I can't recall anyone being ever injured seriously. However I can recall quite a few instances where white belts got in fantasys or tried to test techniques. That sort of thing is not safe.
However seniors at our dojo are very quick to spot that. I had one white belt repeetatldy testing anothers technique stating that it dident work.
I had to show that ikkyo does work.
Once people get over thier egos or "martial arts fantasys" they can become good students though.