Head Injury Criterion
The Head Injury Criterion (short: HIC, in German literature sometimes: HIC value, head injury or head factor load value) is a criterion for the evaluation of acceleration -related head injuries, for example, by a vehicle accident. The dimensionless value allows a comparison of the occupant safety of different vehicle models.
Historical
From crash test experiments with corpses, we know that the severity of an injury can not always be with the maxima of the load at the measuring point, so for example the head measured, crash induced acceleration correlate. In order to still describe relationships between stress and induced injury, especially to be able to compare derived quantities have been defined. One of these variables is the Head Injury Criterion. It is the normalized integral value of head acceleration. Depending on the observed time interval - 15 or 36 ms - even the HIC15 or the HIC36 value is specified for a more precise distinction often.
The Head Injury Criterion is calculated as follows:
Here, a is the resultant head acceleration in g (ie multiple of the acceleration of gravity), t1 and t2, the time interval considered.
Today
The measurement of the Head Injury Criterion is done today under standardized conditions. Thus, approved in the U.S. for example, vehicles must meet the FMVSS 201 and 201u. This safety rule for interior components have been around since the 1990s. The assessment will be based FMH tests ( Free Motion Head ). Various interior surfaces are bombarded with a free-floating aluminum head. This head mold is coated with rubber and weighs 4.54 kg. He must strike the surface to be tested, according to experimental protocol with the front face plate and a speed of 24.1 km / h. Since 1 October 2005, a trial is in the EU for all newly registered vehicles prescribed to reduce the risk of injury to pedestrians and cyclists in a collision with a passenger car. In this test, a 3.5 kg heavier head dummy shot on the hood with a speed of 35 km / hr.
For all tests the limit of the Head Injury Criterion to 1000 is fixed. A comparison with real injury has shown that when this threshold value according to an AIS Level 3 ( Abbreviated Injury Scale) classify injury with a probability of 0.5 (50%) occurs. An injury by AIS level 3 means a serious injury, such as a concussion with loss of consciousness of less than 1 hour or the loss of an eye. If the HIC at 800, is the probability of being less severely injured 0.9. A HIC of 1300 is, conversely, that an even more serious violation occurs in 55 % of cases. A HIC36 of 1000 means the equivalent of a constant head load of 60 g
Instead of experimental measurements HIC values are today often calculated with the help of simulation programs. Its usefulness is, however, now controversial, as observed in crash tests with dummies forms of injury do not always agree with the injuries in real traffic accidents.
The HIC value is not only used in vehicle safety, but wherever the severity of a head injury must be estimated. Even in the safety assessment of aircraft seats, it serves as a reference value.