OSHA was asked whether stairs constructed after January 17, 2017, would comply with 29 CFR 1910.25(c)(3) if they featured a 49-50 degree installation angle, a 9.5-inch tread depth, an 8-inch run, and a 1.5-inch nosing.
The background matters here. OSHA's stair requirements call for installation angles between 30 and 50 degrees from horizontal (29 CFR 1910.25(c)(1)), a maximum riser height of 9.5 inches (1910.25(c)(2)), and a minimum tread depth of 9.5 inches (1910.25(c)(3)). As the letter notes, for a 9.5-inch riser with a 9.5-inch tread depth, the maximum achievable angle is 45 degrees; stairs at 49-50 degrees with a 9.5-inch rise end up with a run of only 8 inches. Stairs built before 2017 fall under a different standard permitting an 8-inch minimum run through the exceptions in 1910.25(c)(5).
OSHA's answer was no. The agency clarified that 'the 9.5-inch minimum tread depth requirement is to provide stepping space that is adequate to protect' workers from falling hazards. Critically, tread depth must be measured horizontally between the vertical planes of the foremost projections of adjacent treads, perpendicular to the tread's leading edge — and beveled or rounded surfaces exceeding 20-degree slopes are excluded from the measurement. Counting a 1.5-inch nosing to get from an 8-inch run to a 9.5-inch 'tread depth' does not satisfy the standard for post-2017 stairs.