GoForSmoke:
And there was oxygen and a spark, even if the hydrogen made the spark.
Wow. Your hubris is amazing. Consummate professionals, who have direct access to the evidence, determine the plant explosion occurred without an initial spark, and yet you somehow divine they are mistaken. Please, tell us the source of your magic power?
While you contemplate your response, bear in mind it took me fifteen seconds to find this reference... Negative Joule-Thomson coefficient; leaking gas warms and may spontaneously ignite.
Getting back on topic: The primary goal with any high risk project is to eliminate and reduce as much risk as possible. No sane person would deliberately add more risk. With helium available, no sane person would use a hydrogen balloon for Mr. Baumgartner's jump.