29 C.F.R. § 1917.121 Spiral stairways.
Title 29 - Labor
(a) Definition. “Spiral stairway” means one with closed circular form, uniform sector-shaped treads and a supporting column. (b) Requirements. Spiral stairways shall meet the following requirements: (1) Stairways shall conform to the minimum dimensions of Figure F–1; (2) Stairway risers shall be uniform and shall range from 6 (3) Minimum loading capability shall be 100 pounds per square foot (4.79kN), and minimum tread center concentrated loading shall be 300 pounds (1334 N); (4) Railings shall conform to the requirements of §1917.112(c)(1). If balusters are used, there shall be a minimum of one per tread. Handrails shall be a minimum of 1 (5) Vertical clearance shall be at least 6 feet, 6 inches (1.98 m) above the top step. (c) Maintenance. Spiral stairways shall be maintained in safe condition. [48 FR 30909, July 5, 1983, as amended at 62 FR 40201, July 25, 1997; 65 FR 40942, June 30, 2000]
Title 29: Labor
PART 1917—MARINE TERMINALS
Subpart F—Terminal Facilities
§ 1917.121 Spiral stairways.
Spiral Stairway_Minimum Dimensions------------------------------------------------------------------------ A (half-tread width) B------------------------------------------------------------------------Normal use by employees......... 11 inches (27.94 6 inches (15.24 cm). cm).Limited access.................. 9 inches (22.86 5 inches (12.7 cm). cm).------------------------------------------------------------------------