Our Methodology
Helmet rating programme
Novel helmet designs and technologies are rapidly entering the market with a range of claims to reduce the risk of brain injuries. All these helmets enter the market once they pass the minimum safety requirements established by standards such as the EN 1078 used in the UK. However, there is no further information available to consumers to enable them to distinguish between helmets available on the market in terms of their safety.
Representative impact conditions
Impacts are simulated on a helmet test rig developed at Imperial College. It tests helmets under oblique impacts that are often seen in real-world data, which produce larger head rotation. It uses a state-of-the-art headform for more accurate and precise helmet testing results.
The Biofidelic Human Headform
Hiper uses a new biofedelic headform to simulate the human head’s response more accurately during helmet impacts. In the lab, helmets are tested using a headform. To replicate real-world head motion effectively, the physical properties of the headform must closely resemble those of the human head. The main physical properties that influence test results include: shape of the head, its mass, the location of the centre of mass, the mass moments of inertia (the head’s resistance to rotation about its three anatomical axes, x, y and z), and the coefficient of friction between the head surface and the helmet.
Head injury criteria
To assess the risk of different types of head injuries, Hiper translates measurements from the sensors using a function known as the head injury criterion. A recent study reviewed 21 papers examining specific head injury types in bicycle incidents, covering approximately 90,000 cyclists. The documented injuries include skull fracture, damage to the blood vessels located between the skull and brain (extradural haemorrhage, subdural haematoma, subarachnoid haemorrhage), damage to the superficial layers of the brain (contusions) and damage to the deep structures of the brain (diffuse axonal and vascular injuries).
Calculation of the Overall Risk and Rating Score
To determine the overall injury risk for each helmet, we first determine the average of the linear and rotational risks for each impact location. We then multiply this average value for each impact location by the weighting of that impact location. The impact location weightings were derived from a meta-analysis of real-world cycling incidents, which included 1,809 head impacts from ten different studies. Finally we add the weighted average risk for each location to determine the overall risk for the helmet.
