Gas dilution

[gianluca belgrado]

Hi everyone! I've been preparing for a couple of years for a school project involving a high-altitude flight. I have already solved the problems with telemetry, cameras, parachutes etc etc, I just need the gas bottle. The seller informed me that he only has one 50 liter hydrogen cylinder available (I will take all necessary precautions). They also told me that I have to choose the gas dilution percentage using another gas of my choice. Which gas should I use and in what percentage? I was thinking helium, 80-90%. (more hydrogen and less helium) Is that ok? Alternative?
The school project with limited funds.

[Andrew Mulholland]

That's odd not to have helium available? I would certainly be recommending helium for a school launch, especially if you want students involved with the filling process. I can't see how a risk assessment could be signed off with using hydrogen and students involved... (although those that use hydrogen might have more to say on that).

Are you launching from within the UK or a different country?

[gianluca belgrado]

I will inflate the balloon , about 50 meters away from other people , at the moment we cannot afford helium (and in any case it is not currently available in sufficient quantities to inflate the balloon) . The launch is expected in 3 months, in southern Italy