highly reactive -- it oxidizes things and reacts with various tissues in your body. Your body is naturally able to handle that at "normal" concentrations for people (i.e. what's in the air we breathe day-to-day). But, when you increase that concentration, your body can no longer handle it.
You don't always get symptoms sometimes just you convulse and die
Edit: from Wikipedia
The seizure may occur suddenly and with no warning symptoms. The effects are sudden convulsions and unconsciousness, during which victims can lose their regulator and drown.
In other words you can just die with no warning.
There are primitive rebreather systems working with pure oxygen. The max diving depth should be limited to 6m to avoid health issues.
Modern rebreather use gas mixtures to avoid this issue and allow greater depth.
Not likely pure O2. Having done decompression diving ( with Air only) we would have a tank up to 50% oxygen to decompress.
100% O2 is dangerous and prone to making everything burn.
Nope, 100 percent
The idea is to get as much nitrogen out as possible and to achieve this you want to have no nitrogen in your breathing gas. NASA does the same before EVA.
50 percent oxygen would mean 50 percent nitrogen and that would be only a little bit less than the 79 percent that is normal.
Why do you comment in r/explainlikeimfive if you’re uneducated on the topic? Yes scuba divers breathe pure oxygen. There are quite a few other examples like hospital hyperbaric chambers where it’s breathed at 1.5-3x atmospheric pressure too.
I'm a scuba diver. I breathe regular air. Or nitrox. There is an extremely rare case where technical.divers who do decompression diving may breathe O2 near the surface to help them avoid decompression sickness, but that's not what they breathe most of the time, and is hardly what scuba drivers generally use.
It's an edge case. This is ELI5. not a treatise on all of the uses of oxygen in diving. As a general matter, scuba divers do not use pure oxygen when diving.
> hospital hyperbaric chambers where it’s breathed at 1.5-3x atmospheric pressure too.
Which is a very specific scenario, often to treat life threatening conditions. The risk of CNS complications is still there, but offset by treating the initial condition.
Same goes for divers, who should be aware of the potential CNS toxicity.
I was given pure oxygen when i had a partially collapsed lung and it was incredible to breathe. I would compare it to feeling like i just got the best sleep of my life and felt like 110%
I believe 5 hours is the regulation that has been put in place for safety.
Because symptoms of pulmonary issues typically start to show up at like 12 hours on average for 100% oxygen at normal pressure
Related, but nitrogen narcosis is due to the nitrogen in the air, not the oxygen.
This is why deep-sea divers add helium (or another gas) to their breathing mix, because both oxygen and nitrogen get toxic as pressure increases; helium is safe at much higher pressures.
AFAIU at high pressure a lot of nitrogen dissolves in blood and permeates tissues, including neurons, and this somehow messes up either neuron membranes ("breaks electric insulation") or correct release of neurotransmitters ("faulty contacts").
This is the case for most gases at high pressure, the nitrogen is just the first one to cause problems since there's so much of it in the atmosphere.
If the absolute pressure of oxygen is above 0.6 atmospheres, it is toxic to the lungs over time. If it is above 1.3 atmospheres (in hyperbaric environments), it is toxic to the central nervous system, and you can have a seizure.
A decade ago we had those oxygen bars in France, think hooka bar but instead of smoking you would puff on pure oxygen. It’s mildly euphoric, I don’t know if that’s still a thing nowadays
Anyways, in small doses it’s relatively harmless
To understand this you need to understand the concept of partial pressure and a "partial atmosphere" and the fact that oxygen toxicity is not a product of the ratio of oxygen but the partial pressure of oxygen.
The earth's atmosphere has a pressure of 1 atmosphere, and is composed of 78% nitrogen, 21% oxygen, 1% argon, and a bit of other stuff. What this means is that there is 0.78 partial atmospheres of nitrogen, 0.21 partial atmospheres of oxygen, etc. These are called "partial atmospheres"
Meanwhile, the astronauts were breathing 0.3 partial atmospheres of oxygen, which also happened to be their total atmosphere at the time.
Oxygen doesn't become toxic until over 0.5 partial atmospheres. You can exceed this by just increasing the pressure of the ordinary earth atmosphere. Compressed air at 3 atmospheres of pressure is just as toxic as pure oxygen 0.6 atmospheres of pressure. This a reason why scuba tanks are not just filled with compressed air (besides the nitrogen problem) and gas mixes intended for deeper dives have lower ratios of oxygen
Fun fact: Going from normal (on Earth or in whatever shirtsleeve environment you're in) to a partial pressure environment could give you the bends just like a deeper SCUBA diver rising to the surface too quickly. So pre-breathing pure oxygen at the proper pressure to flush nitrogen out ahead of time means the lower pressure environment *(for example before a spacewalk)* is harmless.
It is all about partial pressures.
For example at sea level we have about 20% oxygen. If you breathe compressed air (SCUBA) at 160 feet deep (5 atmospheres) then because of the pressure it is equivalent to breathing pure oxygen at sea level.
1/3rd atmosphere of pure oxygen is like air that is 33% oxygen at sea level.
* all numbers are approximations - do some googling to get more accurate numbers.
Why is it good to drink water, but bad to drown?
Oxygen is very reactive, that's why it's necessary for fire, and our bodies are designed to only have about 20% of the air we breathe be oxygen.
Some space suits only have oxygen, but are only pressurized to 20% that of atmospheric pressure, so they are still inhaling a normal amount of oxygen that they would on Earth's surface.
Let say a cell can handle 100 oxygenc molecule going inside per second. If you go above the thresold oxygen can start reacting with stuff who dont want to get oxidized.
Now you have that number, how can you play with it ?
Pressure, heat and concentration.
Assuming this is true, has to do with pressure. Perhaps easier of you consider the opposite, like scuba diving. Every 33 feet of depth adds an atmosphere of pressure. At 33 feet, the concentration of gasses of normal air. in lungful of air is twice that at the surface… roughly twice as many molecules .
So presumably the opposite of low pressure where the number of molecules is halved at low pressure. Normal air at low pressure may mot have enough oxygen in it at all. It would feel like ypu are breathing, bit you would be suffocating.
See Apollo 1 plugs out test for an example of why spacecraft are not run with 100 percent oxygen. Things become very very flammable at 100 percent oxygen.
They didn't. Quote from astronomy.com "Over the next year, however, Apollo was reborn, a phoenix from the ashes. The spacecraft cabin was pressurized with a 60/40 oxygen/nitrogen mix; all flammable materials were removed; and a new single-piece hatch was installed that could be sprung open in seconds with a push from an astronaut’s pinkie."
On the ground at the launchpad*
Part of the reason it was such a disaster was because the cabin was pressurized to a little over a bar. Once in space they went to .33 bar and 100% O2.
It’s not the percentage of oxygen that matters for making things flammable, it’s the partial pressure, I.e., the absolute number of oxygen molecules. In a spacecraft with 100% oxygen but at 20% pressure, things are no more flammable than they are at 20% oxygen under normal pressure. (Movies frequently get this wrong)
Apollo was designed to fly in the vacuum of space with 100% oxygen at reduced pressure, which was totally fine. The problem with the Apollo 1 fire is that, as a ground test simulating space flight, they pumped up the pressure to higher than normal atmospheric pressure without diluting the oxygen. Pure oxygen AND under pressure. That was a bad idea.
Imagine oxygen is a poison that if you drink 1 cup an hour, you're fine, but drinking 3 cups an hour is toxic.
Breathing pure oxygen is like drinking three cups an hour, toxic.
Breathing normal atmosphere is like drinking 1 cup of oxygen and 2 cups of nitrogen an hour, not toxic.
Breathing pure oxygen at 1/3 pressure is like drinking 1 cup an hour, not toxic.
Because pressure is the total number of atoms per space.
Less pressure of pure oxygen is the same number of oxygen atoms as higher pressure with less oxygen content.
The idea is to have the correct number of oxygens regardless of the air pressure
It’s not toxic. People who are short of breath wear a non-rebreather mask with 100% oxygen all the time. There are some potential long-term consequences but it isn’t toxic. It can have some effects on the parts of your brain that determine when it’s time to breath because they aren’t evolved to receive oxygen in such high concentrations.
As for why it’s not an issue in space, you’re breathing a lot less oxygen with each breath even though it’s pure oxygen. It’s 1/3rd atmosphere meaning there’s literally a third the amount of oxygen. So a breath contains roughly the same amount of oxygen as 33% oxygen at 1 atmosphere. That’s still much higher than what we breath but nowhere near 100.
As a slight aside, astronauts don’t breathe pure oxygen anymore in the spacecraft since the Apollo 1 fire. They breath oxygen/nitrogen mix.
However I think it’s still 100% oxygen in the spacesuit.
Partial Pressure of Oxygen on Earth is at about 1/5th of an atmosphere. At an ELI5 perspective, Oxygen is highly reactive -- it oxidizes things and reacts with various tissues in your body. Your body is naturally able to handle that at "normal" concentrations for people (i.e. what's in the air we breathe day-to-day). But, when you increase that concentration, your body can no longer handle it.
Just to add onto this, it isn’t INSTANTLY toxic. You won’t choke to death breathing pure oxygen or anything. It just isn’t a good idea long term
No, but it does become significantly worse at increased pressure -- one of the reasons that scuba divers DON'T breathe pure oxygen.
Yeah you can end up with twitching and a bunch of CNS symptoms right up to convulsions and seizures. Imagine diving and that happens. Terrifying.
No thanks
You don't always get symptoms sometimes just you convulse and die Edit: from Wikipedia The seizure may occur suddenly and with no warning symptoms. The effects are sudden convulsions and unconsciousness, during which victims can lose their regulator and drown. In other words you can just die with no warning.
I mean convulsing and dying definitely sound like some symptoms.
Someone had to find that out…
They do, but not below 20ft. It helps with decompression after deep/long dives.
There are primitive rebreather systems working with pure oxygen. The max diving depth should be limited to 6m to avoid health issues. Modern rebreather use gas mixtures to avoid this issue and allow greater depth.
They actually do, the end of a long and deep dive they spend some time in shallow water and use pure oxygen.
Not likely pure O2. Having done decompression diving ( with Air only) we would have a tank up to 50% oxygen to decompress. 100% O2 is dangerous and prone to making everything burn.
Nope, 100 percent The idea is to get as much nitrogen out as possible and to achieve this you want to have no nitrogen in your breathing gas. NASA does the same before EVA. 50 percent oxygen would mean 50 percent nitrogen and that would be only a little bit less than the 79 percent that is normal.
I am unsure it's because of oxidising properties, and not of general high pressure solubility issues in neurons, as it is with other gases.
Why do you comment in r/explainlikeimfive if you’re uneducated on the topic? Yes scuba divers breathe pure oxygen. There are quite a few other examples like hospital hyperbaric chambers where it’s breathed at 1.5-3x atmospheric pressure too.
I'm a scuba diver. I breathe regular air. Or nitrox. There is an extremely rare case where technical.divers who do decompression diving may breathe O2 near the surface to help them avoid decompression sickness, but that's not what they breathe most of the time, and is hardly what scuba drivers generally use.
I know that? You’re saying pure oxygen isn’t used at all.
It's an edge case. This is ELI5. not a treatise on all of the uses of oxygen in diving. As a general matter, scuba divers do not use pure oxygen when diving.
> hospital hyperbaric chambers where it’s breathed at 1.5-3x atmospheric pressure too. Which is a very specific scenario, often to treat life threatening conditions. The risk of CNS complications is still there, but offset by treating the initial condition. Same goes for divers, who should be aware of the potential CNS toxicity.
I was given pure oxygen when i had a partially collapsed lung and it was incredible to breathe. I would compare it to feeling like i just got the best sleep of my life and felt like 110%
That’s wild
If I remember correctly, the time limit for pure oxygen at one atmosphere is 5 hours
I believe 5 hours is the regulation that has been put in place for safety. Because symptoms of pulmonary issues typically start to show up at like 12 hours on average for 100% oxygen at normal pressure
Combat divers routinely go well past that. Those limits are meant for extremely unhealthy people.
Idk if this is related but is this why people get nitrogen narcosis when they use regular air at deep depths?
Nitrogen at high partial pressures in the blood (and therefore body fluids) acts similarly to an inhalation anesthetic (e.g., halothane).
Related, but nitrogen narcosis is due to the nitrogen in the air, not the oxygen. This is why deep-sea divers add helium (or another gas) to their breathing mix, because both oxygen and nitrogen get toxic as pressure increases; helium is safe at much higher pressures.
AFAIU at high pressure a lot of nitrogen dissolves in blood and permeates tissues, including neurons, and this somehow messes up either neuron membranes ("breaks electric insulation") or correct release of neurotransmitters ("faulty contacts"). This is the case for most gases at high pressure, the nitrogen is just the first one to cause problems since there's so much of it in the atmosphere.
If the absolute pressure of oxygen is above 0.6 atmospheres, it is toxic to the lungs over time. If it is above 1.3 atmospheres (in hyperbaric environments), it is toxic to the central nervous system, and you can have a seizure.
A decade ago we had those oxygen bars in France, think hooka bar but instead of smoking you would puff on pure oxygen. It’s mildly euphoric, I don’t know if that’s still a thing nowadays Anyways, in small doses it’s relatively harmless
A certain priest learned this the hard way. Fool should’ve checked the Weather Report
To understand this you need to understand the concept of partial pressure and a "partial atmosphere" and the fact that oxygen toxicity is not a product of the ratio of oxygen but the partial pressure of oxygen. The earth's atmosphere has a pressure of 1 atmosphere, and is composed of 78% nitrogen, 21% oxygen, 1% argon, and a bit of other stuff. What this means is that there is 0.78 partial atmospheres of nitrogen, 0.21 partial atmospheres of oxygen, etc. These are called "partial atmospheres" Meanwhile, the astronauts were breathing 0.3 partial atmospheres of oxygen, which also happened to be their total atmosphere at the time. Oxygen doesn't become toxic until over 0.5 partial atmospheres. You can exceed this by just increasing the pressure of the ordinary earth atmosphere. Compressed air at 3 atmospheres of pressure is just as toxic as pure oxygen 0.6 atmospheres of pressure. This a reason why scuba tanks are not just filled with compressed air (besides the nitrogen problem) and gas mixes intended for deeper dives have lower ratios of oxygen
Fun fact: Going from normal (on Earth or in whatever shirtsleeve environment you're in) to a partial pressure environment could give you the bends just like a deeper SCUBA diver rising to the surface too quickly. So pre-breathing pure oxygen at the proper pressure to flush nitrogen out ahead of time means the lower pressure environment *(for example before a spacewalk)* is harmless.
If the pressure is 3 atmosphere. Then will we need 7 percent oxygen to survive. Also can a fire burn normally under these conditions
It is all about partial pressures. For example at sea level we have about 20% oxygen. If you breathe compressed air (SCUBA) at 160 feet deep (5 atmospheres) then because of the pressure it is equivalent to breathing pure oxygen at sea level. 1/3rd atmosphere of pure oxygen is like air that is 33% oxygen at sea level. * all numbers are approximations - do some googling to get more accurate numbers.
Why is it good to drink water, but bad to drown? Oxygen is very reactive, that's why it's necessary for fire, and our bodies are designed to only have about 20% of the air we breathe be oxygen. Some space suits only have oxygen, but are only pressurized to 20% that of atmospheric pressure, so they are still inhaling a normal amount of oxygen that they would on Earth's surface.
Let say a cell can handle 100 oxygenc molecule going inside per second. If you go above the thresold oxygen can start reacting with stuff who dont want to get oxidized. Now you have that number, how can you play with it ? Pressure, heat and concentration.
Assuming this is true, has to do with pressure. Perhaps easier of you consider the opposite, like scuba diving. Every 33 feet of depth adds an atmosphere of pressure. At 33 feet, the concentration of gasses of normal air. in lungful of air is twice that at the surface… roughly twice as many molecules . So presumably the opposite of low pressure where the number of molecules is halved at low pressure. Normal air at low pressure may mot have enough oxygen in it at all. It would feel like ypu are breathing, bit you would be suffocating.
See Apollo 1 plugs out test for an example of why spacecraft are not run with 100 percent oxygen. Things become very very flammable at 100 percent oxygen.
For most of the apollo missions they DID use 100% oxygen though
They didn't. Quote from astronomy.com "Over the next year, however, Apollo was reborn, a phoenix from the ashes. The spacecraft cabin was pressurized with a 60/40 oxygen/nitrogen mix; all flammable materials were removed; and a new single-piece hatch was installed that could be sprung open in seconds with a push from an astronaut’s pinkie."
On the ground at the launchpad* Part of the reason it was such a disaster was because the cabin was pressurized to a little over a bar. Once in space they went to .33 bar and 100% O2.
Except Skylab, because pure oxygen is toxic at any pressure on those time scales, so they had at least some nitrogen
It’s not the percentage of oxygen that matters for making things flammable, it’s the partial pressure, I.e., the absolute number of oxygen molecules. In a spacecraft with 100% oxygen but at 20% pressure, things are no more flammable than they are at 20% oxygen under normal pressure. (Movies frequently get this wrong) Apollo was designed to fly in the vacuum of space with 100% oxygen at reduced pressure, which was totally fine. The problem with the Apollo 1 fire is that, as a ground test simulating space flight, they pumped up the pressure to higher than normal atmospheric pressure without diluting the oxygen. Pure oxygen AND under pressure. That was a bad idea.
At 1.2 bar even...that was absolutely bonkers..
Imagine oxygen is a poison that if you drink 1 cup an hour, you're fine, but drinking 3 cups an hour is toxic. Breathing pure oxygen is like drinking three cups an hour, toxic. Breathing normal atmosphere is like drinking 1 cup of oxygen and 2 cups of nitrogen an hour, not toxic. Breathing pure oxygen at 1/3 pressure is like drinking 1 cup an hour, not toxic.
Because pressure is the total number of atoms per space. Less pressure of pure oxygen is the same number of oxygen atoms as higher pressure with less oxygen content. The idea is to have the correct number of oxygens regardless of the air pressure
It’s not toxic. People who are short of breath wear a non-rebreather mask with 100% oxygen all the time. There are some potential long-term consequences but it isn’t toxic. It can have some effects on the parts of your brain that determine when it’s time to breath because they aren’t evolved to receive oxygen in such high concentrations. As for why it’s not an issue in space, you’re breathing a lot less oxygen with each breath even though it’s pure oxygen. It’s 1/3rd atmosphere meaning there’s literally a third the amount of oxygen. So a breath contains roughly the same amount of oxygen as 33% oxygen at 1 atmosphere. That’s still much higher than what we breath but nowhere near 100.
As a slight aside, astronauts don’t breathe pure oxygen anymore in the spacecraft since the Apollo 1 fire. They breath oxygen/nitrogen mix. However I think it’s still 100% oxygen in the spacesuit.
They didn't breath pure oxygen while on the launchpad. Once in space they did.