Section 1917.121 - Spiral stairways(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; View Image
Spiral Stairway-Minimum Dimensions
| A (half-tread width) | B |
| Normal use by employees | 11 inches (27.94 cm) | 6 inches (15.24 cm). |
| Limited access | 9 inches (22.86 cm) | 5 inches (12.7 cm). |
(2) Stairway risers shall be uniform and shall range from 61/2 to 101/2 inches (16.5 to 26.67 cm) in height;(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 11/4 inches (3.18 cm) in outside diameter; and(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