OSHA’s PPE standards do not include exceptions for employees who do not or cannot wear PPE (e.g., due to a medical condition). If a medical issue would make the individual eligible for protections under the Americans with Disabilities Act, then the employer would be expected to make reasonable accommodations that do not impact safety.
OSHA addresses the refusal to wear PPE due to religious beliefs in a directive, STD 01-06-005, “Exemption for Religious Reason from Wearing Hard Hats.” The directive includes the following: “Whenever a citation is being considered because of an employee’s refusal to use personal protective equipment (other than a hard hat) due to a personal religious conviction, the National Office shall be contacted prior to the issuance of the citation.”
In addition, there is no guidance from OSHA to indicate that it would accept a signed waiver from an employee who refuses to wear necessary PPE or to follow any other safety rule.