[flipper35]

If you ask the flywheel mfrs, they will tell you it isn't just the rpm but also the amount of torque applied to the flywheel assembly. That's why they can come apart at seemingly low rpms.

I don't know anyone that had an assembly come apart with a scattershield or blowproof houseing, but I know two very lucky people that have had pieces fly out of/through the car. Remember, that's a lot of weight moving at a high rate of speed when they let loose.