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1.36D MISCELLANEOUS METALWORK (Continued) D. Standard designs of spiral stairways are shown on the following drawings: Reference Drawings Right-hand Spiral Stairway--6–Foot Diameter 40-D-4318 Right-hand Spiral Stairway--5–Foot Diameter 40-D-4456 Typical spiral stairways are shown on the following drawings: Kortes Dam 545-D-445 Salt Lake Aqueduct 244-D-2176 E. A ladder is used where it is necessary to ascend or descend at an angle Ladders with the horizontal exceeding 50 degrees. Ship ladders are used where the slope is between 50 and 75 degrees. No attempt has been made to prepare standard drawings covering this type of ladder; however, Drawing No. 103-D-6 should be used to establish principal dipmensions. Ladders with slopes greater than 75 degrees may consist of rungs embedded in the concrete structure at 12-inch centers, or a fabricated steel ladder bolted to the structure. Ladders frequently extend for considerable distances; therefore, from a safety standpoint the following standards should be adhered to where possible: (1) Maximum length for single ladder, 30 feet. (2) Minimum clear width from center line of ladder to either side, 15 inches. (3) Clearances as indicated on Drawing No. 103-D-6. (4) Ladders greater than 25 feet long should be equipped with a cage or basket; however, where these ladders are used infrequently, the question of installing cages should be determined on the basis of individual requirements. F. Designs of ladders are indicated on the following drawings: Reference Drawings 18-inch Ladder--Standard Design 40-D-3392 15-inch Ladder--Standard Design 40-D-3432 Ladder Rung--Standard Design 40-D-3103 Ladder--Davis Power Plant 351-D-1808 Ladder with Basket--Davis Dam 351-D-1640–41 Ladder with Basket--Heart Butte Dam 203-D-132-33 Ship Ladders--Hungry Horse Dam 447-D-448–50 Ship Ladders--Enders Dam 328-D-578

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