In the movie Tango & Cash, they try to escape from the jail through a large exhaust fan over 6 feet tall. Is is possible to stop a large exhaust fan successfully using a 2x4 or metal pole without a killing yourself?
1. Can you actually stop the fan?
2. Can you hold it long enough for someone to get thru?
3. Can you do it without killing yourself?

those fans do not have a lot of torque at the ends of the blades. consider the motor is working against up to 6 feet of leverage. also, the drive belts are frequently not well maintained. between the combination of the two, yes, you could jam something into the fan, and stop it.

The chunk of metal sounds like it would be strong enough to stop the fan however the speed of the fan should be considered. It would be difficult to stuff the metal between the moving blades. I doubt a human could push it through hard and fast enough.