Document jNgOZv2zLLdzn0wQkjBn9dwJ5
FILE NAME Brakes BRK
DATE 1995
DOC BRK261
DOCUMENT DESCRIPTION Journal Article - Index of Past Asbestos
Exposure as Applied to Car and Bus Mechanics
Pergamon Pergamon
Ann occup Hyg Vol 39 No. 4 pp 441 454 1995
Elsevier Science Lid
Copyright
1995 British Occupational Hygiene Society Printed in Great Britain rights reserved
0003-4878
AN INDEX OF PAST ASBESTOS EXPOSURE AS APPLIED TO CAR AND BUS MECHANICS
Nils Plato G^ranTornling Christer Hogstedt and Staffan Krantz
Department of Occupational Health Karolinska Hospital 17176 Stockholm Sweden Lung Research Unit Department of Medicine Karolinska Institute Stockholm Sweden Divisionof Occupational Medicine National Institute of Occupational Health Solna Sweden and Division of
Aerosol Science National Institute of Occupational Health Solna Sweden
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Recened in final form 26 September 1994
Abstract
to describe historic fibre exposure from containing friction
ways
Different materials were studied and compared for a group of 103 car and bus mechanics with more than 20
years employment and 15 years of asbestos exposure A model was constructed to calculate
asbestos
from friction materials including duration intensity and exposure last
cyueamrulTathievemodel is a ceoxpmobsiunraetion of an additive and a multiplicative model where an asbestos index
was constructed that takes both near field and far field exposure into consideration The model was
performed based upon data from the international literature and quantitative asbestos measurements
1976 1988 in Swedish car repair workshops The fibres were counted by contrast microscopy
with fibre
length > 5 mand aspect ratio 3 The mechanics fibre exposure at 398 repair
criteria workshops during a period of 48 years were calculated using the model The mean cumulative
was estimated to be 2.6 ml ' year The annual cumulative exposure exposure was highest for truck
exposure
mechanics the early
1960s The car mechanics had a weighted average fibre exposure range of
11 41 mlflmean 0.21 ml in 1965 compared to 0.003 0.08 f mlflmean 0.021 fml in
1985. In order to validate the model the mechanics fibre exposure estimated using the model were
compared with representative asbestos exposure measurements for car mechanics during the 1960s
and the 1970s correlation coefficient = 0.69 Five lung physiological variables FVC TLC FEV
TL and CV were used to study exposure response relationships None of the exposure
parameters suggested any significant relationship between exposure and decrease in lung function
INTRODUCTION
|
exposure Asbestos exposure
can cause a variety of lung disorders Lung cancer is an effect of high
asbestos exposure levels in the past Selikoff and Lee 1978 while other diseases may
be the result of more recent exposures Therefore it is important to characterize
asbestos exposure over long periods Information on cancer and other diseases from
studies of level asbestos exposures is inadequate Car mechanics are generally
regarded as a low exposed group no increased risk of lung cancer was found Hansen 1989 Mesotheliomas have been observed R^delspergeret al 1986 Woitowitz and R^delsperger1994 but there is no support for any increased risk for car mechanics or garage workers McDonald and McDonald 1980 Teta et al 1993 J^/rvholmand Brisman 1988 Wong 1992 Lung function data have not been studied systematically
demonstrated with well described exposures High levels of asbestos exposure can cause lung fibrosis
Selik and Lee 1978 is however unknown if low dose exposure can result in
fibrosis Murphy et al 1972
changes in small airways owing to asbestos
i i
el
Author to whom correspondence should be addressed
441
442
N. Plato et al
exposure but the level of asbestos exposure that may cause airway effects has not been
satisfactorily described The aim of this study was to construct a model to estimate the cumulative asbestos
exposure from friction materials to apply the model to one type of employment car
mechanics with low asbestos exposure at different working places and finally to compare the model with other types of exposure and determine its relationship to lung function variables This study is an expansion of a recently published study Dahlqvist et al 1992 as bus mechanics have been included to increase the exposure range
Friction materials in clutches and brakes for vehicles have contained about
30-70 asbestos fibres since 1930 Kauppinen and Korhonen 1987 During repair and changing of friction linings there can be exposure to asbestos fibres worn from the linings This has been demonstrated in several studies Hatch 1970 Lorimer et al 1976 Knight and Hickish 1970 Rohl et al 1976 Kauppinen and Korhonen 1987 In the middle of the 1980s approximately 25000 workers were employed as car and bus mechanics in Sweden and thus exposed to asbestos fibres Asbestos brakes linings
were introduced in the beginning of the 1980s Different methods can be used to describe past exposure depending on the data
sources available quantitative or quantitative models have been used Stewart and Herrick 1991 but no model exists which could fit closely Swedish car mechanics Asbestos exposures during different job activities have been studied but the exposure
pattern over longer periods has not been adequately investigated for car mechanics
STUDY SUBJECTS AND METHODS
Study group A study group was selected from the local health records of the Local Vehicle
Health Service in Stockholm and the local bus transportation company Lung function
examinations and individual exposure assessments were made The criteria for
selection were male older than 40 years and more than 20 years employment as car and bus mechanics Those who had been involved in spray painting or body repair activities or had asbestos exposure from other sources were excluded Ninety car and eight bus mechanics fulfilled the selection criteria Smoking data were collected by interview Dahlqvist et al 1992 The subjects were classified as smokers smokers and smokers groups and the amount smoked was expressed in years Twentysix were smokers 39 had never been exposed to diesel exhausts and just five were
free from both diesel and tobacco exposure
The car mechanics had worked at 386 different repair workshops and the bus mechanics at 12 bus repair workshops The workplaces represented a wide range from small fashioned car repair workshops to large recently constructed repair workshops with good ventilation Until 1975 most of them had used compressed air for cleaning the brake shoes During the observation period 1938 198t6he mechanics had worked at an average of four workplaces range 1-14 workplaces The mean
employment time was 29 years 20-48 years Reference equations for lung function were derived from a control group of 83
suburban bus drivers without asbestos exposure who were investigated in the same way
Dahlqvist et al 1992 Twenty of them were smokers
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| Past asbestos exposure index for car and bus mechanics
443
Exposure assessment
The exposure was estimated by the following procedure
1 construct a model to describe cumulative asbestos exposure by using an
asbestos index and estimate the cumulative asbestos by the model 2 cumulative exposure was compared to other ways of describing exposure
employment duration and exposure duration 3 the model was applied to the 103 car and bus mechanics and exposure estimates
correlated with lung function data
Employment duration is often used as a simple estimate of exposure if no other data
are available The information concerning employment time was collected from
company records and also checked by questionnaires obtained from the study subjects
Exposure duration time was calculated with additional information from question-
naires and interviews described in the Appendix e.g. job activities and location With
the information about more specified activities for we could exclude employment periods with no asbestos exposure
Model construction
The model was designed to calculate asbestos exposure from work with friction
materials such as dust from clutches and break shoes It has been described in detail in
Swedish Plato et al 1991 and is more briefly summarized in the Appendix
By reviewing the international literature a set of parameters that influence the asbestos exposure of car and bus mechanics was selected The magnitude of the
multipliers associated with those variables was estimated and chosen from a large series
of past measurements covering representative values for different work activities technical equipment ventilation technical standard and workshop sizes The derivation is discussed in more detail in Table Al of the Appendix The coefficients
were used in an equation that takes task activity as well as background exposure
general shop exposure into consideration The model was created as a combination of an additive and a multiplicative model Table A2 in the Appendix and makes calculation of cumulative exposure possible The equation in the model expresses the quantative exposure in an asbestos index Asbestos index general shop
exposur+e task activity exposure for each mechanic for each year summed for all
years of employment as a vehicle mechanic
i
Model validation validton validation
The model was validated using representative Swedish measurements in car and
bus repair shops for the period 1976-1988 The fibre measurement criteria using phase-
contrast optical microscopy were length > 5 ...mdiameter < ...mand aspect ratio
reports T3 en
including 23 h measurements personal sampling at different car
repair shops were selected from the data bank of industrial measurements at the
Swedish National Board of Occupational Health to validate the efficiency of the model
These investigation reports were selected because they contained sufficient information
on work activity production rate and other information needed to choose coefficients
in the model Many reports in the databank did not contain adequate information and
could not be used The coefficients and equations in the Appendix were applied for
those 23 measurements Asbestos indices AI were calculated and plotted against the measured fibre level in the transformed curve Fig )
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444
N. Plato et al
y = 0.03 + 0.01 1x r = 0.69
0.20 0.18 0.16 0.14-
ml 0.12
0.10
fibres 0.08 0.06 0.04 0.02
0
=.
{
I
i
|
j
5
10
15
20
25
Al
Fig 1. Transformation curve Comparison between the constructed asbestos index AI and asbestos fibre
level from 23 historic h measurements
The calculated asbestos index was related to asbestos fibre level by the statistically
significant regression line 0.029 x shown in Fig3. The correlation
coefficient was 0.69 for all observations 23 This demonstrates that a quantitative relationship exists between f ml and the AI It also shows that the exposure was generally low
Application
The model was used to characterize the exposures of 103 car and bus mechanics
Each subject answered a questionnaire which asked about the repair shops where they had worked job activities and employment time The administered questionnaire was expanded with a standardized personal interview Two industrial hygienists asked 38 additional questions for each workplace in a subject's work history The questions included the following topics room conditions 11 questions treatment of brake shoes eight questions work activities involved with repair 13 questions and
activities of the bystanders six questions The people interviewed also had to estimate the duration of work to replace brake shoe linings number of changes from year to year grinding of brake lining time and end year for use of compressed air and use of respiratory protection For each decade they also estimated the general condition of the work area and dustiness from different work operations using a level ranking scale with the existing condition as the reference point The aim of the personal interview was to collect information that could have influenced early exposure such as work activities that generate high exposure peaks and also the possibilty of dispersing the fibre in dusts found in brake drums and clutch housings
The Al was calculated by using Equation A1 in Table A2 of the Appendix Work
activity and task frequencies during the whole working life of the mechanics were taken into consideration for each individual By use of the validation curve Fig ) the Al could be converted to approximate f ml year Annual and cumulative asbestos exposure values were estimated for each of the 103 mechanics who participated in the medical investigation Cumulative exposure during their total times as mechanics was expressed as mean and range for the whole group weighted average exposure was calculated as a weighted mean exposure for each individual
Past asbestos exposure index for car and bus mechanics
445
Lung function function
The mechanicsmechanics and unexposed controls underwent examination using lung
function tests tests by Dahlqvist et al 1992 Dynamic spirometry was used to measure vital
capacity VC, N and forced volume in 1 s FEV . N = 103 static spirometry was
used to measure measure total lung capacity TLC N 103 nitrogen breath wash was
used to measure measure closing volume in per cent of vital capacity CV N = 92 and carbon
monoxide single single breath wash was used to measure transfer factor TLC N = 90
equations Reference
for calculation of predictive values for the lung function variables
were derivedderived from 83 asbestos exposed suburban traffic bus drivers Smoking
years , age and height were studied as potential confounding variables
Exposure response response analysis Regression Regresion analyses were done to examine the relationship between the cumulative
asbestos exposure exposure and effects on lung function Dependent variables were observed values divided divided by predicted values for FEV TLC VC and CV Independent variables were were length of employment cumulative exposure and exposure duration
Student's test was used for significance tests in the regression analyses
RESULTS
Exposure The mean mean employment time was 29 years range 20-48 years and mean exposure
time 26 years years range 14-48 years normal distribution 0.98 Shapiro Wilk statistic The The correlation between employment time and exposure time was 0.92 The distribution of cumulative exposures for the car and bus mechanics 103 persons as calculated with the model using their employment at 398 repair workshops during
48 years is shown in Fig The mean was 2.6 year range 0.1-11.6
30
25
20
Frequency Frequency Frequency
Frequency 15
Frequency
Frequency
Frequency
{
10
5y|
|
|0
j
1
1
L
L
| -1
2
5
8
11
14
|
Cumulative asbestos exposure fibres ml *,,year
Fig 2. Distribution of cumulative asbestos exposure for 103 vehicle mechanics Mean cumulative
| exposure year normal distribution W 0.98 SAS
446
N. Plato et al
fml fml * year The annual mean exposure had a range between 0.01 and 0.46 f ml
since 1938. The weighted average for all car mechanics over the period was 0.09
fml fml The annual asbestos exposure decreased during the 1960s and 1970s Fig 2
This decrease was more pronounced for cars from 0.10 to 0.02 f ml than for trucks
0.12f 0.12f ml mainly because of wise changes to disc brakes that generate lower
exposure in small cars
During the period 1938 198t6he mean asbestos fibre exposure was 3.5 times higher for those who had been working with trucks compared to those who had only been
working with cars and the bus mechanics had a 1.6 times higher asbestos exposure
than the car mechanics in 1984 Fig 3 In 1964 the car mechanics had an exposure
0.04
mlfl,,
0.170.4f0.17f mlfl,,mean
0.10
f
mlflcompared
to
0.18-0.46
f
mlflm,,ean
0.36
f
mlfl,,
for the truck mechanics
Most of the mechanics started their career with truck repair activities that generate higher exposure levels The Swedish truck mechanics worked more hours per weck
with friction materials than the bus mechanics The annual asbestos exposure for bus
mechanics was lower than for truck mechanics Fig 3
The variation in annual asbestos exposure levels for the 95 car mechanics showed
that occupation is a poor way to characterize exposure and the correlation coefficient
was only 0.41 The regression line for cumulative asbestos exposure vs employment
time was y =
0.79 x3 shown in Fig 4. Consequently long employment time
or exposure duration does not necessarily mean high cumulative asbestos exposure
Exposure relationship for lung function
The exposed group had a significant decrease in TL with 12.5 0.01
Table , but the decrease was not significantly correlated to either cumulative asbestos exposure or employment time Table 2. No other lung function variable was significantly decreased or correlated with exposure level Tables 1 and 2 The unexposed population had on average a normal lung function compared to reference values Dahlqvist et al 1992
0.45
0.40
0.35
ml ,,0.30-
fibres 0.25
level 0.20
0.15
Asbetos 0.10
----
----
Cars ee Mixed
0.05
0 1944
L 1949
1954
J 1959
I 1964 Year
L 1969
1974
1974
! 1979
a) 1984
Fig 3. Calculated annual mean asbestos exposure levels f ml ) for different vehicle mechanics N= 103
Past asbestos exposure index for car and bus mechanics
447
12
a
)
year
year
*
fibres
8F
fibres
fibres
fibres
exposure 4
exposure exposure
exposure
exposure
exposure
4F
Cumulative
Cumulative Cumulative
Cumulative 2r
Cumlative
Cumulative
0
" 2
a a
s
s
s
os s
aa
Se
a]
_ =
Bs
a
.
Lad) ase
ae s
a"
oil '
as
oR
ae i
a.
=
a:| #
I
L
}
10
20
30
40
50
Employment time year
Fig 4. Correlation Correlation employment time vs cumulative asbestos exposure for 103 vehicle mechanics = -0.793 0.41
Table 1. Mean and standard deviation
for observed O values of five lung function variables for 103 car
and bus mechanics Predicted values
from 83 asbestos exposed bus driver
Value
N
O
SD
TL
TLC
FVC
90
87 *
23.8
103
100.7
11.2
103
99.2
12.0
CV
92
FEV
103
946 99.9
19.2 12.8
0.01
DISCUSSION
A model was developed to estimate past exposure from asbestos friction materials for Swedish vehicle mechanics The model was based on estimations of multipliers for
different exposureexposure variables derived from the worker's task activities and background activities in the workshop The constructed model was applied on interview data from 103 mechanics The mean cumulative asbestos exposure for this population was
2.6 { ml year year Despite the perception that car and bus mechanics constitute a
homogeneoushomogeneous group the variation in exposure was wide 0.1-11.6 f ml year Annual asbestos exposure exposure estimates showed a three times higher mean exposure in 1964 compared toto 1984. A statistically significant % decrease in mean TL was observed for the exposed group compared to the asbestos exposed control group However
no exposureresponse relationship was observed between either cumulative asbestos
exposure or employment time and any ofthe lung function variables TL TLC FEV
VC
CV or VC
448
N. Plato et al
Table 2. Regression coefficients for lung function variables vs asbestos exposure
Exposure
Correlation
+2
N
coefficient
%
Intercept a
Slope b
Cumulative exposure CV
TL
FVC TLC
FEV
Years of employment
CV
TL
FVC TLC
FEV
91 89 102 102 102
91 89 102 102 102
0.106
-0.001
-0.079
0.138
0.138
--0.055
0.093
-0.016 --0.057 -0.082
0.030
1.12 0.02 0.62 1.92 0.31
0.86 0.03 0.32 0.68
0.09
91.8 87.9
100.5
102.9
100.9
86.6 89.3 102.4 105.0 98.1
1.08 -0.16 -0.48 -0.78 -0.36 -0.36
0.28 -0.06 -0.11 -0.15
0.06
0.05 ** 0.01
The following text will discuss the quality of the exposure assessment including the fibre analysis the compatibility with studies from other countries and the relationship with the lung function variables
Qualitative vs quantitative exposure assessment
For most mechanics employment time data from company records correlated closely to the exposure time from interviews or questionnaires correlation coefficient 0.92 Some mechanics had been electricians car conditioners or worked in other
asbestos exposed tasks for example supervisors Their job title in the company records however was still car mechanic which partly explains why the correlation was not perfect Job title combined with job activities might give a higher correlation
The variability in exposure between different car mechanics is due to the product of a large variety to working activities working methods and shops The annual mean
asbestos exposure ofthe 95 car mechanics was 0.09 f ml range 0.01-0.46 fmlfl1 fmlfl1) To
use occupational titles alone to describe exposure would produce large misclassifica-
tions with a maximum factor 45 45 between the highest and the lowest exposure in the
job title
The variation was also large for cumulative exposure 0.1-11.6 f ml * year
Employment time or time in exposed work correlated weakly in this study with cumulative exposure r 0.41 see Fig 4. Duration of exposure close to employment time was 14-48 years which means that differences in exposure can be explained by
employment time by a factor of only 3. The exposure was high in the past and has
diminished owing to improved technology and ventilation The fact that the workshops have improved favours those who have worked only during the last 20
years The correlation between cumulative exposure and exposure time has been poor in several studies Blair and Stewart 1990 Smith 1992
Additional questions can be asked during data collection to reduce misclassification of exposure From the magnitude of coefficients in the exposure model Table A1 in the Appendix it is theoretically possible to have AI range by a factor of 120 using Equation A1 with either all lowest coefficients or all with highest value To get more precise exposure information the interviewer can ask for type of vehicle and thereby
Past asbestos exposure index for car and bus mechanics
449
reduce the theoreticaltheoretical variability by a factor of 40. By putting more precise questions about working working methods the distribution is decreased to 13 and questions about repair
shops conditions conditions will reduce it by a factor of4.Work activities after 1975 give a general
reduction by a factor of 1.5 Each factor type of vehicle type of brakes etc. in direct questions reducereduce the variability by a third Cumulative exposure assessment is time and resource consuming consuming which can be reduced by using a systematic questionnaire technique Aditional Additional information can be obtained by interviews and is important to
reduce misclassification misclassification
Validation the model vs historic measurements
Errors of might have occurred when estimating the value for each variable in the
historic exposure exposure equation The correlation in the validation was 0.69 between asbestos
index and measured asbestos levels A reason for this relatively low value is imprecision
in low levels of asbestos It would have been advantageous to have measurements from
the 1950s and the 1960s for validation of the larger values of the coefficients in the
model but such data were not available Another reason can be poor choices for the
multipliers or variability in the actual effects of the factors One important source of error can be differences in fibre counting techniques between laboratories The fact that
the same laboratory did most of the fibre counting diminished the error in the calibration curve We think that the correlation was good in spite of the usual
systematic
and
and
and
random
errors
in
industrial
hygiene
sampling
strategy
and
fibre
counting
All fibres areare not asbestos fibres The debris debris from brake shoes and clutch linings contains a large number of fibres
with length < mPlato et al 1991 These short fibres may not have the same biological activity activity as the long fibres Brake dust at workplaces has been characterized by size and chemicalchemical contents Jacko and DuCharme 1973 Qualitative analyses by
transmission electron microscopy suggest that brake dust mainly contains short fibres
length < r m that are also so thin that they are invisible with optical microscopy In
a study by Rohl Rohl et al 1976 84 ofthe fibres were shorter than 0.4 mWilliams and
Muhlbaier ( 1982 observed that 99.9 of the original mass of asbestos fibres were broken down at high temperature to fibrous magnesium silicates during the brake process Rohl Rohl et al 1976 observed that only % of the fibres in the debris met the definition of asbestos fibres The morphology of asbestos may be changed during the
temperature increase in the brake process Davis and Coniam 1973 At 650 the
asbestos configuration configuration is transferred to forsterite Koshi et al 1969 which is fibrogenic
in lung tissue tissue Hayashi 1974 Sakabe et al 1971 Woitowitz Woitowitz and R^delsperger 1991 concluded from animal experiments that
exposure to dust from worn brake linings seems to be less hazardous than from unused
{
asbestos
'
I
In this study asbestos was defined as the airborne fibres released from friction
materials brake pads and shoes clutch linings with length > 5 ...mand aspect ratio
23 23 Friction materials brake shoes pads clutch linings contain 30-70 chrysotile
asbestos The fibre counting was performed by contrast optical microscopy
PCOM Qualitative analysis of fibre composition needs scanning electron micro-
scopy SEM with an energy dispersive detector The fibre calculations in the
|
Past asbestos exposure index for car and bus mechanics
449
reduce the theoretical variability by a factor of 40. By putting more precise questions about working methods the distribution is decreased to 13 and questions about repair shops conditions will reduce it by a factor of 4. Work activities after 1975 give a general
reduction bya factor of 1.5 Each factor type of vehicle type of brakes etc. in direct
questions reduce the variability by a third Cumulative exposure assessment is time and resource consuming which can be reduced by using a systematic questionnaire technique Additional information can be obtained by interviews and is important to
reduce misclassification
Validation ofthe model vs historic measurements
Errors might have occurred when estimating the value for each variable in the historic exposure equation The correlation in the validation was 0.69 between asbestos index and measured asbestos levels A reason for this relatively low value is imprecision in low levels of asbestos It would have been advantageous to have measurements from the 1950s and the 1960s for validation of the larger values of the coefficients in the
model but such data were not available Another reason can be poor choices for the multipliers or variability in the actual effects of the factors One important source of
error can be differences in fibre counting techniques between laboratories The fact that the same laboratory did most of the fibre counting diminished the error in the calibration curve We think that the correlation was good in spite of the usual systematic and random errors in industrial hygiene sampling strategy and fibre
counting
All fibres are not asbestos fibres
The debris from brake shoes and clutch linings contains a large number of fibres with length < mPlato et al 1991 These short fibres may not have the same biological activity as the long fibres Brake dust at workplaces has been characterized by size and chemical contents Jacko and DuCharme 1973 Qualitative analyses by transmission electron microscopy suggest that brake dust mainly contains short fibres length < ...mthat are also so thin that they are invisible with optical microscopy In
a study by Rohl et al 1976 84 ofthe fibres were shorter than 0.4 mWilliams and
Muhlbaier 1982 observed that 99.9 of the original mass of asbestos fibres were broken down at high temperature to fibrous magnesium silicates during the brake process Rohl et al 1976 observed that only % of the fibres in the debris met the definition of asbestos fibres The morphology of asbestos may be changed during the temperature increase in the brake process Davis and Coniam 1973 At 650 the asbestos configuration is transferred to forsterite Koshi et al 1969 which is fibrogenic in lung tissue Hayashi 1974 Sakabe et al 1971
Woitowitz and R^delsperger 1991 concluded from animal experiments that cxposure to dust from worn brake linings seems to be less hazardous than from unused
asbestos
In this study asbestos was defined as the airborne fibres released from friction materials brake pads and shoes clutch linings with length > 5 ...mand aspect ratio
Fricti on materials brake shoes pads clutch linings contain 30-70 chrysotile asbestos The fibre counting was performed by contrast optical microscopy
PCOM Qualitative analysis of fibre composition needs scanning electron microscopy SEM with an energy dispersive detector The fibre calculations in the
Past asbestos exposure index for car and bus mechanics
451
would not be correlated with the fibre exposures Such exposures might have affected
Dahlqvist all mechanics but probably not the bus drivers control group et al 1992 found a exposure relationship for cumulative
asbestos exposure and CV based on 50 of the car mechanics When the group was increased to include both car and bus mechanics 103 the significance
disappeared
CONCLUSIONS
-It was possible to make a model for estimation of past asbestos exposure and to validate it This approach may be useful in other applications
-The car and bus mechanics had relatively low overall asbestos exposure at least
during more recent years It had been higher in the past but even the truck
mechanics were exposed at a low level compared to most asbestos exposed
groups
_No significant effects on lung function were demonstrated from these low levels in
this study
Acknowledgements - This work was carried out with financial support of the Swedish Work Environment Fund The authors would like to thank Professor Thomas Smith Ph.D. Harvard School of Public Health
Boston for support on methods and principal discussions We also thank Irena Cynkier Ph.D. then at
the Department of Occupational Health Karolinska Hospital for help during data collection and interview
and finally Monica Dahlqvist Ph.D. then at the Department of Occupational Health Karolinska Hospital
for performance of the pulmonary function examinations and the later data analysis
i
REFERENCES
Bentley M. Z. 1970 Control of the use of asbestos containing friction materials Ann occup Hyg 13,31 32 Blair A. and Stewart P. 1990 Correlation between different measures of occupational exposure to
formaldehyde Am J. Epidemiol 131 510--516
Dodgson.J Cherrie J. and Dodgson.J 1986 Past exposures to airborne fibres and other potential risk factors on the
European manmade mineral fibres production industry Scand J. Wk Environ Hith 12 Suppl 1. 26--33 Dahlqvist M Alexandersson R. and Hedenstierna G. 1992 Lung function and exposure to asbestos
among vehicle mechanics Am J. ind Med 22 59 68 Davis and Coniam S. W. 1973 Experimental studies on the effect of heated chrysolite asbestos and
automobile brake lining dust injected into the body cavities of micc Expl molec Puth 19 339 353 Esmen N. A. 1979 Retrospective industrial hygiene surveys Am ind Hyg Ass J. 40 58 65 Hansen E 1989 1989 Mortality of auto mechanics A ten year follow Scand J. Wk Environ Hith 15 43-46 Hatch D 19701970 Possible alternatives to asbestos as a friction material Ann occup Hyg 13 25 29
Hayashi H. 1974 1974 Cytotoxicity of heated chrysotile Environ Hlth Perspect 9 267 270 Jacko and and DuCharme R. T. 1973 Brake emission measurements from brake and clutch linings from
selected mobile mobile sources U.S. Environment Protection Agency Report 1973 68-04-0020
J^/rvholmB. and and Brisman J. 1988 Asbestos associated tumours in car mechanics Br J. ind Med 45
645 646
Kauppinen T. and Korhonen K. 1987 Exposure to asbestos during brake maintenance of automotive
vehicles by different methods Am ind Hvg Ass J. 48 499-504
Knight K. and Hickish
E. 1970 Exposure to asbestos during brake maintenance Ann occup Hyy
13 17-20
Knight K. and Hickish E. 1979 Investigation into alternative forms of control for dust generated during the cleaning of brake assemblies and drums Ann occup Hyg 13 37 39
Koshi K. Hayashi Hayashi and Sakabe H. 1969 Biological and mineralogical studies on serpentine minerals in
heat treated state Ind Hith 7 66-85
Krantz S. 1976 1976 Asbestos exposure at community bus repair shops
Report for National Institute of
Occupational Ocupational Health Solna Sweden in Swedish
Past asbestos exposure index for car and bus mechanics
451
would not be correlated with the fibre exposures Such exposures might have affected all mechanics but probably not the bus drivers control group
Dahlqvist et al 1992 found a exposure relationship for cumulative
asbestos exposure and CV based on 50 of the car mechanics When the group was
increased to include both car and bus mechanics 103 the significance disappeared
CONCLUSIONS
--- was possible to make a model for estimation of past asbestos exposure and to validate it This approach may be useful in other applications
-The car and bus mechanics hada relatively low overall asbestos exposure at least
during more recent years It had been higher in the past but even the truck mechanics were exposed at a low level compared to most asbestos exposed
groups
-No significant effects on lung function were demonstrated from these low levels in
this study
Acknowledgements - This work was carried out with financial support of the Swedish Work Environment Fund The authors would like to thank Professor Thomas Smith Ph.D. Harvard School of Public Health Boston for his support on methods and principal discussions We also thank Irena Cynkier Ph.D. then at the Department of Occupational Health Karolinska Hospital for help during data collection and interview and finally Monica Dahlqvist Ph.D. then at the Department of Occupational Health Karolinska Hospital for performance of the pulmonary function examinations and the later data analysis
REFERENCES
Bentley M. Z. 1970 Control of the use of asbestos containing friction materials Ann occup Hyg 13,31 32 Blair A. and Stewart P. 1990 Correlation between different measures of occupational exposure to
formaldehyde Am J. Epidemiol 131 510--516 Cherrie J. and Dodgson J. 1986 Past exposures to airborne fibres and other potential risk factors on the
European manmade minera fibres production industry Scand J. Wk Environ Hlth 12 Suppl , 26 33 Dahlqvist M Alexandersson R. and Hedenstierna G. 1992 Lung function and exposure to asbestos
among vehicle mechanics Am J. ind Med 22 59. 68 Davis and Coniam S. W. 1973 Experimental studies on the effect of heated chrysolite asbestos and
automobile brake lining dust injected into the body cavities of mice Expl molec Path 19 339 353 Esmen N. A. 1979 Retrospective industrial hygiene surveys Am ind Hyg Ass J. 40 58 65
Hansen E. 1989 Mortality of auto mechanics A ten year follow Scand J. Wk Environ Hlth 15 43 46
Hatch D. 1970 Possible alternatives to asbestos as a friction material Ann occup Hyg 13 25 29 Hayashi H. 1974 Cytotoxicity of heated chrysotile Environ Hlth Perspect 9 267 270 Jacko M. G. and DuCharme R. T. 1973 Brake emission measurements from brake and clutch linings from
selected mobile sources U.S. Environment Protection Agency Report 1973 68-04-0020
J^/rvholmB. and Brisman J. 1988 Asbestos associated tumours in car mechanics Br J. ind Med 45 645 646
Kauppinen T. and Korhonen K. 1987 Exposure to asbestos during brake maintenance of automotive vehicles by different methods Am ind Hyg Ass J. 48 499-504
Knight K. L. and Hickish D. E. 1970 Exposure to asbestos during brake maintenance Ann occup Hyg
13 17-20
Knight K. L. and Hickish D. E. 1979 Investigation into alternative forms of control for dust generated during the cleaning of brake assemblies and drums Ann occup Hyg 13 37 39
Koshi K. Hayashi H. and Sakabe H. 1969 Biological and mineralogical studies on serpentine mineralisn
heat treated state Ind Hlth 7 66-85 Krantz S. 1976 Asbestos exposure at community bus repair shops Report for National Institute of
Occupational Health Solna Sweden in Swedish
Past asbestos exposure index for car and bus mechanics
453
parameter were estimated from data in a number of internationally published reports Bentley 1970 Hatch 1970 Knight and and Hickish 1970 1979 Lorimer et al 1976 Rohl et al 1977 R^delspergeret al 1986 Kauppinen and Korhonen 1987 The exposure matrix is based on the principle that was applied by Marsh 1987 after a method developed by Esmen 1979 The exposure vectors have been estimated from a geometric ranking ranking scale illustrated in Table Al The extremes for each variable were first selected with
geometric steps because no direct data were available The choice of the size of the coefficients is explained
below
Type of vehicle vehicle K,range 13 13 A truck has about three times bigger brake lining surface compared to a
car and thus generates generates three time more fibres Rohl et al 1976 Coefficient 2 was selected for cars and trucks
due to a larger influence of truck fibres
Rooms ( range 1 3 1 T3 he variability of exposure in the workrooms in this study has been estimated to a factor of3 from the best to the worse condition Riala et al 1984 carlier applied a factor of 5 to unventilated rooms compared compared to ventilation by open windows during painting operation The respirable asbestos distribution pattern pattern is equivalent to that of vapours Nicholson 1982 The worst rooms were ventilated by opening garage doors during the summer and were given a coefficient of 3
Working activities activities K range 1/3 1/3 A factor of 3 has been applied in order to separate the best and the worst working activities as a mean for 8 h activity Compressed air and machinery grinding give the highest exposure The exposure shows a large variation between drum and disc brakes depending on the longer working time spent spent with drum brakes Kauppinen and Korhonen 1987 Rohl et al 1977 Hatch 1970 Knight and Hickish Hickish 1979 Lorimer et al 1976 Nicholson 1982
Working frequency frequency K range 1.8 3.0 The frequency of different working operations drum or disc
brakes has been been estimated to have a coefficient of 3. This was estimated from the mean value from different
studies where drum brakes and disc brakes were evaluated during equivalent cleaning techniques
Table A1 Coefficient table for the exposure matrix
Variable 1. General shop
Type of vehicle K )
Repair shop rooms A
|
2. Task activities Work activities k
Frequence of work K Other factors K
Multiplier
coefficient
Comment
3.0
Work with truck or bus
2.0
Work with truck and car
1.0
Work with just passenger car
3.0
Small bad conditions no ventilation
2.4
Small bad conditions poor ventilation
8
Normal mechanical ventilation medium
1.3
Good condition big size good ventilation
10
Big size excellent condition and ventilation
3.0
Compressed air blowing drilling riveting grinding
with no exhaust
26
Compressed air blowing grinding with separate
exhaust
22
Brushing drilling riveting grinding without
separate exhaust
17
Brushing grinding with separate exhaust
13
Brushing water spray
10
Water spray
)
No activity with fibre material
3.0
Daily drum brake activity
18
Daily disc brake or low frequence drum brakes
10
Low frequence disc brakes
15
Work as vehicle mechanic before 1975
10
Work as vehicle mechanic after 1975
Notes
1 Subjectjob job activities changed across time K and Kand the employer shop changed Shops changed changed across time K,K and K as they expanded and changed the type of vehicle and repair
work they would would do
454
N. Plato et al
Many of the subjects reported very high dust generation during short periods of work on clutch removal During the braking operation on a car nearly 80 of the asbestos fibres and the debris will leave the brake drum and go out into the environment whereas the dust from clutch activity stays within the transmission The clutch often has a total friction surface and amount of debris comparable to the brake linings in the car
Other factors K,range 1.0 1.5Information on the asbestos dust hazard was widely disseminated around 1975 and the introduction of new asbestos regulation rules generally improved the working conditions resulting in a general decrease of % compared to the conditions before that period
The use of a face mask repairatory protection has an exposure reduction factor of 0.3 for activities where a mask respirator was worn Torney and Barnhart 1976 However face masks were not used during the period of interest so were not included in the model
With the coefficients in Table Al and the ranking scale all the exposure situations can be classified for each The ranking scale is geometric in order to give a similar distribution between the coefficients This method was used because measurements were missing for many historical exposure situations
Step 3. The model takes into consideration that the mechanic is both primarily exposed by his own work
task activity and exposed from field air contaminants general workshop exposure Equation A1 is
constructed from the model by Dodgson and Cherrie by using multipliers Cherrie and Dodgson 1986
Literature studies Rohl et al 1977 indicate that the background level has an influence on the total
exposure To include task activity as well as background exposure a combination of additive and
multiplicative model was constructed shown in Table A2 The asbestos exposure has been expressed in the
relative unit asbestos index AI The equation could then be used for each mechanic for annual exposure
calculation
The
AI
has
to
be converted
into
mlfl,,
f mlfl,,by
using
a
transformation
curve
That
curve
was created
using 18 Swedish reports By using information in the reports the coefficients were estimated and the AI were
calculated
Table A2 Equation for calculation of asbestos index AI by using the matrix in Table A1
Model asbestos index Al = general sh-otap sk activity
Variables for general shop exposure
FE
Variables for task activity exposure
NE
for each car mechanics for each year summed over all years with work as a vehicle mechanic
and year
AI K * K, K K,
start year
AI
Note Al calculated based on each subject's personal work history and of the shops where she worked
rN
3oF