(a) Notwithstanding the retroactive provisions of section 27-994 of this article, where required by reference standard RS 18-1, firemen service operation shall be installed in all existing elevators serving any of the following:
(1) High rise buildings or building sections classified in occupancy group C.
(2) All buildings or building sections classified in occupancy group F, G, H or J-1 (except for "residential hotels," as such term is defined by the commissioner pursuant to rules and regulations).
(b) All work necessary to meet the requirements of this section shall be completed on or before April first, nineteen hundred eighty-seven.