From a 1960s British Railways safety booklet
"If a grinding wheel is chipped, damaged or out of true, tell your supervisor at once and have the wheel trued up. Rests in front of wheels should always be kept close up.
Never use a machine without the guard which is provided, and always use it in such a way that sparks are directed away from you.
Grinding wheels should be fitted to machines only by men who have been properly instructed in the way to do it.
Always use goggles for grinding operations."