Do Screamers Work?

Ron Olsen's comment in another forum topic about Yates Screamers caused me to remember something I'd surfed across a few weeks ago.

In brief, an MIT Lecturer taught a seminar on testing rock climbing gear. One project, the results of which "have not been written up" dealt with screamers. See here.

Of interest is the following from the linked page:

"Drop tests were conducted on screamers to see if they limit the force on the rope. The simple answer is no. Initially the force is limited, but the energy absorbed by the screamer is about the same as the additional kinetic energy introduced into the system as the screamer opens up. The resulting force is similar to the force produced by the control drop (no screamer present)."

The proposal for testing the screamers is here. Presumably the proposal mirrors what was actually done.

I googled a bit (but hardly exhaustively) for any other tests or studies that relate to the effectiveness of Screamers; didn't find anything.

Craig Luebben, in "How to Ice Climb!" says (p. 146) that in his drop tests the force reduction afforded by Screamers exceeded the one predicted by a simplistic theoretical analysis. On the other hand, not many argue that the effectiveness of a Screamer decreases with the length of the fall. This is because the kinetic energy of the climber increases, but the Screamer can only dissipate a fixed amount.

What Custer describes is true: The ripping of the stitches increases the length of the fall. First, the top anchor is lowered; second, some rope passes through that anchor that would otherwise stay on the belayer's side.

In Luebben's tests, if I read his account correctly, they used a dynamic belay with some tubing device--a situation in which peak forces are not well predicted by the simple energy balance equation many of us have seen many times. (E.g., on the Beal site.)

I have also seen an Italian experimental study of load-limiting runners that compared different belay methods and showed very mixed results.

All in all, Screamers are a bit of a mystery to me. I would like to know more than I do.

Yates has the following table on their website showing the forces involved in various falls with and without the use of Screamers.

I would hope that these numbers are the results of real-world tests, but I'm not sure if that's the case.

Here is a report of a Screamer test carried out on El Cap.

All I know is my buddy took a 60' lead fall in Ouray on one, it tore all the way and his screw held..........
All caught on video, believe or not all the tests, but well, he's still walking, a little shaky, but is fine and the point is his screw held.

I'm not implying that Yates hasn't conducted serious testing, but the table on the website really does not look like it reports test data.

The gear reviewer on rc.com fell on Screamers, but never gathered any test data.

If ropes were ideal springs, friction were negligible, and so on, Screamers would provide modest reductions in peak force provided the climber's weight were less than half the activation force. They would still be effective on very short, high ratio falls, but not very effective otherwise. Ropes are not ideal springs, friction is present, and one seldom falls on a rope locked at the belay station. Therefore, a simple analysis may be very inaccurate. I'd like to read a more accurate analysis, but I haven't seen one.

For instance, one may conjecture that while the Screamer rips open, the rope's tension is allowed to become more uniform. (Because of friction, the length of rope between the top piece and the climber has higher tension than the length of rope between the belayer and that anchor.) Without proper testing, that remains a conjecture.

Another conjecture is that the reason for the effectiveness of Screamers has to be looked for in the fact that ropes are damped oscillators. It may be that Screamers deploy at such a time during a fall that they make it easier for the belayer to control the slip of the rope through the belay device. Conjectures are cheap and careful study is not. That's probably why we don't see much of the latter.

I'm with Jim (not that everyone else might also on the same thought), they are meant to preserve protection, as far as limiting force on a rope, I don't see the point of that analysis, the rope is already manufactured dynamic to limit force on the climber.

Unless I don't understand what the study is asking.

Also, as the screamer opens up the dynamic belay is also being introduced which also absorbs energy, unless something like the gri-gri is being used, so that when the fall terminates to the extention of the screamer, the impact force does get dissipated.

"Well, yes then the dynamic belay is a key, why use screamers?"; I didn't believe it either, but the studies the manufacturers are providing show they do limit impact force to the protection, so I'm using them, I want to increase the odds of maintaining my lead protection which is in question (i.e. not a bomber placement). Ouray (ice park), with it's layers of ice upon snow upon ice upon snow, etc. -- screamers.

Mark Nelson wrote:I'm with Jim (not that everyone else isn't also on the same thought), they are meant to preserve protection, as far as limiting force on a rope, I don't see the point of that analysis, the rope is already manufactured dynamic to limit force on the climber.

In order to preserve protection, you have to reduce the force applied to it by the rope. That's the principle on which Screamers work.

Mark Nelson wrote:Also, as the screamer opens up the dynamic belay is also being introduced which also absorbs energy, unless something like the gri-gri is being used, so that when the fall terminates to the extention of the screamer, the impact force does get dissipated.

Even with a Gri-gri there is a "dynamic belay" effect. Also, notice that it's energy that gets dissipated, not force. It may look like hair-splitting, but it's an important distinction to understand how Screamers work.

Mark Nelson wrote:"Well, yes then the dynamic belay is a key, why use screamers?"; I didn't believe it either, but the studies the manufacturers are providing show they do limit impact force to the protection

Which studies? I'd be grateful if you could point them to me.

brenta wrote: Even with a Gri-gri there is a "dynamic belay" effect. Also, notice that it's energy that gets dissipated, not force. It may look like hair-splitting, but it's an important distinction to understand how Screamers work. Which studies? I'd be grateful if you could point them to me.

gri-gri - unless the belayer inhibits the cam, I don't think you see enough reduction just by going "hands free" (I use that term loosely, as in the cam is not inhibited, the brake hand is still on the rope); my assumption here is that the belayer is anchored with no slack in the tie-in.

Dissipation, yes, I hate interchanging terms, sometimes it's difficult to write a quick blog post; Yes, sorry about that. This all goes to energy movement & wave properties/perameters.

Studies, I'll see what is available, I remember seeing one that addressed the issue of maintaining protection.

Would you agree though that the dynamic belay is important to consider?

Perin Blanchard wrote: Of interest is the following from the linked page: "Drop tests were conducted on screamers to see if they limit the force on the rope. The simple answer is no. Initially the force is limited, but the energy absorbed by the screamer is about the same as the additional kinetic energy introduced into the system as the screamer opens up. The resulting force is similar to the force produced by the control drop (no screamer present)."

My thought here is the initial reduction from the screamer is needed, then the dynamic belay comes into the picture; both of which (attempt to keep?) the protection in place.

This does bring something to my mind; we had discussed any value to using a screamer clipped to the climbers harness instead of the protection.

Would this setup preserve protection so a climber would give himself a more dynamic belay? Maybe this example is more applicable to the results of the study.

Mark Nelson wrote: gri-gri - unless the belayer inhibits the cam, I don't think you see enough reduction just by going "hands free"

Sorry, I misread your initial comment on the Gri-gri. I agree with you.

Mark Nelson wrote:Would you agree though that the dynamic belay is important to consider?

Yes, this was one of my conjectures, so I have to agree at least until I see evidence to the contrary. :-)

Mark Nelson wrote:This does bring something to my mind; we had discussed any value to using a screamer clipped to the climbers harness instead of the protection. Would this setup preserve protection so a climber would give himself a more dynamic belay? Maybe this example is more applicable to the results of the study.

Some differences I can think of: (1) The fall would be lengthened only by the length of the unstitched Screamer, rather than by twice that length. (2) The Screamer would activate later, because of the lack of pulley effect. (3) A climber would only need one Screamer. (4) By connecting the two ends of the Screamer with a non-extensible connector, one could disable the Screamer if hitting the deck became a concern. (5) Transmission of vibration from the ripping Screamer to the anchor should be less of an issue, because some rope would be between the two.

There may be other important differences that I'm missing.

Think of a screamer like crumple zones in a car.

Yes, the crumple zone absorbes energy by the mechanical deformation of the material (akin to the stitches in the screamer ripping), but the more important effect is that it disperses the fixed amount of energy over more time. So, the accident doesn't happen in 0.1 seconds, but in 0.5 seconds. The average energy/time absorbed by the body is much lower over the longer time (though it might not seem like much longer).

The same goes for ropes -- some mechanical losses through friction/heat loss, but more importantly, the fixed amount of energy created by the climber falling is dispersed over a greater time. Thus the average energy/time on the anchor, harness, climber, etc is less.

All very similar principles.

Avery Nelson wrote:the fixed amount of energy created by the climber falling is dispersed over a greater time.

No, if the stitches rip, the climber falls an additional 1.2m. This adds almost 1 kJ to the energy to be dissipated for the reference 80 kg climber. (The Screamer dissipates a bit more than 1.2 kJ.) The analogy with the crumple zones of a car is less than perfect. If you write the energy balance equation for both cases, you have one extra term in the case of the falling climber due to the additional potential energy lost by the climber.

Noting that it's been waaay too long since I've taken physics and it would take me a while to just figure out all the forces involved (rope stretch, friction thru biners, friction thru device, Screamer ripping, body deformation, harness deformation, etc.) nevermind write the energy balance... Yates makes load-limiting slings for a wide range of industrial and other applications, not just climbing, so I have to assume that they've done a lot of testing (given the potential insurance claims involved). Also, doesn't at least one Via Ferrata rig use Screamers or Screamer-like devices? Granted this is more similar to hooking a Screamer between your harness and the rope, but similar principles are involved. If they didn't dissipate energy and limit the force of a fall, wouldn't people be breaking 'biners and harnesses (and bodies) fairly often on Via Ferrata routes??? But bottom line is that unless someone shows definitively that they make a fall worse, it's worth the money and weight to get any little added advantage I can to protect my ice screws. A buddy took a big whip on a 13cm screw which held thanks to stretchy ropes (Beal Ice lines) and a partially activated Screamer. Haven't yet felt I needed 'em on rock (and hope I don't! :^D)

Yes
Yes
Agreed -- they work
.

Kevin Craig wrote:Yates makes load-limiting slings for a wide range of industrial and other applications, not just climbing, so I have to assume that they've done a lot of testing (given the potential insurance claims involved). Also, doesn't at least one Via Ferrata rig use Screamers or Screamer-like devices?

Yes, in my work we get these lanyard type devices that have a screamer built in, they are 6' so the worker could fall 12' plus screamer extension. They are rated to a limit of 900lbf. (approx 4kN) -- What is different as to a lead climbing situation is that there is an assumption that the anchor does not need to be preserved.

Though, one example I think of are daisy chain Shortys for aid climbing, though again, this is a limiter to the climber from a static fall, the protection is still gonna get impacted.

Kevin Craig wrote:Granted this is more similar to hooking a Screamer between your harness and the rope,

Something we actually thought about for leading trad, but I'm in the mindset there is a (better?) difference with a screamer to a protection point as to just using one at the climber's harness to the rope. Mainly because of what the dynamic belay does. And, I think what this study is pointing out: Why do something like using a screamer on the climber? It won't make a difference anyhow, the force on the protection will be the same if the dynamic belay is not introduced.

Kevin Craig wrote:But bottom line is that unless someone shows definitively that they make a fall worse... Haven't yet felt I needed 'em on rock (and hope I don't! :^D)

I guess the worse fall would be choice of failed protection or hitting/snagging something on the way down. I like a controlled lengthened fall using a dynamic belay with the screamers; I think it's the best way to maintain questionable protection.

To lock off, feed rope, just use a gri-gri/similar, inhibit the gri-gri/similar, anchor/don't anchor the belayer, use/don't use screamers; man, it's all a crap shoot when the leader pops off as to which is the "best" technique for a given situation. I guess we go back to: It Depends.

What I do know for sure, if you do need those screamer things, we'll be there to hold the rope!

I agree that the use of Screamers has potential benefits and low risks. I don't want to come across as opposed to their use. I'm interested in understanding how Screamers work, and what one can expect of them.

I did a little googling this morning and located an old letter by John Yates on the "physics of Screamers."

On the one hand, it was disappointing, because Yates does not distinguish between force and energy. On the other hand, it says that the reduction in peak force, as measured by a load cell, is greater with dynamic ropes than with static ropes and attributes this difference to the longer time given to the rope to stretch.

An ideal spring stores an amount of energy independent of how fast it is stretched. When people write the energy balance equation to compute impact forces, the rope is considered an ideal spring. However, a more accurate model consists of a spring in parallel with a damper. The damper dissipates, but does not store energy. More importantly, it makes the rope effective stiffness increase with the speed of elongation. Hence, it increases peak forces. Conversely, decreasing the speed of elongation--e.g., by adding a Screamer--decreases peak forces.

Unfortunately, not much info is available on the damping coefficients of climbing ropes, and the mathematical treatment gets more involved if damping is considered.

As for the via ferrata rigs, the ones I'm familiar with use friction rather than ripping stitches, but I haven't kept current on what's available. In any case, it's a very different setting, because the rope is too short to absorb any significant amount of energy. In roped climbing, even with a Screamer, it is usually the rope that absorbs most of the kinetic energy of the climber.

Brenta,

You might try contacting Yates directly:

Yates Gear Inc.
2608 Hartnell Ave. #6
Redding, CA 96002

e-mail: info@yatesgear.com
Phone: (530) 222-4606

I'd like to point out that, "my friend fell on a screw, screamer deployed, screw is still there, screamers work" is not a very effective argument. Would the screw have held if you had attached a simple runner? I don't know (although my guess is yes). Screw placement power has a lot more to do with the quility of the ice you put it in.

Also, for a study to be fairly trustworthy, it can't be carried out by the manufacturer. I'm sure these are all honest companies we're talking about, but the bottom line is that they are selling the product they are researching.

Now I don't know how the MIT tests were carried out (1995 being before I attended by a fair bit), but I know they are all certainly capable of solving complex differential equations that may be involved in a damped harmonic oscillator. The other piece involved in their proposal, which I have not seen discussed here so far, was the effect of high frequency loading onto the carabiner caused by the stitching ripping out. Since we don't have the results, it's hard to say what the effect is, but it could include opening of carabiner gates, etc.

Thus far it appears that a dynamic belay is far more important than a screamer. However, in order to really know, testing needs to be done that first isolates all the pieces of the system, ie effects of screamer by itself, effects of dynamic belay by itself, and then puts parts of the system together systematically to see how they interact and work together.

Oh man, I forgot the most obvious:

"Do Screamers Work?"

I would say: Yes! If you fall while using one, you will be screaming!!