GoForSmoke:
hydrogen mixed with air does need a spark to set it off.
Bullshit. The heat generated from pressurized hydrogen escaping its container is enough to ignite it.
You can get sparks from static but hey they send instrumented balloons up on hydrogen all the time... I wonder how many of those burn up?
You failed to include the most important word in your description ... "unmanned". How many funerals have there been for unmanned balloons?
Mr. Baumgartner and his team had a very long list of things to concern them. The last thing they would want on that list is a 30 million cubic foot balloon filled with a very high energy fuel.