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Author: Subject: Hot air balloons- What is % O2 inside the envelope?
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[*] posted on 8-5-2018 at 10:15
Hot air balloons- What is % O2 inside the envelope?

I just asked the technical guy at a USA manufacturer of both hot air and H2/He2 ballons- He didn't know. They make their calculations based on gas temperature, not composition.

Why do I want to know?

We have been requested to blow up a large balloon for an event. I have no desire to be anywhere near enough Hydrogen to fill a 20' balloon, but have made and flown some large (paper, disposable) hot air balloons. These are reasonably safe to handle while filling and to fly, the main danger is from a ground fire if they come down hot or the envelope catches fire in mid air.

One thought I had was to hang a fuel air explosive device in the center of the envelope, if there is enough Oxygen left in the hot gasses there to function.

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[*] posted on 8-5-2018 at 14:14

If you use an electric heater to fill the balloon, then the answer is clearly 21%. I have no idea how you'd work it out if you are flame heating. I'd have thought the result would be highly variable using a flame, as the balloons are usually inflated with cold air before the flame is used so the flame doesn't hit the sides.

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[*] posted on 8-5-2018 at 14:53

How costly is helium with no hydrogen in it?

A helium/ oxygen, or even helium/air mixture should give enough lift for a lightly loaded balloon and have enough oxygen to support combustion.

50/50 helium /oxygen would be about as light as methane.
About the same for Helium/air I think.

EDIT: re below post.

Wow, I hope they were sitting in a bunker behind their wall when they tested that effect. Otherwise they might have wound up as worm food.

[Edited on 9-5-2018 by SWIM]

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[*] posted on 8-5-2018 at 17:24

Back in 1975, the rock group Pink Flloyd
was touring. This was during their "Pigs on the Wing" era.

At several of their concerts they flew a very large
(at least 60 feet long), hydrogen filled pig balloon
over the crowd.

I saw this live at Milwaukee, Wisc.
The concert was outdoors at Milwaukee County Stadium.

About midway into the concert, they flew the pig
high over the center of the stadium. It was tethered
there for well over an hour.

Then, right at the end of their performance an
explosion was heard. It was very loud!
The pig was blown into tiny fragments, most no larger
than a postcard. The flash was unforgettable.:cool:

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[*] posted on 19-5-2018 at 08:55

If you use an electric heater to fill the balloon, then the answer is clearly 21%.

Interesting thought! If the balloon is tethered and fairly large, I could potentially see running an electrical cord up to it and having a hair dryer sort of device inside. :-)

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