Standard Interpretations - Table of Contents Standard Interpretations - Table of Contents
• Standard Number: 1910.23; 1910.23(d)(1); 1910.23(e)(1); 1910.23(e)(2); 1910.24; 1910.24(e); 1910.24(h)

OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at

June 15, 2010

Ms. Darla J. Fanelli, PE, PS
Senior Project Engineer
1645 Indian Wood Circle, Suite 101
Maumee, OH 43537

Dear Ms. Fanelli:

Thank you for your September 3, 2009, correspondence to the Occupational Safety and Health Administration's (OSHA) Directorate of Enforcement Programs (DEP). Your letter has been referred to DEP's Office of General Industry Enforcement (GIE) for clarification of OSHA standards pertaining to winding stairway systems. This constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any question not delineated within your original correspondence.

Your questions are paraphrased and our responses follow.

Question 1: Are stair landings/platforms required along the path of a winding stairway?

Reply: OSHA's Fixed Industrial Stairs standard, 29 CFR 1910.24, does not require stair landings and/or intermediate platforms along the path for stairways that are not used for fire exit purposes. However, OSHA recommends, as outlined in Section 7.1 of American National Standards Institute (ANSI) A64.1-1968, Requirements for Fixed Industrial Stairs1, that:

Long flights of stairs, unbroken by landings or intermediate platforms, should be avoided. Consideration should be given to providing intermediate platforms where practical and where such stairways are in frequent use. [Emphasis added].

It is important to note that in the most recent version of this ANSI standard, ANSI A1264.1 -2007, Safety Requirements for Workplace Walking/Working Surfaces and Their Access; Workplace, Floor, Wall and Roof Openings; Stairs and Guardrails Systems, the standard now states in Section 6.9 that "[f]lights of stairs, uninterrupted by landings, or intermediate platforms shall be avoided." [Emphasis added]. A prudent employer should implement requirements and work practices that would provide increased protection for their employees.

If landings/platforms exist in the structure of the stairway, 29 CFR 1910.24(g) requires that, "[s]tairway platforms shall be no less than the width of a stairway and a minimum of 30 inches in length measured in the direction of travel." Also, please note that if the stairway is used for fire exit purposes, the requirements of Subpart E would be applicable.

Question 2: What rise and tread combination in winding stairways is acceptable to OSHA?

Reply:As outlined in 29 CFR 1910.24(e), "[a]ny uniform combination of rise/tread dimensions may be used that will result in a stairway at an angle to the horizontal within the permissible range." This permissible range is also provided in 29 CFR 1910.24(e) which states, "[f]ixed stairs shall be installed at angles to the horizontal of between 30 deg. and 50 deg."

Question 3: Is there a maximum clearance between a storage tank shell and winding stair where railings with a handrail will not be required on the tank side of the stair?

Reply:OSHA standard 29 CFR 1910.24(h) provides:

Standard railings shall be provided on the open sides of all exposed stairways and stair platforms. Handrails shall be provided on at least one side of closed stairways preferably on the right side descending. Stair railings and handrails shall be installed in accordance with the provisions of 1910.23.

In your situation, if the stairway and the side of the tank are not adjacent to each other to form an enclosure that would prevent a person from falling (having a gap less than 12 inches), then the side would be considered open and must have a rail.

With regards to the handrails, the requirements are outlined in 29 CFR 1910.23(d)(1), which states:

Every flight of stairs having four or more risers shall be equipped with standard stair railings or standard handrails as specified in paragraphs (d)(1)(i) through (v) of this section, the width of the stair to be measured clear of all obstructions except handrails:

(i) On stairways less than 44 inches wide having both sides enclosed, at least one handrail, preferably on the right side descending.

(ii) On stairways less than 44 inches wide having one side open, at least one stair railing on open side.

(iii) On stairways less than 44 inches wide having both sides open, one stair railing on each side.

(iv) On stairways more than 44 inches wide but less than 88 inches wide, one handrail on each enclosed side and one stair railing on each open side.

(v) On stairways 88 or more inches wide, one handrail on each enclosed side, one stair railing on each open side, and one intermediate stair railing located approximately midway of the width.

Question 4:Are midrails on winding stairways required if the posts are less than 18 inches apart and the height of the top rail is 30 inches (keeping it from being a wall opening)?

Reply: OSHA's standard at 29 CFR 1910.23(e)(1) states that, "[a] standard railing shall consist of top rail, intermediate rail, and posts..." Stair railings, in accordance with 29 CFR 1910.23(e)(2), must "be of construction similar to a standard railing..." Therefore, a midrail is required. However, in OSHA's proposed revisions of the general industry standard for Walking and Working Surfaces and Personal Protective Equipment - Fall Protection Systems- (75 Federal Register 28862, May 24, 2010), OSHA states 2:

(2) Midrails, screens, mesh, intermediate vertical members, or equivalent intermediate structural members must be installed between the top edge of the guardrail system and the walking-working surface when there is no wall or parapet wall at least 21 inches (53 cm) high. [Emphasis added].

(i) Midrails, when used, must be installed at a height midway between the top edge of the guardrail system and the walking-working level.

(ii) Screens and mesh, when used, must extend from the top rail to the walking-working level and along the entire opening between top rail supports.

(iii) Intermediate members (such as balusters), when used between posts, must be not more than 19 inches (48 cm) apart.

(iv) Other structural members (such as additional midrails and architectural panels) must be installed such that there are no openings in the guardrail system that are more than 19 inches (48 cm) wide.

Where an employer is in compliance with the provisions of a proposed OSHA standard, it is OSHA's general policy to treat the violation of an existing requirement as a de minimus condition. A de minimus condition does not result in a citation or penalty and need not be abated.

Question 5: If the top rail of a winding stairway railing was 29 inches, instead of 30 inches, would OSHA consider this an acceptable variation from the standard?

Reply:OSHA's standard at 29 CFR 1910.23(e)(2) states:

A stair railing shall be of construction similar to a standard railing but the vertical height shall be not more than 34 inches nor less than 30 inches from upper surface of top rail to surface of tread in line with face of riser at forward edge of tread.

Therefore, the stair railing described in your letter is a violation of the standard.

Question 6: Are areas surrounded by raised earth dikes, such as areas serving as a secondary containment for an aboveground storage tank, considered confined spaces?

Reply: OSHA has addressed this concern in its letter of interpretation dated October 27, 1995, to Mr. William Taylor [(copy enclosed)]. Under question 3 of that letter, OSHA states:

As a containment structure, the design of a dike will determine whether it falls within the definition of PRCS [Permit-Required Confined Space] standard. A dike formed of mounded or sloped earth to a height of 4 to 6 feet would not normally represent a restricted means for entry or exit. Conversely a dike formed of a vertical block or concrete wall of the same height would constitute a restricted means for entry or exit.

The determination of whether a diked area determined to be a confined space would constitute a PRCS would have to be determined based on the hazard(s) present. For example, the potential hazard of engulfment or the potential of a hazardous atmosphere from a heavier-than-air gas or vapor would have to be considered in making the determination.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. Please be aware that OSHA's enforcement guidance is subject to periodic review and clarification, amplification, or correction. Such guidance could also be affected by subsequent rulemaking. In the future, should you wish to verify that the guidance provided herein remains current, you may consult OSHA's website at If you have any further questions, please feel free to contact the Office of General Industry Enforcement at (202) 693-1850.


Thomas Galassi, Acting Director
Directorate of Enforcement Programs


1 National consensus standard, ANSI A64.1 - 1968, provided a basis for the promulgated standard outlined in 29 CFR 1910.24. See 38 FR 24300 published on September 6, 1973.   [Return to Text]

2  Proposed 29 CFR 1910.28(b)(2).   [Return to Text]

Standard Interpretations - Table of Contents Standard Interpretations - Table of Contents