Hazard Trees and Hazardous Cuts

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 tree diameter and species. Photo: Michael Tain

Although the terms “hazard” or “danger” tree get thrown around a lot in the tree care industry, meaning anything from a structurally unsound tree next to a high-value target to an already partially fallen tree hung up in something. For the purpose of this article the latter will be discussed. Natural or human forces can create this type of hazard tree, but regardless of cause, they require special care and techniques to be safely dealt with.

Every tree that is going to be worked on by a tree crew should be recognized as containing some element of hazard, but those lodged on wires, houses or even in other trees due to felling plans gone bad should set off warning signals to any professional tree crew.

The first, and often most important, part of dealing with hazard trees is recognizing that one exists and developing a plan to deal with the situation and manage the forces involved. Once recognized, the crew must have the knowledge, skills and equipment to deal with the tree as safely and efficiently as possible. A hazard tree cannot, in most cases, be made less hazardous, but it can be cut in such a manner that the forces are managed as well as possible, and the dangers of damage, injury or even death minimized. The addition of utility wires to the hazard tree equation obviously requires that the crew involved is trained to recognize electrical hazards and knows how to handle them, and the crew must ensure that the power has been cut off prior to beginning any work.

A mismatch showing the orientation of the pull line in order to pull it toward the side of the "low" cut. Photo: Michael Tain

A mismatch showing the orientation of the pull line in order to pull it toward the side of the “low” cut. Photo: Michael Tain

Situational awareness

As stated previously, recognizing a hazard tree is the first step in this process, and one that is far too often skipped due to ignorance, inattention or lack of situational awareness.

There are two basic forces inside a tree that tree care professionals always need to be thinking about: tension and compression. They are always present regardless of the tree’s orientation or position, but changes in that position typically change the location of the forces, leading to nasty surprises to those saw operators who don’t take a moment to examine the forces’ location and likelihood.

All trees develop tension and compression wood as they grow to counter forces such as gravity or prevailing winds, but the change in position either through nature or humans in the case of a hazard tree can and will affect the location of these forces. In a tree that’s already on the ground, tension and compression can lead to “pinched” saws and frustration, never a fun process, but much less unsettling than a stuck saw when the tree is still up in the air going who knows where with targets, both human and nonhuman, all around.

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. However, counterforces, such as the amount of the tree extending over the top of the wires or the presence of a large root mass, are going to affect the distribution of forces.

 Side view of a knee notch. The final back cut would be below the hinge, and the farther below would likely require more force to separate. Photo: Michael Tain

Side view of a knee notch. The final back cut would be below the hinge, and the farther below would likely require more force to separate. Photo: Michael Tain

It is vital that tree crews take a few minutes to determine where the tension and compression are in the tree; and once cutting, be quickly prepared to react if they figured wrongly. Once the locations of these two forces have 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

The bad dance floor

This refers to the area that the feller or cutter doesn’t want to be in when a “whole lot of shaking” starts going on. Accident research shows 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.

Dancing with a hazard tree with all the additional forces and complications involved inside that 5-foot circle in the first 15 seconds of movement is going to require some Matrix-quality reactions and speed. There are more than enough methods, techniques and tools that allow crew members to be outside that circle at the moment of release of their woody dance partner’s tension and compression, but the trick is knowing about them, understanding their 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 off that dance floor when things start to move.

A completed key notch with wedges in place at the bottom of the key. Remember to put the wedge on the side the key is going to be pulled toward, otherwise frustration will ensue. Photo: Michael Tain

A completed key notch with wedges in place at the bottom of the key. Remember to put the wedge on the side the key is going to be pulled toward, otherwise frustration will ensue. Photo: Michael Tain

Mismatch cut

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 less links in the chain or complexities where things can go wrong. It is almost exactly the same technique 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, especially if they wish to keep their hands and all their other pieces and parts functional.

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 that it is typically easier to “snap” if the tree is pushed or pulled in the direction of the lower cut.

On bended knee

While some crews may feel that begging the tree on bended knee is a bit much, using a knee cut to bend the tree can be quite effective. This technique 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 out of/off the wire or house it is resting 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.

A training situation for cutting techniques for hazard trees. Note the logs/tree leaning against non-energized lines in background. Photo: Michael Tain

A training situation for cutting techniques for hazard trees. Note the logs/tree leaning against non-energized lines in background. Photo: Michael Tain

A key to the tree’s heart

The key notch is the most complicated technique discussed here. It’s also the one that requires the most time for setup and gear for use. However, 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 separate 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 separated from a safe distance.

This is obviously just a brief introduction to the topic of specialized cutting techniques for hazard trees. While all these techniques can be quite effective, the time to first employ them is not in an actual hazard tree situation. Training, practice and repetition in hands-on, controlled field situations will go a long way toward giving operators the knowledge and understanding to use them in a real-life situation. Trees intentionally felled into other trees in obstacle-free felling operations, or even logs laid on suitably strong ropes with grapples or other heavy equipment can help crews learn how to deal with hazard trees before a situation where the costs, and possible loss of life and limb, are all too real.

Editor’s note: This article was originally published June 2013 and has been updated.

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