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August 6, 2002
Mr. Sanford T. Liang
115 Technology Drive
Pittsburgh, PA 15275
Re: §1926.451(a)(6); scaffolds; bridge-painting
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:
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.
- 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.
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:
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.
- 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
- §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.
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