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 http://www.osha.gov.



April 21, 2004

Mr. Davy Passucci, PE
Engineering Manager
Safespan Platform Systems, Inc.
252 Fillmore Avenue
Tonawanda, NY 14150

Re: Composition, span, and deflection of underslung bridge scaffold platform systems; §1926.451(f)(16)

Dear Mr. Passucci:

This is in response to your letter dated July 14, 2003, to the Occupational Safety and Health Administration (OSHA), asking for clarification on OSHA's construction industry standards as applied to under-bridge type scaffold platform systems. We apologize for the delay in responding.

We have paraphrased your questions as follows:

Question (1): We manufacture the Safespan Multi-Span Bridge Platform System ("Platform System"), which is used to form a temporary work surface for work beneath a bridge. The Platform System is suspended from the underside of the bridge by cables. The rigid platform deck, which is made of steel, is supported by cables slung beneath it.

Title 29 CFR 1926.451(f)(16) Subpart L "Scaffolds" requires that a scaffold platform not deflect more than 1/60 of the span when loaded. In the context of this type of system, what does "the span" refer to?

We have illustrated the scenario you describe, as we understand it, as follows:



Depiction of steel Platform System suspended from the underside of the bridge by cables.

Title 29 CFR 1926.451(f)(16) states:

Platforms shall not deflect more than 1/60 of the span when loaded.

Section 1926.450 does not define the term "span," nor does it specify a method for calculating the span.

This provision was drafted to address specific hazards present in traditional scaffold platforms, which typically are made of wood planks or are fabricated, rigid units. The preamble for Subpart L states that:

Final rule paragraph (f)(16) provides that platform units shall not deflect more than 1/60 of the span when loaded. This provision ...is intended to limit the amount platform units can deflect under load without becoming overstressed and without their ends being pulled from their supports.1



Section 1926.451(f)(16) is intended to serve as a visual benchmark of the safe structural limits of the platform. In addition, when the deflection exceeds the provision's requirement, there is a greater likelihood of a platform's ends pulling away from the supports.

In construction scaffolds, the word span typically refers to the length of a rigid-type scaffold platform, measured between the structural supports.
2 In a supported scaffold, the span would be the distance between the scaffold framing members that hold up the platform (or, where there is a cantilever, the distance from the last point of support). In a two-point suspension scaffold, the span would be the distance between the points at which the cables attach to the platform structure.

In the case of the Platform System, the horizontal cables slung beneath the steel platform material are the equivalent of horizontal bearers in a supported scaffold. In light of the purpose of 1926.451(f)(16), "span" in this context refers to the distance between the horizontal cables.

However, for reasons described to the answer below to Question 2, the failure to meet the §1926.451(f)(16) requirement for non-wood platforms used in this type of scaffold system would be, in certain circumstances, a de minimis violation.

Question (2): Is the requirement in 29 CFR 1926.451(f)(16) applicable to this type of scaffold system if the platform is made of a flexible material?

As discussed in Question 1, §1926.451(f)(16) was promulgated based on the use of rigid-type platforms used in traditional scaffolding designs.
4 However, in under-slung bridge scaffolds of the type you have described, the platform is made of long sections of interlocking decking material. In addition, the platform is supported by, and attached to, a grid of horizontal (and vertical) cables. As we understand it, in at least some of these systems, because the material (and the grid itself) is inherently more flexible, a deflection greater than 1/60th of the span is (1) not indicative of an impending failure of the platform, and (2) would not cause the platform to pull away from its supports.

Therefore, in this type of under-slung grid system, which incorporates an engineered, non-wood based platform secured to the grid, as long as the employer can show that the platform was designed to deflect more than 1/60th of the span, and that a deflection greater than 1/60th would not threaten the platform's structural integrity or cause any other failure, the failure to meet the 1926.451(f)(16) would be a de minimis violation.

If you need additional information, please contact us by fax at: U.S. Department of Labor, OSHA, Directorate of Construction, Office of Construction Standards and Guidance, fax # 202-693-1689. You can also contact us by mail at the above office, Room N3468, 200 Constitution Avenue, N.W., Washington, D.C. 20210, although there will be a delay in our receiving correspondence by mail.


Russell B. Swanson, Director
Directorate of Construction





1 61 FR 46104. [ back to text ]





2 Note that the Construction Dictionary, 9th Edition, Greater Phoenix, Arizona Chapter of The National Association of Women in Construction, p. 496 (1996), defines span as: "the clear horizontal distance between structural supports, as those of a bridge . . . ." [ back to text ]





3 Under OSHA's de minimis policy, de minimis violations are those which have no direct or immediate relationship to safety or health. Consequently, no citation is issued. [ back to text ]





4 We note that the language in 29 CFR 1926.451(f)(16) is similar to the language used in paragraph of ANSI A10.8-1988 "Scaffolding - safety requirements," which states that "[w]ood scaffold planks shall be designed so that the deflection, at the center, at design load, does not exceed the span divided by 60." [Emphasis added.] [ back to text ]