 Of the materials used to construct her, 99.5 percent were fireproof, and Johns-Manville asbestos Flexboard paneling covered all of her interior spaces.She was built of heavy steel, and her hull plating and internal subdivision was almost twice that required for a ship of her class, greatly reducing her vulnerability to flooding in the event of a collision.Eight transverse bulkheads extending up to the main deck divided her into nine watertight compartments, and she was designed to withstand the flooding of two of the compartments without sinking; only three of the bulkheads were pierced by openings, and these could be sealed by closing electrically driven watertight doors operated from the bridge.