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Europe's HOPE helmet study

Summary: The European Community has collaborated on a comprehensive study of helmet use in Europe, producing recommendations for changes in helmet design and testing. We have some excerpts below. You can download the final reports here.

The study is titled HOPE: Helmet OPtimization in Europe. It was produced by COST (European Cooperation in Science and Technology), a pan-European intergovernmental framework. Four working groups covered In-depth accident observations and injury statistics, traffic psychology, impact engineering and thermal aspects of helmet use.

Some excerpts from the study that relate to helmet design and testing:

Working Group 1: Optimisation of helmet design based on accident observations

Working Group 1's investigations showed that optimising helmet design, particularly on the sides and edges of the helmet, could have a positive effect on the reduction of severe injury. In terms of shock absorption, extending the protection zone currently identified in the existing standard CEN EN 1078 would be appropriate. Impacts on the side of the helmet appear to result in greater injury severity than impacts at the top of the helmet. Enlarging the protection zone and optimising helmet design would result in further optimisation of shock absorption capabilities and overall protection, both during impact with flat surfaces, and impact with edgy surfaces, such as collisions with the edgy parts of cars and trucks. However, extending the surface covered by a helmet may also increase (thermal) discomfort. Future efforts should continue the multidisciplinary approach initiated in the present network.

Working Group 2: Traffic Psychology

This group studied the confounding psychological factors associated with a cyclists' choice of whether or not to wear a helmet, and the conspicuity criteria of helmets.

The inclusion of psychological and social aspects of helmet usage is crucial in the effective development of both helmet design and legislation. In order to increase and encourage helmet usage, these factors must be taken into consideration. After all, a helmet cannot be effective if it is not worn, and worn properly. The information and guidelines developed by HOPE will help address these issues in a concrete way.

Working Group 3: Impact Engineering

This group reconstructed actual accidents in various countries, and consolidated biomechanical research results, in order to develop new standards for helmets and to improve helmet protection capabilities.

Current helmet testing for impact properties is not based on real accident conditions. Testing methods include a linear shock absorption test, during which a helmet is dropped vertically onto a horizontal flat surface, as well as a kerbstone-shaped surface. However, actual accident reports indicate that angled impact is far more common, and results in more serious brain injury. Compared to linear shock absorption, the rotational movement of the neck and head that results in the angled impact can cause both concussion and more severe brain injury, such as subdural hematoma and diffuse axonal injury. In order to create truly effective bicycle helmets that protect against the most common and severe types of head injury, new testing conditions and pass/fail criteria are essential. The resulting design improvements can, in turn, protect cyclists in both accidents due to falls, and collisions with other vehicles.

Working Group 3's primary output is the proposal of a new bicycle helmet test method, which considers tangential helmet impact and advanced head injury criteria. This progress will allow enhanced protection of bicyclist's heads. The novel test method can be, and already is, considered to be current by the industry. New helmet design can now be evaluated under tangential head impact conditions. In this domain, no less than three helmet evaluation programmes have already be launched in Germany, France and Sweden.

Although the 'most common' impact angle is still difficult to evaluate exactly, it is clear from the reconstructions that impact angles are usually far removed from the direct, 90-degree impact conditions under which helmets are currently tested. There remains a lack of additional, detailed accident reconstructions, which would provide a statistically based decision on the most common types of bicycle accidents. Based on existing data and literature review, Working Group 3 proposes to keep the shock absorption tests defined in EN 1078 and EN 1080, but to complement these with three angled (oblique) tests, using an impact angle of 45 degrees at a speed of 6.5 m/s.

Current testing is shown to be deficient in three key areas. First, it does not include testing for impacts at an angle, although the majority of accident data indicates that angled impacts are common and cause significant injury. Second, testing does not currently account for realistic brain injury criteria, despite the fact that this is shown to have an effect on impact conditions. Third, data is available to analyse the impact location on the helmet after an actual accident. This data indicates that the testing line defined in EN 1078 is too high. Working Group 3, in conjunction with Working Group 1, therefore proposes to lower the test line, so that the helmet covers more of the head, whilst still creating a design that is attractive and accepted by the end consumer.

Working Group 3 proposes new test methods for improving testing in bicycle helmets from these three critical points of view. First, impact testing to accommodate the 45-degree-angle impact condition. Second, testing to account for the effect of a more realistic pass/fail criteria. The third testing improvement would be to lower the testing line for the impact location on the helmet.

The primary aspects of this new bicycle helmet test method are the introduction of tangential helmet impact and improved pass/fail criteria that can predict brain injuries, in addition to predicting skull fractures as it does today. It can easily lead to changes to the way helmets are certified and improve helmet efficacy in accidents. By adding real accident data and new biomechanical knowledge to the current regulation tests EN 1078 and EN 1080, the protective aspects of bicycle helmets can be vastly improved. Specific new testing parameters and methods, based on actual accident data and new biomechanical criteria, would bring the certification standards to a much higher, more effective level.

Working Group 4: Thermal Comfort

The two factors that have a strong impact on the thermal properties of helmets, and consequently on overall thermal comfort, are wind speed and body posture. Helmets must therefore be adjusted for the type of cycling activity. In addition, improved radiant shielding properties contribute to overall comfort, and several design improvements are offered to optimise this effect. These improvements also include the adjustment of inlet and outlet air vents, and the air channels that connect them, to further improve air convection capabilities. Working Group 4's output shows that different methodologies, including computational modelling, can help in the development of new and effective helmet design, while experimental simulation can provide proof of concept and optimisation capabilities. Furthermore, the possibility of adding active cooling systems to helmet design were explored. Dynamic vents or active cooling systems that regulate heat loss can be controlled by models that predict thermal comfort at the head, so as to optimise thermal comfort in the design stages.

Working Group 4 has therefore provided the initial ideas to begin developing a standard for assessing cooling effectiveness. These standards will allow for accurate and consistent testing of products, and will help make thermal comfort a direct priority for manufacturers. It will also allow manufacturers to clearly, objectively and accurately inform customers about the cooling effectiveness of various helmet types.

End of excerpts.

Comment by helmets.org

Many of the recommendations for improvements in standards track our own: lower the test line to provide better coverage, test for angular acceleration and lower the threshold failure level. Unfortunately, the report is very general and provides no actual test line changes or numbers for the thresholds. We don't think there is any need to set a standard for thermal comfort, since that is easily judged by the consumer and the market is taking care of that. The study is based on European helmets, and most of them don't meet our US impact standard. Task groups in our ASTM F08.53 subcommittee have been working on all of those changes for years, but the actual numbers are always controversial and elusive.