Inhaled Particles V. Proceedings of an International Symposium Organized by the British Occupational Hygiene Society, Cardiff, 8–12 September 1980

887 Pages·1982·39.561 MB·English

by  W. H. Walton (Eds.)

ORGANIZING COMMITTEE
Chairman: Mr W. H. WALTON Editor, Annals of Occupational
Hygiene, c/o Institute of Occupational
Medicine, Edinburgh
DrA.CRITCHLOW Health and Safety Executive, Safety in
Mines Research Establishment,
Sheffield
Dr P. C. ELMES Director, Pneumoconiosis Unit,
Medical Research Council, Penarth
Mr G. A. HEDGECOCK Group Occupational Hygienist,
Pilkington Brothers Limited, St Helens
Prof. A. G. HEPPLESTON Honorary Pathologist, Institute of
Occupational Medicine, Edinburgh
Dr R. L. KELL Department of Social and
Occupational Medicine, Welsh
National School of Medicine, Cardiff
Prof. J. c. MCDONALD Director, TUC Centenary Institute of
Occupational Health, London School
of Hygiene and Tropical Medicine,
London
Organizing
Secretaries: Mr J. DODGSON Head of Environmental Branch,
Institute of Occupational Medicine,
Edinburgh
Mr D. A. PHILLIPS Pneumoconiosis Unit, Medical
Research Council, Penarth
Mr C. O. JONES IOM Regional Laboratory,
NCB Maritime Laboratory, Maesycoed,
Pontypridd, Glamorgan
The Organizing Committee is grateful for the help given by Dr J. S. McLintock as
Chairman of the Organizing Committee until his retirement at the beginning of 1980.
INHALED PARTICLES
V
Proceedings of an International Symposium
organized by the British Occupational Hygiene Society
Cardiff, 8-12 September 1980
Editor-in-chief
w. H. WALTON
Discussion Editor
A. Critchlow
Editorial Assistant
S. M. Coppock
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First edition 1982
Library of Congress Cataloging in Publication Data
Main entry under title:
Inhaled particles V.
Proceedings of the 5th International Symposium
on Inhaled Particles and Vapours.
"Published as volume 26 of ... Annals of
occupational hygiene"—Verso t.p.
1. Lungs—Dust diseases—Congresses. 2. Dust—
Toxicology—Congresses. 3. Aerosols—Physiological
effect—Congresses. I. Walton, W. H. II. British
Occupational Hygiene Society. III. International
Symposium on Inhaled Particles and Vapours (5th :
1980 : Cardiff, South Glamorgan) IV. Annals of
occupational hygiene. [DNLM: 1. Lung diseases —
Etiology—Congresses. 2. Air pollution—Congresses.
3. Dust—Congresses. 4. Respiratory system—
Physiology—Congresses W3 IN 1038]
RC773.I554 1982 616.2'4407 82-11231
British Library Cataloguing in Publication Data
Inhaled particles V.
1. Respiratory organs—diseases—Congresses
2. Dust—Physiological effect—Congresses
I. Walton, W.H. II. Critchlow, A.
III. Coppock, S.M. IV. British Occupational
Hygiene Society
616.2Ό0471 RC711
ISBN 0-08-026838-2
Published as Volume 26 Nos. 1 -4 of the journal
Annals of Occupational Hygiene and supplied
to subscribers as part of their subscription.
Also available to non-subscribers.
Printed in Great Britain by A. Wheaton & Co. Ltd., Exeter
PREFACE
Inhaled Particles V contains the refereed and edited texts—and discussions—of 69
papers presented at the fifth quinquennial international symposium, organized by the
British Occupational Hygiene Society and held in Cardiff 8-12 September 1980. The
aim, as at previous symposia, was to present results from recent research on the entry,
fate and effects of respired particles, with emphasis on basic mechanisms and
quantitative exposure-effect relationships. Once again, the contributions offered far
exceeded the capacity of a 5-day meeting and the Organizing Committee had a difficult
task of selection based on early abstracts of often still-incomplete work. Disappointed
authors will realize that the Committee had to consider the overall balance of the
programme when deciding between contributions of otherwise equal merit.
The papers are mostly prime accounts of new scientific work that are not expected
to be published elsewhere. As last time, we express the hope that abstractors will give
them individual attention, as would be accorded to contributions in a regular scientific
journal. To encourage this, the work is being published as a volume of the Annals of
Occupational Hygiene.
The work is divided into sections on much the same pattern as the earlier volumes of
the series:
(1) Particle Inhalation and Deposition 12 papers
(2) Deposition, Clearance and Retention 13 papers
(3) Dust in Human Lungs 5 papers
(4) Biological Reactions to Dust 10 papers
(5) Carcinogenic and Cytotoxic Effects 7 papers
(6) Airways Response to Aerosols 5 papers
(7) Individual Factors determining Pneumoconiosis 2 papers
(8) Epidemiological Studies 15 papers
The preliminary press announcement of the Symposium had mentioned a number
of growth areas of particular interest; in the event, significant advances were reported in
some of these fields (and elsewhere); others remain largely untilled.
Section 1 contains several papers on the size-selective external dynamics of coarse
particles entering the nose or mouth; this aspect has been neglected in most earlier
studies of regional deposition, but it is very relevant to hygiene standards based on
'total dust'. Computerized mathematical models for regional deposition are further
developed in other papers; the ICRP dosimetric model is criticized and theories are
extended usefully to fibrous, charged or hygroscopic particles.
The lung retention of asbestos and other mineral fibres as a function of length and
diameter, the remarkable mobility of fine fibres within the body and the surprisingly
large amounts of amphibole as compared with chrysotile found in human lungs are
covered in various papers in Sections 2 and 3. Studies on shale and coal dusts and fly
X Preface
ash reflect continuing concern with possible adverse health effects associated with the
energy industries.
In Section 4, mechanisms of fibrogenesis by silica are further developed. Differences
in specific harmfulness of coal mine dusts, which are not explicable in terms of the silica
or other mineral content, remain a continuing subject of study; numerous biological
tests have been applied to these dusts with the aim of finding a measure that correlated
with epidemiological findings. It is clear that the action of silica is modified by the
presence of other minerals, which may themselves be harmful. Comparisons of in vitro
cytotoxicity testing of the same coal mine dust samples by different research centres
showed large inter-laboratory differences between the assessments. This needs further
examination.
In vitro and in vivo tests for pathogenicity and carcinogenicity on a variety of fibrous
and other dusts are described in Section 5. One paper reports on the effect of nitrous
oxides (NOx) adsorbed on dust (mentioned as an area of interest) with negative result.
Section 6 contains papers that describe the airways' response to various irritant
aerosols including enzymes and other organic dusts, sulphates and gold mine dust. The
two papers in Section 7 are concerned with the continuing controversies about
relationships between lung function and dust accumulation (as in pneumoconiosis or
silicosis). The wider problems of individual susceptibility—why some workers are
adversely affected by dust while others apparently equally exposed are not—still await
critical analysis.
The final Section 8 is devoted to epidemological studies. Coal mining again features
prominently. For the first time we are given an insight into the relationship between the
routine measurements of dust and pneumoconiosis at all British collieries. The general
correlation is poor; certain cases showing anomalous relationship are selected for
special study and some contributory factors are identified. The results illustrate the
hazards of attempting to use routine measurements of medical and exposure variables
for research purposes. Another paper documents an association between unusually
rapid progression of simple pneumoconiosis accompanied by the occurrence of PMF
and high percentages of quartz in dust exposures, although quartz is clearly not the sole
factor. In earlier studies of British coal miners, any links between pneumoconiosis
progression and quartz have been elusive. Other epidemiological studies are concerned
with diesel emission in coal and potash mines, gypsum and talc dust exposure and,
importantly, asbestos. Two papers of topical interest discuss health implications of dust
from the recent Mount St Helens volcanic eruption—with apparently reassuring
findings.
Thanks are due to the many who helped with both organizational and editorial
aspects of the Symposium. The interpreters were kindly provided by the Commission of
the European Communities. On the editorial side Alan Critchlow served as secretary of
the scientific programme sub-committee and receiver of the papers submitted and also
kindly edited the discussion, John Ellison has 'anglicized' several papers of foreign
origin and Sheila Coppock has scrutinized everything and striven to preserve the
precision of the English language. Above all, the authors are thanked for their willing
co-operation.
W. H. WALTON
Ann. occup. Hyg., Vol. 26, Nos. 1-4, pp.3 19, 1982. 0003-4878/81/010003-16/$03.00/0
Printed in Great Britain. Pergamon Press Ltd.
Inhaled Particles V < 1982 British Occupational Hygiene Society.
APPLICATIONS OF BLUNT SAMPLER THEORY TO THE
DEFINITION AND MEASUREMENT OF INHALABLE DUST
J. H. VINCENT and D. MARK
Physics Branch, Institute of Occupational Medicine, 8 Roxburgh Place, Edinburgh EH8 9SU,
Scotland
Abstract—From considerations of the air movement near the entrance to a blunt dust sampler, a
simple theoretical model has been developed to explain its performance characteristics. This model
predicts quantitatively the performance of a simple idealized blunt sampler with a single orifice facing
the wind, but for more complicated samplers allows only a qualitative assessment to be made. This
can be useful, however, for evaluating practical systems. The head o fa live, breathing human subject
may also be regarded as a blunt sampler and its performance in this respect assessed qualitatively in
terms of the model. Thus the selection characteristic which defines 'inhalability' can be placed on a
physical footing. Some new measurements of the selection characteristics of a model human head are
reported, differing from previously published work in that experiments were carried out in a much
larger wind tunnel with the full head and torso. The results suggest that the presence of the torso may
have considerable influence on 'inhalability' as determined by such experiments. In the light of the
experience gained in performing such experiments, the appropriateness of defining 'inhalability' in
terms of idealized windtunnel-like conditions and the resultant rationale behind the use of 'static'
samplers for inhalable dust are questioned.
INTRODUCTION
IN ORDER to evaluate airborne dust, it is common practice to aspirate a sample of the air
through an orifice and collect the dust on a filter. The question then arises: how
representative of the airborne dust is that which is aspirated? Since the reason for
obtaining such a sample is to assess the potential health risk to humans, this leads to the
closely allied question: how representative of the airborne dust is that which is inhaled
(i.e. entering through the nose and/or mouth during the act of breathing) by a human
subject? These apparently simple problems involve complex fluid and particle
mechanical processes, our understanding of which is still far from complete. This paper
sets out to describe a fresh way of looking at the aerodynamics of dust sampling and to
see whether any useful new generalizations can be made. It then goes on to consider
how these ideas can be applied to practical dust sampling and to understanding the
factors governing inhalation.
SAMPLING WITH THIN-WALLED PROBES
The simplest case is aspiration into a thin-walled cylindrical tube placed with its
entry facing and its axis aligned with a dust-laden stream of moving air. The fact that air
is thus being removed from the main stream implies in general that some distortion in
the air movement outside the sampler must take place. Dust particle movement in this
flow is such that the concentration (c) of particles of given size which actually enter the
orifice may not be the same as for those in the undisturbed main stream (c). The
0
physics controlling the relationship between c and c has been extensively investigated
0
3
4 J. H. VINCENT and D. MARK
by, for example, BADZIOCH, 1959; SEHMEL, 1967; DA VIES, 1968; BELYAEV and LEVIN,
1974, and many others. It can be shown that
£=-i=l + aEo-ll (1)
Co I v )
where E is defined as the sampling efficiency (or aspiration coefficient), U0 is the
undisturbed main stream air velocity, ϋ the mean velocity at entry to the sampling
orifice and a an inertial parameter which describes the efficiency with which particles
'impact' onto the frontal plane of the sampling orifice. In general
a = / | s i ; ^} (2)
where
St = d2y*Uo/lfyS. (3)
The latter is a Stokes number for this system, defined as the ratio between particle stop
distance (at velocity U0) and tube diameter; d is the particle aerodynamic diameter
(being the diameter of a particle of'unit' density (y* = 103 kg m~ 3) and having the same
falling speed as the particle in question), δ the tube diameter, and η the air viscosity. In
arriving at equation (1), the effect of gravitational settling has been neglected; this is
reasonable, since, for example, the falling speed of a particle with aerodynamic diameter
as large as 50 μιη is only of the order of 0.07 ms"1, small in comparison to air velocities
which characterize most practical sampling systems. Brownian and turbulent diffusion,
electrostatic effects and other possible processes are also neglected. Subject to these
limitations, E = 1 when ϋ is equal to l/0, indicating that the aspirated dust is perfectly
representative of the airborne dust. This is the basis of what we know as isokinetic
sampling.
LUNDGREN et al. (1978) have extended this simplest case to include the situation
where the axis of the sampling probe is yawed at an angle Θ to the main air flow, and
they argued that
£=l + a'H°-cos0-lj (4)
where a' is not only a function of St and U0/v, but Θ as well.
SAMPLING WITH BLUNT PROBES
The thin-walled sampling probe just described does not actually exist in reality,
since the tube walls must have finite thickness and so present some obstruction to the
air movement. The broad effects of this are illustrated in Fig. 1(a) by examples obtained
using the electrolytic tank potential flow analogy for two-dimensional flow
(MALAVARD, 1947). Qualitatively, it is found that, for a sampling rate which is below or
close to isokinetic, the flow of air entering the sampling orifice first diverges, then
converges. It can be shown that the magnitude of this effect increases with relative wall
thickness and with the 'bluntness' of the wall profile. The air velocity along the sampler
centre line ([/), obtained from the same electrolytic tank experiments, is also shown.
Applications of blunt sampler theory to the definition and measurement of inhalable dust 5
Sampler centre line
FIG. 1. Examples of potential flow at the inlets to various samplers (two-dimensional) from electrolytic tank
analogue. Also shown are graphs of the centre-line velocity, (a) tube with finite wall thickness (b) 'blunt'
sampler.
For isokinetic sampling, the velocity goes through a minimum just in front of the
sampling orifice. For other conditions close to isokinetic, the effects of the bulge in the
flow pattern appear as inflexions in the velocity distribution. WALTER (1957) carried
out experiments to measure the effect for actual sampling probes in a wind tunnel under
isokinetic conditions, finding the velocity minimum, but incorrectly describing it as a
point of 'stagnation'. The same effect has more recently been observed by ROUILLARD
and HICKS (1978). From this discussion, it is clear that the flow of air into a 'real'
sampling probe, and therefore the movement of dust particles in its vicinity, is more
complicated than for the idealized thin-walled probe.
Many dust samplers used in practical occupational hygiene are much 'blunter' than
the ones described so far and it is reasonable therefore to expect the features described
above to be even more pronounced (as illustrated by the simple electrolytic tank
examples in Fig. 1(b)). The form of these flow patterns is supported by measurements
6 J. H. VINCENT and D. MARK
made in the wind tunnel on 'real' sampling systems. For example, a typical
axisymmetric flow pattern near the entrance to an idealized disc-shaped sampler with a
central sampling orifice, as visualized photographically by means of balsa dust under
slit illumination of a plane through its axis, is shown in Fig. 2. Theoretical discussion of
such a blunt sampler may be based on Fig. 3, where the sampler body dimension is D
and the sampling orifice dimension δ as before. When no air is being sucked through the
orifice, there is stagnation (i.e. zero air velocity) at P. However, when there is suction,
stagnation moves outwards to lie on a ring passing through Q and Q' where the
limiting stream surface enters the sampler body. All of the air contained within this
stream surface (dotted area in Fig. 3) enters the sampling orifice, while all outside it
passes around the sampler body. It can be shown that the characteristic 'spring onion-
shaped' limiting stream surface and the associated minimum in the air velocity along
the axis of the sampling orifice applies for the simple configuration shown when the
ratio
Rate at which air is sampled δ2ν
Rate at which air is geometrically incident on the sampler body D2U
0
is less than 0.5. Other values will apply for different shapes of sampler body. For values
of φ greater than this critical value, the minimum in the axial velocity of the sampled air
disappears.
With detailed knowledge of the flow pattern, it is possible in principle to calculate
trajectories of individual particles from their equations of motion and so obtain E
numerically for whatever conditions are of interest. Alternatively, a less rigorous
approach based on the ideas contained in the simple thin-walled probe theory,
extending them to describe particle movement in the more complicated flow in front of
a blunt sampler, can provide useful insight.
The flow picture outlined above identifies two distinct regions—the outer one
controlled largely by the flow about the sampler body and the inner one by flow into the
orifice. We can apply the ideas contained in the theory for the thin-walled sampling
probe to each of these regions in turn and so obtain an expression for the sampling
efficiency of the blunt sampler which is a combination of two expressions of the type
shown in equation (1). Thus for a blunt sampler facing the wind
+ ι+
Μ' -(ίΗΗ -(τ-')}
where U is an intermediate mean air velocity at the interface between the two parts of
l
the flow, given by
U~vS2/S2 (7)
l
(x and a are inertial parameters given to a first approximation by
l 2
«'-^K/d^2y*Urn\ ) (8)
and
'd2v*U '
«2~/(fta)^/2(-^i) (9)
2
FIG. 2. Photographic visuaHzation of typical flow in front of a disc-shaped sampler with a central circular
sampling orifice (using balsa dust under slit illumination).
7