The hull, superstructure, structural bulkheads, decks and deckhouses shall be constructed of steel or other equivalent material. For the purpose of applying the definition of steel or other equivalent material as given in Regulation 3 (g) of this Chapter the “applicable fire exposure” shall be according to the integrity and insulation standards given in the tables of Regulation 20 of this Chapter. An example where divisions such as decks or sides and ends of deckhouses are permitted to have “B0” fire integrity, the “applicable fire exposure” shall be one half-hour.
Provided that in cases where any part of the structure is of aluminium alloy, the following requirements shall apply:
| (a) | The insulation of aluminium alloy components of “A” or “B” Class divisions, except structure which in the opinion of the Administration is non-load-bearing, shall be such that the temperature of the structural core does not rise more than 200° (360°F) above the ambient temperature at any time during the applicable fire exposure to the standard fire test. |
| (b) | Special attention shall be given to the insulation of aluminium alloy components of columns, stanchions and other structural members required to support lifeboat and liferaft stowage, launching and embarkation areas, and “A” and “B” Class divisions to ensure— |
| (i) | that for such members supporting lifeboat and liferaft areas and “A” Class divisions the temperature rise limitation specified in paragraph (a) of this Regulation shall apply at the end of one hour; and |
| (ii) | that for such members required to support “B” Class divisions, the temperature rise limitation specified in paragraph (a) of this Regulation shall apply at the end of one half-hour. |
| (c) | Crowns and casings of machinery spaces of Category A shall be of steel construction adequately insulated and openings therein, if any, shall be suitably arranged and protected to prevent the spread of fire. |
