A study published in Applied Sciences suggests that current riding helmets do not prevent skull fractures in adults when crushed from the side, as may occur if a horse falls on its rider. The study team comprised Connor, Michio Clark, Pieter Brama, Matt Stewart, Aisling Ní Annaidh and Michael Gilchrist, variously affiliated with University College Dublin, COMFG Ltd, R&D Consulting Engineers Ltd, and Vector Scientific Inc.

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. In addition to impact tests, helmet manufacturers also conduct crush tests, also referred to as the lateral deformation test or rigidity test. These are meant to represent a horse a horse dynamically falling against or rolling over the head of a helmeted rider.

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.

In traditional crush tests a helmet is placed between two metal plates and crushed quasi-statically until a peak force is reached at a specific loading rate. To pass the test maximum and residual crush limits must not be exceeded.

According to the study, in discussions with engineers in the standards industry and with the standards committee members, it is understood that current lateral crash tests are used to ensure that the helmet is is “not too soft” and the structure of the helmet has some “stabilizing effect.” It is not intended to simulate a real-world accident. However, there was also no quantification of what constitutes “too soft.”

Given that in cross country riding and eventing, there is a possibility of rotational falls where a horse can fall on a rider, there is merit to introducing a more realistic crush test to the standards to improve helmet performance while being dynamically crushed.

To that end, Thomas Connor and his colleagues conducted helmet testing research that mimics the forces that might occur when a helmet is subjected to crush forces from the side.

To measure the forces, the team created an adult male sized headform containing sensors and used a commonly-available 57 cm jockey-style helmet. The goal of the research was to determine what loads are likely to be applied to the rider’s head if a horse falls on to it and to investigate to what extent a typical equestrian helmet reduces the load. The researchers hoped that the data will help to inform and create an evidence basis for future standard lateral crush tests.

For the study, the cadavers of two horses of different weights were dropped on the helmeted and unhelmeted headform so the sensors could measure the forces involved. The horses, a 343kg mare and a 370kg male, had been euthanised for reasons unrelated to the study.

The equine cadavers were dropped from a height of 1.2 m onto the headform, which was positioned on a rigid concrete surface. The drop height was chosen following analysis of real-world equestrian accident video footage. The concrete surface was chosen because it was rigid and eliminated surface variability.

Four impact locations were chosen based on the analysis of the video footage of horse falls. They also represented the largest area of the horse that is not covered by a saddle — the left and right hindquarters, lumboscacral vertebrae, and the sacral vertebrae.

In total, 30 drop tests were carried out, comprising 24 unhelmeted tests and 6 helmeted tests.

Discussing their findings, the researchers say horse mass appears to be a factor in the impacts. A 7.3% increase in the mass of the falling horse resulted in, on average, an 11.8% increase in the peak load applied to the headform. The highest peak loads applied to the headform were measured at the bony sacral impact location, with an average of 15.57 kilonewtons (kN) for the lighter horse, to 16.02 kN for the heavier horse.

The researchers noted that the horses used in this study were not large, typically falling into the pony category. Since most sport horses weigh 500 to 600 kg, the impact of a horse with such a larger mass would result in a significant increase in loads applied to the headform.

Helmeted drop tests were only carried out on the sacral and lumbosacral junction vertebrae impact location. Compared with the unhelmeted averages, the helmets provided a reduction in force 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, which is 3.5kN to 12.4 kN for adults and lower for children.

In conclusion, the researchers concluded that current helmet certification tests are not biofidelic — that is, they are not faithfully modeled on a biological system — and do not adequately represent the loading conditions of real-world “lateral crush” accidents in equestrian sports. Using this data, changes to the certification standards test methods could be made to ensure that the test would be biofidelic and could lead to safer helmet designs.

The study, published under a Creative Commons License, can be read here.