Continuing on the theme of storm damage, last Thursday served up a wind-blown birch tree with a tipped root plate, leaning into a hornbeam. Nothing huge, but tricky none the less, as if it were to roll off, the next stop would be the neighbouring building.
After doing a risk assessment, we decided that as the roots on one side of the root plate were still intact and the tree was well jammed up against the hornbeam, with limbs interwoven, it was safe enough to climb, so we proceeded to remove the limbs which were clear of the canopy of the hornbeam…
Next, we rigged up a large 3:1 mechanical advantage system onto a suitably positioned tree. As there was no space to also install the GRCS onto this tree, we rerouted the line by 90° to an adjacent tree off to one side.
The interesting thing with rigging the MA system with Impact Blocks is that it is connector free, using an Alpine Butterfly to attach a large Impact Block onto the line tied to the birch tree, a tRex dead eye sling to attach to the anchor tree and webbing slings doubled through the hollow spindles of the large Impact Blocks to integrate the small Blocks.
We used another, lower diameter pre-rigged MA system to attach to the top of the birch tree, as this had a bit of a back lean on it. I faced the top with a large, open notch, leaving a good 8cm hinge on a 30cm diameter stem, Vito cranked it up, but when it reached the upright position, the hinge snapped and it took off at 90° to the intended direction! Eeeek! It is really surreal watching something go profoundly wrong like that, you’re like, This. Is. Not. Happening! Yes, it is! Nooooooo…
We were lucky, the top clipped the corner of the building on the second (No!), first (Nooo!) and ground floor balconies (Noooooo!)… yet did no damage (Pheeeew!). What went wrong?
It was a cold day, the hinge wood was obviously more brittle than it would normally be, the pull was a little off to one side due to the position of the anchor tree – so really, it was a classic example of factors compiling: had it been only the back lean, only the cold or only the slightly off-set direct of pull, it might have another matter, but the combination of all three led to the hinge failing. Having said that, I had considered this possibility and decided that as there was nothing all too serious to damage, therefore it was worth taking a calculated risk.
After that, we decided to add the small MA system to the large one to redirect the direction of pull to where we needed it, then we tensioned up the large MA system, raising the birch off the hornbeam, removed the interwoven limbs, took a bit of height off the top of the birch to ensure it would come nowhere near the neighbouring building should the base fail, then pulled it over into the garden – which all went smoothly.
I thought this was an interesting case, as it illustrates clearly how storm damage poses its own set of challenges. These can be managed by systematically and diligently assessing the risks – yet even then, you need to expect the unexpected and leave yourself adequate safety margins, anticipating potential failure.