SIST-TP CEN/TR 16148:2011
(Main)Head and neck impact, burn and noise injury criteria - A Guide for CEN helmet standards committees
Head and neck impact, burn and noise injury criteria - A Guide for CEN helmet standards committees
Members of helmet Standards committees frequently need to define limits for test procedures. Such limits relate to test values that indicate the potential for injury and yet it is often difficult for members to know the type and severity of injury that is represented by a given test value. Over the years, criteria have been developed for different body regions and usually these have been derived from a combination of accident and casualty data, and tests on cadavers, cadaver body parts, animals and human volunteers. However, such criteria are often used by the automotive industry as pass/fail values without a clear understanding of human tolerance to injurious forces. This sometimes leads to the mistaken belief that any value below the stated limit implies uninjured and all values above imply a serious or fatal injury.
This misconception gives very little freedom to choose values that are different from the often-inappropriate automotive value. This is particularly true for head injury criteria for which values for a helmeted head may be different to those for the unhelmeted head. Many accidents to wearers of helmets, which cover a wide range of activities from horse riding to downhill skiing, result in a closed head injury. This is when the brain is damaged without any skull or external tissue damage. Conversely, head injuries in automotive accidents are much more frequently open head injuries with skull fracture and soft tissue lesions.
Other misconceptions arise because of the failure to understand that human response to a given dose or injurious parameter varies across a range of the population. The dose response curve tends to be "S" (sigmoid) shaped such that as the magnitude of the injurious parameter increases so does the percent of the population that sustains an injury of a given severity.
Kriterien für Verletzungen durch Einwirkung auf Kopf und Hals, Verbrennungen und Lärmverletzungen - Leitfaden für Arbeitsgruppen, die europäische Helmnormen erarbeiten
Diese Skala erstreckt sich von 0 bis 6, wobei 0 für unverletzt und 6 für tödlich steht. Jede Stufe kann nach einer von der „Association for the Advancement of Automotive Medicine“ (AAAM) erstellten Aufschlüsselungs-anleitung für jede Körperregion angewendet werden. Die Tabellen 1 und 2 geben die Einstufung und den Verletzungsschweregrad an sowie einen Hinweis auf die Kopf- und Halsverletzungen, die bei jeder Stufe klassifiziert werden. Tabelle 3 enthält ähnliche Angaben zu Verbrennungen in Form von Verbrennungsgrad, Oberfläche und Körperregion.
Critères relatifs au traumatisme cervico-facial et aux lésions dues aux brûlures et au bruit - Guide destiné aux comités des normes sur les casques de protection du CEN
Il s’agit d’une échelle de valeurs de 0 à 6, où 0 correspond à l’absence de blessure et 6 au caractère mortel.
Chaque niveau peut être appliqué à toute région du corps selon un manuel de codage élaboré par
Association for the Advancement of Automotive Medicine (AAAM). Les Tableaux 1 et 2 indiquent l’échelle et
la gravité des blessures ainsi qu’une indication des traumatismes de la tête et du cou qui seraient classés à
chaque niveau. Le Tableau 3 fournit des informations similaires pour les brûlures en fonction du degré, de
l’étendue de la surface et de la région du corps.
Merila za določanje poškodbe glave in vratu, ki nastanejo zaradi udarca, opekline ali hrupa - Vodilo za odbore CEN, ki pripravljajo standarde za čelade
Člani odborov, ki pripravljajo standarde za čelade, morajo pogosto opredeljevati meje za preskusne postopke. Take meje so povezane s preskusnimi vrednostmi, ki navajajo možnost poškodbe, vendar pa je članom pogosto težko prepoznati vrsto in resnost poškodbe, ki je predstavljena z dano preskusno vrednostjo. V preteklih obdobjih so razvili merila za različna področja na telesu; običajno so bila izpeljana iz kombinacije podatkov o nesrečah in žrtvah ter preskusov na truplih, delih teles trupel, živalih in ljudeh prostovoljcih. Kljub temu taka merila pogosto uporablja avtomobilska industrija kot vrednosti za uspelo/spodletelo, brez jasnega razumevanja človeške tolerance do sil ob poškodbah. To včasih povzroči napačno prepričanje, da vsaka vrednost pod navedeno mejo pomeni, da poškodbe ni, vse vrednosti nad mejo pa pomenijo resno ali smrtno poškodbo. To napačno prepričanje daje zelo malo svobode za izbiro vrednosti, ki so različne od velikokrat neprimerne avtomobilske vrednosti. To še posebej velja za merila za poškodbe glave, za katere se lahko vrednosti za glavo ob varovanju s čelado razlikujejo od tistih za glavo brez varovanja s čelado. Mnogi tisti, ki nosijo čelade, in ki zajemajo širok razpon aktivnosti od jahanja konjev do smuka, imajo ob nesreči zaprto poškodbo glave. To pomeni, da so možgani poškodovani brez poškodb lobanje ali zunanjega tkiva. Poškodbe glave v avtomobilskih nesrečah so, nasprotno, veliko pogosteje odprte poškodbe glave z zlomom lobanje in lezijami mehkega tkiva.
Druga napačna prepričanja se porodijo zaradi nerazumevanja, da se človeški odziv na dano količino ali parameter poškodb razlikuje med prebivalstvom. Krivulja odziva na količino je po navadi oblike »S« (sigma), tako da se, ko se razsežnost parametra poškodb veča, veča tudi odstotek prebivalstva, ki prenese resno poškodbo.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-junij-2011
0HULOD]DGRORþDQMHSRãNRGEHJODYHLQYUDWXNLQDVWDQHMR]DUDGLXGDUFDRSHNOLQH
DOLKUXSD9RGLOR]DRGERUH&(1NLSULSUDYOMDMRVWDQGDUGH]DþHODGH
Head and neck impact, burn and noise injury criteria - A Guide for CEN helmet standards
committees
Kriterien für Verletzungen durch Einwirkung auf Kopf und Hals, Verbrennungen und
Lärmverletzungen - Leitfaden für Arbeitsgruppen, die europäische Helmnormen
erarbeiten
Ta slovenski standard je istoveten z: CEN/TR 16148:2011
ICS:
01.120 Standardizacija. Splošna Standardization. General
pravila rules
13.340.20 Varovalna oprema za glavo Head protective equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
TECHNICAL REPORT
CEN/TR 16148
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
March 2011
ICS 13.340.20
English Version
Head and neck impact, burn and noise injury criteria - A Guide
for CEN helmet standards committees
Critères relatifs au traumatisme cervico-facial et aux lésions Kriterien für Verletzungen durch Einwirkung auf Kopf und
dues aux brûlures et au bruit - Guide destiné aux comités Hals, Verbrennungen und Lärmverletzungen - Leitfaden für
des normes sur les casques de protection du CEN Arbeitsgruppen, die europäische Helmnormen erarbeiten
This Technical Report was approved by CEN on 27 December 2010. It has been drawn up by the Technical Committee CEN/TC 158.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16148:2011: E
worldwide for CEN national Members.
Contents Page
Foreword .3
Introduction .4
1 Abbreviated injury scale, AIS .5
2 Peak linear acceleration (A.3.1 & A.4) .9
3 Head injury criterion HIC (A.4) .9
4 Rotational motion (A.2.6, A.3.2 & A.4.3) . 10
4.1 Peak Rotational Acceleration . 10
4.2 Tangential force at the helmet surface . 10
5 Skull crushing and penetration force (A.2.2 & A.3.3) . 11
5.1 Crushing force . 11
5.2 Penetration force . 11
6 Neck injury . 11
7 Noise (Appendix section A5.0) . 12
8 Heat: burns and fatigue (A.6) . 12
8.1 Burns . 12
8.2 Heat fatigue . 13
9 References . 14
Annex A Biomechanics of head injury from impact, noise and heat . 15
A.1 General . 15
A.2 Head injuries . 16
A.3 Head injury mechanisms . 24
A.4 Head injury criteria . 29
A.5 Noise . 31
A.6 Heat: burns and fatigue . 35
A.7 Conclusions . 41
Bibliography . 42
Foreword
This document (CEN/TR 16148:2011) has been prepared by Technical Committee CEN/TC 158 “Head
protection”, the secretariat of which is held by BSI.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
Introduction
Members of helmet Standards committees frequently need to define limits for test procedures. Such limits
relate to test values that indicate the potential for injury and yet it is often difficult for members to know the
type and severity of injury that is represented by a given test value. Over the years, criteria have been
developed for different body regions and usually these have been derived from a combination of accident and
casualty data, and tests on cadavers, cadaver body parts, animals and human volunteers. However, such
criteria are often used by the automotive industry as pass/fail values without a clear understanding of human
tolerance to injurious forces. This sometimes leads to the mistaken belief that any value below the stated limit
implies uninjured and all values above imply a serious or fatal injury.
This misconception gives very little freedom to choose values that are different from the often inappropriate
automotive value. This is particularly true for head injury criteria for which values for a helmeted head may be
different to those for the unhelmeted head. Many accidents to wearers of helmets, which cover a wide range
of activities from horse riding to downhill skiing, result in a closed head injury. This is when the brain is
damaged without any skull or external tissue damage. Conversely, head injuries in automotive accidents are
much more frequently open head injuries with skull fracture and soft tissue lesions.
Other misconceptions arise because of the failure to understand that human response to a given dose or
injurious parameter varies across a range of the population. The dose response curve tends to be "S"
(sigmoid) shaped such that as the magnitude of the injurious parameter increases so does the percent of the
population that sustains an injury of a given severity. Thus, a family of "S" curves can be generated for a
range of injury severity such as AIS and a measurement or criterion such as HIC, the Head Injury Criterion.
Unfortunately, the data for such an analysis is generally difficult to obtain because measurements generated
by test apparatus do not relate directly to injury severity because a headform for example does not respond in
an impact like a human head. Hence, it is necessary to find a relationship between these test measurements
and injury severity.
This paper is designed to provide information to convenors that will help in choosing test limits in relation to a
particular injury type and severity. It is worth noting that accident investigators use a scale known as the
Abbreviated Injury Scale, AIS (AAAM). This was developed (in the USA) so that injury severity could be
recorded in databases regardless of the body region and type of injury thus avoiding lengthy medical terms
that were unfamiliar and difficult to interpret. This paper begins by reviewing the AIS scale and its application
to head and neck injuries and burn injuries. Thereafter, each measurement type is reviewed and the severity
of injury for given values is identified where possible. A section on burn injuries and fatigue related to heat
exposure has been included to assist with Standards for equipment to protect firefighters. The Appendix
describes the skin structure and the category and consequence of burn injuries.
Premature deafness because of high noise levels and the converse problem of over attenuation of auditory
warnings was also considered. Suggested levels have been included with details of test methods in Annex A.
1 Abbreviated injury scale, AIS
This is a scale that extends from 0 to 6 where 0 is uninjured and 6 is unsurviveable. Each level can be applied
to any body region according to a coding manual developed by the Association for the Advancement of
Automotive Medicine (AAAM). Tables 1 and 2 give the scale and injury severity and an indication of the head
and neck injuries that would be classified at each level. Table 3 gives similar information for burn injuries by
degree, surface area and region of the body.
Table 1 — AIS scale with head injury severity
AIS 0 AIS 1 AIS 2 AIS 3 AIS 4 AIS 5 AIS 6
uninjured minor slight moderate serious severe unsurviveable
Scalp
superficial abrasions, contusions, lacerations X
major laceration or minor blood loss X
blood loss >20% or total scalp loss X
Intracranial vessels (arteries)
laceration X X
Cranial nerves
contusion, laceration, loss of function X
Brain
swelling, contusions, haemorrhage X
haematoma, large >15cc contusion X
massive >30cc contusions, diffuse axonal injury, large haematoma X
crush, penetrating injury X
Loss of consciousness
< 1 hour X
1 - 6 hours or < 1 hour with neurological deficit X
6 – 24 hours, or 1-6 hours with neurological deficit X
> 24 hours, or 6-24 hours with neurological deficit X
Skull Fracture
simple X
compound X
complex, open, loss of brain tissue X
Table 2 — AIS scale with neck injury severity
AIS 0 AIS 1 AIS 2 AIS 3 AIS 4 AIS 5 AIS 6 unsurviveable
uninjured minor slight moderate serious severe
Whole area
Skin
superficial abrasions, contusions, lacerations X
major laceration or minor blood loss X
blood loss >20% X
Decapitation X
Vessels (arteries)
carotid, jugular and vertebral laceration minor X
carotid jugular and vertebral laceration major X
Nerves
vagus injury X
phrenic injury X
Spine
hyoid fracture X
cord contusion X
incomplete cord syndrome X
complete cord syndrome or laceration C-4 or below X
complete cord syndrome or laceration C-3 or above X
disc injury without nerve root damage X
disc injury with nerve root damage X
Table 3 — AIS scale with burn injury severity
AIS 0 AIS 1 AIS2 AIS 3 AIS 4 AIS 5 AIS 6
uninjured minor slight moderate serious severe unsurviveable
1st degree
unspecified X
2nd degree
< 10% TBS (Total Body Surface) X
3rd degree
< 10% TBS X
< 10% TBS with face, hand or genitalia X
involvement
2nd or 3rd degree
10% to 19% TBS X
10% to 19% TBS with face, hand or X
genitalia involvement
20% to 29% TBS X
20% to 29% TBS with face, hand or X
genitalia involvement
30% to 39% TBS X
30% to 39% TBS with face, hand or X
genitalia involvement
40% to 89% TBS X
≥ 90% X
TBS = Total Body Surface
2 Peak linear acceleration (A.3.1 & A.4)
This is the most frequently used parameter in helmet testing and is derived usually from a tri-axial
accelerometer mounted in the headform unless the headform is rigidly supported and then the source is a
single axis accelerometer. In both types, the helmet is mounted onto the headform and then the apparatus
allowed to fall unimpeded onto a rigid anvil.
Table 4 is a scale published by Newman (1980) and is supported by research that is more recent.
Table 4 — Peak acceleration and typical AIS Equivalent
Peak Acceleration AIS
< 50 g AIS 0
50 g – 100 g AIS 1
100 g – 150 g AIS 2
150 g – 200 g AIS 3
200 g – 250 g AIS 4
250 g – 300 g AIS 5
> 300 g AIS 6
Although not specifically stated in the original research paper it should be considered that the above values
represent 50th percentile, which means that 50 percent of the population would sustain an injury of a given
AIS severity for the corresponding range of acceleration. It is interesting to note that historically, values have
been set which correspond to AIS 5 and that this has resulted in helmets that have given reasonable
protection.
In some standards, the helmet is mounted onto a fixed headform and then a mass is dropped onto the helmet.
Values given in Table 4 may be used with caution provided the falling mass is approximately 5 kg and the
headform is attached to an appropriate neck. Replacing the fixed headform test by a falling headform, guided
or free-fall, should be considered.
3 Head injury criterion HIC (A.4)
Annex A gives details of the derivation of HIC and the formula is given below.
2,5
t
()
HIC = ⋅ a dt ⋅ t − t
res 2 1
∫
t − t
2 1
t
1
max
The benefit of HIC over peak linear acceleration is that HIC is related to time and it is known that pulses with
the same peak value but different duration can give a different injury outcome. Unfortunately, HIC and AIS
values have never been satisfactorily correlated. Although, recent research (COST 327) has provided
tentative values for AIS 2 and AIS 3, see below. Nevertheless, researchers have provided an assessment of
the probability of death for HIC ranges. A summary of the various findings is given in Table 5.
Table 5 — Probability of death for HIC ranges
HIC Probability of death AIS (where known)
1000 10 % - 15 % 2
1500 35 % 3
2000 35 % - 50 %
3000 55 %
4000 60 % - 65 %
It should be noted that where a range is given, this is indicative of more than one source. It should also be
noted that HIC is derived from the GSI (Gadd Severity Index) (see A.4.2) used in some Standards. GSI and
HIC are potentially interchangeable but only for regular pulse shapes. Therefore, it is recommended that GSI
be replaced by HIC.
4 Rotational motion (A.2.6, A.3.2 & A.4.3)
4.1 Peak Rotational Acceleration
This is a parameter that is known to contribute substantially to brain injury but the relationship with injury is
difficult to quantify. It is also a parameter that is considered by test authorities to be difficult to measure
because it requires a nine-accelerometer array in the headform and complex interpretation. Nevertheless, the
research shows, Table 6, that concussion AIS 1-2 can occur at 5 000 rad/sec and fatal injury AIS 5-6 can
potentially occur at 10 000 rad/sec . This correlates with data that indicates that there is a 35 % risk of a brain
injury of AIS 3 - 6 at 10 000 rad/sec .
Table 6 — Probability of brain injury
Peak rotational acceleration AIS Probability of injury
5 000 rad/s 1 - 2
10 000 rad/s 3 - 6 35 %
4.2 Tangential force at the helmet surface
This parameter is measured in motorcycle helmet Standards BS 6658 and Regulation.22-05. It is not directly
related to rotational acceleration at the centre of a headform but is a function of helmet geometry. Thus, the
following information in Table 7 which was obtained from motorcycle accident reconstruction data needs to be
interpreted with care.
Table 7 — Injury related to peak tangential force on a motorcycle helmet
Peak tangential force AIS Probability of injury
1 000 N 1 -
2 000 N 2 -
3 500 N (Reg 22-05) 3 < 50 %
4 000 N 3 50 %
7 000 N 4 -
5 Skull crushing and penetration force (A.2.2 & A.3.3)
5.1 Crushing force
Resistance to crushing and a means of measuring the crush force transmitted to the skull are frequently
discussed in helmet Standards committees. Below in Table 8 is a dynamic force that is typically required to
fracture the facial bones and the skull. The information is from different sources hence the range and
suggested tolerance values.
Table 8 — Typical fracture forces
Bone Fracture Force Range (N) Mean Tolerance Value (N)
Zygoma 614 - 3 470 1 000
Zygomatic arch 925 - 2 110 1 500
Maxilla 623 - 1 980 900
Mandible centre 1 890 - 4 110 3 000
Mandible lateral 818 - 3 405 1 900
Mandible midbody 1 290 - 1 445 NA
Skull tempero parietal (rigid 4 670 - 14 950 8 500
impactor) dynamic tests
Skull tempero parietal (rigid 3 430 - 7 830 5 070
impactor) static tests
Frontal static rigid 3 910 - 11 790 6 360
Frontal dynamic rigid 5 420 - 7 870 6 400
Frontal dynamic padded 5 340 - 15 100 11 260
The above results show that the force required to crush a human skull varies. However, analysis indicated that
when the skull was crushed between two rigid plates the value was typically 5 000 N, and 10 000 N when the
plates were lined with energy absorbing material such as is used for helmet liners. Hence a limit of 10 000 N is
suggested for a helmet type fitted with an energy absorbing liner and 5 000 N for a helmet type that comprises
a hard shell without an energy absorbing liner.
5.2 Penetration force
Assessment of resistance to penetration is included in a number of Standards. The following values are based
upon an impactor with a flat circular plate 25,4 mm diameter. This may not be representative of a typical
object causing a penetration injury but it is helpful information.
Skull region Fracture force range (N) Mean tolerance value (N)
Tempero parietal 2 500 – 10 000 5 200
6 Neck injury
Neck injury potential is assessed against shear, tension and extension (and sometimes compression)
measured using transducers in a dummy neck. Cumulative plots of these values against time are required
because injury potential is also a function of time. The following values (except compression) represent a
greater than 50 % probability of a neck injury of AIS ≥ 3 (Hobbs et al 1999). Compression is based upon
values given by Yamada (1970).
Shear 3,1 kN 1,5 kN for 25 ms to 1,1kN for 45 ms or
35 ms greater
Tension 3,3 kN 2,9 kN for 35 ms to 1,1 kN for 60 ms or
59 ms greater
Extension 57 Nm
Compression 3,7 kN
7 Noise (Appendix section A5.0)
Details of potential test methods to evaluate helmet noise attenuation to prevent premature deafness without
over attenuation of auditory warning signals are given in Annex A, A 5.
For the purposes of the European Directive 2003/10/EC the exposure limit values and exposure action values
in respect of daily noise exposure levels and peak sound pressures are fixed at:
a) exposure limit values: L , = 87dB(A) and P = 200 Pa;
EX.8heq peak
b) upper exposure action values: L , = 85dB(A) and P = 140 Pa;
EX.8heq peak
c) lower exposure action values: L , = 80dB(A) and P = 112 Pa.
EX.8heq peak
Table 9 gives values for maximum exposure times as recommended by the UK Royal Aerospace
Establishment.
Table 9 — Maximum exposure time for different noise levels
Noise level dB(A) Maximum continuous exposure period (hours)
95 3
96 2
99 1
103 0,33
109 0,08 (5 min)
113 0,033 (2 min)
140 0
8 Heat: burns and fatigue (A.6)
8.1 Burns
This section was included for the benefit of those defining Standards for firefighting equipment although it may
be used for other applications. Studies have recommended that the range of environment in which firefighters
operate is categorised by three levels as follows:
Level 1: Routine conditions - air temperatures up to approximately 100 °C and a radiant heat source of up
to approximately 1,25 kW/m .
Level 2: Hazardous conditions - air temperatures up to approximately 250 °C and a radiant heat source of
up to approximately 8 kW/m .
Level 3: Emergency conditions - air temperatures up to and above 800 °C and radiant heat sources from
80 kW/m up.
Table 10 gives the burn injury degree for a range of temperature and exposure time for air and surface contact,
and water. The table is compiled from a range of sources with full details in A.6.4. Table 11 gives the burn
injury degree for thermal energy and time, and radiation.
Table 10 — Burn injury degree for a range of temperature and exposure time for air and surface
contact, and water
Temp.°C Time Contact substance
s – Air or surface contact Water
second
Burn injury degree Burn injury degree
m -
1st 2nd 3rd 1st 2nd 3rd
minute
100 15 s X X
82 30 s X X
71 60 s X X
68 1 s NK X
64 2 s NK X
60 5 s X1 X
56 15 s NK X
53 1 m NK X
51 3 m NK X
49 5 m X X
38 NS safe safe
<0 NS ≥ X
NS = not specified; NK = not known; 1= time not specified for air/surface contact
Table 11 — Burn injury degree for thermal energy and time, and radiation
Thermal Energy/unit Time sec Radiation kW/m2 Injury
area cal/cm2 (kJ/m ) (average for a range of
(average for a range of subjects)
subjects)
3,2 (7,6 ) 0,5 3,8 1st Degree burn
3,13 (7,5 ) 0,5 4,0 2nd Degree burn
4,15 (9,9) 0,5 4,5 3rd Degree burn
8.2 Heat fatigue
Equipment to protect from heat may be available but the greater the temperature against which it is designed
to protect the more of an encumbrance it becomes and the greater the fatigue when it is worn. This dichotomy
needs to be considered when writing Standards for such equipment, for firefighters, for example, and the
following information is presented to help with this.
Table 12 — Maximum exposure for unimpaired mental performance
Temp. (°C) Max. exposure for unimpaired mental
performance.min. (hr)
40 23
34 60 (1)
32 120 (2)
31 180 (3)
<30 Not limited
The information given in Table 12 is taken from graph given in A.6.5. It is intended as a guide for health and
safety at work but is given here to assist with the specification of protective equipment. The graph appears to
be exponential hence, the rapid decrease in the maximum exposure for a given temperature increment.
9 References
The Abreviated Injury Scale (AIS). 1990 Revision; Association for the Advancement of Automotive Medecine
(AAAM), 2340 Des Plaines River Road Suite 106, Des Plaines, Illinois 60018, USA
Allsop, D. L. et. al. (1991). Force deflection and fracture characteristics of the tempero-parietal region of the
human head. 35th STAPP Car Crash Conference, p251
Newman, J A (1980). Head injury criteria in automotive crash testing. 24th STAPP Car Crash Conference
SAE J885 (1986). Human tolerance to impact conditions as related to motor vehicle design. US: Society of
Automotive Engineers
Hobbs, C.A. et al (1999). European New Car Assessment Programme (Euro NCAP). Assessment Protocol
and Biomechanical Limits (Version 2)
Yamada, Hiroshi (1970). Strength of Biological Materials. Published by The Williams and Wilkins Company,
Baltimore, Maryland 21202 U.S.A. S.B.N 683 - 09323 - 1
Annex A
Biomechanics of head injury from impact, noise and heat
A.1 General
In accidents, the human head is exposed to loads greatly exceeding the capacity of its natural protection. This
explains why, despite the extensive research on head injury during the past 50 years and the continuous
improvement of head protection devices, head injury is still by far the most common cause of fatal injury in
accidents. The consequences of severe head injuries are often fatal or long lasting and not fully recoverable.
Head injuries can be divided into two categories: primary injuries, which are a direct consequence of the
physical loading of the head and appear at the time of the accident and secondary injuries, which are directly
related to the severity of the primary injuries and can appear up to several days after the accident. Primary
injuries can result in several physiological changes, such as necrosis, post-traumatic oedema, increased
intracranial pressure, hypoxia, ischemia, intracranial hypertension or other vascular changes. Secondary
injuries are directly related to primary injuries, therefore, decreasing the severity of the primary injuries will
automatically decrease the severity of the subsequent secondary injuries.
A clear understanding of the types of head injury occurring in various types of accident and the injury
mechanisms causing these injuries is important to improvements in protective devices. Extensive medical
research has led to substantial information on the characteristics of head injuries, the locations in the head
and the likelihood of occurrence in the various types of accidents. The characteristics of the most common
head injuries occurring in accidents is indicated in Clause 3.
Mechanisms causing head injury are still not clearly understood. Traditionally, head injuries have been related
to impacts and accelerations of the head and research has concentrated upon the effects of these two types
of loading. Originally, impact and acceleration were studied for their ability to cause only a few particular head
injuries. However, in most accidents, impact and acceleration are inseparable and a wide range of head
injuries occurs. It is shown in this report that the resulting kinematics of the head and the behaviour of the
brain inside the head, rather than accelerations, should be considered as the causes of head injury.
Nevertheless, it is acceleration that is usually measured in helmet impact tests. Thus, the committee members
responsible for establishing the requirements for Standards need to be aware of the relationship between
acceleration and the implied kinematics of the brain and skull and, in turn, the potential for injury.
Although the causes of head injury are not fully understood, various head injury criteria have been proposed
through the years and some of these criteria (Head Injury Criterion, HIC; Gadd Severity Index, GSI) are used
in Standards for head protective devices. Such criteria are reviewed and discussed.
Premature deafness because of high noise levels can also be classed as an injury. This and the and the
converse problem of over attenuation of auditory warnings was also considered. Suggested levels have been
included with details of test methods.
A section on burn injuries and fatigue related to heat exposure has also been included to assist with writing
Standards for equipment to protect firefighters. The skin structure and the category and consequence of burn
injuries is described and discussed as is the exposure related to temperature, time and radiation to cause a
burn of a given degree.
A.2 Head injuries
A.2.1 Head Anatomy
The term head injury comprises various kinds of trauma to the skull and its contents. Often, several different
types of head injury occur simultaneously in an accident. The anatomical location of the lesions and their
severity determine the physiological consequences. In this section, a review of the information found in the
literature on the most commonly reported head injuries in accidents is given. The injuries are divided into
cranial injuries, skull fractures, and intracranial injuries. The intracranial injuries are further subdivided into
injuries to vascular and neurological tissues. This review is intended to provide the reader with sufficient
information on the characteristics of these injuries, their common locations of occurrence in the head, and
their relative importance in terms of severity of outcome and frequency of occurrence. This will give the reader
the required background information for the discussion of the injury mechanisms in Clause 3. Figure A.1
shows the main anatomical structures of the head and their locations inside the head.
Key
1 Arachnoid villus 2 Superior cerebral vein 3 Subarachnoid space of brain
4 Cerebrum 5 Superior sagittal sinus 6 Posterior commissure
7 Intermediate mass 8 Corpus callosum 9 Choroid plexus of lateral ventricle
10 Lateral ventricle 11 Interventricular foramen 12 Great cerebral vein
13 Anterior commissure 14 Cerebellum 15 Pons
16 Pia mater 17 Arachnoid 18 Dura mater
19 Cranial meninges 20 Third ventricle 21 Choroid plexus of third ventricle
22 Straight sinus 23 Medulla oblongata 24 Lateral aperture (of Luschka)
25 Cerebral aqueduct 26 Choroid plexus of fourth ventricle 27 Spinal cord
28 Fourth ventricle 29 Median aperture (of Magendie) 30 Pia mater
31 Arachnoid 32 Dura mater 33 Spinal meninges
34 Central canal 35 Subarachnoid space of spinal cord 36 Filum terminale
Figure A.1 — Main anatomical structures of the head and the locations inside the head
A.2.2 Skull Fracture
Skull fracture can occur with or without brain damage, but is in itself not necessarily an important cause of
neurological injury (Gennarelli 1985; Prasad et al. 1985). Skull fracture can be either open or closed. A closed
fracture is a break in the bone, but with no break in the overlying skin. An open fracture, on the other hand, is
a contiguous break in both the skin and underlying bone and is more serious than a closed fracture because
of the accompanying risk for infections. Usually, skull fractures are subdivided according to their location of
occurrence. A distinction is thus made between fractures in the face, in the vault of the skull and in the base of
the skull. Even though fractures to the face are very painful and inconvenient for the patient, they do not
constitute a threat to life nor cause serious neurological damage. Fractures to the vault can cause meningeal
and cortical injury when fragments of fractured bone enter the cranial cavity. However, the most threatening
form of skull fracture is a basilar or basal skull fracture. This part of the skull contains passages for the blood
vessels, providing the blood supply to the entire brain, and to passages for the neurological connections
between the brain and the rest of the body. Fractures of the skull base around the cavities where the blood
vessels and nerves pass can lead to damage to these vital connections.
Within the above-mentioned anatomical areas of the skull, skull fractures are usually further subdivided into
linear, depressed and comminuted fractures (Thomas et al. 1973). In a linear skull fracture, skull penetration
does not occur and the contact effects are confined to the contact area. The skull is only cracked in linear skull
fractures. Usually, the crack has the form of a single line running from the area of impact and may involve
either the inner or outer table or both (Douglass et al. 1968). A variant of the linear fracture is the stellate
fracture, which is a group of star shaped cracks radiating from the central impact point. The dural arteries lie
close to the inner skull table and are, therefore, sensitive to skull deformation. Linear fractures perpendicular
to the path of a dural artery may rupture the artery and cause an extradural haematoma (see section
Intracranial Haematoma), which can compress the underlying brain (Douglass et al. 1968). Thomas et al.
(1973) stated that approximately 80 % of skull fractures are linear. According to Bakay and Glasauer (1980),
about 50 % of the linear fractures occur in the mid portion of the skull and extend toward the base of the
middle fossa. The remaining half of the linear skull fractures are equally divided between the frontal and
occipital regions
Miller and Jennett (1968) defined depressed skull fracture as a depression of a bone fragment of at least the
thickness of the skull. Depressed skull fractures are similar to linear skull fractures, only the impact surface is
smaller. This causes concentrated contact effects, resulting in skull penetration. The skull fragments that are
driven into the cranial cavity can lead to trauma to the underlying brain and blood vessels (Figure A.2).
According to Bakay and Glasauer (1980), half of the depressed skull fractures occur in the frontal area of the
skull and the remainder are divided between the parietal and posterior regions. About half of the depressed
fractures are associated with dural lacerations, often without clinical evidence of injury to the underlying brain
(Thomas et al. 1973). In comminuted skull fractures, the fractured part of the skull is broken into more than
two pieces. An example of a depressed comminuted fracture is given in Figure A.3.
Thomas et al. (1973) noted that approximately 50 % of all skull fractures occur in the mid portion of the skull
and extend toward the middle fossa. In skull base fractures the middle fossa is most frequently involved,
followed by the anterior fossa and the posterior fossa (Luna et al. 1981). Simpson et al. (1989) found
numerous instances of basilar fractures in vehicular accident victims in Australia. In these cases, transverse
fractures of the middle fossa were most frequent and Simpson et al (1989) and Luna et al (1981) attributed
these injuries to facial impacts. A characteristic of motorcycle accident victims is that fractures of the vault are
rare among helmeted riders, but that basilar skull fractures are frequently encountered, both in helmeted and
unhelmeted riders (Hurt et al. 1986; Thom and Hurt 1993).
Luna et al. (1981) studied motorcycle accidents and found that skull fractures are rarely restricted to one area
of the skull. Usually, the fractures are multiple, often including the skull base. In skull base fractures the middle
fossa is most frequently involved, followed by the anterior fossa and the posterior fossa.
Two common types of basilar fracture are the hinge fracture and the ring fracture. The hinge fracture is a
bilateral fracture of the middle fossa. After this fracture occurs, the anterior and posterior portions of the skull
are free to hinge about the fracture line (Huelke et al. 1988; Thom and Hurt 1993). Ring fractures completely
encircle the foramen magnum. Got et al. (1983) found ring fractures to be associated with laceration of the
brain stem. Smith and Dehner (1969) observed in their studies of military motorcycle fatalities that fractures of
the posterior fossa would typically curve around the foramen magnum.
Figure A.2 — Depressed skull fracture of the vault, with dural laceration and cortical contusion (Bakay
and Glasauer 1980)
Figure A.3 — Comminuted depressed skull fracture (Melvin and Evans 1971)
A.2.3 Cerebral Contusion
Cerebral contusions are bruises of the brain caused by haemorrhages of small blood vessels. Contusions are
the most frequently found type of brain injury (Prasad et al. 1985), crest of gyri being common places for them
to occur. In these cases, the contusions are wedge-shaped with the apex extending into the white matter
(Lindenberg and Freytag 1960). Contusions are most often multiple and are frequently associated with other
lesions such as cerebral haemorrhage, subdural haematoma and extradural haematoma (Prasad et al. 1985).
Clinical findings indicate that most cerebral contusions occur at the frontal and temporal lobes (Gurdjian 1966),
regardless of whether the patients had experienced frontal or occipital impacts (Adams et al. 1982a). This
suggests that the inner geometry of the skull may contribute to contusions.
It has long been considered that contusions and head injury are synonymous. Yet, observations in patients
and in experimental subhuman primates have shown that severe and fatal damage to the brain resulting from
head injury can be sustained without visible contusions. In addition, patients usually make a good recovery,
despite having sustained severe cerebral contusions (Adams et al. 1982a).
Contusions have been studied extensively by various pathologists. Many pathologists subdivide contusions in
coup contusions, occurring at the point of impact, and contrecoup contusion, occurring at remote sites from
the impact (Cooper 1982; Prasad et al. 1985). Some use an even more extensive subdivision, in which
contusions are classified as coup, contrecoup, intermediate, and so-called 'gliding' contusions (Lindenberg
and Freytag 1957, 1960; Voigt and Löwenhielm 1974; Adams et al. 1982a; Gennarelli et al. 1982b). In this
classification, coup contusions are defined as contusions occurring at the point of impact, while contrecoup
contusions occur contra-lateral to the site of impact. The intermediate contusions are vascular disruptions on
brain surfaces that are not adjacent to the skull, while the gliding contusions occur along the superior margin
of the cerebral hemispheres.
The above classifications for contusions may give the impression that the different types of contusion are
caused by different injury mechanisms. However, the only difference between the different contusions in these
classifications is their location inside the head. As will be shown later, the different types of contusion are all
caused by contact of the brain with more rigid intracranial surfaces (skull, meninges). This single mechanism
can cause contusions anywhere inside the skull at an interface between the brain and these rigid surfaces.
Therefore, the different contusion classifications bring more confusion than clarification to the issue of brain
injury and are better avoided.
A.2.4 Intracranial Haematoma
An intracranial haematoma is an accumulation of blood inside the head caused by a haemorrhage. The colour
of the haematoma indicates the kind of blood vessel that has been ruptured: arterial blood is bright red and
venous blood is dark red. The type of blood vessel that is damaged will determine the size of the haematoma
and its effect on the surrounding tissue. Arterial blood is under high pressure, causing blood to emerge in
spurts when the artery is damaged. Since the blood pressure in veins is much lower, blood flows steadily out
of a damaged vein at lower pressure. Damage to minor vessels produces only an oozing of blood. Medical
observations show that at the first instances of a contusion the bruises appear dark in colour, indicating
venous rupture. Although the bleeding inside the head may not be the main cause of injury, as a result of the
bleeding the haematoma may expand causing compression and shifting of the brain and an increase in
intracranial pressure. This expansion of the haematoma determines the amount and severity of the resulting
neurological injury. The effects of two common types of haematomas, extra(epi)dural and subdural
haematoma, are shown in Figure A.4.
The intracranial haematomas are named after the location in the head in which they occur (Figure A.5).
Extradural haematomas (EDH) are caused by rupture of blood vessels lying on or above the dura mater
(Gennarelli 1985). Almost always a meningeal artery is torn, most commonly a branch of the middle
meningeal artery (Adams et al. 1982a). As a result of the rupture of a meningeal artery, blood accumulates
between the vault and the dura mater. The outer layer of the dura is closely attached to the inner surface of
the cranial bones, especially at the sutures and at the base of the skull. In order to be able to expand, the
extradural haematoma has to separate the dura from the skull. Therefore, it will often take several hours
before the haematoma attains a sufficiently large size to compress the surrounding neurological tissues
substantially. According to Cooper (1982), 50 % - 68 % of the patients with EDH had no substantial
intracranial pathology. The remainder of the patients had subdural haematoma and cerebral concussions
associated with the EDH. These associated lesions influence the outcome of the extradural haematoma.
Extradural haematomas are usually secondary to skull fracture and the outcome is worse when they are
accompanied by skull fractures (Chapon et al. 1985).
a) Extra (epi) dural haematoma b) Subdural haematoma
Key
1 Dura 2 Epidural hematoma 3 Subdural hematoma
4 Thick outer membrane 5 Compressed ventricular system 6 Thin inner membrane
7 Arachnoid
Figure A.4 — Effects of two types of haematoma: Compression of the cortex and other intra cerebral
structures as well as shiftingand bending of brain stem are clearly visible (Bakay and Glasauer 1980)
Key
1 Skull 2 Dura mater 3 Arachnoidal membrane 4 Subarachnoidal space
5 Pia mater 6 Brain 7 E.D.H 8 S.D.H
9 S.A.H 10 I.C.H
Figure A.5 — Types of intracranial haematomas See text for meaning of the abbreviations (Chapon et
al. 1983)
A subdural haematoma (SDH) is an accumulation of blood in the space between the dura and the arachnoid:
the subdural space. According to Gennarelli and Thibault (1982), acute subdural haematoma (ASDH) was the
most important cause of death in patients with severe head injuries. This was due to three factors: high
incidence (30 %), high mortality (60 %) and high head injury severity (two-thirds have Glasgow Coma Scale of
3, 4, or 5) (Gennarelli et al. 19
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