# Minimum kN rating?



## MrRecurve (Apr 5, 2007)

What is the minimum kN rating for climbing gear, for example, I have a pulley that is rated at 22kN, would it be considered safe to climb off? I ask because the lowest rating Ive seen on a carabiner is 26kN.


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## BostonBull (Apr 5, 2007)

It is 22, I think.......


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## rahtreelimbs (Apr 5, 2007)

One KiloNewton is equal to 225 Lbs....22 X 225 = 4950 Lbs.


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## Treeman587 (Apr 5, 2007)

While Rah's conversion is correct, You have to also remember that KiloNewtons are a measure of force. So just hanging, 4950 lbs is the limit. But swinging (adding a centrifugal force) and shock loading will have an effect on the load limit. Which is why we have a WLL, or Working Load Limit. For tree work it is said that a 10 to 1 factor is good. Therefore, You would not want more than 495 lbs on that carabiner to be considered safe.


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## TheTreeSpyder (Apr 5, 2007)

kN is a unit of force; 1kN = 224.8+# of force

Rounded i use 225; this still puts 22kN slightly short of 5,000#


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## Treeman587 (Apr 5, 2007)

TheTreeSpyder said:


> kN is a unit of force; 1kN = 224.8+# of force
> 
> Rounded i use 225; this still puts 22kN slightly short of 5,000#




Umm, Yeah, We said that.


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## okietreedude1 (Apr 5, 2007)

MrRecurve said:


> , would it be considered safe to climb off?.



Probably YES to actually answer your question. Now, according to ANSI standards - NO. That number is 5000# and as youve seen the above calculations, 22kn is not quite that.


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## maxburton (Apr 6, 2007)

I agree. If I were you I'd spend a couple bucks and buy something that meets ANSI standards.


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## TheTreeSpyder (Apr 6, 2007)

Ummmmmmmm sorry, i was doing a few things at once and Rah hadn't answered when i started...

A pulley on the support will lengthen the line taking the dynamics of the forces; so give more elastic response/ dampening; more line is better for this. A pulley(s) on Load; will divide the load between the legs of support, so each will have less tension/ so higher SWL/ so reciprocally less elastic shock absorbtion; So, contrary more line (used like this) to make more legs; is worse for dampening.


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## moray (Apr 6, 2007)

TheTreeSpyder said:


> A pulley on the support will *lengthen the line* taking the dynamics of the forces; so give more elastic response/ dampening; more line is better for this.



This part I agree with. But it would perhaps be clearer if you said "the longer the line, the more the stretch." In the case of a falling load, this definitely affects the maximum force experienced by the line as you indicate.



> A pulley(s) on Load; will divide the load between the legs of support, so each will have less tension/ *so higher SWL*/ so reciprocally less elastic shock absorbtion; So, contrary *more line* (used like this) to make more legs; is worse for dampening.



Here you seem to say that more line has the opposite effect. But it is still true, as in the case above, that the more line the more stretch. I think you mean to say that more lines (not talking about length) will divide the load between them, and also divide the stretch between them. 

In a pulley arrangement where the pulley is attached to the load and there are 2 equal-length supporting lines running to the support, the total stretch caused by a load will be 1/2 what it would be if only a single line of that length were supporting it, and 1/4 what it would be if we turned the whole picture upside down, attaching the pulley up above. A falling load will certainly experience more shock in this case, and so will the pulley, though the rope will not.

So it is possible to have a pulley on the support (your first example) where the shock load on the pulley from a falling load would be MORE than in the second configuration: you just need the distance from load to support in the second case to be at least 4 times longer than in the first case.

Finally, as Treeman587 pointed out, the WLL for this pulley is 495 lbs. It is not a variable. It does not go up or down depending on how you hook up the pulley. Your phrase "higher SWL" seems highly misleading to me. Someone might read this to mean you can somehow get more mileage out of a given piece of equipment by hooking it up differently. You can certainly alter the *actual* load experienced by the equipment (which is what you have discussed), but you cannot change the SWL. It never gets "higher."


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## John Paul Sanborn (Apr 6, 2007)

Treeman587 said:


> Umm, Yeah, We said that.



Yeah, but you were 3 min apart on posting, so he was typing when you posted


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## Treeman587 (Apr 6, 2007)

Not my damn fault I can type faster. GEEEEZ it was just a little sarcasm.


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## Treeman587 (Apr 6, 2007)

While we are on this, Has anyone used that rigging software?

Seems it would be to time consuming, and a waste of labor. When most of the time experience and common sense will guide you to the correct path.


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## treevet (Apr 6, 2007)

MrRecurve said:


> What is the minimum kN rating for climbing gear, for example, I have a pulley that is rated at 22kN, would it be considered safe to climb off? I ask because the lowest rating Ive seen on a carabiner is 26kN.


I ve climbed off a pulley or block and don t like it all. Too different/fast w out any friction. Don t mind climbing off crane hook tho.


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## SRT-Tech (Apr 7, 2007)

i have some bomber triple locker steel biners, NFPA rated for over 72KN.


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## adam (Apr 7, 2007)

What is kN rating of a tree you are about to climb? Use common sense, don't make an assumption that your tree is stronger than your shiny, rated, ANSI standards meeting gear! Unless you're climbing only rated trees, one day all those sophisticated calculations will go crushing to the ground together with your rated gear.


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## moray (Apr 7, 2007)

*friction*



treevet said:


> I ve climbed off a pulley or block and don t like it all. Too different/fast w out any friction. Don t mind climbing off crane hook tho.



Ah, but going UP is so easy and silky smooth. 

Coming down you can really see the difference between different friction knots.


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## SRT-Tech (Apr 7, 2007)

adam said:


> What is kN rating of a tree you are about to climb? Use common sense, don't make an assumption that your tree is stronger than your shiny, rated, ANSI standards meeting gear! Unless you're climbing only rated trees, one day all those sophisticated calculations will go crushing to the ground together with your rated gear.



i dont just access trees on rope. I access buildings, cliffs, canyons, caves, towers. I can rig off the biners, as well as ues them for life support. They are rated for 2 person loads (rescue) as well. Besides steel biners of this professional caliber (NFPA standards makes ANSI look like hacks), take more abuse and are more versitial than regular biners. (and really, who rates trees by a KN rating? WTF?)


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## Tom Dunlap (Apr 7, 2007)

NFPA standards are all based on two person loads in case a rescue needs to be done using what is worn. Using NFPA standards as a comparison doesn't have any standing since the two professions are very different.


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## SRT-Tech (Apr 8, 2007)

fair enough, i like bomber gear.


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## arboralliance (Apr 8, 2007)

*Wow, well...*



Tom Dunlap said:


> NFPA standards are all based on two person loads in case a rescue needs to be done using what is worn. Using NFPA standards as a comparison doesn't have any standing since the two professions are very different.



So Tom,

lemme get this right; you use their ropes with our friction descent cords but you dont advocate using their biners...

Well, I guess a double person biner or a 10 x person biner wont save ya once the sheath is cooked...


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## Tom Dunlap (Apr 8, 2007)

arboralliance said:


> you use their ropes with our friction descent cords but you dont advocate using their biners...



Can you be more clear? Who are 'they' ?

As far as I know arbos are the only rope access workers who descend on friction hitches. That's not an indictment either. Arbos collectively know more about rope on rope friction than any other rope access profession. 

The gear that I use has to meet OSHA and ANSI Z133 standards at a minimum. If I choose to exceed the minimum that's my choice. 

In fact, I'd like to see the Z changed to allow the use of 5k# rated ropes like many other rope access professions. The 5,400# rating is not based on science.


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## TheTreeSpyder (Apr 8, 2007)

i'm sorry if i s-lightly abused the terminology; but don't think i'm the first to do so in this way. SWL (to me) is both a ratio, and a highest load acceptable at that ratio. Different manufacturers, industries and situations; use different ratios; just matching the SWL of a krab and a pulley doesn't necessarily mean their strengths are matched if the calculated SWL ratios are different. We have also spoken of the SWL of a system before; if the weakest link is the line, and we set it as a 2/1; then the SWL of the system changes (though not strictly the line component).

This SWL of a system then could be a given force rating that is safest at an agreed on ratio for dragging or lifting etc. Or, at a given load; the ratio to the tensile; or in other words a measure of the fault tolerance; that SWL is about anyway? If this ratio is 4:1; that SWL might be okay for dragging; but you might stop the procedure if that system was to be used for overhead lifting etc. 

Perhaps a little tib lysdexic; but all to the same end; a ratio margin of safety/ fault tolerance to a given loading etc. In dynamic components like rope, under dynamic conditions; this higher tensile to load/ higher SWL ratio gives less elasticity. The elasticity depends on line materials, construction, length taking the hit(which somewhat counter-intuitively includes line length to 1st hitching on Load; so extending this is a way to squeak more elasticity in/ not more shock if still before the CG) and percentage of tensile used as multipliers. So, as the safety ratio/ fault tolerance goes up (less load to tensile) the elasticity/ dampening reciprocally comes down.

This is also true of 2/1's etc. What i meant about the elasticity with them; is that adding more line to extend control end gives more elasticity; while using the same addition of line for more supports to the load decreases elasticity; as a flip side to 2 different ways to add line length(like if only had 100' of line to use, adding it as legs to load decreases elasticity; while using it in system other ways increases elasticity). But, adding more length to the 2/1 legs will help mediate that, yes. Please note, a 2/1 drop in elasticity is not just neatly 1/2 loading on support/pulley. i think

For potential static load on support for both these scenarios; Load + Load/legs to load is fair. So, a 1:1 gives 2x loading at support, but that drops to 1.5x for a 2:1 and 1.333_ for a 3:1 etc. So, we could feel safer with a higher power system to the same load. But, in a dynamic loading; the more legs to load reduce the elasticity, thereby increase the potential loading on a drop, but (same 2/1 system) decreases loading on a static hang.


Enclosed is a chart maid years back with the Rigging Calculator. The calculator is not something you take to a job, but rather sit at home and find patterns to make judgemeant calls later with i think. It has 3 different categories: Line length as variable, Height of CG as variable and Load per leg as variable respectively; to sift these same patterns out of/ confirming deeper correct paths, and perhaps showing fault to other thoughts? Also, the StableBraid / Yellow is most extensive tested; showing how same materials and braid; just set to different tensile strength/ diameter varies things.

In DdRT we have a 2/1(less friction) over our own selves(in this folding force back on it's self scenario, to contain closed force system); but at a loss of elasticity/ shock dampening. All the rope lessons have consequence on climbing (and vice versa) too.


Edit: Tom; in single use, eye spliced devices, perhaps 'software' tensile should equal hardware tensile(?). But in repetitive use devices shouldn't the wearable software have higher ceiling, to allow it to drop/wear in to closer to matched components over useful life? Also, in an open system of rigging, 'room' left for a knot decreasing a line's remaining tensile to closer match krab etc.? Pulley and pulley attatchmeant devices as higher rated, but other single leg of loading hardware; could be rated less than line; to allow line to match after wear and knots.

Smaller Version of Attatchment:


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## moray (Apr 9, 2007)

TheTreeSpyder said:


> i'm sorry if i s-lightly abused the terminology



TS, I know we discussed working load in an earlier thread, and I remember jumping all over you then as well. I hope I haven't been impolite or too harsh.

I am sure there are many people on AS without your understanding of math and physics, but they still have to deal with ropes and forces and angles and loads and mechanical advantage and friction every day, all of these things connected through a tangle of math and physics. Fortunately, for most simple daily operations, the load on your lifeline is never much more than a couple of times your weight, so you don't have to worry about the math. But when you get into the world of rigging, or dynamic loads, or complicated pulley arrangements or redirects, you need to start paying attention to the numbers.

I have recently started experimenting with Tyrolean traverses that I rig up between some big pine trees in my back yard, using half inch Stable Braid for the traverse. While researching the subject online, I ran into a rock climbers' newsgroup where someone asked about how to calculate the load on a Tyrolean he planned to rig across a narrow canyon. Four or 5 people responded they didn't have a clue, but thought there was a formula somewhere, but one person actually supplied a calculated answer. It was wrong, off by a factor of 2. Fortunately, the true load would have been half what was suggested, so the advice, while bad, was on the safe side. But would this climber have actually set up a Tyrolean just from advice received online, without being able to check it for himself/herself? Would they ever have had the ability to specify the Tyrolean without outside help? It worries me.

So this stuff matters. I make my own calculations when the occasion arises, and enjoy the challenge of deriving the numerical relationships and expanding my understanding, as you seem to do as well. But I realize not everyone has the background that would allow them to do this. I hope no one is foolish enough to take anything I say to the Bank. They should do their own figuring, or get some other opinions, and AS is a great place to do that. Nevertheless, I try hard to get my facts straight, and I try to be clear. I don't want anyone to experience a nasty surprise because they relied on something I said that was wrong or misleading.

If I jump on you again in some future thread, at least you will know where I am coming from...


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## arboralliance (Apr 10, 2007)

*Yeh,*



Tom Dunlap said:


> Can you be more clear? Who are 'they' ?
> 
> As far as I know arbos are the only rope access workers who descend on friction hitches. That's not an indictment either. Arbos collectively know more about rope on rope friction than any other rope access profession.
> 
> ...



NFPA abseil ropes being "they", I am referring to last years thread on the use of Arb' specific ropes as opposed to Mountaineering ropes...:deadhorse: 

Thank you for giving me the opportunity to discuss this civilly with you Tom, I apologize now if due respect is not transpired in my post/s, it is with respect of your presence in the industry that I challenge you on this with faith you will debate carefully and succinctly and we can all learn as I have in the past from careful and pointed debate...


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## Tom Dunlap (Apr 10, 2007)

arboralliance said:


> NFPA abseil ropes being "they", I am referring to last years thread on the use of Arb' specific ropes as opposed to Mountaineering ropes...:deadhorse:
> 
> Thank you for giving me the opportunity to discuss this civilly with you Tom



You have a better memory than me  I can't remember what was said about the ropes last year. The ropes that arbos can use in the US must be approved for treeclimbing by the manufacturer. As far as I know there aren't any ropes that are banned for use by arbos. 

The point that I was trying to make was that there are very different strength and use standards for NFPA and arbos. All for good reason too. 

There is nothing in our discussion that would make me think that we aren't carrying on a civil discussion. Let's keep it going


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## TheTreeSpyder (Apr 16, 2007)

Tom Dunlap said:


> There is nothing in our discussion that would make me think that we aren't carrying on a civil discussion. What is a lil'smooshed Spyder? Let's keep it going



Yeah, ummm what he said... (i think)



Perhaps me using the 'word' backwards isn't right. i see were WWL is varied for a device; by type of knot or sling type position. Which is closer to my meaning (a ratio of loading to capacity to give fault tolerance) that is better statically, but there is a change in that dynamically, by the elasticity. 1 leg of line/support taking impact has value X. But, with 2 legs of support line; they will have 1/2 the load each of the single support scenario; but with impact force; they will each have more than half the impact of a single leg of support..... For quite a range; until this is reduced by enough line or other (support flex) elasticity in the system. 

So, even though a ground controlled 2:1 has less support load than a 1:1; if the length from impact to support and/or control tail is not long enough, the 2:1 will give more support loading than the 1:1 for impacts. The tension on all parts of the rope is lower, so the elasticity is lower to dampen the forces. But, Moray's 4x rule is fair. In many loading patterns 4x distance, line etc. is what it truly takes (in calculations) to cut forces in half.

Speedline/ Tyrolean (full functions work best in IE) supports have non-inline legs of support; so are leveraged against by the load. It is easy to forget to divide the load in half, before calculating that on each of the supports x angle; and thus come up with 2x loading. If you need a control leg to alter tension by; there comes a 3rd angle of tension to deal with in a Double Whip Tackle. With IE the Excel plug-ins work best for calculating your own numbers.

i really think lessons of climbing shouldn't be overlooked for sifting comparisons etc. from to rigging. As a climber we are both the load and the control; i think many lessons in 'feel' to be gained in that unique position. How rope pulls on a load, elasticity, friction etc.


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