# Load ratings of climbing equipment?



## pdqdl (Dec 31, 2009)

Do you ever wonder how much weight your climbing equipment is rated for? If you look real close, most hardware has a number stamped on it followed by a "Kn". This stands for Kilonewtons.

While this isn't exactly proper physics, one Kilonewton is equal to 225 lbs (actually 224.808942443 lbs)

So that 27Kn carabiner should be rated to hold a force of over 6,000 lbs.


*******************************************************
Of course the folks that don't use the "English common" weight system won't be concerned with that problem, as they will be converting kilograms... One Kilonewton =102Kg (Actually 101.64525412649).

So that 27Kn carabiner should be rated to hold a force of over 2,700Kg.
(I wonder why the conversion is not an exact multiple of 10 ?)


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## RacerX (Dec 31, 2009)

pdqdl said:


> Do you ever wonder how much weight your climbing equipment is rated for? If you look real close, most hardware has a number stamped on it followed by a "Kn". This stands for Kilonewtons.
> 
> While this isn't exactly proper physics, one Kilonewton is equal to 225 lbs (actually 224.808942443 lbs)
> 
> ...




Care to explain what you're questioning?


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## jefflovstrom (Dec 31, 2009)

:monkey:
Jeff


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## treemandan (Dec 31, 2009)

It's not that I wonder about the load rating on the gear but more-so wonder if I fell asleep and woke up in Europe. I swear one day I am gonna kill that Dewey Decimel son of a #####.


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## ArborSmithNw (Dec 31, 2009)

treemandan said:


> It's not that I wonder about the load rating on the gear but more-so wonder if I fell asleep and woke up in Europe. I swear one day I am gonna kill that Dewey Decimel son of a #####.



Close. 
It's more that the manufacturers woke up and started selling more here in the states, the cost or restamping dies must be too great (plus the french are too proud a people to change things for Zee ozer people'z)


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## treevet (Jan 1, 2010)

My biggest worry is the ability to withstand shock load by all these contemporary devices such as microcenders, ascenders, rope grabs and the like. If some lard ass falls off a limb and after two or 5 feet before engaging, the device is all that is to save him being the weak link in the chain....somebody is in big trouble. I have also read of some instances that rope grabs when shock loaded have severed support lines.


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## John Paul Sanborn (Jan 1, 2010)

treemandan said:


> I swear one day I am gonna kill that Dewey Decimel son of a #####.



What does a library card catalog have to do with anything 



> *Britannica Concise Encyclopedia:
> Dewey Decimal Classification *
> 
> 
> System for organizing the contents of a library based on the division of all knowledge into 10 groups. Each group is assigned 100 numbers. Subdivisions eventually extend into decimal numbers; for example, the history of England is placed at 942, the history of the Stuart period at 942.06, and the history of the English Commonwealth at 942.063. The system was first formulated in 1873 by Melvil Dewey. Many libraries add a book number created from the Cutter-Sanborn, Tables, which further specify author and genre. The Library of Congress Classification has largely replaced the Dewey system.


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## treemandan (Jan 1, 2010)

John Paul Sanborn said:


> What does a library card catalog have to do with anything



Dam you Dewey, dam you!


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## pdqdl (Jan 1, 2010)

RacerX said:


> Care to explain what you're questioning?



Notice that the conversion factor for Kilonewtons is NOT an even multiple of 10; rather, it is 101.64525412649. The whole purpose of the metric system is to keep things simple and easy to convert. 

This small deviation is not enough to make much difference to most folks, but it points out to me that there is some facet of the kilonewtons (force) to Kilograms (mass) conversion that I do not know or understand. I suspect that it is related to the acceleration due to gravity, but I am not sure.
(defined to be precisely 9.80665 m/s2 )


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## tree MDS (Jan 1, 2010)

treevet said:


> My biggest worry is the ability to withstand shock load by all these contemporary devices such as microcenders, ascenders, rope grabs and the like. If some lard ass falls off a limb and after two or 5 feet before engaging, the device is all that is to save him being the weak link in the chain....somebody is in big trouble. I have also read of some instances that rope grabs when shock loaded have severed support lines.



I worry about the micro ascender on my lanyard when I have to push a top or log real hard. Its in the heat of that moment that thoughts like this enter my mind...is this thing really that tough? is it made for this sort of abuse?? I realize this can be avoided by simply putting a rope in the piece, but I'm just being real here. It happens.


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## JeffL (Jan 1, 2010)

My biggest worry is whether or not my spine will withstand a 4 or 5 foot fall and shockload.


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## tree MDS (Jan 1, 2010)

JeffL said:


> My biggest worry is whether or not my spine will withstand a 4 or 5 foot fall and shockload.



Still better than shockloading the pavement coming from 50' up.


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## treevet (Jan 1, 2010)

pdqdl said:


> Do you ever wonder how much weight your climbing
> 
> While this isn't exactly proper physics, one Kilonewton is equal to 225 lbs (actually 224.808942443 lbs)
> 
> So that 27Kn carabiner should be rated to hold a force of over 6,000 lbs.



Well since we are talking climbing gear and not many fat asses even come close to tipping the scales at 6000 lbs we are obviously talking shock load here. I can just picture our friends at ANSI sitting around a big table and Joe says...."Let's make sure a fat ass that slips off a limb and hasn't pulled up slack will fall 5 feet and be ok .....but if he falls 6 feet....well....maybe he deserves it.


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## John Paul Sanborn (Jan 1, 2010)

My understanding of the ANSI load ratings was that these were the SWL of the then available product, e.g. ropes and snaps. People wanted Arborplex to be adopted as the minimum standard.


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## treevet (Jan 1, 2010)

John Paul Sanborn said:


> My understanding of the ANSI load ratings was that these were the SWL of the then available product, e.g. ropes and snaps. People wanted Arborplex to be adopted as the minimum standard.



Boy, that Arborplex was (is?) some miserable stuff. We used to call it "garbor plex"

If they haven't yet rated all these mechanical ascend/descend devices at ANSI they will soon I'm sure. On a slip off a branch or spike peel out I would take my NE Safety Blue w/ taughtline anyday over a miniscender, uniscender, grillon, or any of these exotics but I still use em. How often do you inspect the block that is taking half a leader on shock load over the middle of a house with a slate roof?. We love the thrill and danger of the unknown (unsure) and tee it up and let her fly. What a rush.

most of the time we are working on educated guesses


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## treemandan (Jan 1, 2010)

I went down about 10 feet til my srt line found a crotch it liked better. I was tied to the rope with a Petzl hand ascender, no problem.


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## ArborSmithNw (Jan 1, 2010)

Would it help to know that the load ratings stamped on the gear are something like 40% lower than the actual breaking point? So even a 825 pound fella should be cool! And to me, ANY man that size would be cool, imagine the logs that grunt could shoulder!!!

The one thing that you have to worry about in addition to improper usage is large gouges in the aluminum, they can lead to micro-fractures and cause the piece to fail.


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## outofmytree (Jan 1, 2010)

In physics, force is what changes or tends to change a state of rest or motion in an object. Force causes objects to accelerate, add to the object's overall pressure, or change direction. Force is measured in Newtons (N).

Force has both magnitude and direction, making it a vector quantity.

In english then, force is variable and mass is not. So you cannot use the same measure for both. Newtons for force and pounds/kilograms for mass.


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## John Paul Sanborn (Jan 1, 2010)

outofmytree said:


> In english then, force is variable and mass is not. So you cannot use the same measure for both. Newtons for force and pounds/kilograms for mass.



Since mass and weight are the same here on Mother Earth, isn't it the same in our applications?


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## SINGLE-JACK (Jan 1, 2010)

pdqdl said:


> Notice that the conversion factor for Kilonewtons is NOT an even multiple of 10; rather, it is 101.64525412649. *The whole purpose of the metric system is to keep things simple and easy to convert.*
> 
> This small deviation is not enough to make much difference to most folks, but it points out to me that there is some facet of the kilonewtons (force) to Kilograms (mass) conversion that I do not know or understand. I suspect that it is related to the acceleration due to gravity, but I am not sure.
> (defined to be precisely 9.80665 m/s2 )



_*"The whole purpose of the metric system is to keep things simple ..." *_

Well, it is intended to be simple _WITHIN_ the metric system = Meter-Kilogram-Second (MKS) system:

1 Newton is defined in the MKS system as the force necessary to provide a mass of 1 Kilogram with an acceleration of 1 Meter per Second per Second, which is simple enough.

1 kiloGram is defined as the force of gravity on the _International Prototype Kilogram_ which is almost exactly equal to the mass of one liter of water, which is simple enough.

The "small deviation" (101.64525412649) is due to the difference in the force of gravity on the _International Prototype Kilogram_ and the force to accelerate the _International Prototype Kilogram_ to 1 Meter per Second per Second. The inverse is referred to as the Gravitational Constant, "9.80665 m/s2".

1 kiloNewton = 1000 Newtons

*However: "... easy to convert."  ... not so much!* 

Conversion from the MKS system to the “English” Foot-Pound-Second (FPS) system is simple with a single conversion factor, just not straight forward:*

1 Pound-force is defined in the FPS system as the force necessary to provide a mass of 1 Slug with an acceleration of 1 Foot per Second per Second. 

1 Slug = 32.174048556 Pounds-mass (MKS system ~ 9.80665)
1 Kilogram = 2.20462262185 Pounds-force
1 Meter = 3.2808399 Feet

1 kiloNewton = 1000 X 2.20462262185 X 3.2808399 / 32.174048556 

*1 kiloNewton = 224.8089434 Pounds-force ~ 225 Pounds*


*Ref:  Ed Gohmann, Purdue University School of Technology

Supposition: Maybe the risk of confusion about pound-mass and pound-force (yada-yada) caused some lawyers somewhere to mandate the use of kiloNewtons so there would be no confusion.
:monkey:


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## SINGLE-JACK (Jan 1, 2010)

John Paul Sanborn said:


> Since mass and weight are the same here on Mother Earth, isn't it the same in our applications?



:agree2: makes no practical difference at all for the work we do.


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## mikewhite85 (Jan 1, 2010)

treemandan said:


> I went down about 10 feet til my srt line found a crotch it liked better. I was tied to the rope with a Petzl hand ascender, no problem.



Ouch! That must have been a scare.


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## treemandan (Jan 1, 2010)

mikewhite85 said:


> Ouch! That must have been a scare.



No, had a good feeling my top crotch would break but made sure the rope would fall into another. Felt kinda good actually but that was cause I was prepared. if I suddenly unwittingly started to fall I would scream like a ...


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## SINGLE-JACK (Jan 1, 2010)

treemandan said:


> No, had a good feeling my top crotch would break but made sure the rope would fall into another. *Felt kinda good actually but that was cause I was prepared. if I suddenly unwittingly started to fall I would scream like a ... *



:agree2: I did lol ... would rep that if I could.


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## davej (Jan 1, 2010)

pdqdl said:


> So that 27Kn carabiner should be rated to hold a force of over 6,000 lbs.



So Moray, will the typical hitch slide down and save your spine?


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## outofmytree (Jan 1, 2010)

John Paul Sanborn said:


> Since mass and weight are the same here on Mother Earth, isn't it the same in our applications?



I'm not a physicist JPS I just read Wiki! However if I recall from high school, way back in the stone age, weight and mass are not the same. Weight is relative, mass is fixed. You weigh less at 30, 000 feet in an aeroplane than you do diving for lobster. And of course we all wear our harnesses whilst flying and scuba diving right?


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## John Paul Sanborn (Jan 2, 2010)

outofmytree said:


> And of course we all wear our harnesses whilst flying and scuba diving right?



So I guess we actually agree, since we are at a relatively equal gravimentric, our mass does equal our weight in the given discussion


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## John Paul Sanborn (Jan 2, 2010)

> "The whole purpose of the metric system is to keep things simple ..."
> 
> Well, it is intended to be simple WITHIN the metric system = Meter-Kilogram-Second (MKS) system:



The idea was to make a universal system that would be easy to use, since we calculate in base ten it seamed like the thing to do. But then give it to carpenters, bricklayers, and bakers who think in base four, i.e. half and quarter measures, and it throws things off.

Brion Toss, a great proponent of keeping it english, has a story of working with some Euro woodworkers who had re-invented the fractional system for getting past the .25 measure. they were dumbfounded when he replies "oh, just like English standard!".

It might be burried on his site, I could not find it


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## pdqdl (Jan 3, 2010)

SINGLE-JACK said:


> ...
> 
> The "small deviation" (101.64525412649) is due to the difference in the force of gravity on the _International Prototype Kilogram_ and the force to accelerate the _International Prototype Kilogram_ to 1 Meter per Second per Second. _*The inverse is referred to as the Gravitational Constant, "9.80665 m/s2"*_.
> 
> ...



I thought that when I first looked at the numbers, too. But it isn't the inverse of the gravitational constant. Just divide 1 (or one thousand) by 9.80665, and you will see a different number.

I already checked that! Close, but not quite the inverse. Hence, we don't quite know what we are missing. Perhaps nothing more than internet misinformation, since I only got my numbers from Wikipedia.


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## SINGLE-JACK (Jan 3, 2010)

pdqdl said:


> Notice that the conversion factor for Kilonewtons is NOT an even multiple of 10; rather, it is *101.64525412649*. The whole purpose of the metric system is to keep things simple and easy to convert.
> 
> This small deviation is not enough to make much difference to most folks, but it points out to me that there is some facet of the kilonewtons (force) to Kilograms (mass) conversion that I do not know or understand. I suspect that it is related to the acceleration due to gravity, but I am not sure.
> (*defined to be precisely 9.80665 m/s2 *)





SINGLE-JACK said:


> ...
> The "small deviation" *(101.64525412649)* is due to the difference in the force of gravity on the _International Prototype Kilogram_ and the force to accelerate the _International Prototype Kilogram_ to 1 Meter per Second per Second. The inverse is referred to as the Gravitational Constant, *"9.80665 m/s2"*.
> ...





pdqdl said:


> I thought that when I first looked at the numbers, too. But it isn't the inverse of the gravitational constant. Just divide 1 (or one thousand) by *9.80665*, and you will see a different number.
> 
> I already checked that! Close, but *not quite the inverse*. Hence, we don't quite know what we are missing. Perhaps nothing more than internet misinformation, since I only got my numbers from Wikipedia.



You are absolutely right! It is NOT the inverse (at any order of magnitude). So, I did some additional research and found:

1 kilogram-force (kgf or kilopond) = 9.80665 m/s2 = 9.80665 Newtons
- this value is defined by international agreement.
... inversely
1 Newton = 0.101971621 kgf = 101.971621 grams-force
1 kiloNewton = 101.971621 kgf

An internet search for the number _"101.64525412649"_ had only two hits: your post and my post, referencing it. Though it is close, I was remiss in assuming it to be the inverse of 9.80665 m/s2. So, it appears, the value _"101.64525412649"_ is suspect, as you suggest it is _"Perhaps nothing more than internet misinformation"._


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## lync (Jan 3, 2010)

while climbing srt (line over a crotch,tied off to base of tree) an unseen smaller limb above my tip crotch broke, i dropped about 6 ft. i'm 220 lbs, cmi ascender did no damage to the rope. It was a tall spruce i knew I was in something solid, I bounce tested the ascent rope from the ground before I started.


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## pdqdl (Jan 3, 2010)

Quite frankly, I could not find my original internet source for that screwed up number. At this point, I will assume that:

1. 101.64525412649 is wrong, and that I passed on bad information to you guys.

2. 101.971621298 is correct, that it is 1000 x the inverse of the gravitational constant, thereby making everything fit together the way I wanted it to in the beginning. 

My confidence in the metric system is restored, and my distrust of the internet is renewed. 

SingleJack: Thanks for doing the research that I was too lazy to complete myself!


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## oscar4883 (Jan 3, 2010)

"The metric system is a tool of the devil. My car gets 40 rods to the hogs head, and thats the way I like it"
-Grandpa Simpson when questioning the installation of a mono-rail in Springfield.


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## SINGLE-JACK (Jan 4, 2010)

pdqdl said:


> ...
> My confidence in the metric system is restored, and my distrust of the internet is renewed.
> 
> SingleJack: *Thanks* for doing the research ...



*Ain't-no-thang! * 

I had to do the research ... they hadn't even invented the "kilo Newton" when I went to school ... LOL!!!


- Jack


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## moray (Jan 4, 2010)

davej said:


> So Moray, will the typical hitch slide down and save your spine?



Well, yeah, I do want to do some tests on hitches and dynamic loads, but there are two feet of cold snow sitting on top of my rig right now. Come spring (roughly August in these parts) I'll be back at it.

Do you guys want me to start posting results in kN?


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## SINGLE-JACK (Jan 4, 2010)

moray said:


> Well, yeah, I do want to do some tests on hitches and dynamic loads, but there are two feet of cold snow sitting on top of my rig right now. Come spring (roughly August in these parts) I'll be back at it.
> 
> *Do you guys want me to start posting results in kN?*



LMAO!!! Yeah, what...ev...er, we got the math fingered out now ... pounds are OK ... kN's are kool ... 
maybe: Slugs per Furlong per Fortnight ... :monkey:

Happy New Year *moray*,
Jack


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## moray (Jan 4, 2010)

SINGLE-JACK said:


> ... maybe: Slugs per Furlong per Fortnight ...



That's very good, SJ! Where did they ever come up with slugs? Same place they came up with shillings and pounds and guineas. Those Brits.

I'm off for 3 weeks to a warm place where they don't speak English and no one has ever seen snow. They do have Internet, so I'll have to see if I can get connected...


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## bendtrees (Jan 5, 2010)

The thing that freaks me out is that our saddles our rated for "work positioning" not "fall protection". Always give me a second thought prior to climbing above my TIP. Especially looking down at the silly little clevis' on my Butterfly which probably pull at angles which will double any load placed upon them, (or so I imagine). I'm a bit unclear about what the standards and differences are between the above terms. What are our saddles rated to?


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## outofmytree (Jan 6, 2010)

bendtrees said:


> The thing that freaks me out is that our saddles our rated for "work positioning" not "fall protection". Always give me a second thought prior to climbing above my TIP. Especially looking down at the silly little clevis' on my Butterfly which probably pull at angles which will double any load placed upon them, (or so I imagine). I'm a bit unclear about what the standards and differences are between the above terms. What are our saddles rated to?



Each fixing point on my Sequoia is rated to 15kn. All you have to do now is go back up this thread and figure out what that means.

I think it is safe to say that any fall which creates enough force via gravity to "break" a climbing saddle will be great enough to "break" the climber upon impact. Alternatively if your saddle holds, you will resemble a pretzel. Comforting thought isn't it?


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## SINGLE-JACK (Jan 6, 2010)

outofmytree said:


> Each fixing point on my Sequoia is rated to 15kn. All you have to do now is go back up this thread and figure out what that means.
> 
> I think it is safe to say that any fall which creates enough force via gravity to "break" a climbing saddle will be great enough to *"break" the climber upon impact*. Alternatively if your saddle holds, you will resemble a pretzel. Comforting thought isn't it?



:agree2:

Good point! ... This is an important point to stress, here. You don't have to fall to the ground to die or get seriously injured. If you haven't been tending your slack and fall ten feet, and are positioned wrong, there's a risk you could break your back when your slack snaps tight.

Tree workers use static line because it increases the efficiency when climbing a rope. But, it also increases the risk of injury from even a minor fall because there is very little forgiving shock absorption in static line. Dynamic line, used by rock climbers, is much, much more forgiving ('springy') in a fall.

Thanks for the reminder, *outofmytree*, to keep slack out of life support. ... rep'd


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## lumberjack333 (Jan 6, 2010)

I thought the majority of our lines were dynamic, not to the extent of rock climbing line. But most of the climb line I've used seemed to have some amount of stretch and bounce to it... I have some static kernmantle line as well and it is definatly 0 stretch... The work positioning comment is right though, the stuff we're using is definatly not meant to abosrb a fall as much as it is to hold body weight while positioning around the tree...


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## outofmytree (Jan 7, 2010)

lumberjack333 said:


> I thought the majority of our lines were dynamic, not to the extent of rock climbing line. But most of the climb line I've used seemed to have some amount of stretch and bounce to it... I have some static kernmantle line as well and it is definatly 0 stretch... The work positioning comment is right though, the stuff we're using is definatly not meant to abosrb a fall as much as it is to hold body weight while positioning around the tree...



Yeah it can get confusing. The truth is that all rope is dynamic, that is, stretches under load. Even steel cables will stretch if you put enough load on them. What rope manufacturers do is compare one type of rope to another which is only useful if you are familiar with both ropes.... It would be handy to have an accredited scale where you could pick out a rope because you personally prefer say, a 6.5 on the OOMT rope dynamism scale. (patent pending).


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## pdqdl (Jan 7, 2010)

I might be wrong, but I think the rock climbers are using rope that is quite a bit thinner than the arborists. Overall, they get more stretch to their fall than we do, whether it is because their ropes are smaller in diameter or just got more "give".

It's probably a good thing, too. Case in point: http://www.youtube.com/watch?v=VtP6D7S5LAk
(Check out the unbelievable footlock rope climb at the end of the video!)


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## SINGLE-JACK (Jan 7, 2010)

*The OOMT rope dynamism scale*



lumberjack333 said:


> *I thought the majority of our lines were dynamic, not to the extent of rock climbing line. *But most of the climb line I've used seemed to have some amount of stretch and bounce to it... I have some static kernmantle line as well and it is definatly 0 stretch... The work positioning comment is right though, the stuff we're using is definatly not meant to abosrb a fall as much as it is to hold body weight while positioning around the tree...


:agree2:



outofmytree said:


> Yeah it can get confusing. The truth is that *all rope is dynamic, that is, stretches under load. Even steel cables *will stretch if you put enough load on them. What rope manufacturers do is compare one type of rope to another which is only useful if you are familiar with both ropes.... It would be handy to have an accredited scale where you could pick out a rope because you personally prefer say, a 6.5 on *the OOMT rope dynamism scale*. (patent pending).


:agree2:

*The OOMT Rope Dynamism Scale*

The *OOMT RDS *is defined at follows:

*OOMT RDS UNITS *= Percentage (% - per Sherrill Tree's Percentage of Elastic Elongation @ 540 lbs)

*'ZERO' STRETCH STANDARD *= The *steel cable *used on the Hoover Dam Bypass (0% on left end of the scale).

*'MAXIMUM' STRETCH STANDARD *= The *bungee cord *used to jump off the Hoover Dam Bypass (100% on right end of the scale).

*THE STATIC/DYNAMIC LINE *= The line between the Zero and Maximum Standards at a percentage value such that all DYNAMIC ROPES are to the right (i.e., greater % stretch) and all STATIC ROPES are to the left (i.e., lesser % stretch).

*The exact placement (% value) of the STATIC/DYNAMIC LINE has yet to be determined by international agreement.*

:biggrinbounce2: ... applogies & credits to *outofmytree* 

Seriously though :monkey: Some of examples of Static & Dynamic ropes

*New England "Fly" (Sherrill Tree's Elastic Elongation @ 540 lbs = 2.2%)*





*New England "Apex" (New England's 'Dynamic Elongation' = 29%)*


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## Bermie (Jan 7, 2010)

Arborist ropes are semi-dynamic...
I paraphrase from my LOLER workbook: 

...it is accepted that polyester has the perfect compromise of properties for tree work operations, high melting point and high strength with low stretch but sufficient energy absoption to cushion minor falls.

...never use high strength fibres like kevlar for climbing or rigging line, it requires very high bending radii to operate safely and has extremely poor energy absorption properties, eliminating its safe use for anything other than pulling. 

...high stretch ropes (rock climbing) will not provide sufficient control in close proximity to targets, stretch in a rope is not recoverable after severe shock loading, it will stay stretched rendering it useless for energy absorption.

...loading a braided polyester rope over 40% of breaking strength will result in permenant stretch.

...Loading ropes to 10% of their breaking strength will provide minimum stretch, immediate recovery to support the next load and indefinite safe working life...

Some of the lines are a bit blurred with the advent of SRT techniques but still we need a rope that can bend in a tight radius and is not too stretchy so we are not bouncing up and down an a rope instead of actually climbing it!

on another topic

A fall arrest harness has both pelvic and shoulder straps and relies on the attachment point being in the middle of your chest (sternal) or back (dorsal), so if a fall happens you are caught up higher than your centre of gravity and don't 'snap inthe middle', instead hang suspended in an upright position. FA systems usually have a significant amount of slack, so the tether has the 'deceleration pack' built in that theoreticly slows you down before the big jerk stop at the end. ,The objective of this device is to reduce the fall arrest forces on the body to a maximum of 6kN in a fall arrest situation.

Our tree work equipment is designed and rated for work position, comprising a waist belt and sub pelvic support where the potential for a fall does not exceed 300mm (30cm or about 15") and as such you are supposed to keep minimal slack in your system, we don't incorporate deceleration devices, we rely on working so as to reduce the potential for a fall of any significant distance.


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## outofmytree (Jan 8, 2010)

SINGLE-JACK said:


> :agree2:
> 
> 
> :agree2:
> ...



SJ I laughed until it hurt. 

I have no rep to send you brother but hopefully someone else will top you up.

Thanks for laugh.


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## gemniii (Jan 23, 2010)

SINGLE-JACK said:


> _*"The whole purpose of the metric system is to keep things simple ..." *_
> 
> Well, it is intended to be simple _WITHIN_ the metric system = Meter-Kilogram-Second (MKS) system:
> 
> ...



GAD!!!
I visited this thread for some info on a recommended rope and I'm in a first year physics course!!
Flashbacks to the 70's !!
good info though


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## davej (Jan 24, 2010)

SINGLE-JACK said:


> 1 kiloGram is defined as the force of gravity on the _International Prototype Kilogram_ which is almost exactly equal to the mass of one liter of water, which is simple enough.
> 
> The "small deviation" (101.64525412649) is due to the difference in the force of gravity on the _International Prototype Kilogram_ and the force to accelerate the _International Prototype Kilogram_ to 1 Meter per Second per Second. The inverse is referred to as the Gravitational Constant, "9.80665 m/s2".
> 
> *Ref:  Ed Gohmann, Purdue University School of Technology



You could quibble about the top point he makes here. I don't think this is correct. A kilogram is not defined as a force. It is a measure of mass. Something that is 1 Kg on earth is still 1 Kg on the moon. In the English system you would convert kilograms to Slugs. The "small deviation" is due to the fact that expecting a factor of ten relationship between mass and earth-weight is totally bogus.


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## VA-Sawyer (Jan 25, 2010)

I actually took a Physics course at Purdue in the 70's. It didn't seem so complicated at the time. Must be some rust in the grey matter.

Bermie, Good post. Simple, concise and educational.

It is good for all of us doing tree work to refresh ourselves on the physics of falling and shock absorbing. It applies to the rigging we do as well as to protecting out bodies.

Case in point: I was well aware about having twice the load on a branch when using a pulley to control a load from the ground. A climbing refresher course I attended last fall pointed out that if the pulley is suspended from a rope over the branch that the load becomes 4X on the branch. Suspending the pulley to make it easier to setup is something I started doing shortly before the class. Just hadn't worked out the math on the change. Glad the course pointed it out.


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## pdqdl (Jan 25, 2010)

VA-Sawyer said:


> ...
> 
> Case in point: I was well aware about having twice the load on a branch when using a pulley to control a load from the ground. A climbing refresher course I attended last fall pointed out that if the pulley is suspended from a rope over the branch that the load becomes 4X on the branch. Suspending the pulley to make it easier to setup is something I started doing shortly before the class. Just hadn't worked out the math on the change. Glad the course pointed it out.



Not entirely true. You need to subtract for frictional losses, especially the rope going over the branch. After friction, probably more like 2 or 3x.

I guess with weak branches, this emphasizes the need for isolating the branch, something I am not good at.


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## VA-Sawyer (Jan 25, 2010)

That would be some pretty high friction. Of course there was the time I had my climbing line over a stout branch in a storm damaged pine. Went up SRT to cut loose the broken top before dropping the rest of the tree. When I was back on the ground and untied the line at the base of the tree, I couldn't get it to budge. Had 3 of us hanging on it with no luck. Had to use the Masdam rope puller to get it to pop loose from the sap it was stuck in. Once it moved a few inches, the rest came down with an easy hand pull just like always. I hate pines.


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## Pruning Artist (Jan 25, 2010)

John Paul Sanborn said:


> What does a library card catalog have to do with anything



I thought the same thing !!


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## richiemcbride (May 8, 2010)

*Newton revealed*

HI,
Just thought I'd try to help

A Newton is a unit of Force NOT MASS


Isaac Newton worked out that Force = Mass X Acceleration
So a 1Kg mass in Earth's gravitation field is subject to the acceleration due to gravity which is 9.81 meters per second per second

So, a 1kg mass has a force due to gravity of 9.81 x 1 Newtons = 9.81N

A kilonewton is 1000 Newtons,

Divide by 9.81 and this is the force exerted by 101.95 kg or almost 225 lbs

so 27kN is a force that you get from 225 X 27 lbs or 6075 lbs




pdqdl said:


> Do you ever wonder how much weight your climbing equipment is rated for? If you look real close, most hardware has a number stamped on it followed by a "Kn". This stands for Kilonewtons.
> 
> While this isn't exactly proper physics, one Kilonewton is equal to 225 lbs (actually 224.808942443 lbs)
> 
> ...


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## jefflovstrom (May 8, 2010)

What about distance?
Where do you apply the theory, ( not to say you are wrong but there is a difference in the distance of the fall), There is a max speed given on an object, but distance matters, there is a max speed falling using the same math. Basically, If you are TV and weigh alot and fall 4 feet,(HA!), so "E=MC2? That did not hurt too much, now the same from 40 feet up. 
Jeff, CTSP


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## jefflovstrom (May 8, 2010)

If you drop a baseball from the Empire State building, a catcher could get it no problem, the baseball cannot exceed it's speed. It is set on the gravity pull. You wont get it to faster than gravity (you know what I mean), So, If I throw Treevet off a 2' wall, he will get up and kick my butt! But, If I throw him off the Empire State Building, Well, gives me lots off time to run!
Jeff, CTSP


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## Damon (May 8, 2010)

jefflovstrom said:


> What about distance?
> Where do you apply the theory, ( not to say you are wrong but there is a difference in the distance of the fall), There is a max speed given on an object, but distance matters, there is a max speed falling using the same math. Basically, If you are TV and weigh alot and fall 4 feet,(HA!), so "E=MC2? That did not hurt too much, now the same from 40 feet up.
> Jeff, CTSP




Jeff i think your talking about momentum in other words until you reach terminal velocity which is around 120 mph for humans the further you fall the faster you go before you go splat when you go splat the faster your going in relation to the mass of your body exerts a force on the object you go splat against (newtons law #1 for every action there is an equal and opposite reaction) which means that what ever you hit exerts the same force back on you that you exerted on it the faster you go the more force thats exerted on you from the impact of your harness or the branch or the ground,

as my dad always told me (hes an engineer (the bridge kind not the train kind)) its not the fall that kills its the impact

so by using a dynamic line you slow down the rate of the impulse momentum that you exert on the harness which in turn exerts an equal force back on you and with any luck youll still be able to have kids afterwords!!

so anything you can put in your system that can allow for a controlled amount of slip (grigri comes to mind immediatly) the better off you'll be as far as harness construction and falls go my biggest fall rock climbing was 32 feet which is big but not huge by any means and my harness was completely unskathed from the exeperience, my fiance took a BIG whipper 7 pitches up (700 feet) in mexico that i estimate to be somewhere between 45-47 feet (i actually thought she was gonna hit me on the way down she somehow mannaged to miss me and wind up about 8 feet below me, she had one leg strap on her harness partially sever which was caused by an accesory biner that was clipped on to use as an autoblock so the answer is on 11.5 mm line you can fall somewhere between 30 and 40 feet unscathed but these were deffinitly dynamic falls both of us were trained to catch a fall and allowed rope to move through the device lowering the impulse momentum.


my biggest fall in a tree occured on SRT on 1/2 inch yale xtc 16 when a branch snapped and i fell about 6 feet but i was not using a mechanical ascender at the time and i think that fall hurt as much as pretty much any fall ive taken rock climbing so the impulse was obviously very high durring the shock loading i would be very interested to see literature about shock loading in the situations we encounter daily and see how big a fall in considered safe so you have an idea what a reasonable risk is before you start up a tree i would also like to see the difference between the old jumar style ascenders bds new style and rope grab style in terms of severing a rope

Tom


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## moray (May 9, 2010)

Damon said:


> ...i would be very interested to see literature about shock loading in the situations we encounter daily and see how big a fall in considered safe...



Too bad it's not that simple. As a rock climber, Damon, you must know that the length of fall only tells part of the story--you need to know the fall factor to correctly evaluate a given situation. I can fall quite comfortably 30 feet on static rope if only I have enough rope available to stretch.


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## jefflovstrom (May 9, 2010)

Maybe I am confused, is this a "free-fall" being grabbed by "static / dynamic" because I think it sounds like a controlled jump and I am thinking of a guy falling.
Jeff, CTSP


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## lone wolf (May 9, 2010)

JeffL said:


> My biggest worry is whether or not my spine will withstand a 4 or 5 foot fall and shockload.



it will unless you do it at some weird angle 
i saw a guy fall 30 feet and get stopped sharply no injuries.


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## Mitchell (May 9, 2010)

*cammed ascenders*



treemandan said:


> I went down about 10 feet til my srt line found a crotch it liked better. I was tied to the rope with a Petzl hand ascender, no problem.



A 10 foot fall unto a cammed acender is a recipe for death.

In my other life as a high angle rescue guy cammed ascenders are for capturing the loads movement only, if there could be shock loading, double prussics or a device that "slips" are used. Particularly on static ropes used in rescue and tree work.

If your ascender is like mine, Its a toothed cam. Devices that do not slip under shock loading will sever the rope. A fellow around here died recently from exactly that, falling unto a gibbs ascender. Not sure how far the fall was, but apparently it was in the 10 to 15 foot range. I read of another fellow in WA state that fell 15' unto his hand acenders which severed the rope and he also died. A google search finds lots of info on this subject. I suspect your fall was not a clean fall as you would have damaged your rope at the very least. 

If you doubt your TIP use a double prussic above your ascender


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## Mitchell (May 9, 2010)

*Not trying to be a safety boss...*



lone wolf said:


> it will unless you do it at some weird angle
> i saw a guy fall 30 feet and get stopped sharply no injuries.



Wolf, I would qualify statements like that, new or uneducated climbers can misinterpit. No one would jump off a thirty foot building into a paved parking lot with out expecting to get hurt or killed. Being stopped dead on a rope from thirty feet is the same. 

If the building was over a deep pool of water that would be fun. Same with the rope; if it was a bungy cord thats fun, a steel cable your in big trouble.

I can't remeber the numbers off the top of my head but I believe just a 5 foot fall for a 180 pound guy generates in the neighbourhood of 2000lbs of force. Thats a lot of energy to absorb and if its your spine thats doing it...

I Don't like to climb more then 5 feet above my tip [10 foot fall]. A clean 10 foot fall is where forces are potentially great enouph to start breaking things [like us] in our static systems. 

Have to run to work; stay safe


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## lone wolf (May 9, 2010)

Mitchell said:


> Wolf, I would qualify statements like that, new or uneducated climbers can misinterpit. No one would jump off a thirty foot building into a paved parking lot with out expecting to get hurt or killed. Being stopped dead on a rope from thirty feet is the same.
> 
> If the building was over a deep pool of water that would be fun. Same with the rope; if it was a bungy cord thats fun, a steel cable your in big trouble.
> 
> ...



ok this was not done on purpose it was a slip and a miracle I might add.


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## pdqdl (May 10, 2010)

Mitchell said:


> A 10 foot fall unto a cammed acender is a recipe for death.
> 
> In my other life as a high angle rescue guy cammed ascenders are for capturing the loads movement only, if there could be shock loading, double prussics or a device that "slips" are used. Particularly on static ropes used in rescue and tree work.
> 
> ...




Something to consider: If your ascender severed the line, the prussic would likely be only a few inches above. While it would be some additional security against a fall, it wouldn't be much. 3" of slip before the rope runs out of the prussic isn't much security.

Everybody I have seen using a prussic above the ascender pushes the prussic up the line with the ascender. No real safety there!


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## pdqdl (May 10, 2010)

Just because your equipment holds the fall safely does not mean that you don't get hurt.

I broke several short ribs once when the branch I was standing on broke off. I had anticipated that problem, and was rigged with my lanyard to the branch overhead, so no problem, right?

Nope. My lanyard was clipped to the waist-belt d-rings, which are designed to hold you against the tree. When the belt strap is lifted from an overhead attachment, the heavy fabric was lifted like powerful karate kick into my ribs, and broke several. I was VERY sore for over a month, despite the fact that I never even noticed the injury when I was in the tree.

When it happened to me, I thought how cool I must have looked when the branch fell away from me, and there I was hanging in the air, un-injured and still prepared for tree removal action. 2 hours later, it started hurting. By the end of the day, I was suffering with every breath.

That was for a 2 foot drop. 30' on a static line? OMG! :jawdrop:


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## moray (May 10, 2010)

pdqdl said:


> ...Everybody I have seen using a prussic above the ascender pushes the prussic up the line with the ascender. No real safety there!



Very good point about the prusik! You really REALLY don't want to fall if a standard ascender is going to catch you. Ditto for falling on your lanyard as you have so well described.

If I had about 600 feet of static line to catch me, a 30-foot fall would be like sitting down in an overstuffed sofa. A mere 2-foot fall like yours can be much more rugged.


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## pdqdl (May 10, 2010)

I think a 600' fall on static line would either snap the line or rip you in half. 

You would certainly reach terminal velocity. At 140+ mph, I don't think 1-2% stretch of the average arborist rope would be enough to keep you from being shredded by the experience.

That crazy guy Dan Osman was falling over 1000 feet at a time, but he sure wasn't doing it on arborplex.

I really like that video that shows the dyneema line snapping in one test-drop, and the dynamic line held the same load in multiple drops, despite the fact that the dyneema line was more than twice as strong.


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## moray (May 10, 2010)

pdqdl said:


> I think a 600' fall on static line would either snap the line or rip you in half...



Of course. But a 30-ft. fall on 600 feet of rope? Soft like a bungee.


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## jefflovstrom (May 10, 2010)

A little confusing. Are you saying that a controlled ride of 600 feet of rope or at 600 feet the rope halts you?
Jeff, CTSP


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## Blakesmaster (May 10, 2010)

jefflovstrom said:


> A little confusing. Are you saying that a controlled ride of 600 feet of rope or at 600 feet the rope halts you?
> Jeff, CTSP



I believe he's saying a fall of 30 feet when suspended on 600 feet of rope would be nice and soft. At least that's what I gathered.


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## jefflovstrom (May 10, 2010)

Blakesmaster said:


> I believe he's saying a fall of 30 feet when suspended on 600 feet of rope would be nice and soft. At least that's what I gathered.



Oh, OK, Well maybe with that much rope out in play it might not mess you up too much. Still, 30 feet and then a grab, gotta be awake and prepared I think. 
Jeff, CTSP


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## jefflovstrom (May 10, 2010)

So, 600 feet of rope and a fall of 30 feet. At ground level that would be minimum 300 feet high. This is a tree thread and I guess I was thinking we dont climb 300 plus 30 feet to land on the comfy couch.
Jeff, CTSP


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## pdqdl (May 10, 2010)

Ok, I apologize.

When I posted earlier about Dan Osman, I got to thinking about his spectacular free-fall jumps and I completely forgot about Moray's 30 foot fall restriction. Sorry about the confusion I may have introduced.

Nonetheless, I don't think falling 30 feet on a 300 feet of doubled arborist line would be any fun either. In fact, I'll bet it would hurt a whole bunch. 

This is a wild guess, since I don't want to take the effort to do the math: That would be falling 10% of the rope distance into an approximate 3% stretch (assuming that you are somewhere near the 20% of breaking strength rating of the rope). Fall 30', stop in 9', putting a force of close to 3000 lbs on a doubled rope. Oooohh, my aching back!


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## moray (May 10, 2010)

I should have picked better numbers but everyone by now is getting my point: even a very stiff rope can give you a soft landing if the fall is short compared to the length of the rope (very small fall factor). But even a very short fall can be brutal if the rope itself is very short.

I did some on-purpose jumps onto dynamic rope last year, and to make sure the landing would be extremely soft, I wanted a very small fall factor. Using 3 pulleys I managed to use about 180 ft. of rope for a 20-foot jump. The first 4 feet were free fall and the next 16 feet were rope stretch. The soft landing is quite wonderful and left me smiling all day (and gave me the tiniest glimpse of what Dan Osman must have felt). This is what I had in mind with my rather dopey example with 600 feet of static rope.


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## jefflovstrom (May 10, 2010)

pdqdl said:


> Ok, I apologize.
> 
> When I posted earlier about Dan Osman, I got to thinking about his spectacular free-fall jumps and I completely forgot about Moray's 30 foot fall restriction. Sorry about the confusion I may have introduced.
> 
> ...



pdqdl, we are are on the same page, I think we both know if you dont break your back on that, you are Iron Man, that is why I asked if it was a ( Controlled) fall with 600 foot of rope then the 300 foot drop at 30 foot grab is actuall a 600 foot drop with a controlled 15 foot drop ( into the comfy couch?)

Jeff, CTSP


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## pdqdl (May 10, 2010)

Well sure that was a soft fall, Moray. That was only a 4' drop, not a 20. My little 2' drop on an 8' lanyard felt like fun too, until later that day.

I time my falls from where I begin falling to when the rope starts getting tight. What kind of rope stretches 16' in 180' on a four foot fall? Surely you are just guessing about the distances, or were you jumping on a big rubber bungie cord?


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## moray (May 11, 2010)

No, those aren't guesses. You are right, of course, that it is really a 4-foot fall. The total energy the rope must absorb, though, is 20 ft. times your weight, and the total energy absorbed by 180 feet of rope tells you how much it will stretch. I was using a Porta Wrap for the ground anchor so that I could easily fine tune the rope length. Once the length was right the jumper could just touch a toe to the ground at the bottom of the jump.

This stuff is stretchy! If you take 80 kg (176 lb.) and hang it from 100 feet of rope, it stretches 6 feet.


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## pdqdl (May 11, 2010)

What kind of rope is it? 

I could buy a chunk of that, rig a crazy long section in a big tree, and make one heck of a children's adventure swing with it.


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## moray (May 11, 2010)

Petzl Zephyr, 10.3 mm, static elongation 6%, dynamic 33.7%, UIAA falls 10.


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## Mitchell (May 14, 2010)

*good point*



pdqdl said:


> Something to consider: If your ascender severed the line, the prussic would likely be only a few inches above. While it would be some additional security against a fall, it wouldn't be much. 3" of slip before the rope runs out of the prussic isn't much security.
> 
> Everybody I have seen using a prussic above the ascender pushes the prussic up the line with the ascender. No real safety there!



The prussics would have to be a 6" inches above and dressed; which would be a pita. Better yet, lose the hand ascender and foot lock with a prussics. I have the croll ascender mid saddle which makes this fairly easy. Never tried the foot ascenders but I imagine they would make it that much easier and safe. 

I have had short [3'] static falls with dorsal attachment [rear neck] on a fall restriant sytem that was eye opening but fine. I rig my prussics for ascension to my petzel mid chest attachment for this reason. Besides safety the work position / fall restriant shoulder strap saddles have eliminated heavy saw hip pain compared to the butterfly.


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