Section 51A. Each city, town or district shall equip any fire apparatus operated by it with at least three self-contained breathing apparatus, so-called. Such breathing apparatus shall contain a minimum of 30 minutes of air or oxygen and shall be equipped with an audible alarm to indicate to the wearer thereof and to any other person in the area that there is a specific designated minimum supply of air or oxygen still present and that such wearer should leave a contaminated area. Any such breathing apparatus shall, in addition to the above, meet the requirements of the standards set up by the National Fire Protection Association for self-contained breathing apparatus. The provisions of this section shall not apply to fire apparatus designed solely for extinguishing woods or brush fires.