HIC Value

Head Injury Criterion HIC

The Head Injury Criterion (HIC) is the main criterion adopted to evaluate the impact severity of a motorcyclist against a MPS. It is a measure of the likelihood of head injury arising from an impact. The HIC is intended to judge the head injury risk quantitatively. In the case of an accident, cranial and spinal injuries arise from a deceleration during the crash, in particular at the moment of impact. The higher the head deceleration, higher is the HIC. The dummies used in crash tests have several sensors fixed to the head area which record the absolute value of the deceleration and its dependence on time. It is plausible that this head load is higher the larger the value of the deceleration and the longer the deceleration lasts.

There are 6 different levels to classify head injuries, as we can see on the table 2.

Level

Assessment

1

Slight damage to brain, with headache, dizziness, no loss of consciousness, contusions

2

Concussion with or without skull fracture, less than 15 minutes of unconsciousness, detached retina, face and nose fracture

3

Concussion with or without skull fracture, more than 15 minutes of unconsciousness without severe neurological damage, multiple skull fracture, loss of vision, multiple facial fracture, cervical fracture without damage to spine

4

Multiple skull fracture with severe neurological damage

5

Concussion with or without skull fracture, more than 12 hours of unconsciousness, hemorrhage in skull and critical neurological condition

6

Death, cervical fracture with damage to the spine

Table 5 – levels of head injury based on the Abbreviated Injury Scale (AIS)

A small HIC value doesn’t means that the head injuries will be of low levels. Likewise, a high HIC doesn’t imply high level injuries. The real meaning is that with higher HIC values, the higher the probability of getting high level head injuries.

For example with a HIC of 650 the probabilities are of 90% injuries level one, 55% of injuries level 2, 20% of injuries level 3 and 5% injuries level 4 (combined injuries are possible).

The TS 1317-8 has two levels of acceptance according to the HIC, level 1 for tests results equal or less than 650 and level 2 for results equal or less than 1000. What we need to have in mind is that smaller the HIC value, the better it is.

An interesting point is that if two products approved by the TS 1317-8, one obtained a HIC of 150, and the second a HIC of 640, for example, they will be classified with the same level. Also a third product with a HIC of 670 would be classified as level 2. Defining the severity in only 2 levels can be dangerous, and sometimes not point very well the difference between the MPS.

Picture 10 – forces and moments measured for the HIC

Neck Injury Criterion

For the evaluation of the neck injury, the European Standard takes into account the forces and also the time these forces act on the neck. Putting in a very simple way, bigger the time, small shall be the forces, to have an acceptable result.

This criterion is classified in 2 levels as well. The forces are measured and each standard and test procedure has its own table to classify if the values are valuable or not. Smaller values mean that the product is safer.

Graphs 1 to 6 shows gives the maximum permissible load durations for given neck loads levels.

Graph 1 – Anterior-posterior neck shear force criterion neck for level I

1 – Pass           3 – Anterior-posterior neck shear force (N)

2 – Fail 4 – Permitted duration for a given shear force (s)

Graph 2 – Axial neck tension criterion for level I

1 – Pass           3 – Axial neck tension (N)

2 – Fail 4 – Permitted duration for a given tension force (s)

Graph 3 – Axial neck compression criterion for level I

1 – Pass           3 – Axial neck compression (N)

2 – Fail 4 – Permitted duration for a given compression force (s)

Graph 4 – Anterior-posterior neck shear force criterion for level II

1 – Pass           3 – Anterior-posterior neck shear force (N)

2 – Fail 4 – Permitted duration for a given shear force (s)

Graph 5 – Axial neck tension criterion for level II

1 – Pass           3 – Axial neck tension (N)

2 – Fail 4 – Permitted duration for a given tension force (s)

Graph 6 – Axial neck compression criterion for level II

1 – Pass           3 – Axial neck compression (N)

2 – Fail 4 – Permitted duration for a given compression force (s)