The Force that Works or: How I Learned to Stop Worrying and Love the EDK

This past weekend, I spent about 14 hours strapped to an 11,000 ft. granite peak in Colorado’s Front Range. Multi-pitch climbing, or large-scale climbing ventures that require several climbs linked together, necessitate lots of ropes, heavy gear, and knots. Most of the time when I’m climbing, I’m focused on choosing and executing the correct not, and am not typically concerned with how the know works, but, after hours anchored into the same rock face, the mind begins to wander. 

 

After the death of a Washington climber in late September due to a rappel knot failure, I decided to do some research into the knots that I trusted with my life this past weekend. After an 11 pitch climb, our descent required about 7 rappels and would have required more had my partners and I not tied our ropes together. When you have to depend wholeheartedly on two ropes and one knot, it helps to know the force at work behind them. 

Rock and Ice Magazine attributed the Washington climber’s death to the failure of a flat figure 8 (see picture), a knot that should NOT be used to join rappel ropes. The extra bend in the flat figure 8 can actually cause the knot to walk and collapse in on itself, and the smaller the diameter of rope, the more likely it is to collapse in on itself. The flat figure 8 is frequently referred to as a variation of the European Death Knot, a relationship that I contest due to the vast difference between the ability of each knot to tolerate certain loads. The direction of force on the flat figure 8 actually pulls the two lengths of ropes in a different direction, which can cause the knot to fail.  Recent tests by Black Diamond reveal that the flat figure 8 will collapse under significantly lighter loads than its paradoxically named counterpart - the European Death Knot.



 

The European Death Knot, or flat overhand bend, is commonly referred to as the EDK.  Similar to the flat figure 8, it is also an asymmetrical knot used to join rappel ropes. The asymmetry of the knot gives it a flat underside that makes the rope easier to pull down rocky slopes that are prone to snagging. Where the flat figure 8 is prone to failing at loads as small as 750 lbs, the EDK when properly tied and dressed, will hold 1,400 lbs. The direction of force on the EDK pulls the two lengths of rope in the same direction, again making it a safer knot for joining two rappel ropes.  When properly pre-tensioned and tied, failure is typically attributed to a physical failure of the rope rather than the knot.

 

 


 

Photo: Rock and Ice Magazine

Photo: Rock and Ice Magazine

Though like many asymmetric bends, it has the ability to walk to the end of the rope, this is easily prevented by tying a simple backup stopper knot such as an additional overhand that will add to the symmetry and decrease the chances of your knot walking off the end of your rope and failing. Flat knots, such as the EDK and the flat figure 8, are extremely sensitive to mis-tying, which gives the EDK another distinct advantage in that it is very simple to tie. That being said, there is no margin for error thousands of feet above the ground, so practice, diligence and leaving a tail is key for correctly tying any knot.

 

Salt Lake County Sheriff's Office Search and Rescue has performed weight tests on different versions of nearly every climbing knot - wet, cold, non-redundant and poorly tied to test their strengths and weaknesses. Four accidents and three fatalities have been attributed to EDK failure: Zion in 2002, Grand Teton National Park in 1997, Big Cottonwood Canyon in 1995 and Seneca Rock in 1994. Moyer, the source for my data, contests that these mishaps were most likely flat figure 8 failures mislabeled as the EDK. Moyer promotes the use of the EDK, and contest that the few deaths that have previously been attributed to the EDK were, in fact, the flat figure 8. Their test results of the EDK can be found here.

Delving into spreadsheets of weight tests of various climbing knots probably isn’t most people's idea of a good time, but the forces behind these commonly used (and confused) knots are fascinating and comforting. The only remaining issue? Lets rename the EDK.