UKC

No matter what you might think, even for experienced climbers a VF set is an essential purchase if attempting a via ferrata. These two sets from Climbing Technology both offer good value for money and excellent performance.

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In reply to UKC/UKH Gear:

Anybody else think that the way he's wearing the helmet right on top of his head, to an extent, lessens the protection of the helmet, I'm always telling my boys that it needs to be on properly to protect the forehead and the back of the head.....

am I wrong, no one tell my boys.....

In reply to robal:

It looks too small for his head...

In reply to UKC/UKH Gear:

Hi,
I weigh 90-odd kilos. If you factor in a lot of gear and ropes, I could easily top the 100kg mark. Are there products rated for people like me?

In reply to Potemkin:

To be honest, it's people who weigh less who have historically no been catered for as the impact increases as weight decreases with all current systems. The only difference between this (and the other newer child "safe") systems and the older ones are that the stitching is designed to rip at a lower load. This means that as a consequence you need more sling to rip for an adult to absorb the necessary impact - not something which is addressed in the article. It means that you are falling further because of the legislation which has just been implemented. Hey ho. To be honest, even if you were 120kg with a pack etc. I would not be particularly concerned...

In reply to robal:

Helmet looks back-to-front to me.....

In reply to Potemkin:
I weigh about 115kg and tend to end up carrying heavy stuff for the group as I don't notice it...this takes me way over, I'd expect to about 125 or 130 all up...there don't seem to be relevantly rated products about unfortunately. However most VF falls aren't going to be worst-case unless you are on the very hard stuff, which could if necessary be pitched using a rope to mitigate the risk of hitting the bottom of your screamer.

I do recall talking about the idea of adding a second screamer in series (to allow a longer deployment and therefore safely stop a heavier climber falling at the expense of falling further and potentially hitting things on the way) or parallel (to keep the fall distance the same but at the expense of a harder catch) - I preferred the idea of the former but didn't bother as it would make the lanyard unwieldy.

It does seem to be a gap in the market, though.

In reply to beardy mike:


Must admit I find it hard to get my head round this...does the stitching rip at a specific impact force (single kN value) or is it more complicated than that?

In reply to Neil Williams:

It's not a gap in the market, it's purely to do with CE rating. The gap in the market is the one that is now being addressed which is for children who on the old systems received double the impact! And don't forget, the longer the sling deploy is, the more likely you are to hit something which stops you rather than the absorber...

In reply to Neil Williams:


Yes - exactly that. If you apply half the load, the energy is insufficient to make the absorber deploy. So what they have effectively done is reduce the stength of the stitching but increased the distnce over which it can rip to compensate for adult impacts. It's more or less a linear relationship...

In reply to Neil Williams:

Would something like a kong kisa with an extra long length of rope be a reasonable solution?

In reply to robal:


My son (and I) have an awkward head shape and I have struggled to find a helmet that fits properly. In this case the Petzl Meteor is actually a good fit. I acknowledge it doesn't look right in some of the photos but this was a really easy via Ferrata with no-one else on it, and it was about 35 degrees. When it really matters he tightens up the chin strap better than here. He also has 'big hair' which makes it look worse than it is.

Alan

In reply to beardy mike:

So, given that the absorber will rip only until the impact force is reduced to that point, why will a child get a harder catch? Surely their catch will top out at the same impact force as the adult's, just with no need to deploy the screamer to get it down to that force (or deploying less of it)?

It might be that their smaller body can't handle that so a *lower* force is needed - but I genuinely don't understand why they would experience a *higher impact force*.

Just trying to understand, that's all?

In reply to beardy mike:

It's both - there is no device on the market which claims to give me adequate protection on VF. If that's because the CE rating involves a test to 100kg that is in itself no issue - there is nothing stopping a manufacturer going for a higher specification, is there? (That would realistically mean a longer screamer I guess). Or is a longer screamer a breach of the standard? If it is, I would say I consider the standard faulty as it does not allow for a fairly large proportion[1] of the adult population to engage in VF per the specifications of the equipment. If that is the case, there really need to be multiple specifications of set for multiple weight bands.

[1] Most adults don't weigh over 100kg, 75kg is often used for lifts. But once you add clothing, gear, extra gear, a rope, lunch, water etc a far higher proportion will tip over it.


True, but a "dead stop" on the sling is as bad, and unlike whacking your feet against a rock or ledge may cause it to fail and you to fall to your death. (I've always taken the view that VF kits are for preventing death, not preventing injury - you *really* don't want to fall, and if you might it's time to get a rope out).

Edit: interesting, the new standard appears to also increase the required test to 120kg. Might have to grab myself a new one and lose a bit of weight

https://www.skylotec.com/eu_en/2016/08/informationen-zur-neuen-klettersteig...

In reply to Alan James - Rockfax:

My sons dont want to mess up their hair, which is why they wear it in exactly the same way, I keep telling them that they look like their old man so their chances are screwed with or without good hair.....

In reply to UKC/UKH Gear:

The problem that I can see with this 'ripper' VF systems is that, if you take a fall part way up a VF, and the system does its job, for the rest of the VF you have no fall protection left (unless you carry a second VF system). Surely the older Petzl systems that had a friction device to absorb the energy of the fall are better in these circumstances?

In reply to phizz4:


Don't forget that VF systems have a built in redundancy element anyway since you always use them in pairs so as to never be unattached, but they work on their own in case you fall when only one was attached.

It is possible in a really bad fall that you might rip both of them however a full on rescue may well be called for in those circumstances since the consequences of a big fall on a VF are pretty terrifying and the lanyards only really stop you plummeting the full distance, not clattering into all sorts of things as you fall. If you are able to continue after a big VF fall that ripped both lanyards then I would suggest that a bit of DIY knot tying to make them the correct length will protect you sufficiently to finish the VF.

The best idea when you are on a via ferrata is not to fall off.

I don't know anything about the Petzl system you talk about but it is an evolving industry with a lot of recalls. Petzl appear to use a tear system on their current models - https://www.petzl.com/GB/en/Sport/Lanyards/SCORPIO-EASHOOK#.V9gDgTvfQt9

Alan

In reply to phizz4:

Have you try to reset a friction plate system? Good luck with that...

In reply to UKC/UKH Gear:



I struggle with the good value part of this statement. VF kits often seem unduly pricey when you look at the individual components.

In reply to Neil Williams:

I know it's counterintuitive... So think about it in the form of energy and time. The absorber absorbs energy at a set rate. You have to put that energy in whatever to start it ripping. So if you have a lower mass, you have a lower energy. The absorber effectively resists that energy, so because it is a smaller amount, it will stop it in a shorter space of time. This more abrupt stop means that the resultant force exerted is much higher over a shorter space of time. It's a bit like a car crumple zone - the more rigid the crumple zone the sorter the window of time the energy is absorbed over. The issue is really that the previous standard was historically derived from an industrial standard and didn't account for children at all. Now it's been updated, it does, but conversely, adults who's are the majority of users will suffer instead with longer falls and potentially increased danger from hitting things. The thing you need to bear in mind is that although the standard states a set range of weights, that doesn't mean that manufacturers aren't testing to above this standard or that it will be inadequate. Hence why I say you won't need to worry about it - there will be a quite large margin of error built into the system.

As for a dead stop after an extended period of deceleration being more serious than falling 3m onto a ledge being more serious, I'd beg to differ. Chances are that you could break legs, a pelvis, lacerate arteries, smash your head, etc. To my mind at least, these are as significant problems for the vast majority of users as the inverse issue for children was.

In reply to phizz4:
The problem with the frictional devices is that as the set wears and the rope fluffs, the amount of friction is increased to a point at which it will cease to work all together. Both the systems are not ideal for sure. Also you have to be aware that falls on VF can be up to fall factor 5 if you manage to deploy your absorber you really do have major worries as it is a much worse fall even when small than any climbing fall. The maximum fall factor experienced in a standard climbing fall is 2, not 2-3 as suggested in the article. 2mis pretty much the minimum in a VF fall, so you'll be pretty lucky to walk away without at the very least severe bruising. I understand that a reset able system has its appeals but there are inherent problems with them just like the ripper versions. And you can still get this type, I believe from Kong casein and a few others I believe.

In reply to Alan James - Rockfax:



Hang on Alan - are you confused here or am I misunderstanding what you are saying? There are of course two krabs on a VF set but only one shock absorber 'screamer' thingy in the pouch. So phizz4's point is valid, if like you did 'rip' the shock absorber you wouldn't have it to protect you for the rest of the climb, but as you point out, chances are you would need a helicopter anyway to come and get you.

I did a bunch of french VFs this summer on holiday with my kids. Following Mike's advice given here on UKC before we set off, I just short roped my younger son who is nowhere close to weighing 50 kgs yet.

In reply to phizz4: the VFs I did this summer had signs at the start of most of them explaining the friction style devices are no longer considered safe (so you can't hire them anywhere for example). The problem was there was no standardisation of rope pieces used so I think then there was lots of variability in the amount of impact that was needed to make the rope run and absorb some of the impact.

In reply to beardy mike:

Except I'm not convinced it does - and reading the article I linked upthread seems to confirm that idea, namely that the screamer rips at a specific *impact force*, so anyone falling on the set will, assuming they don't reach the end, experience either that impact force, or if they don't rip it then less - the issue being that 6kN (to pluck a random figure out of the air) is going to do a *lot* more damage to a typical 10 year old than it will do to a typical full sized adult with stronger, fully developed bones etc. Therefore the child does experience a lower impact force than 18 stone me, but my heavyweight body frame is less likely to be severely injured by it.

Maybe I am misunderstanding - but has anyone got any maths and related product specifications to confirm what you are saying?


If they were, would they not state this, though? But personally I do think there should perhaps be more than one standard - perhaps three - one for a child (up to say 50kg), one for a normal adult (up to 100kg), one for a heavy adult (up to say 150-160kg, you won't get many people in excess of that all-up who can haul themselves up a VF). I guess the standard writers are concerned there will be more deaths/injuries from mixing them up?


The risk of the dead stop is not that it's a dead stop in and of itself[1], it's that a dead stop is likely to cause equipment failure and therefore for the user to fall to their death. Think slings - a very small slump onto a totally static sling can and does cause sling or harness failure.

[1] Though if I was getting a dead stop, I'd rather get it on my feet (to at least have some hope of bending my knees to absorb some of it) than on a harness, as the latter, due to its not-exceptionally-dynamic nature, would have a fair chance of serious back injuries. I'd rather have two broken legs and need helicoptering off than a serious lifelong back injury. Indeed, as I mentioned upthread a VF kit exists to reduce the chance of you dying in a fall vs. scrambling/climbing unprotected, it is very likely that if you take the kind of VF fall that would rip most or all of a screamer you'll be going down in a helicopter anyway. If you think you're likely to fall, you need to get a rope out.

In reply to TobyA:

Agreed, it's not redundancy as such. The modern ones have one screamer and a Y shaped lanyard, so whatever you have clipped in the same deployment will occur (the lanyards and krabs are rated to work alone if necessary). The old ones had the rope that moved back and forth, so clipping both ends was dangerous as that would leave you with no more protection than a pair of dynamic rope cow's tails.

In reply to Neil Williams: here you go: http://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html

I hope you'd agree that if the force exerted by the sling ripping is constant (I.e. The energy required to rip it is constant) then the acceleration experienced by a lower mass object is greater than a higher mass object. It will come to rest more quickly. I.e. Time to stop is reduced. It is analogous to hitting a harder surface in the link. So yes, impact on the lower weight person is greater.


Because that would be an endless task. Where do you stop? A standard has been set which has been devised by people who have studied what is appropriate and that's what they adhere to. Do you question plug manufacturers how much over spec their plugs are rated to or do you accept their is a margin? In fact, do you ask nut manufacturers how much over the rated strength their is capable of (which would be impossible to say because it varies).

The standard has been written that way because they do not want misuse of equipment to occur. I.e. They don't want a child to get hold of an adult set and die, and likewise they don't want an adult to die because there are multiple standards.


No, it's not. The whole point is that you reduce the force to such a point that by the time you get to the end of the deploy, the energy has been disappated to an acceptable level so as to prevent equipment failure, even if you get a "deadstop". You will at some point stop, and that stop is never going to be smooth!


Ok, so you think that you'd rather receive landing unhindered on your legs from a height of 3-4 metres (distance by the time you slide 2m which is the recommended bolt and cable install distance + lanyard length and hopefully some extension) than the disappated energy after the absorber has fully deployed of let's say 4-7kN which is a regular climbing fall... Hmm.

In reply to TobyA:


Of course, stupid of me. Yes, there is only one shock absorber per VF set. I was looking at a bundle of the two sets we used this summer and saw two shock absorbers! Doh!

Still the advice to tie the system back together to finish the VF remains good.

One thing that we found very useful was a short static (ish) cows tail made from a sling which I mention in the review. I used it to take photos from etc. but it would be extremely useful for people who were getting tired arms and needed a rest. You could use the elastic VF lanyards on full stretch but they tend to be a bit long for that.

Alan

In reply to beardy mike:

Force = mass x acceleration. Less mass at a higher acceleration can result in the same (or lower) force. So no, it isn't.

If the sling rips at a given *impact force*, then the impact force experienced by every user will be that stated figure, or less if it doesn't rip. (It has to be less, or it *would* rip).


I'd question a plug manufacturer/definer of standards if the only standard was based on a 10A current (but people "know" 13A is sort of OK) when many appliances require 13A, yes.

I prefer to use climbing equipment fully within its specifications - but because of this standard I can't.


That's not the same at all, because different nuts have different stated strengths. This is a situation where a standard means that there is (until the new standard) no VF kit certified to be safe for my use, therefore unless I take an unknown risk or do a lot of pitching and annoy other users VF is effectively not for me at all. As it happens I do take the risk but I would prefer the equipment was rated for my use correctly. I'm quite big, but not excessively so.


Yes, I do understand. The new standard has clearly taken that line.


That's relying on the fact that people test over the specification with a margin, though, not on the original specification. And a totally static "dead stop", even with relatively small force, *can* cause equipment failure. Go and take some (low down) short slumps on some slings using old retired gear if you don't believe me


Who's saying I would land unhindered? The new standard does not extend the static sling parts of the equipment, it lengthens the screamer and reduces the impact force required to start it ripping. So the choice is between, with the old standard, getting a dead stop on the end of the screamer, or hitting the ledge on my feet having been decelerated by the screamer, but not quite as much so as in the former case. Yes, I would certainly prefer that scenario.

In reply to UKC/UKH Gear:

Always worth a watch to remind you what a fall might be like and why not to use slings!
youtube.com/watch?v=Z7Y2WgtnemY&

Marq

In reply to Marq:

Interesting that 80kg on a very long fall didn't even nearly fully deploy the screamer.

In reply to Neil Williams:

Yes, does suggest that if you are not too battered after your severe fall you may have enough screamer left to get off the route ok.
Marq

In reply to beardy mike:
Not the first time I agree with Beardy Mike: important to highlight most VF kits don't work for children and lighter people: we're talking about 5% of adult women here so it's not a negligible part of of the population.

We struggled a lot to get safe VF kit which would work for my girlfriend, who only weighs 40Kg. In the end we went for the Edelrid Cable Vario (http://www.edelrid.de/en/sports/cable-vario-oasis-night.html) which allows you to adjust the breaking resistance to the user's weight.

On a different note, nearly all VF kit tests are done with dummy weights. Unfortunately you don't get the same impact force if you drop a 1kg round ball as if you drop a 1kg long stick or, more to the point, a human shaped dummy. the DAV did some VF kit tests measuring deceleration of different dummy parts (head, waist) for different weights of dummies and the results were scary for lighter people. Also not great for very thin people.

Take home message:

If you're average weight/size: don't fall off a VF.
If you're light or thin or a child: REALLY don't fall off a VF.

In reply to Juan S:

What I potentially disagree with (or more accurately find it hard to understand) is precisely *why* VF kits are not suitable for lighter climbers. I certainly agree it is an issue.


Interesting that that one gives a maximum weight of 80kg rather than 100kg - is the standard not mandatory? This appears to be exactly what I was calling for - a dedicated system for lighter climbers.


Most likely you will get a lower one. The laws of physics dictate so - and only because air resistance to a larger object will slow it down.

A 1kg streamlined block of lead would give you the near worst-case fall.


Did they measure impact force? If so, do you have a reference to it?

>

True.

In reply to Neil Williams:

I'm afraid my arguments here are similar to ones you've disliked above. Here is a brief attempt:

VF kits need acertain amout of force to be activated. Say 5KN.

Because F = ma, the smaller the mass of the user, the greater the acceleration.

This means that lighter climbers, such as children or lighter women would experience lethal decelerations when using VF kits.

If it helps, think about the climber being a rock, and the VF kit being a mattress. When the rock hits the mattress, the mattress sinks in a bit, dissipating the energy of the rock. The mattress needs to be soft enough to disipate the fall, but firm enough you don't hit the ground/other things below you. The lighter the rock, the firmer the mattress will feel. For a small enough a rock, the mattress won't sink in at all.


Here is some literature:

(in German): http://www.alpenverein.de/chameleon/public/3db1ff97-911a-e3be-8c0b-023d142d...

(a blog on the DAV results, more readable but in Spanish): http://deandar.com/post/disipadores-ninos

(a paper in English): http://ac.els-cdn.com/S1877705812017249/1-s2.0-S1877705812017249-main.pdf?_...

In reply to Alan James - Rockfax:


Do the Climbing Technology ones not have a point at the apex of the V bit where the two lanyard arms meet for this? We bought two sets of the lightweight Edelrid ones http://www.edelrid.de/en/sports/via-ferrata/cable-ultralite-pro-night-oasis... Basically, you clip a krab in (I found a big plain-gate worked best - DMM Shadow in my case) and it works as a cows tail for resting etc. On the first go I used a sling like you said, but of course you would never want to fall even a wee bit on to that (and I wasn't sure if my kids really understood that), but looking at the instructions more carefully revealed they had designed that feature in and I didn't need the sling! Always reads the instructions etc.

In reply to Neil Williams: Ok, will give it one last go.

So think about what happens with a spring. If you drop a large mass onto a spring, and then drop a small mass onto the same Spring, what happens. The small mass comes to rest more quickly, I.e. It decelerates more quickly. What you have cited is what force the mass will exert to counteract it as it falls. This is not the same as impact force as impact force as shown in the link I sent you also has to do with deceleration and the distance/time it's stopped in. The quicker something comes to rest, the more impact force is transferred back to the falling mass. If you put numbers into the calculator I posted you you will see that as the distance the deceleration occurs over decreases, impact force decreases. Let's say for arguments sake that a 50kg child will come to rest in approx 1/4 of the distance an 80kg adult would. Put the numbers in and you'll see the impact is basically double.

As far as standards go, you'd better stop climbing because rope impact certification is conducted at 80kg for single and paired twin ropes and at 50kg for a single strand of double rope. They just can't conduct a test which covers every eventuality, It just doesn't work. The reason there WAS an 80kg test is because that was the only requirement previously as via Ferrata was regarded as an adults sport. That has changed significantly in the last 20 years and hence they have changed the standard. I swear on my life and my mothers life that you have nothing to worry about. The nut comparison I made is relevant because they build in a margin of safety. My point was that they don't just see the sling so that in a severe fall, you'll be left directly on a fully extended sling. Believe it or not, it has occurred to them that there are people who are heavier than 80kg. Just because a standard states a thing, doesn't mean that manufacturers in general don't test beyond that standard and ensure that their kit is safe to use. The one major omission to this has been children as I don't think the industry foresaw the change in usage of the equipment.

With regards distance fallen and broken legs, let's say previously lanyards would have been 1m long to start with and 2m fully deployed. Now because of the change in standard, it starts off 1m long and ends up 3m long fully deployed. This means that by the time you reach the bottom of the section, and unfurl your lanyard you may have travelled 5m in total. There is a very significant risk that during that 5m, maybe at 4m that there might be a ledge. Think what you like but you are not going to land a 4m fall on your feet and feel happy as Larry. Add to this that on many VF in Italy bolts are spaced outwith standard spacing distance, sometimes 3 or even 4m apart. A 1m deployed lanyard reduces that risk. So in my view as someone who has to assess and make recommendations to manufacturers of this type, the new solutions are not without a serious compromise and one which in my view needs to be mitigated. Any way, nite, and if I don't respond for a while it's cos I'm on the plains of northern France.

In reply to Juan S:
Cheers. So what you are saying is that it is the *acceleration* (deceleration) that is the dangerous thing, and not the force in and of itself, which will indeed be lower for a lighter climber?

If I am following that correctly (am I?) then I can now understand.

In reply to Neil Williams:


Yes, in the case of VF falls it's the deceleration that's dangerous (as well as hitting solid things on your way down of course).

I think I've spotted where you're disagreeing with Beardy Mike. You're talking about the force needed to stop a falling climber (F = ma). He's talking about the impact force. The impact force is directly proportional to the mass (so you're right a lighter climber means less force) but it's also inversely proportional to the stopping distance. As per Mike's example:if you half the weight but quarter the stopping distance, you double the impact force.

Yes, that's it, roughly.

The way I was thinking about it, the stitching rips to decelerate over a longer distance if the impact force exceeds a set figure, say 6kN. Therefore, unless you hit the end of the screamer, the impact force cannot exceed 6kN. If someone doesn't rip the screamer at all, the impact force must be <6kn. so nobody should be able to experience a force of over 6kn unless they are say 200kg and so hit the end of the screamer.

But there must be a flaw in that. I still can't see quite where. I think I need to read some of those studies when I have a little more time.

In reply to Neil Williams:

Been thinking a bit more about what you have been looking at, trying to think of how to explain it adequately. F=ma - so that is the mass of the person multiplied by gravity in this case. I.e. its the force exerted on the person by gravity during the fall, impact force is a separate issue. As long as they are falling, no "work" is being done to slow the fall and no damage occurs.

As soon as the sling starts to rip, work is being done and it is the change in energy which is relevent to how violent the catch is.

If the energy required to unzip the sling is high by comparison to the energy of the falling mass then the rate at which that change of energy occurs is higher, ergo. acceleration is greater ind impact force is greater and that's where the damage occurs - similar to a pilot experiencing high G's in aerial maneuvers.

With a larger than standard spec mass, you are effectively ripping through more sling during the fall, i.e. the time over which deceleration occurs is longer. So providing you don't reach the end of the sling, it will be a gentler catch, not a harsher one. If you do manage to rip through the whole sling then yes you will experience a hard stop, but by that point the amount of energy present with in the system will have been massively reduced. If you think about it, at some point, even if you do not reach the end of the sling there will come a point where the energy you are putting into ripping the sling is less than that required to rip it a which point the system becomes static and ceases to rip, bringing you abruptly to a stop. When I talk about a margin of safety, what I'm talking about is that they sew the slings to a length which they know is going to be longer than required in a heavy fall.

Hope that all makes sense?

In reply to beardy Mike, Juan and Neil - I had the same struggle as Neil to get this - the spring analogy was very helpful, so thank you

In reply to beardy mike:

Doing a sterling job, it's been an interesting thread to follow despite most of it been over my head!

Don't fall off. And especially don't fall off twice...

In reply to beardy mike:
So, to clarify a little further, under what precise circumstances does a row of stitching rip? If the impact force is over the specified value, or something else related more to kinetic energy?

If it's impact force, that's what hurts the body, isn't it? Other than, as I mentioned, that a child's body can't stand a force anywhere near as high as an adult's.

(I'm not being deliberately obtuse, I'm just still finding it really hard to get it - thanks for persisting! )

Edit: this: http://www.climbandmore.com/climbing,440,0,1,brand.html seems to suggest that on the old rope brake systems the force to start the rope moving was higher than the force to continue it moving, which would back up this theory for those systems - but it isn't the same for stitching, is it? That is, each row of stitching stands effectively alone? Or maybe it is, and in that case therein lies the reason.

In reply to Neil Williams:


Once it's subjected to a force greater than X (varies from model to model, under 5 KN). This is the F = ma part (which is entirely different from the impact force). Which is why it breaks more easily for heavier climbers (safer) and doesn't get triggered by lighter climbers (dangerous)


It's the deceleration that hurts the body since there is no impact as such.

You can also think about this in terms of impact force (though doing so is the source of the confusion), but this impact force isn't the one you've been thinking of (the F=ma part). It's the one relating to how fast the climber comes to a stop as Mike and I mentioned above.

VF kits aren't more dangerous for lighter climbers because they can't take as much deceleration. VF kits are more dangerous for lighter climbers because they subject lighter climbers to much higher decelerations than heavier climbers.

A heavy climber will take a while to come to a stop. That's safer because the energy disipates over a longer period, the deceleration is lower. Think of it as a softer catch.

A light climber will come to stop much faster (higher decelerations - more dangerous) . In extreme cases, after falling the same distance, a very light climber won't weigh enough for the stitching to break. They come to stop very suddenly, since their VF kit is effectively useless.

In reply to Neil Williams:

To start with they aren't rows of stitching like a bar tack, they usually are zigzagEd lengthways along the sling. If it was bartacked you would see a break then drop in force before another break etc. So zig zaps just rip smoothly ish.

Kinetic energy and impact force are related directly with mass of the fallee, the distance they fall and the distance in which they stop. The stitching rips at a set force. If that force is not exceeded then it doesn't. This is why a light person is such a problem for old systems, because the rip force (or slide force in frictional systems) was high, meaning that the impact force created was simply not high enough to even start it ripping or if it did stops them in a very short, abrupt catch. This means high energy and high force is transferred. It basically the energy that is doing the damage but it's all related to one another. Will take a look at the link in a second... but typing from a phone so don't want to lose message!

In reply to Neil Williams:

The link is correct in what's saying. We've basically been talking about a simplified model of the system unail now when the rip force is constant. But in reality the initial break takes a little more energy than the subsequent rip. Thing about ripping a small pile of paper... initially you have to put in a bit more effort to start it off... interestingly that mammoth system has varied webbing thickness and is pulled through a frictional device so that as the thickness varies the webbing gets harder to pull through which is to increase the force as it extends progressively so that the adults stop more quickly...