Ascender advice

Re: toothed vs ridged

This could also be posted in 'Rules and Regs', but, since the subject here is lanyard adjusters, I'll post this here.

I've asked people at Petzl, Sherrill, Frescoe and (when it was around)Rock Exotica about the strength rating of the Microcender. Answers have ranged from 3500 to 4400 pounds, which is below the standard of 5000 pounds that is required for other hardware that is used for life support in tree work.

When doing gear inspections I have not allowed the use of Microcenders. People have criticized this because Microcenders are so prevalent and have been used for many years. But, Microjusters (now called Micrograbs), Gibbs and Rescuecenders, as well as Macrocenders and Macrograbs, are all rated at 5000 or more pounds and are adequate substitutes. The Positioner is rated at 22kN (4945.6 pounds) and, because that is the European standard, I would allow that.

Should the Microcender be allowed, even though there are several other devices that are very close in design and function which meet, or are much closer to, the 5000 pound requirement?

Mahk
 
Re: toothed vs ridged

Mahk,

This is a hard call. In Tim Walsh's article on ascenders he found out from the manufacturers that some of the shells deformed or failed above 5k#. But, the bigger issue is that they slipped at a lower rating. It points out a part of the rating system that makes the breaking strength a bit irrelevant.

I've DQ'd shell ascenders that didn't have bolts. CAn't think of not allowing any other ascenders though.
 
Re: toothed vs ridged

Tom;

The tensile strength of the microcender may be higher than the point at which it will slip, but there are some variables and there may be times when the unit is loaded and can't slip. For example, the rope may not have a fair lead into the 'cender and could therefore catch on the side of the 'cender. Another example is that the user may be at the end of the rope where there is a stopper knot. Also, the strength and slippage ratings are for certain size rope and the climber may be using a rope that is larger or smaller than what was tested.

Your point about using a bolt rather than the quick release pin is valid and I agree the bolt is safer. But, a bolt is not required by any of our standards, so there is really no regulatory basis for dq'ing the quick release pin. Also, if you argue that a bolt should be used (and I agree that it should) than why not use a micrograb? The only advantage of the microcender over the micrograb is that the 'cender has a quick release pin. If you replace the pin with a bolt then there is no advantage over the 'grab. Since the 'cender is rated below standard and the 'grab is rated above standard, the 'grab should be the choice. And if a quick release pin is desired (eg. for some type of SRT setup) then a Gibbs, which does meet industry standard, could be used.



Dave;

If we allow a below standard microcender for a doubled system why not allow the carabiner that holds the microcender to be rated at 2500 pounds?
A lanyard is a doubled system, but a climber may use a microcender for just that--ascending a single rope. In that case it would be subjected to the climbers full weight.


But, the larger point is that the device doesn't meet the standards. We routinely dq carabiners that are rated at 22kN, which is only about 55 pounds shy of the requirement. The microcender (based on the ratings that I have found) is somewhere between 600 and 1500 pounds shy.

I could understand accepting gear that is rated slightly lower than our standards if the gear meets the standards for tree work in some other locale. But, the microcender wasn't designed for treework and, as far as I know, it doesn't meet any tree industry standards.

It may seem like a small point, but judges and officials have been equally strict about other equipment. I don't understand why this particular piece of sub-standard gear is allowed to be used, especially when there are several comparable substitutes that do meet the standards.

I understand both of your arguments, but I'm not convinced there is adequate reason to allow a microcender in official competition. If it's my decision, I'll still dq it.


Mahk
 
Re: toothed vs ridged

Mahk,

You make very valid points as usual ;)

There are many examples of things in use that need more thought.

You've given me a bunch to think about. Most of our climbers use the 'cender as an adjuster.

Tom
 
Re: toothed vs ridged

[ QUOTE ]
I've asked people at Petzl, Sherrill, Frescoe and (when it was around)Rock Exotica about the strength rating of the Microcender. Answers have ranged from 3500 to 4400 pounds, which is below the standard of 5000 pounds that is required for other hardware that is used for life support in tree work.

[/ QUOTE ]

From Canadian Arborist Supply:
CanadianArboristSupply.com

"Description: Petzl Micrograb - Rope Clamp/Grab. A great cammed device suitable for creating an adjustable work positioning lanyard. A favorite choice among arborists, easily installs on rope 3/8"-1/2" diameter. Cam is equipped with a steel retention cable to prevent accidental loss while disassembled. Unit is equipped with a steel allen bolt a nylox lock nut for permanent installation on a lanyard. Specifications: Individually tested, exceeds 5000lbs breaking strength, meets EN 567 standard, high grade aluminum construction."

I wonder where they got their information?

- Robert
 
Re: toothed vs ridged

[ QUOTE ]
...strength rating of the Microcender. Answers have ranged from 3500 to 4400 pounds,...

[/ QUOTE ]

From Canadian Arborist Supply:
CanadianArboristSupply.com

"Description: Petzl Micrograb ... exceeds 5000lbs breaking strength."

I wonder where they got their information?

- Robert

[/ QUOTE ]

Robert;

I think their information is correct. The terminology is confusing here. Depending on what catalogue you look at (and how old it is) you can find the terms Microcender, Microjuster, and Micrograb. There are also Macro- versions of each of these and a Rescucender (which has a quick release pin).

A few years ago I was confused about these terms and did some rersearch. In short (there is more detail on pages 112 - 113 in Don Blair's "Arborist Equipment"): in the beginning Rock Exotica made the Microcender. Sierra Moreno (an arborist supply house) saw this as a great device to use as a lanyard adjuster, but also recognized that the quick release pin could be a hazard for treework and the shell was not up to tree industry strength requirements. SM worked with Rock to develop a device that could be used for treework and the result was the Microjuster. The quick release pin was replaced with a bolt and the sides of the shell/body were beefed up to make it stronger. If you compare a 'cender (red body) side by side with a 'juster (purple body) you can see that the body of the 'juster is slightly bigger.

The Macro-'s are slightly bigger than their Micro- siblings and are intended to be used with slightly bigger rope--a little too big for what we (arbo's) do. The Rescu- has a bigger shell, but fits the same size rope as the Micro-'s--it is intended for more gear and weight (rescue situation).

When Rock was bought out by Petzl the name of the Microcender was retained, but the name of the Microjuster was changed to Micrograb (I can only speculate as to why this was--I guess that SM had something to do with it).

I've made numerous calls to manufacturers and suppliers about the ratings, but really had trouble finding consistent specs about these--in part, because, as Tom noted, they may slip before they actually break. Nonetheless, all of the data that I did find showed that the 'cender was below tree industry standards. The once 'juster now 'grab was specifically designed for treework and does meet our industry standards.

One of the reasons that I started looking into this was that I very rarely saw any strength ratings given for the 'cender in the supply catalogues. I now think that this is because, in addition to the slippage issue, the 'cender doesn't meet ANSI standards. I did see one 6,000 pound rating given in a Buckingham catalogue, but nobody at B'ham could say where they got that number. They mumbled something about 'it has to be at least 5,000 pounds to be used in tree work', but it seems that that number was just inserted because they assumed the 'cender had that rating, not because they got it from the manufacturer.

The Microcender is allowed 'just because lots of people use it'. Yet there are adequate substitutes. The Micrograb (formerly called Microjuster) has a bolt and is very close in size to the 'cender. The Rescucender and a Gibbs have a quick release pin and are only very slightly bigger than the Microcender. To these options can be added the Positioner, the Grillion and various setups with friction hitches.

Another loooonnng post./forum/images/graemlins/zzz.gif

Hope this helps.

Mahk
 
Re: toothed vs ridged

My personal thought is that the quick release pins on both the micro and the gibbs are well thought out and very safe. I defy anyone to try to create a situation with a twig or anything else we find in trees that will cause it to release.(realistic or not) I have used both in trees and on rock and I am very comfortable with them. I would not want them permanent (bolt) because I like to switch uses all the time.

Dave
 
Re: toothed vs ridged

Dave;

My point is about the strength rating of the Microcender, not the pin. If someone wants to use a quick-release pin they could use a Gibbs or a Rescucender, both of which have a quick-release pin and meet the ANSI strength requirement.

Mahk
 
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