Yes, above 75% it won't burn but if you get near a source of ignition while
filling your balloon it will go up because the atmosphere surrounding the
balloon supplies the required oxygen. A balloon full of propane would do the
same thing. It matters not that the balloon itself contains pure hydrogen.
You might prevent an explosion but not burning.
Have you ever seen footage of the Hindenburg disaster ?
Anyway, helium is non flammable but boring so go with the hydrogen, just
take the usual precautions. Also be very carefull with concentrated caustic
soda solution. I got some on my hand when I was about 14. It hurts about the
same getting burning molten plastic on your hand i.e. its bloody sore.
Interestingly it turns your hand into soap. You can feel that the burn is
soapy. Just to add to the unpleasantness.
> Date: Mon, 2 Jul 2001 18:13:37 +0100
> From: <info.host@...>
>Subject: Re: Re: Heavy Theory--gas pressure debate etc.
>Critical limits as per BOC's manual say it will need atleast 4.1% hydrogen
>to air to combust. Above 75% it will not burn.