Jim Higgins wrote:

[total BS]

Crack the valve on a tank of hydrogen for a sec or two, in the open.
Now attempt to light a match and ignite it, you can't, it is already
above your head.

Crack the value on a tank of propane and light the match, place the
match near the ground (propane is heavier than air) and WATCH OUT,
you're pants are on fire ...

JS