(f) For the purposes of this chapter, occupational disease means a disease incurred in the course of and resulting from employment. No ordinary disease of life to which the general public is exposed outside of the employment is compensable except when it follows as an incident of occupational disease as defined in this chapter. Except in the case of occupational pneumoconiosis, a disease is considered to have been incurred in the course of, or to have resulted from, the employment only if it is apparent to the rational mind, upon consideration of all the circumstances:

1. (1) That there is a direct causal connection between the conditions under which work is performed and the occupational disease;
2. (2) that it can be seen to have followed as a natural incident of the work as a result of the exposure occasioned by the nature of the employment;
3. (3) that it can be fairly traced to the employment as the proximate cause;
4. (4) that it does not come from a hazard to which workmen would have been equally exposed outside of the employment;
5. (5) that it is incidental to the character of the business and not independent of the relation of employer and employee; and (6) that it appears to have had its origin in a risk connected with the employment and to have flowed from that source as a natural consequence, though it need not have been foreseen or expected before its contraction: Provided, That compensation is not payable for an occupational disease or death resulting from the disease unless the employee has been exposed to the hazards of the disease in the State of West Virginia over a continuous period that is determined to be sufficient, by rule of the Insurance Commissioner and Industrial Council, for the disease to have occurred in the course of and resulting from the employee’s employment. An application for benefits on account of an occupational disease shall set forth the name of the employer or employers and the time worked for each. The commission may allocate to and divide any charges resulting from the claim among the employers by whom the claimant was employed. The allocation shall be based upon the time and degree of exposure with each employer.

(h) For purposes of this chapter, a rebuttable presumption that a professional firefighter who has developed a cardiovascular or pulmonary disease or sustained a cardiovascular injury or who has developed leukemia, lymphoma, multiple myeloma, bladder cancer, mesothelioma, or testicular cancer arising out of, and in the course of, employment as a firefighter has received an injury or contracted a disease arising out of, and in the course of, his or her employment exists if:

1. (A) The person has been actively employed by a fire department as a professional firefighter for a minimum of two years prior to the cardiovascular injury or onset of a cardiovascular or pulmonary disease or death;
2. (B) the injury or onset of the disease or death occurred within six months of having participated in firefighting or a training or drill exercise which actually involved firefighting; and (C) in the case of the development of leukemia, lymphoma, multiple myeloma, bladder cancer, mesothelioma, or testicular cancer, the person has been actively employed by a fire department as a professional firefighter for a minimum of five years in the state prior to the development of leukemia, lymphoma, multiple myeloma, bladder cancer, mesothelioma, or testicular cancer, has not used tobacco products more than six times in a calendar year for at least 10 years, and is not over the age of 65 years. When the above conditions are met, it shall be presumed that sufficient notice of the injury, disease, or death has been given and that the injury, disease, or death was not self-inflicted. The amendments made to this section during the regular session of the Legislature, 2024, to include bladder cancer, mesothelioma or testicular cancer arising out of, and in the course of, employment as a firefighter as a rebuttable presumption expire on July 1, 2027, unless extended by the Legislature.