Originally posted by RescueMan
Yes, SWL, WLL, MWL, rated load, rated capacity are synonymous.
But I don't think there is any universal definition of any of those terms.
Mahk, if you have any official definitions of SWL for the arborist industy I'd like to see references.
- Robert
Robert;
My original post disappeared into cyber space. What I posted above is a hastily typed and somewhat abbreviated version of what I originally wrote. Some of the missing statements that I should have included are
--these definitions are for the arborist industry (and, more narrowly, the arborist industry in the US), which is really just beginning to understand and define these concepts
--the measured dynamometer forces that I mentioned occur at various places in the system; for :
"...the force generated by a piece that is allowed to run can be approximately 3 to 7 times the weight of the piece."
the 3x's occurs at the friction device and in the lowering line, while the 7x's occurs at the block and sling. For:
"A piece that is snubbed off can generate a force that is about 10 to almost 20 times the weight of the piece."
the '10 to almost 20X's' occurs at the block and sling. The forces at the friction device and in the rope itself are about half of what occurs at the block and sling.
SWL and WLL are the terms that most often appear in various training media. I hadn't considered MWL, rated load, and rated capacity.
I am not sure what you mean by 'official'. To my knowledge the various ANSI standards are the only publications that have any obligatory bearing on the work that arborists perform. But,there are other texts that heavily influence what we do and how we define things.
'Arborist Equipment' (1995), by Don Blair, and its cousin the two video set and workbook 'Rigging for Removal'(1998), published by the then NAA, now TCIA, led the arborist industry into technical tree removal and are still important references.
Another, more recent, work, the 8 video set and workbook 'The Art and Science of Practical Rigging' was published in 2001 by the ISA. The core text was written by Peter Donzelli, a mechanical engineer and assistant professor of biomedical engineering. He was killed in 2000, before the videotaping of the training series, and the text was edited and amended by Sharon Lilly of the ISA. ArborMaster Training collaborated with the ISA on the entire project. ArborMaster and ISA have been the principle (but not the only) trainers and educators in the industry in recent years.
Unfortunately, none of the above works gives as explicit a definition as I have. In AE and R for R that definition of SWL can be gleaned by cross referencing definitions of other terms, but it is not directly stated. For example, in AE p. 101, in a reprinted monograph from the Cordage Institute, it is stated "Total potential load (TPL) is the weight to be lifted, towed, restrained, suspended or secured. TPL applies not just in a static condition, but in a dynamic condition as well....dynamic forces with a total potential load that may well exceed, sometimes substantially, the static weight of the load..." [Note that 'weight' is used to mean both pounds and pounds force. More confusion.] And p. 102 "The TPL applied to a cord or rope should never exceed the WLL."
This has been long, so I will try to make the rest less detailed.
In ASPR the definition of WLL is "...tensile strength divided by design factor; maximum load that should not be exceeded in a rope or rope assembly when performing its normal working function."
This really doesn't help. ISA's next publication on climbing and rigging (a DVD to be released (hopefully) in August) will give a more specific definition. I have assisted in some of the ISA's publications so it may seem that I am trying to support my own viewpoint, but I did not create the definition that the ISA uses for WLL. I have only encouraged the ISA to make the definition more precise.
Again, it helps to plug some numbers into both definitions and then compare them to the dynamometer tests.
Mahk
