The “barber chair” is a dangerous and unpredictable failure that occurs when a tree splits vertically up its trunk during the felling process. This phenomenon is considered one of the most serious safety hazards encountered in tree cutting operations. Instead of the tree falling smoothly on its hinge, massive internal forces cause the wood fibers to tear apart longitudinally. Understanding this failure mechanism is important because it results in the rapid, uncontrolled movement of large sections of wood directly toward the cutter, posing a severe risk of injury or death.
Defining the Barber Chair Failure
The term “barber chair” comes from the visual appearance of the failed trunk, which resembles the back of an antique barber’s chair. When the vertical split occurs, the lower part of the trunk being felled is violently thrust upward and often backward, pivoting on the remaining hinge wood. This upward motion can launch a large piece of the trunk with lethal force in the direction of the saw operator.
This sudden, aggressive split happens before the tree has fully committed to falling in the intended direction. The splitting wood acts like a spring, releasing stored energy that propels the butt end of the log back over the stump. The force is great enough to strike the operator or crush them against the stump. A key visual indicator is the vertical separation of the wood fibers, which tears straight up the trunk rather than bending and folding over at the hinge.
Root Causes of the Vertical Split
The primary cause of a barber chair failure is the overwhelming force of tension placed on the wood fibers opposite the direction of the tree’s fall. When a tree has a severe natural lean, the wood on the side opposite the lean is under extreme tensile stress. This tension is concentrated in the hinge wood, the narrow strip of uncut wood designed to guide the tree’s descent.
A common structural factor is an insufficient felling hinge, meaning the uncut wood is too narrow or too shallow to sustain the load. If the hinge is too thin, the wood fibers cannot withstand the stress, leading to a shear failure instead of a controlled tear. The hinge is meant to bend and tear gradually, but when the tension exceeds its capacity, the wood splits vertically along the grain.
Another element is an improperly executed back cut, the final cut made on the side opposite the face cut. Cutting the back cut too low or too close to the face cut prematurely severs the wood fibers holding the tree’s weight. This action releases the tension too quickly, causing the trunk to suddenly pull away from the stump before the hinge can effectively guide the fall. The trunk’s momentum then forces a vertical failure as the remaining wood is instantly overloaded.
Essential Prevention Techniques
Preventing the barber chair failure centers on controlling tension within the tree and maintaining the integrity of the felling hinge. Professional standards suggest leaving a hinge thickness that is approximately ten percent of the tree’s diameter at the point of the cut. For example, a tree with a 20-inch diameter should have hinge wood left at least two inches thick to provide adequate strength and control, ensuring the tree falls predictably.
For trees exhibiting a heavy lean, the use of a bore cut, also known as a plunge cut, is an effective technique to manage tension. This cut is made into the center of the trunk from the back side, stopping short of the face cut to leave the hinge intact. This method allows the operator to insert felling wedges into the cut before the hinge is fully engaged, which is safer than driving wedges into a partially cut trunk under tension.
The bore cut technique isolates a small section of holding wood at the back of the tree, which is the last part to be cut. By cutting the center of the trunk first, the tension is not released all at once, allowing the operator to fully establish the hinge and wedge system. Once the wedges are set, the final section of holding wood can be cut. The wedges are then used to push the tree off the stump in a controlled manner, preventing the dynamic forces that cause the vertical split and ensuring safety.