Inquiry into the Occurrence of Disease of
the Lungs from Dust Inhalation in the Slate
Industry in the Gwyrfai District
C. L. SUTHERLAND, M.D., D.P.H.
S. BRYSON, D.P.H.
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MEMBERS OF THE
HEALTH ADVISORY COMMITTEE OF THE
|Sir EDWARD TROUP, K.C.B., K.O.V.O., LL.D.
|Professor E. L. COLLIS, D.M., M.R.C.P.
|Sir W. M. FLETCHER, K.B.E., C.B., M.D.,
|Sir K. W. GOADBY, K.B.E., M.R.C.S., L.B.C.P.,
|Dr. J. S. HALDANE, C.H., M.D., F.R.S.
THE EFFECT OF SLATE DUST ON THE LUNGS.
Evidence was gathered by a Departmental Committee as long ago
as 1895 which suggested the possibility that an unduly high
death-rate from phthisis experienced by slate workers in
Merionethshire was, to some extent, due to inhaling slate
The subject remained, however, without further investigation
until 1927, when a report by Dr. Wade was published, which dealt
in particular with the occupational and domestic environment of
slate quarrymen and workers in the Gwyrfai Rural District of
Carnarvonshire [Caernarfonshire], and with their mortality from
pulmonary tuberculosis and other respiratory
diseases2. Mortality records concerning all slate
workers in England and Wales for 1921-23 were there given for
Dr. Wade found that all slate workers in England and Wales
experienced an unduly high mortality from phthisis occurring late
in life, associated with high mortalities from bronchitis and
pneumonia; and that mortality records for Gwyrfai slate workers
exhibited similar characteristics. Further, when slate miners and
quarriers were distinguished from slate masons (millmen), higher
mortalities were found to be exhibited by the group which was
more exposed to dust (i.e. the masons).
Penrhyn slate, worked by these men, was found to contain from
25 to 42 per cent. of quartz; while dust arising therefrom
contained from 50 to 80 per cent. of fine quartz. Further
analyses carried out since by the Government Chemist give the
following results: (i) Dust collected from a ledge eight feet
above the floor and directly above the heads of a splitter and
hand dresser contained 46.5 per cent. of free silica and 9.5 per
cent. of combined silica, and (ii) dust collected at another
quarry from a beam nine feet above the floor contained 39.7 per
cent. free silica and 10.3 per cent. combined silica.
Additional mortality data, bringing the records up to the end
of 1928, have also been obtained through the courtesy of Dr.
Parry Edwards (see Appendix A). These data display the same
characteristics as those collected by Dr. Wade, and may therefore
be said to support, so far as statistical evidence can do so, the
conclusion he came to that "with regard to the slate workers the
problem of prevention of lung disease among them arising out of
their occupation is the dust problem."
Dr. Wade held, however, that a clinical and X-ray
investigation of a number of workers should be undertaken.
By arrangement with the Refractories Industries Compensation
Fund, the services of Drs. C. L. Sutherland and S. Bryson,
members of the Medical Board under the Refractories Industries
(Silicosis) Scheme, were obtained, and the inquiry was entrusted
by the Mines Department to these gentlemen.
Their report is now presented. Definite indications were found
both through clinical and X-ray examinations that the dust
exposure in the industry is harmful. Thus out of 120 men
examined, chosen from among those who were actively employed at
the time, clinical evidence suggestive of pulmonary fibrosis was
found in 56. Forty-seven of these 56 cases were found among
millmen, the group most exposed to dust. These 47 together with
five other millmen were X-rayed; as the result of the additional
evidence so obtained, silicosis was definitely diagnosed in 14 of
these men, that is to say in 14.6 per cent. of the 96 millmen
examined (see Table I). All these cases of silicosis had more
than twenty years' service in the industry. Eight of the cases
had more than forty years' service (see Table IV).
The evidence here given appears to corroborate that obtained
from mortality records, and to indicate that, as met with
industrially, slate dust, if the exposure is sufficient, is
definitely harmful; but that it takes longer to exert its effect
than does dust composed wholly of silica.
1 Report of Departmental Committee upon
Merionethshire Slate Mines, 1895. (0._7692), Eyre &
2 Ministry of Health Reports on Public Health and
Medical Subjects. No. 38. Investigation into the alleged high
mortality rate from Tuberculosis of the Respiratory System among
Slate Quarrymen and Slate workers in the Gwyrfai Rural District:
T. W. Wade. H.M. Stationery Office. 1927.
REPORT ON AN INQUIRY
Occurrence of Disease of the Lungs from Dust Inhalation in the
in the Gwyrfai District
Object and Nature of the Inquiry.
This inquiry was instituted by the Mines Department to
ascertain the possible relationship between the high death rate
from pulmonary disease in the Gwyrfai Rural District and the
chief local occupation of slate quarrying. The inquiry consisted
of the medical examination of a number of workers engaged in
slate quarrying and was confined to the slate quarries in this
district. A total of 120 workers was chosen for examination of
the chest, and after clinical examination 61 of these were
selected for radiological examination.
Selection of Workers.
Arrangements had been made as to the quarries which were to be
visited and the employers at these quarries gave every assistance
possible for the carrying out of the investigation. The
representatives of the North Wales Quarrymen's Union had informed
the workers of the object of the proposed medical examination and
this materially facilitated the proceedings.
As many of the workers had no great command of English the
assistance of Mr. Rhys Williams, H.M. Inspector of Quarries, was
invaluable as an interpreter. Dr. S. W. Fisher, H.M. Medical
Inspector of Mines, attended the inquiry and gave great
assistance in arranging for the X-ray examinations of the
The Clinical Examinations.
The workers examined were all at work at the time of the
examination and the investigators themselves selected the workers
to be examined. All the examinations took place on the quarry
premises and in the most suitable rooms that the managements
could provide. Very few of those approached with a view to being
examined refused to submit themselves. The various processes in
the getting and manufacture of slate were viewed and only those
workers who were engaged in dusty occupations were selected for
A full personal, family, and industrial history was taken in
each case and each investigator then examined the chest.
The Radiological Examinations.
These were carried out at Bryn Seiont Hospital by Dr. Emrys
Jones and the films were forwarded to the investigators. Each
investigator examined the films and then a joint decision was
come to as to the result.
Description of the Processes in Slate Production.
In the Gwyrfai district, slate is obtained from large open
quarries, and is transported from the quarries to sheds or mills
where the finished article is produced. The getting of slate here
is carried out entirely in the open, although drifts may
occasionally be driven for prospecting purposes. Large masses of
slate are broken off from the quarry face by means of blasting
and wedging. Suitable sizes of slate so obtained are carried to
the mills by aerial railway, and the waste material is dumped on
tips outside the quarry. As the quarry expands a varying amount
of overburden has to be removed and this may include inferior
slate, igneous rock, and soil.
In the mills the large blocks of slate are placed on the
sawing machine tables and sawn into the required sizes. The
smaller blocks of slate are then split to varying thicknesses and
trimmed or dressed to the different sizes. In some mills the
latter processes of splitting and dressing are carried out in the
main shed or sawing mill, but in others cubicles off the main
shed are set apart for this purpose. At the smaller quarries
there may be no mills and the work is carried out by manual
labour in the open. In the larger quarries a few of the older
workers are employed in salving better classes of slate from the
waste tips, and making slates from these.
Description of Occupations.
The Rockmen are employed in the quarries in the getting of
large Blocks of slate, by breaking these off the quarry face by
means of pick and crowbar. They may also take part in the
drilling and shot firing and assist in the trimming of these
large blocks of slate to suitable sizes for transport to the
The Labourers in the quarry or "pit" are engaged in assisting
the rockmen in any of the above operations, and in removing any
Drillers may be employed in manipulating the pneumatic drill
apart from any other work.
In addition to the above, other workers are employed in
connection with the aerial railway and in loading and unloading
slate, and other material.
The Millmen are those workers employed in sawing, splitting
and dressing. They usually work in pairs in close proximity, one
as a dresser, the other as a splitter, and both attend to the
sawing of their own blocks of slate. They are skilled in both
splitting and dressing', having served an apprenticeship which
covers both processes. The dressing may be done by hand or by
machine but in either case the splitter works in close
juxtaposition to his partner.
There are also a few general labourers in the mill, and one or
two saw sharpeners work inside the sheds and act as general
The above is a brief description of the occupations met with
during the investigation. No crushermen, polishers, nor miners
were seen. The workers examined have been classified into five
groups as follows :-
- Labourers to Rockmen
- Saw Sharpeners
Method of Examination.
The following particulars were taken in each case :-(1) Name,
(2) Address, (3) Age, (4) Name and address of employer, (5)
Present occupation and its duration, (6) Duration and precise
nature of any other work in the slate industry, (7) Duration of
occupations outside the slate industry, (8) Family history, (9)
Personal history, (10) General Physique3, (11) Chest
measurement, (12) Symptoms :- dyspnoea, cough, expectoration,
pain, (13) Condition of nose and throat, (14) Clinical
examination of the lungs, (15) Radiographic examination, (16)
Condition of other organs.
Grouping and Tabulation of the Results.
Table I gives for each of the five occupations, the number of
clinical examinations, the number of radiological examinations,
the number of cases of fibrosis, and of silicosis. Table II
summarises the particulars of each of these occupations. They are
arranged in groups according to the number of years of
employment, viz., 0-9, 10-19, 20-29, 30-39, 40-49, 50 years and
over. The particulars given are as follows :-
- Number in each group.
- Average age.
- Average number of years in the occupation.
- Average number of years in the slate industry.
- Average chest measurement at full inspiration in inches.
- Average chest expansion in inches.
- General physique.
- Number of cases of fibrosis.
- Number examined radiographically.
- Number showing definite silicosis, radiographically.
The diagnosis of fibrosis was based on the following physical
signs :-limitation of movement of the chest, changes in the shape
of the chest, diminution of air entry with alterations in the
quality of the breath sounds, especially at the bases, the
presence of adventitious sounds, viz., coarse rales or rhonchi,
impairment of percussion note
generally. All of these need not be present for a diagnosis of
fibrosis : the earlier stages may only show slight variations in
the breath sounds and slight impairment of percussion note.
The diagnosis of silicosis was made entirely on the
radiographic appearances detailed in Appendix B.
Results of Examinations.
(1) Rockmen.-Fifteen Rockmen were examined clinically
and six of these submitted to X-ray examination. No case of
silicosis was found among those X-rayed. The average age for the
group was high, viz., 52.53 years. The age of the youngest was 40
years and that of the oldest 69 years, The average number of
years spent as rockman was low compared with the time spent in
the slate industry as a whole, viz., 18.60 as against 30.86
years. However, in the latter age groups of the occupation these
periods more closely correspond, viz., 32.33 as compared with
37.66. The other occupation at which these men had been employed
was mainly that of millmen, and in the case of the oldest
workman, 33 years had been spent at this occupation and 20 as a
rockman. Some of the rockmen had spent some time as labourers in
the quarry. With regard to the occupations worked at outside the
slate industry, five of the rockmen had at one time been engaged
in stone work in coal mines. None of these workers was sent for
(2) Labourers to Rockmen.-This group consisted of two
workmen who acted as labourers for the rockmen, but were not
engaged in drilling. Both were found to be healthy.
(3) Drillers.-Six drillers were examined clinically and
three of these X-rayed. An average of only three years had been
spent in drilling, most of those in this group being really
labourers to the rockmen. No silicosis was revealed by the X-ray
(4) Millmen formed the largest occupational group, the
total number examined clinically being 96, of whom 52 were
examined radiographically. Of those X-rayed 14 were found to be
suffering from silicosis. The average age for this group was
46.37 and the ages ranged from 19 to 71 years. The average period
in the occupation as millmen corresponds very closely to the
average total time spent in the slate industry. A number of the
millmen had worked in coal pits for a few years and of these
seven had been employed in hard heading work. None of these was
included among those X-rayed.
(5) Saw Sharpeners.-One saw sharpener was examined.
Nothing of any interest was found.
Radiographic evidence of silicosis was found, therefore, only
in the group of millmen. In none of the other groups did the
radiograph show silicosis. This condition of affairs is no doubt
related to the fact that the processes of sawing, splitting and
dressing are carried out in a confined space in the mill sheds.
On the other hand the rockman works in the open air and in
addition, except when engaged in drilling, does not seem to be
exposed to so much dust. It must be remembered, however, as
already noted, that many of the rockmen had worked as millmen in
the mill sheds. With regard to the drillers the duration at the
occupation was not sufficiently long to enable any conclusion to
be drawn. The saw sharpener is exposed to the same atmosphere as
the millman. In the case of the labourers to the rockmen there
would appear to be little risk.
The clinical examinations show that severe fibrosis exists
amongst the older millmen. Fibrosis is also present in the older
rockmen but to a less extent. In the drillers there is evidence
of fibrosis of a slight degree, but in the remaining two
occupations no evidence was found.
Degree of Silicosis Found.
The classification adopted was similar to that adopted in the
Report on the Occurrence of Silicosis among Sandstone Workers.
4* In that Report three stages of the disease were
defined, and the first two of these stages were further
subdivided into three stages according to the radiological
appearances. (Details of this classification will be found in
The fourteen cases of silicosis found among the millmen could
be placed as follows :-twelve in the first stage, one in the
second, and one in the third stage. By the further subdivision
the twelve first stage cases were found to be grouped into four
in the stage la, six in the stage Ib, and two in the stage Ic.
The one case in the second stage was placed in stage lib.
Tables III and IV show these stages of the disease according
to age groups and period of occupation groups respectively. The
earliest age at which silicosis was found was 40 years. Most of
the cases, however, occurred in the 50 to 59 years age group.
The earliest period of occupation group to show silicosis was
the 20 to 29 years group but the majority of cases occurred in
the 40 to 49 years group.
History and Symptoms of the Positive Cases of
Among the positive cases a family history of tuberculosis was
elicited in three instances. In the personal histories, pneumonia
was found in one instance and pneumonia and bronchitis in
another. In the remaining 12 cases no history of previous chest
illness was given.
In four of the cases no symptoms were complained of. In six
cases the sole complaint was shortness of breath, a further two
had cough and dyspnoea, and the remaining two complained of
cough, spit and dyspnoea.
Dyspnoea was therefore the most common symptom. Pain was not
complained of in any of the cases.
Tuberculosis apart from silicosis was diagnosed in three
instances, one rockman and two millmen. The radiograph in these
three cases showed no definite indication that silicosis was
present. The case of silicosis in stage III was also probably
accompanied by tuberculosis. Three of these cases were in the age
group 60-69, and one in the 40-49 years group. The number of
years employed in the slate industry in the four cases was 26,
42, 47 and 53 years.
Examples of Cases.
No. 1, age 40, had worked as a splitter and dresser from the
age of 14, with the exception of 2½ years' Army service. He gave
a family history free from tuberculosis and he had had no
illnesses. He had no symptoms. The chest expansion was 3 inches.
Clinical examination revealed fibrosis and X-ray silicosis
No. 2, aged 55, had been in slate quarries as a splitter and
dresser for 37 years, having been away 3½ years on munitions and
six months as a repairer in a coal pit. There was no tuberculosis
in the family history and the personal history was negative. He
complained of cough, spit, and shortness of breath. His chest
expansion was 2½ inches. On clinical examination there was
fibrosis and on X-ray silicosis (Ib).
No,. 3, aged 53, had been a splitter and dresser for 33 years,
and in addition had spent seven years in a cotton factory. There
was no family history of tuberculosis. He had had typhoid fever
25 years ago. He complained of considerable shortness of breath
on going uphill. The chest expansion was 3¼ inches. Fibrosis was
found on clinical examination and silicosis on X-ray (Ic).
No. 4, aged 58, had been employed as a splitter and dresser
for 45 years. The family history and personal history were
negative. The only symptom was shortness of breath. The chest
expansion was 2¼ inches. The clinical examination revealed
fibrosis and X-ray showed silicosis (lib).
No. 5, aged 61, had been a splitter and dresser for 42 years
and had been employed as a general labourer outside the slate
industry for five years. The family history was negative for
tuberculosis. He had had pneumonia at the age of 19 and a year
ago had had an attack of bronchial catarrh which kept him off
work for 21 weeks. The symptoms were cough and severe dyspnoea.
The chest expansion was 3 inches. Severe fibrosis was present on
clinical examination and the X-ray revealed silicosis (III) and
probably a superadded tuberculosis.
No. 6, aged 42, had been employed for 26 years as a splitter
and dresser and had also spent two years in a coal mine as a
repairer. There was no history of tuberculosis in the family. A
year ago he had had an attack of bronchial catarrh which lasted
for four months, for two of which he was confined to bed. He
admitted that he suffered from a slight cough but had no other
symptoms. The chest expansion was 2¼ inches. There was fibrosis
on clinical examination and on X-ray pulmonary tuberculosis was
diagnosed, but no evidence of silicosis was seen.
Silicosis was revealed among millmen but no definite evidence
was obtained so far as other occupations were concerned. The
earliest age at which silicosis was found was 40 years, but the
disease appears to be most common after 50 years of age and after
30 years in the occupation.
||CHAS. L. SUTHERLAND,
3 This was based on a general summing-up of the
development, musculature, and nutrition. The individuals were
classified as follows :-Average normal individual (+1), excellent
physique (+2), fair physique (0), much less than ordinary (-1),
bad (-2). For a group of 20 individuals comprising 10 of the
normal average (= 10), 3 of excellent physique (=6), 4 of fair
physique (=0), 2 much less than ordinary (=-2), and 1 bad (=-2),
the average would be +10+6+6+0-2-2=12+20=+0.6
4 Report on the Occurrence of Silicosis among
Sandstone Workers. C. L. Sutherland and S. Bryson. H.M.
Stationery Office, 1929
Source: HMSO, 1930.