Mich. Comp. Laws § 324.5537
The department shall grant a variance from any rule to, and suspend the enforcement of the rule as it applies to, any person who shows in the case of the person and of the source, process, or process equipment that the person operates that his or her compliance with the rule or regulation, and that the acquisition, installation, operation and maintenance of a source or process, or process equipment required or necessary to accomplish the compliance, would constitute an undue hardship on the person and would be out of proportion to the benefits to be obtained by compliance. A variance shall not be granted under this section if the person applying for the variance is causing air pollution that is injurious to the public health or if the granting of the variance would violate the clean air act. Any variance granted shall not be construed as relieving the person who receives it from any liability imposed by other law for the maintenance of a nuisance.
MCL 324.5537