a. The ability of a volunteer fireman to perform on a five-day or six-day basis either the work usually and ordinarily performed by him in his remunerated employment or other work which for any such worker would be a reasonable substitute for the remunerated employment in which he was employed at the time of his injury, or b. The ability of a volunteer fireman to perform on a five-day or six-day basis either the work usually and ordinarily performed by him in the practice of his profession or in the conduct of his trade or business, including farming, and from which he could derive earned income or other work which for any such person would be a reasonable substitute for the profession, trade or business in which he was engaged at the time of his injury.
Every volunteer fireman shall be considered to have earning capacity and, if the provisions of paragraphs a and b above are not applicable in any given case, the workmen's compensation board, in the interest of justice, shall determine the reasonable earning capacity of the volunteer fireman with due regard to the provisions of such paragraphs and the work he reasonably could be expected to obtain and for which he is qualified by age, education, training and experience. The ability of a volunteer fireman to perform the duties of a volunteer fireman, or to engage in activities incidental thereto, may be considered in determining loss of earning capacity, but the inability of a volunteer fireman to perform such duties or to engage in such activities shall not be a basis of determining loss of earning capacity.