applied sciences Article An Evidence Basis for Future Equestrian Helmet Lateral Crush Certification Tests Thomas A. Connor 1,2,3, J. Michio Clark 1,4, Pieter Brama 5, Matt Stewart 2, Aisling Ní Annaidh 1 and Michael D. Gilchrist 1,* 1 School of Mechanical & Materials Engineering, University College Dublin, Belfield, 4 Dublin, Ireland; [email protected] (T.A.C.); mclark@vectorscientific.com (J.M.C.); [email protected] (A.N.A.) 2 COMFG Ltd. (Charles Owen), Royal Works, Croesfoel Ind. Park, Wrexham LL14 4BJ, UK; [email protected] 3 R&D Consulting Engineers Ltd., Leeds LS17 6AF, UK 4 Vector Scientific Inc., Golden, CO 80403, USA 5 School of Veterinary Medicine, University College Dublin, Belfield, 4 Dublin, Ireland; [email protected] * Correspondence: [email protected] Received: 20 March 2020; Accepted: 3 April 2020; Published: 10 April 2020 Abstract: The aim of this study is to determine what loads are likely to be applied to the head in the event of a horse falling onto it and to determine by how much a typical equestrian helmet reduces these loads. An instrumented headform was designed and built to measure applied dynamic loads from a falling horse. Two differently weighted equine cadavers were then dropped repeatedly from a height of 1 m (theoretical impact velocity of 4.43 m/s) onto both the un-helmeted and helmeted instrumented headforms to collect primary force–time history data. The highest mean peak loads applied to the headform by the lighter horse were measured at the bony sacral impact location (15.57 kN 1.11 SD). The lowest mean peak loads were measured at the relatively fleshier right ± hind quarter (7.91 kN 1.84 SD). For the heavier horse, highest mean peak loads applied to the ± headform were measured at the same bony sacral impact location (16.02 kN 0.83 SD), whilst lowest ± mean peak loads were measured at the more compliant left hind quarter (10.47 kN 1.08 SD). When ± compared with the un-helmeted mean values, a reduction of 29.7% was recorded for the sacral impact location and a reduction of 43.3% for the lumbosacral junction location for helmeted tests. Notably, all measured loads were within or exceeded the range of published data for the fracture of the adult lateral skull bone. Current helmet certification tests are not biofidelic and inadequately represent the loading conditions of real-world “lateral crush” accidents sustained in equestrian sports. This work presents the first ever evidence basis upon which any future changes to a certification standards test method might be established, thereby ensuring that such a test would be both useful, biofidelic, and could ensure the desired safety outcome. Keywords: skull fracture; dynamic crush; lateral crush; roll over; head protection 1. Introduction Equestrian helmet certification tests are designed to ensure that a minimum performance and quality level is achieved in terms of helmet crashworthiness and structural integrity. As equestrian sports are high risk [1–5], with the primary type of accident involving a fall from the horse resulting in a head impact [6], it makes good sense that the main helmet functional test in the standards involves recreating some simplified impact conditions [7–9]. The next most significant test in most equestrian helmet standards is referred to as the lateral crush test, also referred to as the lateral deformation test or rigidity test. However, Appl. Sci. 2020, 10, 2623; doi:10.3390/app10072623 www.mdpi.com/journal/applsci Appl. Sci. Sci. 20192020,, 910, x, 2623FOR PEER REVIEW 22 of of 12 11 deformation test or rigidity test. However, unlike impact tests, the origins of which are well dunlikeocumented impact in tests, the theliterature origins [10 of, which11], the are rationale well documented and evidence in the basis literature for the [10 crush,11], thetest rationaleare unclear and. Essentially,evidence basis this for particular the crush test areis formulated unclear. 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