Sketchy Anchors... and how to survive them
Amongst Rope Access trades, arborists are in the unique position of having to rely on unrated anchors for all of their work. So, whereas an Industrial Ropes Technician would have full knowledge of the strength of the anchor point, arborists must use a combination of intuition, experience and careful inspection in order to ensure that their anchor is safe.
A healthy, mature oak tree, with a 5" diameter high tie-in can be pretty confidence inspiring, however it is rare that we are hired to work with these trees. As arborists, we are often called to deal with trees that are in decline, dying or completely dead. That 70' anchor point, with no leaves and sloughing bark, is not something you want to consider lightly.
So what is our system for assessing these trees?
Being safe begins with the quote. While it is inevitable that we will quote on some trees, and then, in climbing, recognize that they are unsafe to continue, it is rare. Using proper estimating and recognizing during the quoting process the likelihood that the tree is too dangerous to climb, are critical skills for the estimator. It is pretty stressful to back off a climb- a job you quoted - and then inform the homeowner that not only is it unsafe to climb, but that the price will be substantially higher due to necessary specialized equipment.
Once committed, how you access the tree is very important. SRS (Static-Rope-System) is a great way to access the high canopy. However, setting a climbing line high up, in a failing tree, without close inspection of the anchor, is a recipe for disaster. We avoid doing this at all cost, and even with healthy trees, we use SRS to access a point that, while high in the canopy, is nonetheless at a point below what likely would be our TIP (Tie-in Point). It is much more confidence inspiring climbing a rope around an unknown 12" limb, with several 'backup limbs' should it fail, than fully committing to a 3" limb high in the canopy. From the lower, stronger (and redundant) tie-in, a climber can then advance the rope, or switch to MRS, while closely inspecting the tree. This way, the climber may catch weaknesses in the wood that he or she might not have with a ground TIP setup.
Case in Point
In July, we were hired to remove 7 tall, dead or declining Ash Trees over some cottages. They ranged in height from 40' to 70' and all showed significant decline due to Emerald Ash Borer. One tree in particular had little taper, and though it had quite a few green watersprouts growing off the trunk, the canopy was completely dead. For safety reasons, we tend to climb as high up in the canopy as possible before topping the tree. The higher you are (and thus, the smaller the top you are removing) - generally, the safer the operation.
This time, though, was different.
As I gained height in the tree, I felt the tree moving excessively and my spurs were sinking very deep (as in, unnaturally deep). I climbed maybe 2/3rd the height of the tree, and decided to take the top out there. My groundman was not used to my taking such a large top, but when he asked if I should climb higher, I told him that I didn't think the tree felt right. I setup a rigging block, and tied off the top with a half-hitch and running bowline. When we pulled the top over, the wood around which the rigging rope was tied (on the top) completely disintegrated. Possibly, had I topped the tree 5 or 10 feet higher, the tree may not have been able to withstand the forces of catching the top in the rigging- the anchor might have failed (with possibly fatal consequences).
This was a good lesson. Had I setup an SRS/Basal Anchor setup (instead of spurring up) I would have blissfully rope-walked the height of the tree in a few seconds, then likely missed how badly the tree was compromised.
By climbing the tree directly (instead of ascending the rope), to feel how unnatural the tree moved, to inspect it closely as I ascended, and weighing both movement and visual inspection against my experience, my plan changed. As I gained height, I realized this was quite a dangerous tree, and opted take a larger top, and directionally fell it, with a tagline, into a small drop zone in the back yard.
It was the right call.