Post-accident evidence basis for new equestrian standards: Relationship between helmet liner residual crush and accident parameters

Abstract

An in-depth analysis of 216 equestrian helmets involved in real-world accidents, with accompanying laboratory drop-test experiments has focussed on the crushing of energy absorbing liners. The mean measured residual crush (i.e., damage in the form of permanent deformation of helmet liner expressed as a percentage of the local undeformed thickness) was 21.5%. For front, rear and side impacts that occurred against both rigid and soft surfaces, the amount of residual crush varied linearly with impact velocity, peak translational acceleration, and maximum dynamic crush. For all impact locations, the percentage of energy absorbed by the helmet during an impact with a rigid surface is significantly less (between 4% and 20%) than those of both un-helmeted and helmeted headform soft surface impacts. Thus, the amount of helmet residual crush provides important insight into real-world equestrian accidents. This approach provides an evidence basis to improve future certification standards. There is clear scope to improve helmet designs, as helmet performance is clearly not optimised either for impact against soft surfaces or for relatively low velocity impacts. We suggest a peak impact power threshold that would improve equestrian helmet energy absorption for soft surface impacts without altering current standard test methodologies.