Notwithstanding the provisions of this chapter, for purposes of the South Carolina Workers' Compensation Law, any impairment or injury to the health of a fire fighter caused by heart disease or respiratory disease resulting in total or partial disability, or death, shall be presumed to have arisen out of and in the course of employment, unless the contrary is shown by competent evidence, if such fire fighter is at the time of such impairment or injury a bona fide member of a municipal, county, State, port authority or fire control district fire department in this State. In order to be entitled to the presumption provided for herein, any person becoming a member of a fire department after May 29, 1968 must be under the age of thirty-seven years and must have successfully passed a physical examination by a competent physician upon entering into such service, a written report of which must have been made and filed with such fire department, which examination failed to reveal any evidence of such condition or conditions, and such condition or conditions developed while actively engaged in fighting a fire or within twenty-four hours from the date of last service in such activity.