Tech Tip: Impact forces during a fall

Petzl’s revamped line of ice tools arrived in climbers’ hands in Fall 2018, and over the past few months they have undergone intense scrutiny, most particularly the new Nomic. The original Nomic was a game-changing tool for many climbers, and I still know quite a few that have — and climb on — their original pair. The Nomic underwent a minor redesign a few years after its initial introduction that, arguably, ‘broke’ the tool. The second generation was plagued with loose heads and broken pommels, especially here in the Canadian Rockies where ice tools see much greater temperature extremes which, when combined with significantly higher overall usage, contribute to greater potential failure rates. This newest Nomic — the generation three — has seemingly improved upon every shortcoming of the 2nd-gen, and even added the much-requested spike and clip-in point at the bottom of the pommel.

Though there have been a few isolated incidents of the lower pommel snapping and breaking off — most often as a result of repeated impact against ice due to improper swing angles— it wasn’t until one particular Facebook post that numerous questions about the design and durability of the 3rd-gen Nomics’ pommel came to light.

As you can see from the photos posted above, this particular Nomic suffered a disastrous failure of the lower pommel as the direct result of a fall. In an effort to understand what happened, I reached out to the climber involved. The below is a rough, shortened, translation of our conversation, which took place in Polish:

“I had my leash clipped into the hole where, according to the instructions, you’re supposed to clip them. I took a fall, about 0.5m (approx. 1.5feet) above my screw. Nothing happened to the leash but the lower handle ripped off and my tool fell two pitches down to the ground. This was my first time using them. Not only was the lower pommel broken, but the retaining teeth were also damaged, rendering the ice tool unusable.”

The climber in question was using the Petzl V-Link leash and weighs around 58kg. For the record, the store where she bought the tool replaced it outright.

So what happened? And what can we learn from this incident?

First, I think we should examine the reasons why people use leashes, or tethers, with their tools. For me it is simply a tool-retention system. I don’t use leashes often, but when I do it’s on funky, chandeliered, very steep or awkward ice where I feel that there’s a chance of knocking my tool loose or it falling out of a shitty placement. I don’t — ever — rely or have relied on my leashes as either a fall-protection system or as a static rest. From the online discussions, however, it appears that many people treat the clip-in point and leashes as a temporary anchor system, something neither product is designed for.

This disparity in usage stems partly from the various way we all climb and use our ice tools. Here in the Canadian Rockies, using a tool as part of your anchor is a last resort. I’ve seen equalized pitons, tied-off 10cm ice screws and questionable spectres all used as part of a belay anchor — not all at once, mind you — but I have yet to see a climber fully commit one of their ice tools to a belay anchor.

The situation is similar in the Alps, where the use of an ice tool as part of an anchor has long passed from common use.

However, things are a little bit different in Scotland, where the use of natural gear is paramount and using ice tools as part of the anchor still appears commonplace. I have never climbed in Scotland so I am loathe to question their methods, but there is a piece of equipment designed to specifically replicate the placing and retention that an ice tool provides: the spectre (aka bulldog). If you’ve never seen one it’s kind of like a half-length ice-tool pick but instead of being attached to the shaft of an ice tool it’s got a sling on the end. They’re bomber when placed correctly, which in my mind brings forth the question of ‘why not just bring a couple spectres?’ instead of using your ice tool as part of the anchor. But, again, I’ve never climbed in Scotland so maybe the spectre idea just doesn’t work…

Based on this information, and some historical details, I think it is safe to ascertain that while certain climbing areas have adapted to modern tool design and climbing techniques, others remain entrenched in the style of their forebears. There was a time when the only style of climbing tool was straight-shafted with riveted heads and riveted spikes: every point on the tool could be considered full strength. But, modern tool design has changed significantly and now there are additional pommels and spikes and other clip-in points that are not necessarily full-strength.

The latest, third-generation, Nomic has several full-strength anchoring options. Pierre Plaze, head of Petzl’s Sport climbing division, says: “We will not recommend to use the tool or tools to reinforce a belay station. But if you want to do this, use the cut-outs in the NOMIC handle, or tie a sling around the shaft.”

The spike, or pommel, is “dedicated to tethers, this is only a loss prevention system.” It isn’t even meant to be a rest position: “If you want to rest, tie a sling around the shaft or thru the cut-outs in the NOMIC handle.” Of course, figure 5.3 in the Petzl Technical Tools Manual shows a tool being clipped through the spike hole, however Plaze says “This diagram is dedicated to the QUARK only, we may need to make this information more clear with an update.”

What this means is that if you’re clipping through the spike hole on the new Nomic (or Ergonomic if you’ve swapped the pommel for a spiky one) then please understand it’s not designed to hold any weight — this hole is for tool retention only. If you want to clip in, either for a rest or to use the tool as part of the anchor, then there are multiple cut-outs in the handle that will accommodate slings, and certain models of carabiners will also fit through the lower (largest) cut-out. Still, however, this is not something that Petzl recommend. “The ice tool is dedicated for progression while climbing,” says Plaze. “In any case, the tools are not supposed to be full strength in case of fall on your tethers, the energy created is way too high.”

I am fortunate to have access to a load cell and out of curiosity thought I’d see just what kind of forces are generated during a small slip. I threw a sling over a handy goal post, clipped myself directly into the load cell and kicked my feet out. The ‘fall’ couldn’t have been more than 10cm or so but my 75kg mass generated 2.06 kN of force (that’s 210kg or 463 pounds of force). With a slight jump to increase the height of the fall, the impact forces went up to 3.66 kN (that’s 374 kg or 823 pounds of force)!!

Going back to the incident that sparked all this conversation, it is clear from Petzl’s design that the tool didn’t ‘fail’ in an unexpected manner. The force generated during the climber’s fall was so much greater than the 1.5kN rating that if the spike hadn’t broken it would’ve been the leash — most leashes are designed to withstand a max 2kN of force — and if for some reason the pommel and the leash held then I’m sure the tool would’ve been ripped out of the placement.

There’s been quite a lot of discussion around the design of the Nomic but to me the issue appears to be a misunderstanding of the design rather than a failure on the part of the manufacturer. The instruction manual clearly states the strength of the lower pommel, though I do agree that there can be some misunderstanding in using the lower pommel as a ‘rest’ based on figure 5.3 in Petzl’s own technical notice.

Please read the manual and ensure you understand the limitations of your equipment. There’s an old saying that “a poor craftsman always blames his tools” but when it comes to your safety, there’s nobody to blame but yourself.

Damaged pommel photos by permission of photographer.

14 thoughts on “Tech Tip: Impact forces during a fall

  1. JD says:

    Interesting. I had my doubts about the spike (I have the Ergonomic which doesn’t have cutouts in the handle) so I asked Petzl about a month ago.

    “Subject: Clipping Griprest Nomic to hold body weight

    Hello,

    The tool in the diagram for “resting position” in the technical notice is a Quark. Is it OK to weight the Griprest Nomic on a Nomic or Ergonomic the same way? I know they are constructed a bit differently. ”

    Their reply:

    “Hello,

    The artwork showing this clipping is from a shared section of the ‘technical ice axe’ technical notice applying to multiple models, so it does reflect the recommended technique for the Nomic. In the Nomic specific section of the technical notice Petzl does state the 150 daN rating of this point.”

    I’ve never weighted a leash or tool to rest but I’d like Petzl to get the story straight. Just want to be aware of the options in a pinch. I think I’ll go with my gut instinct which was not to trust the spike hole.

    • Raf says:

      Thanks for that! My information is coming straight from Pierre Plaze who is the Product Line Manager for the Sport Verticality division so I’d trust his information over customer support. I’ll pass this on to Petzl so they can ensure the proper information is disseminated.

  2. Alan Halewood says:

    I’d question whether its ‘commonplace’ for us Scots to use our tools as part of the anchor in the way you describe. I’d call it a last resort used usually on turfy ‘mixed’ climbs where you have no other options and have used up all your turf gear like Bulldogs/Spectres or Warthogs. I’d far rather carry extras of these than rely on my tools in the belay and it’s certainly not taught as a mainstream technique. We are slowly moving into the 21st Century 😉 Al

  3. Toby says:

    I don’t want to speak for all British winter climbers (not just Scotland – there’s a bit of winter climbing in England and Wales too!) but beyond learning about buried axes, T-axe anchors and so on when you start out, I don’t think using your axes placed by their picks as part of the belay is really a ‘thing’ in Scottish winter unless you’re completely desperate and there’s nothing else. And then trusting a bungy leash is even worse as clearly they’re not very strong. In the old days with wrist loops attached to the head of a tool, you might clip the wrist loop if you knew it was well tied and made out of full strength nylon tape, but only as part of a t-axe anchor. But perhaps for a few people that’s drifted over into thinking they can rely on bungy leashes on modern tools in a similar way? Terribly bad idea though! There have been cases I’ve read about in the UK of people falling off their tools when pumped and being caught by their leashes, but I remember hearing about leashes breaking in that situation too – so not something to rely on!

  4. Magnus Strömhäll says:

    Thank You for informing the general public. Was the climber involved unaware of the forces involved in falling onto a tool lanyard? I’d say the pommel performed as expected during this incident.
    As the Scottish already have said they do use spectres/bulldogs. Only used axes once, at the top where there was only heather. Ground stakes would have been perfect;)
    /Magnus Strömhäll
    from the west coast of Sweden

  5. yw says:

    Hello,
    How strong the”full strength” is? Does it mean the same load resistence to the T/B rating of the ax shaft itself ?
    I’ve read this term in articles, tools specs, etc. but never found a definitiion about it.

    Thanks

    • Raf says:

      That has always been my understanding, but in light of all these issues and questions I will confirm with Petzl later this week.

  6. Mike says:

    I’m curious what sort of forces are generated when on lead and your feet blow and you shock load a well planted tool with body weight through your arm. Your arm obviously is a lot more dynamic than your load cell setup, so I would expect lower numbers. However, it just seems that 1.5 kn is a pretty low number given that it’s not uncommon to see climbers who weigh close to 1 kn when you consider a pack and the like.

    • Raf says:

      Me too – I am going to set up some scenarios later and perform a whole bunch of tests over the next few months.

  7. Jon says:

    Hi,

    In your photo about half way down your text pointing at the spike hole says “Not a full-strength clip-in hole – 1.5kN MAX”. In the respective quark- and nomic-specific technical notice pdfs on the petzl site, this same rating is given for the spike holes for both axes. This would suggest to me that both are ok for resting but neither are “full strength”. Reading your text just below your photo, are petzl saying in their reply to you that the spike hole is ok for resting for the quark, but not for the nomic even though they have the same apparent rating? Sorry – I may well have misunderstood!

    • Raf says:

      Yes, the ‘diagram’ is meant for Quark not Nomic tools. I’ve mentioned this to Petzl and they know about it and are working on a fix so expect a new tech notice soon. But in the meantime, please don’t put a lot of weight on the Nomic lower pommel — it’s not designed for it!

  8. Dave Rose says:

    Hi,

    I have recently experienced this first-hand, I took a lead fall in Rjukan approximately 3 metres above my last screw (which I understand is not the norm, however I was at the belay so I deemed it unnecessary to place a screw). I had held of one axe and the other was in a placement, the one I held came with me and I assume the pommel snapped on the placed one which actually landed beside me. I fell around 10 metres with rope stretch so I assume I generated quite a lot of force but not enough to snap my leashes the pommel broke before the leash. What would you suggest the best course of action is ? Return to the store I purchased from or speak to Petzl ?

    • Raf says:

      Ouch! Are you ok? Did you hurt anything?

      As far as your tools, I’d say head to the shop and explain what happened: a good shop will sell you new pommels at a discount, while a great shop will just give you new ones. (Or that’s how I’d run my shop if I ever have one, anyway!)

  9. Ron Dempster says:

    Interesting article, the load cell setup is interesting and raises further issues when climbing and the benefits of using (dynamic) rope in the belay. The lifting sling used will have little stretch whereas if a dynamic half rope was used the impact would be greatly reduced. I often use the rope in belays to reduce impact loads, using different knots (Fig 8 or 9 rather than clove hitch) can also reduce impact loads on the anchors. Static dyneema slings do not stretch and as such increase the impact loads on anchors.

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