[wkat4242]

That's more because of the ozone layer.

While it's not good to use halon in a semi contained space like an airplane, it is incredibly effective at killing fire. It really sucks the heat out of it. Thus in most cases the fire is killed quickly and not much toxins are produced. This is important too because fire itself produces a lot of lethal toxins too, most people in a fire don't burn to death but get poisoned by the smoke.

So it's a big loss imo. I understand why because it's one of the most potent ozone layer killers. But still.. you're not using the stuff unless you have no other choice. If you're not using it it doesn't end up in the environment.

In this case it didn't work because the cargo bay in question was not fitted with extinguishers if I remember correctly.

[bitwalker]

> It really sucks the heat out of it.

One of the problems with halon, and the write-up mentions this, is that it is super effective at starving the fire of oxygen, but has zero effect on the heat of the fuel that was burning. So the fire goes out, but if oxygen is reintroduced before the fuel has a chance to cool sufficiently, it reignites - and now not only are you back where you started, but you have all the toxic byproducts that burning halon produces, which will kill you in a hurry if you breathe them in.

[cyberax]

> One of the problems with halon, and the write-up mentions this, is that it is super effective at starving the fire of oxygen

That's not actually quite how it works. But yes, the end result is the same. I'll copy-paste my comment from the Medium:

That's NOT how halon works! It's a common misconception, but it's incorrect. In fact, halon doesn't react with pretty much anything, it's very chemically stable. You can mix halon with pure oxygen and it'll just sit there, doing nothing.

This stability is exactly why it works so well. You need only a few _percent_ of halon by volume to stop the fires, not even close to consuming even a fraction of the 21% of oxygen.

Normal oxygen consists of two atoms bonded together (thus "O2"). And fire is spread by oxygen radicals, lone oxygen atoms that have an unpaired electron, eager to make bonds. In a fire, an oxygen radical reacts with a molecule of fuel, and this reaction produces enough energy to create at least one more oxygen radical, sustaining the chain reaction.

But halon has these chlorine and bromine atoms, they are bound tightly to carbon, but not as tightly as oxygen would be. So oxygen radicals have enough energy to displace them and bind to the central carbon atom. But the resulting energy release is not enough to create _more_ radicals, so the chain reaction is stopped.

Moreover, the chlorine radical can then snap back onto another carbon atom (from the fuel source), releasing a bit of energy, but not enough to create a new oxygen radical. And the cycle can repeat again.

[kergonath]

> That's not actually quite how it works.

What you wrote is not contradicting the parent, who just said that it was “super effective at starving the fire of oxygen”. You just described the mechanism. You also contradict yourself by first saying that halon is inert, and then that it neutralises oxide ions by swapping halogens, which is the opposite of non-reactive. The effect of that is that it immobilises reactive oxygen before it oxidises the fuel. And it indeed does nothing to decrease the temperature, which does mean that the fire restarts as soon as oxygen is re-introduced. I know you’re not wrong, but the delivery could be improved.

Anyway, you can elaborate and provide information without disagreeing with the comment you’re replying to. It’s fine, and often informative.

[cyberax]

Typically, "starving of oxygen" means that there's not enough oxygen around anymore. That's how CO2 extinguishers work, for example. They literally remove enough of the oxygen to make the combustion stop.

Halon does NOT remove the oxygen, there's always plenty of it available. Instead, it stops the chain reaction.

> You also contradict yourself by first saying that halon is inert, and then that it neutralises oxide ions by swapping halogens, which is the opposite of non-reactive.

As I said, you can mix halon and oxygen, and they won't react (even if you try to ignite them). Halon is very unreactive, but it's obviously not _totally_ inert like helium.

[userbinator]

As I said, you can mix halon and oxygen, and they won't react (even if you try to ignite them).

That makes me wonder if any of the original designers of the oxygen system considered whether a halon-oxygen mix would've been better than pure oxygen.

[cyberax]

Not really. Adding oxygen for sure won't help. Also halon is stored in extinguishers as a pressurized liquid, not gas.

[wkat4242]

As far as I understood it reduces temperature also because it boils so easily (very low boiling point). That pulls energy from the fuel. As well as capturing oxygen.

This is why it was used as a refrigerant also.

Also if the fuel is below the auto ignition temperature but above flashpoint it would need another spark to re-ignite.