Well That’s Knot Right

Look Up! High-rise window cleaning is pretty amazing. To a passerby, it looks effortless on the part of the window cleaner. But in reality, high-rise window cleaning takes a very stringent set of skills to remain safe and efficient. We have recently been confronted with many window cleaners unsure about whether knots are acceptable to use during high-rise practices. In this post, we will address how this common misconception arose, what the truth behind this idea is, and the pros and cons to the alternatives window cleaners have been using in place of a knots.

  • Close up of High Rise Window Cleaner
  • Close up of High Rise Window Cleaner
To begin, we will address the idea that knots are not allowed in high-rise window cleaning. This thought is very common in the window cleaning industry, and the truth of the matter is, it’s not completely wrong. Knots can actually decrease the strength of your rope up to about 50%. This can lead people to believe knots are not allowed in practice because they make your rope too weak and are not safe. A figure 8 on a bight, for example, decreases your strength 20%, a bowline 27%-33%, a butterfly 25%, and overhand 35%-40% (Rescue Knots for Roco Students). These percentages are approximations and can vary a bit from test to test, but the point is that all of these are all common practice knots and show a significant percentage of strength decrease.

…knots are fine, so long as your system maintains strength of 5,000lbs
So 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?

So here is the other half of the story. We know the system needs to maintain the strength of 5,000lbs and that knots weaken the strength of the rope, but what hasn’t been brought up is the rope itself. You see, if we take a look at the most common knot, the Figure 8 on a bight and consider it’s 20% strength loss, we need a rope of at least 6,250 lbs in order to stay over 5,000 lbs. Taking the high estimate of 33% on the bowline, we’d need a rope of 7,463 lbs. This is well over 5,000lbs strength necessary. So if this is the requirement, what is the strength for most rope? Well, 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!

 

 

 

Amy LavinWell That’s Knot Right

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