By Michael “House” Tain
The term hazard/danger tree, in the scope of this column, refers to trees that are no longer upright in their natural form; and due to this change, present particular challenges to chain saw operators’ safety and security during removal or release. A wide variety of forces, both natural and human inspired, can create these hazard or danger trees.
Often the misjudgment or poor estimation of a given tree’s side lean can lead it to become lodged in another tree or obstacle during felling operations, creating what can be called a hazard or danger tree. In this case, the tree may or may not still be attached to its stump, depending on whether or not the hinge broke. But the forces acting on the tree have changed radically with its change in position and orientation. Failure to recognize this change in forces along with the use of attendant specialized cutting techniques may result in an accident or injury to the chain saw operator or other members of the tree crew.
Storm clean-up also often presents tree care professionals with hazard/danger trees. The trees may be completely wind thrown with their root plates still attached and elevated, or snapped off by the force of the wind at various levels along the length of the tree’s pedestal, while resting on utility wires, houses, buildings, or simply the ground. These trees though created by natural forces — present the same challenges as those caused by human error, and are just as hazardous if not evaluated and dealt with appropriately.
Compression and tension are forces that are present in every tree, standing or fallen, yet their location, interaction, and the reactions they produce can vary widely with the tree’s orientation. In a general sense, trees use the development of compression and tension wood as part of their natural strategy to compensate and adapt to different conditions and situations, adding strength and layers as and where needed. However, the compression and tension forces present in chain saw operation are much different.
A simplistic example is a tree that is to be felled that has a heavy forward lean. The tree will have tension forces on the back of it and compression forces on the front. This same tree, should it be felled into another mistakenly, will have much different locations for the tension and compression forces. The upward support of the second tree may very well result in compression forces on the top of the felled tree, and tension forces on the under or bottom side. An excellent and simple way to remember how to sever compression and tension fibers, developed by the instructors at Arbor Canada, is the acronym “CUT:”
Begin the cut on the Compression side
Finish the cut on the Tension side
“U” are in the middle
Statistics have shown that 90 percent of the accidents that occur during felling operations happen in the first 15 seconds of movement within a 5-foot circle of the stump. This rule also applies when an operator is dealing with a hazard or danger tree; and may in fact be of even more vital importance due to the changed forces and inherent instability of the tree. Due to this, tree care professionals should attempt, whenever possible, to use cutting methods and release techniques that enable them to be safely outside this 5-foot circle. Tools such as push sticks, ropes, winches and mechanical advantage systems will all help chain saw operators release the cuts they have set up from a safe distance, and should be employed whenever possible.
The simplest cutting technique in dealing with hazard/danger trees is the mismatch or bypass cut. This cut is basically the same as that used when “cutting and chucking” down a spar or removing a horizontal branch — with one very important exception. As noted previously, chain saw operators in hazard/danger tree situations should endeavor to release the tree from a distance — in the case of a mismatch cut either a rope tied above the cut or a push stick will suffice. In no circumstances should the operator be “snapping” off the cut as they would in a spar or branch situation. Additionally, users will find it much easier to break the cut if they are directing the force toward the side with the lower cut, pulling it in that direction if with a rope, or pushing it in that direction if with a push stick. The offset cuts are made from the sides of the fallen tree, as the tension/compression forces will typically be present on the top and bottom of the tree; and should overlap each other slightly. As when using this cut for spars or branches, the distance between the cuts will vary with wood strength and diameter.
Knee cut or hinge
The knee cut is a technique in which a face notch is used to attempt to fell the top of the tree away or out from the obstacle in which it is lodged. An open face notch is cut on the upper side of the tree, this notch should be of at least a 90-degree opening; and a five percent of diameter hinge is created through the use of a bore or plunge cut. Unlike felling operations in which the tree would be released by simply severing the strap at or below the level of the hinge, in hazard/danger tree situations distance is paramount. Thus, a mismatched back cut is used below the level of the hinge, dependent once again on wood strength and diameter. The farther below the bore cut level this cut is made, the more force it will take to snap off or release the cut. Any variety of tools may be used to generate this force from a safe distance. Care should be taken to evaluate the tree’s forces and tendencies prior to using this cut. For example, a tree that has a great deal of its top overhanging a utility line is going to have tension forces on top and compression forces beneath its trunk, making it unlikely that the knee cut will work correctly; and making one of the other cutting techniques a better option. Wind-thrown trees with the root plate still attached can also be difficult on which to use the knee cut due to the forces enacted on the tree by the root wad and stump.
The key notch, though a quite complex cutting technique requiring mechanical advantage or a winch to effect release, can be quite useful for safely removing a hazard/danger tree. A key or tongue is formed within the tree through the use of bore cuts and standard cuts which “lock” the two parts of the fallen tree together, to be released or pulled apart at the time of the operator’s choosing. The length of the key or tongue should be at least the diameter of the tree, though a longer tongue may very well provide more security; and is started by dividing the tree into thirds. From the side of the tree two vertical bore cuts are done on either side of the third in the middle, which will be the key. A horizontal bore cut is then completed to connect the two sides of the key. Wedges are placed in this horizontal bore cut on both sides of the tree to provide support and help prevent the chain saw from becoming pinched as the final two cuts are made. The operator then cuts from the outside to the edge of the vertical bore cuts that mark the edge of the key or tongue, first the compression side and then the tension. A wedge in the compression cut can be quite helpful. At this point the tree should be severed into two parts, but locked together by the key or tongue and groove joint created; and can be pulled apart by a winch or a rope with appropriate mechanical advantage.
All of the cutting techniques discussed here can be of great value when confronted by hazard/danger trees. But training and practice are paramount prior to attempting their use in an actual storm or felling situation. The wide variety of forces and inherent instability involved with hazard or danger trees require not only a great deal of vigilance and caution on the part of tree crews, but very careful examination of each tree for the forces involved, the location of these forces, and likely reactions as work progresses. However, once the situation has been well examined and evaluated, and the techniques understood and practiced, these hazard/danger tree cutting techniques can be a valuable component of every climbing arborist’s mental toolbox.
Michael “House” Tain is a contract climber, splicer, educator and writer associated with North American Training Solutions www.northamericantrainingsolutions.com and Arbor Canada Training and Education www.arborcanada.com. He is currently located in Lancaster, Ky., and can be reached via e-mail at firstname.lastname@example.org.