...
(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;
| A (half-tread width) | B | |
| Normal use by employees. | 11 inches (27.94 cm). | 6 inches (15.24cm) |
| 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 (4.79 kN), 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.
[62 FR 40201 July 25, 1997; 65 FR 40942, June 30, 2000]