backing up a rappel with prussic

way back in the day when I learned how to rappel, I was taught to back up my rappel by tying a prussic(or variation) above the belay device that you then advanced with your upper hand. the prussic being connected to your belay loop. now I see the standard is to tie below the belay device and advance with your lower hand. is there an advantage to this? both systems stop you if you let go of the rope but by tying in above the belay device the prussic will stop you if you rappel off the ends of your rope(as long as you let go of the knot), tying in below your device will not do this. thoughts?

Anecdotally, prussiks above the ATC fail to catch the rope if you rappel off the ends. Theoretically, sure, it might catch, but they usually don't, especially because most people are holding the prussik "open" so they can actually descend.

Keeping the prussik below the ATC reduces the gripping force necessary to arrest your descent and further, you can easily unweight the prussik and continue descending. If you rest for any amount of time on a prussik ABOVE the ATC, it tends to tighten up like crazy, making loosening it very difficult.

In the 1970s, we were taught to place the prusik backup on the rope above the rappel device, which at the time seemed simple and logical. But, after an incident in which a prusik backup seized and the suspended climber was unable to release it (and suffocated, hanging in his swami), this system was the subject of much debate. What use was a backup, some argued, if it could kill you?

Today, none of us is apt to die this way because we wear leg loops. Still, an ascender or prusik on the rope above your rappel device can leave you in a pickle. For instance, make your connecting sling too long—even a single inch can be too much— then, fast as a flash, your ascender or prusik can shoot out of reach, cinch up, and leave you stuck, dangling on the rope. Or, even if you dial the sling length perfectly, the prusik or ascender can lock up and leave you lacking a second ascender or prusik—unable to unweight and release it. Stranded again!

source: Rock and Ice

For me using a prussik as a backup in a rappel setup is fine, but anyone using it should be prepared to transition back to rappel in the case that they actually need to use the backup, which is the hard part I think.

As mentioned, if it is set above the rappel device than once it is loaded it takes a few steps and a little bit of knowledge to unload and untie and continue rappeling.

If it is set on the brake strand, than it takes advanced skills to rig otherwise it can get caught in your rappel device. I believe this was a contributing factor to a rappelling death in The Subway in Zion NP last year.

I'd prefer a fireman's belay or a top belay.

Not to hijack the thread, but what about extending your atc from your harness? I had never done it before last weekend (and I've been climbing nearly 10 year's) and it was sweet. I might make it a habit. Do any of you do it? Pro's and cons?

+1 to what John said.

In addition, when he talked about the prussic binding in the ATC, it's important to understand that if your brake-hand prussic backs against the bottom of your ATC, it will no longer function as an auto-block. That's why it's important to extend your rappel device with a sling or PAS, just to keep it out of reach of the prussic on your leg loop.

Doug S wrote:That's why it's important to extend your rappel device with a sling or PAS, just to keep it out of reach of the prussic on your leg loop.

Or make sure your prusik cord is the correct length.

Use an "auto block" knot off your LEG loop on the break side (rigged below the tap device) and extend your device as needed. Then ANYTIME you let that go of the break, the block should hold. Tie block knots to prevent raping off the end of the rope. If wind+knots getting your rope stuck is a concern, flake the rope in a sling and take it with you.
-Mackley
Edit: ^Steve said it better.

Robbie Mackley wrote:Use an "auto block" knot off your LEG loop on the break side (rigged below the tap device) and extend your device as needed. Then ANYTIME you let that go of the break, the block should hold. Tie block knots to prevent raping off the end of the rope. If wind+knots getting your rope stuck is a concern, flake the rope in a sling and take it with you. -Mackley Edit: ^Steve said it better.

Yup autoblock is the way to go. i've adopted this earlier this year and it is awesome. i used to rappel with a prusik above the belay device and never liked it.

@Ryan N, yes, your method works and i've seen it in a few guide books, but the autoblock is better in my opinion, it's super easy.

i made a prusik and used it for my autoblock but just discovered that sterling makes one so i don't have the bulk of the double fishermans knot. just received it today, can't wait to try it;

Sterling Autoblock

^good to know. Thanks for the link.

Steve,
Just to clarify, are you suggesting that we extend the device, and run the block off of the belay/rap loop. Or do you run the block on a leg loop as well?
-Mackley

Pro's and Cons to using a Klemheist instead of the prussik?

I don't think its a matter of pros/cons, but more of materials. Cordage, use the auto block. Webbing use the klemheist. I think this is true, but I'm sure someone will be here to correct me sooner or later.
-Mackley.

the kleimheist will work with all normal materials climbers carry

and its less "catchy" which in the case of below the device is an advantage as the rap will be smoother ...

i show newer rappers the kleimheist as its exceptionally easy to remember and tie ... and they can use it with slings or cord ...

;)

I also use 5mil cord. FWIW.

Steve Levin wrote:Check out the Sterling Hollow Block also.

yup, i ordered two of those as well to take place of the prusiks i made, again the bulk thing. those came with my autoblock.

Hollow Block I ordered the 13.5" one because that's my my previous prusiks were.

i took a rescue class a couple of weekends ago out at jtree and discovered i prefer using the kleimheist, which works fine with cordage BTW, over the prusik. just easier and less fussy. the kleimheist is my go to now. works with cordage or webbing.

Just a question, but how does rigging the auto block closer to the rap device (belay loop vs leg loop) make things safer? I was taught to keep them apart to avoid either disengaging.
Not an argument, just a question.
-Mackley

Robbie Mackley wrote:Just a question, but how does rigging the auto block closer to the rap device (belay loop vs leg loop) make things safer? I was taught to keep them apart to avoid either disengaging. Not an argument, just a question. -Mackley

This setup is for situations in which the rap device has been extended.

^I understand extending the device. But how is this better? My brake hand is usually near my leg, outside my hip. If I had my block on my rap loop, that would put my brake between my legs. How is this better? Please excuse my curiosity, I'm just making sure I didn't miss something. Thanks in advance.
-Mackley

As Steve Levin put it, if you have an accident and lose control of your body, your leg could possibly lift up and bring the auto-block to the rappel device and make it fail, as in the scenario he described. I'd like to try this, but it sounds like he's right. Putting the auto-block between the belay loop and the ATC would remove one potential human error from the system. In other words, the block can't fail due to your body position.

@ Steve: I'm curious how well this set-up works in practice and what size sling to use to extend the ATC... a single? Do you attach the auto-block at the lower tie-in loop or the belay loop? How easy is it to weight/unweight?

OK it's like this: girth hitch a shoe lace to your leg loop , tie it with double fisherman first, then have a non locking biner on your leg loop too. Wrap the shoe lace 3 times around your rope below your rap device then clip it into the biner attached to the leg loop. Tadaa! When I rap on single strand or clean my own routes I use that.