The Adequacy of Falling Object Protection Design Criteria for Feller Bunchers

This article develops a model for estimating the energy transferred to the falling object protection system of a feller buncher (impact energy) by a tree falling under its own weight. The impact energy for a range of tree sizes and rotation angles to impact is estimated and compared with the WorkSafeBC design criteria for feller bunchers. For many scenarios, the impact energy is greater than the design criterion of 11.5 kJ. In addition, increasing the stiffness of the falling object protection system (FOPS) results in a minor reduction in the impact energy when the tree is free to rotate about the feller buncher. However, increasing the stiffness of the FOPS also results in a very large increase (relative to the reduction in the impact energy) of the maximum force at impact. A large impact force could be a concern when acceleration of the operator within the cab is a concern. Future work should investigate whether the design criteria should be revised to include both a maximum allowable deflection of the FOPS into the operator area under specified conditions and a maximum allowable acceleration of the operator for a given impact energy.