This work evaluated the crush protection of equestrian helmets. Four helmet models were tested: two jockey style helmets to Product Approved Specification (PAS) 015 - the British equestrian safety standard - (Champion Pro Plus and Charles Owen Competitor) one jockey helmet to American Society Testing & Materials (ASTM) F1163 - equestrian safety standard used in the United States - (International) and one lightweight helmet to ASTM F1163 (Troxel Equestrian).

A helmet may be designed to protect against crush in two distinctly different ways. The most obvious is to provide a helmet that is extremely stiff in order to resist the magnitude of the force transmitted during a typical crushing accidents. Alternatively, the helmet may absorb the energy transmitted during an accidents in such a way that the force on the skull does not exceed that which is known to cause skull damage. Transport Research Laboratory, (TRL, Old Wokingham Road, Crowthorne, Berkshire, RG45 6AU) conducted a literature search to determine the tolerance to skull crushing injuries.

It was found, that when subject to a lateral crushing load, via padded plates, the onset of fracture of the temporo-parietal bones occurred at 10,000 N. (Newton, a unit of force.) It was considered that below this level most people would not suffer skull crushing injuries. The PAS 015 1998 prescribes a crush test whereby the helmet is loaded between parallel plates, incrementally, up to a maximum force of 630N during which the deformation should not exceed 30mm. The helmet does not contain a headform and is free to collapse. The TRL advocates that the PAS 015 test procedure is not appropriate for evaluating the crush performance of helmets for three reasons: (1) the load of 630N is extremely low compared with the tolerance for skull crushing injuries (10,000N); (2) The performance of a helmet when fitted to a human head is quite different from the performance of an unsupported helmet. A well designed helmet may perform to conjunction with the characteristics of the skull and, therefore, the applied load should be resolved in terms of forces exerted on the head; (3) the applied load is quasi-static and therefore the energy absorption capacity of the helmet is not evaluated.

Nevertheless, TRL conducted crush tests on all four helmet models in accordance with PAS 1105 1998. All helmets achieved the requirement. The maximum deformation was 9mm for the Troxel (ASTM) 20mm for the Champion (PAS), 22mm for the International Riding (ASTM) and 23mm for the Charles Owen (PAS).

The PAS lateral deformation test was repeated, but with a headform fitted and the external load was increased to 10,000N. The loads exerted on the headform were between 8,000N and 9,000N for all helmet models. This result showed that only 10% -20% of the crushing load was resisted by the helmet and the vast majority (80%-90%) was exerted on the headform.

The TRL devised a more appropriate dynamic impact crush test whereby a dynamic lateral st protection from crushing injuries. However, what is not known, is whether an impact energy of 200J is representative of a equestrian crushing accident.

SUMMARY PENETRATION TESTS

The TRL evaluated the penetration protection of equestrian helmets by conducting tests in accordance with PAS 015 1994 which specified that a 3 kg impactor with a 60° conical point be dropped onto the helmet from a height of 1 meter. These tests are designed to assess the resistance of a helmet to penetration by a sharp object which for horse riders may be a twig or branch of a tree. However, the inclusion of such a test in a standard should relate to frequently of occurrence in accidents.

In this respect the U. S. and U. K. disagree because the PAS 015 requires a penetration test, whereas the ASTM 1163 does not. Instead the edge test is specified and this is quite different in principle. It should be noted that the penetration requirement of the more recent PAS 1998 is that the same impactor should be dropped from a lower height of 0.75 meter which is a less stringent requirement.

The same four helmets where tested. Two tests were conducted on each helmet model, one to the front (crown) and one to the rear (crown). It should be noted that the Troxel helmet was fitted with ventilation holes and normally the technician would aim for such areas. However, the purpose of these tests was to evaluate the relative performance of the helmet shell and liner and, therefore, the ventilation holes were not impacted.

It was found that all helmets satisfied the penetration requirement of PAS 015 1994. It is, therefore, certain that all of the helmets would also satisfy the penetration requirement of the more recent, but less stringent PAS 015 1998. The three jockey helmets were fitted with a relatively thick outer shell that may have been expected to provide good penetration protection. However, the Troxel helmet, with a lightweight thin shell was, surprisingly, also found to provide a similar level of protection from penetration when tested away from the ventilation holes.

SUMMARY OF SMALL HELMET TESTS

The aim of this work was to compare requirements prescribed by ASTM F1163 and PAS 015 for size small helmets,. The mass of the headform is a key factor when evaluating the impact performance of a helmet. Both PAS 015 (and EN 1984 European) and ASTM F1163 specify a range of test headforms, and each size of helmet is tested with an appropriate size of headform. However, within PAS 015 the mass of each headform is proportional to the size, the smallest headform is the lightest and the largest headform is the heaviest. Whereas, within ASTM F1163, all sizes of headform have the same mass. For medium size headforms, both PAS and ASTM prescribe a similar mass, but for small and large headforms the difference in mass is considerable.

The impact energy during a test is proportional to the mass of the headform for a prescribed drop height. Thus, the impact energy of a heavier headform is greater than a lighter headform. As a consequence, when a helmet is tested with a heavier headform, it is required to absorb more energy and is more likely to crush the liner to the limit. This may suggest that a helmet that was certified with a heavy headform, such as a small ASTM helmet, would be safer because it has the capacity to absorb more energy. However, the acceleration level measured during a test also relates to the mass of the headform, whereby a lighter headform will accelerate at a higher rate for a given impact force. (At a given force, a lighter mass will accelerate at a higher rate than a heavier mass. Editor) As a consequence, a helmet that was certified with a heavy headform such as a small ASTM may yield a higher peak acceleration when tested with a lighter headform. The aim of the small test work was to investigate which of these conflicting mechanisms is predominate.

Two sizes of helmets were evaluated (size medium and size small) using two helmet models, PAS 015 jockey (Charles Owen Kids Own) and ASTM F1153 lightweight (Troxel Equestrian). Impact test were conducted at 6 m's in accordance with the procedure prescribed by ASTM F1163 except that for the size small helmet test a lighter headform to PAS 015 was used. The ASTM helmet was found to provide very good protection in both sizes medium and small. However, although the PAS helmet was found to provide very good protection in size medium, the size small PAS helmet provided a lower level of protection, particularly at the front and rear. The small PAS helmet was found to bottom out during these test.

The small ASTM helmet was, therefore, found to provide a higher level of protection than the small PAS 015. helmet. The test prescribed by ASTM for size small helmets, whereby helmets are tested with a "heavier" headform, may be expected to result in size small ASTM helmet which are slightly stiffer than equivalent size medium ASTM helmets. However, the difference is marginal. Furthermore, the size small ASTM helmet was able to conform to the requirement of ASTM even when tested with the light PAS headform whereas the size small PAS did not meet the requirements.

Information provided by:

Mark Davies Injured Riders' Fund
Little Woolpit
Ewhurst, Cranleigh, Surrey
United Kingdom
GU6 7NP