(a) On and after January first, nineteen hundred eighty-two, all dwelling units within occupancy group J-1 and occupancy group J-2, except such units which contain operational automatic wet sprinkler systems pursuant to article four of this subchapter, and dwelling units in buildings within occupancy group J-3 shall be equipped with approved and operational smoke detecting devices as hereinafter provided. Buildings within occupancy group J-1 may, in the alternative, be equipped with a line-operated zoned smoke detecting system with central annunciation and central office tie-in for all public corridors and public spaces, pursuant to rules and regulations promulgated by the commissioner. The commissioner may, upon good cause shown, extend the period of compliance for occupancy groups J-1 and J-2 to June thirtieth, nineteen hundred eighty-two.
(b) Approved and operational smoke detecting devices shall be installed in mechanical rooms, electrical switch gear rooms and electric and telephone closets over seventy-five square feet in gross floor area in all buildings in all occupancy groups.