You're on a plane. The oxygen masks have dropped. While you're screaming and crying, does it occur to you to wonder where that oxygen comes from? It's not a scuba tank. Here's how weed killer, fireworks, and candy destroyers keep you alive.
If the oxygen masks drop on your plane, it's natural to be scared, but don't start making your final confession just yet. As we've seen, there are a number of situations in which oxygen masks drop, but the plane is in little danger. Now, since you're going to live, you might as well be educated.
The safety demonstration at the beginning of each flight has taught you that you have to tug on your mask to start oxygen flowing. Are you aware that, once the oxygen is flowing, nothing is going to stop it? You're not all hooked to some communal scuba tank with a valve that can be turned on and off. When you tug on the mask, you "pull the pin" on a chemical process, and quite a violent one. Airplanes use oxygen generators, otherwise known as "oxygen candles." These are chemicals that, when burned, release oxygen as a gas. Any extra chemicals get filtered out when the oxygen goes through to your mask, and the entire thing keeps going until it burns down.
The most straightforward chemical you'll find in an oxygen candle is barium peroxide. It's a fine white powder with two atoms of oxygen to every atom of barium. It's used in fireworks to do exactly the same job it does on planes. Heat it up enough and it splits, giving off oxygen. In a firework, that oxygen allows the other material inside the firework to burn and burn quickly. In a plane, that oxygen gets sent down a tube and allows a person to breathe.
Sodium chlorate was primarily used as a weedkiller. It kills nearly any plant, which is part of what got it banned in Europe. There were concerns about it leaching into the water supply and sterilizing larger patches of soil. There were also concerns that careless gardeners could blow themselves up, since sodium chlorate explodes into flame at the relatively low temperature of 300 °C. How concerned should you be that you're breathing in a weedkiller? Not at all. The chemical formula for sodium chlorate is NaClO3. For those of you who know kitchen chemistry, that's salt (NaCl) plus three atoms of oxygen, which is what sodium chlorate turns into when it's burned.
Finally, we have a chemical that has featured in many science classes. Some oxygen candles use either potassium chlorate (2KClO3) or potassium perchlorate (2KClO4). The difference is a single oxygen atom but a world of prestige. Potassium perchlorate was used as an oxygen candle on the International Space Station when their method of generating oxygen via electrically splitting water went on the fritz. Potassium chlorate is seen in science classrooms demolishing gummy bears. Still, the screaming gummy bear (yes, it screams), is as good a way of demonstrating this as any. The potassium chlorate gets heated up until it starts to decompose into potassium chloride and oxygen. A gummy bear, laden with sugar, gets added to the mix and the heat from the potassium chlorate decomposition plus the generous supply of oxygen causes the gummy bear to burn very, very rapidly. It doesn't look encouraging but think of function, not form. As long as the gummy bear screams, you can breathe.
The typical oxygen generator, on a plane, lasts twelve to twenty minutes. Unlike scuba tanks, which are both heavy and bulky, oxygen candles are about the size of a package of tennis balls. They burn reliably and well but they do have drawbacks.
Their primary drawback is that they burn. This isn't really a danger. It's true that in the 1990s, a plane crashed due to oxygen generators, but they were part of the cargo. They were listed as spent and were missing their safety caps. A jolt ignited one of them and they all burned. In emergency deployment situations, their drawback is psychological. The last thing that passengers want, when they're breathing through oxygen masks on a plane making a quick descent (which feels to some like a nose dive), is to smell something burning.
Top Image: Aleksandr Markin