HEAD INJURY CONTROL - Injury Biomechanics and Control: Optimal Protection from Impact - page 233

CHAPTER 7

HEAD INJURY CONTROL

When a person experiences a head impact and the event is simulated, the
severity of the injury is evaluated from the Head Injury Criterion (HIC). To
mitigate the potential injury to the brain, the head must be isolated from the
surface it hits by a soft structure, such as a helmet liner or a special surface
on a playground. Limiting performance analysis enables finding either the
minimum head displacement needed to have an acceptable HIC value or
the lowest HIC value for a given maximum value allowed for the head
displacement.

7.1 HEAD INJURY CRITERION: HISTORICAL PERSPECTIVES

The HIC is an empirical integral criterion that evaluates the possible sever-
ity of human brain injury induced by an impact in terms of kinematic
parameters of this impact. Formally, this criterion is defined by

(t 2 − t 1 ) , a(t) dt 2 . 5

t 2

1

HIC = max

t 1 ,t 2 ,t 2 − t 1 ≤

(7.1)

t 2 − t 1

t 1

where a(t) is the magnitude of the acceleration of the center of mass of
the brain and is a constant parameter having the dimension of time. The
criterion of Eq. (7.1) reflects the dependence of the severity of the injury
on both the mean magnitude of the head acceleration induced by an impact