A LEADING safety engineer from Birmingham University* has spoken out against the SHARP helmet rating scheme, believing the system should be scrapped following the results of a recent scientific study.
Dr Nigel Mills, who has worked on helmet testing and design for 30 years, believes the European helmet testing system is flawed. During an intensive six-month study, Dr Mills found areas of concern, which has prompted the scientist to ask for SHARP ratings to be scrapped.
Dr Mills has pointed out three major factors within SHARP that are of serious concern. Speaking exclusively to Visordown earlier today, Dr Mills said:
"First, the impact velocities in oblique impact tests must be realistic; gentle impacts used to determine helmet friction coefficients differ from more severe impacts in which the helmet starts to roll on the road.
"Second, the test headform must simulate the human scalp and hair which allow significant helmet rotation. A test headform without scalp or hair responds differently and may overemphasise the friction of the helmet shell. The rotational acceleration of the test headform must be measured.
"Third, the pass/fail criterion must be set. Only ballpark figures for human tolerance to rotational acceleration are known. You might imagine that independent researchers had agreed on the details, and the industry was convinced of the benefits of these radical new tests. However the SHARP scheme was developed by the government Transport Research Lab for the DfT without public debate."
Dr. Mills criticises the oblique impacts in the SHARP scheme, as they don’t measure rotational head acceleration. Presumably to save money, they use a mechanics model, a friction coefficient and a direct impact test result to estimate the oblique impact performance.
Mills’ study shows the model is too simple, so the estimated performance parameter (a linear head acceleration multiplied by a function of the friction coefficient) is meaningless. They weight test results from different sites in a complex way to estimate how many lives would be saved by a particular helmet design. This overemphasises test ‘results’ at the sides of the helmet, and totally ignores impacts on the chin bar region. Hence he concludes that the estimates are meaningless.
Dr Mills feels that the British and European helmet standards could be amended to include tests for oblique impact protection, based on scientific consensus, with the design consequences considered.
* under review by a journal, available on perg.bham.ac.uk
