Archive for May, 2010

Technical Tree Falling – Faller Escape Routes, Understanding the 5-15-90 Rule (Article 4)

Monday, May 3rd, 2010

By Dwayne Neustaeter

Having a clearly identified and prepared escape route is one of the most important parts of any felling plan. Statistics show that a well-planned and utilized escape plan has a significant impact on your personal safety. Accident and fatality reports also reveal some useful information regarding workers injured when falling trees.

People falling trees have learned over the years that the area directly on either side or directly behind the tree is very dangerous. This is because branches, tops and trunk sections often fall near the base of a falling tree.

One type of falling mishap, know as a barber chair, is particularly dangerous. A barber chair occurs when a tree being felled delaminates vertically before the hinge is cut thin enough to bend. The term refers to the sliding action of the old style barber chair that positioned patrons in a head down, feet up position so the barber could more easily shave with the straight razor.

In falling, a barber chair occurs when using conventional back-cuts where the hinge is formed by cutting the wood from the back of the tree towards the hinge. As the saw severs the more resilient sapwood fibres typically found in the outer rings of a tree, the more brittle heartwood must resist the bending load. In cases of heavy forward lean and in older trees, this can result in the hinge wood splitting upwards as the tree falls. When the tree top contacts the ground the section of tree that has split upwards crushes either the remaining wood column straight backwards or the split standing section tears and rolls off to either side. In either case, the best place to be is away and at an angle.

Another compelling justification for the escape route is that while a tree is being cut, vibrations sent up through the entire tree can cause branches and tops to loosen. This vibration dislodges branches, where the sway from wind will not. As a tree begins to fall the force of gravity acting on it changes as well and a branch or dead top that is hung up for many years will suddenly dislodge during the first several seconds the tree is falling. These loosened limbs and tops fall generally within a few feet of the base. Trees that have dead tops or dead branches often referred to as widow makers for this very reason, because many a tree faller has been struck or killed.

The 5-15-90 rule is a concept we can use to emphasize the importance of using an escape route. Review of where tree falling accidents and fatalities occurred revealed that 90% of all accidents and fatalities happen within the first 15 seconds of the tree falling and within 5 feet of the base of the felled tree. Therefore, if you identify, plan and use an escape route you can increase your chance of survival or escaping injury by 90% and that the best escape route is at an angle away from the falling tree.

The most advisable angle of escape is away from the direction of the falling tree at an angle approximately 135 degrees from the direction of fall or 45 degrees from the opposite of the direction of fall.  (see diagram)

Many times obstacles or terrain influence the escape route plan, therefore it is not an exact science but rather the escape zone is at an angle diagonally away from the direction of fall, as illustrated in the diagram.

Remember:  Identify, Prepare and Use an Escape whenever you fall a tree.

Both of the escape routes shown here are 135 degrees from the direction of fall. It is also 45 degrees from the opposite of the direction of fall.

Technical Tree Felling – Assessing Lean (Article 3)

Monday, May 3rd, 2010

 

 By Dwayne Neustaeter

An important step of any falling plan (and one I believe that is often the most overlooked) is assessing the lean. In almost all cases whenever possible it is best to fell a tree in the direction it is naturally leaning. That is to say that if all of the strength of the wood fibres holding the tree up against gravity were to be severed or be instantly released then the tree would fall exactly where gravity is taking it. Therefore, if you can fell a tree in the direction of its natural lean gravity will ensure it falls that direction.

In my last article, I touched on height measure and how, if you have determined how tall the tree is and accurately assess the lean, then there is little that can cause the tree to fall anywhere other than planned.

 Assessing lean is much more than the angle of the trunk.  Other factors must be considered.  I tell my students to consider the entire ‘bio-mass’ of the tree as this is what truly creates bendin gon the trunk.  The ‘bio-mass’ is all of the parts of the tree combined – every branch and trunk.  This is best assessed as part of your outer perimeter survey s described in the previous article.

 The bio-mass and lean is best assessed from a distance from the tree.  In your mind’s eye, draw a line around the entire tree, being sure it touches the tips of every branch, start at the base of the trunk and then proceed left or right around the entire canopy or bio-mass of the tree.  Once you have this visualized, split that shape in half (it usually is an oval or egg shape) and imagine a line plumb down the center.  The distance this line is in relation to the notching area of the trunk tells you how much lean you are dealing with.

This tree shows about 5 - 7 feet of lean.

This tree shows approximately 1 foot of lean

 It is important to look at the tree from all sides and assess lean as you go because the lean will change from different viewing locations.  Using this method the natural lean may be determined and the fell should proceed in that direction.  If there are obstacles in the way of this natural lean, then other technical felling or rigging techniques are needed and worked into the plan.

 What I have just described is how to calculate ‘forward lean’.  There is another aspect of lean that is also important to evaluate.  Once the ‘forward lean’ is established, it is important to eliminate any side lean in relation to your direction of fall.  Often side lean is not considered.  The problem is when obstacles are in the way of the ‘natural-lean’, the faller must obviously choose to fell the tree away from the obstacle.  In doing this – side lean becomes a factor.

 Side lean is lean that is perpendicular to the felling notch and hinge.  This is important because wood is much weaker in the vertical plane than the horizontal (imagine trying to split a log by hitting along the side, yet when you hit it from an end, it splits relatively easily).

 Gravity acts on the hinge much the same way; as the tree falls it can cause the hinge to break prematurely, sending the tree once again in the direction of the ‘natural lean’.  Therefore, once natural forward lean is determined, be sure that there is no side lean acting on your hinge 90 degrees to your direction of fall.

 Mastering how to perform a lean assessment will ensure all of your trees fall exactly where you want them to.  By using the outer and inner perimeter survey and height measure you can predict accurately and confidently where the top of the tree will land.

 There are more factors to consider in your felling plan and in my next article I will discuss establishing and using an escape route.