UKC

If I buy a sling with a 20Kn rating, does that mean it will bear weight of up to 2 tonnes before braking?

In reply to saturn:

Weight = mass x gravity

20KN is already a weight, if we are being pedantic. But we can divide 20,000N by gravity, 9.8 to find the mass in Kg.

Being a bit fast and loose with the numbers, yeah its rated for about 2 tonne.

But then if the climbing gear standards are anything like the lifting gear, pipe pressure etc standards, they will have some safety factors in it so the design breaking strength is higher than the rating.

In reply to jdh90:

If a climber weighs 10 stone, how much extra force is added to that weight if they take a fall, and how much does that force increase by the longer he or she falls?

In reply to saturn:

Yeah part of it how fast your falling, so the longer the fall the faster they are travelling.  How much slack is out is important, so is the fall factor.

But the other really important factor is how quickly they are brought to a stop.

As the decelleration time gets closer to 0s, the force required to cause that stop gets infinitely higher.

Things like elasticity in the rope, knots tightening, belay device slippage, belayer getting moved about etc all increases the time it takes from starting to slow them down to actually coming to a stop, which means the shock load is reduced.

As far as I'm aware, gear is designed around a certain scenario, like prescribed weight taking a fall factor two fall over a certain distance.

In reply to saturn:

Depends on the length of the fall compared to the amount of rope out.

Worth checking out the YouTube channel How Not to Highline.

In reply to saturn:

There are so many factors involved in how those Kn ratings are measured that in real life your conditions will be slightly different and also a lot of kit might on average break slightly higher if you tried to break test

Because of all that taking the figures in your context with academic accuracy is a fool's errand. Just use a factor of 10, it's more than accurate enough for your purpose.

1Kn = 100Kg

20Kn = 2 tonnes

(Yes I'm an Engineer not physicist. Yes,  I used that "=" above to bait/enrage the pedants. I nearly used ton instead of tonne as more bait, but thought the thread would explode )

In reply to CantClimbTom:

Factor of 100 surely?

In reply to saturn:

20kN (small k, big N) would be the safe working load (SWL) for a static load. But static loads are rare, and you can generate 20kN with a much smaller weight if movement is involved, as in catching a falling weight, which is what fall factors take into account a bit. We instinctively understand dynamic loading - if you were on the end of a rope at its strength limit you wouldn't bounce around would you|? And we walk 'softly' over thin ice. This to avoid dynamic loading where the  accelerations involved have reaction forces that can add to the gravitational forces in play. The sums are complicated unless this is your day job, with inertial impulse, rope elasticity, strain deformation and friction factors playing a part. All that said, the SWL will usually have a safety margin so the rope doesn't fail as soon as it sees 20kN, and the degree of stretch in a climbing rope at that point will be noticeable. Less so in a dyneema sling.

In reply to Iamgregp:

10 instead of 9.8 I took this to mean..

In reply to Iamgregp:

Yes, I was nerding out on g as 10  (rather than ~9.81) and had that stuck in my head

In reply to CantClimbTom:

Gotcha.  Was a genuine question.  Started to think I didn't understand the word factor!  Which is very possible, I'm terrible at anything to do with numbers.

Are Dyneema slings just the exact same material and consistency of a harness belay loop, albeit longer?

In reply to saturn:

Comparing my dyneema slings to my belay loop, I'd say the belay loop is wider, thicker, less supple.  So even if they are the same material, I'd expect different characteristics between the two.  All other things being equal, stronger belay loop due to extra material. But perhaps some other characteristic differences from a different weave.

Because they feel so different, I'd question whether the belay loop on my harness is dyneema at all or another material like nylon.

If I was designing a belay loop I'd be keeping in mind other factors like abrasion resistance or even temperature if its going to be near a carabiner thats just done a long abseil.

In reply to jdh90:

They are not. Lifting gear will be rated to lift the specified load, so will have a large safety factor, at least 5x and probably 10x. So a 1 tonne lifting sling will hold a static weight of at least 5 tonnes. Climbing gear specifies the breaking load. So a 20kN sling will be designed to hold a static load of 20kN. It will hold a little more just to account for manufacturing variance, but nothing like the safety factor on lifting gear.

In reply to Hooo:

Interesting, thanks. Is climbing gear failure a total tensile/shear failure or a yield/deformation?

In reply to Hooo:

A very good point that.

This BD page provides a good idea of how much variance there is in climbing gear. All of the new/unused stuff failed in excess of the specified breaking loads, some by quite a large margin.   

https://www.blackdiamondequipment.com/en_US/stories/experience-story-qc-lab...

The 'How not to slackline' and 'Hard is Easy' YouTube channels also provide loads of interesting testing to destruction and force generation measurement videos. 

In reply to Phil79:

https://www.youtube.com/@HowNOT2

https://www.youtube.com/@HardIsEasy

In reply to Hooo: in materials testing for metals , concretes and probably fabrics too, results from a number of tests on the same material specification will vary, and when plotted will roughly follow a normal distribution (bell) curve. The specified strength for the group is usually set at the level at which  95% of tests pass, so the mean (average) failure load will be above the specified strength. On average then, this will give you a bit of fat over the specified strength. Remember that  5% of test results fall  below the specified value though. In structural design design loads effectively have a safety factor applied before calculating the size of a structural member, which gets round the 5% that will fail, and other safety allowances often overlap. 

In reply to Hooo:

Pedant warning! It's 7:1 for lifting equipment

In reply to saturn: climbing gear is for shock loading rather than static loading, thankfully elasticity in dynamic climbing rope greatly reduces the peak load in arresting a fall. The peak forces in a long lead fall using a static rope would snap your body long before snapping the rope or runners

In reply to saturn:

There's a calculator on this page: https://www.alpinetrek.co.uk/fall-factor-calculator/

Stick in weight of climber, fall distance and rope out and get the force in kN. Equations too. 

In reply to Fiona Reid:

There's some good info there, but they didn't point out that the calculation is the force on the climber. The force on the gear will be higher, and nearly always the more important number.

In reply to kevin stephens:

Has a climber ever been 'snapped' or severely injured in that way? There must have many long falls before dynamic ropes and frequent runners.

Menlove Edwards held Noyce in a 180 ft fall on hemp rope and Noyce was badly injured but not by the rope itself AFAIK. Of course the belay would have been dynamic (Edwards' hands badly burnt, body belay).

IIRC there was a death in the Cairngorms when a climber's back was broken due to a homemade chest harness but with dynamic rope and waist belaying.

In reply to oldie: I think hemp rope may have been a lot more dynamic than modern static caving ropes. Also waist belays would have been a lot softer catch?

In reply to Hooo:

A very good point.  FWIW, I actually started hunting for the calculations after looking at the article on the breaking strain of dynema mentioned in this post:

https://www.ukclimbing.com/forums/gear/giving_away_an_old_harness-770392?v=.... 

I got a bit spooked with how much strength it loses (most of my trad quick draws are dynema) so wanted to get an idea of the kN likely to be generated in a fall. I'm now fairly happy that I'm unlikely to snap a quick draw and unless I take a big lob on a micro the gear is likely good too. 

In reply to oldie:

I think, although I'm not certain, that the climber who was killed on the Muir a few years ago might  have died in that manner; fell to the end of the static haul line, which would have been simply tied off rather than belayed. It's also possible, of course, that the dislodged rock which had cut the lead rope hit him when he stopped falling.

In reply to Wide_Mouth_Frog:

Time to up the pedantry: 

Some lifting equipment has a factor of safety of 7:1. It can be a lot lower.

In reply to Fiona Reid:

When you say unlikely… it’s just never going to happen to a draw that’s not already damaged.

In reply to kevin stephens:

I've no idea about hemp rope being dynamic but I can't imagine it stretched much. There was some criticism of nylon ropes early on because the stretch might mean a climber was more likely to deck. Showell Styles described a lifeless body dangling back up in the air after hitting the ground. Modern methods of belaying and frequent runners must make this even more unlikely.

Waist belays would be dynamic ie soften catch. I always wore gloves when belaying a leader to prevent burns if the rope ran through a lot (using nylon rope). The waist belay method advocated by Tarbuck (50s/60s?) in the UK with a twist round the braking hand probably greatly increased braking ability (I don't think the twist was widely used abroad, eg USA, but I may be wrong). Perhaps a good waist belay in ideal conditions can even approach the stopping power of an original ATC? Probably the waist belay would be even safer nowadays with more frequent protection . I'm musing here and not advocating it's use.

In reply to iani:

Worth noting that the standard is normally stricter than that for climbing gear ratings. 3-sigma is often used, which requires 99.7% of failures to be above the rating.

In reply to CantClimbTom:

After you have made the correction of x 100 instead of x 10 remember that the human body will start to display various aspects of breaking apart at about 7kN. ((A Newton is a force not a weight!)

In reply to Luke90:

Interestingly (because they didn't visibly shout about it to my memory) DMM were the first to implement 3 sigma testing for climbing equipment:

https://dmmwales.com/pages/quality

Wild Country crowed loudly about it back in 2012, they soon after got stung by a dip in quality (moved production line abroad) meaning that they needed to issue a product recall for many batches of rocks around the same time as the quality didn't meet the heavily advertised 3 sigma standard:

https://dmmwales.com/pages/quality

https://www.wildcountry.com/media/pdf/4b/91/62/Wild-Country-Voluntary-Recal...

You probably know all of that anyway Luke but I thought it would be relevant extra information for the thread.

In reply to Luke90:

No, the standards give a value to be exceeded and nothing else.

In reply to jimtitt:

Sorry, yeah, my use of the word 'standard' was a bit loose. I didn't mean to imply it's actually a formal part of 'the Standard'. I just meant that it wouldn't be normal/common/typical/standard for any climbing gear manufacturer to accept a 5% failure rate!

In reply to johncook:

Yeah, the breaking strain of a human spine in shear (unpleasant thought) is lower than a 22kn sling for sure.

But the original question related to weight versus kN and we can do that with a fudge factor of 10 as g for rules of thumb type calculations (not actual correct physics)

Ignoring those pesky m^-2 and following our American cousins who used lbs for both force and weight then we would have that xkN=100xkg and as mentioned I used  "=" purposefully  rather than say "~" as pedant bait

(lbs and lbs force used to enrage my inner pendant, but it does mean that rocket fuel impulse comes out in dimension: seconds, which although blatantly wrong, is kind of elegant)

In reply to Fiona Reid:

That calculator gives force on the rope/climber, but not on the top piece of gear which is typically the more interesting value as it is a higher number and gear is generally rated lower than rope.

In reply to spenser:

Hm? I could have sworn that the production move happened after those Rocks were produced.

In reply to Alkis:

My memory suggests that they attributed it to issues with the new production line (which I had thought was abroad). I may of course be totally wrong as it was more than a decade ago and I didn't own any rocks at the time.

The closure of Tideswell was several years later.

In reply to spenser:

I seem to remember that it was before production moved abroad. I’ll ask my WC friends.

Yeah, my climbing partner was doing his year in industry there when they closed, and got shipped off to Italy for the remainder of the year.

In reply to CantClimbTom:

Nerd more...

Gravity of Earth - Wikipedia

https://en.wikipedia.org/wiki/Gravity_of_Earth#:~:text=Gravity%20on%20the%2....

It varies about 0.7% apparently. 

In reply to jdh90:

Being pedantic, ropes* are tested using a FF1.7 fall with an 80kg mass as shown on page 2 of this .pdf: https://www.theuiaa.org/documents/safety-standards/Pictorial_UIAA101%20Dyna...

However, it is a minimum standard they have to achieve to hold the UIAA Safety Label/CE Mark. They are designed to the performance characteristics the manufacturer is hoping to achieve, hence why impact force, handling, cut and abrasion resistance etc all vary from one brand or model to another.

*I am assuming you are discussing ropes due to alluding to a FF2 fall. There is no dynamic test for slings, for example, just a static test to 22kN.

In reply to saturn:

This is a complicated topic and is often confused by certification tests, lab tests using "dead weights" and a lot of conjecture.

In a climbing fall, in very simplistic terms (ignoring friction in the rope system) there are three locations where a force acts: the belayer, the top bolt/piece of gear and the climber.

Ignoring friction, the forces on the belayer and climber added together approximately equal the force on the top piece of gear.

The main way of reducing peak forces is by elongation of the rope. The more rope if between the climber and the belayer, the more the rope can stretch and the lower the peak force will be. This has lead to falls being described by a fall factor.

The fall factor is calculated as the length of the fall/the length of rope. In a scenario when a climber falls when they are 7m above their belayer, and 1m above the gear, the fall is 2m and the rope length is 7m, so the fall factor is ~0.3.

In this scenario, with a standard belay with limited friction in the system*, "real world" tests show the forces to be approx:

Belayer: 1.5kN

Top Bolt/Gear: 4kN

Climber: 2.5kN

*i.e. including friction from the rope running though krabs but excluding rope drag due to poor gear extension and the rope rubbing against the rock etc.

So, that's for a relatively common, safe (in terms of load on the gear etc) fall. What would increase those loads?

Fall Factor - Bigger falls compared to rope length will put those numbers up. A similar scenario tot he FF0.3 fall but FF1.0 would increase the loads by approx 50%.

Friction - Rope drag will increase the loads on the top piece of gear and the climber but decrease the load on the belayer. This is because drag effectively increases the fall factor as it decreases the effective rope length that can stretch to reduce the peak load.

Belay devices - Using the same belay technique, some belay devices give a harder catch then others and this affects falls with a larger FF more.

Hopefully this gives you so idea of what happens in a fall, some "real world numbers" on the forces involved and an idea of what can affect those numbers.

This is VERY simplified to get you started but please feel free to ask more.

In reply to galpinos:

Not scientific research but has some of the answers 

https://youtu.be/m8z6adEqaOs?si=F6wb_jsweNNt-lFc

In reply to CantClimbTom:

The end result of this was a peak force below 5kn on the bolt. I've seen other videos where people have tried the hardest catch on a factor 0.8 and got similar results. This correlates well with the recommendation of 'safe' gear for climbing (e.g. BMC recommendation not to use certain micronuts). I personally draw the line at 5kn for 'safe' gear and won't use anything less (and prefer 6-7kn for most things)

In reply to Ian Parsons:

Googled and it is correct that the climber died from the impact after a 280 ft fall on a tied off static haul line. It seems the impact may have been taken on a chest harness not designed to take a fall, rather than his sit harness. Coincidentally the fatal accident (on dynamic rope) in the Cairngorms was also on a chest harness, homemade IIRC. Possibly the Yosemite fall might not have been fatal on a sit harness and with a dynamic belay. 

In reply to timparkin:

I own a DMM "HB" brass offset in size 0 as it was part of a set, but it's only ever been deployed for use as a comedy prop. The day I ever use that on rock? will be a truly desperate brown-trousers affair. Not sure I trust it for more than bodyweight (assuming a good placement) even then I'd be bricking it.

In reply to oldie:

It turns out that the original report of the haul line being attached to his chest harness was incorrect; it was actually clipped to the haul loop on the back of his sit harness. See telemon's post fourth down here:

http://www.supertopo.com/climbing/thread.php?topic_id=2141546&tn=300

and Tom Evans' El Cap Report the following day:

http://www.elcapreport.com/content/elcap-report-52013

In reply to saturn:

I wonder what lies behind your question? If it is ‘what KN rating do I need my gear to have?’ my answer, for my own purposes, looks like this:

Most karabiners are well strong, just try not to cross load them.

For runners, anything over 7KN is pretty solid. 5 or 6KN less so, but still strongish, 4KN is the lower limit and much more likely to fail. Anything under 4KN has psychological value but will likely fail in a fall.  

I’ve placed RP0s and been very relieved to do so, but it’s to compose myself before placing better gear, not to lob onto.

Soft gear like slings loses strength with age, so I’d want 150% or 200% of those values if the kit is a few years old.

In reply to mrjonathanr:

Do you mean 'Soft gear like slings loses strength with wear'? Or do you know something about degradation of unused kit that I don't?

In reply to john arran:

There are a few answers to that. In respect of your question, probably not. Things you will already know:

Guidance for professional use of ropes and webbing recommends always retiring after 10 years, as nylon is assumed to undergo significant strength loss over a decade even if never removed from packaging. How that stacks up in real world application is open to debate. The table at the bottom of this is typical:

https://www.mtalpine.com/when-to-retire-a-climbing-rope/

Nylon loses strength with use and UV- UIAA info on weakening of ropes and slings

https://theuiaa.org/documents/safety/About_Ageing_of_Climbing_Ropes.pdf

BMC advice:

https://www.mountain-training.org/media/qeaepit1/bmc_ropes_-_a_guide_for_cl...

In reply to mrjonathanr:

From that article:

"Ageing caused only by storage can
almost be neglected compared with
ageing during use. This also holds for
ageing by the influence of ultraviolet
radiation; ropes may lose their colour
with time, but virtually no loss of
strength (more precisely, no loss of en-
ergy absorption capacity over an edge),
because since the beginning of the
1960’s all perlon and nylon (poly-
amide) has been UV-stabilised."

As I suggested earlier, nylon certainly weakens with use (particularly so if visibly abraded, I believe), but I'd be gobsmacked if there was any evidence at all of it significantly weakening simply with age.

In reply to mrjonathanr:

On reflection, I’m wondering if Saturn is a human being, or a computer programme.

In reply to mrjonathanr:

I'm 50/50 between Saturn being a bot, or a ten stone man that thinks ten stone is average for a man, with no climbing experience but on a mission to begin lead rope soloing on crags they aren't sure whether or not they are allowed to be on.

...and a habit of starting threads but not engaging much after the inital question.

In reply to mrjonathanr:

I reckon they're on another planet.