Critical evaluation of the SHARP motorcycle helmet rating

The Department for Transport introduced a safety helmet assessment and rating program (SHARP) for motorcycle helmets sold in the United Kingdom. The mechanics behind the part of the scheme that uses a rigid sphere head-plus-helmet model to estimate the peak headform acceleration in oblique helmet impact tests is assessed and the approximations exposed. When finite element analysis (FEA) of a deformable helmet with a realistic shape was used, the predicted levels of oblique peak acceleration were much smaller than those estimated by the SHARP scheme. The statistical data of motorcyclists' impact velocities, sites and impact type, used to weight the SHARP impact results, were shown to overemphasise impacts at the sides of the helmet. It was concluded that the derived oblique impact test results, based on an inappropriate mechanics model, are meaningless. Consequently, the helmet star ratings are not related to head protection levels.