An industrial cleaner wasn't wearing safety glasses as required.  When a supervisor told her to put them on, she verbally abused him, using profanity in front of others.   So the employer fired her.  The union filed a grievance on her behalf.  The Arbitrator said the employer had a clear policy on wearing proper eye protection and the cleaner had attended three safety talks on this policy.   She'd also been warned earlier by a supervisor and a union steward about not wearing safety glasses.  And considering the cleaner's "checkered disciplinary record" and unprofessional conduct, termination was warranted, concluded the arbitrator.

Source.....OHS Insider

This just under scores the need to have clear safety policies in place, to train your workers on the policies and to enforce them when workers are not following them.  The policies are in place to protect the safety of your employees and the company as a whole.  PPE should always be worn when it is part of your policy.