If the column of air is really moving at 300 MPH, they'd better diffuse that at the bottom so people (and things) aren't sucked into the chimney (it would suck

If the column of air is really moving at 300 MPH, they'd better diffuse that at the bottom so people (and things) aren't sucked into the chimney (it would suck to be ejected at the top without a parachute but you could probably sell a ride to the top to the wing-suiters).