…knots are fine, so long as your system maintains strength of 5,000lbsSo instead of thinking knots decrease strength of rope and therefore are not allowed, this idea can be looked at as only half the story. The I-14 states “the securing of a rope to an anchor with a knot is permitted providing the specific knot does not decrease the initial breaking strength of the rope below 5,000 pounds (2268 kg) considering the operators intended deceleration and the reduction of tensile strength over the course of daily use.” In layman’s terms, they are saying that knots are fine, so long as your system maintains strength of 5,000lbs. ANSI Z359 used to say that knots weren’t allowed in fall protection. That standard had in mind a construction type worker that would be connecting to an SRL and would have no need for knots. However, the new ANSI Z359.15 makes allowance for knots. Since rope has to maintain strength of 5,000lbs and knots weaken rope, it is understandable to make the conclusion that knots are knot okay, see what we did there? KMIII for example is 8,000lbs for 7/16″. That easily exceeds the strength required. The fact of the matter is that most kernmantle ropes exceeds the 5,000lbs strength requirement. And that is the full story.
But what are the alternatives to knots and how do they compare? One thing window cleaners have used to replace knots in the high-rise window cleaning industry is sewn eyes at the end of their ropes. They will only lose 0% – 15% of the strength, depending on the rope. In addition to being stronger than knots, they are compact, and can’t be tied wrong. Having a sewn eye makes connecting the rope to your anchor incredibly easy. The downside is that they add cost to the rope and usually increase the lead-time by a week or more. Termination plates are also popular. We couldn’t find any data about strength loss on these plates, but presumably it’s better than knots. Termination plates are great because they are strong and are removable but they suffer from being bulky, heavy, and expensive.
All in all, knots are completely allowed in the high-rise window cleaning industry. Though the strength of the rope must be maintained at least 5,000 lbs, most kermantle rope well exceeds that, even with knots tied in. Regular rope is also the most economical option. Sewn eyes and termination plates are good alternatives used for knots. They offer safety, strength, and presumably decrease the rope strength less than knots. These alternatives, though, tend to be more costly than simple rope. When it comes down to what’s best, it’s a personal choice. But, the fact is that knots are allowed in the high-rise world. For more information, check out some great resources about knots, how to tie them, and their statistics about strength decrease. As always, this blog is not a substitute for proper training!