The sport of equestrian cross country eventing has seen many serious and even fatal injuries due to rotational horse falls in recent years. The sport originally consisted of horse and rider teams jumping stationary, wood fences. However, in a move towards increasing safety for horses and riders, frangible and deformable safety devices have been emerging in the field. This thesis provides an overview of safety designs that are currently available and those that are on the horizon. Also, a path-finder method of evaluating and developing safety fence designs was outlined and applied to two distinct designs, a hinged gate and a collapsible table fence. A full size prototype of the hinged gate was constructed and tested in the field in two different locations. The collapsible table fence design was developed and then a ½ geometric scale prototype was constructed to demonstrate design feasibility and to analyze design development challenges.

Rotational falls, or somersault falls, have led to serious and fatal injuries during the cross-country phase of Eventing competitions. Research to improve the safety of the sport began in 2000 after five fatal injuries occurred in the 1999 Eventing season. These efforts led to safety devices such as air jackets, improved helmets, and frangible/deformable fences. The focus of this thesis is to develop a more complete understanding of the horse-fence interaction as the approach motion transitions to a rotational fall. To achieve this, a large distribution of inertial properties was compiled through the development of a cylinder-based inertia approximation and a citizen science effort to gather equine geometrical measurements through a survey distributed by the United States Eventing Association (USEA). Furthermore, fundamental kinematic properties of the horse and rider were gathered from the literature. These distributions were used to conduct a Monte Carlo analysis to examine if the approach conditions of the horse and rider would result in a transition to a rotational fall upon horse-fence contact. Through the analysis the sensitivity of the main control parameters was explored to determine the dominant variables in the transition.