Releasable rigging using a Petzl Stop

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Releasable rigging using a Petzl Stop

Postby OpenTrackRacer » Apr 25, 2013 4:30 pm

We're going to be working on a project soon that will have us descending 700' down a 900' vertical mine shaft (which has multiple additional levels at a range of depths). We have 1,000' of PMI 11mm Pit Rope to work with. I was thinking of setting up releasable rigging with an extra Petzl Stop and leaving the excess rope on the surface rather than at the bottom of the shaft. The idea is that if someone is injured while on rope, we could lower them down to the next level rather than trying to haul them directly out or do a on rope rescue.

My plan is to place a pulley over the shaft and then run the rope down to the Stop which will attached to a low anchor. Once the needed amount or rope is down the shaft we'll lock off the Stop and also secure the free end of the rope to another anchor. It'll stay like that unless we have an incident.

I figured it was worth posting this just to make sure no one sees any issues with this rigging.

Thanks!
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Re: Releasable rigging using a Petzl Stop

Postby Anonymous_Coward » Apr 25, 2013 6:46 pm

Sounds okay to me. Be aware that there are many other methods of releasable rigging that are worth learning as well. Munter mule, rappel rack, contingency eight, to name a few.

I would make sure you have a braking biner for the Stop, if it will have to operated at angles other than what is traditional. If you have any inkling that the friction will be on the low side of controllable, eliminate the pulley and run the rope through a steel biner or two instead. Probably a good idea to practice unlocking, lowering, and locking this setup under load in a controlled situation. Then you will find out any issues for yourself.
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Re: Releasable rigging using a Petzl Stop

Postby Scott McCrea » Apr 25, 2013 7:04 pm

Your set up sounds pretty good, except...

The pulley on a redirect is a concern. Not a problem, just something to consider and make sure it is safe. The way you describe the set up, the redirect anchor may see more of the load than the main anchor will. Make sure the redirect anchor is bomber.

Here's a nifty little web page that calculates the forces involved in redirects. Just drag the red arrow around and watch the numbers. http://www.lifeonaline.com/toys/deviation.php

This thread also discusses, at length, deviation forces.
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Re: Releasable rigging using a Petzl Stop

Postby Stridergdm » Apr 25, 2013 9:52 pm

Off the top of my head, that'll work. As Andy points out, there's several ways of doing this.

By the way, another advantage of this sort of setup is that you'll have slack at the top which can be useful. Keep in mind you'll only have a few hundred of "extra" feet so you won't be able to lower in all cases.

But by having slack, you give yourself more options for setting up a haul system at the top and then pulling up the rope once you've released the remaining slack and disengaged the stop.
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Re: Releasable rigging using a Petzl Stop

Postby snoboy » Apr 26, 2013 12:50 am

Pretty much what they all said above... sounds workable to me.

If you are sure that you will lower, I would probably use a biner at the redirect, if there's a chance you will haul then a pulley is wise. My choice for releasable rigging with one person involved would usually be a tied off Munter hitch, but I don't have 'extra' STOPs lying around. ;) If you expect to lower any significant distance, the STOP is probably better for the rope. Also gives you an autostop function which the Munter lacks.
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Re: Releasable rigging using a Petzl Stop

Postby NZcaver » Apr 26, 2013 6:11 am

You're planning for possible contingencies, and that's great. I wish more people would think like that. Kudos to you.
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Re: Releasable rigging using a Petzl Stop

Postby OpenTrackRacer » Apr 26, 2013 6:59 pm

Thanks for all the feedback. It's a very good point about swapping out the pulley for a carabiner. I was originally going to use a Petzl Fixe anchored by two slings. Since we'd likely only be using the rig to lower someone, I'll swap that with a steel carabiner. The redirect will be loaded somewhere around 150-175% compared to the main anchor point.

The shaft has multiple drift levels and 300' of spare rope will allow us to lower someone down to the next lower level, no matter where they are in the shaft.

I have a spare GriGri but I figured the Stop would be better since it's the device we use all the time. The way it'll be rigged, operating it will be the same as when using it to rappel. The positioning will be the only thing that's different (and that could be an important difference).
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Re: Releasable rigging using a Petzl Stop

Postby Stridergdm » Apr 26, 2013 10:07 pm

OpenTrackRacer wrote:Thanks for all the feedback. It's a very good point about swapping out the pulley for a carabiner. I was originally going to use a Petzl Fixe anchored by two slings. Since we'd likely only be using the rig to lower someone, I'll swap that with a steel carabiner. The redirect will be loaded somewhere around 150-175% compared to the main anchor point.

The shaft has multiple drift levels and 300' of spare rope will allow us to lower someone down to the next lower level, no matter where they are in the shaft.

I have a spare GriGri but I figured the Stop would be better since it's the device we use all the time. The way it'll be rigged, operating it will be the same as when using it to rappel. The positioning will be the only thing that's different (and that could be an important difference).


I do like the idea of keeping things as similar as possible between setups. I think it's a good idea.
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Re: Releasable rigging using a Petzl Stop

Postby NZcaver » Apr 27, 2013 2:28 pm

OpenTrackRacer wrote:Thanks for all the feedback. It's a very good point about swapping out the pulley for a carabiner. I was originally going to use a Petzl Fixe anchored by two slings. Since we'd likely only be using the rig to lower someone, I'll swap that with a steel carabiner. The redirect will be loaded somewhere around 150-175% compared to the main anchor point.

I understand using a steel carabiner at the redirect point - as we often do with a munter hitch through it for rope practice - but in your situation I would tend to stick with a robust pulley *just in case* you need to haul somebody. I suggest not using a plastic pulley, and if you can find a 2-inch rescue pulley all the better. What goes down must come up, right? Less friction at that point means you need to manage lowering through the Stop a little more carefully. Running the tail through an offset braking carabiner at the anchor point should help. If that's still not enough friction (like with a thinner/newer rope), tie a munter through the braking biner. Make sure everybody in you group knows how and why the rope is set up this way, and how to operate a lower/haul if they need to. Pulley or biner - it's your choice. There are pros and cons either way.
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Re: Releasable rigging using a Petzl Stop

Postby chh » Apr 30, 2013 5:01 pm

Sounds good. I would echo Scott's coment about making sure your redirect is truck enough if you and your lock off are both going to be under it. I would probably also rig with a pulley if I had one handy. Heck, if you're going to go full bore, go ahead and leave a long prussic and an extra biner at the pitch head to help initiate a haul, cause you already have one in your pack....right? :big grin:
Another handy trick to have practiced ahead of time is how to rap a weighted line on a Simple or Stop.
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Re: Releasable rigging using a Petzl Stop

Postby jharman2 » May 1, 2013 9:16 am

chh wrote:Another handy trick to have practiced ahead of time is how to rap a weighted line on a Simple or Stop.


Cool! I had no idea this was possible. Please explain how to do this. Do you rig the bobbin in a "C" config? Thanks!
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Re: Releasable rigging using a Petzl Stop

Postby hunter » May 1, 2013 11:50 am

If you look at the Petzl Technical notes for the stop (available online) they show a stop rigged to an anchor for lowering. I would just use this method with a fairly tight backup knot.

Also avoid loading the stop and bending it over an edge or protrusion.
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Re: Releasable rigging using a Petzl Stop

Postby NZcaver » May 1, 2013 8:22 pm

jharman2 wrote:
chh wrote:Another handy trick to have practiced ahead of time is how to rap a weighted line on a Simple or Stop.


Cool! I had no idea this was possible. Please explain how to do this. Do you rig the bobbin in a "C" config? Thanks!


See this:

Image

From "Vertical" available online at http://www.cavediggers.com/vertical/9DISASTR.pdf Technique is not officially recognized/recommended by Petzl as far as I am aware. Practice with extreme caution! An alternative method is to use a Valdotain Tresse (VT) hitch in place of a descender, as previously discussed here.
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Re: Releasable rigging using a Petzl Stop

Postby OpenTrackRacer » May 1, 2013 9:21 pm

It's pretty unlikely that we'd use it for hauling but you never know. I have a Petzl Rescue pulley I can use which has a much wider radius than the Fixe. Petzl's diagram for lowing a load using the Stop is not what I expected. It looks like they place the Stop directly over the load. I guess they expect the rope to just slip through without anyone pressing the release handle. I'm not sure I really like that. Also, I don't think we'd be able to rig as shown with another anchor point above the Stop. My intention was to rig the Stop low and have the rope redirect up to the pulley. The Stop would then be operated just like one was rappelling off it. I think Petzl's diagram is strictly for lowering a load, not releasable rigging that some is going to rappel and ascend on. Gotta think about this one.

That diagram for ascending using the Stop on a loaded rope is giving me nightmares. That is a SCARY looking setup. That would need some serious practice on the surface first. Even then... I think if this ever came up I'd finally have a use for my Petzl Shunt!

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Re: Releasable rigging using a Petzl Stop

Postby jharman2 » May 2, 2013 9:59 am

Thanks for the link NZ. I'm going to try this with a belay. Looks pretty sketchy and would certainly be a situation where you'd want a shunt or other method of stopping.
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