85B.9A  Apportionment of occupational hearing loss.
  Apportionment of the total hearing loss between occupational and nonoccupational loss, for purposes of determining occupational hearing loss, may be made by an audiologist or physician with qualifications set forth in section 85B.9. In determining occupational hearing loss, consideration shall be given to all probable employment and nonemployment sources of loss. The apportionment of age-related loss shall be made by reducing the total binaural percentage hearing loss as calculated pursuant to section 85B.9, subsection 3, by the same percentage as the decibels of age-related loss occurring during the period of employment bears to the total decibel hearing level in each ear. The decibels of age-related loss shall be calculated according to tables adopted by the workers’ compensation commissioner consistent with tables of the national institute for occupational safety and health existing on July 1, 1998, and consistent with section 85B.9, subsection 3.
98 Acts, ch 1160, §7