WAC 296-24-74030. Alternating tread-type stairs

Alternating tread-type stairs have a series of steps between 50 and 70 degrees from horizontal, attached to a center support rail in an alternating manner so that a user of the stairs never has both feet at the same level at the same time. (See Figure D-11 of this section.) (1) You must ensure that alternating tread-type stairs are designed, installed, used, and maintained in accordance with approved manufacturer's specifications, and have the following: (a) Stair rails on all open sides; (b) Handrails on both sides of enclosed stairs; (c) Stair rails and handrails of such configuration as to provide an adequate handhold for a user grasping it to avoid a fall; (d) A distance of 17 to 24 inches between handrails; (e) A minimum width of 22 inches overall; (f) A minimum tread depth of 8.5 inches; (g) A minimum tread width of 7 inches; (h) A maximum rise of 9.5 inches to the tread surface of the next alternating tread; and (i) Open risers if the tread depth is less than 9.5 inches (24 cm). (2) You must ensure that alternating tread-type stairs have not more than a 20-foot continuous rise. You must provide one or more intermediate stair platforms in accordance with WAC 296-24-74005 where more than a 20-foot rise is necessary to reach the top of a required stair. Angle Type ≤ 30° Ramps 30° - 50° Standard Stairs 50° - 70° Ship Stairs 50° - 70° Alternating Tread-Type Stairs 60° - 90° Ladders Angle Type ≤ 30° Ramps 30° - 50° Standard Stairs 50° - 70° Ship Stairs 50° - 70° Alternating Tread-Type Stairs 60° - 90° Ladders Figure D-10 - Angles for Stairs, Ramps, and Ladders Figure D-11