First You Zig & Then you Zag! Petzl Zig Zag Pt.1

When you think of mechanical prusiks, what is the first mechanical that comes to mind? For most, I would think an image of Petzl’s Zig Zag is mentally displayed, and for good reason too. Now, this doesn’t mean the Zig Zag was the first mechanical prusik to hit the arborist market, rather it has amassed a great following. For the remainder of this blog, I’ll be going over Petzl’s Zig Zag (if you haven’t guessed it yet) along with some tips that I find to be helpful when climbing trees with this mechanical prusik.

What is it?

By tradition, we arborists begin our tree climbing career on a Blake’s hitch (traditional closed system) or an open climbing system – referring to the use of approved carabiners, prusik cord, and the use of a micro pulley to assist with slack tending. In other words, it's rope-on-rope friction that we rely on to keep us in position while we’re suspended aloft. So, a solution was thought of; the Petzl Zig Zag. I scoured the internet trying to pinpoint who was involved with the creative process, aside from Petzl, but I was unable to do so. 

The Zig Zag is a mechanical prusik, replacing the need for rope-on-rope friction by utilizing friction links. The issue with friction (rope-on-rope) created this way is the inconsistency; dependent on the hitch and number of wraps applied, tree climbing rope being new or old, dirty rope, burnt cordage – there are too many variables. With mechanical prusik, it eliminates most and provides consistency.  The friction links when collapsed and/or expanded are like that of a finger trap toy. Think about it; when the links are depressed and fully collapsed, the rope is allowed to glide through without issue – when a finger trap is compressed, one can free themself from the toy. Conversely enough, releasing the links and allowing them to expand (on the rope), creates the necessary friction contact between the links and rope to clamp onto the rope and prevent the climber from sliding down; same as when the finger trap is expanded – traps the user’s fingers in place. Slack tending is made easy, thanks to the pulley mounted on sealed ball bearings. This means reduced friction and allows for smoother rotation and an increase in efficiency. 

Useful Technical Information

Before we cover some tips involving this mechanical prusik, there is some information that must be shared and understood. The Petzl Zig Zag has a working load limit set at 140kg, which translates to 308 lbs., and that WLL includes tree climbing gear, chainsaw, boots, whatever you are hauling up with you. Rope diameter acceptance ranges from 11.5mm to 13mm; in their testing to acquire an EU certification, Petzl tested with Teufelberger Tachyon (11.5mm) and Hi Vee (13mm) ropes. They also require ropes that meet EN 1891 Type A ropes. Having been around plenty of Zig Zag users, pairing it with a 13mm rope and then wishing to pair it with a smaller diameter rope may not be ideal as the links may see increased wear and the new smaller diameter rope could cause slippage with the device. Instead, begin using the Zig Zag with an 11.5mm rope, and as the device begins to wear, begin increasing the rope diameter; provided it still passes inspection and the amount of material worn-down isn’t excessive. However, this can be dictated by safety personnel at the respective company one may work for. 

Petzl carabiners such as the OK and Am’D are compatible, no questions asked, and I distinctly recall being instructed that they were the “only” carabiners allowed to be used with the Zig Zag. But in reviewing the technical specifications (yes, I do read it), Petzl states that if another connector is used, it must pass a compatibility test checking for proper installation and function. It does get specific on which carabiner(s) can be used to attach the Chicane to the device; using only H-frame Petzl Am’D or OK carabiners. Installing the correct carabiner to the Chicane can prove to be cumbersome but don’t fret, this was by design to eliminate the carabiner from shifting while in the Chicane. My advice, marry a carabiner to the Chicane and have a separate carabiner for MRS application, no more headaches. At the attachment point from device to harness, it's recommended a Petzl Captiv Bar be used. These little guys prevent the carabiner from side-loading at the attachment point, which forces the load to shift to the spine of the carabiner.

Let's get to it!

There have been three versions of the Petzl Zig Zag, I believe but I could be mistaken. The first original model had a thin eye splice return attachment point and an almost nonexistent flare at the bottom. There was an issue with the Zig Zag involving the top attachment point and the rating it carried and was pulled from the approved mechanical list for competition. Shortly thereafter, the second version was released, where a change on the device was noticeable. The attachment point for the returning eye splice had been “beefed” up and a grommet was inserted between both side plates at the same location, which was done to prevent carabiner cross load. 

As SRT began gaining immense popularity, people began experimenting with the Zig Zag, eventually to the point where various people reached out to Petzl and began asking for clarity as to whether the Zig Zag could be approved for SRT and compatible with a Rope Wrench. At the time, Petzl did NOT give consent for their device to be used that way, it was still only an approved DDRT (Moving Rope System now) device and had not been tested and approved for that climbing style. It’s understandable; they did not want to give a thumbs up to something they had not done their due diligence and be held liable for a potential misconfiguration. 

In April of 2019, Petzl launched the new Zig Zag in two different designs, Zig Zag Plus and just, Zig Zag. What are the differences you might ask? The plus version is complimented by a swivel while the other version at the request of many, provides a fixed attachment point, providing the user a “peace of mind”. This 2019 version was considerably larger, has an additional connection point, to what Petzl calls an “auxiliary attachment hole”, and is approved for SRT climbing applications provided it is only paired with the Petzl Chicane. The Petzl Chicane is an “auxiliary braking device”, it adds friction to the system when climbing SRT which is needed to keep the device functioning properly. The arrival of the Chicane sparked controversy amongst the tree climbing community, stating it was done in an attempt to “control” sales. 

Only the Petzl Chicane is meant to pair with the Zig Zag, even though it has the same purpose as a Rope Wrench, but there are specifics to this. The Chicane is designed onto a stiff body tether, allowing the climber to use it as a handle during short burst ascents; the soft tether of the Rope Wrench is not a handle and should not be used as such. Perhaps the most important reason; when attached correctly to the Zig Zag, the head of the Chicane cannot contact the links and will not send the user in an uncontrolled descent; the soft tether being flexible can allow the Rope Wrench head to inadvertently contact the links, which can lead to an undesirable outcome.

Along with the newly revamped 2019 models, they were followed by a Safety Inspection Notice in 2021. Users had reported slippage with the device and Petzl quickly acted, they issued a stop sale to distributors, a request for inspection and if the device proved to fail the inspection, an exchange was then given. Their technical investigations led to a variance in the production process which then led to the discovery of two defects in the release levers. 

1. Random malfunction of the spring effect of the upper release lever,

1. Variance in the surface treatment resulting in a modification of the geometry of the release lever.

Whether using this climbing device in moving rope or SRT, only the uppermost attachment point is used to connect a splice or Chicane. If the auxiliary hole is used for the returning eye splice connection, the device is thrown forward and risk for the release levers to contact the splice or knot is now greater and if the returning eye splice is connected to the harness rather than to the device, the rope can wear the plastic portion of the device quickly. 

Inspecting your gear is important!

From climbing equipment to rigging gear, it all needs to be inspected, some more than others. Here are some key points to inspect with your Petzl Zig Zag while it is off-rope:

• Cracks, deformation, wear, or corrosion. Special attention is required at the release lever for wear.
• Check the effectiveness of the spring located within the release lever. Collapse the links, depress the release lever, it should immediately spring back to an upright position. 
• While at the links, extend and compress them; they should move freely.
• Along the rivets of the chain links, there should be no play; look closely for cracks. 
• The rivets along the main body must all be present, and there should be no play. 
• The sheave should turn freely, and there should be no play in its axle. 
• At the main attachment point for the returning eye splice, check the positioning ring for cracks, corrosion, and deformation. 
• We don’t have x-ray vision, so checking the swivel consists of making sure it turns freely. 

This blog is to be continued…