N.Y. Comp. Codes R. & Regs. tit. 12, § 14-9.39 – Access and firing doors.

(1) The minimum size of an access door to be placed in a boiler setting shall be 12 by 16 inches, or equivalent area, 11 inches to be the least dimension in any case. The minimum size of firedoor opening in an internally fired boiler in which the minimum furnace dimension is 24 inches or over shall be not less than 11 by 15 inches, or 10 by 16 inches in size. A circular opening shall be not less than 15 inches in diameter.
(2) The bonnet or smoke hood of a vertical flue or tubular boiler shall be provided with an access opening at least six by eight inches for the purpose of inspection and cleaning the top head of the boiler.
(b)
(1) A water-tube boiler shall have the firing doors of the inward-opening type, unless such doors are provided with substantial and effective latching or fastening devices or otherwise so constructed as to prevent them, when closed, from being blown open by pressure on the furnace side.
(2) These latches or fastenings shall be of the positive self-locking type. Friction contacts, latches, or bolts actuated by springs shall not be used. The foregoing requirements for latches or fastenings shall not apply to coal openings of downdraft or similar furnaces.
(3) All other doors, except explosion doors, not used in the firing of the boiler, may be provided—with bolts or fastenings in lieu of self-locking latching devices.
(4) Explosion doors, if used and if located in the setting walls within seven feet of the firing floor or operating platform, shall be provided with substantial deflectors to divert the blast.

(a)