Under 1917.121(a), what is the OSHA definition of a "spiral stairway"?
A spiral stairway is defined as one with a closed circular form, uniform sector-shaped treads, and a supporting column. See Definition in 1917.121(a) for the exact wording.
OSHA 1917.121
Spiral stairway requirements
1917 Subpart F
Questions & Answers
Under 1917.121(b)(1), what are the minimum tread dimensions required for spiral stairways used for normal employee use versus limited access?
For spiral stairways the minimum dimensions in Figure F‑1 apply: for normal use by employees the half‑tread width (A) must be 11 inches (27.94 cm) and the minimum tread depth (B) 6 inches (15.24 cm); for limited access the half‑tread width (A) may be 9 inches (22.86 cm) and the tread depth (B) 5 inches (12.7 cm). See Requirement in 1917.121(b)(1).
Under 1917.121(b)(2), what are the allowed riser heights for spiral stairways and must risers be uniform?
Yes — risers must be uniform and must range from 6 1/2 inches to 10 1/2 inches (16.5 to 26.67 cm) in height. See 1917.121(b)(2).
Under 1917.121(b)(3), what load capacities must spiral stairways meet for uniform and concentrated loading?
Spiral stairways must support a minimum uniform loading of 100 pounds per square foot (4.79 kN) and a minimum concentrated center loading on a tread of 300 pounds (1,334 N). See 1917.121(b)(3).
Under 1917.121(b)(4), what railing and handrail requirements apply to spiral stairways?
Railings on spiral stairways must conform to the guarding requirements at 1917.112(c)(1). If balusters are used there must be at least one baluster per tread, and handrails must have a minimum outside diameter of 1 1/4 inches (3.18 cm). See 1917.121(b)(4).
Under 1917.121(b)(5), what is the minimum vertical clearance required on spiral stairways?
Vertical clearance above the top step must be at least 6 feet 6 inches (1.98 m). See 1917.121(b)(5).
Under 1917.121(c), what does OSHA require for maintaining spiral stairways?
Spiral stairways must be maintained in a safe condition. Employers must keep stairways free of hazards (for example: loose or damaged treads, corrosion, or insecure railings) so employees can use them safely. See 1917.121(c).
Under 1917.121(b)(4), if balusters are used on a spiral stairway, how many are required?
If balusters are used there must be a minimum of one baluster per tread. This requirement is in 1917.121(b)(4).
Under 1917.121(b)(4), is there a required minimum size for handrails on spiral stairways?
Yes — handrails must be a minimum of 1 1/4 inches (3.18 cm) in outside diameter. See 1917.121(b)(4).
Under 1917.121(b)(1) and the figure F‑1, when is a stairway allowed to use the "limited access" dimensions instead of the normal use dimensions?
A stairway may be designed to the smaller "limited access" dimensions (A = 9 in, B = 5 in) only for locations intended for limited access rather than normal, frequent employee traffic; normal use areas must meet the larger "normal use" dimensions (A = 11 in, B = 6 in). See 1917.121(b)(1).
Under 1917.121(b)(3), can spiral stair treads be relied on to carry heavy equipment or concentrated machinery loads?
No — spiral stairways are required to meet a minimum uniform loading of 100 pounds per square foot and a minimum concentrated center load of 300 pounds; loads above those limits require alternative access or structural design. See 1917.121(b)(3).
Under 1917.121, must spiral stair treads and risers be uniform around the stair?
Yes — spiral stairways are defined to have uniform sector‑shaped treads and 1917.121(b)(2) requires risers to be uniform within the allowed height range. See 1917.121(a) and 1917.121(b)(2).
Under 1917.121(b)(4), to which guarding standard do spiral stairway railings have to conform?
Spiral stairway railings must conform to the requirements of 1917.112(c)(1). See 1917.121(b)(4).
Under 1917.121, where can I find the minimum dimensions diagram (Figure F‑1) for spiral stairways?
The minimum dimensions diagram (Figure F‑1) is included with the spiral stairway rule at 1917.121(b)(1) and is shown in the regulatory text for 1917.121. See 1917.121 for the full section and illustration.
Under 1917 and the 2017 Letter of Interpretation, do Part 1917 spiral stairway requirements always apply at a designated waterfront facility?
No — Part 1917 (including requirements like 1917.121 for spiral stairways) does not apply to designated waterfront facilities that fall outside the scope of marine terminals. OSHA explained this in its Letter of Interpretation about applicability to waterfront facilities: see 2017-05-31 Letter of Interpretation and 1917 for the Part 1917 regulatory scope. Employers at such facilities must determine which OSHA standards apply to their specific operation.
Under 1917.121, can employers use spiral stairways where workers must carry tools or materials frequently?
They can only be used if the stairway meets the normal‑use minimum dimensions (A = 11 in, B = 6 in), required riser uniformity, and loading capacity. Because spiral stairs have smaller tread areas than straight stairs, evaluate task requirements — if employees frequently carry bulky loads or equipment, a different stair or access method may be needed despite compliance with 1917.121. See 1917.121(b)(1)–(3).
Under 1917.121(c), who is responsible for keeping a spiral stairway in a safe condition?
The employer is responsible for ensuring spiral stairways are maintained in a safe condition; that obligation derives from the maintenance requirement in 1917.121(c). Employers should implement inspections and repairs as needed to keep stairways safe for employees.
Under 1917.121, does the standard specify maximum tread thickness or material types for spiral stairways?
No — 1917.121 sets dimensional, load, railing, and clearance requirements but does not prescribe specific tread thicknesses or materials. Designers must meet the minimum loading and other requirements in 1917.121(b)(1)–(5) and choose materials and dimensions that satisfy those performance requirements.
Under 1917.121(b)(3) and related marine‑terminal rules, does OSHA allow modifications that could affect stairway load capacity without approval?
Modifications that affect the safe operation or capacity of equipment or structures should be treated carefully; while 1917.121(b)(3) sets load requirements, other Part 1917 rules (for example rules controlling modifications to powered equipment) call for manufacturer or engineer approval when changes affect safety. Employers should follow the performance requirements in 1917.121(b)(3) and consult relevant Part 1917 provisions and, where applicable, OSHA guidance on modifications. See also OSHA's discussion on facility applicability in the 2017-05-31 Letter of Interpretation.
Under 1917.121, if a spiral stairway is installed under low ceilings or obstructions, what clearance rule must be followed?
You must provide at least 6 feet 6 inches (1.98 m) of vertical clearance above the top step. Installations under low ceilings or obstructions must comply with the minimum vertical clearance specified in 1917.121(b)(5).
Under 1917.121, are the spiral stairway tread loads (100 psf and 300 lb concentrated) minimums or maximums?
They are minimum required load capacities — stairways must be able to resist at least 100 pounds per square foot uniform loading and a 300‑pound concentrated center load on a tread. Employers must design and install stairways to meet or exceed those minimums as stated in 1917.121(b)(3).