Why is carbon monoxide more dangerous than other non-breathable ?gases?

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So from what I understand, when you breathe in an unbreathable gas like CO2 it dilutes the oxygen in the air so you get less oxygen each breath. But carbon monoxide seems to be deadlier and kills far more people than other non-breathable gases. Is this just because more things can expose you to carbon monoxide in a closed space or is there something different about it and what exactly happens when you breathe in gases that aren’t oxygen, like CO2 or CO. Do they actually enter the blood and get carried by red blood cells or are they filtered somehow and just exhaled?

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The issue is heamoblobin (in your red blood cells) loves oxygen and wants to bind to it. Unlike CO2 all the bonds are in use.

With CO there is a spare bond that binds with haemoglobin and this bond is unbreakable. In effect killing the ability for the Red blood cell to carry oxygen.

Over long enough exposure you become drowsy, pass out, then suffocate (but at a molecular level)

The way your blood takes up oxygen and other gases from your lungs is though diffusion. Essentially there is a small blood vessel with a thin barrier between it and one of the air sacs in your lung, and gas can diffuse across it.

Gas will diffuse towards the lower concentration of it, so gases will diffuse into your blood until the concentration in your blood matches the partial pressures of the various gases in the air – so all kinds of gases can dissolve into it. (Sidenote: this is why it is dangerous for scuba divers to ascend too quickly if they’ve been diving at high pressure – the nitrogen dissolved in the blood can form bubbles, which is bad.)

However, since the blood is specifically set up to carry oxygen (and carbon dioxide), it has hemoglobin molecules (in your red blood cells) to do so – the hemoglobin binds the oxygen, allowing far more of it to get into your blood than through regular diffusion. Hemoglobin also binds carbon dioxide, but more weakly than oxygen, allowing it to get rid of the CO2 and picking up fresh oxygen in the lungs easily.

Carbon monoxide can also bind to hemoglobin, and it does so *far* more strongly than either oxygen or CO2. In essence, when enough CO binds to your red blood cells it disables them completely, essentially rendering them useless until they are naturally broken down and replaced.

Most other non-breathable gases are just non-breathable, not actively toxic, so they can only kill you if their presence means an absence of oxygen. CO actively disables your system for carrying oxygen.

So, where nitrogen would reduce oxygen getting into your lungs and asphyxiate you, carbon monoxide preferentially binds to your blood instead of oxygen and effectively stops it working: it does this in absolutely tiny amounts too. 200 parts per million is fatal in hours, 800 parts per million will kill you in minutes: it’s not easily treatable as your blood likes it so much, so normally patients are given oxygen therapy. Coupled to this it makes you drowsy and confused so it’s hard to register what is going on, and it’s colourless and odourless. You breathe about 80% non-breathable (ie oxygenated) gas all the time.

> But carbon monoxide seems to be deadlier and kills far more people than other non-breathable gases

Because it’s highly toxic. It is not merely diluting the oxygen in the air, it binds to your red blood cells and makes them unable to carry oxygen, so you will suffocate despite having plenty of oxygen. Less than 1% concentration of CO in the air can kill you very rapidly.

In order to die from inhaling an inert gas like nitrogen or helium, you would need a lot of it in order to reduce the oxygen concentration to a fatal level. The air we breath is 70% nitrogen and that’s not harmful.