A fundamental requirement of using respirators is NO facial hair that could interfere with the respirator’s operation or the respirator’s fit. OSHA states:
1910.134(g)(1)(i) The employer shall not permit respirators with tight-fitting facepieces to be worn by employees who have:
1910.134(g)(1)(i)(A) Facial hair that comes between the sealing surface of the facepiece and the face or that interferes with valve function; or
1910.134(g)(1)(i)(B) Any condition that interferes with the face-to-facepiece seal or valve function.
I think we should not be fit-testing employees with facial hair. That is against the respirator policy. I will post an old document from the early days of NIOSH that show acceptable and unacceptable facial hair. I actually include this one-page sheet as an official appendix to my policy/procedure.