The compensation payable under this chapter shall be reduced and limited to the proportion of the compensation that would be payable if the occupational disease were the sole cause of disability or death, as the occupational disease as a causative factor bears to all the causes of the disability or death when the occupational disease, or any part of the disease:
(1) is causally related to employment with a non-Utah employer not subject to commission jurisdiction;
(2) is of a character to which the employee may have had substantial exposure outside of employment or to which the general public is commonly exposed;
(3) is aggravated by any other disease or infirmity not itself compensable; or
(4) when disability or death from any other cause not itself compensable is aggravated, prolonged, accelerated, or in any way contributed to by an occupational disease.