An Evidence Basis for Future Equestrian Helmet Lateral Crush Certification Tests
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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. Essentially, as a quasi this-static particular test to test represent is formulated a horse as dynamically a quasi-static fallingtest to representagainst or a rolling horse dynamically over the head falling of a helm againsteted or jockey. rolling over the head of a helmeted jockey. TheThe lateral crush test itselfitself isis relativelyrelatively simple.simple.A A helmethelmet is is placed placed between between two two metal metal plates plates and and is iscrushed crushed quasi-statically quasi-statically until until a peaka peak force force is is reached reached at at a specifieda specified loading loading rate rate (see (see Figure Figure1). 1) There. There is isno no headform headform in thein the helmet. helmet. To pass To pass the test, the maximum test, maximum and residual and residual crush limits crush must limits not must be exceeded. not be exceededPeak loads. Peak are setloads to are be 800set to N be for 800 both N for PAS both 015 PAS [9] and 015 EN[9] and 1384 EN [8] 1384 and [ 10008] and N 1000 for the N for Snell the E2016 Snell E2016standard standard [12]. In [12] all. In cases, all cases, the maximum the maximum permitted permitted crush crush is 30 is mm 30 mm and a thend residualthe residual crush crush may may not notexceed exceed 10 mm. 10 mm. Figure 1. LateralLateral crush crush test. test. InIn discussionsdiscussions with with engineers engineers working working within within the standards the standards industry industry and with and standards with standards committee committeemembers, itmembers, is understood it is understood that the lateral that the crush lateral tests crush are usedtests toare ensure used to that ensure the helmetthat the is helmet ‘not too is ‘notsoft’ too and soft’ that and the structurethat the structure of the helmet of the has helmet some has ‘stabilizing some ‘stabilizing effect’. 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Additionally, Additionally, reported rates of concussion or mild mild traumatictraumatic brain injuryinjury (mTBI)(mTBI) areare higher higher for for equestrians equestrians than than those those in in boxing boxing and and American American football football [6]. [6]However,. However, when when compared compared with with the number the number of falls of andfalls headand head impacts, impacts, crush crush injuries, injuries, particularly particularly to the tohead, the head, appear appear to be rare to be with rare few with reported few reported in the literaturein the literatur [14]. Nevertheless,e [14]. Nevertheless in some, in situations some situations such as suchcross-country as cross-country riding or riding eventing, or eventing, a horse cana horse somersault can somersault during aduring jump anda jump land and on land the rider. on the In rider such. Incases such the cases injuries the can injuries be catastrophic can be catastrophic and sometimes and fatal sometimes [14]. There fatal may [ be14] merit. There in introducingmay be merit a more in introducingrealistic crush a more test to realistic the standards crush test if the to the objective standards of the if testthe objective is to improve of the helmet test is performanceto improve helmet while performancebeing dynamically while crushed. being dynamically However, there crushed are no. However, primary empirical there are data no primary on which empirical to base such data a test.on whichIt is not to known base such what a typicaltest. 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