OSHA Industry Guidelines on Spiral Staircases
Spiral staircases provide a unique look for a living space, but are generally not suitable for the workplace. The lack of a uniform depth for the spiral stairs presents a hazard for employees going up or down the stairs, particularly while carrying bulky items. The Occupational Safety and Health Administration sets standards for walking and working surfaces in the workplace that limit the use of spiral stairways.
OSHA's general industry standards, which apply to most workplaces, cover the safe design and construction of fixed stairways. These are stairs necessary for employees to use on a routine basis to access different levels in the workplace. OSHA standards state that spiral stairways are not allowed in the workplace except for special limited usage; however the standards does not specify what constitutes a "special limited usage." The standards also allow spiral stairways as a secondary access, if it is impractical to construct a conventional stairway.
If a workplace includes spiral stairways under one of OSHA's exceptions, they must comply with OSHA's general stairway standards. These standards specify that stair strength shall be at least five times the anticipated usual load; the angle of stairway rise shall be between 30 and 50 degrees; stair treads shall be reasonably slip resistant; stairway platforms shall be at least the width of the stairs and 30 inches in length; railing and handrails shall be included; and the minimum vertical clearance of any stair tread shall be at least seven feet. A special standard applicable to spiral stairways requires that handrails shall be offset enough to prevent walking on the part of each step that is less than six inches wide.
In addition to the general stairway standards, OSHA set stairway standards specifically for the construction industry. These standards prohibit, without exception, the use of any spiral stairway by construction employees that will not be made a permanent part of the structure under construction. If the spiral stairway is being made permanent, OSHA general standards for stairways should be followed, except if the stairway is being constructed as a part of a private residence. OSHA stairway standards do not apply to private residences.
OSHA sets standards specifically for marine terminal facilities such as wharves, docks and other berthing locations. These standards include requirements for spiral stairways at such facilities, both for normal employee use and for limited access areas. Among the requirements is the minimum stair width. Spiral stairways for normal employee use must have a stair width of at least eleven inches as measured from the center of the stair to the edge. For limited access use, the stair width can be as small as nine inches. Railings are required and the vertical clearance must be at least six feet and six inches from the top step.