Loads for window cleaning safety rope guides

[wikidcool]

Are there any fall protection engineers hanging out in here? I've been tasked with designing a "rope guide" for the safety line of a Controlled Descent Apparatus (CDA) for window cleaning/Exterior Building Maintenance (EBM). This is an isolated task for the fabricator of the guide - I am not designing the overall arrest system. The guide is a bent round bar welded to a flat mounting plate and attached to the top of the parapet, in order to re-position the safety/descent line to the correct location from an offset roof anchor.

The rope doesn't "anchor" to the rope guide, instead it passes through it and attaches to the roof anchor. Per the EBM designer who is responsible for the overall maintenance and arrest system, the hanging load on the line is 350 pounds, with a 900-pound impact load at fall arrest. They've given these loads as unfactored service level loads.

For the most part, the roof anchor and the safety line itself are required to resist 5,000 pounds. Is that true for things like parapets, building projections, guardrails, rope guides, etc that the line has to go over/around/through, but not actually anchor to?

 

[dik]

Your loads are likely light... In most jurisdictions and depending on the authority, loads are from 2000# to 5000#, with the latter being more prevalent. It is common to find carabiners rated for 22 kN.

Dik

 

[dhengr]

Wikidcool:
Dig out your state’s adoptions of the OSHA stds. and start reading and trying to make sense of the various req’mts., OHSA will basically control this design. Then, when all else is still unclear, and that’s pretty much true for all of us non-OSHA’ers., get to know the people at your local OSHA office, as they will sorta have the last word if there is ever a question or problem. In the last few years, they have been told to be more helpful, cooperative, educational, rather than just confrontational and fine levying in their efforts, by the Fed. OSHA. Talk with several different people, some are more willing and helpful than others, get to know them by name, and their phone numbers if you do much of this kind of work. They are generally willing to help an engineer with an intelligent and meaningful question or situation, they are less willing with scoff-laws. They would sooner you ask for meaningful help and clarification, than just ignore their req’mts. altogether.

You might be better off if your rope guide was a larger radiused bent pl., or a piece of pipe, or a sheave of some sort, with a keeper loop. I would be worried about the same rope, chaffing on the same pin, at the same spot on the rope, every time the system is used. The biggest question is going to be its attachment to the parapet and the strength of the parapet w.r.t. the anticipated loads. The parapet may have to be strengthened at that location. Maybe it would be better to run a permanent wire rope from the fixed structure to the parapet guide point, and then provide the rope tie-off at that point. I believe there is some verbiage which allows a load less than 5k for a well thought out and properly engineered design, done and stamped by a registered engineer, and properly attached to adequate structure for the purpose intended. Something like…, (load factor, 4 or more likely 5)(max. actual load, plus impact, etc.) = design load. The 5k all over the place, is kind of a catch-all number to prevent some dummy from saying this loop will carry (5)(actual load) and then fixing the loop’s base plate to some exterior sheet metal with a few self-tapping screws. The 5k is intended to get their attention, and do a proper design, so as to keep their … out of the wringer.