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. The third consideration is that ability of the specific component to deal with impact loads. In cases like these, OSHA would be sanctioning a factor of safety that is significantly less than standard practice would allow.
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. The stresses developed are a function of the natural frequency of the component and the time duration of the load.Īs you may know, scaffolds can be soft structures particularly at the time they are being erected or dismantled. 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. 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.
In this case, the fall factor would be two. 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. I recommend that the following criteria should be considered before any definite conclusion is reached concerning the proper design of such systems.įirst, there is the probability that the experienced load will be greater than the anticipated load. 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. 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. 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). 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.Īs you know, I received a letter from John Miles who referred me to you or Dale Cavanaugh if I had any questions. If you require further assistance, please do not hesitate to contact either myself (ext. The opening will be announced in the Federal Register later this year. 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. 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. The alternative anchorage criteria referenced in. the scaffold) to be capable of supporting at least 5000 pounds per employee attached. 502(d)(15) which requires the anchorage (i.e. We agree that during the erection and dismantling process the typical scaffold is unable to comply with the criteria of. 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. 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.
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