(a) Standard fire test. A “standard fire test” is one which develops in the test furnace a series of time temperature relationships as follows:

(b) “A” Class divisions. Bulkheads or decks of the “A” Class shall be composed of steel or equivalent metal construction, suitably stiffened and made intact with the main structure of the vessel; such as shell, structural bulkheads, and decks. They shall be so constructed, that if subjected to the standard fire test, they would be capable of preventing the passage of flame and smoke for one hour.

(c) “B” Class bulkheads. Bulkheads of the “B” Class shall be constructed with approved incombustible materials and made intact from deck to deck and to shell or other boundaries. They shall be so constructed that, if subjected to the standard fire test, they would be capable of preventing the passage of flame for one half hour.

(d) “C” Class divisions. Bulkheads or decks of the “C” Class shall be constructed of approved incombustible materials, but need meet no requirements relative to the passage of flame.

(e) Steel or other equivalent metal. Where the term “steel or other equivalent metal” is used in this subpart, it is intended to require a material which, by itself or due to insulation provided, has structural and integrity qualities equivalent to steel at the end of the applicable fire exposure.

(f) Approved material. Where in this subpart approved materials are required, they refer to materials approved under the applicable subparts of Subchapter Q (Specifications) of this chapter, as follows:

(g) Stairtower. A stairtower is a stairway which penetrates more than a single deck within the same enclosure.