3, 2, 1… off to Monza!

… tomorrow, to be precise, to set up the European Tree Climbing Comp.

The weather looks like it might play along nicely for a change…

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Oh yes, I can handle that. Will make a nice change from struggling to get gear away before the torrential downpour kicks in, the way it seems to have been the last couple of years. But maybe I should not be shooting my mouth of here, tempting fate and all that.

Stay tuned, I will do my best to keep you updated with the news as it happens. No promises though, things can get a little frantic.

Mind the bend

Over the weekend I was reading up on the story of the de Havilland Comet. The reason for this was that it came up in a conversation with my dad the other day: I had read about it before, but had forgotten the story since…

The Comet was the first commercial jet airliner. The maiden flight of the first prototype, the Comet 1, flew in 1947, with the debut for regular flights following in 1952. The aircraft boasted an aerodynamically clean design with four de Havilland Ghost turbojet engines buried in the wings, a pressurised fuselage, and large square windows. At that time, the Comet was the leader of the pack, de Havilland was well ahead of its competitors’ offerings.

Then, in 1954 two disastrous hull losses occurred to Comets belonging to BOAC and South African Airlines that broke up in mid-air, resulting of the loss of all passengers and crew on board. The inquiries looking into the causes of these incidents examined various scenarios, from sabotage to clear air turbulence, but in the end came to the conclusion that the principal cause of the accidents were much simpler: square windows.

Stress around the window corners was found to be much higher than expected, while stresses on the aircraft skin were generally more than previously expected or tested. This was due to stress concentration, a consequence of the windows’ square shape, which generated levels of stress two or three times greater than across the rest of the fuselage.

As a consequence of the inquiry, this issue was addressed by modifying the square window design and replacing it with round ones – yet for de Havilland the damage was done: competitors had learned from the Comet’s design flaws and had drawn ahead in the race for the skies.

Rather sad actually and certainly a cautionary tale, as it illustrates the risks innovators run and how these may – or may not – pay off. Things that in retrospect seem blindingly obvious were not so at the time. One thing is for sure though: next time I fly, the Comet tale will make me look at the round aircraft windows with fresh sense of appreciation.

All this brought to my mind discussions regarding bend radiuses for synthetic lines, as this also involves the deflection of forces, with failure occurring at the point of maximum deflection. This is one of the reasons for knots reducing the breaking strain of lines and also why we consider the ratio of the width of pulleys to the lines we run over them.

The other aspect it highlights is the need for high-cycle testing. I have mentioned this before, but I will say it again:

It is simply insufficient to only test the maximum force that an assembly or component can withstand, it is crucial that the fashion in which it responds to cyclical loading has also been assessed. One of the things that the Cohen Committee did when looking into the reasons for the Comet crashes was to build a dedicated water tank in RAE Farnham that enabled them to repeatedly re- and over-pressurise the hull of the aircraft. After 3’057 pressurisations the hull burst open.

Regardless of whether it is metal or synthetic components being considered, cyclical failure needs to be considered and tested for.

Dramatising vs. trivialising

I stumbled across a video this morning discussing the issue of gaffing out, which describes the situation in which spikes or gaffs are used as a work positioning aid and are unintentionally knocked out of the wood, resulting in a slip or a fall.

The video’s general tone was that it is not a big deal and suggested that if you think gaffing out is a big deal you ought to harden up. It also suggested that gaffing out is as much part of working on spikes as tripping is part of walking.

This got me thinking.

Is it really a simple as that? Gaffing out: is it a big deal, a major hazard we have to deal with – or a minor risk that we just take into account? This post is not intended in a confrontational fashion, rather it is an attempt to gather the thoughts that have spent a day kicking round my head whilst contemplating this question into something more or less coherent, so bear with me.

So if indeed our premise is that, as I wrote above, gaffing out is a much part of working on spikes as tripping is part of walking, then my response to that would have to be: ok, but when I walk I attempt not to trip, as depending upon when and where a trip occurs the consequences can be either negligible – or very significant.

Probably the same can be said of gaffing out: it is ultimately down to the situation in which it occurs whether is is more or less serious.

Gaffing out while using a chainsaw is obviously not a good idea. Doing so on low diameter, smooth-bark stems with no or little taper can lead to potentially hazardous situations, this can be exacerbated by an unfortunately positioned stump in the way of your fall. Wet or freezing conditions can further change the picture radically.

If we are complacent and suggest that all that is needed in order to address this situation is to harden up, then we do so at our own peril, as the solutions to addressing this risk are really quite easy and plentiful, such as:

  • using the right length gaffs for the tree species you are working on. Hard wood is easier to position on with short spikes, whereas thick-barkes species are easier to work with longer ones. Switch this around and you will find yourself struggling either to get a good purchase through the bark or to place the spikes well into the stem.
    Gaffs come in all sorts of shapes and lengths. Use the right ones for the type of wood you are working on. Image: Treetools NZ
  • double wrap the lanyard on low diameter stems to prevent sliding down. This is not a trivial matter – essentially it is an uncontrolled fall, despite the fact that you have a lanyard around the stem whilst it is happening.
  • use a link between the two parts of the lanyard either side of the stem, for example a low diameter prusik loop with a karabiner on it. This link can be pushed up against the stem, by doing so you are able to prevent a sliding fall. In France this is a legal obligation as defined per legislation.
  • understand the tool you are working with: I alway cringe a bit when I see people ramming their spikes into the stem repeatedly before making a cut… Just making sure it is really well in!. This to me is indicative of a person who does not trust their tools. If the spikes are sharp and well placed, there is a low risk of them popping out.
  • place the spikes in a radial orientation towards the middle of the stem rather than tangentially, across the stem. Do not balance on the spikes, rather rotate your foot in, so that your big toe makes contact with the stem, this position increases the contact area and is therefore inherently more stable.

I am stymied by the fact that for a tool that is so ubiquitous in our trade there is so little formalized guidelines on how to use it. I assume this is because the general assumption is that it is self-explanatory. I disagree with this position quite strongly as it is not reflected by my experience when training people to use it or observing climbers moving around on spikes.

I agree with the sentiment expressed in the video that used correctly, gaffs or spikes are a great tool. I am less convinced by the argument that gaffing out is inevitable and therefore simply to be accepted. Rather, I would suggest that this is a further example of a risk that we are perfectly able to manage and have the means to address. By doing so, the question of whether gaffing out is a drama or a triviality becomes a moot point.

When terra firma meets SpongeBob

This was another interesting aspect of the crane job we finished up yesterday I wanted to mention.

As I wrote in yesterday’s post we had been on site two months prior with exactly the same model of crane with nary a sign of this very heavy vehicle passing through. Margarethen Park is situated on the southern edge of Basle on a north-facing slope which is full of natural springs, so there is an abundant flow of water down the hillside allowing trees to grow very tall, with many very beautiful, mature specimens of a range of species forming a spectacular display in the tradition of English landscape parks. One of the largest hornbeams I know of is on this site with a height of probably close on 30m.

Anyway, I digress. There has been prolonged, heavy rainfall the past week or so, leaving soils well saturated with water.

We arrived in the park just after the crane had arrived and I was surprised by the amount of damage to the tarmac it had caused on its way in. The spot we had to manoveuver it into is pretty tight, it was a hassle the first time and proved to be no better this time round: the lads from the city and the crane crew were fiddling around trying to get it in the right position… when I was struck by how the crane was sinking into the tarmac as though it were jelly. You could actually watch is sinking in! Ack! Not something you see every day and not very reassuring…

As you can see in the pics above, the struts were on non-reinforced ground and despite the plates to distribute the load over a larger area were being depressed into the ground considerably. I was really struck by how differently the ground responded to being loaded between the first time we had been on site, in dry conditions, and this second time when it was wet. Obviously the foundation under the tarmac had been washed out over the years and the layer of tarmac itself was not very thick. These factors combined led to terra firma being, well… somewhat less than firm, more like trying to position a very heavy machine on a sponge.

I was feeling increasingly uneasy about all this until I decided that enough was enough and got everybody together to discuss how to resolve this issue – and if this were not possible to call off and postpone the whole operation. After a chat with the crane crew and their dispatcher we decided to give it another crack with larger load-distributing plates to spread the load over an even larger area, but these had to be brought in first, which meant another 45 minutes of waiting. When these finally arrived and were positioned, things started to feel somewhat more coordinated and together.

What this situation illustrated very clearly to me is that ultimately as I was going to be positioning the chains off the hook and was going to be positioned downhill from the crane during the lift it was my right to question a situation that I felt uncomfortable with. More than that: as the crane company was a subcontractor to us it was my duty to ensure that all possible measures were being taken make procedures as safe as possible.

Obviously, getting the crane stable is a prerequisite.

This is another example for a situation where if it cannot be sorted out satisfactorily – and despite the fact that machinery and personell are on site – saying no is always a viable and permissible option.

Documentation, documentation, documentation

A good aim in life, in my books at any rate, is to strive to constantly improve, to get better at what you are doing and not to repeat the same old mistakes.

In order to do so, you need to have the means to evaluate feedback, to recognize strengths and weaknesses – only then are you able to define areas in which you can get better. I suppose in the broadest sense of the meaning this is a form of quality control, a rolling evaluation of the work you are performing.

Take for example crane fellings: I do not understand how people can do these without documenting lifts, estimating loads and recording the actual weight. We have been doing this for a fair number of years now and it has helped me a lot in becoming more accurate when it comes to estimating loads – this does not mean that I do not sometimes underestimate a load, I do, but rather that when this is the case that I realize that I have done so.

Below are two shots of the lift documentation of an Ash tree we removed recently. We ended up having to do it in two goes separated by a few months, this was due to a colony of protected crows that had young in the nests at the time it was decided to remove the tree. As it was deemed to be structurally unsafe and right over a tennis court, the decision was taken to remove it in two steps. The crane we used on both occasions was a Liebherr MK110. We were maxing out its reach, with a load capacity of around 2t at the outmost point. During the briefing with the crane operator we decided to aim for one ton picks.

I felt this was an appropriate safety margin, especially in view of the fact that the weight of Ash can be quite tricky to estimate, due to its large vessels that introduce a high degree of variability in weight, depending on the amount of water that is being pumped through the system at that point in time.

Used in a responsible and competent manner, cranes are a great tool. At the same time, the other side of that coin is that if you get it wrong, bad things can happen. And bad things involving big machinery tipping over really are quite bad. Badbad. Doubleplusbad – potentially.

Attaching loads correctly so that the mass is held in position during the lift, correct work positioning, correct cutting techniques, clear communication between the climber, the team on site and the crane operator – and last but not least, documenting the lifts are all indispensable tools to ensure we are managing risks to the highest degree possible when big machinery meets arborist techniques.

Finding solutions

I used to worry about the fact that I started training and working as an arborist straight out of school – and had no other formal training that I could fall back on in case I was not able to do tree work any more.

More and more though I have come to realize that the work we do demands a very wide range of skills and makes you very good at finding practicable and efficient solutions to problems. Take rigging as an example:

Every tree poses its own unique set of problems, there is not one size fits all here, every time you are having to decide on the spur of the moment how you are going to tackle this specific set of problems in a safe and efficient fashion. Sometimes this may simply involve free falling bits of the canopy, other times it may demand complex rigging techniques, drift lines or load transfer systems, for example. Or a combination of both.

I love these challenges: they force me to keep an open mind when approaching them, to have an accurate feeling of where my abilities lie and what my limits are, to be prepared for situations to change suddenly, to be able to respond when unforeseen things occur. Rigging really is where all the different aspects and skills of tree work come together, the climbing, knowledge of the species you are working on, physics and knowledge regarding the tools you are using.

Sometimes solutions are unexpected.

I was taking down a Birch with Pascal yesterday. In the pouring rain. Covered in ivy. Yes, Monday indeed. Anyway, ideally I needed to redirect the line to position it over the part of the canopy I wanted to lower, but I did not have a redirect pulley at hand… how to solve it?


Pass the rigging line through a handy cavity and hey, presto! you have a redirect.

The really handy thing was that afterwards I could simply tie a running bowline onto the same point and lower that limb. Made me smile (how appropriate, come to think of it: “smile” shares the same letters as “slime” – and slimy is exactly what all the gear was after Monday morning! Days like that make you appreciate de-humidifiers).

So there you go. The point I was trying to make is that I have come to realize that by being able to work towards and implement solutions, you have acquired a really useful skill set that will do you good services in life.

And have stopped worrying – well, about that, at any rate, makes room for new worries.

Nie mój cyrk, nie moje małpy

Came across this Polish idiom – that translates as Not my circus, not my monkey – which is used to state that something is not your problem.

I think it is grrrrreat! Circus? Monkeys? Count me in! Therefore I have decided to promote this heavily and spent the afternoon trying to think of some way to incorporate it into a blog post… so far it is all a bit tentative, but who cares? After all, I am the person writing this blog, so here we go…

Situations in which you could use Not my circus, not my monkey:

My tree is dead, it died maybe two… or three, no actually, make that four year ago. I really need you to take it down, Mr. Bridge. Oh yes, and by the way, we do not have much of a budget for this work.

We need one of your guys on site for tree protection this afternoon. Short notice? Maybe, but I forgot to phone before.

I want you to top my neighbour’s birch, it gives my wife hay fever.

I’ll give you €50 if you lop of a bit more of that branch you are sitting on so that I get a better view of the river/ cathedral/ bridge/ mountains/ lake …

If you don’t like it, there are plenty of others who will be glad to do so.

You get the idea. I can think of any number more examples, but either they are not politically correct or might be offensive. Or both, so I will leave it at this.

Not my circus, not my monkey: Get it out there, spread the word.

Things that puzzle me, number … I’ve lost track, but one of many, that much is for sure

Tree people know all about rigging.

We dismantle trees with rigging systems of lesser or greater complexity, depending upon the situation. Sometimes, when the situation allows for it, we will rig speed lines, zip lines, Tyroleans, Flying Foxes… a range of names basically describing the same thing: a tensioned line between two anchors allowing to move a mass from the higher to the lower anchor point avoiding an obstacle below the structure being dismantled. The image below from a report commissioned by the UK HSE/ Forestry Commission, Evaluation of current rigging and dismantling practices used in arboriculture, illustrates the elements which might be employed in such a set-up.

Rigging a speed line can be fairly complex, involving floating anchor points, putting anchor points in compression by rigging beyond the high anchor or combining lowering systems with the tensioned line. The forces that a tensioned line can generate onto the anchors can be considerable, therefore speed lines are never used in a dynamic fashion, i.e. limbs or stems are never snatched directly onto them.

So far, so good.

I saw some imagery the other day of a Tyrolean at a tree care event as part of the family fun part that kids and spectators could zip down on. I was concerned by the fact that this was being run on a single line, on a single sheave pulley. Why is this an issue you ask? I think the following video of a rescue exercise in Peru that went seriously wrong is quite self explanatory…

There have been a number of very serious incidents, one of them resulting in a fatality, with Flying Foxes in the past years rigged by Scouts or similar youth groups here in Switzerland that led to insurances clamping down hard on the practice and refusing to ensure your event if you were planning such an installation as part of an activity. Only recently have they been allowed again, albeit under the condition that you fulfill certain, quite stringent, criteria and conform to best practice guidelines (see image below), such as doubling up the lines you are running the trolley on.

The incident in the video above could have been prevented if a backup had been used… as it was, it was the brake line that saved the two climbers – but only just. Further an appropriate pulley shall be used that can handle the sorts of speeds that are to be expected when running the speed line.

Example of a pulley suited for use at high-speeds

I was discussing something similar with a friend the other day who is rigging an installation for a big art show in town next week. He has planned the whole thing around 6 to 8mm Dyneema hollow braid lines that have a very high breaking strain – on paper. The installation will be anchored onto massive concrete pillars and sturdy steel collars with eye bolts welded onto them. Yet the span they are rigging across is very wide, about 45m per side, and the rigging is quite complex involving bridles and floating anchors, so whilst the weight of the strips of fabric suspended off the lines may be negligible, the over-all mass, combined with the high tension required to keep the whole thing at the height it needs to be at makes me wonder where the weak points in this system are and whether the specced materials are up to it. In the end we decided that the best thing to do would be to to integrate a load cell into the assembly to be able to keep track of the loads and to prevent overload and/ or failure.

The point I am trying to get to here is that I find it hard to understand how we can be so diligent and thorough in our professional life when it comes to rigging lumps of wood out of a tree on a speed line, to then in our spare time rig up something that is obviously inappropriate and potentially not up to the task – and then use it to transport people?

In both cases I believe we should attempt to always integrate backups where and when possible, to strive for the highest degree of control possible at all times and be very wary on the overall load on the system due to high loads on anchor points.