It shall be unlawful for any municipality, or any officer or employee thereof, in municipalities which maintain or may hereafter maintain an organized paid or part-paid fire department, to require any person in the employ of the fire department who is engaged in fire fighting or subject to the hazards thereof to be on duty in such employment more than 24 hours, or to be off duty less than 24 consecutive hours out of any 48-hour period. All persons in the employ of any organized paid or part-paid fire department who are engaged in fire fighting or subject to the hazards thereof shall be entitled to an additional 24 consecutive hours off duty in every 12-day period, beginning July 1, 1966, thereby requiring firemen to work not more than an average of 63 hours per week, and effective July 1, 1967, an additional 24 consecutive hours off duty in every 6-day period, thereby requiring firemen to work not more than an average of 56 hours per week.