Stairways get less attention than ladders on a jobsite, but Subpart X treats them with the same specificity.
The trigger. Stairways having four or more risers or rising more than 30 inches, whichever is less, must be equipped with at least one handrail and one stair rail system along each unprotected side or edge (29 CFR 1926.1052(c)(1)). The "whichever is less" matters: three tall risers that climb 32 inches already qualify.
Landings and construction. Stairways that will not be a permanent part of the structure must have landings of at least 30 inches in the direction of travel and 22 inches wide at every 12 feet or less of vertical rise (29 CFR 1926.1052(a)(1)). Riser height and tread depth must be uniform within each flight, with variations of no more than ¼ inch (29 CFR 1926.1052(a)(3)).
Where a stairway is required at all. A stairway or ladder must be provided at every personnel point of access with a break in elevation of 19 inches or more where no ramp, runway, sloped embankment, or personnel hoist is provided (29 CFR 1926.1051(a)). Where there is only one point of access between levels, it must be kept clear; if it cannot be, a second point of access must be provided and used (29 CFR 1926.1051(a)(3)).
Related: stairs under construction. Stairways with metal pan landings and treads may not be used until the pans are filled, temporarily or permanently, and skeleton metal stairs may not be used until treads and landings are in place (29 CFR 1926.1052(b)(1), 1926.1052(b)(2)).