The article is devoted to a topical problem of human safety in accidents. It considers biomechanical characteristics of a human skull and brain concerning the choice of criteria for the evaluation of human head injury risk in accidents. The results of biotechnical research on human head impact are given. Basing on the results of tests and calculations, the criteria for evaluation of human head injury risk at impact we suggest using the velocity lost by a head under impact within the function of g-load rate of onset measured in the head of a dummy. The data of the comparative analysis of human head injury risk are provided based on the materials of car crash tests of some automobiles. The illegitimacy of use of the HIC (Head Injury Criteria) is shown, as the method of its calculation considerably (several times) lowers the real injury risk of impact loads measured in the head of a dummy in car crash tests.
Rabinovich Boris Abramovich. Born in 1932.
Graduated with the excellent degree from Moscow Aviation Institute in 1956 as an aviation engineer.
In 1956-1995 he worked in aerospace industry in the positions of Processing Engineer; Calculation and Testing Chief Designer; Head of Department.
Specialization: designing and testing emergency systems – shock-absorbing and ejecting seats for pilots and astronauts; human biomechanics under extreme accelerations.
He took part in tests and implementation of the first human space flight under the Vostok program, in the manned Voskhod and Soyuz space programs, and in Buran program.
Since 2000 he is taking the position of Vice-President of Russian Association of Amusement Parks and Attractions (RAAPA).
Doctor of Technical Science, Professor. The author of more than 100 scientific papers including 2 monographs “Human Safety Under Acceleration” and “Astronaut Safety by Touchdown Impact”, co-developer of a number of safety standards for amusement rides.
Kulakov Nikolay Alekseevich. Born in 1947.
Graduated from Moscow Aviation Institute in 1971, specialization: mechanical engineer of aircraft engines.
Graduated from Moscow State University (MSU) in 1972, specialization: mathematics.
In 1977, at the Academic Council of Mechanics and Mathematics Faculty of MSU he defended his dissertation for the degree of Doctor of Physical and Mathematical Sciences.
Professor, Department of Resistance of Materials, University of Engineering.
Head of Scientific and Technical Center “Automobiles”, University of Engineering.
Specialization: calculation and experimental methods of development and testing of protection means for automobiles under crash impact. Development and application of test-measurement systems involving dummies.
Author of more than 70 scientific papers and 10 patents.
Since 1977 to the present day he has been working in University of Engineering (MAMI).
On Illegitimacy of HIC Application for Evaluation of
Human Head Injury Risk under Impact Boris A. Rabinovich. Prof. Vice-President of Russian Association of Amusement Parks and Attractions (RAAPA). Moscow. E-mail firstname.lastname@example.org
Nicolay A. Kulakov. Prof. Head of Scientific and Technical Center “Automobiles”, University of Engineering. Moscow. E-mail email@example.com
1. Statement of the problem.
This article is devoted to risk evaluation of head injury that can cause a craniocerebral trauma.
To evaluate human safety in accident, safety criteria applied to crash tests are of significant importance; nowadays the head injury risk under impact criterion is HIC (Head Injury Criteria) introduced in .
HIC is used in automobile crash tests; it is also used in crash tests of antistrike helmets, airplane and helicopter seats, shock-absorbing seats of various application etc.
The goals of the given article are as follows:
- to summarize modern scientific data about the structure and physical-mechanical properties of the human skull and brain, and also to converge the results of experimental surveys with regard to the problem of craniocerebral criteria choice;
- to formulate modern evaluation criteria of head injury risk on the basis of analyzing test data concerning craniocerebral trauma investigation and the data on the structure and physical-mechanical properties of the human skull and brain;
- to analyze grounds for HIC in evaluation of head injury risk.
2. Structure and physical-mechanical properties of the human skull and brain.
Anatomically , a skull is composed of three parts: the vault, the base and the facial bones.
The base of the skull is formed by bone structures and cartilaginous ligaments that lie on the plane inclined at an angle of ≈ 250 to the horizontal plane. The base has a number of foramen with the brainstem and other nerve fibers going through them.
The paper  gives the results of experimental determination of the vault and the base rigidity under static loads.
The tests circuit is shown in Fig. 1.
Fig.1. The tests circuit. 1 – Skull sealing contour; 2 – Skull under experiment fastened with its front on a stable stand; 3 - Cranial cavity impacted by excess pressure; 4 - Vault deformation; 5 – Base deformation.
Five skulls were tested. The air pressure 0,5∙104 Pa was delivered into the skull cavity. Deformations in specific points of the vault and the base were measured in relation to the stand on which the skull was set.
It was determined that under the loads applied inward the skull the base central zone was deformed approximately 10 times as much versus the deformations of the vault, i.e. the base is more compliant with loads than the vault.
Paper  analyzes the test results of base deflections under the impact of the frontal and the occipital parts against a rigid barrier. 7 dry non-macerated skulls were tested; 22 experiments with the front impact and 26 – with the back impact. The tests showed that under the front impact an outward deflection appeared relatively to the skull cavity; under the back impact an inward deflection appeared relatively to the skull cavity.
In Fig.2 the corresponding circuit of the skull deformation is given. As a result of the base plane incline at an angle of ≈ 250 to the horizontal plane, the skull base buckles towards the forehead under the influence of inertia at the start point of impact. We can assume that the basal skull structures shall be deformed correspondingly.
It is worth noting that when the skull is deformed like Fig.2 shows, inside skull cavity volume alters where the brain is located. Under the similar deformations, brain tissue shifts relatively to the vault and the base of the skull. Papers [5;6] set forth that impacts do leave deformations and shifts of brain tissues relatively to the skull bone structure.
Fig. 2. Scheme of skull base deformations under a frontal impact; 1 – Skull vault; 2 – Skull base in the initial position before the impact; 3 – Skull contour under the impact.
In tests  on a living and dead brain the constant load was applied to the plate set on the brain surface. As it is seen in Fig.3, initially, deformations are proportional to the load which is evidence to elastic properties of brain tissue. With time the brain tissue pressure is declining which is a characteristic feature of a viscoelastic medium.
3. Experimental data of craniocerebral injuries.
3.1. Craniocerebral injury research involving biomancer (cadaver).
In papers [8;9] there are given the results of experimental research of biomechanics of brain injury of biomancer under the dosed impact loads. Totally, there were over 450 tests held.
Both the head impacts against the rigid barrier using special stands and the head impacts with impactor of different forms were studied.
On the basis of the research, the authors have drawn the following conclusions.
3.1.1. During the impact loads (with no skull fractures) which affected the head from every direction – the forehead, the back, a temple, and the cranium – the brain deformations were located in the area of basal structures.
3.1.2. The pathogenetic connection between basal structure deformations and the skull base deformation was proved.
In the tests the apparent dependence between the bones thickness in the area of the orbit, greater wings of sphenoid bones and the brain deformation intensity were noted. The thinner these bones were the more considerable were the deformations of the frontal lobe base and the temporal poles of the brain.
3.2. The analysis of craniocerebral injuries after traffic accidents.
In paper  the results of the analysis of 69 craniocerebral injury cases with a lethal outcome are systematized.
Under the impact loads on a head from different directions in all the cases brain injuries occurred in the area of basal structures and the skull base bones. This result coincides with the conclusions drawn in [8;9] (see 3.1.1).
4. The analysis of craniocerebral injuries using the clinical evidence. Influence of the impact velocity.
In  there are given the results of the analysis of the archive data collected by the traumatology department of USSR N.N. Burdenko Scientific Research Neurosurgery Institute of the Academy of Medical Services since 1938 to 1970 (3000 medical reports). The cases when the initial isolated head trauma was the result of the fall from the standing position onto the solid surface were processed. The velocity of the impact was calculated in consideration of the trauma circumstances given in the medical report.
The parietal region traumas were excluded from the processing as they usually resulted from traffic accidents or a fall of objects onto the head.
In consideration of the given limitations 317 medical reports were selected out of 3000 (112 – the trauma of the frontal region, 84 – temporal region, 121 – occipital region).
As it can be seen in the given materials, the condition of the injured people considerably deteriorated in the nearest aftereffect, the higher was the head and barrier impact velocity.
The focused analysis of unconsciousness cases caused by craniocerebral injuries showed that the initial velocity threshold of a head and barrier impact causing the loss of consciousness is V=3m/s [11;12].
It shall be noted that the similar data on the threshold of human head safe impact against a solid barrier is given in  Table 1.
Head Injury Criteria for the impact against a barrier . Table 1.