Ventilation by cowls
31.—(1)  Ventilators shall be provided to each upper between deck and shelter deck space and shall have an aggregate area of not less than 5 square inches for each passenger accommodated in the compartment, that is 2½ square inches as inlet and 2½ square inches outlet.
(2)  The ventilators referred to in paragraph (1) shall be exclusive of side scuttles, doors, hatchways, skylights and other apertures not built solely for ventilation.
(3)  If the compartment is in the wings between the ship’s side and the boilers or engine room the area of the ventilators shall be increased by 33%.
(4)  All cowl ventilators must be carried to a convenient height above the deck and be clear of obstructions. In these ventilators the area of the cowl shall be at least 50% greater than that of the pipe.
(5)  When the pipes of cowl ventilators have curved bends or knees, and the angles do not exceed 30°, no additional area need be provided; but for curved bends or knees where the angle exceeds 30° the following additions to the area must be made:
(a)Curved bends. —Angles from 30° to 60°, add 5% for each bend.
 Curved bends. —Angles from 60° to 90°, add 10% for each bend.
(b)Knees. —Angles from 30° to 60°, add 16% for each bend.
 Knees. —Angles from 60° to 90°, add 36% for each bend.
If the radius of the inner side of a bend is less than the diameter of the pipe, the bend shall be regarded as a knee.
(6)  Ventilators unless specially approved must not exceed 452 square inches in area (24 inches in diameter), unless they communicate to two or more compartments, in which case the area of the passage or pipe leading to any one of the compartments so ventilated must not exceed 452 square inches.
(7)  Plans of special forms of cowl ventilators may be submitted to the Surveyor-General of Ships for consideration. If the ventilator is found satisfactory, it will have an area value assigned to it.
(8)  Ventilating side scuttles, if made according to plans approved by the Surveyor-General of Ships, may be accepted as equivalent to a cowl pipe having an area equal to the aggregate area of the orifices or valves, the area being measured at the most contracted part.