Foot wear in clinical settings

I need some help finding an authoritative source about foot wear.
I need some reference(s) that recommend that nurses and all clinical personnel wear closed toe, non-canvas shoes in the clinical setting to prevent dropped sharps, etc from striking the feet. I have some NP's in my facility that want to wear street clothes with lab coat and then sandals while they are seeing patients in the clinic. These NP's give injections, start IV's and perform other minor procedures. Even with safety sharp devices, accidents can happen.

I would appreciate any help on this.