Safety Line Test

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  • Evan
    Senior Member
    • May 2003
    • 41977

    Safety Line Test

    I decided to do a field test of my safety line setup. It's the only way to quantify the actual performance and to provide some real data for all the interested parties. Note that I haven't read the Safety Project thread since my last post and don't see a reason to do so.

    Most of the test results can be seen from the pictures. I used a spare length of line identical to the line on the roof, it was a backup line. It is now useless for that purpose but will still serve for tree falling.

    I strung the line between two trees in my driveway at the same 45 foot distance and at the same approximate tension, about 50 lbs. I used the lifting pole on my Land Rover with a pulley mounted on the end and hung a total of 180 lbs of iron from it using the same type of line used to clip on the safety line. I weigh 172.5 lbs fully clothed as of this afternoon so this fairly approximates the situation on the roof.

    I measured the distance from the center of the line to a nearby tree as a static no load reference, about 14 inches. I then raised the load to perform a static test. The line stretched so that the distance to the tree became about 100 inches. Subtract the original 14 inches and that is slightly over 7 feet. When I am rigged on the line on the roof I rig it so that when at the very edge of the roof the line is deflected about 1 foot. This is a negligible amount and one can deflect the line one foot by pulling with a finger. It does however subtract from the total static load distance that would exist if I fell off the roof.

    In the worst case, at the center of the line span, I would be hanging off the edge of the roof by 6 to 7 feet. I would expect to wait no more than a minute or less for my wife to show up with a ladder.

    Judging by the way the line responded to the dynamic load test it will stretch permanently after dynamic load by enough to increase the deflection by about one foot. It seems that I was somewhat conservative in making the posts able to fold in order to absorb shock load. I don't think it is necessary. It does still serve the purpose of preventing the brackets from tearing out of the ends of the roof although I don't think that is likely either.

    I haven't done the math to calculate the tension on the line under static load but the deflection ratio is about six to one so 180*6=1080lbs is close. With 1800 lb test line this gives an 800 lb safety margin. In actual use no free fall is possible before the line takes load so shock loading with multiple gees cannot occur.

    Regardless, I ran a simple dynamic test that undoubtedly placed at least 2 times the load on the line, twice. It performed just fine and shows no sign of failing other than the expected permanent stretch.

    My judgment is that the safety line I have designed and built is entirely adequate for the intended purpose which is to perform maintenance on the gutters and first row of shingles on either side of the roof. It isn't intended for use at the end of the roof and different rigging will be used for that.

    Pictures follow with a video of the dynamic test. I expect my server to be clobbered by this post so if not all the pics show up please try again later.

    Comments are welcome.









    Link to the dynamic test video. It is one megabyte so shouldn't be too long to download on dialup.

    Free software for calculating bolt circles and similar: Click Here
  • mochinist
    Senior Member
    • Oct 2003
    • 2425

    #2
    You guys crack me up

    Comment

    • A.K. Boomer
      Senior Member
      • May 2006
      • 20865

      #3
      OHHH dear god!

      Im at least glad to see you used your robust tree's to do the anchoring instead of what peices of crap you have mounted on your roof,,,,



      I also noticed how you edited the picture to avoid any detail of the way you have your masts anchored to the roof, smooth touch, it is however strong evidence for the amount of vector forces that would still ensue , again, as always, a master of manipulation and damage control -------- left out one important thing,,, Not on my watch bucko............................................ not for your freakin life and not impressed.

      Comment

      • J Tiers
        Senior Member
        • Jan 2004
        • 44281

        #4
        With the new information, (new unless we didn't "get it" before)...... you have an "engineered system" as far as the ropes are concerned. Before, you had a "guessing game".

        It appears you now have data on the ropes, which was not available before.

        And, what I think is the KEY element, what you have is NOT a safety system for falls, but a "fall prevention system".

        As you NOW describe it (leaving out the end supports, which I still don't care for much), you are apparently already experiencing a pull-back before you get TO the edge. Possibly 50 lb worth, if your estimates are correct. That radically changes the system, as it eliminates complete free-fall distance, and also lowers the likelihood of a fall of any sort. Impact loads are very much reduced.

        It raises the chance you will get your eyebrows scraped off on the way down if you DO fall, since it is forcing you back against the edge of the roof. But it does potentially lower your total fall distance.

        naturally, in the one picture, there is a lot less than 14 feet over that railing.... maybe 8 feet, so I think you could still be in trouble there. Looks like the top of the railing is about 6 foot up.

        With 1 foot deflection at the roof edge, and 6 more down, plus perhaps 4 feet from the harness attachment to your feet, it looks like you could still get into the railing to the extent of 2 feet or so, which could be painful.

        If the end supports hold, but bend, I think you would be in more trouble, as the 2 feet (maximum) that could be added (length of post ) would change the angle and bring the total deflection up to about 12 feet, not 7. The added 5 feet would allow your feet at least to strike the ground, and could be a real problem over the railing and porch. probably the bending would not be so much, if the posts are pretty strong, and IF they hold (I am dubious).

        As the porch and railing look to be roughly in the center of the house, it is right where you would fall the farthest, with maximum deflection per your test.

        But, at least now you have DATA, and can adjust the system to compensate for deficiencies that can be identified.

        BTW, this ignores stretch in the lanyard..... if it is also the 7% that the other rope shows, and if it is 15 feet long, there is another foot of stretch. That allows you to get in trouble with the railing more easily, even without any bending of supports. I think you could hit them above your knees, hopefully not straddling the railing
        Last edited by J Tiers; 08-08-2007, 12:17 AM.
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        Comment

        • Rookie machinist
          Senior Member
          • Jul 2007
          • 302

          #5
          Here we go again

          Can I see that same test using the actual system you have on your roof and not those trees. You can't compare two systems that have only 1 common factor, the rope. You need to test the whole system not just a single component.

          Comment

          • Fasttrack
            Senior Member
            • Jul 2005
            • 6300

            #6
            Evan you crack me up - and i say that with the greatest amount of respect.


            Personally i agree with JT, and, now that i've finally seen the setup, i'd say that is a perfectly suitable, one-time use fall prevention set-up. I'm scared of heights, but even i'd be willing to work up there. I wish you had answered my question earlier though





            Anyhow, i'll give you a little virtual bow - i think i would have done the same thing you did if i was in your place. I mean testing it and making a video... when i think i'm right i'll argue until i can prove that i'm right.

            <edit> i don't think the supports on the roof or the line itself is suited for a "fall protection" but rather a fall prevention. It gives you a little something to slow you down and keep you from going over the edge. After working on roofs and grain bins (which are 60-80' in the air, have metal roofs slick with corn dust) with no safey harness and never running into a problem, i think that the system is a good one to help recover if you stumble, but not save you if you take a jump.
            Last edited by Fasttrack; 08-08-2007, 12:22 AM.

            Comment

            • Evan
              Senior Member
              • May 2003
              • 41977

              #7
              I also noticed how you edited the picture to avoid any detail of the way you have your masts anchored to the roof, smooth touch,
              I left that out on purpose. I still don't want anyone to try and duplicate the system. Now, back to reading this thread.
              Free software for calculating bolt circles and similar: Click Here

              Comment


              • #8
                NASA will be knockin' on your door for advice by midnight.

                Comment

                • Evan
                  Senior Member
                  • May 2003
                  • 41977

                  #9
                  JT,

                  As you NOW describe it (leaving out the end supports, which I still don't care for much), you are apparently already experiencing a pull-back before you get TO the edge. Possibly 50 lb worth, if your estimates are correct. That radically changes the system, as it eliminates complete free-fall distance, and also lowers the likelihood of a fall of any sort. Impact loads are very much reduced.
                  That is how it was described before. Go back and read some of the existing posts. I said that there was no free fall involved. As for the 50 lbs, that is the preload tension on the line. It takes much less than that to deflect it one foot in the center. I can do it with a little finger. But, it still comes off the dangle distance. The stretch is very non-linear and the line is not noticably holding me back from the edge.

                  I am not concerned at all about the supports. They are lagged with six 3/8" lag bolts 3" into solid fir. The top two act as a fulcrum point for the bottom four. The bottom rail that has the ends lagged down will bend out if the strain is too high so that the lag bolts go into shear instead of tension. Before they can shear or pull out the posts will fold over and then there is no way to pull out the support. It's being pulled in instead. This is intended, at most, to be a single use system.

                  As for the porch, I can reach the gutter with my extension ladder from the porch. I added a wide bottom foot to it to make it more stable.

                  Can I see that same test using the actual system you have on your roof and not those trees. You can't compare two systems that have only 1 common factor, the rope. You need to test the whole system not just a single component.
                  No. It would destroy my gutters.
                  Free software for calculating bolt circles and similar: Click Here

                  Comment

                  • Tinkerer
                    Senior Member
                    • Oct 2004
                    • 1328

                    #10
                    Evan... If your happy with it and feel comfortable with it so be it. It's for you and not the general public.
                    Wow... where did the time go. I could of swore I was only out there for an hour.

                    Comment

                    • kendall
                      Senior Member
                      • Sep 2006
                      • 2501

                      #11
                      With the exception of the poles, it's very similar to the OSHA approved system we used for pretty much everything.

                      We did this buildings roof:

                      For a rough idea of scale, the towers where they extebd above the roof are large enough to be an apartment by themselves. it doesn't show in those pics, but there is an architectural steel 'dummy' roof surrounding the building that protrudes 14ft.

                      As an aside, to finish trimming out the 'towers' we had to remove our safety anchors and finish without harness.

                      on ours, we were supposed to keep things arranged so we would not fall more than six feet before the rope caught you, then the three foot lanyard would stretch by another three foot in a one shot deal.

                      All of our equipment was marked at 5000lbs working load, I fell 10ft with the harness on, and you would not believe the shock load when the rope catches you, it feel like your legs stretch a foot just from the weight of your boots.

                      Ken.

                      Comment

                      • Evan
                        Senior Member
                        • May 2003
                        • 41977

                        #12
                        When I was about 14 I fell 40 feet from a line, no harness. Broke both bones in my right arm. Not fun. We used to scramble all over the boulders on Mt. Diablo in Central California when I was a kid, great place to tune up some climbing skills. I used to live in sight of it near Alamo.


                        The 5000 lb working load is intended to accomodate any possible combination of heavy people carrying heavy equipment with possible poor maintenance of the system as well. For the circumstances in which that sort of equipment may be used it is necessary and makes good sense. My circumstances are far more specific and controlled. For that reason I can easily work with far less safety margin and still be safe.

                        Jerry,

                        With the new information, (new unless we didn't "get it" before)...... you have an "engineered system" as far as the ropes are concerned. Before, you had a "guessing game".
                        Before the test I wasn't guessing, I was working from experience as well as mathematical analysis. The test confirms that my experience is valid. I would love to do a failure test on the supports just to show what will happen but that would be a lot harder to arrange. I would have to build a test structure that approximated the end of the roof as well as a test line mount and then test it to destruction. I don't have any instrumentation that can handle those loads so I would have to build and calibrate that as well. Again, I am relying on experience building structures to judge what is sufficient as well as some strength calculations.
                        Free software for calculating bolt circles and similar: Click Here

                        Comment

                        • Your Old Dog
                          Senior Member
                          • Dec 2004
                          • 7269

                          #13
                          Originally posted by Tinkerer
                          Evan... If your happy with it and feel comfortable with it so be it. It's for you and not the general public.
                          ditto.........................
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                          • johnhurd
                            Senior Member
                            • Nov 2004
                            • 156

                            #14
                            I would expect to wait no more than a minute or less for my wife to show up with a ladder.
                            If she happens to ask just before mounting the roof how "she looks in this dress"........ please reply "Devine Sweetheart just devine".

                            Comment

                            • HL Holmberg
                              Member
                              • Mar 2007
                              • 48

                              #15
                              ..................................
                              Last edited by HL Holmberg; 08-10-2007, 04:47 PM.

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