Why do we use helium and not hydrogen balloons?

25 November 2007

Question

Why is it helium in balloons and not hydrogen?

Answer

In order to get a floating balloon you want a gas which is as light as possible. Helium is quite a lot lighter than air: it's about an eighth of the density of air. Hydrogen is about a sixteenth the density of air, so it'll float in air and will in fact float upwards.

You'd have thought that hydrogen would be a better gas as it would give slightly more lift than helium because it's lighter. This is true. The problem is that hydrogen is explosive, and if you have children running around with balloons that could catch fire and blow up in their faces, it may have some health and safety implications!

The other thing is that, although hydrogen is half as heavy as helium, it doesn't give you twice as much lift because the amount of lift you get is determined by the difference in density with respect to air. So it's actually only another sixteenth of the density of air, meaning it's a little bit better but not very much, so it's not worth the danger.

Helium is quite expensive, though, because it's a limited resource here on the planet. It's only created by radioactive decay on Earth: atomic nuclei emitting alpha particles. These are actually helium nuclei. They slow down and gain some electrons and turn into a helium atom.

Helium tends to be found in oil wells where you get a gas-proof layer of rock above a load of rocks containing radioactive elements. These break down to helium. This floats up and becomes trapped, often at the top of an oil well . The amount of helium that we can access cheaply is very limited because not all our oil wells have it.


Comments

Is it illegal to use hydrogen balloons for outdoor decoration if no people get near them and they are taken down immediately after the event?

which is faster to climb hydrogen or helium???

Hydrogen

Why do you think that? I'm not saying you are wrong, but what's your evidence for this?

Its in the 3rd and 4th sentences of the answer above.

Helium is becoming more and more limited. It takes a long time for the earth to create helium and we are using it very quickly. This is why helium is very expensive and you can no longer find cans of helium for blowing up balloons in the store any more.

The part about us running out of helium is just false.

Helium is in limited supply on Earth and we are using and losing a lot more than is accumulating. The gas is so light that it escapes into space.

thank you for your answer it really helped

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