I know this is more climbing per se, but, folks here are prone to rappel single line maybe more so than climbers, so, applicable to canyoneering too.
http://www.supertopo.com/climbers-fo...e-the-Awahanee
The discussions are pretty interesting, ranging from the type of knots folks use to tie ropes together, to the use of pull cords, and, different rappel backups and devices.
Additional discussion here:
http://www.supertopo.com/climbers-fo...he-music-dufus
Anyhoo, FYI.
-Brian in SLC
Damn. So simple to avoid. Hard to read the accident report written by the climbing partner. That would be devastating.
Attachment 33749
Thanks for posting; makes me realize it's time for some spring refresher-training.
Here is the partner's write up so you don't have to wade through 20 pages to find it....
May 10, 2010 - 01:47pm PT
Dear friends and members of the climbing community,
Thanks to everyone for your thoughts, for your support, and for sharing your compassion for the tragic accident that unfolded.
Brian Ellis is one of my closest friends, and my main climbing partner for five years. We were descending from Sunset Ledge after completing the Serenity-Sons link up when the accident happened.
It has been incredibly difficult trying to process what happened, but I feel that it is important to learn from this tragedy, and to ensure that it never happens again.
Here is my analysis on the cause of the accident:
------------------------
The system:
The rappel system we used is also known as the "Reepschnur" method, where the 6 mil tag line is used as a pull cord. The lead line was a 10.2 mil. At each rap station, the two ropes were joined together with an overhand knot ("EDK"). This was backed up by an additional overhand knot, nested and dressed cleanly right next to the primary knot, with long tails (always at least 12").
The knot was tied so that the load was on the 10.2 mm lead line (i.e, the knot was on the side of the pull cord). A backup knot - figure 8 on a bight - is just below the two overhands on the 6mm, and clipped with a locking carabiner to the lead line. This photo illustrates it perfectly.
http://www.supertopo.com/photos/3/55/157018_6169_L.jpg
via Petzl -- edit: this photo doesn't show the two strands of rope tied together with overhand knots and long tails.
Credit: slobmonster
Brian insisted on using his Cinch to rappel on. It was his favorite device. As others have noted, using the Cinch (or Gri-gri), you HAVE to do a single-rope rappel. He rappelled first with his Cinch, and after he clipped in to the next anchor, I remove the backup knot and carabiner (so that there's no carabiner whizzing in space towards us, and so that it doesn't get snagged while pulling). I rappel next with an ATC. This is basically our system. I have a few more words below regarding this system.
What caused the system to fail?
The primary cause of failure was that the knot passed through the rappel rings as Brian was mid-rappel on the single 10.2 lead line. This is something that is unthinkable to a lot of us. Anyone who has ever tied two ropes together to rappel knows this.
Still, the unthinkable happened this time, and it was critical that the backup knot with a locking carabiner was present to jam up against the rappel rings. Unfortunately, this is where the BIGGEST MISTAKE was made. When Brian set up this system and tied the knots (I was coiling the ropes in the meantime preparing for tossing), he forgot to tie the backup knot. When I checked the system for him, I too, committed the same mistake and only observed the main knot. He checked it a THIRD time, and made the same oversight.
The only explanation I have for this oversight is distraction and complacency. Brian MAY not have been 100% focused on the task (there were several things going on... party coming behind us and he was excited to take photos of the leader below... a few moments earlier on the last pitch, we were rudely and inconsiderately passed up by a speeding simul-climbing party; this bothered both of us considerably). I am equally guilty of the same distraction and complacency for not having noticed the absence of the backup.
http://www.supertopo.com/images/SqBullet.gif The accident was NOT equipment failure (the rope, Cinch, tag line, all performed the way they were supposed to).
http://www.supertopo.com/images/SqBullet.gif The accident was NOT knot failure (the knot was tied properly, with long tails).
http://www.supertopo.com/images/SqBullet.gif The accident was NOT anchor failure (the bolts, webbing, and rings - albeit a little larger than chains - were not faulty).
During every single rappel that Brian and I have done together with this system, we have tied the backup knot. The principle overhand knot had NEVER passed through the rings before. However, the one time it was forgotten, sadly, was when it was most critical.
You don't lose often when climbing, but when you do lose... you lose big. I'm just absolutely devastated by this harsh lesson.
Other thoughts:
Brian introduced this system to me several years ago after learning about it on the internet. We were both partly inspired by this video. When doing the research on this system, there are several issues that I didn't discover.
The first is that, although Brian was using the system properly for a single-rope rappel (yes, I know the backup knot was not tied when the accident happened), when I hopped on rappel with an ATC, I was using the system improperly. Although I'm rappelling on both the 10.2 line, and the 6mm cord, only the 10.2 line is properly rated to withstand the force temperatures that a friction device can create. Pull cords of that diameter have a much lower melting point.
The second is that there are variations in rappel ring sizes. The smallest ones (like rappel chains) are just about impossible to pass the knot through. However, the larger models, like the ones atop Sunset Ledge (or even things like Cold Shuts or Mussy Hooks), warrant that the knot is ABSOLUTELY never going to pass through. Additionally, the 10.2 line tied with an EDK to a 6mm cord makes a smaller knot than two 10mm lines tied together.
All of these factors make the rappel system more complicated, which means that more steps need to be taken to ensure that it is bomb-proof. If a system requires Steps 1,2,3, and 4, it is critical that ALL the steps are performed even though Steps 3 and 4 may only be back-ups. Simpler setups that require fewer steps, as a result, should be the ones that people should be using. There is less room for error in simpler setups.
Brian and I tested the knot atop Sunset Ledge and made sure that it wouldn't pass through the rings. When he started rappelling on the single line, he descended about 15 ft, locked off his Cinch and started taking photos of the leader on the P3 crux of Serenity for about 10 minutes. While he was taking photos, he moved a bit to the left, and then to the right to check out the climber. Then, after having spent about 10 minutes taking photos, he went back to descending the single line. This is when I heard a pop and the sound of the rope whizzing. I tried to grab it with my bare hands and held on tightly as long as I could. My instinct even tried to wrap it around my waist for an emergency brake, but the rope just burned through my hand.
The shock load that Jesse talks about is the result of the tag-line getting tangled up and getting jammed up on the rings. The heat generated on the rings then burned the 6mm line, and a clump of the tag line fell on the ledge where I was.
It is so ironic that the day we were climbing was the first time that I convinced Brian to bring along an ATC to do the rappels on. I never do single-rope rappels, and am scared of rappels in general, so I have tried for a long while to get Brian to rappel with a traditional friction-device. The ATC was in his backpack.
I have asked myself "what would I do differently?" so many times. It hurts so bad to think that this was preventable. I hope that we can take this lesson to heart and learn from it. When reading whats out there on the forums (RC, Mountainproject, Summitpost, etc.) the subtle factors that led to this system failure (knot passing through, variations in rap ring sizes, knot size for 10mm/6mm combo) are not discussed very thoroughly.
I have many thoughts about the accident, and am available if anyone wants to learn more. Please email me directly: japhyd[at]gmail[dot]com.
I want to extend a deep and sincere thanks to everyone involved in the rescue. My condolences go out to Brian's family, his girlfriend, his pet bunnies, and all of his friends.
Brian made the world a better place with his presence, and I miss him dearly.
http://www.supertopo.com/images/SqBullet.gif Japhy Dhungana