May 17, 1918.

THE COLLIERY GUARDIAN.

997

by an aged workman or a “ compensation ” man who
has the use of both hands. Only one person is
required, and his duties are very light indeed, the
only work entailed being that of carrying the sprayer,
which is not heavy.

But the most essential point of the method is its
effectiveness. The sprayer sends such a cloud of dust
along the roadway and into the workings as they get
nearer the coal face, that the operation cannot be
carried on during working hours. Consequently it
has to be done between shifts, when the general body
of workmen are out of the mine.

AN INSTANTANEOUS OUTBURST OF
COAL AND GAS*

By F. N. SlDDALL.

The Trencherbone seam of South-west Lancashire
is very subject to “ washouts.” In large areas the
seam is entirely or partly missing, or “ washed out.”
Such an area is supposed to exist over the greater
part of the royalty worked by Messrs. John Speakman
and Sons at their Bedford collieries, near Wigan,
and it was with considerable doubt that they sank
their shafts, but they persevered and eventually found
the seam of good workable thickness round the shafts.
In view of the fact that adjacent collieries had found
barren ground in the locality it was necessary to
proceed with caution in laying out the workings, and
headings were driven in various directions to prove
the existence and extent of the “ wash out ” or
“ want.” In one part of the workings three headings
to the rise of the seam were driven for 700 or 800
yards, without touching barren ground; from these,
other headings were driven in a level direction, some
of which touched the washout on one side, but not
on the other. In March last, one of these exploring
levels had reached a point some 150 yards from the
last main brow. The seam had not emitted any extra-
ordinary volume of firedamp—in fact, the amount
of gas given off had been comparatively small, and
ventilation was maintained with ease. Previous to
driving the level mentioned, a fault 14 ft. downthrow
was encountered in the brows and passed, and the
coal afterwards remained of normal quality and thick-
ness up to the day of the occurrence now to be
described.

An experienced collier was working in this level
on March 18 last, maintaining the face of his working
parallel to the cleavage of the coal; in other words,
“ working face on.” The cleavage, or “ facings,” in
the seam made an angle of some 30 degs. with the
level direction. At 12-40 p.m. he noticed that water
was beginning to issue out of the floor against the
face, so he sent his drawer for the fireman. Thinking
that either the floor would lift, or the roof come
down, he proceeded to erect a wooden bar close to
the face. The coal face at this time, having just been
cleaned up, was vertical and solid from floor to roof.
The fireman came along directly and found the water
boiling up, some 6 in. high, from a crack in the
floor against the face. On putting his lamp down
to it to get a better view, he found firedamp was issu-
ing with the water, and at once ordered the drawer
to take the tub out, and also told the collier to gather
up his tools and retire. The collier suggested stop-
ping to finish setting the prop under the bar
already erected, and the fireman offered to help him.
Up to this time there had been no sound of cracking,
settling, or “weighting” of the roof, and the place
seemed perfectly safe and quiet. The collier knocked
up the prop and turned to retire along the higher
side of the place above the brattice cloth. The fire-
man bent to pick up his lamp, when a large portion
of the solid coal face blew off like a cannon shot,
the place being instantly filled with coal dust and
firedamp. The fireman’s lamp was buried in the small
coal, and he himself was knocked down and rolled
over by the blast. The drawer, who had gone some
50 yards down the level, said that the air was instantly
reversed by the gas. All lamps in the near vicinity
were put out by the heavy concussion. The fireman
obtained a lamp from some workinen outbye and
returned to examine the face. He was just able
to get about 170 yards from the face by crawling
with his lamp on the floor. He found that a wedge
of solid coal, 4 ft. in thickness, had been blown off
the face in a cone-shaped formation. The sides of
the cone were all as smooth as if cut by a fine
pick. In the middle of the face there was an oval
hole 12 in. wide and 20 in. high out of which gas was
blowing like steam from a broken steam range. A
bank of small coal, some of it ground to the finest
dust, lay piled along the floor for 10 yards to where
it struck the side of the heading, which was plastered
with the small coal. The coal had blown out the
prop and bar just set, and four others. The fireman
fenced off the level, collected all the men in the
district, and retired He then reported the occurrence
to the under-manager.

It was afterwards discovered that a cavity existed
beyond the oval hole, which was in shape somewhat
similar to a kidney bean, and had the general dimen-
sions of 8 ft. in length, 3 ft. in width, 3 ft. in
height. The cavity was partly filled with small coal,
of which samples have been preserved. Some breaks
or crevices were visible at the extremities of the
cavity, and it was noteworthy that the coal in the
cavity was rusty, thus showing the action of water.
The fireman and the collier said the level was dry
previous to the outburst, and that the coal and dust
in the outburst were dry also at first, but that water
followed. It was estimated that at least 2,000 gals,
of water had issued from the cavity since the
occurrence.

It is worthy of note that this is a virgin field of
coal; there are no workings in the seam within many
hundreds of yards, and those are on the other side
of washouts. The seam at the scene of the outburst

* Paper read before the Manchester Geological and
Mining Society on May 14.

is 4 ft. 4| in. thick, and a further thickness of 14 in.
of inferior coal known as ‘‘ callis ’ ’ is left up as a
roof. In the section there are two bands of very
hard coal. The seam has a general dip of 1 in 16.
It is about 620 yards deep at the shaft, and the
place of the accident, being in the rise, is some 500
yards from the surface. No faults are known except
the one in the brows already mentioned. The seam
is separated by some 200 yards of cover from old
workings, both above, in the Bickershaw Seven Foot
seam, and below, in the Yard seam. Up to the time
of the occurrence the coal in this level had been
particularly hard and dense, even for the Trencher-
bone. It was much harder than usual for the last
three yards approaching the hole, except that while
driving the last half yard the collier found a soft
patch 4 ft. long from the cutting in the lower side
at about a foot high from the floor. There is no
change known at present in the strata round the place.
There are no clay facings, but a break or crack occurs
in the floor against the face 4 ft. long from the
cutting in the lower side. The quantity of air passing
is 2,000 cu. ft. per minute, measured at the bottom
of the last opening cut through. The quantity of
gas given off when the outburst occurred was 22,600
cu. ft., and it filled the level for 110 yards, and also
the openings as shown in the plan. The weight of
the coal blown out of the hole was taken very care-
fully and found to amount to 25 J cwt. A noticeable
feature is that this coal is so small that it appears as
though crushed in a grinding mill. Gas was still being
given off 67 days after, the occurrence. Up to Friday,
May 10, the amount of issue was practically the same
as immediately after the outburst, that is to say,
it was not possible before that date to get to the
face with a safety lamp. A lamp would be extin-
guished some 10 yards from the face. At present
there is about 2| to 3 pei’ cent, of gas at the face,
and it can be heard bubbling through the water in
the floor. No more water has been given off since the
first flush came.

The following accounts of previous similar outbursts
have been published in the Transactions of the
Federated Institution of Mining Engineers.

Vol. 1, p. 27-29. Account of an outburst of gas
in the Haigh Moor seam at Whitwood Collieries, by
Wm. Jackson. This outburst occurred in a drift being
driven through a washout, and caused an explosion.
Several of those who took part in the discusssion
advised boring in advance as a preventive measure.

Vol. 3, p. 1070. This is an extract from the
Annates des Mines, relating to outbursts of gas at
French collieries. Many exceedingly sudden out-
bursts of coal and gas occurred at the Mines de
Besseges between 1886 and 1892, and are also referred
to in the Transactions. Many hundredweights of coal
were blown into extremely fine dust which filled the
workings and blackened areas of land around the
shafts. The emission of gas ceased with the projection
of the coal. All occurred in narrow headings, 8 in
down runs, 6 in levels, and 5 in stone drifts. In 11
cases they occurred near faults. Cavities were after-
wards found in the coal, and between the coal and
the roof. The authors suggested that gas existed in
a free state in the cavities, and was also contained
in porous coal particles, “ and that it was to the
existence of these cavities exposed by boreholes, pick-
work, or shot firing, that the instantaneous outbursts
were due, which, once commenced, were propagated
in consequence of the rupture of equilibrium.”

A paper by Mr. John Gerrard on “ Instantaneous
Outbursts of Firedamp and Coal at Broad Oak
Colliery, Ashton-under-Lyne ” (Transactions, Vol. 18,
pp. 251-8), which was read at the general meeting of
the institute held at Sheffield in September 1899,
relates the facts concerning 20 outbursts of coal and
gas, four or five of which caused fatalities by smother-
ing the men in fine coal dust. The seam was
eventually opened out on longwall instead of pillars,
and no further outbursts occurred In the discussion
on that paper there appeared to be a general con-
sensus of opinion that the longwall system of working
generally obviated the occurrence of such outbursts.
Boring was considered to be of very little use as a
preventive. Pressure of gas existing in the coal was
regarded as the cause of such outbursts, and the
places liable to such mishaps were those in which areas
of soft or disintegrated coal alternated with harder
coal, which might be more impervious to gas.

Vol. 10, p. 56. Mr. J. Ashworth gave an account
of “ Outbursts of Coal and Gas at Morrissey Collieries,
British Columbia.” The coal seam was very thick,
varying from 14 to 40 ft., and was worked into pillars
by comparatively narrow headings. Huge outbursts
of coal occurred from time to time, 3,500 tons of coal
being blown off the face at one of these outbursts.
The coal was very soft and the mine was eventually
abandoned as no means could be found to work it
with safety.

Mr. William Walker, the Acting Chief Inspector
of Mines, has called the attention of the author to
a case of an instantaneous outburst which occurred
at Valleyfield Colliery, Scotland, and was recorded in
his report as Chief Inspector in Scotland for the year
1911. In that case the longwall method could not
be adopted, as the places where the outbursts occurred
were in the shaft pillar. Boreholes were proved in
this case to be useful in giving warning of gas coming
off and easing the pressure under which it was given
off. Mr. Walker agreed that “ where the longwall
method can be worked the gas will be given off much
more gradually, aiid the pressure therefore consider-
ably lessened, but it is not always possible to adopt
this method of working, and in such cases boring is
most useful.”

The author ventures to think that the conclusions
to be drawn from the foregoing records might be
summarised as follow : —

(1)	Outbursts of coal with gas are liable to occur
in coal seams where the nature of the coal varies from
hard to soft in patches.

(2)	Such outbursts are so much more liable to occur
in headings, particularly when the headings are being

driven rapidly, than in longwall working, that the
longwall method may be said to obviate them.

(3)	Boring is not an absolute preventive, but in
cases where the longwall method cannot be adopted,
boring is useful in giving warning, and to some extent
in lessening the pressure at which the gas is given
off.

(4)	Outbursts are unlikely to occur when the depth
of the seam is less than 400 or 500 yards from the
surface.

REFRACTORY MATERIALS.

The Refractory Materials Section of the Ceramic
Society held a meeting at Sheffield University on May 14
and 15, the president, Mr. W. J. Jones, Deputy-Con-
troller of Iron and Steel Production (Ministry of
Munitions), occupying the chair.

After the Vice-Chancellor had welcomed the
section on behalf of the University authorities, the
programme commenced with a paper on “ The Supplies
of Refractory Materials available in the Sheffield
District,” by Prof. W. G. Fearnsides.

Mr. J. Holland followed with “ Notes on the Evolu-
tion of the Ganister Industry in the Sheffield District.”
This was mainly historical, it being noted that ganister
was originally used for road metal, then for lining the
holes of crucible furnaces (being got for this purpose by
scraping the roads), by Huntsman, between 1742 and
1772, and gradually came into extensive use. Two
papers by Dr. A. Scott, on the “ Constitution of Silica
Bricks ” and a “ Micro-Study of Magnesite Bricks ”
were chiefly concerned with microscopic observations.
The last contribution during the morning sitting was by
Mr. Alleyne Reynolds on the “ Essential Properties
of Refractories used in Steel Production.” His main
contention was that in the final treatment of steel it
should not come into contact with acid materials at all,
but that neutral inactive refractory should be used, if a
suitable substance can be found.

At the afternoon session two papers by Dr. A. Bigot
came first, on “Silica Refractories (Raw Materials) ”
and “ Refractory Materials derived from Bauxite.”
Perhaps the most important point connected with the
first of these was the assertion that heating siliceous
material to 1,710 degs. Cent, enables a satisfactory
opinion to be formed as to their suitability for making
silica bricks.

The next paper, by Mr. E. Steiger, related to a kiln
for magnesite, cement, etc. Then followed Mr. H. V.
Thompson’s contribution on the “ Dissociation of Salt,”
which has some bearing on coke-oven practice, for it
was shown that salt vapour in the presence of water
vapour acts on silica, ferric oxide, alumina, and clay,
the products in the case of silica and ferric oxide
being an insoluble silicate of soda, and crystallised
magnetic iron oxide respectively. In the case of alumina,
analysis indicated the possibility of formation of an
aluminate of the empirical composition 2 A12O3, 9 NaoO.
Greater action was noticed in the case of clays, but
this was not studied in detail.

The last paper read in the afternoon was by Mr. J. P.
Leather, on “ Refractories in Gas Works from a User’s
Point of View.” (See p. 999.)

Increase of Home Supplies.

The President stated that the average output of
refractories for munition purposes alone amounts to
200,000 tons per month, or 720,000,000 bricks per year.
The output of silica bricks has increased from about
74 millions per month to between 11 and 12 millions.
The position as regards magnesite bricks is also safe,
the quality also showing continual improvement.

Methods of Manufacture Criticised.

There is still room for improYement as regards the
processes for manufacture of silica bricks, firebricks,
and coke-oven bricks, but careful investigations are in
progress, and it is hoped that more attention will be
given to details which greatly affect the results.
Improvement will certainly be necessary to maintain
the position in the industry under normal competitive
conditions. Special attention is needed with respect to
refractories for electric furnaces.

On Wednesday Dr. J. W. Mellor presented the first
Report of Committee on the “ Standardisation of Tests
for Refractory Materials.” This included the following
items:—

I. Details for Analysis of Fireclays, Raw Ganisters,
Quartzose Rocks, and Manufactured Products. II.
Details for Analysis of Dolomite and Magnesite,
differing slightly from those given in I. III. The
Identification of the various forms of Silica in Silica
Bricks. This has been specially drawn up by Dr. H. H.
Thomas. IV. Tests for Porosity, Water Absorption,
and Specific Gravity. V. Shrinkage Tests for Clays on
Drying and Firing. VI. Tensile Strength of Dried
Clays. VIII. After-Contraction or After-Expansion
of Refractory Materials. VIII. Normal Refractoriness
of Firebricks, Fireclays, etc. IX. Refractory Test under
Load. X. Thermal or Reversible Expansion of Refrac-
tories (Hot and Cold Sizes of Firebricks). XL Crushing
Strength—Cold.

While the proposed tests were in general favourably
received, there was some criticism, mainly on the ground
that some of the tests are not suitable for works labora-
tories. But it was pointed out that tests which would
satisfy the requirements of works laboratories would not
be equally satisfactory as standard tests.

The remainder of Wednesday morning’s programme
consisted of two notes—one on “Electric Furnace
Treatment of Refractories,” by Dr. R. S. Hutton, and
the other on a “Firebrick from the Crown of an Electric
Steel Furnace,” by Mr. W. J. Rees.

In the afternoon members availed themselves of the
opportunity to inspect, in three separate parties, the
works of Messrs. Steel, Peech and Tozer Limited, John
Brown and Company Limited, and Vickers Limited.

In the evening a lecture was delivered by Mr. Cosmo
Johns on “ Science and the Practical Man.”