458

THE COLLIERY GUARDIAN.

February 27, 1914.

line silica is included. When ground, it is of a light-grey
colour ; it is, therefore, quite easy to see when stonedust
has been applied on any roadway. The following table
shows the fineness of the stonedust, all of which is
passed through a 3-mesh sieve :—

Per cent.

Through a 3-mesh and remaining on a 10-mesh sieve...

,5	10 „		,> 30	33
	30 „		„ 69	
33	60 „		„ 90	33
	90 „			

10

30

14

8

38

This mixture is found to be more suitable than all fine
dust, which does not “ spread ” well, nor does it dislodge
the fine coaldust anything like so efficiently as the
mixture used.

The stonedust is sent down the pit in tubs containing
about 16 cwt. Where necessary the length of roadway
to be dusted is first cleaned up by shovelling the dust off
the floor. Stonedust is then applied by throwing it in
handfuls on the sides and roof until they have a white
appearance, commencing at the outbye end in the
intakes and in the inbye end in the returns. In some
cases a small hand shovel is used where the velocity of
air is high. One youth will usually “ spread ” about
one and a-half tubs of stonedust in a shift. The length
dusted varies considerably, according to the nature and
formation of the sides and roof and the quantity of fine
dust present before the application, varying from 15 to
30 yards for the first application, and 25 to 50 yards for
subsequent applications. In a measured length of
well-dusted road, with rough sides, timbered roof, and
low velocity of air current, two tubs covered 50 yards.
The perimeter of the sides and roof was 18 ft. giving about
2T lb. per square foot of surface. It may be taken that
the quantity of stonedust required to thoroughly dust a
road varies between 56 lb. and 2 cwt. per yard of road-
way. A good deal of the dust applied falls, of course,
on to the floor, and it is therefore not considered neces-
sary to specially apply any to the floor of the roadway.
Stonedusting can only be done efficiently on the
repairing shift.

The cost of sorting and grinding the stonedust, - inclu-
ding depreciation of plant, is about 3s. lOd. per ton ;
the cost of transport and applying the stonedust is
about 9s. 2d. per ton ; or a total cost of making and
applying of 13s. per ton of stonedust.

Stonedusting was commenced in August 1912, and
during the subsequent 12 months 1,100 tubs of stonedust
have been applied to a total length of 13,800 yards of
roadway (or 1*27 cwt. of stonedust per yard), consisting
of 3,900 yards of main haulage roads, 2,100 yards of
travelling roads, 3,700 yards of main returns, 3,500
yards of crossgates, and 600 yards of roads since
abandoned, &c.

Before determining the conditions as to safety, it is
necessary to know (1) the amount of fine dust, (2) the
proportion that the fine dust bears to the rougher dust,
and (3) the percentage of ash in the fine dust. All these
factors have a bearing on the amount of stonedusting
necessary to make the roads safe. They vary consider-
ably for different mines, and for different roads in any
one mine.

Method of Sampling.

A few samples of dust were taken before stonedusting
was commenced, as follows :—

Samples of Dust taken in Places not Stonedusted.

Ash p.c.

Main endless-rope haulage roads, average of 4 samples

Travelling roads................ ,,	4	„

Main returns ................... ,,	8	,,

Crossgates (very little dust) ... „	3	,,

Face ........................... ,,	10	,,

Tables I. and II. give some idea of the quantity and
quality of dust at the face :—

Table I.—South-east District Face Advancing Regu-
larly, Turning Over Once a Week. Sample
Collected by Brushing a Belt from Coal Face to
Pack 2 ft. in Width by 7 ft. Across, and
THROUGH A 10-MESH SlEVE.

46’7
51’7
43’1
38’7
43’7

Passed

Description.	co  <D  Pl  <D  • S  Per cen	T5 CD.m PlrO £ P e, . O O-P  Ph  t.	2  o P d p  O gj	<X> - 1 P C3 02 <D-P e3  8 o
Passing through 10/30-mesh	sieve 65’2..	. 12’45.	.. 5’26.	.. 47’6
„	„	30/60	20’5..	. 3’90.	.. 1’65.	.. 46’4
,3	„	60/90	5’5..	. 1’04	. 0’44.	.. 47-8
„	„	90/200	3’5..	. 0’66.	.. 0’28.	.. 46’9
Through	200	,,	5’0..	. 0’95.	.. 0’40.	.. 43’7
Table II.—North-east	District.	Face	HAD	BEEN

S3

Pl Q

Standing for a Week.

Before,, but between two Packs,
by 11| ft. Across.

Sample Collected as
Belt, 2 ft. Wide

Description.

Passing through

Through

10/30-mesh
30/60 ’ „
60/90
90/200
200

•S

Ph
Per cent.

sieve

o

Ph



61’5...

18'5...

5’5...

5’5...

9’0...

9’59... 2’80...

2’88... 0’84...

0’85... 0’25...

0’85... 0’25...

1’40... 0’41...

42’8

39’5

38’2

37’8

37’3

The whole of the mine was systematically sampled
in June and July 1913, full particulars of which
are recorded in tables. These are summarised in
Table III.

Samples from the floor, roof and sides were taken,
and analysed separately. A small portion was taken
from five or six points over a distance of about 10 yards,
mixed together for each sample, passed through a
10-mesh sieve, and the larger particles rejected, the
part passing through being re-sifted through a 90-mesh
sieve. The proportion passing through the 90-mesh
sieve was determined and also analysed for ash. The
following conclusions may be drawn from the tables :—

Main Haulage Roads.—The amount of fine coaldust
deposited does not appear to be very great. The quan-

Table III.—Summary of Record of Stonedusting.

District.	Number of samples taken from			Average percentage of dust passing through a 90-mesh sieve.			Average percentage of ash in dust passing		
							through  Floor.	a 90-mesh sieve.	
	Floor.	Sides.	Roof.	Floor.	Sides.	Roof.		Sides.	Roof.
West	.’		13	13	• 3	25’40	31’70	40-30	72-30	85’10	85’90
South-west		33	33	9	27’31	35’82	32-77	65’04	71’40	71’40
South-east 		19	19	i	4	24’70	26’80	46’30	68’80	73’70	67’50
East 		24	23	10	26’00	33’60	60’00	53’90	61’60	55’30
North-east 		15	13	2	24’10	37’00	63-70	64’50	72’50	52’60
Totals and averages		104	101	28	25’84	33’33	47-43	64’00	71’53	65’30
					Percentage of ash in dust passing				
						through a 90-mesh sieve.			
Average for the whole mine (total of 233 samples) 									..	67-46		

tity of dust deposited by the air current is, perhaps,
greater within 300 or 400 yards of the face than it is
outbye ; but this dust naturally contains a higher per-
centage of ash, owing to the stonedust made by ripping
the roof and sides. Within 300 or 400 yards of the face,
however, the application of stonedust should be fairly
frequent, because the ripping displaces the artificially-
applied stonedust. Further outbye, when once the
workings have been thoroughly dusted, a further
application every four to eight months should be quite
sufficient to keep the percentage of ash above 66 in the
finest dust. The dust on the floor also varies consider-
ably, but on the whole is somewhat lower in ash and
contains a very large percentage of coarse dust. It is,
therefore, safer than might be expected from looking at
the tables, which only give the analyses of the dust
passing through a 90-mesh sieve.

Travelling Roads.—The dust on these roads, without
stonedusting, contains apparently always considerably
more than 50 per cent, of ash. Those which have been
stonedusted only once or twice show a very high
percentage of ash. It is quite probable that no further
application will be necessary, but at any rate one
application every 12 months will be quite sufficient.

Main Returns.—Some of these roads contain a large
quantity of naturally-deposited exceedingly fine dust,
which is only moderately high in ash, varying from
about 30 per cent, near the face to 55 per cent, outbye
near the shafts. The increased percentage outbye is
apparently due to the stonedust made by ripping in the
returns themselves. When once thoroughly stone-
dusted, these roads will require a further application
every four to six months, especially from the face to
300 or 400 yards outbye.

Crossgates.—These are frequently ripped; the dust
deposited is fairly high in ash, and never in large
quantities. They require thoroughly stonedusting once,
and a further application after each ripping.

General.—Under the present existing conditions at
this colliery it may be said to be a practical proposition
to keep the main haulage roads, travelling roads,
returns and crossgates in a thoroughly safe condition,
with the average percentage of ash in the fine dust from
several samples between 50 and 60 per cent., or some-
thing like in the proportion of just over 1 of stonedust
to 1 of coaldust. To get and keep a much higher
percentage of stonedust than this would, the writer
thinks, be impracticable, owing to the very large
quantity that would have to be constantly applied.

He does not think that it is practicable or necessary
to stonedust the crossgates immediately contiguous to
the face, oFthe ordinary gates. The quantity of dust is
small, and what dust there is is very coarse, the
percentage of ash present in the finest part being
generally over 37, except in isolated cases.

It appears to be quite unnecessary to stonedust the
face, as the quantity is small, the dust is coarse, and it
contains well over 37 per cent, of ash. It is also
impracticable, owing to the fact that the face roads are
turned over twice or three times a week, and it would
be necessary to stonedust the face every turnover.

The proportion of 10 of stonedust to 1 of coaldust has
been frequently mentioned as a practical proportion by
mining engineers, as well as by some inspectors of
mines. In the writer’s opinion, it is absolutely impos-
sible to keep any roadway up to this standard, and it is
quite unnecessary to do so.

It is necessary to exercise great care, in taking the
samples, so that a fair average sample is obtained; and,
owing to the variation which is found to exist at all
points of the roadway, in order to obtain a true result,
an average of several average samples should be taken.
For the same reason, it is not possible to lay down any
rule as to the amount of stohedust necessary, say, per
yard of roadway for any one mine or part of a mine.

In looking through the samples obtained from
Bentley, it will be seen that the natural dust deposited
on all the roadways, and in the face itself, is exceedingly
high in ash (from 28. to 55 per cent.). In this case, there-
fore, a smaller quantity of stonedust is necessary to
produce a safe percentage of ash than would be the case
in mines which produce a more dangerous dust.

The naturally-deposited dust at Bentley will probably
be found to be considerably higher in ash than that
found in the average dry and dusty mine. This is due
to the thin layer of soft friable chinch (2 to 10 inches)
between the main seam and the top soft coal, and also
to the 3 ft. of soft clunch and shale above the top softs
ripped in the gates.

It is natural to suppose that a, road containing
nothing but fine dust of an explosive quality will be
more dangerous than if the dust consists of a large
proportion of coarse dust.

The samples taken after the explosions at Courrieres
and Talk-o’-th’-Hill at points where the explosions

ceased show a lower percentage of ash than the limit
given in the Eskmeals report, where fine dust only was
used. At Courrieres an analysis of samples demon-
strated that the flame traversed the roads where the
dust contained up to 28 per cent, and less of ash, and in
one case there was only 8’8 per cent, of ash. They also
showed that the explosion stopped where the dust
contained 42’3 to 59’9 per cent, of ash. At Talk-o’-th’-
Hill the flame traversed the roads where the dust
contained up to 31’5 per cent, of ash. The explosion
stopped where the dust contained 44 per cent, and
possibly 39 per cent, of ash. It is difficult to draw any
conclusions from the data given in the report on the
Cadeby explosion, but the writer understands that in all
cases the explosion ceased where the dust contained
36 per cent, or more of ash. No analyses of dust are
given in the report on the Auckland Park explosion,
although it appears to have afforded an excellent oppor-
tunity for thorough investigation of the dust question.

The experiments carried out at Eskmeals up to the
present have been with dust (shale and coaldust) passing
through a 200-mesh sieve. As the dust met with in
mines contains more frequently than not a high percen-
tage of coarse dust, the writer thinks that further
experiments should be made to test the explosibility of
the coarse dusts, and also mixtures of fine and coarse
dust, such as—

1.	The maximum of ash at which a 90/200-mesh
dust will propagate an explosion.

2.	The maximum of ash at which a 30/90-mesh dust
will propagate an explosion.

3.	The maximum of ash at which a 10/30-mesh dust
will propagate an explosion.

4.	The maximum of ash at which various mixtures
of coarse and fine dust will propagate an explosion.

The analyses have been made by Mr. T. F. Winmill,
chief chemist to the Doncaster Coalowners’ (Gob Fires)
Committee, and Mr. J. I. Graham, chemist to Bentley
Colliery. The samples were collected by Mr. F. M.
Weeks. The writer is indebted to the above-mentioned
gentlemen for assistance is preparing much of the
information upon which this paper is based.

Discussion.

In the course of the discussion that followed, the
President said that papers like that were exactly the
sort that were required on the new subject of stone-
dusting. If gentlemen would put on paper the details
of their arrangements, they would confer a greater
favour on those who were considering the question than
they could possibly imagine. Personally, he almost
thought Mr. Clive’s paper would be taken as a sort of
small text-book on the subject. The president thought
most of them would have had a little shot at the
dusting problem. Some of them, probably, had been
led into it by statements as to the extremely low cost
that dusting was likely to put them to, but he was sure
most of them who had tried it would have abandoned
that position. He had been wondering whether it was
costing anybody else as much as it was costing himself,
but he found that Mr. Clive’s figures and his own would
run pretty much on the same lines, He thought
perhaps at his colliery they prepared the dust a little
cheaper, but they certainly did not distribute it any
cheaper. He thought the problem of distribution was
likely to be one of the things which would attract the
attention of engineers and practical people about the
collieries. He saw from the Colliery Guardian that
that particular phase of the subject had been discussed
at a meeting of the North of England Institute the
previous week. The writer of the paper there (Mr.
Halbaum) had put forward a method of distributing
stonedust which, if it really was practical, would seem to
go a long way towards making the process considerably
cheaper. Personally, he should very much incline to
the method which Mr. Clive had adopted—and which he
thought most people had adopted up till now—the
method of dislodging the coaldust on the roof and sides
by means of stonedust tnrown at it. They got all sorts
of suggestions for adding to the safety of their mines,
but most of them were found to be extremely costly to
put into operation. This particular system, which
appeared to be going to do more for them than almost
anything else had done in the past towards preventing
the continuation of explosions in mines, seemed, to be
the very cheapest that could have fallen upon them. He
thought the mining industry would lack a very great
sense of duty if they did not put themselves into shape
for taking in advance anything that might be suggested
in the way of legislation.

Mr. T. H. Mottram (H.M. divisional inspector of
mines) joined in congratulating Mr. Clive upon having
produced a paper of such great importance to all of