Sorry about your injury buddy! I have had the same thing happen to a PC 3 1/4 VS running a 4 1/2" cove bit, speed control burnt out and defaulted to 21,000. Had hands on and shut it off but it scared the daylights out of me. I got rid of the internal speed control and went with a separate for the rest of that job. In my case I feel that it was probably overloaded as the bit is a very heavy Nordic Tool custom bit, but in your out of cut blowout ???.

Been doing this and construction my whole life and injuries happen, as you have said it is dangerous work and sometimes things beyond our control line up against us. All we can do is look at what happened and change our procedure. I think the guys that do this for a living and make it through their whole life without a mishap are the exception rather than the rule. Hope you heal well.