Bicycle helmets--are they up to standard?

On the 3 September, British Columbia's new mandatory bicycle helmet law came into effect. All cyclists on public roads and highways are now required to wear a bicycle helmet that meets one of the following standards CAN/ CSAD1 13.2-M89, Snell B-90, B-90S, B-95 and N-94, ASTM F1447-94, ANSI Z90.4-1984. The implementation of this law largely reflects the unremitting efforts of Glenna Ayerst, Director of the National Bicycle Safety Foundation, but as Glenna says, 'the new law is just the start'. The law has been introduced to reduce the incidence of head injuries from cycling and a news release from British Columbia's Ministry of Transportation and Highways quotes studies which have shown that helmets reduce the risk ofhead injuries by 85% and brain injury by 88%. But how effective is the law really likely to be? Arguably, BC's mandatory bicycle helmet law alone will not result in such a dramatic reduction in head injuries. Experience in other jurisdictions has shown that legislation is an effective way of rapidly increasing helmet wearing rates. For the law requiring their use to be effective, however, bicycle helmets must be fitted and worn properly. A casual view of the riding population suggests helmets are often incorrectly worn, off the forehead and loosely secured. Locally, finding a good fitting helmet is often difficult, especially for a child, and the retention straps are often difficult to adjust. There is considerable real-world crash data which confirms the reduced risk and exposure to head injuries from wearing a helmet. However aside from helmet fit, there is a limit to the protective capabilities of a properly worn bicycle helmet certified to a recognised standard. Modern bicycle helmets comprise two essential features: * An energy absorbing liner which through its own destruction reduces the violent movement and distortion of the brain and skull. * A retention system in the form of adjustable straps buckled together to secure and position the helmet on the wearer's head. The design ofcurrent bicycle helmets largely reflects the minimum performance requirements of helmet standards. The energy absorbing capabilities of a helmet are tested in accordance with helmet standards by placing a test helmet on a rigid anthropometric headform and dropping it from a predetermined height in guided free fall on to a steel anvil. The area ofthe helmet that is impact tested in helmet standards is confined to the zone above a prescribed test line. The energy absorbing helmet material may extend beyond the test area, however in reality the test line often represents the edge of the helmet as effective protection. Modern helmets cover a relatively small area of the head and field evidence confirms the need for helmets that afford better head coverage with energy absorbing material. A bicycle helmet can only protect the area of the head which it covers. Impact tests in current bicycle helmet standards only assess the ability of the helmet to reduce linear or translational acceleration. In light of the established effectiveness of helmets in preventing injuries, it is reasonable to assume that helmets that reduce linear acceleration are also successful in protecting against rotationally induced head injuries. However, given rotational movement of the brain may result in severe injuries, it would be prudent to develop test methods to assess a helmet's ability to reduce rotational acceleration. It is reasonable to expect bicycle helmets to provide good protection over a broad range of survivable impact levels. Many helmet standards test helmets only in conditions approximating severe impacts. To pass these impact tests, helmets are often fabricated with dense liners that arguably fail to provide optimum protection against the more common and less severe impacts. The inclusion of both low and high energy impacts in the Canadian cycle helmet standard (CAN/CSA-D1 13.2-M89) with more demanding pass criteria for the low energy impact is an attempt to promote good protective capabilities over a range of impact levels. Laboratory tests and field experience suggest that the dynamic strength of bicycle helmet straps and buckles is adequate. The stability of the fitted helmet, however, depends largely on the proper adjustment of the retention system by the cyclist. There is no test to assess the ease with which the straps may be correctly adjusted. There is no guarantee that the rider will wear the helmet properly. In local cycling traffic, helmet fit is often poor and large parts of the cyclist's head are often exposed. Finally, bicycle helmet standards are based on adult anthropometry and head protection criteria. It is unlikely that scaled down versions of adult bicycle helmets will provide the best protection to the growing child. A recently introduced amendment to the Canadian cycling helmet standard includes lower peak acceleration limits for helmets designed for Rona Kinetics and Associates Ltd, PO Box 54020, Lonsdale West PO, North Vancouver, BC, Canada V7M 3L5