954

THE COLLIERY GUARDIAN.

November 17, 1916.

colour, and the cloud raised by merely blowing lightly
on the sides was also white. Then the film covering
the stone dust was not composed entirely of coal dust.
It contained at least 28 per cent, of incombustible
matter, if the road had been properly treated. The
existence of this proportion of incombustible material
in the suspension dust film would in itself ensure that
degree of violence necessary to disturb the stone dust,
independent altogether of the resistance caused by
the irregularities of the roadway. He was quite
in agreement with Mr. Ashworth that the dilution
of this film to the greatest possible extent was
essential to the success of any stone dusting opera-
tions as far as haulage roads were concerned. He did
not think that a barrage formed by a stone dust
zone, or by blowers perpetually throwing dust into
the atmosphere, would alone solve the problem.

Dust v. Water Zones.

Certainly a 75 per cent, mixture would not be sufficient
on such zones unless they were at no great distance
apart. The greatest asset stone dust possessed was its
capacity to prevent ignition, and that alone gave
sufficient reason for making its use general instead of in
zones. If zones were to be relied on, then a watered
zone of sufficient length was the best, but such a system
could only limit the extent of an explosion. On the
other hand, there was good reason to believe that the
general use of stone dust would in many cases prevent
ignition and would always mitigate the violence, and
with certain exceptions, which were still being narrowed
down, would stop propagation. Mr. Ashworth asked
why protection was needed for electric cables. He
(Mr. Budge) admitted that with a system of double
armoured cable independent earth wire, and with neutral
point earthed at the lower station there should be no
flame from a cable underground provided that the trip
gear was in working order. Still, protective devices
might get out of order, and the flame from a breakdown
of a cable might or might not be capable of igniting coal
dust. He had known a lightning discharge travel through
lightning arresters (which were set wrongly) pass through
the sub-station gear and blow out the armoured cable
at the bend at the pit bottom. The flash was blinding.
The shaft was wet, kept purposely wet by allowing
garlands to overflow. Coal dust had been ignited by
electricity in a laboratory, but not quite in such circum-
stances as would justify the belief that the flame from
a cable underground would cause an explosion with
coal dust alone. It all depended on the relationship
between the flame from a failure in a cable and that
from a blown-out shot. The chances were against the
arc igniting coal dust, but until information based on
experiments was available, he had thought it necessary
to adopt some protection for the cables.

Proposed Experimental Gallery.

Sir "William Garforth, who was cordially greeted,
in the course of an interesting address mainly treating
of the history of stone dusting for minimising the
explosive effects of coal dust in mines from the time of
the Altofts explosion some 30 years ago, which had first
served to direct his attention to the subject, suggested
that the Welsh members of the council of the Mining
Association should ask the Government to allow them
to have the use of some of the tubes now lying idle at
Esk meals for the purposes of a gallery to represent as
far as possible the average coal face in local mines.
Fitted up at a convenient distance from Cardiff, they
might conduct experiments in the gallery, under the
supervision of a committee, to test the efficacy of stone
dust in pure coal dust and in coal dust and gas, the
chances of ignition of gas by the electric arc in connec-
tion with mechanical cutters, and in other ways to try
and solve the problem of coal dust at the face.

Mr. Hugh Bramwell said it appeared, from what
they had heard, that the cleaning of the roads was a
necessity if stone dusting was to be efficient, which, of
course, meant the absolute brushing of the sides and
roof. One must bear in mind that the very operation
of cleaning was dangerous. They were raising clouds
of dust in the mine, and, as Mr. Budge said, it could
only he done at week ends, and they might be trans-
ferring quantities of dust from comparatively safe
places to places where greater danger might exist. This
consideration had been pointed out by several speakers
who had taken part in the discussion, but he thought it
ought to be emphasised. No doubt the heavier particles
of dust, when the cleaning operation was in process,
could be caught by sprays or water shields, several types
of which had been introduced into the coal field with
comparative success, but he believed every observer
would tell them that the really fine coal dust penetrated
any spray and travelled fast. Now, that must go either
into the workings or by short-circuiting into the upcast
pit, or, as Mr. O’Connor suggested, up the downcast by
a reversal of the ventilation. To reverse the ventila-
tion in a Welsh mine was a thing that most of them
would not like to do. He only wanted to emphasise
this point as to cleaning the roads—that it was
in itself dangerous andmightlead to greater dangers than
previously existed; at the same time, it was a necessary
danger if stone-dusting was not to lose the whole or
part of its efficacy. It should not be overlooked that
the two remedies, watering and stone dusting, were
distinct in character. Watering had been very largely
practised in South Wales for the last 25 years. Its
object was to destroy—to kill—coal dust absolutely.
In an ordinary damp mine no dust was seen. In some
in South Wales there was no dust at all; whilst the

same seam only a short distance off might be found to
be extremely dry and dusty. Stone-dusting was simply
dilution of coal dust—nothing more; watering, on the
other hand, as he had said, destroyed coal dust.

Specific Gravity of Goal Dust.

Therefore, he could not agree with Mr. Budge’s recom-
mendation that, f>*r shot firing, stone dusting was
preferable to watering. Mr. Budge stated in his paper
that the specific gravity of coal dust passing through a
180 sieve was 0*475. In view of the well-known specific
gravity of coal, and therefore also of coal dust, he
imagined that Mr. Budge had something different in
his mind from what was ordinarily understood by the
specific gravity of a material. Then he noticed with
regard to Mr. Budge’s collection of dust that his results
were rather less in quantity, if calculated out per cubic
foot of space, than those obtained in the experiments
made in a number of collieries in that district by
the Treforest School of Mines, and published by the
Colliery Officials Association, and this notwithstanding
the fact that Mr. Budge’s tests were made after he
had used stone dust, when there ought to have been
more dust—coal dust and stone dust—in his roads than
in the roads tested by the Treforest School of Mines.
This difference, of course, might be due to different
conditions. He noticed in one or two parts of the paper
Mr. Budge referied to naturally wet roads and compara-
tively wet roads, which would apply to the Monmouth-
shire area of the coal field, while the Treforest School of
Mines tests were in collieries in the Rhondda area. As
a matter of fact, there was a great difference in the
amount of dust present in the Monmouthshire section
compared with the drier mines of, at any rate, the
lower part of the Rhondda Valley. Then there was the
question of taking the samples. It was agreed that the
samples they desired to get were what Mr. Budge called
the suspension dust—the dust that was normally in
the air and was being momentarily deposited in
the mine. Dust brushed from the sides and roof was
different in character from the dust collected on
plates from the air. Mr. Budge tested both simul-
taneously. The dust he brushed off roof and sides he
analysed for ash content, and at the same time and
in the same place he collected the dust deposited
from the air and similarly tested it, with the result
that one sample was quite incomparable with the other
in ash content. In each case the sample obtained by
brushing was comparatively high in ash content, due
to the stone dust, whereas the sample deposited from
the ah' was invariably lower—generally running in the
neighbourhood of about 20 per cent, of ash, while the
brushed samples ran up to 50 per cent, or more. Now,
if Home Office new rules or fresh legislation had to be
faced, and no doubt they would have to be faced, there
must be laid down some standard method of taking dust
samples, otherwise there would be hopeless confusion.
Before any rules and regulations were made it was
absolutely necessary that very many more experiments
should be carried out on this question of taking samples
underground. The method of taking these samples
at present was very crude, and perhaps some ingenious
person would invent something better and more
reliable. But unless some standard method was de-
vised it would be found they would be talking of
different things and nobody would exactly know what
was meant.

Arching and Watering.

Mr. W. W. Hood said with regard to Sir William
Garforth’s suggestion, the Committee of the Treforest
School of Mines had already decided to ask the
Government to lend them tubes from Eskmeals for six
months to experiment with under conditions prevailing
in South Wales. He adhered to his view that the only
real remedy for the stoppage of propagation in Welsh
collieries was by arching and watering. At Altofts no
doubt it would be madness to water, and therefore the
next best thing was stone dusting. If stone dust was
distributed at the face during the night shift it would
very soon be covered with a thick layer of coal dust,
especially where conveyors and coal cutters were used.

Mr. Edgar C. Evans, B.Sc. (Glamorgan Collieries),
congratulated Mr. Budge upon having presented to
the institute the most complete, exhaustive, and
scientific description of st-ne dusting experiments that
had yet been introduced into mining literature. On the
subject of specific gravity, as had been pointed out, the
specific gravity of coal would be in the region of 1*2 to
13, while, as Mr. Budge indicated, the specific gravities
of coal dust and stone dust, to pass through a 180 sieve,
were respectively 0*475 and 0 795. He could quite
understand the cause of the figures Mr. Budge had
obtained, because when they were dealing with
such exceedingly minute particles a number of
factors came into consideration which bad to
be accounted for. The paper contained a most
interesting series of figures relating to the analyses of
suspended dust. Mr. Hood had pointed out that the
results were lower than those obtained in the experi-
ments of the Treforest School of Mines; and in order to
compare the two sets he would ask Mr. Budge to give
them the exact dimensions of the roadway in which his
samples were taken and the distance from the down-
cast. Under the conditions at Mr. Budge’s collieries
it was possible to get a suspended dust with an ash
content of between 40 per cent, and 50 per cent, con-
tinuously ; but he did not think it wrould be possible to
get the same in some of the more dusty collieries in the
Rhondda. As to the proprotions of stone dust and coal

..	..■! ........................   ■..... . ■IIIIMBh

dust, before accepting the 50 per cent, as absolute
safety he would have to see certain discrepancies in the
British, French and American experiments reconciled.
Let them, by all means, go on stone dusting and
watering, but do not let them think they had secured
absolute safety when they obtained a 50 per cent,
mixture in the main haulage roads of their collieries.

Ash Content of Dust.

Mr. Robert Clive (Doncaster) wrote that it could
hardly be disputed that if the dust on all roadways
leading from the shafts to the face were treated with
stone dust so as to maintain a minimum ash in the fine
dust of 50 per cent, the result would be a sufficient
safeguard to warrant the expenditure, even if there was
a doubt about the proposition of 1 to 1 being sufficient
to prevent the propagation of an explosion. On the
ether hand, where 65 per cent, ash could be maintained
it should certainly be done. A colliery manager usually
liked to have as high a factor of safety as he could
reasonably get. In a paper read by the writer before
the Midland Institute of Mining Engineers in January,
1914, details were given of 233 samples taken in the
Barnsley seam at Bentley Colliery, where stone dust
had been systematically used for the previous 12
months, an average of 1*27 cwt. per yard being
applied by hand to 14,000 yds. of roadway. The
average ash for the whole mine was 67’46
per cent, although several samples were taken
from roads which had not been stone dusted. With
regard to returns, he agreed with Mr. Budge, except as
to close to the face. Where there was a high velocity
along the face the dust accumulated quickly in the
windway to about 30 yds. back from the face, and the
ash percentage was low. These roads required frequent
application of stone dust within 50 yds. of the face.
Further outbye the dust was deposited much more
slowly, and contained a higher percentage of ash. The
information from samples taken after explosions had
occurred was very meagre, but such as it was it rather
pointed to the fact that a 1 to 1 mixture was very
nearly, if not quite, diluted enough to stop the propa-
gation of an explosion. The Courrieres explosion in
1906, and the Talk-o’-th’-Hill explosion in 1901, for
example, served to establish this. It would be of great
benefit if careful samples were taken in future with a
view to find out the ash percentage at all points where
explosions were presumed to have stopped.

Reversing the Air Current.

Mr. Jacob Ray (Ocean Coal Company) wrote that, to
reverse the air current on the occasion of cleaning
operations would be dangerous, because the cold
air passing through the returns and the warm air
travelling through the intakes, thus causing a difference
in temperature of 20 degs. or more, would have a very
serious effect on the roof, sides and timber in the respec-
tive roadways. It would bring about serious falls of
roof and sides and other dangers. Since Mr. Budge
had stated that watering the floors affected the stone
dust on the lower parts of the sides to a height of only
about 2 ft., he (Mr. Ray) had carefully observed the
intake and the haulage roads of the collieries in his
charge, and had found that this dampness affected the
stone dust up to the roof. This effect was plainly to be
seen on suck timbcr as Norwegian and Swedish, having
no rough bark on it. He found the stone dust covering
the arms in small globules, and the coal dust sticking
to the stone dust, so that it could not be blown off
separately from the latter—a very favourable feature.
Both could be raised together in suspension in the air,
but not so quickly as if the stone dust was perfectly
dry. On the occasion of a recent fall in one of the
main intakes and haulage roads, the overman, who got
at the in-bye side, came out looking more like a miller
than a collier, and he experienced the same effect from
the stone dust as Mr. Budge described.

On the motion of the President, seconded by Mr.
G. D. Budge, the meeting passed a hearty vote of
thanks to Sir William Garforth for making the journey
to be with them on that occasion. The president said
inasmuch as there were othei’ papers awaiting consider-
ation he should have now to declare the discussion on
Mr. Budge’s paper closed. He had no doubt there
were others present who had desired to speak on the
subject, but in view of the late hour be asked them to
send their proposed observations to the secretary for
inclusion in the Proceedings. The hole problem was a
most important one, and they could not have too many
suggestions and criticisms. It afforded him the
greatest pleasure in moving a vote of thanks to Mr.
Budge, to whom all colliery owners and managers were
greatly indebted.

Mr. Hugh Bramwell seconded the proposition of
thanks to Mr. Budge, and it was supported by Mr.
Greenland Davies, H.M.I.M., and adopted with
acclamation.

On the motion of Sir William Garforth, thanks
were accorded to the president.

Hull Coal Imports and Exports.—The return issued by
Mr. W. H. Truman, coal inspector of the Hull Corporation,
states that the quantity of coal brought into Hull during
October amounted to 292,364 tons—275,062 tone by rail, and
17,302 tons by river—as against 365,103 tons in the corre-
sponding period last year. The exports (not including coal
for Admiralty purposes and for the Allied Governments) were
120,773 tons, against 258,722 tons in the corresponding period
last year.