Tree Services Magazine - November, 2012
Tools & Techniques: Dealing with Dangerous Trees
Special trees require specialized techniques
Hazard and danger trees can certainly present themselves at any time and in any place and may even be created by the tree crew themselves when a felling plan goes wrong and the tree ends up lodged in another tree or resting on some hopefully nonenergized wires. However, they most commonly occur in storm situations, which is more likely to occur as winter approaches.
A side view of a knee notch. The final back cut would be below the hinge, and the farther below would likely require more force or pull to separate.
To the honest, professional arborist, each and every tree to be felled or cut holds a certain amount of hazard and danger, but the term hazard/danger tree refers to those specimens that present challenges far beyond an upright tree to be felled. These are trees that, through the forces of nature or humans, have ended up in spots where the forces involved are hard to determine, the wood fiber is under strange strains and stress, and the tree is just waiting for Johnny B. O'Doughnuts to make the wrong move or cut prior to exploding with ferocity.
A tree of this type is most dangerous when it is not recognized as such, as the typical cutting techniques will often go wrong very quickly, so the first step is recognition. After that, tree crews need to understand and employ the techniques and methods that will help them release those ferocious forces in as controlled and safe manner as possible, hopefully from a distance to avoid shrapnel and "crushage." As always, when confronted by a tree involving wires, crews need to make sure the power is off before even thinking about doing anything.
What's going on?
With all due deference to Marvin, what's going on in the wood of a hazard/danger tree is just as vital as what's going on in the world. There are two basic forces inside a tree that tree care professionals always need to be thinking about: tension and compression. They are present regardless of the tree's orientation or position, and changes to the tree's position will typically change the location of the tension and compression. Saw operators who don't take the time to examine the location and likelihood of those forces may get a nasty surprise.
In the larger sense of tree biology all trees develop tension and compression wood as they grow in order to deal with impacts such as wind and gravity, but when that tree has been felled, or in the case of hazard/danger trees, blown or thrown onto the wires or the roof of a townhouse, that existing tension and compression changes. These are the same forces that lead to colorful language and stuck saws when bucking up trees on the ground, but when the tree is hung in the wires, still towering in the air over the saw operator, with the root wad possibly still attached, a great deal more than embarrassment and a bent bar are at risk.
Typically, a tree that has fallen into or onto something is going to have tension on the lower side and compression on the upper side, but counter forces, such as the amount of the tree extending over the top of the wires or the presence of a large root mass, are all going to affect the distribution of forces. It is vitally important that tree crews take a few extra moments to determine where the tension and compression are in the tree, and, once cutting begins, be prepared to react if the determination was wrong. Once the location of these two forces has been determined, an excellent way to deal with them is the acronym developed by the instructors of Arboriculture Canada Training and Education: CUT.
Compression side is severed first
Tension side is cut last
And "U" are in the middle
Where not to be
The statistics and accident investigations show that the majority of injuries and deaths that happen when trees are being cut down happen within a 5-foot circle of the stump and most often in the first 15 seconds of the tree starting to move. This information provides the basis for the 5-15-90 rule, which is meant to remind chain saw operators that being inside that 5-foot circle when the tree starts to move puts them at risk of becoming one of those statistics, and that's just during standard felling operations. Add in the quirks and challenges of a hazard/danger tree, and that 5-foot circle in the first 15 seconds of movement is definitely not the place to be.
A completed key notch with wedges in place at the bottom of the key. Remember to pull the wedge on the side the key is going to be pulled toward otherwise frustration will ensue.
PHOTOS BY MICHAEL (HOUSE) TAIN
There's no shortage of methods, techniques and tools that allow crew members to be outside that circle at the moment of release of tension and compression, but the trick is knowing about them, understanding their need/value, and then using them consistently. Tools such as ropes in a mechanical advantage system, come-alongs or winches, or even a simple push stick will all assist folks in being out of that danger zone when things start to move.
An overhead view of a mismatch, or bypass, cut with rope in place to snap it apart to the low cut side. Note the overlap of the cuts, which will vary with diameter and species.
This cut is the simplest and most basic technique for releasing a hazard/danger tree, and as such should be the first considered when planning out the job. After all, simple is typically quick and efficient, with fewer links in the chain or complexities where things can go wrong. It is almost exactly the same technique as used up in the air when "cutting and chucking," with the main difference being the orientation of the wood being cut and the fact that the operator's not going to be snapping the piece apart by hand.
A mismatch showing the orientation of the pull line in order to pull it toward the side of the "low" cut.
The cuts are made at mismatched levels from opposite sides of the tree, remembering the CUT acronym. The amount of overlap or bypass and/or distance between the mismatched cuts will change with the diameter and species of the tree. The cut can then be "snapped" from a safe distance with a line or push stick, though keep in mind it is typically easier to "snap" if the tree is pushed or pulled in the direction of the lower cut.
Knees bend, why not trees?
The knee cut would be the next choice if the mismatch is not suitable. It's a little more complicated and in a sense involves trying to "fell" the tree off the wire or house it is laying on. The crew will put an open-face notch of at least 90 degrees on the upper side of the tree and then make a hinge equal to 5 percent of the diameter of the tree by using a bore or plunge cut. Obviously, a tree with a large enough diameter to allow the bore cut is required. The operator would then make a mismatched back cut beneath the level of the hinge, thereby allowing him time to get out of that vital 5-foot circle and finish the process from a distance with a pull line.
The distance between the hinge and the mismatched back cut is once again going to depend on diameter and species, but typically the farther below the back cut, the more force required to start the "felling" process.
Open that locked tree with this key
The key notch is the most complicated technique discussed in this article. It's also the one that requires the most time for setup and gear for use, but should a hazard/danger tree require it, the key notch is an excellent and useful technique.
Bore cuts are used in a manner to create a tongue, or key, that "locks" the two parts of the tree together. They can then be pulled apart to remove the two parts from a safe distance. Due to the forces and weights involved, even a smaller tree will most likely require a mechanical advantage system or a winch to pull apart the two parts, so users should make sure they have all the gear needed on hand before cutting.
The length of the key should be at least the diameter of the tree, and a key of greater length will provide even more strength and security.
The user should mentally divide the tree into thirds from the side, with the center third being the intended key and the outer edges of the key being completed with somewhat vertical bore cuts along the edges of the key. A horizontal bore cut is then made at the end of the key to finish it and wedges placed on both sides to help support it. At this point the two outer thirds of the tree are still intact. Remembering the acronym CUT, the key notch is completed with a cut from the outside compression edge of the tree to the edge of the vertical bore cut, forming the edge of the key, followed by a cut from the outside tension edge of the tree to the other vertical bore of the key. A wedge in the compression side cut may be helpful to prevent pinching. Carried out correctly, the two parts of the tree should still be stable and securely connected by the key. The wedge on the side the tree is being pulled toward is now removed, and the two parts pulled separate from a safe distance.
While all of these specialized techniques can be handy in the case of hazard/danger trees, they all should be practiced in non-hazard situations prior to use in an actual hazard situation, as bad things can happen any time humans, wood and chain saws are involved. Once understood and practiced, all of these methods can lead to the safe, efficient removal of a challenging storm-thrown tree resting on the wires or a house.
Michael (House) Tain is a contract climber, splicer, educator and writer associated with North American Training Solutions/Arbor Canada Training and Education, currently located in Lancaster, Ky.