ATC Guide

As it happens there was a thread on another forum about using guide plates for roped soloing and I went off and pull tested a few to see what happened under load:-

First Fail Mode:
The trapped rope escapes sideways from under the tensioned rope and gets trapped between the tensioned rope and the side of the slot.This is very difficult to free off and you have to dismantle everything and twist the locking krab brutally to release the rope. Take your Prusiks.

Second fail mode:
Apply yet more load and the trapped rope where it crosses the tensioned rope goes down through the slot with a bang. At this point the holding power drops off considerably but not catastrophically, though pretty near!
Easy to release, just unclip the krab when unweighted. Still need to take your Prusiks!

ATC Guide. 10.2 Mammut, used, non-treated. First fail mode 4.8kN. No second fail mode, rope sheath cut at ca 9kN.
ATC Guide. 9mm Edelrid, used, non treated. First fail mode 2.96kN. Max fail load 5.58kN. Residual load 1.6kN
ATC Guide. 8.2mm Edelrid, new,treated. First fail mode 2.05kN. Max fail load 4.06kN. Residual load 1.2kN

Reverso³. 10.2 Mammut, used, non treated. First fail mode 3.68kN. No second fail mode. Rope sheath cut ca 9kN
Reverso³. 9mm Edelrid, used, non treated. First fail mode 2.25kN. Max fail load 3.60kN. Residual load 0.9kN
Reverso³. 8.2mm Edelrid, new,treated. First fail mode 1.6kN. Max fail load 2.38kN. Residual load 0.7kN
All with Petzl Attache 12mm round profile karabiner.

Not my idea of a reliable roped-solo device!

Jim,

Cool test, but I'm having a hard time picturing the second failure mode, any chance you have pictures?

Good thread and good comments. Being aware that the anchor needs to be set up with the proper directional pull as Greg D mentioned, has anyone actually witnessed rope slippage while using the ATC in autoblock mode?

I admit that I have used the ATC Guide hands free, but always paying very close attention on how the ropes are running through it so there is no twisting and that is will load properly in case of a fall.

Tom Grummon wrote:Jim, Cool test, but I'm having a hard time picturing the second failure mode, any chance you have pictures?

I think what he's saying is that in the first mode, the load strand squeezes past the brake strand into the V-grooves. Everything get's wedged in and damn near impossible to take apart. You can neither continue to belay or lower.

If i catch what he's saying correctly, the second mode is a continuation of the first. In the first mode, the brake strand is starting to come out the top while the load strand is squeezing past it into the V-grooves. The second mode is when this twist continues thru the slot and you essentially end up with the device rigged backwards (brake strand on top), except there is possibly has a twist in the rope between the device and the biner.

Exactly, the first failure is both strands are crossing inside the device and it jams up solid, you hear a sharp bang as this happens (we though something had broken). Then the crossing point of the ropes is forced out of the bottom of the plate and the original rope positions is reversed with a twist at the karabiner.
With thicker ropes as the crossing point starts to come out below the plate the rope is forced onto the underneath of the sides of the plate and core-shots so it doesn´t really ever reverse completely but shreds itself instead.
You can get a good idea of what happens by using a thinnish (6mm or so)cord and bouncing on it.

The fact that this can start to happen at 2 kN is a little worrisome. But I 'spose you don't tend to see the really high forces when you're belaying a second. Also I have a thicker rope so its not as much of an issue for me. I'm just thinking how much it would suck to have your belay device completely jam up on a wall.

Jim,

These numbers seem quite low. 2 kN is slightly more than twice my body weight. Can you provide more details about the test? How long was the rope, for example. Also, what was the pull test time frame? In slow pull test the rope's ability to absorb energy diminishes with time as you are pulling. In a real world scenario a follower falls and comes to rest relatively quickly compared to a pull test.

Perhaps drop test with different masses and different distances (representing slack in the line cause the belayer is picking his nose, eating pizza, etc) would be more meaningful than pull tests. Thanks, Greg

The numbers are low. With the 8.2mm rope a bit of flailing trying to get my foot in a foot loop was enough to dump me on the ground. However to be fair Petzl warn against using the Reverso³ in guide mode on a single strand of this diameter. I have no info on what BD recommend.
The speed, rope length and energy have no bearing on the force required to cause failure.
The lock up is virtually instantaneous and slip negligable until failure.

Jim Titt wrote:The numbers are low. With the 8.2mm rope a bit of flailing trying to get my foot in a foot loop was enough to dump me on the ground. However to be fair Petzl warn against using the Reverso³ in guide mode on a single strand of this diameter. I have no info on what BD recommend. The speed, rope length and energy have no bearing on the force required to cause failure. The lock up is virtually instantaneous and slip negligable until failure.

So, you are telling me that a 200 lb person on tr with 2 feet of slack falling when 100 feet from the belay is identical to the same person falling with 4 feet of slack when 10 feet from the belay?

Think again.

Greg D wrote: So, you are telling me that a 200 lb person on tr with 2 feet of slack falling when 100 feet from the belay is identical to the same person falling with 4 feet of slack when 10 feet from the belay?

The way I read it, Jim is saying that the device fails at a certain force that depends on the type of rope. It does not matter how that force ("the force required to cause failure") is produced; what matters is its value. Your two scenarios result in different forces, so one may cause failure even if the other doesn't.

Good man! Glad someone understands the basics.

Jim is also talking about rope soloing, which places completely different stresses on the device. I wouldn't worry about it failing at 2 kN while belaying a second!

I don't know if this helps any, but recently I decided to try out my ATC guide for rope soloing in a tree in my front yard. Basically I wanted to test it out in a safe setting before trying it at my local crag. So I set everything up (I used a New England 10.5 mm rope) and led out on a branch to where if anything failed it wouldn't hurt very much to hit the ground, but where I climbed long enough to see how the rope fed (which it did great). After my last sling I climbed out enough for about a 5-6 foot fall and the device held beautifully, but as per the topic of conversation it did bind up pretty darn good, but not impossible to undo once I unweighted the rope. In a situation that I could not unweight the rope I would be in a world of trouble (prusiks are mandatory!). I doubt I will ever use this setup in a real world setting after all that has been said (I just need to break down and buy a grigri or similar device), but it was fun to play around with.

We're talking about belaying a second with a plaquette right? I'll say this and post this pic. I also have a video of the test I did using a VW Eurovan with a V6 motor to break the rope as I did here. I've been belaying the second directly off the anchor for over 15 years and have never experienced slippage of any kind. Stop worrying! You can start worrying when you have to belay a VW Eurovan. Then the rope will break at the plaquette as it did here.
I'll post the video if you like.

JF

I'll add this:

Belaying the second directly off the anchor, loads are relatively low.
Belaying a VW Eurovan off the anchor, loads are "massive"
Doing your own test to satisfy your own curiosity...priceless!

JF

Jim Titt wrote:Good man! Glad someone understands the basics.

Not a useful comment. I understand perfectly well your tests and failure loads. I was more curious to see actual loads generated on autoblocks in tr situations. I thnk others reading here may benefit as well. I suspect these loads are quite low but would be nice to see some numbers. Personally, I don't worry about them slipping at all they way I use them. I started using autoblocks (Kong Gigi) long before petzel and bd started making them.

If you don't care to do theses test just say so.

I knew when I put that reply up it would be a total waste of time!
If you feel you need hard numbers, try gross mass weight of the vehicle x .007 and do your own test.
My point here was this...you are wasting your time here, the rope broke! There is no slippage, The device does not simply fail under normal usage! Yet...still not satisfied?

JF

This was the original question posted:-

Tom Grummon wrote:Out of curiosity how reliable is the auto-block on an ATC Guide?

And I gave the answer of exactly how reliably they hold under load which is considerably more useful than "they never slip" or " I tested one by....".
How the loads are generated is of no particular interest since climbers inevitably find ways to do things no-one else thought of, there might be a 400lb housewife hanging on the rope or a roped-soloist pushing it out too far, who knows?
I generally only test gear not falls but in a top-rope situation it would be fairly easy to get an impact of 5kN and we´ve seen over 9kN on a short factor 1 on the drop tower so anything under that is is possible. The ASCA got over 1000lbs in their tests.

j fassett wrote:I knew when I put that post up it would be a total waste of time! If you feel you need hard numbers, try gross mass weight of the vehicle x .007 and do your own test. My point here was this...you are wasting your time with this, the rope broke, there is no slippage! Still not satisfied? Do your own frickin test! I won't be back on this one! JF

Folks,

Jeff is right. If using the appropriate rope size and the device set up properly, the autobloc on the ATC guide is bomber. I've been using plaqette devices (reverso, atc guide, gigi [NOT grigri] for 10 years and have found that they lock without fail.

It is probably for this reason that the AMGA (and I believe the PCGI, and probably every other reputable certifying body) considers the device hands-free when the device is being used in autobloc mode off the anchor and appropriately set up.

If you're really worried about it, do your own tests. Nothing builds confidence like real-world, in-person tests.

Geir & Jeff -- I can understand the ultimate strength & rope diameter arguments, but the failing of the device in a normal operation of belaying a second or two seconds when hit from the side has been shown to be a weakness of this type of device.

It's a fairly big statement to say the AMGA is countering a manufacturer's safety requirement. Especially when Eli has stated numerous times not to put complacency when using these devices while autoblocking.