WAC 296-24-76555   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-12.)

     (1) Alternating tread-type stairs shall be designed, installed, used, and maintained in accordance with approved manufacturer's specifications, and shall 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 minimum of 17 inches between handrails;

     (e) A minimum width of 22 inches overall;

     (f) A minimum tread depth of 8 inches;

     (g) A minimum tread width of 7 inches; and

     (h) A maximum rise of 9 1/2 inches to the tread surface of the next alternating tread.

     (2) Alternating tread-type stairs shall not have more than a 20-foot continuous rise. Where more than a 20-foot rise is necessary to reach the top of a required stair, one or more intermediate platforms shall be provided in accordance with WAC 296-24-76515.

     (3) Stairs and platforms shall be installed so the top landing of the alternating tread stair is flush with the top of the landing platform.

     (4) Stair design and construction shall sustain a load of not less than five times the normal live load, but never less strength than to carry safely a moving concentrated load of 1,000 pounds.

     (5) Treads shall be equipped with slip-resistant surfaces.

     (6) Where a platform or landing is used, the width shall not be less than the width of the stair nor less than 30-inch depth in the direction of travel. Stairs shall be flush with the top of the landing platform.













[Statutory Authority: Chapter 49.17 RCW. 92-17-022 (Order 92-06), § 296-24-76555, filed 8/10/92, effective 9/10/92; 91-03-044 (Order 90-18), § 296-24-76555, filed 1/10/91, effective 2/12/91.]