Load ratings of climbing equipment?

[lumberjack333]

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...

 

[outofmytree]

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).

 

[pdqdl]

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!)

 

[SINGLE-JACK]

The OOMT rope dynamism scale

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:

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%)

 

[Bermie]

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.

 

[outofmytree]

:agree2:


: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%)

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.

 

[gemniii]

"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:

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

 

[davej]

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.

 

[VA-Sawyer]

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.

 

[pdqdl]

...

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.

 

[VA-Sawyer]

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.

 

[Pruning Artist]

What does a library card catalog have to do with anything

I thought the same thing !!

 

[richiemcbride]

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

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.

So to your question: It's not an exact multiple of 10 because gravitational force exerts an acceleration of 9.81 m/s/s on any mass in its field on earth's surface. It suffers from being almost 10 so people think there's been a mistake made rather than yet another example of nature being it's own boss and not fitting the decimal system too well!


*******************************************************
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 ?)

 

[jefflovstrom]

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

 

[jefflovstrom]

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

 

[Damon]

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

 

[moray]

...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.

 

[jefflovstrom]

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

 

[lone wolf]

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.

 

[Mitchell]

cammed ascenders

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