I was thinking that this might be a method of saving on Helium in a story I’m working on (i.e., “cutting” the Helium used to fill a Balloon/airship with some percentage of Hydrogen), but I’m not sure what the practical effects would be. I assume there’d be no chemical reaction, and I’d guess that the Hydrogen would float to the “top” of the Helium, like oil in a bowl of water. Can anyone fill me in on what other effects there might be from inflating a balloon like this, or even if someone’s actually tried this before, like in the early days of powered flight?
The hydrogen won’t “float to the top”. The nitrogen in a balloon filled with air doesn’t float on top of the oxygen, either.
It will work, but why would you bother? If you’re going to put any hydrogen in the balloon, you have to deal with effects of hydrogen. You may as well leave out the helium and completely fill it with hydrogen.
The lower explosive limit of hydrogen is 17%. If the mixture of H2 to HE is only 17%, any mixing of this combo with air will immediately result in a H2% lower than 17%, rendering it safe (from a fire standpoint).
You probably could realistically have a higher H2 concentration and still have it not flammable once further diluted by air, but I can’t do the calcs right now.
For that matter, you could realistically have an H[sub]2[/sub] concentration of 100%, and still be safe. The reason that hydrogen isn’t used in blimps is not because it’s dangerous, but because the public thinks it’s dangerous. Everyone knows that the Hindenburg burned, but most folks don’t know that it wasn’t the hydrogen burning, it was the envelope, which was basically coated with rocket fuel. It would have been nearly as bad, had the gas been helium.
So if you put any hydrogen at all into your balloon, folks would panic. But if you did it anyway, it would work just fine.
No problems I see with that :). Hydrogen is a lot safer than the common person thinks. Yes it is explosive, but it is the most diffusive gas - so it diffuses out before u get any buildup.
Agrees on CHronos on that.
The only problem I can see is that Hydrogen will diffuse through the envelope faster than the Helium.
I think that’s going a bit far. Hydrogen is definitely a dangerous gas to handle. A tank of hydrogen may be as safe as a tank of propane, but they’re still a lot more dangerous than helium. Why else would scientific balloons use helium, when they use every other trick in the book to make them lighter and larger to reach higher altitudes?
Chronos or andy_fl: Where can I get more information on that? I’m intrigued. I’ve heard stories of WWI (I think…) fighters attacking german blimps with tracer rounds, resulting in >>WHOOOFF!!<< no more blimp. Are those just fanciful stories?
That sounds like a great idea to me.
What would make it perfect is if there were some flame inhibitor that could also be added to disperse with the hydrogen.
Quote from there - "What is often not acknowledged about the Hindenburg tragedy is that because hydrogen dissipates quickly, no Hindenburg fatality was the result of a burn from hydrogen. "
Also, I had a cite, where they did tests on Hydrogen and Gasoline Cars and proved that Hydrogen cars were less prone to fire damage - I can dig that up if you want.
I’m not disputing either andy_fl or Chronos, but would just point out that just because there were no fatalities due to hydrogen burns, that does not imply that there was not any signifcant amount of hydrogen which burned.
IIRC, tracer rounds - and incendiary rounds for that matter - use phosphorus which ignites when exposed to air. Seems to me that oridinary rounds would just punch holes in the envelope.