OSHA standard at 29 CFR 1910.25(c)(4) applies to places of employment and requires standard stairs to have a minimum width of 22 inches (56 cm) between vertical barriers. OSHA does not consider a handrail to be a vertical barrier or obstruction to that required minimum width.
The note at the bottom of 1910.28(b)(11)(ii) Table D-2 is meant to indicate that the handrails are not considered obstructions or vertical barriers for purposes of measuring standard stair width. The preamble to the final rule states “[§ 1910.25(c)(4)], … requires that employers ensure standard stairs have a minimum width of 22 inches between vertical barriers. Examples of vertical barriers include stair rails, guardrails, and walls.” 81 Fed. Reg. 82494, 82560 (Nov. 18, 2016).
The standard stair width is measured between the vertical barriers, not between handrails. Please note that stair width requirements are different for means of egress and shall be in accordance with OSHA standard 1910.35.
Source: https://www.osha.gov/laws-regs/standardinterpretations/2024-10-17