1184

THE COLLIERY GUARDIAN

December 10, 1915.

coal yields 50 per cent, or more of ash, it is very probably
of indifference whether the shale itself contains some
organic matter

Powdered clay or chalk (free from flint or grit) would
doubtless be as effective as shale dust in stopping explo-
sions, and both of these substances are known from
human experience to be practically harmless as regards
inhalation. Dust from hard limestone gave an unfavour-
able result in Beattie’s experiments. Our experience
with flue dust indicates that gritty material of the nature
of powdered slag, clinker, or flue dust should be avoided.
Sand is relatively ineffective for stopping explosions,*
and is too coarse to become easily suspended in the
air. For the same reason, and probably also because
the particles are rounded, it cannot be regarded as
dangerous from the point of view of inhalation unless the
sand particles are broken up by some violent process.
For stone dusting, a substance is required which is as
easily suspended in the air as coal dust, which is as
harmless to breathe, and which passes along with the
coal dust to such positions as the tops of timber bars on
the roof. That shale dust fulfils all these conditions is
shown, I think, in a striking manner by the experience
of the Nottingham coal field, and the investigations,
made under Mr. Fryar’s direction, of the fine dust from
the floor, sides, and roof timbers.

Dust Prevention on Hygienic Grounds.

It may not be out of place to add a few words as to
the desirability of reducing the dust, of whatever kind,
breathed by miners. Although coal dust and shale dust
are relatively harmless when breathed, there is good
reason for believing that they must do some harm in
the long run; and the fact that (as shown in Table I. and
the diagram) above the age of 55 there is a somewhat
undue rise in the mortality from lung disease (mainly
bronchitis) among coal miners is very probably connected
with inhalation of dust. Between the ages of 55 and 65
the death rates per 1,000 from bronchitis are 3’1 among
all occupied males, 1*7 among farm labourers, 5*6 among
coal miners, and 4*0 among Nottinghamshire and
Derbyshire coal miners.f

It seems to me, therefore, that apart altogether from
the risks of coal dust explosions and the discomfort
caused by dusty air, it is desirable on grounds of health
to prevent dust as much as practicable. The dust can
be diminished in various ways, for instance, by using
tubs which will not scatter small coal and dust along the
roads, by cleaning up roads when much dust accumu-
lates, and by not putting on more stone dust than is
really necessary to make the roads secure from dust
explosions. A good admixture of coarse with fine shale
dust seems 'also desirable, as this will tend to keep both
coal dust and shale dust down, besides making the
application of the shale dust more easy. Occasional
watering of the floor will also help, or application of
hygroscopic salts, such as calcium or magnesium
chloride. It does not seem desirable to grind up the
shale dust too fine, as the probability of grains of silica
being thereby broken up would be increased.

The facts which indicate that even coal dust or shale
dust has, in the long run, some prejudicial effect on the
lungs, make it the more necessary to be very cautious
as to the use for stone dusting purposes of any material
as to the effects of which on the lungs there are good
grounds for suspicion.

Summary.

(1)	Both from human experience in coal mines and
from experiments on animals there is clear evidence that
shale dust, when inhaled, is no more deleterious than
coal dust, so that shale dust may be used quite safely
for stone dusting in coal mines.

(2)	Flue dust, when inhaled, produces in animals
effects which point to the conclusion that it may be
unwise to employ it for stone dusting in mines.

(3)	Indications are given as to what varieties of stone
dusting material may be used in mines without detri-
ment to health.

(4)	It is desirable from the point of view of health to
reduce, as far as practicable, the inhalation of any kind
of dust in mines.

APPENDIX.

Experiments on the Inhalation of Different Varieties of Dust.

By A. Mavrogordato, M.A., M.R.C.S., L.R.C.P.

This report is an account of a portion of an investi-
gation undertaken for the Medical Research Committee
under the National Insurance Act, and deals with an
attempt to ascertain whether certain materials can be
safely used for stone dusting.

Since, under industrial conditions, miners are exposed
to mixed dusts, and neither the clinical history nor the
post-mortem examination can settle which dust, if any,
was at fault, in these experiments guinea-pigs were
exposed in groups to particular dusts, each group to a
single variety of dust. The dusts so far used were four
in number—coal, shale, flue dust, and quartz dust from
the Transvaal gold-bearing reef. Six guinea-pigs were,
in each series, placed in a box, and, by means of a fan,
a thick cloud of dust was kept in the atmosphere. In
each series there were 12 such exposures, each lasting
about two hours. The animals were killed by coal gas
at intervals varying from an hour to four months after
the last exposure. The lungs were removed, fixed, and
stained for microscopical examination. Films were also
made from the cut surfaces of the lungs immediately
after death with a view to learning whether there might
be any variation in the cytological reaction to the
different dusts. The sections were also studied with
crossed Nicols and a rotating stage, as by this means
an attempt has been made to recognise crystalline quartz.

* Sixth Report of Explosions in Mines Committee, p. 13.

I At the same age period the death rates from phthisis are
2-2 among all occupied males, 1-8 among coal miners, 1-0
among farm labourers, and 1-5 among Notts and Derbyshire
coal miners. The relative immunity of coal miners to phthisis
lasts, therefore, up to old age, though they are more liable to
bronchitis in old age.

Crystalline silica has about the same refractive index as
balsam, the ordinary mounting medium : consequently
it may not be visible by transmitted light, but owing to
its property of double refraction, may be brought into
view if examined with crossed Nicols by polarised light.
As a control, various dusts were examined in balsam.
While it is, of course, possible to recognise different
crystals by suitable optical methods, I have not hitherto
found this simple expedient at all useful. Many dusts,
e.g., powdered pumice stone, behave in a similar fashion
to silica, and many minute fragments which are certainly
not silica are brought out when a diseased lung is thus
examined.

The lungs consist essentially of large tubes, the
bronchi, rapidly breaking up into small tubes, the bron-
chioles, which terminate in blind extremities consisting
of bunches of small sacs, known as alveoli. Each sac
is a thin film of cells, and might be compared to a bubble
containing it its walls a basket-work of minute blood
vessels. The whole lung is pervaded by a scaffolding of
connective tissue, partly fibrous and partly elastic. The
main bronchi and blood vessels lie in the main trabeculae
of this tissue, which is largely fibrous in this coarse
region, and elastic where its fine divisions support the
alveoli. Dust, when inhaled, passes down the tubes
and into the alveoli. On arrival in this region it acts
as an irritant, causing proliferation and shedding of the
alveolar cells. These cells rapidly take up the dust.

General Results.—None of the guinea-pigs of our series
suffered obvious ill-effects as the result of dusting, and
out of 40 used only one died in the course of the five
months during which the work has been carried on.

The general sequence of events was in most respects
the same in all cases. In animals killed just after the
last exposure, dust was found ii> the bronchial tubes,
free in the alveoli and in the cells. Many of the cells
had been cast off, and dust was found both in these and
in cells in situ. The free dust mostly disappears both
from the bronchial tubes and the alveoli within three
days, but the cell proliferation at first increases, and
there is considerable congestion of blood vessels. Some
of the dust-laden cells pass to adjacent lymphoid tissue,
and in many of the small bronchi one finds plugs con-
sisting of mucin, dust, and cells in various stages of
breaking down. By the 10th day the free cells are com-
paratively few, but the fixed cells containing dust are
present in numbers giving, in the severer cases, the
appearance of areas of broncho-pneumonia. Even these
areas gradually clear up, and though some of the lungs
from animals used four months ago still contain dust,
it is obvious that the whole lung is on its way to com-
plete recovery. In none of our cases, with compara-
tively mild exposures, have we produced either fibrosis
or pleural lesions. With severe exposures, Arnold pro-
duced fibrosis with emery and sandstone dust, and
Beattie produced it with emery, carborundum, grind-
stone, and other dusts. Where fibrosis has been pro-
duced it presumably persists.

Comparative Results.—The experiments fall into two
groups : (1) The guinea-pigs exposed to coal and shale;
(2) those exposed to Transvaal dust and flue dust. While
about the same quantity of dust appeared to find entry
in each case, the reaction was much slighter in the
animals of group 1 than in those of group 2. Not only
was there less cell proliferation, but the dust was more
readily got rid of. In the case of the shale, the dust
disappeared completely after three months, and the
lungs appeared normal. In the case of the coal, isolated
dust cells were still to be seen after four months, but
there were no areas of condensed lung tissue. In both
the Transvaal and the flue dust series, the reaction was
much more marked and lasting—it was most marked
with the latter. Considering the state of the lungs, it
was surprising that the animals showed no evident con-
stitutional symptoms. Even in these cases the lungs
were clearing up, though in specimens taken from
animals killed four months after the last exposure there
were still patches of proliferation and condensed lung
tissue.

Two further series of experiments have been partly
carried out; one with flue dust and one with shale dust.
The duration was the same as in the previous cases, but
the exposures were more severe, the dust cloud being
maintained at a greater degree of intensity. The shale
dust animal so far examined presented surprisingly little
reaction; for some reason less dust appeared to have
gained access to the alveoli than in the previous series,
and only very fine particles were to be seen. It
may be mentioned that the guinea pigs used were
younger and smaller than those of the earlier experiment.
There was but little cell proliferation, and the blood
vessels were not congested. The corresponding flue dust
guinea-pig repeated the results obtained in the earlier
series, and presented them to a more intense degree.
The flue dust used was from a different colliery to the
sample previously employed. There was a curious
absence of free dust in the alveoli, although there were
large numbers of free dust-laden cells.

Examination of Films.—The cells found on the films
were partially lung cells and partially blood cells. The
lung cells were of the large and small endothelial type,
the former preponderating in the earlier stages, the
latter in the later. It wras the large cells that were
especially dust-laden. Fragments of dust-laden non-
nucleated protoplasm were to be found on the slides,
presumably broken off from the large cells. The
typical granular cell of the guinea-pig’s blood is of the
eosinophil type, and these occurred in varying propor-
tions in all the films, but though dust was to be found
in them, it was not at all common.

The endothelial cells from the lungs are also granular
in some cases, and when stained by Leishman’s method
both baso-phil and acido-phil granules were to be seen,
but not in the same cell. No definite qualitative differ-
ence has been so far made out in the cytological reaction
with different varieties of dust, but the experiments are
being continued.

SOUTH AFRICAN MINERS’ PHTHISIS
PREVENTION COMMITTEE.

Special Report on Injurious Mine Dust.

The report deals with the percentage of injurious particles
in mine dust, and the results of counting the particles of
dust in the air. The committee made tests of dry and wet
drilling under various conditions, as far as possible on the
same mine, the Village Deep. The tests for the efficacy of
water blasts were made consecutively in one development end.
A tabular statement attached to the report gives full particulars
of each of the samples taken. The Commissioners remark :
“ During our investigations it was found that, in the use of
Leyner drills, care has to be taken that these do not become
so leaky as to atomise the water used, unless such water is
clean water, free from sediment. In the case in point, mine
water from the pump column was being used, and was being
sprayed into the air by leaks from the machine, causing a
dense fog. The sediment in the water consisting largely of
very fine injurious silica particles, was thus being transferred
to the air and into the lungs of the person inhaling such air.
The water contained no less than 23 million particles per
c.c., and it was found that the dense fog created contained
9-2 c.c. of sprayed water per cu. m. of air, so that 210 million
particles were derived from this source. The number of
injurious particles per cu. m. of air was thus being increased
from about 29 million particles derived from the drilling
operations to 239 millions. It is obvious that similar con-
tamination of the atmosphere takes place when dirty mine
water is being atomised at any point of the mine. It is
probably as dangerous to breathe the foggy air caused thereby
as the clear air left after the evaporation of the fog. For
atomising purposes only water quite free from injurious sedi-
ment should be used. A further point that emerges from our
investigations is that, as a measure of the injurious character
of any air breathed, the number of particles of dust per cu. m.
is a better criterion than its weight. A small number of
comparatively innocuous large particles add greatly to the
weight, but not to the count, of the particles of dust, as was
shown by the fact that in the great majority of instances the
number of very fine injurious dust particles exceeds 98 per
cent, of the total.”

The Findings.

Having analysed the results of wet and dry drilling with
a variety of drills, the committee summarises its deductions
as follow :—

(а)	Blasting operations produce enormous quantities of
dust, the great bulk of which is very fine, and of a most
injurious character. Its inhalation should be avoided at all
costs.

(б)	Machine drilling without water produces a smaller
quantity of dangerous dust than blasting, but the amount is
still very large, and is liable to be inhaled over a much longer
period than that produced from blasting operations.

(c)	By the use of water applied in a proper manner with
suitable devices, the dangerous dust during drilling can be
diminished to a small fraction of that produced when drilling
dry.

(d)	In drives and similar confined spaces the amount of
dangerous dust produced by blasting operations can be
reduced by the application of suitable water blasts for a period
of half-an-hour, to less than 1 per cent, of its original quan-
tity, and is then comparatively innocuous.

(e)	The imperative necessity of using proper devices for
laying dust and of constant vigilance in their application is
emphasised.

(/) The dangerous character of any dust contained in mine
air is more nearly gauged by the number of particles in
suspension than by their weight.

(g)	In laying the dust by means of water, the very fine
injurious dust is laid in practically equal proportions with
the less fine dust.

(h)	Ordinary mine water should not be used for spraying
by means of atomisers, and where such water is used in a
Leyner drill, the latter should be discarded if the air-leaks
are such as to atomise the water, and cause a fog.

(i)	The dust in crusher houses can be easily rendered
innocuous if reasonable precautions are taken.

(j)	It may reasonably be hoped that the adoption of proper
and readily applied methods of dust laying, and of pre-
cautions in avoiding the inhalation of air charged with dust
from blasting, has led, and will continue to lead, to a marked
decrease in the incidence of miners’ phthisis.

The Institution of Mechanical Engineers. — An ordinary
general meeting will be held on Friday, December 17, at
6 o’clock p.m., at the Institution of Civil Engineers, Great
George-street, Westminster. A paper on “ Engineering
Colleges and the War,” will be read by R. Mullineux
Walmsley, D.Sc., F.R.S.E., and C. E. Larard.

Hull Coal Exports.—The official return of the exports of
coal from Hull to foreign countries for the week ending
Tuesday, November 30, is as follows :—Amsterdam, 1,315
tons; Aalesund, 25; Bahia Blanca, 1,843; Boulogne, 1,362;
Buenos Ayres, 3,288; Calais, 1,269; Christi a ns a nd, 44;
Christiania, 5; Dunkirk, 1,899; Dieppe, 3,214; Gefle, 1,748;
Gothenburg, 4,977; Halmstadt, 738; Harlingen, 1,408;
Honfleur, 622; Norrkoping, 1,378: Rouen, 24,025;
Rotterdam, 3,085; South Georgia, 2,034; Stockholm, 1,109;
Treport, 631; total, 56,019 tons. The above figures do not
include bunker coal shipments for the British Admiralty or
the Allies’ Governments. Corresponding period November
1914, total 20,179 tons. Corresponding period November
1913, total 112,078 tons.

Important Wagon Owners’ Meeting in London. — On
Monday last, at the London Coal Exchange, a mass meeting
was held -to take into consideration the Board of Trade
recommendations that all coal wagons should be “ pooled ”
in order to facilitate the quicker movement of rolling stock
generally, and from the railway point of view, to enable
empties to be loaded and utilised for the conveyance of
material from the Metropolis and other large centres info
the Midland and northern colliery areas. Mr. Geo. C.
Locket, J.P., and Mr. Geo. Rose voiced the opinions of
the London owmers of coal wagons, and it was unanimously
resolved to oppose the recommendations as far as private
owners were concerned. The original proposal was under-
stood to have reference to the “ pooling ” of railway com-
panies’ wagons only, but now that the proposal purports to
include all private owners’ wagons it was viewed with con-
siderable misgiving and apprehension. The larger owners of
lolling stock would be entirely at the mercy of the railway
companies and the colliery companies; and by many of the
principal traders it was felt that it wrould be an impossibility
to carry on their business unless they controlled a certain
number of their own wagons.