-The Sharp End-
life, technology, and the pursuit of adventure

One of the con­tin­u­ing top­ics I see come up in climb­ing classes is the use of per­sonal anchors: should you use them, what you should use, what is com­mon prac­tice. This is an age-old debate which I can­not do jus­tice describ­ing in a blog post. There are entire books and papers writ­ten on each topic, and depend­ing on how deep you want to go, you can spend all your days buried in sci­en­tific data.

Most of us just want to know how to be safe and get out­side! So, let’s dis­cuss some areas which are inter­est­ing to con­sider when look­ing at these safety sys­tems. From here, you can start to think crit­i­cally about the dif­fer­ent options and dig deeper as you wish. 

What are per­sonal anchors?

Wikipedia describes an anchor as: 

 […] any way of attach­ing the climber, the rope, or a load to rock, ice, steep dirt, or a build­ing by either per­ma­nent or tem­po­rary means. The goal of an anchor depends on the type of climb­ing under con­sid­er­a­tion but usu­ally con­sists of stop­ping a fall, or hold­ing a sta­tic load.^[1] 

All anchors have mul­ti­ple uses. A com­mon use for per­sonal anchors is at belay sta­tions to pre­vent your­self from falling from your belay stance, and/or allow your­self to hang off the anchor.  Before we go into the var­i­ous options you have avail­able, let’s first look a lit­tle more at what you’re pro­tect­ing against: falling. There are two main things to think about: 

1. Fall fac­tor is a derived num­ber used to eval­u­ate shock loads gen­er­ated on the climber, belayer and anchors that occur when a climber falls. The higher the fall fac­tor, the greater the forces placed on the com­po­nents of the sys­tem. SouthwestClimbing.com has a great write up which dives into more detail. You can also ref­er­ence wikipedia or do searches online.
2. Dynamic force is cre­ated when falling onto your pro­tec­tive pieces. This is usu­ally mea­sured in kilo­new­tons (or kN). Mate­ri­als used in climb­ing are lim­ited by var­i­ous prop­er­ties such as mate­r­ial strength. Essen­tially, you want to min­i­mize dynamic force to avoid reach­ing the lim­i­ta­tions of the com­po­nents in your climb­ing system.

Why bother?

Now that we under­stand that we are pro­tect­ing against the dynamic forces when tak­ing a fall, we can more closely look at the mate­ri­als avail­able to pro­tect that fall. I could go into all mate­ri­als such as trad gear, bolts or bin­ers, but since we’re talk­ing specif­i­cally about per­sonal anchors, let’s focus on the meat of the debate — the soft goods: slings, cords, web­bing, rope. 

As men­tioned above, mate­ri­als have var­i­ous prop­er­ties such as strength, weight, elon­ga­tion, mois­ture effects, degra­da­tion, abra­sion resis­tance, melt­ing point, and chem­i­cal resis­tance. As such, mate­ri­als will have pros and cons for their appli­ca­tion in var­i­ous situations. The key to mak­ing deci­sions on which mate­r­ial or method is best for you, is to start under­stand­ing these prop­er­ties and mak­ing informed deci­sions. Most solu­tions you decide on will have a down­side. Look­ing at the options, you can eval­u­ate if the trade­offs are an accept­able risk for you. 

The below table out­lines typ­i­cal prop­erty val­ues for mate­ri­als used in ropes, slings, and cord (see also: rope). For the pur­poses of this dis­cus­sion, we will be focus­ing on nylon and HMPE (aka spec­tra or dyneema). If you don’t know what your mate­ri­als are made of, some research with the man­u­fac­tur­ers or the web can help. To gen­er­al­ize, web­bing and cord are made from nylon (though not always). Spec­tra and Dyneema mate­ri­als are HMPE.

CORDAGE FIBER PROPERTIES — TYPICAL VALUES               Cordage Institute

	Nylon	Poly­ester	Polypropy­lene	Poly­eth­yl­ene	HMPE (Spec­tra 900)
Strength
Break­ing Tenac­ity — dry (grams/denier)	7.8–10.4	7.0–9.5	6.5	6	30/35
Wet Strength vs. Dry Strength	85–90%	100%	100%	105%	100%
Shock-load Absorp­tion Ability	Excel­lent	Very Good	Very Good	Fair	Fair
Weight
Spe­cific Gravity	1.14	1.38	0.91	0.95	0.97
Floats	No	No	Yes	Yes	Yes
Elon­ga­tion
Per­cent at Break	15–28%	12–15%	18–22%	20–24%	2.7–3.5
Creep (exten­sion under sus­tained load)	Mod­er­ate	Low	High	High	Mod­er­ate
Mois­ture Effects
Water Absorp. of Indi­vid­ual Fibers	2–8%	<1.0%	None	None	None
Resis­tance to Rot, mildew & dete­ri­o­ra­tion due to marine organisms	Excel­lent	Excel­lent	Excel­lent	Excel­lent	Excel­lent
Degra­da­tion
Resis­tance to UV in sunlight	Good	Best	Fair	Fair	Fair
Resis­tance to aging for prop­erly stored rope	Excel­lent	Best	Black is best Excellent	Black is best Excellent	Excel­lent
Abra­sion Resistance
Sur­face	Very Good	Excel­lent	Good	Fair	Very Good
Inter­nal	Excel­lent	Excel­lent	Good	Good	Excel­lent
Ther­mal
High Temp. work­ing limit	250°	275°	200°	150°	150°
Low Temp. Work limit	–70°	–100°	–20°	–100°	–200°
Melts at	420°-480°	490°-500°	330°	285°	297°
Chem­i­cal Resistance
Effect of Acids	Decom­posed by strong min­eral acids;resistant to weak acids	Resis­tant to most min­eral acids;disintegrate by 95% sul­phuric acid	Very resistant	Resis­tant to most weak acids.Strong acids will attack; espe­cially at high con­cen­tra­tions or high gemps	Very resistant
Effect of Alkalis	Lit­tle or none	No effect cold;slowly dis­in­te­grate by strong alka­lis at the boil point	Very resistant	Resis­tant to most weak alkalis.Strong alka­lis will attack; espe­cially at high con­cen­tra­tions or high temps	Very resistant

Mate­r­ial Testing

Data! Now we’re start­ing to get somewhere. Let’s start look­ing at how these mate­ri­als per­form under testing.

There are sev­eral com­mon tests for mate­ri­als, but the two I’ll men­tion here are: 

• slow-pull tests: under what load will the mate­r­ial will fail when pulled at a steady rate (sta­tic load)
• drop tests: under what load will the mate­r­ial fail dur­ing a dynamic fall (dynan­mic load)

A good place to start is Tom Moyer’s Com­par­a­tive Test­ing of High Strength Cord. A few things to draw out about var­i­ous test­ing I’ve seen:

• Nylon is a heav­ier mate­r­ial, but has excel­lent shock-load abil­ity. This is mostly due to it’s elon­ga­tion prop­er­ties, which acts as a shock absorber as it stretches. It will absorb water and you will see slight per­for­mance degra­da­tion when wet.. It has a higher melt­ing point, which helps it resist break­ing dur­ing dynamic falls where heat dis­ap­a­tion can occur with friction.
• Spec­tra has excel­lent weight to strength ratio. It’s elon­ga­tion prop­er­ties are low, which lim­its it’s abil­ity to han­dle shock-loads. It does not absorb water and there are no per­for­mance effects when wet. It has a lower melt­ing point which makes it more prone to break­ing when friction/heat is involved.
• Knots will reduce the mate­r­ial strength depend­ing on the matier­ial and the knot. TMoyer’s paper shows that spec­tra will lose 40%-50% of it’s strength when knot­ted with a figure-8 and nylon 10% or so. The Free­dom of the Hills also lists break­ing strength of knots in a kern­man­tle rope (see index under “knots”) in the realm of 15–30%.

One thing to think about when look­ing at test results is how the mate­r­ial was tested and how it applies to your use. For exam­ple a lot of anchor test­ing involves the use of a rope, which will help absorb dynamic forces. Also, the slip­page in the sys­tem from other pro­tec­tion, belay devices, and the acts of a belayer/climber, will help dis­si­pate energy and reduce the direct force on the anchor. In the case of a per­sonal anchor sys­tem, you are directly con­nected to the anchor and there­fore a fall’s force is applied most directly on the mate­r­ial used to anchor (not to men­tion your body). 

Com­mon Per­sonal Anchors

With that primer, let’s start look­ing at per­sonal anchor­ing meth­ods. Com­mon methods: 

• Daisy Chains. Recently Black Dia­mond posted a blog entry regard­ing use of their daisy chains for per­sonal anchor devices. Daisy chains are a sin­gle loop of web­bing mate­r­ial which is tacked into small loops. Intended for aid climb­ing, this gear is built toward sta­tic loads. In a fall, you are rely­ing on the strength of the bar tacks, which are not rated to take a dynamic fall.

 

• Per­sonal Anchor Sys­tem (PAS). A prod­uct devel­oped by Meto­lious to address the need for use in a dynamic envi­ron­ment. It con­tains indi­vid­ual loops which are bar tacked sep­a­rately. Since each loop is it’s own sling, it per­forms well under slow-pull sta­tic tests because each loop is full strength. What about dynamic load? The PAS prod­uct is a hybrid of spec­tra and nylon. We already know that spec­tra mate­r­ial strength is sig­nif­i­cantly impacted in a dynamic fall. In drop tests done by Mike Gibbs @ Rig­ging for Res­cue, fall fac­tors of 1.25 or higher will cre­ate a com­plete fail­ure of the sys­tem. His conclusions:

The intro­duc­tion of high per­for­mance fibers into climb­ing and rope res­cue equip­ment has some worth­while appli­ca­tions. How­ever, the use of HMPE like Spec­tra ® or Dyneema ® in the con­struc­tion of daisy chains is sim­ply a bad idea. The prop­er­ties of HMPE include the ben­e­fits of high strength, the abil­ity to float and excel­lent resis­tance to chem­i­cals and U.V degradation.However, HMPE prop­er­ties also include very low elon­ga­tion at break and a low melt­ing point.It is these last two prop­er­ties that are likely the key con­tribut­ing fac­tors to:
(1) the high peak force val­ues observed in our test­ing of lan­yards con­structed out of these mate­ri­als.
(2) the break­ing of these same lan­yard types on cer­tain drops 

• Slings or Nylon Daisy. I’ve seen slings used by girth hitch­ing them to the har­ness and then tying knots into them. This sim­u­lates the loop sys­tem sim­i­lar to a daisy chain or PAS, but avoids bar tack­ing by use of knots. It also allows you to choose mate­r­ial. Based on infor­ma­tion pro­vided already dis­cussed, use of a spec­tra sling would not be advis­i­ble in a fall. What about nylon? Drop tests by Mike Gibbs shows that Nylon Daisys (such as Climb High 25mm) can catch a fac­tor 2 fall with no sign­fi­f­i­cant vis­i­ble dam­age. Also worth a look is DMM’s dyneema and nylon drop tests (video), which looks at both sling mate­r­ial and knots in drop tests.
• Pur­cell Prusiks. In the res­cue world, the use of pur­cell prusiks have been intro­duced as an alter­na­tive for per­sonal anchor­ing. I have not seen this in much prac­tice except from peo­ple who have watched Rig­ging For Res­cue drop test videos (which are quite an eye opener!) and are famil­iar with these stud­ies. In 2006, Mike Gibbs fur­thered this study in another set of drop tests. His sum­mary:

The test­ing con­ducted on Pur­cell Prusiks was by no means a com­pre­hen­sive exam­i­na­tion. How­ever, the test­ing con­ducted cer­tainly sug­gests that a Pur­cell Prusik con­structed out of 6mm cord with a 3-wrap prusik hitch meets the rec­om­mended lan­yard per­for­mance guide­lines of being able to with­stand a fall fac­tor 1 event with accept­able lev­els of MAF and no observ­able degra­da­tion of the lan­yard. The test­ing also demon­strates that the mar­gin over and above that min­i­mum per­for­mance cri­te­ria is approach­ing the 50% level at fall fac­tor 1.5. 

• Rope. Ropes are prob­a­bly the best under­stood mate­r­ial for use in a dynamic fall. After all, lead climbers may take dynamic falls and a rope is a core piece of the sys­tem. A dynamic rope is intended to use elon­ga­tion as a means to absorb the force of a fall. Ropes sold for climb­ing meet UIAA stan­dards for test­ing in both a sta­tic load and dynamic fall sce­nario. Dif­fer­ent ropes have dif­fer­ent fall rat­ings, so it’s always best to edu­cate your­self on how the ropes were tested and the UIAA rat­ing. It’s also best to under­stand the his­tory of the rope and it’s cur­rent con­di­tion. To use a rope as a per­sonal anchor, the climber attachs their rope to the anchor. A com­mon method is the clove hitch.

Final Thoughts

Some final points of con­sid­er­a­tion as you start aborb­ing the infor­ma­tion out there: 

• Test data is not incred­i­bly abun­dant for mate­r­ial use in climb­ing, but you can find infor­ma­tion by search­ing the web. Search results will improve as you start under­stand­ing the lan­gu­gage of mate­ri­als, and under­stand­ing which orga­ni­za­tions typ­i­cally pub­lish this sort of infor­ma­tion. Under­stand­ing the indus­try will help you tap orga­ni­za­tions who have done test­ing, but don’t post results online. They will often send you the results if you ask, or will charge a small fee. Look for non-biased sources such as UIAA.org, Amer­i­can Alpine Jour­nal, or Inter­na­tional Tech Res­cue Sym­po­sium. Man­u­fac­tur­ers are also good sources, but be aware of mar­ket­ing. Read and par­tic­i­pate in debates climbers are hav­ing on active forums such as supertopo.com or cas­cade­climbers.
• What’s is com­mon prac­tice may not nec­es­sar­ily be based on the “safest” method. Since climb­ing is very much an appren­tice­ship, often these meth­ods are passed down from climber to climber because that is how they were taught. Learn­ing from mul­ti­ple peo­ple and mul­ti­ple sources is use­ful. Triangulate! 
• Man­u­fac­tur­ers may report mate­r­ial strength only as a func­tion of slow-pull tests, not drop tests or other test meth­ods. For dynamic sit­u­a­tions, make sure to research both and under­stand how prod­ucts are rated.
• Material’s have mul­ti­ple prop­er­ties which will impact it’s per­for­mance in var­i­ous sit­u­a­tions. You must look at the spe­cific sit­u­a­tion to bet­ter under­stand the material’s performance.
• Mate­ri­als used in climb­ing are only as good as their care and use. For exam­ple, an anchor built with the best mate­ri­als has no bear­ing if it’s in poor rock qual­ity. A soiled rope exposed to garage chem­i­cals, same thing.

Mike’s more recent paper rec­om­mended some guide­lines for lan­yards based on his drop tests. The key takeaways:

• Avoid the use dyneema or spec­tra for per­sonal anchors. They are known to fail at rel­a­tively low forces.
• Choose a mate­r­ial which will absorb energy, such as nylon web­bing, cord, or your climb­ing rope.
• Give your­self a mar­gin of error by choos­ing a sys­tem which will keep func­tion­ing after a severe drop. Sewn nylon slings, pur­cell pur­siks, and use of the rope all faired well in drop tests.
• Reduce your fall fac­tor by keep­ing unnec­es­sary slack out of the system

For most occas­sions (when multi-pitching), I clove into the anchor with the rope. I choose this method because it’s one less single-use thing I need to carry. I also carry a sewn double-length nylon sling. This run­ner can exist as part of my rack as a draw or I can throw in a few knots and use it as a per­sonal anchor.

Under­stand­ing what you should use as a per­sonal anchor is a process of know­ing why you would want one, what mate­ri­als are avail­able, and how they would per­form in your spe­cific sit­u­a­tion. Each solu­tion has it’s pros and cons which may vary given dif­fer­ent sit­u­a­tions. What’s accept­able risk for one climber, may not be for another. The infor­ma­tion here is an overview of areas to con­sider and start research­ing. It’s not a sub­sti­tute to pro­fes­sional training, doing your own research, and mak­ing your own deci­sions. I hope you found some use­ful sources here to start you off!

Thanks for read­ing!

Dis­claimer: Rock climb­ing is inher­ently dan­ge­ri­ous and poten­tially deadly. All con­tent should be con­sid­ered com­men­tary on the sub­ject. Make informed deci­sions. Climb at your own risk.

Tags: anchors, climbing, how-to, material, testing, video

This entry was posted on Tuesday, September 28th, 2010 at 7:03 pm and is filed under climbing, tips & tricks. You can follow any comments to this entry through the RSS 2.0 feed. You can leave a comment, or trackback from your own site.