1. 1. Losses of hearing due to industrial noise for compensation purposes shall be confined to the frequencies of five hundred, one thousand, and two thousand cycles per second. Loss of hearing ability for frequency tones above two thousand cycles per second are not to be considered as constituting disability for hearing.
2. 2. The percent of hearing loss, for purposes of the determination of compensation claims for occupational deafness, shall be calculated as the average, in decibels, of the thresholds of hearing for the frequencies of five hundred, one thousand, and two thousand cycles per second. Pure tone air conduction audiometric instruments, approved by nationally recognized authorities in this field, shall be used for measuring hearing loss. If the losses of hearing average fifteen decibels or less in the three frequencies, such losses of hearing shall not then constitute any compensable hearing disability. If the losses of hearing average eighty-two decibels or more in the three frequencies, then the same shall constitute and be total or one hundred percent compensable hearing loss.
3. 3. There shall be payable as permanent partial disability for total occupational deafness of one ear forty-nine weeks of compensation; for total occupational deafness of both ears, one hundred eighty weeks of compensation; and for partial occupational deafness in one or both ears, compensation shall be paid for such periods as are proportionate to the relation which the hearing loss bears to the amount provided in this subsection for total loss of hearing in one or both ears, as the case may be. The amount of the hearing loss shall be reduced by the average amount of hearing loss from nonoccupational causes found in the population at any given age, according to the provisions hereinafter set forth.
4. 4. In measuring hearing impairment, the lowest measured losses in each of the three frequencies shall be added together and divided by three to determine the average decibel loss. For every decibel of loss exceeding fifteen decibels an allowance of one and one-half percent shall be made up to the maximum of one hundred percent which is reached at eighty-two decibels.
5. 5. In determining the binaural (both ears) percentage of loss, the percentage of impairment in the better ear shall be multiplied by five. The resulting figure shall be added to the percentage of impairment in the poorer ear and the sum of the two divided by six. The final percentage shall represent the binaural hearing impairment.
6. 6. Before determining the percentage of hearing impairment, in order to allow for the average amount of hearing loss from nonoccupational causes found in the population at any given age, there shall be deducted from the total average decibel loss, one-half decibel for each year of the employee's age over forty at the time of last exposure to industrial noise.
7. 7. No claim for compensation for occupational deafness may be filed until after six months' separation from the type of noisy work for the last employer in whose employment the employee was at any time during such employment exposed to harmful noise, and the last day of such period of separation from the type of noisy work shall be the date of disability.
8. 8. An employer shall become liable for the entire occupational deafness to which his employment has contributed; but if previous deafness is established by a hearing test or by other competent evidence, whether or not the employee was exposed to noise within six months preceding such test, the employer shall not be liable for previous loss so established nor shall he be liable for any loss for which compensation has previously been paid or awarded.
9. 9. No consideration shall be given to the question of whether or not the ability of an employee to understand speech is improved by the use of a hearing aid.

(L. 1959 S.B. 167 § 287.202, A.L. 1967 p. 390, A.L. 1998 H.B. 1237, et al.)