Q. Design Stairways - Ladders and Platforms?
Stairways, rather than ladders, should be provided for main access to elevated structures. Ladders should be reserved for isolated points which are visited infrequently. Ladders and platforms shall be provided as required for access to manways, operating valves, and instruments. Ladder arrangements should be established early in the project in order to avoid reworking and re-orientation. Ladders should be side step off rather than through.
Combined tower platforms shall be furnished when practical or economical on "lined-up" towers with common manway elevations, providing tower differential expansion permits. Platforms or catwalks joining two towers together should have a slide plate or hinged section to allow for vessel movement or expansion.
Side platforms are to be provided for access to manways, instruments, valves and equipment, and for cross-overs between ladders. The size of these platforms should be kept to a minimum. The width should be minimum 900 mm (3 ft.), but shall be enough to permit opening of the manway cover or to provide a minimum of 450 mm (1.5 ft.) clearance between the handrail and piping such as a level controller, gauge glass, level switch or safety valve. Platforms need not extend underneath valves and equipment to make them accessible.
Tower manways, depending on tray arrangement, access, and maintenance area for vessel, shall generally be located to the rear of the vessel (away from the pipe rack), with all manways on or about the same centerline of orientation. Manways shall be located to give good access to the tower drop down area, so that tower internals removed through the manway require minimum manhandling to access the davit or crane.