Hi Dunc,The only holes are the brush cooling gaps - if It gives way do bits of the commutator fly out of these holes?
Yep. If the commutator comes apart due to overspeed, those segments (sometimes called bars) can become detached and exit the motor at pretty high speed. Most times the bars mushroom out and it comes to a grinding halt. But they can and do fly out of there, like copper bullets. I think that automotive body panels and floor pans made of steel would be sufficient protection. But when series motors were used in racing applications, tech required scatter shields. Some guys used flak jackets.