This is a very insightful study done by dmm which looks at the forces put on runners when falling onto them with slack in the system.

I think it applies to people that have slack in their system at a belay, and also if you fall onto a spectra daisy chain if aiding.

Check it out, it's pretty fasinating:
Main page: http://www.dmmclimbing.com/...nid=293&ngroup=1

Direct link to video: http://www.dmmclimbing.com/video.asp?id=5

ps- if any moderators have a better forum to put this in, feel free to move it.

Since I started hearing about this stuff a couple seasons ago, I went back to using more nylon runners. Probably 50/50 nylon and dyneema now. nice to have a few of the skinnies on hand, but the nylon isn't just 100% static like the skinny stuff.

Meh. Kinda irrelevant to me. These kinds of tests are done by dropping something on a sling attached to a static anchor. However, this isn't really how they are used. If you're taking a fall on an anchor attached directly by a dyneema sling, you did something horribly wrong.

These are runners. There is a key factor that's missing from these kinds of tests: the rope. That's what reduces the peak forces during the fall. If used appropriately, the additional stretch from the runner is negligible compared to that of the rope and belay system.

IMO, the real negatives of skinny dyneema slings are as follows:
1) Cost. They're pretty damn pricey compared to nylon
2) Durability. Gotta retire them faster, and cost more too replace, too.
3) Difficult to use as a friction hitch. They're pretty slippery. I certainly wouldn't use one as the friction hitch for holding me personally, though if I need to rig it for my feet, whatever.
4) Difficult to tie to things. Slippery, skinny enough to cut through other stuff.

That said, I use skinny slings exclusively nowadays. The weight and cluster savings is pretty fantastic.

Meh. Kinda irrelevant to me. These kinds of tests are done by dropping something on a sling attached to a static anchor. However, this isn't really how they are used. If you're taking a fall on an anchor attached directly by a dyneema sling, you did something horribly wrong.

After watching the video I'm sure you'll agree that dogging a move on a sport climb while clipped to any sling is a dangerous idea and that having any slack in a belay system is best avoided - you wouldn’t want to fall off a ledge clipped into a slack sling.

Clearly, taking advantage of the shock-absorbing capability of the rope by using it to tie directly into anchors as opposed to using a sling, will reduce the chances of dramatically shock-loading the anchors. If you do use slings then ensuring there is no slack in the system is paramount.

From the DMM web page...


They're not talking about a sling on a piece of pro while using the rope, but connecting yourself directly to pro/bolts/anchors with a sling.

I agree with you that the test used isn't a very accurate reproduction of real life climbing scenarios, but useful for learning about the properties of the two materials. I also agree that the dyneema runners are twice as expensive and wear out twice as fast (which makes them 4x as much?)

But i disagree that the weight savings is noticeable, and the bulk issue I haven't really found to be a problem using 5 nylon slings and 5 dyneema ones. If you're happy going all dyneema that's great, I did that for several years. But for me, I like having an extra dynamic element in the system rather than something 100% static. An added benefit is that if I need to leave sling material behind at anchors it's cheap, and I can cut the nylon and tie it.

Meh. Kinda irrelevant to me. These kinds of tests are done by dropping something on a sling attached to a static anchor. However, this isn't really how they are used. If you're taking a fall on an anchor attached directly by a dyneema sling, you did something horribly wrong.

The point of the study was looking at using them by having them to attach the climber to an anchor (think: multipitch, you are using these to keep you tied in), but that there could be let's say 12" of slack floating around. Then suppose your climber takes a fall and pulls that slack out of the system; this is supposed to give you an idea of how this could affect your tie-in.

You're right, this isn't about how they work in a lead fall with a dynamic rope involved.

You don't know anyone that has ever attached to the main anchor via a sling? And you've never seen slack in such a system?

It's pretty simple.

Yes, your right that it's a test and doesn't perfectly describe things, but it does a great job at helping us think about our belay system and how high the forces can be on things... at least some of us.

The fleshy human body is not made of steel.

No fall possible if there isn't any slack, now is there?

Yes, I have. If the leader falls, said person is pulled up. Force is mitigated via the rope, the belayer being pulled upward against gravity, and any additional friction in the system.

If, in the worst case scenario, the climber falls factor 2 style onto the anchor, peak force is reduced through the rope, the belay device, and the belayer's belay loop.

In other words, there is NO SCENARIO in which a leader fall will result in static load onto the anchor.

Neither of these is a lead fall.