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QC Lab: Autoblock Misuse

Wednesday, September 7, 2016
Lately I've been getting quite a few questions on the use of the Black Diamond ATC-Guide and/or similar "autoblock"-style belay devices—and another installment of QC with KP was born.

I've seen some curious/scary autoblock uses/misuses out there and I had the boys in the QA lab test a couple of the setups I've seen, which were:

a) Incorrectly using a standard belay device as an autoblock device.
b) Using multiple biners as the "brake bar" in order to make taking in rope easier.

1. INCORRECTLY USING A STANDARD BELAY DEVICE AS AN AUTOBLOCK DEVICE

An autoblock-type belay device is awesome for belaying up one or two people on a multi-pitch route. When used correctly (utilizing a SOLID anchor, threaded correctly, always having your brake hand on the rope, etc) it is easy to take in rope and lock one or both strands should the seconding climber(s) happen to fall. However, I think the recent popularity in these devices has caused some confusion. A few weeks ago I was at Red Rocks on a super classic (read: crowded) route belaying my partner as he led upward. A climber below us joined me at the belay ledge and set up his belay system by equalizing the two-bolt anchor with a cordelette (the tie-in point was at chest height) and used a standard ATC device as an autoblock. I politely suggested that the belay setup wasn't ideal as the belayer would need to raise their arm up above their chest (see photo) in order to lock off the climber, and they may not be able to hold the fall. The climber assured me that they "do this all the time" and that the seconding climber wouldn't fall anyway because the climbing was "so easy."


Incorrectly setting up a standard belay device off the anchor

Now whether this was a case of not understanding exactly how an autoblock device works, I'm not sure. I hope that it's obvious to most people reading this that when using a standard belay device as described above it DOES NOT LOCK automatically if a second falls, and is VERY DIFFICULT to hold the climber by hand if he/she were to weight the rope. When using a standard belay device to bring up a second, I always belay off my harness' belay loop, with the rope running through the anchor as a directional—that way if the seconding climber were to fall, the load is on the anchor. Some people belay off the harness straight down to the climber, but in the case of a fall, the belayer is now being yanked off the ledge and being pulled in two directions (the belayer is tied off to the anchor, but the pull from the fallen climber is downwards).

The correct setup of an autoblock device is shown below.


Correctly using an autoblock device off the anchor

The full instructions for the Black Diamond ATC-Guide can be read in  ATC-Guide page or watch the How-To-Video for more information.


2. USING MULTIPLE BINERS AS THE "BRAKE BAR" IN ORDER TO MAKE TAKING IN ROPE EASIER

I've had a few people write me claiming that, while using an autoblock device such as the ATC-Guide, they get pumped taking in rope when belaying their seconding climber up. It's true that pulling up fat ropes (i.e. 10.5 mm and greater) has increased friction and therefore requires more effort than pulling up skinny cords. So other than not using such a fat rope, what are the options to make life a little easier? Well, I've had several people claim that they use multiple carabiners as the brake bar to help save the pump, but they're worried about the potential loss of locking ability should their seconding climber fall. So I asked one of the members of the crack-crew of QA engineers here at Black Diamond to run a few quick, unofficial tests using two of our most popular models of locking carabiners, the RockLock (rounder cross section) and the VaporLock (flatter cross section). Here are the results:

Take-Up Force

 

Take-Up Force

Carabiner Quantity/Style
Force (lbf)
1 RockLock
25
2 RockLocks
29
1 VaporLock
28
2 VaporLocks
35


In the testing we did, using multiple (two) biners actually INCREASES the amount of force required to take rope in.

  • I believe this is because though the radius of the rope going over at the top of the device is larger, the radius at the bottom, where the rope pinches, is tighter. As well, I think multiple biners are assisting in forcing the rope harder into the grooves of the device, therefore causing more friction and thus more force required to take up rope.
  • What the data also showed is something that is pretty intuitive and many have noticed and realized in the field: the shape of a biner's cross section had an impact on the amount of take-up force required. (i.e. round cross section biner = easier to take rope in; flat cross section biner = harder to take rope in).


Holding Force


Holding Force

Carabiner Quantity/Style
Force (lbf)
1 RockLock
1218
2 RockLocks
1316
1 VaporLock
1466
2 VaporLocks
1825


We found, once again in the limited testing we did, that using two biners actually INCREASES the amount of holding force.

  • Once again, for the same reasoning, though the radius the rope takes at the top of the setup is larger and you would think reduces the amount of holding force, the multiple biners cause the radius at the bottom of the setup, where it clamps on itself in the device, to be tighter and therefore INCREASES the holding force.
  • And once again, the data showed that flatter cross section biners had a greater holding force than rounder cross section biners.


What is the ultimate solution? You need to find a balance that works for the given situation. I'm usually climbing on anywhere from two 8.1s, to a single 9.1 mm, 9.7 mm or even a 10.2 mm. I typically use a VaporLock (flatter cross section) when using skinnier ropes, and a RockLock (rounder cross section) when using fatter ropes.

Again, this is pretty rough stuff; as always don't take it as the Gospel. More in-depth testing would need to be performed to come to any concrete conclusions. I'm sure there's a point where more biners would reduce the take-up force and reduce the clamping force. Is it three biners? (No, because we tested that…) Could it be four or five? Not sure, as we didn't take it that far. And it goes without saying that I'm not a climbing guide and I don't even play one on TV. If you want official instruction get it from a qualified, certified instructor.

Climb safe out there,

KP


Kolin Powick (KP) is a Mechanical Engineer hailing from Calgary, Canada. He has nearly 20 years of experience in the engineering field and has been Black Diamond's Director of Global Quality since 2002. Kolin oversees the testing of all of Black Diamond's gear from the prototype phase through continual final production random sample testing. If you have a technical question for KP, please email him at askkp@bdel.com and he will TRY to respond.

 


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