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 https://www.osha.gov.



August 6, 2002

Mr. Sanford T. Liang
KTA-Tator, Inc.
115 Technology Drive
Pittsburgh, PA 15275

Re: §1926.451(a)(6); scaffolds; bridge-painting projects

Dear Mr. Liang:

This is in response to your letters of September 6, 2001, and March 26, 2002, and to subsequent telephone conference calls of April 21 and 22, 2002, with Dan Adley, yourself and Stephen Stock of my staff. Your original questions were limited and modified based on these conversations; the questions are paraphrased below. I apologize for the delay in providing this response.

Background: Your employees work from scaffolding on a variety of bridge painting projects, although they neither erect nor modify the scaffolding. Your letter provided several diagrams of the work platforms that your employees use in their work. These platforms consist of chain link fencing (with safety netting or metal sheeting) suspended from the bridge structure by cables (see illustration below). The bridge painting scaffold scenario on which your questions are based is below:


Bridge deck curb and railings
Image of bridge deck curb and railings

  • Sections of chain link fencing or flexible netting are used to construct an envelope that combines a work platform and containment walls. This envelope is supported from the underside of the bridge support structure and is attached to the bridge deck or to horizontal bridge deck outriggers. Envelope sections may or may not be overlapped. Typically, the fencing or netting is connected together with metal clips or tied together with rope (typically synthetic fiber rope, such as polypropylene). Various methods may be used to connect the fencing or netting sections to the bridge and to each other to form the platform and walls of the envelope. Poly-tarpaulin sections, which are used to contain dust within the envelope, are attached together and to the fencing by various methods.

Limitations: Since you are not asking about scaffold erection and dismantling requirements, we will not address them. Additionally, we will not address requirements regarding employee access to the work platform inside such scaffold envelope systems.

Question: Is there a simple way for employers to assess the adequacy of a chain link scaffold envelope system?

Answer: No; the nature of the construction of this type of scaffold makes it extremely difficult for the user to determine whether it is safe. Section 1926.451(a)(6) requires all scaffolds to be designed by a qualified person and constructed and loaded in accordance with that design. Due to the materials and configuration of the system, a complex engineering analysis would be needed to assess the capacity of such a system. The analysis is further complicated by the fact that the capacity may diminish over time due to wear and corrosion of materials or as a result of events during use.

We have listed below some of the complications involved in assessing such a scaffold:




  • The strength requirement in §1926.451(a)(1) that the scaffold and each component have a capacity of four times the maximum intended load will take considerable calculation to assess. The same is true for suspension ropes and connecting hardware under §1926.451(a)(3) (six times the maximum intended load).
  • §1926.451(d)(12)(iv) requires pre-shift inspection and re-tightening of suspension wire-rope clips.
  • §1926.451(f)(16) requires that scaffold platforms not deflect more than 1/60th of the span when loaded.
  • If the envelope is constructed in such a way that it falls into the category of a catenary scaffold, under §1926.451(g)(1)(i), the employees must use personal fall arrest systems. If the scaffold to be used does not conform to one of the types described in §1926.451(g)(1)(i)-1926.451(g)(1)(vi), then the fall protection requirements of §1926.451(g)(1)(vii) must be followed.
  • Another complication to consider is that §1926.451(f)(13) prohibits accumulation of debris on scaffold platforms. Debris accumulation by itself or in conjunction with other loads, including your employees, could put stresses on the scaffold above those it was designed to support. Your responsibility as the employer of the exposed employees includes determining whether debris has accumulated to the point where it adversely affects compliance with the loading limitations.

Other requirements may also apply, depending on how the envelope system is constructed. In sum, as you can see, use of such systems requires considerable expertise and watchfulness on the part of the user.

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

[Corrected 6/2/2005]