Apparently it was an equipment malfunction and Blaine himself has expressed some dissapointment with how it turned out. Which really is unfortunate as what was supposed to happen sounds like it would have been pretty neat and put a much more magical twist on his stunt - hopefully a sign of what his goal is for the future.
It seems Mr. Blaine has even jumped on the bandwagon, and now President George W. Bush is responsible for failed magic illusions. He has blamed the problems with the finale on his speech preempting the broadcast.
I head that the finale wasn't as good as intended due to equipment malfucntion. This is worrying, if he'd had the same 'malfucntion' on safety or breathing apparatus in previous stunts, he'd be dead.