Head Injury Criterion

The Head Injury Criterion (in short: HIC , in German literature sometimes also: HIC value , head injury factor or head stress value ) is a criterion for evaluating head injuries caused by acceleration, e.g. B. by a vehicle accident. The dimensionless value enables a comparison of the occupant safety of different vehicle models.

Historical

It is known from crash tests with corpses that the severity of an injury cannot always be correlated with the maximum load at the measurement location, for example the impact-induced acceleration measured on the head. In order to describe the relationships between stress and induced injury, and above all to be able to compare them, derived parameters were defined. One of these sizes is the Head Injury Criterion. It is the normalized integral value of the head acceleration. Depending on the observed time interval - 15 or 36 ms - the HIC ₁₅ or the HIC ₃₆ value is often given for a more precise differentiation .

The Head Injury Criterion is calculated as follows:

${\displaystyle HIC={\left[{\frac {1}{t_{2}-t_{1}}}\int _{t_{1}}^{t_{2}}a(t)dt\right]}^{2,5}(t_{2}-t_{1})}$

Here, a is the resulting head acceleration in g (i.e. a multiple of the acceleration due to gravity ), t ₁ and t ₂ the time interval considered.

today

The Head Injury Criterion is measured under standardized conditions. As approved in the United States have vehicles such as the FMVSS meet 201 and 201u. This safety regulation for interior components has existed since the 1990s. The assessment is based on the FMH test (Free Motion Head). Various interior surfaces are shot at with a free-flying aluminum head. This head shape is coated with rubber and weighs 4.54 kg. According to the test instructions, the front face plate must hit the surface to be tested at a speed of 15.2 km / h. Since October 1, 2005, a test has been mandatory for all newly registered vehicles in the EU in order to reduce the risk of injury to pedestrians and cyclists in the event of a collision with a passenger car. In this test, a head dummy weighing 3.5 kg is shot at the bonnet at a speed of 35 km / h.

For all tests, the limit of the Head Injury Criterion is set at 1000. A comparison with real injuries has shown that at this limit value, an injury classified according to AIS level 3 (Abbreviated Injury Scale) occurs with a probability of 0.5 (50%). An AIS level 3 injury means a serious injury, for example a concussion with loss of consciousness for less than 1 hour or the loss of an eye. If the HIC is 800, the less likely to be seriously injured is 0.9. Conversely, an HIC of 1300 means that 55% of the time, an even more serious injury occurs. A HIC ₃₆ of 1000 means, converted, an average head acceleration of 60 g .

Instead of experimental measurements, HIC values ​​are now often calculated with the help of simulation programs. However, its usefulness is now the subject of controversial debate, as the injury values observed in crash tests with dummies do not always match the injuries in real traffic accidents .

The HIC value is not only used in vehicle safety , but everywhere where the severity of a head injury has to be estimated. It is also used as a reference value for safety checks on aircraft seats .

Individual evidence

1. ↑ § 571.208 Standard No. 208; Occupant crash protection. (PDF; 945 kB) US Government Publishing Office, June 30, 2016, p. 586, S6.2 , accessed February 10, 2017 .