(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;
[GRAPHIC] [TIFF OMITTED] TC21OC91.020
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).------------------------------------------------------------------------
(2) Stairway risers shall be uniform and shall range from 6\1/2\ to 10\1/2\ 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 Sec. 1917.112(c)(1). If balusters are used, there shall be a minimum of one per tread. Handrails shall be a minimum of 1\1/4\ 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]