8.1.2 Ventilators from deep tanks and tunnels passing through pontoons, columns and
‘tween decks are to have scantlings suitable for withstanding the pressures to which they
may be subjected, and are to be made watertight.
8.1.4 On self-elevating units, it is recommended that closing appliances for
ventilators situated on the freeboard deck are fitted at or below the deck level.
8.1.5 Mushroom ventilators closed by a head revolving on a centre spindle
(screw-down head) are acceptable in Position 2, and also in sheltered positions in Position
1, but the diameter is not to exceed 300 mm on self-elevating units. On self-elevating
units, a notice indicating ‘keep closed while unit is afloat’ is to be attached to the
head.
8.1.6 A ventilator head not forming part of the closing arrangements is to be not
less than 5,0 mm thick on column-stabilised units and 6,5 mm thick on other units.
8.1.7 Wall ventilators (jalousies) may be accepted, provided they are capable of
being closed weathertight by hinged steel gasketed covers secured by bolts or toggles, or
equivalent arrangements provided.
8.1.8 Fire dampers are not acceptable as ventilator closing appliances unless they
are of substantial construction, gasketed, and able to be secured weathertight in the closed
position.