Where a thin plated

D.5.7.2 Where a thin plated duct with a free cross-sectional area equal to, or less than, 0.02 m2 passes
through "A" class bulkheads or decks, the opening shall be lined with a steel sheet sleeve having a thickness
of at least 3 mm and a length of at least 200 mm, divided preferably into 100 mm on each side of the
bulkhead or, in the case of the deck, wholly laid on the lower side of the decks pierced.
D.5.7.3 Where ventilation ducts with a free cross-sectional area exceeding 0.02 m2 pass through
"A" class bulkheads or decks, the opening shall be lined with a steel sheet sleeve. However, where such
ducts are of steel construction and pass through a deck or bulkhead, the ducts and sleeves shall comply
with the following:
D.5.7.4 The sleeves shall have a thickness of at least 3 mm and a length of at least 900 mm. When
passing through bulkheads, this length shall be divided preferably into 450 mm on each side of the bulkhead.
These ducts, or sleeves lining such ducts, shall be provided with fire insulation. The insulation shall
have at least the same fire integrity as the bulkhead or deck through which the duct passes.
D.5.7.5 Ducts with a free cross-sectional area exceeding 0.075 m2 shall be fitted with fire dampers in
addition to the requirements of D.5.7.4. The fire damper shall operate automatically, but shall also be
capable of being closed manually from both sides of the bulkhead or deck. The damper shall be provided
with an indicator which shows whether the damper is open or closed. Fire dampers are not required