N.Y.C. Admin. Code § FGC_AppG.2.2.1: G.2.2.1 Shaft requirements.

Vertical runs of high pressure gas piping within a building shall be enclosed in masonry shafts constructed of walls not less than 4 inches (101.6 mm) in thickness and sealed to prevent any gas leakage from the shaft. Such shaft shall be vented to the outdoors at the top. Such shaft shall not be located adjacent to an exit stairway or exit passageway unless the shaft wall separating the exit stairway or exit passageway from the shaft is designed to resist a potential gas explosion in accordance with Section 1615.6 of the New York City Building Code.