the ducts where they

D.5.4.4 The ducts where they pass through a machinery space of category A, galley, vehicle space,
ro-ro cargo space or special category space are constructed of steel, suitable supported and stiffened
(see D.5.3.1) and
D.5.4.5 Such ducts are insulated to "A-60" standard within the machinery spaces of category A, galleys,
vehicle spaces, ro-ro cargo spaces or special category spaces.
D.5.5 Ducts are to be routed in such a way that neither machinery nor switchgear can be endangered
by condensation or spray water. Where necessary, water traps, baffles and similar devices are to
be fitted. Effective water traps are to be provided with appositely directed baffle plates. The lowermost
baffle of the water trap is to be provided with a drainage pipe.
D.5.6 Natural ventilating systems shall not employ a branched ducting system.
D.5.7 Duct penetrations
D.5.7.1 Duct penetrations through "A" class divisions shall be of an approved type 4. Where steel
sleeves are directly joined to ventilation ducts by means of riveted or screwed flanges or by welding, the
approval is not required.