Standard Interpretations - Table of Contents|
| Standard Number:||1926.502|
February 14, 1996
Mr. Michael S. D'Alessio, P.E.
Dear Mr. D'Alessio:
This is in response to your letter of September 1, 1995, to the Occupational Safety and Health Administration (OSHA) in which you set forth your concerns with OSHA's policy regarding the use of scaffolds as fall arrest system anchors.
With respect to the question of whether or not scaffolds can be used as anchorage points for personal fall arrest systems, please be advised that we understand the Scaffold Industry Association and the Scaffolding, Shoring & Forming Institute are concerned that scaffolds and scaffold components have not been designed to accept the forces imposed by employee falls. We agree that during the erection and dismantling process the typical scaffold is unable to comply with the criteria of 29 CFR 1926.502(d)(15) which requires the anchorage (i.e. the scaffold) to be capable of supporting at least 5000 pounds per employee attached. The alternative anchorage criteria referenced in 29 CFR 1926.502(d)(15)(i) and (ii) (e.g. a system designed, installed and used under the supervision of a qualified person as part of a complete personal fall arrest system which maintains a safety fector of at least two) may be used if the partially erected or completed scaffold is considered a part of the complete personal fall arrest system criteria and is capable of resisting the forces involved should there be a fall.
With respect to your comments on the specific criteria for personal fall arrest systems, please be advised that OSHA is in the process of opening a new rulemaking on Subpart M and your comments have been forwarded to the Office of Construction Standards and Compliance Assistance for incorporation into the record. The opening will be announced in the Federal Register later this year.
If you require further assistance, please do not hesitate to contact either myself (ext. 150) or Mr. Dale Cavanaugh (ext. 149) of my staff at (202) 219-8136.
Roy F. Gurnham, Esq., P.E.
Dear Mr. Gurnham:
Thank you for the pleasant and informative conversation we had Friday, 8/25/95, regarding the occupational safety and health regulations (OSHA regulations) addressing fall protection.
As you know, I received a letter from John Miles who referred me to you or Dale Cavanaugh if I had any questions.
The letter from Mr. Miles was in response to a letter I wrote to Joseph Dear, Assistant Secretary of Labor, requesting an interpretation of paragraph 1926.502(d)(15). The reply from Mr. Miles implies that a scaffold may be considered a part of a complete personal fall arrest system and, as such, would only require a 2:1 factor of safety on failure. I am not privy to the consideration that brought about this suggestion, but I do feel that 2:1 is too small a factor of safety to be used on this kind of equipment. I recommend that the following criteria should be considered before any definite conclusion is reached concerning the proper design of such systems.
First, there is the probability that the experienced load will be greater than the anticipated load. In erecting or dismantling a scaffold, the force on the fall arrest system could easily be doubled if the worker left the lanyard connected where it was and climbed up to the next level. In this case, the fall factor would be two. If someone fell from that position, the fall arrest system would need to deal with loads up to and exceeding the failure load that a 2:1 factor of safety would provide.
Secondly, when designing systems for suddenly imposed load, one must consider that the stresses so developed can be as much as five times those that would occur if the load were gradually imposed. The stresses developed are a function of the natural frequency of the component and the time duration of the load.
As you may know, scaffolds can be soft structures particularly at the time they are being erected or dismantled. A natural frequency of one cycle per second is quite common so that a load duration as long as 1/4 second can impose significant stresses on the structure. In cases like these, OSHA would be sanctioning a factor of safety that is significantly less than standard practice would allow.
The third consideration is that ability of the specific component to deal with impact loads. Considerations such as notches, sharp abrupt changes in cross sections, residual stresses developed as a consequence of the welding process, welding of dissimilar metals, all of which provide stress risers which significantly decrease the ability of the component to deal with suddenly applied loads.
Scaffolds, as you know, are replete with this kind of construction. Sharp changes in cross section are the rule rather than the exception and, to my knowledge, no special heat treatment is performed to reduce residual stresses or to address the problem of suddenly applied load in any way.
No scaffold system in existence in the world today is designed to safely support the kinds of loads that would be imposed upon them by fall arresting systems. For this reason, every major United States manufacturer of scaffolding has signed a letter to the users of our equipment warning against such attachment.
The question now arises, how much suddenly applied force can scaffold safely sustain. I would offer the number of 400 lbs., with a load duration of 1/2 second or longer. To stay within these limits, we would have to limit the fall to approximately three feet or less, which means that the scaffold erectors would need to employ a lanyard of that length. Scaffold erectors insist that such a length would curtail their movements to the point where they could not work at all. They do not even feel that this length lanyard is acceptable for a worker who remains in a stationary position. Erectors would prefer to build guardrails around such people rather than restrict them to this limited movement. Since most scaffolds in the world are built on seven, eight and ten foot centers, approximately, we can see that erectors would not be able to reach the next post location unless the post spacing was closed down to the three-foot dimension, and so we have reached the realm of the preposterous. We must either employ one erector for each post of a scaffold or tie off to a horizontal component that has not yet been fixed to the scaffold in order that the erector may walk across from one post to the other to finish the attachment of the horizontals. In short, it is impractical to try to erect a scaffold with a lanyard whose length would be short enough so that the forces imposed into the scaffold from a fall would be of a magnitude that the scaffold could safely support.
We must also bear in mind that even if the scaffold component does not fail, the forces generated by the fall arrest system could topple the scaffold. The industry has demonstrated often that in most cases when a 220 lb. weight falls off the scaffold that the scaffold itself topples. This has been demonstrated by Safway on frame and system scaffolds. I would be very happy to demonstrate this to anyone who would care to see it.
In cases when the component does not fail or the scaffold is not toppled, the erector/dismantler is still not protected when using a fall arrest system. The scaffolder will most certainly swing into the scaffold with all the energy generated by the fall. Such an occurrence would be, of course, much better than falling all the way to the ground. However, we should bear in mind that the lanyard itself will cause most of the falls. Even the proponents of attaching fall arrest systems to the scaffolds admit to four or five falls per year; whereas, we who do not use the fall arrest system have not had an injury to a leading edge scaffold erector due to a fall in the past eight years.
Roy, we think that we have demonstrated that attaching fall arrest equipment to scaffolds is not a suitable fall protection policy. When we met with OSHA on January 27, 1995 we thought that OSHA and the representative of the scaffold industry had agreed that scaffolding in the state of being erected or dismantled was not a suitable anchorage for fall arrest systems. Mr. Miles letter seems to indicate that we do not have such an agreement.
Please let me know if there is anything I can do to further clarify any of the points mentioned above or in any way help us arrive at a mutually agreeable fall protection policy for scaffold erectors.
Very truly yours,
Standard Interpretations - Table of Contents|