Two Tension Rope Systems

[FiremanLyman]

So surfing the ITRS papers collection, had read a few before and didn't know there was a whole library avalible (thanks DC), and came across this one http://www.itrsonline.org/PapersFold..._ITRSPaper.pdf

It deals with testing of some Two Tension Rope Systems. This is our preferred method in our TRT for lowers lately, thought I was pretty up on them. But something new (to me) was presented in them; the "Twin" system. From what I can tell in the "Twin", both ropes are run through the same DCD.

Now this was presented by a Mountain Rescue bubba. I know they are famous for doing more with less equipment and such. I guess coming from an Urban TRT team, the idea of putting both tensioned lines into the same DCD really is taking out the redundancy that a Two Tension Rope System, with two anchors and two DCD's provide.

I am not against it, just never heard of this "Twin" system. Thoughts?

[bburton]

Being from a rural area and having a background as a climber prior to the fire service, our infatuation with redundancy is amusing sometimes. With the twin rope system you posted, both strands of rope would effectively equalize in the decent device, thereby that same 600lb load is resting on two strands of rope.

To directly answer your question, ratings aside, two lines passing through a single device are going to cause tangling issues and possibly a device to jamb. Much less the added equipment and weight that accompanies it when you haul all of this stuff anywhere. Two lines would give more friction in a device due to more friction caused by the congested rope channel. But for real, I would go with one, well maintained life safety line through one appropriate decent device and hook all of it to a bomber anchor rather than rigging an elaborate system with the intention of part of it failing.

[DCFDRescue2]

Being from a rural area and having a background as a climber prior to the fire service, our infatuation with redundancy is amusing sometimes. Our books teach that a 600lb load must be suspended by a rope that is rated for 9000lb, a rating that itself has an actual breaking strength of 2 or 3 times the rating, sometimes as much as 18000lb to 27000lb. With the twin rope system you posted, both strands of rope would effectively equalize in the decent device, thereby that same 600lb load is resting on two strands of rope rated to 18000lb with an actual breaking strength of 36000lb to 56000lb. All this is running through a friction device with a liberally rating of 10000lb. This doesn't even take a belay line into account as the twin line diagram you posted shows.

Ok, it is still only a 600lb load, right.

To directly answer your question, ratings aside, two lines passing through a single device are going to cause tangling issues and possibly a device to jamb. Much less the added equipment and weight that accompanies it when you haul all of this stuff anywhere. Two lines would give more friction in a device due to more friction caused by the congested rope channel. But for real, I would go with one, well maintained life safety line through one appropriate decent device and hook all of it to a bomber anchor rather than rigging an elaborate system with the intention of part of it failing.

Interesting numbers, I'd love to see how you arrived at them.

In the meantime, here is a link to some research that CMC did a while back. The actual breaking strength of the rope was averaged at roughly 120% of the listed strength.

http://http://www.cmcrescue.com/Asse...s/RopeLife.pdf

From what I remember, Rocky Mountain Rescue Group uses a Twin system and has a custom piece of aluminum, similar to a whale tale, to run both ropes through. I'm not sure what their anchoring methodology calls for.

Picture here (along with every other friction device known to man!):

http://http://storrick.cnc.net/Verti...xMulti918.html

I think if you were going to have a tangling issue, you would have it no matter what device or devices you were using.

ATtwin system will have the same amount of friction that a TTRS has, it's just that the one device is providing the friction instead of two. The ropes will not provide any appreciable additional friction as they will be moving at the same speed and same direction.

Nobody rigs with intention of having a part fail, that's why they're called accidents. The more likely cause is that a human brain fails long before a carabiner does. Single rope technique does have a place, just not in a place where people believe their ropes are 300% stronger than they actually are, despite easily found documentation. I can only guess what passes for a bombproof anchor that cannot be tested!

Sorry to sound like a schmuck, but that is some really inaccurate info that you put out.

[Halligan84]

We learned that technique years ago through RSI. They use (or did at that time) a heavy duty "U" shaped rack which easily accepted both 1/2" ropes. The anchor system was properly constructed for a 3 person load. I used the 2 rack concept also through Roco and found the single rack much more effective personally. Once the basket was properly oriented a single firefighter performing the lower was able to match the speed of the lines by matching the tracers on the rope. I personally found it a bit easier to coordinate with one person and one rack

[DCFDRescue2]

We learned that technique years ago through RSI. They use (or did at that time) a heavy duty "U" shaped rack which easily accepted both 1/2" ropes. The anchor system was properly constructed for a 3 person load. I used the 2 rack concept also through Roco and found the single rack much more effective personally. Once the basket was properly oriented a single firefighter performing the lower was able to match the speed of the lines by matching the tracers on the rope. I personally found it a bit easier to coordinate with one person and one rack

That's real similar to what RMRG does with their friction plate IIRC. They did some some testing and showed that, while it doesn't pass the whistle test, they did not have any problem controlling the load even when the operator had no idea which line was being cut.

[bburton]

Interesting numbers, I'd love to see how you arrived at them.

Sorry to sound like a schmuck, but that is some really inaccurate info that you put out.

Just quoting instruction. No hard feelings though.

Point being that with smooth transitions and lowering, even shock loads will have a hard time reaching the safety factors involved in rope construction. If it's a belay issue, you're relying on a single piece of hardware to control both ropes anyway. With the twin technique listed, it seems that with only one device, only one rope is necessary.

[rmhinkle]

Did you get taught by DJ Walker...? haha The ole 2 tension discussion... He is with Austin and TX-TF 1. My issue would be the distance of the drop and the tangling issue. I know in particular cave situations have become fatal due to ropes twisting and guys on rope dying from exposure to the elements. Those are big drops though.

[FiremanLyman]

Nobody rigs with intention of having a part fail, that's why they're called accidents. The more likely cause is that a human brain fails long before a carabiner does. Single rope technique does have a place, just not in a place where people believe their ropes are 300% stronger than they actually are, despite easily found documentation. I can only guess what passes for a bombproof anchor that cannot be tested!

Rig for success. I agree, we never rig anything expecting something to fail. But we are also taught to use redundancy; either using a two tension rope system with separate anchors or DCDs or a tensioned main/ untensioned belay, again with two anchors and DCD or belay device.

There is my point. I am not overly concerned about rope breakage for what we do, I am concered about the human element. Most of the time, we will SRT the litter attendant anyways. I have just never seen both tensioned lines running through the same DCD. Not against it, just new to me. Wondering if anyone outside of the mountain rescue community does it?

Did you get taught by DJ Walker...? haha The ole 2 tension discussion... He is with Austin and TX-TF 1. My issue would be the distance of the drop and the tangling issue. I know in particular cave situations have become fatal due to ropes twisting and guys on rope dying from exposure to the elements. Those are big drops though.

I know DJ, he has been an instructor for two classes I have been in and I recently worked with him and the RESET group on setting up RESET's Confined Space curriculum. Unfortunately I got injured and could not teach our first class in December.

[TRT24]

Did you get taught by DJ Walker...? haha The ole 2 tension discussion... He is with Austin and TX-TF 1. My issue would be the distance of the drop and the tangling issue. I know in particular cave situations have become fatal due to ropes twisting and guys on rope dying from exposure to the elements. Those are big drops though.

You are looking at two different situatiuons here. The fatalaties in caving were not the result of lowering two parrallel lines. The twisting only becomes an issue when rappelling or climbing, as you get to a point where further progress becomes impossible. (If memory serves, the most well known incident in Ellisons involved ascending.) When lowering, all the new line being put into play is coming straight out of the rope bag, no twist until it is through the descender. You would get the same amount of twist with a single main line and a belay line on long lowers.

[servantleader]

I've been involved in mountain rescue in WA state for 15 years. There is NO mountain rescue team in WA that would consider using such a technique. MAYBE 25 years ago, but not now...

I do not believe the authors were advocating the technique, rather, they were pointing out that it is out there and might still be in use. Not in WA state though...

[FiremanLyman]

I've been involved in mountain rescue in WA state for 15 years. There is NO mountain rescue team in WA that would consider using such a technique. MAYBE 25 years ago, but not now...

I do not believe the authors were advocating the technique, rather, they were pointing out that it is out there and might still be in use. Not in WA state though...

Cool, that was what I was wondering.

[rmhinkle]

You are looking at two different situatiuons here. The fatalaties in caving were not the result of lowering two parrallel lines. The twisting only becomes an issue when rappelling or climbing, as you get to a point where further progress becomes impossible. (If memory serves, the most well known incident in Ellisons involved ascending.) When lowering, all the new line being put into play is coming straight out of the rope bag, no twist until it is through the descender. You would get the same amount of twist with a single main line and a belay line on long lowers.

Yea, that's a good point. However, if you do a long lower or rappel to access the patient and then raise a patient you still run into the problem of tangling and losing forward progress...

[MtnRsq]

My team regularly uses a two tension rope set-up but with 2 DCDs (see 2 DCD twin model in orig post). Certainly using one DCD is possible but the use of 2 simplifies situations requiring knot passes.

We've used this configuration as our "preferred" method for going all the way back to Goldline days.

Not sure if Rocky Mountain Rescue is using the single DCD method for everything or primarily the so-called "scree" rescues. I'm not sure there are too many DCDs that are designed to handle 2 ropes through one device. Even in the lightweight world of mountain rescue the weight difference between 1 and 2 DCDs would be negligible. One device would have its advantages in terms of working space when dealing with very confined spaces such as a small ledge. There are of course ways to work around space limitations as well.

As a mountain rescuer I have not seen wide use of the single DCD set-up.

[FiremanLyman]

My team regularly uses a two tension rope set-up but with 2 DCDs (see 2 DCD twin model in orig post). Certainly using one DCD is possible but the use of 2 simplifies situations requiring knot passes.

We've used this configuration as our "preferred" method for going all the way back to Goldline days.

Not sure if Rocky Mountain Rescue is using the single DCD method for everything or primarily the so-called "scree" rescues. I'm not sure there are too many DCDs that are designed to handle 2 ropes through one device. Even in the lightweight world of mountain rescue the weight difference between 1 and 2 DCDs would be negligible. One device would have its advantages in terms of working space when dealing with very confined spaces such as a small ledge. There are of course ways to work around space limitations as well.

As a mountain rescuer I have not seen wide use of the single DCD set-up.

Thanks, for the confirmation. We use two tension rope systems a lot in our urban world too now. Really have gotten away from the untensioned belay (don't like the fall factor, love the load sharing). When I had read the ITRS paper, the single DCD concept really wow'd me, not in a good or bad way, just never heard of it.

Thanks again.

[servantleader]

MtnRsq and Drew

We currently allow the belay line to share part of the tension by placing a friction device (an ATC for 11 mm rope and a Scarab for 1/2" rope) behind the TPs. The TPs are managed with two fingers in a scissor configuration placed in front of the TPs. We adopted this method after an RFR instructor showed it to us along with the testing data. I'm wondering what you think about this.

I've never used the MPD, but I'm aware that it makes two tensioned rope systems that pass the whistle test seamless and that a number of teams have adopted it as their go-to system. I'm wondering how whistle test compliance is incorporated into two tensioned rope systems that don't use the MPD. I think I might have had this conversation with Drew awhile back regarding two tensioned rope systems with munter hitches as the DCDs. Thanks.

[FiremanLyman]

Sounds like your current set up is moving towards a two tension system, diffrence is you are not trying to equaly share the load, right? I would love to see this system in action. Have no experience with the Scarab, though it looks like a modern spin on combining a bar rack and a rescue 8.

I have not used the MPD either, it sounds like the people who have had a life changing experience and use it for darn near everything. Have not heard anything really bad about it, except the price.

Anyways, as for the whistle test, not a fan as you already know. We train to be proficent enough not to have either DCD's unmanned, let alone both when running a two tensioned system. But I understand the principle, and appriciate it when people are acquiring rope skills.

If you want to run a two tensioned system that will meet the whistle test, you only have to set up some prusik rope grabs attached to an anchor inline with the lower. They have to remain minded, and you have to have a haul system in place and ready incase you load one. I would veiw this as overkill, but it would pass the whistle test.

[MtnRsq]

I agree with Drew. Using a prusik or other rope grab will ensure the system passes a whistle test.

The MPD does function as advertised and allows easy mirroring of systems. Pretty pricey though....