Oblique Impact Testing of Equestrian Helmets

Introduction: Equestrian sports contribute 45% of all sports-related traumatic brain injuries and have a higher risk of severe head injury compared to both American football and motorcycling. [1,2] Given the high risk of head injuries in equestrian sports, it is important to have intensive helmet safety standards to evaluate equestrian helmet performance. However, the current standards used to test equestrian helmets have several limitations, including only measuring one energy level, not considering rotational acceleration, and being pass/fail. To address these gaps in equestrian helmet testing, we designed the Equestrian STAR rating system. This methodology uses a pendulum impactor to create linear driven impacts toward the head’s center of gravity. It incorporates three locations, multiple impact speeds, and rotational acceleration. Recently, the International Federation for Equestrian Sports (FEI) recommended that oblique testing is added to Equestrian STAR to better represent equestrian falls that occur at high speeds by integrating a tangential velocity vector to the impact direction. Therefore, the objective of this study was to examine equestrian helmet performance in oblique impact testing.

1. Ball C. G., J. E. Ball, A. W. Kirkpatrick and R. H. Mulloy. Equestrian injuries: incidence, injury patterns, and risk factors for 10 years of major traumatic injuries. The American Journal of Surgery 193: 636-640, 2007.
2. Winkler E. A., J. K. Yue, J. F. Burke, A. K. Chan, S. S. Dhall, M. S. Berger, G. T. Manley and P. E. Tarapore. Adult sports-related traumatic brain injury in United States trauma centers. Neurosurgical Focus FOC 40: E4, 2016.

Materials and

Methods: A drop tower was used for each oblique impact test (Figure 1). The tower uses a NOCSAE headform instrumented with a six degree of freedom sensor package consisting of three accelerometers (Endevco 7264B-2000, PCB Piezotronics, NC) and a triaxial angular rate sensor (DTS ARS3 PRO, Diversified Technical Systems Inc., Seal Beach, CA). Data were sampled at 20,000 Hz and filtered using a 4-pole Butterworth low pass filter according to SAE J211, with a cutoff frequency of 1650 Hz (CFC 1000) for accelerometer data and 256 Hz (CFC 155) for angular rate sensor data. The helmeted headform was positioned on a support ring, then dropped onto a 45-degree anvil covered with sandpaper. The helmet was held in place by a support arm that released upon impact.

Following FEI recommendations, helmets were dropped from a height of 2.2 m for an impact speed of 6.56 m/s. However, the NOCSAE headform was used instead of the recommended EN17950 headform, which was not for sale at the time. Each helmet was impacted at four locations: the left front boss, right front boss, left rear boss, and right rear boss (Figure 1). The resultant accelerations from the left and right locations were averaged. We tested 45 equestrian helmets, resulting in a total of 180 impact tests.

Results, Conclusions, and Discussions: There was a large range of performance between helmets in the oblique tests. Average linear acceleration values ranged from 117.3 g to 197.4 g, and average rotational acceleration values ranged from 3420 rad/s/s to 12149 rad/s/s (Figure 2). This demonstrated that some helmets were much better at reducing head accelerations than others.

For the 45 helmets included in both the oblique drop tests and the pendulum impacts, the correlation between each test method’s peak acceleration was computed. Peak linear acceleration was moderately correlated (r = 0.56) between both the oblique and pendulum impact test systems (p = 0.0001). This shows that helmets with lower linear accelerations from the oblique tests generally had lower linear accelerations from the pendulum impacts. However, we did not see this same trend with rotational acceleration. Peak rotational acceleration was not correlated (r = 0.19) between the two test systems (p = 0.22). This suggests that the oblique test’s method of generating head rotation provides unique information on helmet performance. A limitation to this analysis was that the impact energies and locations were different between the oblique and pendulum impact tests. If we matched the impact energies and locations between the two systems, we suspect that the correlation in linear acceleration would increase, but the same would not be true for rotational acceleration.

The addition of oblique drop tests to the existing pendulum impacts in the Equestrian STAR rating system would provide a more comprehensive assessment of equestrian helmet performance, as both impacts are possible in equestrian environments. Equestrian STAR assigns helmets a rating from 1 to 5 stars, with 5-star helmets greatly reducing head acceleration and concussion risk. STAR ratings are publicly accessible, enabling consumers to make informed decisions when buying a helmet.

Acknowledgements (Optional): The authors would like to thank Jacqueline Mars, the United States Hunter Jumper Association (USHJA), the United States Equestrian Federation (USEF), the United States Eventing Association (USEA), the Federation for Equestrian Sports (FEI), and the Institute for Critical Technology and Applied Science (ICTAS) for their continued support throughout this project.