Remember 761.6 miles per hour (1225.67 Kilometers per Hour)= Mach-1, Speed of Sound there could be a Boom if he can reach the target speed.
"For about the first 30 seconds he's not going to feel anything," says Mike Todd, a life-support engineer at Sage Cheshire Aerospace and a member of the Red Bull Stratos team. This is particularly dangerous because, even though the air is so thin that it won't feel like he's even falling, Baumgartner must get into exactly the right position -- the so-called delta position -- to attain the speed he wants and survive the five-and-a-half-minute descent.
Todd expects Baumgartner will reach Mach1 somewhere between 100,000 and 90,000 feet. But it won't be overly uncomfortable. At that altitude, he says, "It will feel like putting your hand out the window of a car going 35 mph."
There's a video too: