Leaf blower

I found this exploring the internet and decided to figure out the man's top speed before he falls. He appears to have reached his top speed after seven rotations in 4.5 seconds. I approximate the chair to have a diameter of about half a meter, so r=0.025m. Since circumference = 2(pi)r, he rotates seven times, and Δl = rΔtheta, Δtheta = 44.8 rad. From this, I can use kinematics to find the angular velocity. Thetaf = 0.5at^2 + w0t + theta0 --> a (angular acceleration) = 4.42 rad/s^2. wf = w0 + at --> wf = 19.89 rad/s which is 3.17 rev/s