What are ship-stair treads and open risers?
Ship-stair treads are the horizontal surfaces that support the user’s feet; open risers are the unobstructed spaces between them. OSHA regulates their depth, width, rise and uniformity as parts of a complete general-industry access system.
| Design or safety factor | Federal OSHA criterion | Citation |
|---|---|---|
| Tread depth | At least 4 inches, measured front to back and including any nosing | 29 CFR 1910.21; 1910.25(e)(3) |
| Tread width | At least 18 inches | 29 CFR 1910.25(e)(4) |
| Vertical rise | 6.5–12 inches between tread surfaces | 29 CFR 1910.25(e)(2) |
| Risers | Open | 29 CFR 1910.25(e)(5) |
| Uniformity | Riser heights and tread depths uniform between landings | 29 CFR 1910.25(b)(3) |
| Vertical clearance | At least 6 feet 8 inches above the leading edge of each tread | 29 CFR 1910.25(b)(2) |
| Stair load | At least 5× anticipated live load and at least 1,000 lb concentrated | 29 CFR 1910.25(b)(6) |
| Handrails | Both sides of every ship stair | 29 CFR 1910.28(b)(11)(iii) |
What are ship-stair treads and open risers?
Ship-stair treads are the horizontal members on which a person steps. Open risers are the unobstructed vertical spaces between successive treads. Together, they create the characteristic geometry of a ship stair: a permanent access stair that rises more steeply and occupies less horizontal space than a standard stair. In federal general-industry rules, these features are not merely descriptive. OSHA §1910.21 defines a ship stair—also called a ship ladder—as a stairway equipped with treads, stair rails and open risers, with a slope between 50 and 70 degrees from horizontal. Section 1910.25(e) then specifies a minimum tread depth of 4 inches, a minimum tread width of 18 inches and a vertical rise of 6.5 to 12 inches between tread surfaces. These are minimum or boundary conditions, not a complete design recipe. A usable system also depends on consistent geometry, traction, clearance, rails, structural capacity, installation and the surrounding walking-working surfaces.
How OSHA measures tread depth, width and rise
Regulatory dimensions are useful only when their reference points are understood. OSHA defines tread depth as the horizontal distance from the front to the back of a tread, including the nosing when one is present. For a ship stair, that measured depth must be at least 4 inches. Tread width is the side-to-side usable span of the stepping surface; §1910.25(e)(4) sets its minimum at 18 inches. Vertical rise is measured between the surfaces of adjacent treads and must be between 6.5 and 12 inches. The leading edge, or nosing, becomes an important datum for other measurements as well: OSHA measures required vertical clearance from the leading edge of the tread to the overhead obstruction, and rail height from the leading edge to the top surface of the rail. Drawings sometimes use “going” to describe the horizontal advance from one tread nosing to the next. That can be a valuable layout dimension, but it should not be assumed to equal OSHA tread depth. A specification should state each dimension and its measurement points rather than relying on terminology alone.
Why ship stairs have open risers
An open riser means there is no vertical panel closing the space between one tread and the next. OSHA makes open risers part of both its ship-stair definition and its ship-stair requirements. This is a categorical feature: adding closed riser panels to a steep assembly is not a neutral cosmetic change when the assembly is being evaluated as a ship stair under the federal rule. The open arrangement can preserve toe and foot clearance in compact geometry and makes the individual tread surfaces visually distinct. It can also allow light, liquids or small objects to pass through, depending on the installation. Those practical effects require attention beyond §1910.25(e). Openings near work areas may interact with falling-object hazards, process contamination or housekeeping needs. The connected platform may need toe boards, screens or other protection under §§1910.28 and 1910.29 where objects could fall to employees below. The correct solution depends on the complete workplace; the phrase “open riser” does not remove the employer’s separate duties to address other recognized hazards.
Why uniform tread and riser geometry matters
People climb stairs by forming a rhythm. An unexpected change in tread depth or riser height interrupts that rhythm, and the effect can be amplified on a 50- to 70-degree ship stair. OSHA §1910.25(b)(3) therefore requires riser heights and tread depths to be uniform between landings. Uniformity must be evaluated in the fabricated and installed condition, not only in a nominal product schedule. Floor finishes, shims, attachment elevations and the transition onto a landing can change the first or last rise. Tread plates, nosings or added anti-slip materials can change the effective surface or depth if they are not incorporated into the design. A sound review checks every rise and tread within each flight from consistent datum points, including the top and bottom transitions. It also checks that each tread remains level, stable and unobstructed after installation. OSHA does not publish a separate ship-stair tolerance in §1910.25; a designer should not invent one or imply that a small discrepancy is automatically acceptable. Fabrication tolerances and field conditions require qualified, project-specific review.
How tread surfaces support traction and safe use
The dimensional minimums do not describe how a tread performs when wet, oily, icy, worn or contaminated. OSHA §1910.22 requires walking-working surfaces to be kept clean, orderly and, to the extent feasible, dry; hazardous conditions must be corrected or guarded before the surface is used again. OSHA §1910.29 also requires handrail and stair-rail surfaces to be smooth and free of hazards that could puncture or lacerate employees or snag clothing. For treads, the project team should select a surface suited to the exposure—such as an appropriate plate, grating or applied anti-slip treatment—and consider drainage, debris, footwear, cleaning methods and corrosion. A pronounced nosing can improve edge recognition, but it must not create an avoidable trip or snag condition. Maintenance is equally important. Coatings wear, grating can deform, fasteners loosen and contaminants can fill traction patterns. Inspection should compare the current tread condition with the approved design and manufacturer instructions rather than treating “non-slip” as a permanent product attribute or a guarantee against falls.
How loads affect tread and stair design
Tread width and depth describe geometry; they do not establish strength. Under §1910.25(b)(6), each stair must support at least five times the normal anticipated live load and never less than a concentrated load of 1,000 pounds applied at any point. The requirement applies to the stair as an installed system. Treads, welds, stringers, brackets, fasteners, supports and the supporting structure must work together to transfer load safely. The anticipated use also matters: one employee carrying tools, repeated maintenance traffic and a bulky component moved between levels can create different design demands. Deflection, vibration, local tread deformation and connection behavior should be evaluated by qualified parties even where nominal capacity appears sufficient. Rails have separate strength requirements under §1910.29, including a 200-pound top-edge load for stair rail systems and handrails in specified directions. Neither a configurator nor a dimensional table can verify these structural conditions without the material properties, connection details, support conditions and design calculations for the actual installation.
How treads connect to rails, clearance and landings
A tread is one element in a continuous access route. Every ship stair must have handrails on both sides under §1910.28(b)(11)(iii). OSHA §1910.29 sets criteria for handrail height, clearance, graspability, continuity, surface condition and strength, while stair rails may be required to protect exposed sides. Overhead clearance must be at least 6 feet 8 inches, measured vertically from the leading edge of each tread. At the ends of the flight, landings and platforms must be at least as wide as the stair and at least 30 inches deep in the direction of travel. Doors and gates opening directly onto a stair require a platform. For platforms installed on or after January 17, 2017, their swing cannot reduce the effective usable depth below 22 inches; the retained threshold for older platforms is 20 inches. These related dimensions shape how a user places a foot, reaches a handrail and transitions between surfaces. They also explain why an isolated tread drawing cannot establish compliance. The review must follow the user’s path from the approach area, across every tread and rail, onto the destination platform and around any opening or obstruction.
What should be inspected and documented?
Inspection begins before fabrication. The project record should identify the intended stair classification, document why standard stairs are not feasible, show dimension reference points and preserve the assumptions used for loading, materials, tread surface and exposure. During fabrication and installation, reviewers should verify tread width and depth, every vertical rise, the open-riser configuration, angle, headroom, attachment elevations and landing transitions against approved information. Before use—and at intervals appropriate to conditions—the employer should look for loose or missing fasteners, cracked welds, bent or unstable treads, corrosion, sharp edges, worn traction surfaces, accumulated contaminants, obstructed clearance and changes to adjacent equipment or platforms. Section 1910.22 requires regular inspection of walking-working surfaces and correction or guarding of hazardous conditions before employees use them again. Section 1910.25(b)(9) also requires permitted ship stairs to be installed, used and maintained according to the manufacturer’s instructions. Dated records, photographs and documented corrective work can support a disciplined safety program, but paperwork does not substitute for an installation that meets all applicable requirements.
Configure ship-stair geometry around your space
The Ship Stair Builder helps project teams translate field measurements into an initial custom configuration. Enter the floor-to-floor height, stair width, angle, tread depth, target rise, headroom and landing depth to explore how the selected values affect the stair geometry and concept drawing. The builder checks selected dimensional ranges—including ship-stair tread depth, width and rise criteria drawn from OSHA §1910.25—and flags covered inputs that fall outside those checks. Used early, this can help uncover preventable measurement and specification issues, reduce avoidable redesign and address dimensional conditions that could contribute to an OSHA citation or penalty. It is a planning and quotation tool, not an OSHA certification or a compliance guarantee. It does not verify tread traction, fabricated uniformity, structural capacity, rails, connections, field installation, standard-stair feasibility or the surrounding workplace. State-plan rules, building and fire codes and site-specific requirements may also apply. Have qualified parties review the complete application before fabrication and use.
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This article summarizes selected federal requirements and is not a site-specific compliance determination, engineering approval or legal opinion.