(1) The liable insurer in occupational disease cases is the insurer on risk at the time of the last injurious exposure to the injurious substance or hazard of disease during employment within the coverage of Title 51 RCW which gave rise to the claim for compensation. Such Title 51 RCW insurer shall not be liable, however, if the worker has a claim arising from the occupational disease that is allowed for benefits under the maritime laws or Federal Employees' Compensation Act.

(2) The compensation schedules and wage base for claims shall be based on the schedule in effect on the date of disease manifestation. Compensation shall be based on the monthly wage of the worker as follows:

(a) If the worker was employed at the time the disease required medical treatment or became totally or partially disabling, whichever occurred first, compensation shall be based on the monthly wage paid on that date regardless of whether the worker is employed in the industry that gave rise to the disease or in an unrelated industry.

(b) If the worker was not employed, for causes other than voluntary retirement, at the time the disease required medical treatment or became totally or partially disabling, whichever occurred first, compensation shall be based upon the last monthly wage paid.

(3) Benefits shall be paid in accordance with the schedules in effect on the date of manifestation. Manifestation is the date the disease required medical treatment or became totally or partially disabling, whichever occurred first, without regard to the date of the contraction of the disease or the date of filing the claim.