PC2127: Softer Foam in Bicycle Helmets Reduces the Impact Force in a Simulation Model

Background: Bicycling accidents are a leading cause of unintentional injury in children, resulting in many emergency department visits and associated costs. Efforts to increase bicycle helmet use have resulted in fewer head injuries and decreased bicycle-related mortality. Currently, most bicycle helmets are lined with crushable expanded polystyrene (EPS) foam, designed for a single hard impact. However, soft/rubbery foams are typically used in helmets designed for sports with a high risk of head injury, such as football, hockey, and skateboarding. This study compared the linear acceleration generated from an impact to a manikin's head wearing an off-the-shelf “standard” bicycle helmet (stdBH) compared to a modified bicycle helmet (modBH) (original foam replaced with softer polyolefin foam).

Methods: Pairs of 5 different bicycle helmets from a wide price range ($20-$90) were tested (standard versus modified). The head impact was simulated by striking the test bicycle helmet placed onto the head of a Century BOB boxing manikin, with a conventional football helmet (4.6 kg additional weight added) swung from a 1.2 meter rope and released from an angle of 45º serially for multiple data points. The manikin's bicycle helmet was struck by the football helmet in the frontal, left parietal, and occipital locations for 12 trials each. Each of three accelerometers located at the manikin’s forehead, apex of the head, and right ear collected data on linear acceleration in the X, Y, and Z planes. Additionally, we collected data for strikes in the same positions with the manikin wearing an off-the-shelf baseball helmet lined with soft ethylene-vinyl acetate foam instead of a bicycle helmet.

Results: Peak linear acceleration in G's (9.8 m/sec/sec) was obtained from three accelerometer locations on the manikin's head for each striking position. Mean strike forces sustained by the manikin's head were higher for the stdBH compared to the modBH. Mean values respectively for frontal strikes were 42.68 vs 18.90 (forehead accelerometer), 39.75 vs 20.13 (apical accelerometer), 27.39 vs 14.58 (right ear accelerometer). For occipital strikes, the same respective values were 52.09 vs 21.16 (forehead), 69.16 vs 23.08 (apical), 32.20 vs 12.40 (right ear). For left parietal strikes, they were 43.01 vs 15.98 (forehead), 83.41 vs 22.73 (apical), 31.94 vs 15.29 (right ear). All differences were statistically significant at the p< 0.05 level. For the single baseball helmet, mean linear acceleration for frontal strikes were 72.18 (forehead), 37.06 (apical), 37.03 (right ear); occipital strikes 50.19 (forehead), 54.94 (apical), 43.44 (right ear); and parietal strikes 34.97 (forehead), 47.67 (apical), 34.34 (right ear).

Conclusion: These results suggest that softer foams in bicycle helmets may reduce injury from bicycle accidents. However, foam that is too soft may not be as beneficial. Further research on this topic can lead to the development of safer and more effective bicycle helmets.