the protective performance of bicyclists' helmets in accidents

Accid. Anal. & Prcv. Vol. 23. Nos. 2/3. pp. 119-131. 1991 alo14575/91 s3.M)+ .oo Printed in Grear Britain. 0 1991 Pergamon Press plc

THE PROTECTIVE PERFORMANCE OF BICYCLISTS’ HELMETS IN ACCIDENTS

MARTIN WILLIAMS Engineering & Research Group, Technisearch Limited, Royal Melbourne institute of

Technology, Melbourne, Australia

(Received 23 ~ovg~ber 1989)

Abstract-A study of the injuries sustained by 1,892 bicycle riders during accidents indicated that 432 of the bicyclists had been wearing a helmet and 64 of the latter group had sustained an impact to the helmet. The 64 helmets were evaluated in this project to relate the nature and severity of the impact they had sustained to the head injury experienced by the wearer. The protective performance of the helmet shells, impact absorbing liners, and retention systems were evaluated. and the severity of the impacts sustained by the helmets was simulated in the test laboratory. The simulation was performed by dropping sample helmets from progressively greater heights in a test apparatus until the damage observed on a sample helmet matched that observed on an accident damaged helmet. The severity observed in the simulated impacts was compared with the severity of test impacts prescribed in estabiished helmet performance standards (ANSI 1984; Snell 1984; AS 1986). It was found that all of the impacts occurred against flat objects; a high proportion of helmets sustained more than one impact; most impacts occurred on areas of a helmet which were not tested during certification to a standard; and many impacts were more severe than those stipulated in performance standards. The predominant form of head injury recorded was low severity concussion --AK-l, AIS-2, AIS-3. All serious head injuries occurred when the helmet came off the rider’s head and collapsed due to a material defect or was struck predominantly below the rim. A high proportion of helmets worn by young riders had been misused, and many helmets displayed defects in the impact-absorbing liners. Recommendations have been made for improving helmet construction and altering current standards to reflect the conditions encountered in the field.

INTRODUCTION

A group of 64 helmets worn by bicycle riders during accidents has been evaluated to determine the level of protection they provided and to gain some insight into the efficacy of bicycle helmet performance standards.

The helmets were obtained during a study of the injuries sustained by I.892 bicyclists who were admitted as casualties to one of 11 public hospitals in the State of Victoria, Australia during two periods: nine months from 9 March 1987 until 16 December 1987 and eight months from 1 September 1989 until 10 May 1989 (McDermott et al. 1990).

Four hundred thirty-two of the bicyclists in the study were found to have been wearing helmets at the time of their accidents. Sixty-four of them had sustained an impact to the helmet. The helmets they had been wearing were submitted for evaluation in the testing laboratory of Technisearch Limited. The hospital records of injuries sustained by the riders and descriptions of the circumstances of the accidents were also provided.

METHOD

Basic data Helmer characterisrics. The helmets were examined and records were made of the

helmet user, manufacturer, and country of origin, model, size. standard to which it conformed, and the materials used to form the shell and protective liner.

S~eli~e~~o~~~~ce. The shells of the helmets were examined to determine the nature of damage including splits, tears, fractures. penetration, impact locations, the number of impacts, and shell degradation.

Impuct absorbing liner performance. The liners of the helmets were examined to determine the nature of damage including splitting, cracking, moulding defects, detach- ment, and the depth, area, and shape of permanent crushing.

119

120 M. WILLIAMS

Retention system performance. The retention systems were examined to determine whether any failure had occurred in the webbing, buckles, support structures. or fittings.

ESTIMATION OF IMPACT SEVERITY

A principal objective of the study was to estimate the severity of the impacts the helmets and their wearers could have experienced during the accidents and to relate it to the measures of impact severity prescribed in helmet testing standards, that is, test drop-height and permissible transmitted radial acceleration.

Transmitted radiai acceleration The transmitted radial acceleration was estimated by subjecting new helmets of the

same type as the damaged helmets to controlled impacts in a guided free-fall drop assembly. The assembly was typical of the type used widely in impact testing of protective helmets (ANSI 1984; AS 1986; Snell 1984).

A specimen helmet was strapped onto an instrumented aluminium headform and the combination was dropped in guided free-fall onto a steel anvil. The instruments measured the acceleration that was transmitted through the helmet structure into the centre of the headform.

The transmitted radial acceleration values recorded in testing of this type were taken to represent an approxjmatjon to the radial acceleration that helmet wearers could have experienced in impacts of similar severity (Slobodnik 1979).

New samples of the helmets were dropped from progressively greater heights until the damage sustained by the test helmet was similar to that produced on the original helmet during the accident.

The principal indicators of damage were found to be the depth, area, and shape of permanent crushing that remained on the surfaces of the expanded polystyrene (EPS) liner after it had recovered from the impact. Two surfaces of the expanded polystyrene liners were found to be permanently crushed; the surface in contact with the rider’s head and the surface in contact with the underside of the helmet shell. Characteristic patterns of deformation were produced on both of these surfaces during impact.

The testing gave an approximatjon to the equivalent height of fall and the acceleration in units of gravity (g s) transmitted in the origmal impact.

Accuracy of estimation of radial acceleration The simulation was subject to several known variables as follows: Drop height of rest impact. When the impacts were simulated by progressively in-

creasing the height from which helmets were dropped. it was possible to find to within 5% accuracy the drop-height required to reproduce the damage observed on an original helmet. A 5% variation in drop-height produced a variation in transmitted acceleration values of 5%. This variation was taken to be the magnitude of a primary source of error in the simulation.

Variabifity of impact perfor~~ance of ~efmets. All simulated impacts were performed on new helmets, whereas the original helmets were up to six years old. Large numbers of helmets have been tested by T.echnisearch Limited for impact performance. it has been found that the impact performance of a single model of helmet can vary by 15% over a period of years. The variability is considered to be caused by variations in the consistency of moulding of EPS foam.

An additional level of error of 15% was assigned to the estimation of transmitted acceleration from this source to yield an estimated total error of 20%.

Non-rigid impact conditions. The objects that came into collision during the original accidents were neither rigid steel anvils nor aluminium headforms, but, rather, were vehicle panels. an assortment of sand, dirt, gravel, and bitumen surfaces. and the heads of the bicycle riders. All of the objects in the field would have had different viscoelastic properties to the test apparatus and all had the potential to dissipate some of the energy of impact. Consequently, the test impacts probably overstated the true values of accei-

Protective performance of bicyclists’ helmets

Table 1. Types of helmet

121

Number Type Origin Standard

30 Stackhat 10 Guardian 8 Atom PBl 3 Hartop 2 4pollo I Atom PB2 1 Cobra 3 Vl PRO 1 Biker 1 Avenir 1 Corsalite 1 Vl Pro copy 1 Giro 1 SK600

Rosebank, Australia Britax, Australia Scott Aspen, Australia Davies Craig, Australia Prolite, New Zealand Scott Aspen, Australia Gemray, Taiwan Bell, USA Bell, USA Kajima. Japan Vetta, Italy -1 Taiwan Brancale, Italy Coooer. Canada

AS 2063.1, .2 AS 2063.1. .2 AS 2063.1. .2 AS 2063.2 AS 2063 AS 2063.2 AS 2063.1 Snell Nil, EPS liner ANSI-Z90.4 ANSI-Z90.4 Nil, EPS liner Nil, No Liner Nil. No Liner

eration transmitted during the original accidents and underestimated the drop-heights associated with them.

RESULTS

Types of helmet The majority of helmets (61, 95%) consisted of a hard shell with an EPS foam

impact-absorbing liner. Fifty-three (85%) were designed to meet the requirements of either the original Australian Standard for lightweight protective helmets, AS 2063 (25 helmets) or one of its later variants, AS 2063.1 (15 helmets) and AS 2063.2 (15 helmets).

Other hard shell helmets included three Bell Vl-Pro models that were certified to the U.S. Snell Standard, a Kajima Avenir helmet certified to ANSI-Z90.4, an early Bell Biker that was not certified, and a Taiwanese Vl-Pro copy that was also not certified. A single foam helmet (Vetta, Corsa Lite) was present in the sample. It was certified to ANSI-Z90.4. Two helmets, the Brancale Giro and the Cooper SK600, consisted of hard shells with no protective liners. They were not certified to a standard (Table 1).

Circumstances of accidents Twenty-five accidents (39%) involved a single bicycle (Table 2). Thirty-nine acci-

dents (61%) involved a collision between a bicycle and another road user. Most of the collisions (33, 52%) involved a larger motor vehicle. These collisions produced all of the severe head injuries.

Apparent cause of accidents In the majority of the collisions with motor vehicles (21, 64%) the cyclist had right

of way according to road traffic regulations. Most of the single vehicle accidents (18, 72%) appeared to have resulted from the bicycle rider’s own actions including, oddly, riding into parked cars (Table 3) (Otte 1980).

Objects struck by helmet Four of the bicycle helmets had not been struck during the accidents. The remaining

60 helmets sustained a total of 84 impacts. Nineteen (25%) of the impacts occurred

Table 2. Circumstances of accidents

Configuration Number %

Single bicycle 25 39 Collision with motor vehicle 33 52 Collision with bicycle 5 8 Collision with jogger 1 1

Tab

le

3.

App

aren

t ca

use

of a

ccid

ents

Sing

le B

icyc

le

Col

lisio

ns

with

mot

or

vehi

cle

Col

lisio

n w

ith

Col

lisio

n w

ith

Cau

sed

by r

ider

? O

ther

ca

use?

C

ause

d by

dri

ver?

C

ause

d by

rid

er?

bicy

cle

pede

stri

an

Spee

d do

wn

hill

5 H

it do

g 2

Car

str

ikes

fr

om

behi

nd

7 B

ike

turn

s in

to

path

2

Ris

ing

para

llel.

one

Bik

e st

rike

s jo

gger

on

sw

erve

d 4

foot

path

I

Hit

park

ed

vehi

cle

5 R

ode

in t

ram

tr

acks

2

Car

ahe

ad

turn

s in

to

Bik

e be

side

tu

rns

into

C

olIi

sion

-cau

se

path

5

path

2

not

know

n 1

Ove

rbal

ance

d an

d R

ode

over

spe

ed

Car

bes

ide

turn

s in

to

Bik

e st

rike

s fr

om

the

fell

3 hu

mp

1 pa

th

2 si

de

1

Los

t co

ntro

l, St

ick

caug

ht

in w

heel

1

Car

str

ikes

fr

om t

he s

ide

4 C

ause

U

nkno

wn

brak

ing

2

On

skat

eboa

rd

Los

t co

ntro

l, w

et

Car

doo

r op

ens

3 C

ollis

ion-

caus

e no

t ra

mp

1 ro

ad

1 kn

own

7

Rod

e in

tre

nch,

po

or

light

s I


Table 4. Objects struck

123

Objects struck Number %

Bitumen road Sand path or track Dirt path or track Panels of motor vehicle Type of motor vehicle Windscreen of motor vehicle

52 62 8 9 3 4

15 18 5

4 2

against some parts of a motor vehicle, 52 (62%) were against a bitumen roadway, and 11 (13%) were against a path or track.

All of the objects struck were flat or essentially flat. None of the helmets displayed evidence of having sustained any form of concentrated or penetrating impact (Table 4).

Number of impacts A high proportion of helmets (16.30%) sustained more than one impact during the

accidents. Seven (12%) helmets had been struck three, four, or five times. In three cases, two impacts had occurred at the same place on a helmet (Table 5). All of the severe head injuries sustained by riders occurred when they were subjected to more than one head impact.

Location of impacts The location of impacts on the helmets has been shown in relation to the test line

designated in the Australian Standard AS 2063.1-1986 (Fig. 1). The Standard specifies that helmets cannot be subjected to performance tests below the test line. Fifty-four impacts (63%) occurred below the test line.

The test fines prescribed for the Australian Standard (AS 1986) and the U.S. Snelt (Snell 1984), and ANSIZ90.4 (ANSI 1984) standards have been shown in Fig. 2. The majority of impacts observed in this study also occurred below the test lines of the two U.S. standards.

Location of impacts below test line Most of the impacts that occurred below the test line were concentrated on the

front or temporal region (28, 51%) of the riders’ heads (Walz et al. 1985). This region corresponded with a step upwards in the test line of the Australian Standard at the front and temporal regions of the helmet. The impacts were located at an average distance of 39 mm below the test line in this region. The remainder of impacts on the sides (19, 35%) and rear (7, 13%) of the riders’ heads were also centred well below the test line (Table 6).

Severity of radial impacts From the total number of 84 observed impacts on helmets, sixty-eight radial impacts

were simulated. The impacts that were not included involved cases in which the helmet came off the rider’s head, the helmet was run over by a motor vehicle, or more than one impact occurred on the same site.

Drop ~ejg~f. The variable used to indicate the absolute severity of an impact was the drop-height from which a new helmet had to fall to sustain damage similar to that

Table 5. Number of impacts

Number of impacts Number of helmets %

: 42 9 73 15 3 S 8

[t 1 1 2 2

124 M. WILLIAMS

/ TEST LINE

5 2 4 cc----

_--.-J _ --I

@

2 ‘11 5

c 4

\

RIGHT SIDE

2 1 -_- ---

2 9

~

Zj(~

FRONT

(APPROXIMATE)

LEFT SIDE

0 I ___ SW_

@

4 1

REAR

Fig. 1. Location of impacts on helmets.

observed on an accident-damaged helmet. The test drop-height could be regarded as an approximation to the height of drop of a bicycle rider’s head onto a surface during an accident.

The majority of impacts were of low to moderate severity. Forty-six (67%) of the impacts were reproduced at a drop-height less than .75m and 61 (90%) at a height less than 1.5 m (Table 7). Seven impacts (10%) corresponded to a drop-height of 1.5 m or more with the highest at 2.4 m (Fig. 3).

Helmets are tested from a drop-height of 1.5 m for certification to the Australian Standard, but a significant proportion of the simulated impacts were more severe than this test. The drop-height for ANSI-290.4 (ANSI 1984) is 1 m while the drop height for the Snell Standard (Snell 1984) is 2 m.

ANSI-290.4 *._.__*

AUST~I~ - - - - -

SNELL -

Fig. 2. Test lines prescribed for various standards (approximate)


Table 6. Site of impacts below test line

125

Site Number % Average distance below

test line (mm)

Forehead 11 20 Temple 17 31 Ear 19 35 59 Rear 7 13 28

Transmitted radial acceleration. The variable that approximated the severity of a head impact experienced by a rider was the radial acceleration transmitted during a test impact to the headform. The majority of simulated impacts (39, 57%) produced transmitted radial acceleration values between 0 to 100 g. Sixty-one (90%) were below 200 g (Table 8). Seven helmets (10%) produced acceleration values above 200 g, but in all of these cases the impact experienced in the accident was more severe than that used for tests to the Australian Standard.

The Australian Standard helmets in this group were designed to transmit no more than 400 g in an 1.5 m test drop (AS, 1986). They experienced impact severities ranging from 1.5 m to 2.05 m and produced radial accelerations from 210 g to 245 g. A Snell standard helmet, designed to transmit no more than 300 g in a 2 m test drop (Snell 1984), experienced a 2.4 m drop and produced 335 g.

The results indicated that the helmets designed to each standard provided a margin of protection greater than their respective standards required, but in the case of Aus- tralian Standard helmets they are likely to be exposed to impacts of still greater severity.

Severity of concussive injuries The predominant form of head injury sustained in the accidents was an alteration

to level of consciousness (Table 9) (Dorsch, Woodward, and Somers 1984; Friede et al. 1985). The relationship between impact severity and injury severity has been shown in Fig. 4 for single impacts and Fig. 5 for multiple impacts.

Major concussive injuries. All of the major concussive head injuries (AIS4, AIS- 5, and AIM) and one of the moderate injuries (AIS-3) involved either the helmet’s coming off the rider’s head, the helmet’s collapsing due to a material defect, or the impact’s occurring predominantly below the shell of the helmet. All of these accidents involved a collision with a motor vehicle, and in all cases the rider was struck on the head more than once.

Effect of correctly fanctio~ing helmet. When a helmet functioned correctly and stayed on the rider’s head, no major concussive injuries occurred, even though many impacts were of high severity and exceeded the conditions stipulated for tests to the Australian Standard. Seven simulated impacts (10%) were equivalent to a height of fall from 1.5 m to 2.4 m, but in none of these cases did the helmet wearer suffer serious injury.

Low severity impacts. It has been postulated that individuals who wear helmets may be prone to sustaining concussive injuries during impacts of low to moderate severity. All but two of the 57 impacts in which radial acceleration was below 200 g coincided with no injury or minor (AIS- concussive injuries. The two exceptions produced moderate (AIS-3) concussive injuries.

The helmets which sustained these low to moderate severity impacts provided ad- equate protection to their wearers.

Table 7. Severity of simulated impacts- Drop-heighf of impact

Drop-height (mm) Number %

O-750 46 67 750-1500 15 22

1500-22.50 6 9 2250 t 1 1

AAP 23:2/3-B

126 M. WILLIAMS

2400

I

.

2000

1600 1% . TEST DROP HEIGHT 15OOmm .

!G --------__:_----_- 2 -- It+

:: 2 1200 . 18 . cl.8 : 1s

B . * cI : 122

800 *r... . . *.. . . .: .

If

. *. I- 400 . . *.

*. . . - .‘#. . .-: : 8 * I

I

100 200 300

RADIAL ACCELERATION (g’s)

Fig. 3. Characteristics of simulated radial impacts.

400

High density EPS foam liners. It has also been postulated that helmets with “hard,” high density EPS foam liners might be more likely to cause concussive injuries in moderate impacts than “softer” helmets. Three samples of one type of helmet with high density (115 kgmm3) foam liners were involved in accidents. In two low severity impacts (0.8 m, 115g; 0.77 m, 177g), the riders sustained no concussive or other head injuries, and in one high severity impact (2.4 m; 335g), the wearer sustained a slight (AIS-1) concussive injury.

The helmet type with a high density EPS foam liner provided a high level of protection in impacts with a wide range of severities.

Severity of nonconcussive head and neck injuries Most of the nonconcussive head and neck injuries (23, 60%) were minor and in-

volved lacerations, contusions, and abrasions (Table 10). The three skull fractures occurred when the rider’s helmet came off; the skull was

struck predominantly below the rim of the helmet or the helmet collapsed due to a defect. The other fractures (10, 26%) involved exposed parts of the rider’s face and were not life-threatening.

Six neck injuries (15%) were recorded, of which one was serious. None of the neck strain or cervical fracture injury cases involved sliding of the helmets on the surfaces they struck.

The location of the injuries that occurred below the helmets has been shown in Fig. 6. Most of them (33,85?J’ ) o were associated with impacts on the lower edge of the helmets.

Durability and material defects Twenty-one (33%) of the helmets displayed some form of material defect (Table

11) but some of the faults may have arisen partly as a result of misuse of the helmets (Vallee et al. 1984).

Table 8. Severity of simulated impacts-transmitted radial acceleration

Transmitted acceleration ks) Number o/o

O-100 39 57 100-200 22 15 200-300 6 9

300+ 1 I

127 Protective performance of bicyclists’ helmets

Table 9. Severity of concussive head injuries

Injury code Number Special circumstances

No injury 18 Slight AIS- 10 Minor AIS- 27 1 helmet came off, Moderate AIS- 5 1 helmet came off, 1 helmet run over Serious AH-4 1 1 helmet came off Severe AK.5 2 1 below helmet, 1 helmet collapsed Fatal AIS- 1 1 helmet came off.

~ef~ef misuse. The outer she11 of 23 (36%) helmets had been damaged prior to the accident. The shells had extensive areas of old score and scrape marks that were consistent with the helmets’ having been dropped onto the ground or other coarse surfaces up to 200 times. The individuals who wore the damaged helmets were mostly younger than 15 years but their age group appeared to have reflected the population of helmet wearers (Fig. 7).

All of the shells of the misused helmets had been able to withstand harsh treatment, but in some cases major damage had occurred to the EPS foam liners.

EPS foam liners-poor fusion. Four of the misused helmets were found to have sections of foam larger than 6 cm x 6 cm missing and in 11 cases the foam liner had been split extensively. In one of the latter cases the liner had broken into five large pieces and was held into position only by the internal comfort liner of the helmet.

The damage to the liners may have been refated to misuse, but it was not solely due to it, because eight of the misused helmets displayed no liner damage. Furthermore, four other helmets that had not been misused had large sections of foam split or missing.

An examination of the expanded polystyrene foam liners from the helmets indicated that the foam had not been properly fused at the sites of damage and could not sustain bending loads. Poor fusion of EPS foam is a moulding defect that can be prevented during manufacture.

The helmets in this group happened to have been struck at locations away from the missing or split EPS foam. It was evident from other specimens (mentioned below) that if the impacts had occurred at the sites of missing or damaged foam, then the wearers could have sustained severe head injuries.

EPS foam liner-fusion faif~re. The iiner of one helmet exhibited complete fusion failure. The EPS foam liner had crumbled into small beads at the position of impact. An internal head support cradle in this helmet also had ripped off its mountings. The wearer sustained concussive (AIS-5) injuries.

Shell-brittle failure. The shell of one helmet was polycarbonate, which collapsed in brittle failure at the site of impact. The wearer sustained severe head injuries (concussive AIS-5) as a result of the impact.

300

200

100

INJURY INJURY NONE AI.5 1

INJURY INJURY AIS 2 AIS 3

Fig. 4. Single impacts. Severity of concussive injuries relative to severity of impacts.

300

200

100

INJURY NONE

. . lili I M. WILLIAMS

INJURY INJURY AIS- AIS-

-i

. Up to three impacts on one helmet

Fig. 5. Multiple impacts. Severity of concussive injuries relative to severity of impacts.

Attachment of finer to shell. The liners of three helmets of one type had become separated from the shell and, as a consequence, had commenced to break up into smaller pieces. Positive fastening of the liner into the shell would have prevented this fault.

Sizing pads. The internal sizing pads of five helmets of one type were unserviceable because they had pulled off the backing fabric or ripped off the EPS foam. This fault would not have compromised the protective capacity of the helmets.

Retention systems Helmet stability. Four helmets were pulled off the riders’ heads in similar circum-

stances during the accident. In each case the rider was struck by a car and hit the bodywork of the vehicle before falling onto the ground. The helmets had been subjected to prolonged sliding contact with the bodywork of the vehicle from the rear to the front of the helmet and had been dragged off. In three cases, the riders sustained severe head injuries.

Three of the helmets were of a type whose retention system was modified later when a helmet stability test was introduced into the Australian Standard in 1986. The test evaluated the capacity of a helmet to resist fore-and-aft motion when on a rider’s head. The fourth helmet had a retention system that was attached with press studs, and it would not pass the helmet stability test. This finding emphasised the need for a helmet stability test in performance testing of bicycle helmets.

Webbing. All helmets were fitted to the wearer’s head with various configurations of webbing attached to buckles and ear pieces. In some cases the process of threading the webbing into the hardware was moderately complicated.

The webbing of five helmets had been undone and was left hanging from the fittings. The helmets then did not provide correct fit or resistance to fore-aft motion.

Retention system webbing should be installed in such a way that it cannot be removed from buckles and ear pieces.

Sharp edges. In five cases impacts occurred directly on either the ear pieces of the retention system or on the rim of the helmet near the wearer’s ear. All of the ear pieces and the rims had sharp edges, and the wearers sustained lacerations of various severities

Fig. 6. Location of injuries below helmet.

Tab

le

IO.

Sev

erity

of

no

ncon

cuss

ive

head

an

d ne

ck

inju

ries

1 IC

II~Y

I CII,

IIC

ofI o

r col

laps

ed

Hcl

mct

st

ruck

-inju

ries

hclo

w

hclm

ct

Hel

met

no

t st

ruck

Lnc;

tti~n

~ ln

iurv

N

umhc

r Lo

catio

n ln

iurv

N

umhc

r Lo

catio

n ln

iurv

N

umhc

r

I Ica

d F

r;tc

lurc

(s

kull.

A

K-?

) I

Hea

d F

r;tc

turc

(s

kull.

A

K-3

1 I

Tcm

plc

c‘hc

ch

Fra

ctur

e tz

ygom

a.

AIS

-2)

I E

ar

Che

ck

Jaw

Mou

!h

Nos

e

Nec

k

Fra

ctur

e (s

kull.

A

IS-3

) I

Jaw

F

ract

ure

(man

dibl

e.

AIS

-I)

I La

cera

tions

. co

ntus

ions

or

abr

asio

ns

I T

cmpl

c La

cera

tion.

co

ntus

ions

or

ahr

asio

ns

I La

cera

tions

. co

ntus

ions

or

abr

asio

ns

4 E

ar.

Mou

th

Lace

ratio

n.

cont

usio

ns

or a

bras

ions

I.1

F

ract

ure

(zyg

oma,

A

IS-2

) 2

Lace

ratio

ns.

cont

usio

ns

or a

bras

ions

F

ract

ure

(man

diht

c.

A&

I)

‘s

Lucc

ratio

ns.

cont

usio

ns

or a

bras

ions

3

Fra

ctur

e (t

eeth

. A

IS-J

) 2

Lace

ratio

ns.

cont

usio

ns

or a

bras

ions

I

Fra

ctur

e (A

&l)

I La

cera

tions

. co

ntus

ions

or

abr

asio

ns

2 F

ract

ure

Cl.

C2,

Ch

I S

trai

n La

cera

tions

. co

ntus

ions

or

ab

rasio

ns

:

130 M. WILLIAMS

Table 11. Material defects

Observed material defect Number

EPS liner Split 11 Detached from shell and split 3 Sections missing 5 Fusion failure 1

Polycarbonate shell Brittle failure 1

during the impacts. The injuries were not life-threatening but could have been avoided if sharp edges had been removed from fittings that could contact the wearer.

1.

2.

3.

4.

5.

6.

7.

RECOMMENDATIONS

The test line of helmet standards should be lowered to provide protection to the forehead, temple, and ear regions of helmet wearers’ heads where most impacts occur. The impact test of helmet standards should be performed from a drop-height of 2 m to reflect the severity of impacts likely to be experienced in accidents. Most of the helmets in this study were designed to a standard that permitted the transmission of radial acceleration up to 400 g (from a drop height of 1.5 m). The helmets were found to provide a margin of protection greater than that required in the field. A reduction of the permissable level of radial acceleration to 300 g or below would provide an additional factor of safety above that which already appears to exist. A performance test should be developed to evaluate the degree of fusion achieved in the moulding of EPS foam in helmet liners in order to ensure that the liners maintain a reasonable level of protective capacity in the lifetime of the helmet. Performance tests used for evaluating bicycle helmets should take into account the fact that the helmets can be subjected to more than one impact during an accident. Bicycle helmet performance standards require a helmet stability test that evaluates the capacity of a helmet to resist fore-and-aft motion when on a rider’s head. A dynamic helmet stability test should be developed that reflects the circumstances of accidents known to be capable of removing a helmet from a wearer’s head.

20

15

&z

B 2 10

5

TOTAL HELMETS --- ---- MISUSED HELMETS

35 40 45 50 55 60 65

AGE

Fig. 7. The number of misused helmets in various age groups.

8.

9.

10.

11.

Protective performance of bicyclists’ helmets 131

Consideration should be given to developing environmental degradation tests of shells formed from materials, like poiycarbonate, that are susceptible to significant deterioration after manufacture. The expanded polystyrene liners of helmets should be positively fixed into the outer shells. The webbing of retention systems should be installed in such a manner that it cannot be removed from buckles and ear pieces. Components of the retention systems or other fittings of a helmet that can come in contact with a wearer’s skin should not have sharp edges.

Acknowfedgemenf-The author wishes to acknowledge the State Bicycle Committee of Victoria and the Road Trauma Committee of the Royal Australasian College of Surgeons for funding the project.

REFERENCES

AIS. The Abbreviated Injury Scale 1980 Revision. Morton Grove, IL: The American Association of Auto- motive Medicine; 1980.

ANSI. American Nationai Standard for Protective Headgear-for Bicyclists. ANSI-Z90.4. New York: National Standards Institute; 1984.

AS. Lightweight protective helmets (For use in pedal cycling, horse riding and other activities requiring similar protection) Part 2-Helmets for pedal cyclists, AS 2063.2. Sydney: Standards Association of Australia; 1986.

Dorsch, M. M.; Woodward, A. J.; Somers R. L. Do Bicycle Safety Helmets Reduce Severity of Head Injury in Real Crashes? Adelaide, Australia: National Health and Medical Research Centre, Road Accident Research Unit; 1984.

Friede. A. M.; Azzara, C. V.; Gallagher, S. S.; Guyer, B. The Epidemiology of Injuries to Bicycle Riders. Pediatr. Clin. North Am. 32(1):141-151; 1985.

McDermott, F. T.; Brazenor, G. A.; Lane. J. C.; Klug, G. L. The injury profile of pedal cyclist casualties wearing and not wearing safety helmets. In preparation. Melbourne, Australia: Royal Australasian College of Surgeons Foundation, Monash University Department of Medicine; 1990.

Gtte, D. A Review of Different Kinematic Forms in Two-Wheel Accidents-Their Influence on Effectiveness of Protective Measures. 801314. Warrendale, PA: Society of Automotive Engineers; 1980.

Slobodnik, B. A. SPM-4 helmet damage and head injury correlation. Aviat. Space Environ. Med. 50: 139- 146; 1979.

Snell. 1984 Standard for Protective Headgear-For Use in Bicycling. Wakefield: Snell Memorial Foundation: 1984.

Vallee. M.; Hartemann, F.; Thomas, C.; Tarriere, C.; Patel, A.; Got, C. The Fracturing of Helmet Shells. In: Proceedings of the International IRCOBI Conference on the Biomechanics of Impacts. Bron. France: IRCOBI Secretariat; 1984: 99-109.

Walz. F. H.: Dubas. L; Burkhart, E; Kosik, D. Head Injuries in Moped and Bicycle Collisions. Implications for Bicycle Helmet Design. Proceedings of the International IRCOBliAAAM Conference on the Bio- mechanics of Impacts. Bron. France: IRCOBI Secretariat: 1985; 92-103.

the protective performance of bicyclists' helmets in accidents

Documents