Any affected employer may apply to the Administrator for a rule or order for a permanent variance from a standard adopted under this chapter. Affected employees must be given notice of each application and an opportunity to participate in a hearing. The Administrator shall issue the rule or order if the Administrator determines on the record, after opportunity for an inspection where appropriate and a hearing, that the proponent of the permanent variance has demonstrated by a preponderance of the evidence that the conditions, practices, means, methods, operations or processes used or proposed to be used by an employer will provide employment and places of employment to his or her employees which are as safe and healthful as those which would prevail if the employer complied with the standard. The rule or order must prescribe the conditions the employer must maintain, the practices, means, methods, operations or processes which the employer must adopt and utilize to the extent they differ from the standard in question. Such a rule or order may be modified or revoked upon application by an employer, employees or by the Administrator on his or her own motion, in the manner prescribed for its issuance under this subsection at any time after 6 months after its issuance.