Ascener article page 2
The Microcender is intended for use on ropes 7/16 inch to ½ inch and is rated at 3,500 pounds (15.57 kN) minimum breaking strength. Rope slippage begins at about 900 pounds. The Rescucender works on 7/16-inch to ½-inch ropes but has a breaking strength of 6,000 pounds. The Macrocender is designed for ropes between 5/8 inch and ¾ inch and is rated at 6,000 pounds. It also begins to slip at approximately 900 pounds.
Another type of ascender is the CMI Ropewalker. The Ropewalker has made some changes on the original Gibbs design, such as creating gaps in the shell to allow dirt and debris to fall out of the ascender, so that it does not compromise the ascenders' holding power. The Ropewalker is rated at 7,500 pounds but rope damage (sheath failure) occurs at just over 3,000 pounds.
There are some ascenders designed to work on two strands of rope. The Rock Exotica Footlocker was specifically designed
to be used when ascending a doubled rope while footlocking. There are two separate cams within one shell and each cam has
its own channel for one strand of rope. The Footlocker has a two-stage, spring-loaded pin that locks the cams in place. The
tensile strength is in excess of 6,000 pounds, but when shock loaded in a drop test, it slipped at around 3,800 pounds.
Another cammed ascender that works on two strands of rope is the Petzl Shunt. The Shunt is designed for either one or two
strands of rope, but was designed for ropes that are smaller than ½ inch (11mm maximum). The attachment point breaks at
4,496 pounds (20 kN) and the device may begin to slip with only a few hundred pounds (1-8 kN).
There is a greater diversity of the toothed type of ascender, but they have more limitations than the cammed. The toothed types
are used for ascent on a single or doubled rope. The Jumar, by Blue Water, is a commonly used ascender in other disciplines.
It will accept rope sizes from 6 mm to 14 mm (.236 - .551 inches), but its breaking strength is 1,600 pounds. Some are
stamped at 1,100 pounds.
CMI makes a few different types of toothed ascenders that have found their way into some tree climbers' gear bags. The
largest, the Expedition, is rated at 4,000 pounds. The Large Ultrascenders are rated at 4,600 pounds and the Small
Ultrascenders are rated at 3,500 pounds. Under test conditions, the ascenders caused the ropes to fail at significantly lower
loads than the minimum breaking strength of the ascender itself. When the rope failed, the sheath on the kernmantle cord
ruptured at between 1,000 and 2,000 pounds. These tests were run on kernmantle rope, where the majority of the strength is in
the core. We do not have data on how they would react if tested on arborist rope.
The use of Kong equipment has become more prevalent in the past few years. Kong has a variety of devices that can be
adapted for use in arboriculture, and they have neat colors, too. Kong has a toothed, double ascender that has combined a left-
and right-handed cam and one handle with places for both hands. This is used to ascend a doubled rope like that used for
footlocking. It has been designed to take ropes between 7/16 inch and 1/2 inch. As with other toothed cams of this style, it is
designed to be used for vertical ascent, and the rope can slip out if used to traverse or if it is pulled to the side. They are tested
to hold a load of 1,124 pounds (5 kN) without damaging rope. The top eye is rated 4,271 pounds (19 kN) and the bottom is
3,372 pounds (15 kN).
Petzl has a number of toothed ascenders, but the most commonly encountered are the Ascension ascenders. The right- and
left-hand ascenders are color coded - blue: right, yellow: left - and feature a large opening for easy access with a gloved hand.
They will accept ropes between 8 mm and 13 mm (.314 - .511 inches). There are three attachment points in the body of the
ascender: the upper point is rated at 18kN; the large lower point is rated at 20kN; and the smaller is rated at 15kN. The
ascender will cause the rope (kernmantle) to fail between 4 kN and 6.5 kN.
The Petzl Pantin is somewhat similar to the Ascension, but it looks like it is missing the handle. The Pantin is designed as a foot
ascender and comes with a trap designed to hook to the foot. It will take 7/16-inch to ½-inch rope. This device was not
intended for personal support so it has not been tested and rated.
As technology advances, we sometimes struggle to keep up. It seems as if there are new gear choices and techniques every
time you go to TCI EXPO or the annual ISA meeting, or read the latest magazine. There is a newer classification of ascender,
called a "swing sided self-jamming pulley." There are currently two of these products being used by arborists: the Mini Traxion
and Pro Traxion by Petzl. Tensile strengths are reported as 20 kN for the Mini and 22 kN for the Pro Traxion.
So, to wrap things up, we need to ask, "Are ascenders good or bad?" By now, most of you know the answer to that
question… yes. Ascenders offer us a wide range of ways to make our jobs safer, easier, and often times more efficient, too.
Caveat emptor though. Many of these devices were designed to be used on kernmantle rope and in very different situations
than we use them while climbing in trees. The manufacturers repeatedly stress that they are not meant for shock loading. They
are almost always used as one part of an ascent system, with backups where and how appropriate.
Based on my experience and this research, I think cammed ascenders are well adapted to be used for personal support as
lanyard adjusters. Put a bolt and locking nut in or buy one that has a locking system that minimizes the chance of the cam falling
away from the shell.
The toothed ascenders do not seem to be as well adapted to our profession, especially when you keep the current Z133.1
standard in mind. Many of them are below 5,000 pounds minimum tensile strength. In testing, many cause severe damage to the
ropes at loads much less than the tensile strength of the device. Keep in mind that these tests were done on kernmantle rope,
which they designed them for. We do not know what the test results will be when arborist climbing lines are used.
Single Rope Technique can allow for convenient, safe backup for toothed ascenders, but doubled rope ascension systems are
much more difficult to back up without installing a separate belay line. (See The TreeWorker, February 2002, for more on
backing up these systems.)
So please think about what you are using, its strengths and its limitations. Keep climbing safely.
Tim Walsh is a staff arborist for the National Arborist Association.
