EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS, 57

Analyses of cout-dust samples taken in tests shown in preceding table, 4

Volatile 7
‘Test Character of sample, | eo ised | ssh.
cose |{Pust before shot. a 5.20
G-2000 {Dist ator sgt a : i]

-oyg7 | Dust before shot.
sour Yu

Aust atter shots... SeanaeannnnaEe
as {pa before shot. ..... a
|ADust after shot aoe 0
Dust before shot... an
Dust after shot. . oO
[Dist tre oi 0
Dust after shot. 80
‘Dust before shot... -_ 7.80
{Dust afier shot enna 15
Dust betore shot. : : ra

A.C, Fleldner, analyst,

In the first experiment (G-2966) the total moisture content of
the coal was 8 per cent, which is about 6 per cent in excess of the
normal moisture content of the standard dust. This amount was
insulflicient to prevent complete propagation of the flame throughout
the gallery.

In the second experiment (G-2967) the moisture content was
19.20 or 17 per cent excess moisture. This also was not sufficient
to prevent complete propagation.

Experiment G-2968 was to observe how far the flame would go
under the same conditions as in the previous experiment except
that only the first three sections of the gallery (20 feet) and the
horse were loaded with damp dust. ‘The flame traveled only to the
ninth window, equivalent to 57 feet. This experiment was made
with the same percentage of moisture (17 per cent excess) as the
previous one.

In the fourth experiment (G-2969) the moisture content was
raised to 29.70 per cent or 27.70 per cent excess moisture. The
result was ignition but not propagation of the explosion, the flame
traveling only 30 feet.

Experiment G-2971 was made with dust from the Fairmont
district, West Virginia. Tt was moistened to the extent of 30.90
per cent, or about 29 per cent excess moisture. There was slight
ignition, but not propagation. The dust used in this experiment
was allowed to dry over night and after being mixed was put back
on the shelves. The moisture content then proved to be 11.80 per
cent, or 10 per cent of excess moisture. The result was complete
propagation.

The final experiment (G-2973) was a repetition of the fifth experi-
ment (G-2971). The moisture content was also practically the
same, 30.70 per cent, or about 29 per cent excess. The result was
ignition but not propagation.



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 115

volume of air space, the excess dust may have opportunity for more
or less complete combustion, giving a sudden burst of greater energy.
Many observers have commented on the great explosive force often
manifested at turnouts, overcasts, and sidings.

Probably the most sensitive record of heat is provided by the hair
of victims. On the other hand, the observation of the writer is that
damp paper and cloth are resistant to the quick flame of the explosion.
When combustible material like loose paper is found in the path that
had been traversed by the explosion, careful consideration is necessary
to determine if it might not have been brought out from its former
resting place by the depressive wave following the cooling of the
burned gases. In the interior fields, where the practice prevails of
taking 25-pound kegs or cans of black powder into the mines, the
writer has observed, after a number of dust explosions, empty kegs
that had been drawn out from the room gobs into the entry through
which the explosion has traversed, though the explosion evidently did
not enter the rooms.

Coal-dust explosions show little violence near the point of origin
unless originating from the ignition of a considerable volume of fire
damp or from the discharge of a large quantity of explosive.

The characteristic dust explosion increases in violence as far as the
dry, inflammable dust extends, until the entrance of the mine is
reached, unless there are retarding influences like long, wet ateas or
areas containing an excess of shale or rock dust.

LABORATORY INVESTIGATIONS OF THE IGNITION OF
COAL DUST.

By J. ©. W. Frazer.
INTRODUCTORY STATEMENT.

Although perhaps laboratory experiments had no great share in
bringing about the general knowledge of the explosive character of coal
dust, they are a valuable means of gaining information in advance of
experiments carried out on a scale large enough to simulate mining
conditions. The acceptance of the theory has come about only
through such large-scale experimental work, which has shown con-
clusively that coal dust alone may be the cause of serious disasters
or may propagate and prolong a comparatively harmless explosion
caused from some other source, so as to produce a disaster extending
through great areas.

The object of this part of the report is to describe in some detail
the work which has been done on a laboratory scale bearing on the
question of coal-dust ignition and inflammation. Many of the experi-
ments on a somewhat larger scale are excluded, but some such early


THE COAL-DUST QUESTION IN THE UNITED STATES. 29

It may be stated that after the mine was reopened fire damp was
not detected in subsequent operations.

For some years after the Pocohontas explosion the coal-dust prob-
Jem attracted little attention in this country, and operating men were
content to await the results of experimenting abroad. Each was
chiefly concerned in his own part in the tremendous development
going on in the various great bituminous fields. Interest in coal dust
awakened when explosions began to occur in mines in the western
region of the interior coal province, particularly in Iowa. Many of
these explosions were in shallow mines in which fire damp had never
been found before the explosions and was not found after them.
The Iowa coal is neither gassy nor coking, in the ordinary sense; it is
high in ash, and carries from 12 to 14 per cent of moisture when
freshly mined.

EXPLOSION AT PEKAY MINE, IOWA, 1892.

The first of the Iowa explosions was at the Pekay mine November
8, 1892, on a holiday, when only 4 men were in the mine. Three of
these were killed. The writer examined the mine the next morning.
Much violence was manifested in several pairs of entries and the main
entries on one side. The fan was partly wrecked. The mine was
dry and dusty. Coked particles were not seen, but there was burned
dust and the flames had ignited kegs of powder at points in the mine.
No fire damp had ever been found in the mine and none was found
after the explosion. The evidence indicated that the explosion
began in a room where three greatly overcharged dependent shots *
had been fired at or about the same time, throwing to a distance a
large mass of coal. No undercutting nor shearing had been done.
What was termed “‘blasting off the solid” was then being introduced
in Iowa. In the opinion of the writer, the flame of the shots ignited
coal dust, which spread the explosion throughout the mine?

Shortly after this explosion several others occurred in Iowa, at the

Jedar mine and elsewhere, These were also ascribed to either blown-

out or overcharged shots ‘‘on the solid.” Similar explosions, gen-
erally small, because the conditions were unfavorable for wide-
spread explosions, occurred in the fields of southeast Kansas, also
remarkably free from fire damp, and in the McAlester field of Indian
Territory (now Oklahoma), where, however, the situation was com-
plicated by the presence of more or less gas.

@ Dependent shots are those prepared at the same time as adjacent shots, and thetr success depends on the
success of the latter. Owing to theuncerlainty of the first shots removing their burden cleanly, dependent
shots should not be fired at the sume tine. The act Is forbldden by the laws of sume States.

> Rice G.&., ‘The Pekay explosion: ‘Trans. Illinois Min. Inst., vol. 2, 1898, . 54.


144 THE EXPLOSIBILITY OF COAL DUST.

An objection to the use of a platinum coil as a source of ignition
is the possible catalytic action of the platinum.

It is hoped that further experiments can be performed on the
ignition of coal dust by the use of pressure alone. It should be under-
stood that the record given above is to be taken as a preliminary
report of a few experiments performed under limited conditions,
which are to a large extent repetitions of previous experiments, with
some minor alterations of apparatus and method of manipulation.

SECOND SERIES OF EXPERIMENTS AT PITTSBURG TESTING STATION.

A second series of experiments is now in progress in which the
pressures developed in the explosion vessel are measured by a dif-
ferent method. This method was adopted because the maximum
pressure in many cases is not developed instantaneously, and the
method previously used would on that account not give a true
measure of the force of the explosion. The explosion vessel now in
use is a 1,500-cubic centimeter glass globe with two tubulures on
opposite sides. The dust is puffed into the vessel through the lower
opening in much the same manner as in the experiments described
above. Into the top opening is inserted a stopper carrying the same
platinum coil used in the previous work. The measurement of the
pressure is accomplished in the following w: A brass tube of 7
millimeters diameter 4s passed vertically through the rubber stopper
which carries the connections of the platinum coil. (See Pl. VIII, A.)
The top of this tube is ground so that a ;-inch steel ball fits on it
practically gastight. The pressure developed within the explosion
vessel is measured by ascertaining by several trials the smallest
weight which must be placed on the steel ball to prevent it from
being lifted. Thus the total pressure exerted on a known area is
obtained directly. The experiments have given concordant results,
as the table below shows. The above method of testing the inflam-
mability of coal dust is being used in the Bureau of Mines laboratory
at Pittsburg, Pa.

Results of second series of experiments with explosive coal dusts at Pittsburg station.

[in all tests the amount of dust used was 0.04 gram.]

Results of tests.

Source and proximate analysis of col dust used and pressure _————_
developed In tests. Weight Equivalent | Ffect on steet
applied. per sg. cm. ball.

Grams.
1. Bituminous coking coal from Hastings mine, Las Animas 779 | Not lifted.
County, Colo. (Lab. No. 9780 as Do.

Moisture... leseeseees 148 a9 Do.

Volatile matter... 33.98 584 Do.

Fixed carbon. 5146 alg Do.

Ash... ! ] 713 454 Do,
B ;

Sulphur. ---- ee
‘Pressure developed, jess tian 454 grams por square centimeter. | t



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 41

of the different coals to take up oxygen from the air or to undergo
spontaneous combustion.

In this connection it seemed desirable also to determine, if possible,
the relative inflammability of some of these same coals, and quite
recently, with this in view, a series of experiments was carried out
on some of the same dusts used in studying the rate of oxidation.
The apparatus used for this work is a modification of that of Bedson
and Widdas described above.

Plate VIII, A, shows the form of apparatus used. A is an ordinary
2-liter aspirator bottle. B is a small filter flask of about 250 cubic
centimeters capacity, connected at a by rubber tubing with C, a
glass bulb of about 150 cubic centimeters capacity, and through the
rubber stopper with the open manometer c. JD is a glass tube 6.5
millimeters in internal diameter and 20 centimeters long, passing
through holes in opposite sides of a box support, and set in firm and
level position with plaster of Paris,

Through a rubber stopper in the mouth of A pass two large copper
wires, which form the terminals for the platinum coil d. Through a
hole in the same stopper passes a glass tube 13 millimeters in internal
diameter, which is closed at the top, and to which is sealed a side tube
(e) of the same diameter as D. This side tube is connected closely,
end to end, with D by means of a short rubber tube. The platinum
coil d is made from about 120 centimeters of No. 26 platinum wire,
is suspended in two sections from a small perforated porcelain plate,
and is connected with the copper terminals. The porous plate serves
not only as a support for the coil but as a protection to the rubber
stopper above from too high heating during the experiment, and also
tends to disseminate the dust more uniformly in the upper part of the
flask. The platinum coil when in position hangs slightly above the
center of the bottle.

The tube f passing through the stopper in the tubulure at the bot-
tom of the bottle is bent at a right angle and is made funnel-shaped
at one end. The end carrying the funnel is directed upward inside
the bottle toward the platinum coil, and directly under and within
about 5 centimeters of it. In this funnel is placed the coal dust
which it is desired to examine. The funnel and the fine wire gauze
with which it is covered aid in securing a more complete dissemination
of the dust when it is ejected from f. By means of a rubber tube f
can be connected with @. Pinchcocks are at g, h, and j.

The terminals of the coil d are connected in series with an ammeter
and rheostat, The relative pressure produced by the ignition of
different dusts is measured by the distance to which a small steel ball
(6) is projected, when this ball is placed at a definite point in D and
in which it fits snugly.




MANIFESTATIONS OF COKED COAL DUST. 111

As the explosive wave traversing the relatively narrow passageway
becomes more intense, which it usually does if there is dry coal dust
to feed upon, the timbers are frequently swept along by the advance
air wave, so that their evidence is lost unless their former position
can be definitely located.

As the explosive wave gains in velocity practically no coke is
deposited in the main passageway traversed, and is then to be looked
for in isolated splashes on the lee side of corners of crosscuts or
other side openings on the coal rib or on timbers in these openings.
Another place worth observing is the roof behind such corners,
where careful search will sometimes disclose occasional particles
adhering or hanging in separate globules.

In a wide-sweeping explosion that traverses the main entries
the violence usually becomes so great that little or no coke is deposited
there. This was notably true in the recent Primero explosion, in
which, though abundant coke showed in the rooms and cross entries,
only a few isolated particles (on outby facing exposures) were
observed along the main slope or in the immediately adjacent open-
ings for the inner 2,000 feet, and none at all were found by the
author in the outer 2,000 feet traversed by the explosion. Despite
this scarcity of coke evidence in the main slope, bodies that were
found under a fall of rock at the mouth were burned. Also a
brakeman who was on a motor trip of mine cars about 100 feet
from the mouth of the slope, but who was in line with the slope,
was slightly burned.. A telephone post about the same distance
away from the slope, but 30 feet off the direct line of it, had con-
siderable coke scales adhering to the side facing the mouth.

The position of the scale on this post brings to attention the mode
of deposition of coked particles when an explosion dies away, as in
the instance described above. They are thrown upon the facing
exposures. This fact was also admirably illustrated in the Primero
explosion in a certain side entry (A~8 entry), into which a branch
explosion wave penetrated about 1,800 feet from the main slope, and
there died away at a wet place in the road. At this point the tim-
bers were all standing and no violence was indicated. There was
loose coke on the outby sides of the timbers. Several hundred feet
out toward the main slope, where violence was shown, increasing
toward the slope, the coke particles and scales were generally on the
inby surfaces, or those facing away from the approach of the explo-
sive wave. The coked dust is sometimes located on the facing side
in very wide places, as in wide rooms where the velocity of the wave
becomes | from opportunity to spread laterally.

‘The fact that coke is not deposited where the sweep of the explosive
wave is greatest is possibly accounted for by the extreme speed



64 THE EXPLOSIBILITY OF COAL DUST.

This equation is not exact, because neither Dalton’s law of evap-
oration nor the assumption regarding the heat received by the bulb
from surrounding objects (Newton's law) is strictly true. The value
of c depends on the wind velocity or the rate at which the bulb is
moved through the air. For the Schleuder psychrometer c = 0.00069.
As a matter of convenience, it is customary to use tables in which
p is given as a function of (Tz—Ty) and Ty.

METHOD OF MAKING HYGROMETRIC OBSERVATIONS IN MINES
AS USED BY ENGINEERS OF THE BUREAU OF MINES.

The observer must be equipped with a hygrometer, a small bottle
of clean water, anemometer, barometer, watch, and tape. Before
entering the mine he should make observations of outside atmos-
pheric conditions, selecting, if possible, a point where he will be in the
shade, but not where there is any steam or local heat from fires; also,
if the shaft or mine opening is an upcast, the point must be selected
on the windward side of it in order to obtain correct readings of the
relative humidity. Having selected the point, the observer swings
the hygrometer, and if there is any wind he should stand so that the
instrument receives the wind direct; that is, his body must not
obstruct. Having noted the depression of the wet bulb below the
dry bulb, he reads the barometer to obtain the atmospheric pressure.

The observer, having gone underground, makes observations at
certain stations. It is best, where possible, to select these in advance
from the mine map. In gencral, it is desirable to make observations
at the intaké and return of cach split in the ventilating current, and
in particular the main return should be read as close to the outlet as
possible.

The method of making all readings underground is the same.
After wetting the cloth covering the wet bulb the observer swings
the hygrometer, standing sidewise to the current of air, the hygrom-
eter facing the wind. Ilaving repeated the reading a number of
times, to insure that the mercury column in the wet-bulb thermometer
is depressed as far as it will go,? and having recorded the reading, he
reads the barometer to obtain the mercurial pressure, which is a
combination of the atmospheric pressure and the mine ventilation
pressure at that point. The latter pressure is negative or positive
according as the fan is exhausting or blowing. Then the velocity of
the air current is obtained by means of the ancmometer, and the
volume of air is obtained by multiplying the velocity by the effective
cross section of the passageway. ‘The time of taking the observations
at each station, inside and outside, should be recorded, so that the
changes in outside atmospheric conditions can be correlated. It is

@ When the air is below 32° F., the wet-bulb reading remains stationary for soma minutes ax the water
freexes, but as the swinging {s continued it will lower proportionately to the temperature and humidity.




REMEDIES FOR COAL DUST. 75

chloride, which was made February 27. The calcium chloride was
spread on dry to the amount of 1 pound per linear foot of the entry,
which was from 8 to 9 feet wide. The road was ballasted with coal
and shale fragments to the depth of the ties and from 6 to 10 inches
deep along the sides.

In the second area the coal dust had not been cleaned or watered
for a long time before the application, which was made on February
12, and the fine coal and shale dust was thick along the track and on
the sides. This was treated with the dry calcium chloride to the same
amount as the first section. The calcium chloride had been received.
in large drums, and was cemented in a solid mass, which had to be
broken down by hammer to pieces about one-half inch in size and
less. In both the dry treatments the roof and ribs were not consid-
ered. As it was a “butt” entry, the smooth, bright coal ‘‘faces”
parallel with the road gave no lodgment for dust. The roof, which
was shale and top coal, did not require timbering. The roads had
been so dry that dust was raised in walking.

In the third area, also 400 feet long, the calcium chloride was
applied February 14. It was in solution, containing 8 per cent of
calcium chloride by weight. ‘The entry was sprinkled by means of a
force-pump sprinkling car, which sprinkled the top, sides, and floor.
The total amount of caleium chloride put on was 1 pound per linear
foot with 124 times as much weight of water. The watering was done
not only on the floor, but also on the ribs and roof.

On March 7 an investigation of these areas was made by the writer.
In the first area the coal dust in the roadway was damp to the touch
and would pack in the hand. This was eight days after treatment
with the dry calcium chloride. There was an entire absence of dry
dust. The sides and roof felt dry, but, as stated, these were not
treated and had been practically free from dust.

In the second area, twenty-three days after treatment with the dry
calcium chloride, the floor dust was damp and sticky and was more or
ess packed in the roadway. There was an entire absence of dry dust.

Jn the third area, treated with the wet solution February 14, the
road dust was more or less dry. When kicked it would rise as float
dust. Tt did not seem as dry as it had been before the application, but
the effect of the calcium-chloride treatment had been practically lost.
The ribs and roof were also dry, but as they were smooth no dust
had collected.

Samples were gathered of the dry road dust of the three areas before
their treatment, and on March 7 after treatment. These samples con-
tained all sizes of fragments of coal and shale. The portton that passed
through a 20-mesh sereen was considered dust, and the remainder
was rejected. In the samples from the areas thai had been treated
the particles were stuck together and could not be screened until air



THE COAL-DUST QUESTION IN EUROPE. 19

The royal commission summarized their conclusions in the follow-
ing words: ¢

(1) The danger of explosion in a mine in which gas exists, even in very small quan-
tities, is greatly increased by the presence of coal dust. (2) A gas explosion in a fiery
mine may be intensified and carried on indefinitely by coal dust raised by the explo-
sion itself. (3) Coal dust alone, without the presence of any gas at all, may cause a
dangerous explosion if ignited by a blown-out shot or violent inflammation. To pro-
duce such a result, however, the conditions must be exceptional, and are only likely
to be produced on rare occasions. (4) Different dusts are inflammable, and conse-
quently dangerous, in varying degrees; but it can not be said with absolute certainty
that any dust is entirely free from risk. (5) There appears to be no probability that
a dangerous explosion of coal dust alone could ever be produced in a mine by a naked
light or ordinary flame.

By the time the royal commission had issued this final report, in
1894, the mining experts in England had became very generally con-
vinced that coal dust was not only a factor, but the most important
element in the great explosions occurring in collieries, and thereafter
the experiments and investigations were directed to remedies. In
1896 a coal-mine regulation act was passed by which power was given
to the secretary of state to prohibit the use of dangerous explosives.
This necessitated the testing of explosives used in mines, and to this
end a testing station with necessary apparatus was erected at Wool-
wich and opened for testing June 5, 1897. As an explosive mixture
of gas is more sensitive than coal dust, it was reasoned that an explo-
sive that will not ignite gas would not ignite coal dust, hence the appa-
ratus was designed primarily to determine the-relative liability of the
various explosives to ignite an explosive gas mixture.

GERMAN, FRENCH, AND BELGIAN STATIONS FOR TESTING EXPLOSIVES.

In Germany the education of the mining public to the danger of
coal dust had gone on simultaneously with that in England. In 1894
a station for testing mine explosives in the presence of dust and gas
mixtures was established at Gelsenkirchen in Westphalia by the
mine operators and placed under the supervision of a government
engineer. The testing gallery is 34 meters long. In cross section
it is elliptical, 1.80 meters (5.9 feet) high and 1.35 meters (4.4 feet)
wide. This gallery and the other apparatus for testing the explo-
sives, also apparatus for testing safety lamps, mine motors, etc., have
been in continuous use since the establishment of the station.

A similar station was established by the Belgian Government at
Frameries, and the same general methods of testing explosives in the
presence of gas and coal dust are used for the formation of a Belgian
“permitted” list.

aSecond Rept. Roy. Comm., 1804, p. 24.


USE OF STEAM AND WATER SPRAYS. 179

up this deficiency it is intended to put a brattice immediately behind
the fan, with sliding doors, so that the area can be contracted to a
point where the engine will indicate 100 horsepower while still
delivering the same quantity of air.

It has been suggested that for the additional steam live steam be
used, thus saving the extra work of the engine or replacement by a
large engine. The effect would be the same, but its regulation would
not be under control, and, furthermore, there would be nothing to
indicate whether the live steam was actually in continuous operation.
Every fan is or should be equipped with a recording water-gage
chart, and if the steam goes through the engine this water-gage
chart will indicate both the quantity of air supplied and the amount
of exhaust steam used, with sufficient accuracy for practical purposes.
It would be much too easy for a sleepy or lazy fireman to shut off the
live-steam pipe with no one the wiser for it, and this is sufficient
reason for putting the steam through the engine. It is true that
steam meters could be used, but these would show only the total
quantity supplied, and unless a recording instrument could be
added they would fail in their purpose. Furthermore, additional
horsepower is required only in exceptional cases, and in them only
temporarily.

To apply the method of watering mines with exhaust steam, out-
lined in the preceding pages, a blowing fan is necessary. The method
can not be applied with an exhaust fan because of the dense fog
which necessarily occurs at the intake and for some distance in from
the mouth of the mine. In most mines it is possible to change from
exhaust to blowing ventilation, and if other conditions do not pre-
vent it would pay to do so. There are strong arguments in favor
of exhaust fans in some mines, particularly mines that were origi-
nally planned for such ventilation and worked by methods adapted
to it. In such mines an air preheater must be used. While experi-
ments along this line indicate that preheating can be successfully
done, it will require constant attention for its control, besides the
expense of erecting and maintaining the air heater.

USE OF STEAM AND WATER SPRAYS IN OKLAHOMA
MINES.

By Carn Scnow

PURPOSE OF INQUIRY.

The writer’s investigations in the Oklahoma field were begun
because of the comparatively large number of mine fires and mine
explosions in that district; also because of the trouble from falls
of roofs, which add constantly to the dangers and cost of mining
operations,


120 THE EXPLOSIBILITY OF COAL DUST.
EXPERIMENTS OF HALL AND CLARK.

Hall and Clark ¢ performed certain special experiments to study
the effects of blown-out shots. They were the first to carry out
experiments under conditions approaching those existing in mines.
They ignited various charges of powder at the bottom of an inclined
gallery along which was placed the coal dust under investigation.
The length of the flame was determined by suspending pieces of
inflammable cloth at regular intervals along the gallery. In many
of their experiments the flames were voluminous.

This work is mentioned in more detail elsewhere, and is repeated
here merely because it forms the beginning of the great amount of
work which has been done on an extensive scale, and because it was
repeated on a smaller scale shortly after by Marreco and Morison.?

These investigators carried out experiments on a much smaller
scale than those of Hall and Clark, but otherwise there was some
similarity in their method of working. The apparatus used consisted
of a long rectangular box divided longitudinally into two compart-
ments by a vertical partition reaching nearly to the bottom of the
box. One of the longitudinal chambers thus formed was 3.6 meters
long, the other 3 meters. One end of the apparatus was closed, and
at the second end of the longer gallery was attached a connection
for introducing a regulated current of compressed air. The second
end of the shorter gallery was left open. Two small cannons were
placed at the closed end, each directed along the axis of one of the
galleries. They were discharged electrically and the connections
so made that they could be fired either simultaneously or one at a
short interval after the other. The air current which came into the
longer gallery passed under the partition and through the shorter one
and had a velocity of 14 to 3 mete The charges of powder used
were not given, nor the composition of the coal.

The results of the work showed that dusts conducted themselves
very differently under these conditions, according to their nature.
With some the flame issued from the box, with others the flame was
only a small fraction of the length of the box. The greatest effects
were produced when the cannons were fired at short intervals apart,
the first shot serving to charge the air of the second gallery with dust.
The shot then fired into the second gallery produced more violent
explosions, In many of their experiments the box was burst open.

As the result of these experiments they concluded that if they had
been able to perform their experiment on a sufficiently large scale,
the results would have been comparable in every way with a inine
explosion.

«Communicated to the North of England Inst. Min. and Mech
» Northof England Inst. Min, and Mech. Eng., 1879, p.88; Annales des mines,

S76.
er.7, vol. 15, 1879, p.374.



126 THE EXPLOSIBILITY OF COAL DUST.

mines, and whether the dust is inflammable or not the conditions
do not permit doubting the presence of methane. Lignite mines
which are slightly gaseous, if at all so, but which contain dusts more
inflammable than coal dust, have never suffered from serious explo-
sions. Further, all the accidents attributable to dust alone are caused
by blown-out shots directed to the floor of the mine. The results
of their experiments have confirmed these facts by showing the
reason for them—the slight inflammability of the coal dust.

According to Galloway and to Mallard and Le Chatelier, the
quantity of dust which must be suspended in the air to give an
inflammable mixture is far beyond what could possibly be in the
air even in the most dusty parts, and it requires a very violent
agitation to bring such an amount of dust into the air and maintain
it in suspension. Further, the authors have shown that dusts are pre-
cipitated very rapidly from the air whenever the causes which brought
them into the air cease to operate. Their experiments on the velocity
of propagation of the flame in air and dust mixtures show it to be
practically zero. These two facts tend to limit the extent of a dust
explosion, because before the flame can travel an appreciable distance
there ceases to be a sufficient amount of dust suspended in the air to
propagate the inflammation, They conclude, therefore, that coal
dust alone is of very little danger in mines, but in the presence of
small amounts of methane the danger is much increased. Coal dusts
play an important part in mine accidents only by lowering the explo-
sive limit of an air and methane mixture,

LATER EXPERIMENTS BY GALLOWAY.

After his first investigation on the question of the explosion of
mixtures of air and coal dust, Galloway performed a number of
other experiments, as a result of which he altered his first opinion,
which was stated above in discussing his work. His first conclusion
was that coal dust, to be a factor in mine explosions, must be sus-
pended in air that contains at least some methane. Tis later work
led him to the conclusion that coal dust alone mixed with air would
under the proper conditions form an explosive mixture, and that
in all probability it figured at times as the sole cause of certain mine
explosions.

EXPERIMENTS OF THORPE,

From this time on work on the question of coal-dust explosions
was done on a comparatively large scale. Interest was then taken
in the matter by several European governments, and special eom-
missions were appointed by these to investigate the question by
instituting experiments to demonstrate conclusively the explosive
character of a mixture of pure air and coal dust. These experiments


EXHAUST STEAM AS A PREVENTIVE.

OBSERVATIONS OF MINE AIR
WITHOUT EFFECT OF STEAM.

i T
I
i

It was anticipated that the

full effect, as calculated above,

17
Degrees Fahrenheit Percent .
3.8 6 6 8 3 8 88
T qe

= :
oa

would not be obtained, and in

‘AvaNOW

order to test the efficiency of
the exhaust steam two record-

c

ing instruments were placed in

the mine, one in front of the

blowing fan and the other

avossnn

about 400 feet beyond the fan.

epee syeuore sre foes

A week’s record was produced

during the cold season under

normal conditions; that is,

LYN

without the use of the ex-

haust steam. The two records

Avasanaam

are reproduced in figure 24,

which shows two temperature

curves and two representing
humidity, the latter being ex-

pressed in percentages (relative
humidity) instead of gallons

ee rea ee ye foes yee e

ayaa,

of water, as in the previous

charts.

Exhaust steam had been in
use the previous week and was

Pevore sre
vals

turned off six hours after the

records began, which accounts

cy

for the 100 per cent humidity
for the first six hours. The

distinctive feature shown by

this chart is the equalizing ef-

fect of 400 feet of entry on both
the temperature and humidity.

avauruve

‘Yo19 7294 pur Yo wEANS ISNEqNE YI 22 aAMFUF JO AITPIUMY aa/yepo4 pus amnyeroduray jo IzeU)—Fe THAT

The average temperature 400
feet. inside the mine is but *

i
Fares see e ere

4

slightly higher than that at on en ee

the fan, but it does not show = ["

the sudden fluctuations of the

Avene.

+c yoee+ ena e

latter. The humidity inside i“

of the mine was naturally af- AT

fected by the previous wet Poi aos 3

conditions, but the effect had — [LNG = Ss
B

more or less disappeared C i

later in the week. Like the


162 THE EXPLOSIBILITY OF COAL DUST.
TESTS OF EXPLOSIVES.

Pending future investigation of other means of preventing prop-
agation of coal-dust explosions, due attention has at all events been
given to means of preventing their initiation through explosives.
A number of experiments have been conducted at Frameries with
permitted explosives in order to test their relative safety in the pres-
ence of coal dust alone. These tests were carried out in the same
way and under the same conditions as when testing in presence of
fire damp, the temperature in the gallery being maintained as nearly
as possible at 25° C.

The coal dust used for all tests was taken from one of the Agrappe
mines, and contained 21 per cent of volatile matter. Some of the
coal raised in Belgium contains as much as 35 per cent, but as the
number of collieries where this coal is found is small, and the quan-
tity of dust given off by the coal insignificant, the other quality of
dust mentioned was chosen.

At first the practice was to bring the coal dust into a state of
suspension, but ultimately this was found to be unnecessary, as the
agitation caused by the shots proved sufficient.

The tests were made in the gallery at Frameries. The bore hole
of the cannon was 55 millimeters, the charging density being kept
within the limits of 0.4 and 0.6.

Freshly ground dust, passing through a No. 90 mesh (1,280 to the
square centimeter), was used throughout, as it was found to be more
inflammable than dust kept for fifteen or twenty days. The moisture,
averaging from 0.5 to 2 per cent, was eliminated by drying the dust
at a temperature of 30° C,

The gallery was charged with 150 grams of dust per linear meter.
Higher dust charges did not materially affect the ‘‘charge-limite”
of the explosives.

The test comprised ten shots for each explosive and these were
fired on different days, so as to introduce different hygrometric
conditions.

The result of this series of trials has led to a slight revision of the
list of permitted explosives. Of 24 explosives tried, only seven proved
less safe in coal dust alone than in gas; five of these belonged to
the ammonium nitrate class, one to the chlorate class, and one to
the carbonite class.

A revised list of permitted explosives now called ‘‘Explosifs
S. G. P.” (Sécurité-Grisou-Poussiéres), canceling all previous lists, is
published in a ministerial circular dated October 18, 1909. The
maximum charges are given for cach explosive, both as to gas and
as to coal dust; they vary from 300 to 900 grams. A minimum



70 THE EXPLOSIBILITY OF COAL DUST.

REMEDIES FOR COAL DUST.
REVIEW OF REMEDIES PROPOSED.
As soon as the dangers of dry coal dust became recognized, sug-
gestions for remediés began to appear. The British accidents in
mines commission in its final report in 1886 (p. 48) stated:

‘The removal of accumulating dust is practiced to some extent here and there; but
this measure is obviously attended by many difficulties, and even if carried out as
thoroughly as practicable, it would generally only be the main roads that could be kept
fairly free from dust. * * * Tf, however, * * * the mine ways fare kept] as
free irom dust as practicable, and the removal of the principal part of dust accumula
tions from the working places can be supplemented by the application of some efficient
method of rendering the remaining dust innocuous in the presence of a blown-out
shot, there can be no doubt that the dangers arising from coal dust will be very greatly
reduced, if not rendered altogether insignificant.

Since the time of the foregoing report numerous means have been
suggested, and some tried out, to secure immunity from the coal-dust
danger. A summary of the methods already put forward follows: ¢

1. Loading and cleaning up dust.

2. Sprinkling from water cars.

3. Application of calcium chloride and other deliquescent salts.

4. Sprinkling and washing down with hose and nozzle.

5. The use of pipe lines and permanent sprinklers.

6. Humidifying the intake-air current by steam sprays.

The foregoing comprise the general methods of rendering coal dust
inert. There are other methods which contemplate the prevention
of explosions from blown-out shots and the limiting of initial explo-
sions. These may be summarized as follows:

7. The use of quick-flaming or short-flaming (‘permissible’) ex-
plosives.

8. Coating the walls and floor of the passageways with rock dust,
either throughout or in zones, or placing large quantities of the dust
on easily overturned shelves or platforms above the roads.

9, Limiting the extent of explosions by the construction of briek
or concrete linings of definite length and at predetermined intervals
and keeping them perfectly clean.

LOADING AND CLEANING UP DUST.

Loading dust into pit cars and hauling it out of the mine does not
require extended explanation. The method is obvious and has been
more or less practiced in maintenance of roadways. In rooms of the

"wo new methods have been brought out recently in German: One method recently patented,
called the Kruskopf process, employs a viscous paste applied to all surfaces. Tt is stated that a recent
experiment in a Westphalian mine showed that the ‘‘walls remained dattrp 3,000 hours after the apptica-
tion of the paste, but they dried up within 6 hours when water was used.” (Seientific American, May 21,
1910.) Uydraulie impregnation of the coal face or hydrautic blasting is a system devised by Carl Meissner,
oles are bored 5 to 10 fect into the coal and water is forced in imder a pressure of 10 to 40 atmospheres,
‘The system is sucessful in porous evtls where the roof and slrata are Light. ‘The coal is loosened, so no
explosives ure required and no dust is made, The method is appilicalre to the long wall systein of mining.
See paper by Trippe, “Stosstriinken and hydraulische Kohlensprengung in Steinkohlenttdzen.” Tater-
nationaler Kongress, Diisseldorf,19i0. Berichte der Abteilung fiir Bergball, p. 231. See also p. 164 of this
bulletin.



36 THE EXPLOSIBILITY OF COAL DUST.

depth of each cut was 4 feet. As it is the practice of this company
to “block” or ‘‘snub” down the coal in the center of the room
after cutting with a chain machine, this blocking was done in each
instance to a height of 18 inches. The coal seam is indicated in a
diagram in the published account as 8 feet thick.

The reported figures gave the weights of cuttings ‘‘over” and
“through” various mesh from 14-inch to 80-mesh, and the percentage
that each portion was of the total cuttings. In accordance with the
definition of dust already given, only the cuttings that passed through
20-mesh will be considered here. In the following table the per-
centages of the different sizes have been refigured on a basis of the
theoretical amount of coal produced from the undercut face, assum-
ing a uniform thickness of seam of 8 feet and 82 pounds per cubic
foot of coal in place.

Comparative weights of cuttings and percentages of total coal in Fairmont experiments.

Chain (breast) machine. Puncher.

“Soft” coal (ent 20) “Hard” coal (cut | “Soft coal (eut 20 | « Hard” coal (ent

16 feet by 4 feet).

feet by H feet). | 16 feet by 4 feet) | feet by 4 fe
i
| Pounds. | Per cent.

Pounds. | Per eon

Pounds. | Percent! Pounds. | Per cont

Hl
39] 0.84

‘Through -mesh. 1.03 sis | 1.06 al 1.53
‘Through 40-mesh. part 40 a 20 ota “52 318 “78
‘Through 8-mesh 126 Br 125, 50 165 {31 12 | 46

Mr. George R. Wood, in a paper read before the Coal Mining Insti-
tute of America, June 29, 1909, made some comparisons of the dust.
produced by mining machines, a: orted by Mr. Randolph, formerly
with the Pittsburgh Coal Company. The results were given for dust
passed through a 40-mesh sieve only, in pounds per square foot of
undercutting, as follows:

Pounds of dust passed through 40-mesh sieve, per square foot of undercutting, by several
methods.

Washington Coal and Coke Company mines, Connellsville region,
Pennsylvania:
Hand imining..
Puncher machine. . _
Chain machine with pick-point bits.
Pittsburgh Coal Company,
Puncher machine...

Chain machine (two triald)....00...0c000cceeeeeeeeeeeseeee |

Comparison of the results of the foregoing series of machine-dust
and hand-dust experiments can be made on the only size in com-
mon—40-mesh. In order to compare the weights of dust produced


(veipieng fioijog wioig) “48u ye yenp ouos Yim paean {yeH [49] Ve [NPM JeINIENL

"SNOISOTdXI 40 BALLNEAZYd ¥ SY LSM SNOLS ONIATddY 40 COHL3W ONIMOHS ‘3NIW S1JOLTY NI AVMOYOY 40 3015
SS —— a

ha auvia 92 waving SaMw 40 nvaHi9R


EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 41

the fans were cut out by valves, and the shot was fired about two min-
utes later. The time given in the tabulation of the results is the
period from the moment of injecting the dust to the middle point of
the time used to take the sample.

Ignition of the dust was considered to have occurred in all five
tests, and complete propagation in all but test G-2891, in which the
coal-dust charge was 2 pounds, equivalent to 0.0253 ounces per cubic
foot (or 25.3 grams per cubic meter) for the 40 lineal feet of gallery
used in the tests. The powder charges were tamped with clay.

Results of explosion-gallery experiments on explosibitity of 200-mesh dust (more or less
in suspension).

Flame £ 2
Amount of dust | showed (in- 3 3
used. dieating its S|?
Tengthyat— 3a | §
Date of 4 ‘S
Gallery Explosive used |—; , | #8 be
No. test ba lee]? |e a | %. | 28
test No. | 15) ‘in shot. ay [e2/,]/2,|.| 4 za | 28
al ef [ezlesleul a] 9] 48) 4
#| 83 |25/<3|53] 3 a2 |S
b) Be |gelax (fel e1e | 1
alée |ssja |e | ®@)/2)e [A
| | eng
1] G-2487..| Sept.7..] No charge®.....| $3] 0.0008 | 68.8 |......].----J-..-- | Bo |
1 pounds (567 i ‘7
2) G-2s8s. 'grams) FEF 0035 | 63.5; 1-7] 1-9} ¥es.| Yes.) 288
lack powder. | 0
3 | G-2800. . 2] coset | 35.2) 1-3] 16} ves.) ves.|! 28
i 282
i 85
4] G-2s01. 2| 023] 25.9] 1-3] 14] Yes.! No..|} 282
390
8
5 | G-2s02..|. 2] osi7 fa] 15) 8 { ao
4
«fm. | sna [RARE 9) or nz] a) neve] veal 3
c-2806..| Sept. 9..|) “grams) FFFF }} 23] .ast7! 31.7] 14] 1-6| ves.) ves.) 728] ¢OMe,
| Bitekpoveder. a | | 07
it

Grams per cubic meter can be obtained, approximately correct, from ounces per eubie foot by mult
plying by 100,
5 No charge of powder fired; this test was made to observe the density of dust at successive Intervals
following injection.
All samples were taken at door 3 except these two in test 6, which were Laken at door 1.

Analyses of 200-mesh dust used in experiments and of coked dust resulting from them.¢

Volatile

Moisture| combus- | Fixed
Uble.

carbon, | 48h.

34.00! 59.70] 4.30
1449 | 65-59 | 17,92
Teas) Grae T6.78

&3s

@ Analyses of these coked dusts were not, made until over six weeks after the test; it is probable that
the moisture shown had been absorbed in the meantime.

bin the explosion of the coal dust, the analysis of which is given in the first line of the table, the
quantity of ash for a given amount of the dust would remam unchanged, as in this experiment there
was no contamination. Hence It is possible to calculate the total amount of combustible matter dis-
appearing in the explosion and the distribution of this combustible matter between the volatile matter
and the fixed carbon. The following result fs obtained: ‘That 89.4 per cent of the volatile matter of the
original dust and 73.6 per cent of Its fixed carbon have been consumed.

fA. ©, Pieldner, analyst.



152 THE EXPLOSIBILITY OF COAL DUST.

The spring carries a fine scribing point which rests lightly against
a smoked surface of paper fastened on a heavy drum which can be
made to revolve by means of an electric motor; a continued record of
the development of pressure is thus obtained.

The speed of revolution of the drum is obtained by a special
yy-second time marker (Pl. IX, A). An accurate standard of
time is obtained by measuring the time that a weight takes to fall
from rest through a measured distance; this distance is so arranged
that the time interval shall be exactly one-tenth second. A break
in the electric circuit occurs at the begininng and at the end of the fall
of the weight, and these breaks are recorded on the surface of the
smoked paper on the manometer drum by the movement of a light
style attached to an electro-magnet.

Measurement of velocity. —In order to record the speed of passage
of pressure along the experimental gallery, contact breakers are
screwed into the top 50 feet apart. They consist of light plungers,
which can be weighted at will to withstand from 2 to 20 pounds
initial pressure per square inch, and which on the slightest move-
ment upward break an electric circuit. Plate X, A, shows the posi-
tion before firing and Plate X, B, that after firing. The breaks in
electric current are recorded by means of a standard chronograph.
In order to be able to record a large number of breaks (as many as
12 have been used), and to avoid the error caused by differences in
the latency or ‘‘lag’’ of the electro-magnets on the chronograph, a
special automatic commutator has been devised which enables all the
breaks to be registered by one electro-magnet. An escapement
wheel carrying the commutator brush tends to be pulled round over
the stops, but is held back by an anchor escapement attached to the
armature of an electro-magnet. The cireuits from the contact
breakers on the gallery are connected through this commutator before
passing to the chronograph. One lead of each circuit passes to the
electro-magnet terminal and the other leads are connected, in order,
to the numbered terminals of the stops of the commutator.

The value of this instrument depends upon the time that the
brush takes to pass between two successive steps. This. has been
reduced to less than one-sixtieth seeond, so that, if the contact
breakers on the gallery are 50 feet apart, velocities as high as 3,000
feet a second can be determined.

Sampling of after-damp.—The B. C.D. sampler (P]. XI, A and
B) cons sentially of an exhausted bottle which can be opened
to the explosion gallery at a known time and closed at will alter a
short interval; these conditions are essential for a correct interpreta-
tion of the results obtained.

A pipe pass: s through the side of the gallery 2 feet into the interior.
It is closed at the inner end by a small glass bulb fastened in by



62 THE EXPLOSIBILITY OF COAL DUST.

thermometers held in a rapid current of air or swung at a rapid rate,
The United States Weather Bureau considers that the most reliable
instrument for measuring relative humidity by this method is a sling
or whirled psychrometer. The standard instrument used by the
Weather Bureau consists of a pair of thermometers mounted on a
thin metal plate, to which a swivel handle is attached by a loose link.
The wet-bulb thermometer projects below the dry-bulb thermometer
and the bulb of the former is covered with a thin tight-fitting muslin
sack which, just before the observation, is dipped into water. This
instrument is described in the psychrometric tables issued by the
Weather Bureau.

To make standard readings with the sling psychrometer, the speed
of the revolving bulb must be 15 feet per second. The psychrometer
should be whirled for fifteen or twenty seconds and then quickly read,
the wet bulb first. This should be repeated until successive readings
of the wet bulb agree closely.

HYGROMETER USED BY BUREAU OF MINES,

In a mine it is difficult to use the standard sling ps
without breaking it. The mining engineers of the United States
Bureau of Mines have been supplied with a psychrometer, more
commonly called a hygrometer, in which the thermometers are
mounted on the hinged covers of a shallow box. Opposite the
thermometer bulbs the covers are slotted to allow free circulation
of air. In the use of this hygrometer as designed, the covers are
opened wide, held firmly, and swung to and fro, facing the air cur-
rent. The motion must be violent to obtain the necessary speed.
Another method of using it has therefore been improvised by the writer.
A hole has been bored through the top of the box parallel with the face
of the hinged lids and thermometers and a long pin inserted. The
covers are held open by a loop of string passed around the back of
the box and attached to a pin. The instrument can thus be whirled
like the standard sting hygrometer, with much greater ease than it
can be swung. A picture of the instrument with this rearrangement
is shown in Plate V. A further improvement could be effected by
making the box of aluminum.

STATIONARY HYGROMETER,

There are several types of stationary hygrometers in which the air
current is produced by small fans. In another type the hair hygrom-
eter, the rapid change that takes place in the length of a strand of
hair with changes in the amount of atmospheric moisture has been
utilized to move u pointer by means of a delicately adjusted lever
arm. This pointer carries on the end an inking arrangement, so that
it can trace a line on sectional paper wrapped on a revolving cylinder


BIBLIOGRAPHY. 185

Gatroway, Witura. On the influence of coal dust in coltiery explosions (II).
Proc. Roy. Soc. London, vol. 28, 1878, pp. 410-421. Describes experiments at
Llwynpia colliery.

Sur les explosions des poussitres charbonneuses. Bull. Soc. Ind, Min,, vol.

1878, pp. 617-684

The accident at Llan colliery. Iron, vol. 11, June 8, 1878, p. 708.

Explosion at Fowler’s steam coal colliery, Pout-y-Pridd, Wales. Iron, vol. 12,

July 13, 1878, p. 34.

De V’influence des poussitres charbonneuses sur les explosions dans les hou-
illéres. Bull. Soc. Ind. Min., ser. 2, vol. 9, 1880, pp. 157-174.

ve LA Gourmitre, Haton. Commission chargée de I’étude des moyens propres &
prévenir les explosions du grisou dans les houilléres, 1878. Cites opinions of De
Souich and others on explosibility of dust.

Hau, Henry, and Cuarx, Goro. Mechanical effects of blown-out shots on ven-
tilation. Trans. North of England Inet. Min. and Mech. Eng., vol. 25, 1876, pp.
239-248. Describes experiments with coal dust in adit 45 yards long. Authors
conclude dust may greatly lengthen flame of a blown-out shot. Discussion in
vol. 26, 1877, p. 101, vol. 28, 1879, p. 85.

Marreco, A. Fretre-, and Mortson, D, P. Results of some experiments on the
effect of coal dust in colliery explosions. Trans. Chesterfield and Derbyshire
Inst. Min. Civ. Mech. Eng., vol. 5, 1878, pp. 267-277. Describes experiments
in box 8 feet long. Authors conclude that coal dust and air without any fire
damp are inflammable by a blown-out shot. Discussion of the paper, vol. 6, pp.
49, 203, 244, 290.

An account of some recent experiment with coal dust. Trans, North of
England Inst. Min. and Mech. Eng., vol. 28, 1879, pp. 85-100. Abstract of the
paper, by Louis Dombré: Annales des mines, 7th ser., vol. 15, 1879, pp. 374-383.

von Meyer, Ernst. Gases inclosed in coal. Jour. Chem. Soc., vol. 25, 1872, pp.
798-801. Abstracts of paper in Journal fiir praktische Chemie, ser. 2, vol. 5, pp.
144-183, 407-416.

Peck, L. W. Explosions from combustible dust, Sci. Am. Suppl. No. 166.

Pecknam, S. F. On the explosion of the flouring mills at Minneapolis, Minn., May
2, 1878, and the causes of the same. Am. Jour. Sci. and Art, ser. 3, vol. 16, 1878,
pp. 301-306.

Screntiric AMERICAN. A great flour-mill explosion. May 18, 1873, vol. 38, p. 315.
Brief comment on explosion at Minneapolis.

Vrrat, -------. Recherches sur l'inflammabilité des poussidres de charbon. Annales
des mines, ser: 7, vol. 7, 1875, pp. 180-197. Describes explosion at Champagnac
colliery, November 2, 1874, and experiments with dust.

1881-1880.

Axet, F. A. Report on the results of experiments made, etc. Report to the Home
Department, March, 1881, with appendices, on Seaham colliery explosion.

Sur le réle des poussiéres dans les explosions de mines. Annales des mines,

ser. 7, vol. 20, 1881, pp. 125-159.

Some of the dangerous properties of dust. Proc. Roy. Inst. Great Britain,

vol. 10, pt. 1, 1882, pp, 88-113. Mentions several explosions in flour mills, and

reviews the coal-dust problem. Speaks of certain noncombustible dusts exerting

a contact or catalytic action on gas mixtures. Discusses preventive measures.

Some of the dangerous properties of dusts. Abstract of lecture at Royal
Institute. Nature, vol. 26, 1882, pp. 19-22. Also Trans. Chesterfield and
Derbyshire Inst. Eng., vol. 10, 1882, pp. 245-280.

-———- Accidents in mines, Proc. Inst. Civ. Eng., vol. 90, 1887, p. 160.

—— Mining accidents and their preventions. 1887.



140 THE EXPLOSIBILITY OF COAL DUST.

reduction of carbon dioxide to carbon monoxide, was not as great
as had been expected. Thi: especially true in the flame itself, as
the amount of carbon monoxide there is very small. It requires a
certain amount of time to bring about the reduction of carbon dioxide,
and the amount of carbon monoxide became appreciable only after
elapse of such a period.

At first it was impossible to explain the part played by finely
divided schist in retarding the propagation of the flame, as 100
grams of that material should lower the theoretical temperature only
50° C. Even after allowing for the absorption of heat that takes
place when the chemically combined water of the schist is expelled,
the calculated temperature was higher than the temperature in
certain experiments in which propagation was obtained with coal
dust alone.

The explanation given for this discrepancy is the difference in the
screening action of coal dust and an inert dust. The effect of a dust
cloud in front of the flame is to form a screen. With respect to coal
dust, the greater the concentration the greater the surface of this
screen per unit of volume, and the more favorable are the conditions
for propagating the flame. But with a dust cloud composed partly
of inert particles, these serve the same screening purpose, but do not
take part in the combustion. They do not act like an excess of
carbon, but merely by their screening effect they exercise a retarding
influence in addition to that of the heat which they absorb in attain-
ing the temperature of the flame.

By a careful interpretation of the analyses of gas taken during the
explosions, it was demonstrated that certain particles of the coal
were completely consumed, while others participated only to the
extent of their volatile matter. For the propagation of the flame
it is necessary that the proportion of substances undergoing rapid
combustion—that is, the fine dusts and the distilled gas—should be
somewhat more than enough to make the mixture inflammable, so
that a suflicient amount of heat shall be disengaged to raise the dust
cloud in front of the flame to the temperature of ignition. This may
result from the volatile matter, or from the finest coal dust, or from
a combination of the two. These, however, are complicated ques-
tions to be dealt with only by further experimental work.

FIRST SERIES OF EXPERIMENTS AT PITTSBURG TESTING STATION,

During the past year the writer has studied a number of coals with
respect to their relative absorption of oxygen from oxidizing agents,
especially standard solutions of chromic acid, with the thought that
the amount of absorption would be indicative of the relative tendency


‘NOLLVIS ONIS3L OYNESLIId ‘1 “ON AYATIVD 1SNG GNY SYD NI 4SNG WO WOY NOISOTdx3

Vaivrg og NLaTIAG sania 40 avaung



HUMIDITY OF MINE AIR. 63

turned by. clockwork. In this way a permanent and continuous
record is obtained.* This instrument is sometimes combined with a
temperature recorder. Such combination instruments are used by
the Fairmont Coal Company at their Monongah mine. They are
described by Frank Haas in a part of this bulletin (p. 169).

PRINCIPLE OF WET AND DRY BULB THERMOMETER.”

The operation of the wet and dry bulb thermometer is based on.
the fact that the evaporation of water requires a certain amount of
heat. When a current of dry or partly saturated air passes over a wet
surface, such as the wet bulb of a thermometer, some of the water
is evaporated and carried along by the air in the form of vapor.
The absorption of the heat required to evaporate the water causes a
cooling of the bulb.

The lower the relative humidity of the air, the more rapid is the
evaporation at the surface of the wet bulb, and consequently the lower
its temperature. As the bulb is moved through the air its tempera-
ture falls to a point where the amount of heat absorbed by evapora-
tion is just equal to that received from the surrounding air. The
first quantity of heat is proportional to the rate of evaporation, v.
If we assume that the second quantity is proportional to the surface
of the bulb, A, and to the difference in temperature between the
surrounding air (measured by the dry bulb), and the wet surface,
Ta—Ty, then A (Tg--T,,) =av, where a is a constant.

Dalton found that the rate of evaporation of water is. proportional
to the surface exposed and to the difference between the pressure of
saturated vapor at the given temperature, and the vapor pressure of
the surrounding air, p,—p, and inversely proportional to the baro-
metric pressure, H; then—

bA(pi—p)
ya JP Pp?
where b is a constant. Hence—

A(Ty~T,) = PAG)

H
or, Pi—P= gp (Ta-Tw).

Writing are: .
p=p,—cH(Ta—Ty).

@ Bergassessor Forstmann ((ltickauf, January 5 to February 12, 1910) states that the hair hygrometer
tried in the recent (erman experiments did not give consistent results. It was thereforo abandoned in
favor of swinging wet and dry bulb thermometers.

This explanation and the calculations are given by Dr. J. K. Clement, physlefst, now of the United
States Bureau of Minos.



174 THE EXPLOSIBILITY OF COAL DUST.

temperature, the humidity
within the mine showed a
tendency to equalize itself and
—| produced a more nearly
straight line. The fact that
it ran higher than the humidity
~—}--} at the fanis due entirely to the
previous wet condition.

BoNOAY
steiz2 46810]

OBSERVATIONS OF EFFECT OF
STEAM.

A record (fig. 25) was also
taken with the instruments in
the same position and with the
exhaust steam going into the
mine. The faninstrument was
to show the atmospheric hu-
midity, while the instrument
400 feet inside the mineshowed
the full effect of the steam.

SATORDAY

24 egioie2 se eto] 246 s10i22 48 810

The moisture made itself
apparent immediately by satu-
rating the air and holding the
humidity at 100 per cent,
irrespective of the outside
condition. The temperature
showed an average increase of
only 8°.

5 i The exhaust steam was not
mies i 1 turned into the mine until six
fs 827 T +
Et 3} tt hours after the instruments
= aes started recording.
t
i

THuRaDAY
24 este 4 6510

WEDNESDAY

EFFECT OF HEATING MINE
AIR.

Fiupe 25—Chart of temperature and relative humidity of mine air with exhaust steam on and heater off.

It is to be noted, however,
that the increase in tempera-
ture was greatest when the
outside temperature waslowest.
The amount of heat supplied
: ear aa being uniform, a constant in-
afte TES GS crease in temperature should
$622 ee ee 8 5 © be expected if there were no
T Mead sewwonge eo0vseq disturbing elements present.

FoEOAY
Stolze eqtoiz2s saso| 24 6 eioia2s oto

i
Ht
y

— | “4

ae
y



178 THE EXPLOSIBILITY OF COAL DUST.
MOISTURE CARRIED AS FOG.

The capacity of air to carry water vapor is limited by its tempera-
ture, but the quantity of water that can be carried mechanically
in the form of a fog is limited only by the velocity of the air current.

The relative proportions of water that can be carried in the form
of vapor and as fog have not been determined. The proportions
can very readily be determined, however, and observations were to be
carried out on this point during the winter of 1909-10. The first
effect of exhaust steam on air would be the saturation of the air
with water vapor, the remainder of the steam being deposited as
water or carried in the form of a fog. This fog near the inlet of the
exhaust steam is in the form of a dense white cloud, so thick as to
hide the light of a mine lamp only a few feet away. In traveling
with the air from the exhaust-steam intake the cloud gradually
becomes thinner; farther in the air is clear near the side walls and
the roof, the fog traveling in the center of the entry in the form of a
cylinder with a revolving forward motion. The cylinder or cone
form gradually grows less in diameter, ending in an indefinite point.
This approximate point has been designated the fog line. It is
remarkable how promptly the position of this fog line responds to
a rise or fall of outside temperature by shifting backward or forward.

For practical purposes and comfort to miners it is advisable to
keep this fog line from advancing to the working face. This can be
done in several ways—first, by reducing the volume and thereby
the velocity of the air current; second, by increasing the number or
area of air ways; third, by so changing the air courses that the dis-
tance to the working face is increased. Conditions in a developed
mine where a blowing fan is used would be very unusual if no one
nor any combination of methods could be utilized to bring the fog
line within the limits of practical application.

QUANTITY OF STEAM NEEDED FOR SATURATING MINE AIR.

In the observations made and the results obtained so far the nec-
essary quantity of exhaust steam for a unit quantity of air has not
been definitely determined. An approximately correct figure was
assumed to be three-quarters of a horsepower of exhaust steam (from
a simple reciprocating engine) for each 1,000 cubic feet of air sup-
plied. The size of the mine does not enter into the assumption. In
mines of small development the ratio of fan horsepower used to
quantity of air supplied is less than that noted above as necessary
for saturation. In mines older and of larger developed area, the
tatio may be greater than necessary. In Monongah No. 8 mine,
in which most of the experiments have been conducted, the ratio is
about 0.4 or only 53 per cent of what is necessary. In order to make




INVESTIGATIONS AT EUROPEAN STATIONS. 153

sealing wax. The outer end of the pipe is screwed to the sampling
bottle and the whole then evacuated. A small hammer head is
fixed just over the glass end, held back by a fuse wire. On the fusing
of this wire the hammer falls and breaks the glass, thus allowing the
gases to enter the exhausted bottle. The same current that fuses
the wire also releases a small weight, which, after falling a certain
distance, pulls out a pin, thus allowing a heavy weight to fall and
in falling to close a tap at the head of the bottle. The gases are
afterwards withdrawn through a mercury pump for analysis. The
time that the bottle remains open depends upon the distance that the
small weight falls; this can be varied at will.

The time at which the bottle is opened to the gallery by the break-
ing of the glass bulb is determined by causing the explosion itself
to make the electric current pass through the fuse wire; this is effected
by means of the B. C. D. contact maker shown in Plate XII, A
(before firing), and B (after firing).

CALCULATION OF TEMPERATURE AT ALTOFTS.

The temperature of explosion (T) is calculated at Altofts from
the pressure on the assumption that T=Z+pt; Z being the original
temperature (absolute) of the gases, p the observed pressure, and t
the normal temperature. For example:

Let p=10 atmospheres;
t=10° C. and therefore
Z= 10° +. 273° = 283° C.
Then T= 283 4- 2,830 =3,113° C.

CHANGES IN GALLERY AT LIEVIN.

At Liévin station an important change has been made since Jast
summer in the construction of the intake portion of the principal
gallery. This was trapezoidal in section, buried under stone débris,
and constructed so as to permit different kinds of timbering, the
idea being to imitate, as far as possible the structural features of a
roadway in the mine.

The violent dislocations of timber frames, however, and other
heavy damage caused by the foree of explosions, necessitated a
stronger construction, and the whole of the buried part of the gallery
(38 meters) has been replaced by boiler shells 10 millimeters in
thickness and 2 meters in diameter. The gallery is lined with
wooden boards and ballasted outside with débris so as to leave the
top free. (See fig. 14.)

The gallery, which was 230 meters long in October, 1909, will be
extended to a total length of 400, perhaps 500, meters.


118 THE EXPLOSIBILITY OF COAL DUST.

Before the apparatus was used the following facts were ascertained:
With the gas unlighted, the air blast carrying coal dust laid a heavy
deposit of it on a porcelain plate set a few centimeters from the end
of the tube. With the gas lighted, burning with pure air, the burner
gave a blue flame, scarcely visible, 5 centimeters long. When the
blast was operated with air containing coal dust in suspension a
bright blue flame was obtained which showed many brilliant sparks
of burning carbon, but did not deposit soot. With the two indi-
cators in position, the gallery free from dust, the flame of the
lamp fed by dust-laden air and directed into the gallery, the flame
did not change color, but elongated about 2 centimeters. The indi-
cators were not charred; the pendulum recoiled, but without shock.

These preliminary facts having been ascertained, the gallery was
charged successively with dusts 1, 2, 3, and 4. When the dust-fed
flame was directed into the tube, a red flame traversed the gallery
rapidly, and the tube was left filled with fumes. After these were
removed the walls were found to be covered with a coating of dust
impregnated with water and bituminous matter. The indicators
were burned, and the pendulum received a shock. The results of
these experiments are given in the following table:

Results of Vital’s experiments

Observations. Dust 1. | Dust 2. Dust 3. | Dust 4.

Flat

Mo ethecceceeec| Hi8mge {aso osm | scam

dulum

Conduet: TU) Regutar? Regular, Regular. 2.10.07... Regular.
Color... 22202 Rell without bril-| Red without brit’ | Blue and red with’ Red without bril
Viant particles. | liant particles. | out burning par- lant particles.
ticles.

Indicator: |

NO. Mecessseeeossee] Burnt. ! Burnt. Intae Burnt.

No.2 ST) Charred: Do.
Angular niotion of pen "id". oe DINER TITS ape,

Dusts 1 and 2 when removed f from the tube had lost their black
color and become reddish. No crystalline particles were observed,
but globules composed largely of water were found on the inside of
the tube. The crucible tests on these dusts before and after the
experiments gave the results contained in the following table:

Analyses of dusts before and after ignition in Vital’s experiments.

Dust} Dust 2.

Before | After | Before | Atter
(@) it

}. (ce). 1 (dd).
| a _
Moistores.ccccseeseceeece cee eee oa ns] amp at
Dry di | vr —
alti mat ge] BS
4) 83

ined orion



1 2 3 4 5 é 7
» Gs

a
b
Cc
a nu
e te s
hk tg 7/4 es

Pe". ; e)
iP NT te,

5 r= — |_|
kN Zi
Z
;

COKE PRODUCED FROM 80 TO 100 MESH DUST.

Photographed on half-inch squares.

Experiment G-2894,


REMEDIES FOR COAL DUST. 83

France does not maintain an official testing station, but the mining
regulations require that an explosive for use in coal mines shall not
develop sufficient heat to ignite fire damp, the flame temperature
being determined by calculation of the chemical reactions taking
place at the moment of explosion.

It has thus become a requirement in the coal-mining countries of
Europe to employ only such explosives as have passed certain tests
or have met certain requirements. It is fully recognized that no
explosive has yet been produced that is absolutely free from flame,
but when the explosive used in a shot does not exceed the amount
specified as allowable, it has so little flame that gas and dust under
ordinary conditions will not ignite from its discharge. The quantity
that may be used of each explosive is therefore specified. It has been.
termed the “charge limit” by Victor Watteyne, head of the mining
department of Belgium, and this term has been generally adopted.

In the United States, so-called “safety” blasting powders were
introduced in the bituminous coal fields of Pennsylvania and West
Virginia in 1902, and in the anthracite field of Pennsylvania at a
later date. Their use slowly increased, but was not widely extended
until 1909; in fact, some of the early brands were withdrawn from
the market by their manufacturers.

Soon after the Pittsburg gallery was established and tried out
informally, a letter was sent by the Director of the United States
Geological Survey, on January 9, 1909, to the manufacturers of
explosives in the United States setting forth the conditions under
which explosives would be examined and the nature of the tests to
which they would be subjected. By May 15, 1909, 29 explosives
had been tested. Of these 17 passed the test requirements and were
termed ‘permissible explosives.” A circular was issued to this effect
on May 15. By October 1, 1909, 14 additional explosives had passed
tho requirements and a second circular was issued reporting this fact.
A third circular, issued May 16, 1910, lists 14 additional explosives,
or 45 in all. A fourth circular, issued by the Bureau of Mines in
January, 1911, as Miners’ Circular 2, contains the names of 71 per-
missible explosives.

Although, as it is made clear in the circulars, no explosive is abso-
lutely safe under all conditions, there is, nevertheless, very little
chance of causing an explosion of fire damp or coal dust with one of
these permissible explosives under any ordinary conditions, provided
it is used in accordance with the conditions set forth in the circular.

The contrast between the ‘‘permissibles” and black powder is very
great. With equivalent quantities the flame of black powder is more
than three times as long and has a duration from 2,500 to 3,500
times that of a “permissible explosive.”



12 THE EXPLOSIBILITY OF COAL DUST.

The remarkable evidence given by Faraday on the importance of
coal dust as an explosive agent was overlooked for many years.

OBSERVATIONS BY FRENCH ENGINEERS PRIOR TO 1890.

The final report of the accidents in mines commission (1886) gives
the following account (p. 31) of the first French publication on this
subject:

Although the reports of Faraday and Lyell were published in 1845, these publica-
tions appear to have remained long unknown in France, for in 1855 M. du Souich,
chief government engineer of the Sainte Etienne Arrondissement, when referring to
an explosion which had occurred at Firmininy, advanced as new the view that the
deposition of crusts of light coke on the props was due to dust which had been swept
up and transported to a distance by the violent current produced by the explosion
and which, becoming in part inflamed, had extended and prolonged the destructive
effects originated by the fire damp. On the occasion of two explosions in 186)
M. du Souich again dwelt upon his views regarding the part played by coal dust
in increasing the disastrous effecta of fire-damp explosions.

In 1867 M. Verpilleaux made some experiments with coal dust
and concluded that it is an important factor in mine explosions.
M. Vital, in 1875, while studying the effect of an explosion in a part
of the Campagne colliery, France, where fire damp had never been
found, made experiments and from the results decided that “very
fine coal dust, rich in inflammable constituents, would increase the
intensity of an explosion of fire damp and prolong its extent.”

In 1882 M. Mallard and M. Le Chatelier, members of the French
fire-damp commission, reported, as the result of their inquiries, that
“they rejected the theory that coal dust was any serious danger, and
maintained that no colliery explosion of any importance could be
attributed with any probability to the action of coal dust.”#

This unfortunate conclusion delayed recognition of the danger of
coal dust in France for many years, and apparently the explosibility
of coal dust did not receive general acceptance among French engi-
neers until after the Courrieres disaster of 1906.

EXPERIMENTS IN ENGLAND BETWEEN 1850 AND 1885.

In 1870 Mr. William Galloway, former government inspector in
Scotland, and then in charge of mines in Wales, began a special study
of colliery explosions. He had observed that all the great explosions
in Wales had occurred in dry and dusty mines; also the only great
explosion in Scotland had occurred in the only dry mine in Scotland
known to him. In 1875 he commenced a series of coal-dust. experi-
ments in a long box or miniature gallery, and on March 2, 1876, read
a paper before the Royal Society in which he stated that ‘‘if coal

Second Rept, Roy, Comm., 1894, p. 5


CONTENTS,

Tentative conclusions on the dust problem—Continued.
Advantages and disadvantages of proposed remedies
Cleaning up dust—washing down walls.....
Permanent sprinklers—zonal linings
Use of exhaust steam spray
Stone dust.
Observations on manifestations of coked coal dust in mine explosions.
Character of coked dust. .
Position of coked dust after an explosion
Special features in dust explosions.
Laboratory investigations of the ignition of coal dust, by J. ©. W. Frazer
Introductory statement
Early experiments of Galloway .
Ignition of dust falling on flame.
Experiments of Vital........
Experiments of Hall and Clark.
Experiments of Abel
Experiments of Mallard and Le Chatelier.
Later experiments by Galloway. .
Experiments of Thorpe...
Reduction of pressure following
Experiments of Engler. .
Lecture experiment of Bedson ‘ind Widdas.
Experiments of Holtzwart and Meyer
Laboratory experiments of Bedson and Widdas.
Experiments at Liévin, France. .....
First series of experiments at Pittsburg testing station
Second series of experiments at Pittsburg testing station
Significant points in experiments. . .
Coal-dust investigations at European testing stations, by. ‘Axel Larsen.
Protective measures under study.
Apparatus and methods at Altofts and Liévin.
General statement. ...............-- -
Instruments at Altofts. .
Calculation of temperature at Altofts. ..
Changes in gallery at Liévin
Instruments at Liévin.
Results at Altofts and Liévin.
Experiments with Protection zones at Liévin.
Conditions at Altofts. .
Experiments with protection zones at ‘Altoft
Experiments at Altofis on means of ignition .
Distribution of stone dust in Altofts gallery and mine
Investigations at Frameries in Belgium.
Direction of inquiry... ....
Objections to watering roadwa;
Tests of explosives.
Extension of gallery. . .

Investigations in Prussia. .
Special preventive measures
Breaking coal by direct. water pressure.
Kruskopf spraying process.



142 THE EXPLOSIBILITY OF COAL DUST.

Before each experiment the bottle A is thoroughly cleaned out and
fresh air aspirated through it. Fresh air is also forced into B and C
through g (pinchcock & being also open) until the desired pressure of
mercury is indicated in the manometer c. The cock & is then closed
and remains closed during the remainder of the experiment. The
stopper carrying the coil is put in place, and the tubes ¢ and D are
connected. The tube f, containing the coal dust, is inserted in its
proper place and connected with C.

To secure comparable results the coil is always heated the same
length of time, three minutes, before the dust is scattered from /.
The same current is used each time, and is kept perfectly constant
the entire three minutes. With the coil used in these experiments a
current of 6 to 7 amperes has been found satisfactory.

Just before scattering the dust the steel ball is placed exactly
in position. At the end of the three minutes the cock 7 is released
instantaneously, and the air entering A puffs the dust into the bottle
and about the coil. It has been found better for the operator to
replace the cock 7 and pinch the tube with his fingers before releasing,
as the instantaneous release can be accomplished much more cer-
tainly in this way. The pressure in the bulb (of 150 cubic centime-
ters capacity being 165 millimeters of mercury, the pressure resulting
therefrom in A would be only about 12.7 millimeters.

With the apparatus and method of procedure described above, the
ignition of a number of coals has been studied. In every experiment
ignition has taken place readily, except those with anthracite, natural
coke, and charcoal.

With a pressure in (’ of 165 millimeters of mercury, and a current of
6 to 7 amperes, 0.04 gram of dust was found quite sufficient for pro-
ducing decided inflammation with all the coals investigated, with the
exception already noted, and with some coals even less than this
amount was required to produce measurable results.

Tn the table below are given the results of experiments with 11 coals
of varying character and from different sources. In each experi-
ment 0.04 gram of dust was used, dust meaning coal finely ground and
passed through a 100-mesh sieve. The current employed was 6.4
amperes; the pressure in @ was 165 millimeters of mercury.

In the first column of the table is given the character of the coal,
while the third column shows, in centimeters from the end of the
barrel D, the distance to which the metal ball was projected.




BUREAU OF MINES BULLETIN 20 PLATE 1%

=

A, TIME MARKER, ALTOFTS EXPERIMENTAL GALLERY.

B. MANOMETER, ALTOFTS EXPERIMENTAL GALLERY.


HUMIDITY OF MINE AIR. 69

Gallons of water per 100,000 cubic feet of air for specified temperatures and percentages of
saturation—Continued.

Relative humidity (per cent)—

‘Tempera- Z
ture, I
10 20. 90, 40, 70. 80. #. 100.
i | ee L
1.012 | 1.518 3.541 | 4
vodg | 1.574 3.672 471
1.088 | 1-632 3.807 4.595
1.128} 1.602 3.947 | 5.075
1169} 1.754 4.092 5.261 |
\
122] 1.818 | 4.241 5.483 |
1.256 | 1.883 4.395 5.650
1301] 1/952 | 4.555 5.856
1,348 | 2.022 amis | 6.066,
1.396 | 2.084 | 4.885 6.281 |
1.446 | 2.169 | $060 | 6.506,
1497 | 2.246 | 52a 6.738
1.550 | 2.325 5.46) 6 6.976
1.005 | 2.407 5.616 | 6.418} 7-221
L661 | 2.492 B.S | 6.645 | 7.473
2.578 6.014} 6.874) 7.738
2667 624] T1138] som
2.760 6.430 | 7. 8.279 |
2.855, 6.661] 7. 8564}
{ 2.953 6.890 8.859 )
Los | 3.054 7.125 0.161! 10.17
1-088 | 3.158 7.368, 9.473 | 10.525
1088 3.264 T6l6 9.792 | 10.880
125 | 3315 a8 10124) 1149
1.163 | 3.488 8138 10.468.) 112626
1.282 3.725 S691 WIT) 12.415
1.382 3.897 5.97 11 b§2 12. gD
1335 3.074 9.974 11,933 | 13.248
1.360 4.106 9.580 qwesi7 | 13.686
1.413 4.240 9.892 12.719; 14.132
1.450 4.378 18.185 | 14.504
1507 4.520 8. 15.066
1.556 4.067 15. 556
1.605 4816 16. 054
1.657 4.971 16.569
L710 5.130 17.090
: 5.293 17.643
5.461 18.202
5.633 18.776
5.810 19.365
3. 5.901 19.971
4119} 6.178 20, 504
4246 [6.370 21.232
4.378 | 6.566 21. 888
85. 4.518 2.564
a 4.651 23.254
88. 4703 11.982 | 28. 64
89. 4.939 M7 24. 64
90. 5088 12.720 | 25.438
OL. 2.621) 5.241 23.586 | 26.207
2 2 5.399 in | 24205 | 26.904
98 2.780 | 5.560 25.000 | 97° 800
4, 863 | 5.726 ' 786 | 28. 629
95. Dogs | 5.895 14.739 29.477
15.173 30.346
15.020 31.239
16.078 { 22.156
: 16.549 33.008,
100.0200°7"] 2.406 13.623 | 17.029 34058



78 THE EXPLOSIBILITY OF COAL DUST.

constant effort and the employment of men to go continually from
point to piont. It has the merit that water can be effectually applied
where most needed, and it is not interfered with by the haulage sys-
tem. Undoubtedly it requires a strong roof and a floor that will not
heave from ess of water; otherwise the cost of maintaining the
roadways is high.

PERMANENT SPRINKLERS.

The use of permanent sprinklers to dampen coal dust began in
England shortly after the report of the royal commission of 1886.
It is spoken of in a paper read in 1887 by Professor Abel.t He
mentions the Harris Navigation colliery, in which ‘‘the temperature
was reduced 6 degrees” by water sprays. He also refers to the sys-
tem of water and compressed-air sprays invented by Mr. Henry
Martin, who appeared before the royal commission in March, 1892,
and asserted that he had employed the system since 1886 in the
Dowlais collieries. Mr. Martin stated that the sprays used air
compressed to 45 pounds and water under a pressure of 90
pounds to the square inch. The water was used under high pressure,
so that if the air compressor stopped for any reason a fine spray
might be produced with water alone. The effect of using compressed
air was to make the spray very light, so that it would travel a long
distance in the air current. Mr. Martin stated that the sprays were
located 50 to 80 yards apart, although it is not strictly necessary to
have them less than 200 yards apart. Where they were nearer
together it was not necessary to use cach one continuously. Mr.
Martin said that the system incidentally improved the ventilation
and temperature of the mine. They used the sprays at night but
not during the day. He submitted a list of hygrometric readings
taken 20 to 60 feet distant from each of the sprays to show that prac-
tically complete vapor saturation was obtained in every instance.

There does not appear to have been any wide extension of the use
of compressed air and water sprays in mines, but the system has been
applied in cotton mills in New England to humidify the air, both for
the health of the employees and for the effect that it has upon the
weaving process. In mines of the United States some attempt has
recently been made to introduce such sprays, but as yet they have
not been used to any considerable extent.

At the Pittsburg station, in the experiments carried on in the
explosion gallery to try the effect of humidity in rendering coal dust
inert, compressed air and water sprays were employed. As they
were installed, the water has very little head, a few pounds only; the
air is under 35 pounds compression. A very fine spray like a mist is

Abel, Frederick, Mining explosionssnd their prevention, 1889, pp. 116, 182,


Bulletin 20
DEPARTMENT OF THE INTERIOR
BUREAU OF MINES

JOSEPH A. HOLMES, Director

THE

EXPLOSIBILITY OF COAL DUST

BY
GEORGE S. RICE
WITH CHAPTERS BY

J. C. W. FRAZER, AXEL LARSEN, FRANK HAAS,
AND CARL SCHOLZ

[Reprint of United States Geological Survey Bulletin 425]

WASHINGTON
GOVERNMENT PRINTING OFFICE
pL


100 THE EXPLOSIBILITY OF COAL DUST.

atile matter of the particle has been partly volatilized and burned
in the surrounding air, If this is true, the oxidation of the fixed
carbon probably does not, except in dust particles of minutest size and
greatest purity, take place in time to assist in the first extension of
the flame, although it is undoubtedly an important factor in the
succeeding moment, intensifying the flame, and hence increasing the
violence and pressure of the explosive wave.

The analyses of burned dust from explosions, both in mines and in
the Pittsburg gallery, show an increase in percentage of ash over the
ash content of the original coal often considerably greater than the
increase due to expelling the volatile matter. Such an increase
shows that there has been combustion of the fixed carbon. The
increase in ash has been especially marked in the 200-mesh dust used
in the Pittsburg density tes (See p. 41.)

M. Taffanel’s experiments with antliracite and those of the Pitts-
burg station indicate that under the conditions in the galleries used
anthracite dust will not propagate an explosion.* This supports
the view expressed above that it is the burning volatile combustible
gases that carry forward the initiating flame and that the combustion
of the fixed carbon is secondary.

MOISTURE,

Moisture contained or carried in coal dust is probably converted to
steam before gas is evolved from the dust particles, and if enough moi
ture is present the absorption of heat in this way may prevent sufli-
cient heat from being imparted to adjacent dust particles to evolve
the volatile gases and raise them to the ignition point. Further-
more, if the moisture in or surrounding each particle of dust is suffi-
cient in quantity, the vapor therefrom will dilute the evolving gases
or else tend to surround them with an outer incombustible envelope

a Since the foregoing was written, experiments have been made at the Altofts station with wood charcoal
and Welsh anthracite dust. The charcoal was very fincly divided, 78 per cent passing through a 240-mesh
sereen. The rate of propagation with this dust was very slow, from 116 0 215 feet per secon”, and the pres:
sures developed were relatively low, less {han § pound

‘The Altofts’ observers consider that these results indicate that: ‘‘A finely divided carbonaceous dust,
incapable of giving off combustible gas, on heating will form an explosive mixture with air,"' and add,
“The thne that must be allowed for distillation of gas from coal dust. to take place seems to preefude the
possibility of that gas playing any important part separately from the dust in the propagation of the
explosion. Moreover, the decomposition of coal, yietding inflammable gases, absorbsenergy.” (Record
of first series of British coal-dust experiments, p. 159.)

‘Two tests were made with Welsh anthracite of the following composition, ash and moisture f
matter 8 per cent, fixed carbon 92 per cent.

‘The coal as received contained 1.4 per cent moisture and 3.9 percentash. The eowldust zone was placed
260 fect in front of the point of ignition on the downeast of Intake side

“In neither case did (he flame travel any distance toward the downcast, i. e., against the normal dir
Uon of the air current, but toward the return the flame was propagated 4 distance of 280 feet in Experi
ment No. 40 and 285 feetin Experiment No. 40-4.” (Record of first series of Brilist:coat-dust experiments,
P. 371.) This shows 8 very Imperfect propagation; more of an indammation than a true explosion.

2 Volatile



166 THE EXPLOSIBILITY OF COAL DUST.

Although not without useful features, possibly in connection with
protection zones, the invention has been presented in a form that is
not likely.to be adopted in practice, being too costly and of doubtful
efficacy. The inventors refused to give particulars, owing to a pend-
ing application for American patent rights.

EXHAUST STEAM AS A PREVENTIVE OF DUST EXPLO-
SIONS.

By Frank Haas.
MOISTURE IN COAL DUST.

HOW MOISTURE PREVENTS EXPLOSION.

Exhaust steam is used to prevent coal-dust explosions on the theory
that wet coal is more difficult to ignite than dry coal; also that a
flame propagating through moist air suffers a greater temperature
loss than one propagating through dry air.

To make coal dust absolutely and theoretically inert as a combus-
tible—that is, to make a mixture of such composition that it would
not ignite or consume from heat of its own generation—would require
six or seven times its weight of water. This quantity of water is so
large, causing, in fact, a condition practically equivalent to sub-
mergence, that its use is impossible. Fortunately the total quantity
of heat which coal dust supplies is not the important factor in dust
explosions, but rather the temperature of ignition. If the temper-
ature is under control absolute safety may be attained. Before it is
possible to ignite the combustible portion of coal dust or any other
combustible containing water, physically or otherwise, such water
must be evaporated.

RESISTANCE OF COAL DUST TO MIXTURE.

A very serious obstacle to complete success in preventing ignition,
not only by introducing water by exhaust steam, but by any other
method of application of water, is the property of coal to resist
mixture with water, except to a very limited extent, It has been
shown, in experiments described by the writer, that extremely fine
coal dust, after being submerged in water and thoroughly stirred
with it, in a way that with almost any other material would result
in a mixture, will rise to the surface so dry that a slight breath of
air will throw it into a cloud, leaving the water almost clear,

@Haus, Frank, Is coal dust ss such explosive? Mines and Minerals, December, 1908, pp. 227-229,



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 128

from the others. Another sample of a different dust was found to
be inflammable from all four sources.

The conclusion of the authors was that an inflammable mixture of
coal dust and air required for its ignition a flame of a certain minimum
volume, varying with the nature of the dust. The same is true of
explosive mixtures of gases ignited by an electric spark, a certain
minimum spark being necessary, varying with the character of the
gas mixture. The great difference is the enormous size of the source
of heat necessary to ignite the dusts as compared to the electric
spark. By increasing the size of flame above this minimum the
rapidity of inflammation is increased and for a certain volume
becomes practically instantaneous and nothing is gained by increasing
the size of the flame beyond this volume. This maximum volume
seemed to be less than a cubic decimeter for the dusts investigated.

Some indication of the effect of the size of the dust particles is
seen from the above-described experiments, in which it was found
that the more finely divided were the dusts the more inflammable
they became and the smaller was the size of the flame necessary for
their ignition. Yet in many tests these authors thought that fine-
ness of division was a secondary matter. Some coals were found.
inflammable whatever the size of the particles. This fact is not
opposed to the principle of greater inflammability of finely divided
coals, for the authors explain that the dusts used by them were not
screened to a certain size, and in all samples there was a sufficient
amount of the fine dust that remains longest in suspension to cause
ignition on arrival at the source of heat. In this way the occurrence
of fine dust in a sample, the average size of whose particles was large,
would mask the effect that might be anticipated from the relatively
large average size of the particles. For instance, two samples of
dust may be very different with respect to fineness when introduced
into the apparatus, but in the course of their passage to the flame,
situated some distance away, the largest particles are deposited
and only the particles smaller in size reach the flame, so that at
this point both dust clouds are very similar as regards the size of the
particles remaining in suspension.

The velocity of the air current which carried the dust in suspension
was found to have a great influence on its degree of inflammability.
One of the samples studied ceased to inflame for velocities under 1
meter or above 4 meters. The reason appeared to the authors to be
that with the weak air current dust was deposited from suspension
before reaching the flame, while with currents faster than 4 meters
the particles traversed the flame too rapidly to become ignited.

In the course of the experiments mentioned above the authors
established the fact that dusts of certain coals might be considered
inflammable while others yield noninflammable dust. Many authors



INVESTIGATIONS AT EUROPEAN STATIONS. 149

This fact is illustrated by the work of Galloway, and that of Mallard
and Le Chatelier (who used for the source of ignition different kinds
of naked flames, and accords with the conclusions which they reached
as a result of their work. It will be recalled, too, that Holtzwart and
Meyer drew attention to the fact that no ignition was obtained if
they introduced lignite dust into their apparatus, and, after establish-
ing the spark between the terminals within, disseminated the dust in
the air by shaking the tube. But when the dust was puffed between
the terminals by compressed air ignition occurred. Dust explosions
in mines and in successful experiments in galleries specially designed
for these investigations are preceded by violent compressions simul-
taneously with the production of a large flaming area by the charge of
explosive (the means of ignition always used). Attempts will be
made to ascertain the effect of pressure alone on coal dust suspended
in air and in some inert gas.

COAL-DUST INVESTIGATIONS AT EUROPEAN TE
STATIONS.

By Axes, Larsen,

PROTECTIVE MEASURES UNDER STUDY.

The investigation of coal-dust explosions is naturally divided by
two purposes: (1) Demonstration of the inflammability of coal dust,
and (2) determination of the best means of preventing or arre:
explosions. Inflammability may now be regarded as demonstrated.
‘The second purpose, however, is likely to involve further experiments
on astill largerscale than at Altofts in England and Liévin in Fra
Systematic scientific study of all phenomena and conditions bearing
upon the combustion of coal dust, from the moment of its ignition
through all subsequent stages of propagation until the highest point
of velocity, approaching true detonation, is reached, has been gener-
ally recognized as an indispensable guide to gallery experiments; but
it is felt that even the largest existing galleries are not long enough
to admit of definite conclusions regarding the preventive measures
to be adopted in actual practice

Foremost among such measures are the so-called protection zones.
Of these, three kinds have been experimented with, namely: Dustless,
watered, and stone-dust zones.

The stopping power of dustless zones has proved comparatively
slight, especially where the explosion has traveled a long distance and
developed both high velocity and a dense “ vanguord’ ’ cloud.
Besides, it is not easy to remove coal dust completely and prevent
its reaccumulation, even on comparatively short lengths of roadway
in a mine.

ng



4 CONTENTS.

Experiments with explosible coal dusts—Continued.
Effect of chemical composition
Past experimenta......
Investigations in the United States by Chamberlin.
Experiments of Bedson and Widdas.
Investigation in France by Taffanel.
Comparison of Taffanel’s methods with those used at Pittsburg gallery...
Informal tests at Pittsburg station...
Informal tests with road dust...
Experimenta at Pittsburg with coal dust.
Use of coal dust for stemming... .
Experiments with coal dust in humidified air.
Humidity of mine air
Natural principles. . .
Saturated air at different temper:
Amount of moisture in mine air.
Effect of seasonal changes of temperature on mine air.
Instruments for measuring atmospheric moisture.
Sling psychrometer. . .
Hygrometer used by the Geological Surv
Stationary hygrometer.
Principle of wet and dry bulb thermometer.
Method of making hygrometrie observations in mines.
Relation of moisture content to temperature and pressure of mine air.
Remedies for coal dust.
Review of remedies proposed.
Loading and cleaning up dus
Sprinkling from water cars.
Calcium chloride and other deliquescent salts.
Sprinkling and washing down with hose and ni
Permanent sprinklers
Humidifying by steam jets
Quick-flaming explosives. .
Rock dust.
Experiments with F rocl ock or shale dust at Liévin, France.
Experiments at Altofts, England
Application of stone dust in British mines.
Cost of applying stone dust. ....
Brick or concrete linings and wet zones.
Tentative conclusions on the dust problem
Factors affecting explosibility......
Volatile combustible matter.
Structure and size

‘Ash content.
Outward conditions.
Conditions affecting propagation of explosions.
Amount of dus!
Moisture in dust and in air
Mixture with inert substances.
Advantages and disadvantages of Proposed remedies
Force sprinklers in cars.
Chemicals.

102

103


BUREAU OF MINES BULLETIN 20 PLATE XIV



BIBLIOGRAPHY. 198

Graves, W. H. Coal-dust explosions in mines; conditions under which they have
occurred and the methods suggested for their prevention, Mines and Minerals,
February, 1905, vol. 25, p. 336.

Jackson, T. A. Coal dust. and explosions. Min. Mag., March, 1905, p. 262.

——~ Explosiveness of coal dust. Eng. and Min. Jour., vol. 79, 1905, p. 422.

Mines AND Minerazs. Explosions in Iowa coal mines. Vol. 22, 1902, p. 397.
Report of state commission.

Mines AND Miverats. Coal-dust mine explosions, Vol. 22, 1902, p. 402. Wditorial
reference to report.

Coal-dust experiments. Vol. 23, 1908, p. 551.

- Warwick mine explosion. Vol. 24, 1904, p. 487. Report by board of mine

inspectors who investigated immediately after the explosion.

Dangers in the use of incandescent lamps underground. Vol. 26, 1905, p. 74.
Notice of paper by Hall before Manchester Geological Society.

Monroz, H. S. Dusty shots as a factor in mine explosions. Eng. and Min, Jour.,
vol. 75, 1903, p. 963.

Nuwsam, Ricuarp, Excessive use of powder. Peoria (Ill.) Star, January 8, 1905.
Fuel, vol: 4, 1905, p. 422.

Picxerinc, W. H. The dust danger. Trans, Fed. Inst. Min. Eng., vol. 29, 1904,
p. 134. Discussion, vol. 29, p. 138; vol. 30, p. 26. Discusses preventive meas-
ures. Noticed as Prevention of coal dust. Eng. and Min. Jour., vol. 79, 1905,
p. 374; vol. 80, 1905, p. 112.

Royar Commission on THE Mount Kemuta Contry Disasrer. Report. Sydney,
1903. Explosion of dust by great fall of roof.

Warreyye, Vicror. ‘The office of accidents in mines and of fire damp, and the testing
station of the administration of mines at Frameries, Brussels, 1904, 38 pp. Report
in English prepared for the Louisiana Purchase Exposition, 1904, by Belgian
Department of Industry and Labor. Refers to accidents and describes station.

Winxnaus, . Sprinkling dusty galleries at the Anna and Carl shaits of the
Kélner Bergwerkeverein collieries at Altenessen. ‘Trans. Fed. Inet. Min. Eng.,
vol. 23, 1902, pp. 739-740. From Gliickauf, vol. 37, 1901, pp. 189-194.

1907-1910.

Aevitzou, J, Un mot sur la question des poussidres. Bull. Soc. ind. min., Octo-
ber, 1910, pp. 309-317.

Awwates prs Mives. Statement of the commission appointed to investigate the
Courridres disaster, ser. 10, vol. 12, 1907, pp. 445~483.

Asaworra, James. Coal dust and safety lamps. Coal, November 26, 1908, p. 24.
Comment on paper by Henry Tall before the Institute of Mining Engineers, on
the effect of dust in lowering protection given by safety lamps.

——— The,coal-dust problem. Engineer, March 15, 1907, p. 255.

Influence of damp air on coal dust. Coal, November 12, 1908, Reprint of

article in Colliery Guardian discussing paper by Stokes on Hygrometric observa-

tions in coal mines.

Coal dust. Science and Art of Mining, January 28, 1909, pp. 276-277. Abstract

of address before mining school at Stoke, England. Comment on Altofts experi-

ments; secondary explosions; watering coal dust. Also Colliery Guardian, 1909,

vol. 97, p. 38.

Air percussion and time in colliery explosions, Trans, Inst. Min. Eng, vol. 34,

1907, pp. 270-277. Discussion, vol. 34, pp, 272-281; vol. 38, pp. 334-344.

‘The protective value of humidity. Mines and Minerals, October, 1910.

AsnworrH, JAMES AND Jony, The coal-dust problem. Science and Art of Mining.
December 26, 1908, pp. 228-229. Abstract of paper before Canadian Mining
Institute. Refer to Monongah and Darr explosions; discuss nature of fine dust;
preventive measures.

88006°—Bull. 20—11-——13,



TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 101

and so prevent the immediate ignition of the combustible matter
necessary for propagation.

ASH CONTENT.

The ash content of the coal, within ordinary limits, does not appear
to affect the explosibility of the coal dust; but if an inert dust, such as
stone dust, is raised into the atmosphere with the coal dust by the
advance air wave, it will affect results in two ways—-by separating the
coal-dust particles with a barrier and by absorbing some of the heat of
the impinging flame, and thus lowering the temperature below that
necessary for the ignition of the gas distilled from the adjacent coal-
dust particles.

OUTWARD CONDITIONS.

The writer concludes that the outward circumstances under which
coal dust will explode may be summed up as follows: Sufficient dust
must be brought into suspension by a preliminary shock or concussion.
producing a violent air wave; or else the dust must be so minute
that it is already suspended in a dense enough cloud at the moment
when the flame impinges. The latter effect is produced only under
some peculiar circumstances by which a large amount of fine coal
dust is thrown into a strong air current and carried to the igniting
flame. The former effect may be produced by a heavy shock like
that from a falling body, but is much more likely to result from
a preliminary explosion of fire damp or, more commonly, of an
explosive.

CONDITIONS AFFECTING PROPAGATION OF EXPLOSIONS.
AMOUNT OF DUST.

The weight of coal dust that must be thrown into suspension to
permit propagation of an explosion depends on (a) the percentage of
volatile combustible constituents; (6) the amount of contained and
adhering moisture; (c) the presence of foreign substances like stone
dust; and (d) the size of the dust particles, the effect of which is two-
fold—the smaller the particles the more easily the air concussion
can raise them, and the more surface is exposed for the evolution
of gas.

The minimum density of the dust cloud necessary to propagate an
explosion evidently varies with the initial cause as well as with the
character of the dust. Using 190-mesh bituminous dust, M. Taffanel
obtained explosions regularly with a density of 70 grams per cubic
meter (0.07 ounce per cubic foot), and in one instance obtained

an a recent Instance in Colorado, a trip of cars running swiftly on a dusty motor read, jumped the
track and knocked out some limbers. ‘The cloud of dust thus stirted up was ignited efther by the trip
rider's open light or an areing fom the trolley wire, and a widespread explosion thereby resulted. Tho
point of ignition was near the mouth of the mine on au intake entry.


34 THE EXPLOSIBILITY OF COAL DUST.

propagate flame in the incipient stages of an explosion, as determined
at the Pittsburg station under the conditions hereafter stated. By
this definition coal particles passing through a 20-mesh wire sieve
(20 wires to the linear inch) will be termed dust. In the Pittsburg
gallery tests only partial flame propagation was obtained under the
prescribed conditions with coal that passed through the 20-mesh and
remained on a 40-mesh sieve, but the partial propagation was suffi-
cient to indicate that under slightly more severe conditions, namely,
a larger initiating charge of black powder, the propagation might
be complete. In fact, under the definition given, subsequent ex-
periments may demonstrate that larger particles of coal than 20-
mesh should be included.

IGNITION AND PROPAGATION.

Ignition of coal dust, as the term is applied by the writer to tests
in the Pittsburg gallery, is an inflammation of the dust, caused by
the flame of the explosive, with consequent extension of that flame
more or less; and the term ‘‘propagation” is used for conditions in
which the inflammation extends through and beyond the area in
which coal dust has been laid along the shelves of the gallery, or be-
yond the area in which dust has been put into suspension by fans,

COAL-MINING METHODS AND DUST PRODUCTION.

Breaking down the coal at the face of the mine is done by one of
the following methods: By undercutting in the underclay or coal
itself and wedging, as in long-wall work; by undercutting or shearing
by hand in the coal and blasting with light shots; by the same method
with machines; and finally by ‘‘shooting off the solid.”

Of the foregoing manifestly the long-wall system will produce much
less coal dust than any of the other systems, and its general intro-
duction in this country would probably very much Jessen the number
of dust explosions. The system has been little used in this country,
pattly because the natural conditions are not generally favorable,
and, where they are, because it costs more to mine a ton of coal by
this than by the more wasteful room-and-pillar system. However,
one type of the long-wall system, the ‘‘retreating” long wall, is gen-
erally applicable and is the cheapest of all methods to work, but takes
a large investment of capital. The Wilmington and Third Vein
fields of northern [llinois, in which the natural conditions allow the
use of ‘advancing long wall,’ comprise the only important long-
wall district im the country, having an output of 5,000,000 to
6,000,000 tons annually. No explosion has ever occurred in this
field.

As between the methods of mining the coal at. the face in room-and-
pillar work—‘‘shooting off the solid,” and cutting the coal by hand


BIBLIOGRAPHY. 195

Counsinonam, J. S. Mine disasters—causes and remedies. Coal, October 15, 1908,
pp. 21-22. Abstract of paper before West Virginia Mining Association. General
discussion of gas and dust explosions and remedies suggested.

Cunyxename, H. H. Recent advances in means of saving life in coal mines. Lecture
before Royal Institute. Colliery Guardian, vol. 97, 1909, pp. 422-424. Discusses
explosibility of coal dust and preventive measures.

Safety in mines. Science and Art of Mining, March, 1909. Abstract of
lecture before Royal Institute. Reviews coal-dust problem from time of Faraday.

Cunyyename, H. H., AND Argrvson, W. N. Report on the disaster at Courridres
mines, Pas de Calais, France. London, 1906. Bluebook issued by Home Office.
Gives description of mine and nature of explosion; rescue work, etc.

Czartivsxr, -, AND JicsKy, Jarastav. Experiments with coal dust at the
Rossitz gallery. Colliery Guardian, September 24 and October 1, 1909, vol. 98,
pp. 635 and 687. Describes gallery and experiments with coal dust and dynamite;
influence of character of coal dust, of water screens, wet zones, and stone dust on
explosions.

Versuche mit Kohlenstaub im Versuchsstollen der Rossitz Steinkohlenreviers,
Oest. Zeitachr. Berg- und Hiittenwesen, May 28, 1910, pp. 295-298. Abstract of
report printed in Colliery Guardian, Vol. 100, 1910.

Dawie1, J. Les poussitres des houilles. Paris, 1909. 76 pp. Reprint of article from
Annales des mines.

——~ Les poussitres des houilles. Annales des mines, ser. 10, vor. 15, February,
1909, pp. 142-212. Discusses formation of dust; preventive measures, use of
sprays, deliquescent salts, etc. Refers to French, English, and German practice.

Davis, Henry. The application of the hygrometer in coal mines. Trans. Inst. Min.
Eng., vol. 35, 1908, pp. 285-290.

Deason, E. J. Explosives in mines. Mines and Minerals, vol. 28, 1908, pp. 269-273.
Reprint of article in Coal and Iron Trades Review. Describes Woolwich tests;
experiments with dust.

Desnoroven, Artaur. Report of departmental committee on the use of bobbinite.
London, 1907. 67 pp.

Dinrer, L. French commission on explosives and coal dust. Coal, December 10,
1908, pp. 15-16. Abstract of paper in Bull. Soc. ind. min. Discusses origin of
dust and preventive measures.

Doserestery, ©. Durchtriinkung und Lockerung des Kohlenstosses mit Hilfe von
Druckwasser. Gliickauf, vol. 45, November 6, 1909, pp. 1641-1643.

Eavenson, N. Il. Bifect of humidity on mine explosions. Trans. Am. Inst. Min.
Eng., vol. 40, 1909, pp. 835-847. Gives lists of disastrous explosions at. North
American coal mines.

Evomeen. Coal-dust experiments. Vol. 108, October 9, 1909, pp. 376-377. An
account of experiment at Altofts.

Exoineeninc. Coal-dust explosions. Vol. 91, January 6, 1911, pp. 21-23. Reviews
experiments at Liévin.

ENGINEERING AND Mintno JouRNAL. Coal-dust experiments. Vol. 88, October 30,
1909. Refers to experiments at Altofts and report of royal commission on mines.

How Furopean collieries are safeguarded. Vol. 89, April 15, 1910, pp. 820-831,

Exeter, C. Einfacher Versuch zur Demonstration der gemischten Kohlenstaub- und
Gasexplosionen. Chem, Zeitung, vol. 31, 1907, p.358. Jour. fiir Gasbel, vol. 50,
p. 488.

Forsmaws, R. Untersuchungen itber die Austrocknung des Grubenbaue und die
Bekimpfungen des Kohlenstaubes. Gliickaui, January 15, 1910, pp. 37-46.
Gattoway, Wrutam. Colliery explosions and rescue appliances. London, 1908.

120 pp.



REMEDIES FOR COAL DUST. 85

which created the fatal condition. On the other hand, a mine might be perfectly
dry and yet not dangerous, the coal dust having become well mixed with clay.

In the course of the investigation into the cause of the great explo-
sion at the Monongah mines, West Virginia, December 6, 1907,
Mr. R. T. Chamberlin, of the United States Geological Survey, ob-
served two varieties of dust adhering to the opposite sides of the
props in a certain room in No. 8 mine. He says:

In this room the deposits of both varieties of dust were unusually heavy, particu-
larly upon the props. ‘The outby sides of these timbers (lacing the entry) were thickly
covered with dust, which showed no indication of charring of other visible evidence
of having passed through an explosion. ‘The inby sides of the same props were com-
pletely plastered with well-charred dust.o

Samples of these dusts were taken, together with a sample of the
fresh coal from the face. The analyses disclosed that while the fresh
coal contained but 3.6 per cent of ash, the uncharred dust from the
outby sides of the timbers showed about 30 per cent of ash, while
the charred dust from the inby sides of the props showed about 15
per cent of ash.

Mr. Chamberlin’s conclusion, drawn from his observations and
from the analyses, is that—

The explosion flame was able to burn with sufficient vigor to coke the dust with
which only 15 per cent of shale was mixed, but where the shale impurity amounted

to 28 to 30 per cent of the total the flame seems to have failed to reach the intensity
necessary to coke the dust.

Mr. Chamberlin considers that the explanation of the difference in
the quantity of fine shale in the coatings on the opposite sides of the
timbers is to be found in the difference of the specific gravity of the
coal and shale:

‘The lighter coal-dust particles would be most easily deflected from their previous
courses and most abundantly plastered on the lee side by the eddy, while the heavier
particles of shale, because of their greater momentum, would tend to continue in less
deflected lines beyond the influence of the prop. It follows that on the inby or lee
side of the timbers there would be proportionately more coal dust and proportionately
less shale dust than on the outby exposures.¢

« Notes on explosive mine gases and dusts, U. $. Geol. Survey, Bull. 383, 1909, p. 45.

> Op.cit., p.47. The writer of this bulletin does not agree with Mr, Chamberlin’s Interpretation of the
Phenomenon. From his observations, made after other mine explosions, he believes that the charred
or coked dust was thrown, while in 2 hot plasti¢ condition, against the timbers by the explosive wave, and
the uncharred dust was deposited at a later tyne by a nonexpiosive wave or wind blast, which picked up
‘the excess of unburned or slightly burned dust on the entry roads, where the proportion of shale would be
higher, and a branch wave entering the room plastered the dust on the props. Not having personal knowl
sdge of this particular case, the writer will not hazard a conjecture whether the explosfon and the subse-
quent wind blast were from opposite directions or not. Asa result of many investigation, his belief is thal
where the speed of a wave is relatively slow the material s deposited on the face of obstructions, and
where the speed is rapid the material fs deposited only on the back of lee side of obstructions. The
uncharred dust samples reported by Mr. Chamberlin contalned Jess than 30 per cent of ash. The experi:
ments at Pittsburg and at foreign stations have shown that dust containing as high as 40 or even 50 per
cent of ash will propagate an explosion, and with coking ¢oal, such as that at Monongah, the coal partleles
in the mixture will show charting or coking, many of the coke crusts Including inert, particles.

© Op.clt., p. 47.



USE OF STEAM AND WATER SPRAYS. 181
APPLICATION OF STEAM AND WATER SPRAYS.

The writer had a steam coil installed near the top of an intake
shaft for use in cold weather, consisting of several hundred feet of
pipe through which exhaust steam was passed. The moisture con-
densed from the steam was carried in with the downcast air cur-
rent, heating the air to some extent and adding to its humidity.
However, the amount of steam that could be exhausted into the
hoisting shaft was limited by the necessity of having the atmos-
phere at the bottom clear of fog. This was found not to be
suflicient. The mine continued dry within 1,000 feet of the in-
take. Water sprays were tried with good results, and then installed
more extensively. As the main intake slopes were naturally more
or less wet, the working faces farthest down the slope, but
first on the air currents, were not troubled with drying out as
were those farther along the air current. Hence it was necessary
to place sprays at intervals for remoistening or humidifying the air,
the places being determined by the hygrometer or wet and dry bulb
thermometers. In general it was found that a relative humidity
of over 85 or 90 per cent gave the working places a satisfactory degree
of dampness. Such increased humidity lessens the chances of a dust
explosion, both because it dampens the dust and because in the
presence of a blown-out shot a higher temperature would be required
for ignition of both gas and dust by reason of the higher percentage
of water vapor in the atmosphere.

The spray heads found to be best were those of a type that will
make as fine a spray as possible for more ready absorption by the
air currents. They should be of such design that they will not clog
easily. Clogging is one of the chief troubles in the use of these
sprays, and close attention must be paid by the foremen to see that
they are running freely. This takes only a moment's attention. A
spray head in a heading is shown in Plate XIV, B.

On a main intake and haulage slope a different type of spray has
been tried---a short vertical pipe with a groove cut in it and holes
perforated at intervals in the thin metal left at the back of the
groove. These holes are easily cleaned by running a point down the
groove. This spray pipe is placed at one side of the road and throws
the spray against the air current.

‘The arrangement of sprays in the mine where the principal experi-
ments were conducted is shown in figure 29.

An example of some of the results obtained is shown in the table
below. The readings were taken by the ordinary dry and wet bulb
thermometer, the air volume was determined with an anemometer,
and the barometric fluctuations were noted at the surface, at the
head of the most important splits, and at the foot of the upcast.


80 THE EXPLOSIBILITY OF COAL DUST.
HUMIDIFYING BY STEAM JETS.

The use of steam for humidifying was mentioned in the discussion
on Sir F, Abel’s paper, read in 1887.4 Prof. Arnold Lupton said:

Perhaps one of the most ingenious ways was that of Mr. Stratton, in the Pochin pit,
Tredegar collieries. He tuned the exhaust steam of an engine into the downcast shaft
and it had the effect of heating the air and damping it at the same time. It did very
well in spring, summer, and autumn, but in winter it was not sufficient, because it
would not heat the air enough, and therefore the steam was supplemented by water
carts for laying the dust. This method of damping the air by steam was only applic:
ble to mines of moderate depth, and consequently low temperature, say under 65° F.,
because it would make deeper mines too warm. The steam had done no harm to the
roads or timber at the Pochin pit and it made the mine much pleasanter.

Apparently this system made no progress in England, as there are
only casual remarks about it from time to time in current literature.

In the United States the plan of turning the exhaust steam from
fan engines in winter into the downcast shaft has been considerably
used in the western coal fields for many years, but the scheme has
been mainly used in freezing weather to prevent ice from forming in
the downcast shaft.

There does not appear to have been any systematic use of exhaust
steam for humidifying ventilating currents until the last few years.
Mr. Frank Haas, consulting engineer of the Fairmont Coal Company,
has been an earnest advocate of this method of humidifying mine air
to dampen coal dust and render it harml In an instructive
paper ® read before the West Virginia Mining Association, October 17,
1908, he proposes humidifying the mine air as an ‘‘eflicient. prevent-
ive. At about that time Mr. Haas installed a system of exhaust
steam spray for humidifying the ventilating currents of the Monongah
mines of the Fairmont Coal Company, and carried on a series of
observations and tests during the following winter. The results of
these important and successful experiments are presented by Mr.
Haas as a part of this bulletin (pp. 166-179).

In a communication dated March 8, 1910, received from Mr, IT. K.
Knopf, general superintendent of the Pittsburgh-Westmoreland Coal
Company, he state:

I wish to advise that in the fall of 1907 we installed a system of meistening the air at
nearly all of our mines, especially at the shaft mines

At our Acme mine at Bentleyville we now exha’ into the air shaft all steam from
our fan engine, and during the severest weather we have always had live steam from
the boilers frem a 2-inch line. We find that we have at this mine from 98 fo 100 per
cent of saturation at all times. The steam at this mine carries back into the workings
between 3,000 and 4,000 feet and in two years’ time with the use of steam we have had
no trouble with the roof; in fact, the roof, in my opinion, would hold up better with «

@ Mining accidents and their prevention: Proc. Inst. Civil Engineers, London, vol. 91, 1887, pp. 91-92;
republished in book form.
Is dust, as such, explosive: and if so, what are the chemical reactions and the most efliclent pre-

veutives? A pamphlet published by the West Virginia Mining Association,



16 THE EXPLOSIBILITY OF COAL DUST.

According to the evidence given by Mr. William Galloway before
the British royal commission in 1891, the Prussian investigators
obtained inconsistent results when they attempted to classify dusts
in the order of their relative explosibility. He said:*

One of the dusts which they described as nonexplosive came from a colliery called
Camphausen and they named it as quite a safe dust. Shortly afterwards an exceed-
ingly violent explosion occurred at Camphauson colliory killing some 200 men, and
the government director of mines in the district wrote to me immediately afterwards
stating that the mines were so entirely free from fire damp that he could come to no
other conclusion but that coal dust had been the sole cause of that explosion. * * *
It is a remarkable and noteworthy fact that the degree of explosiveness of the coal
dust with which the members of the Prussian commission made their experiments
appeared to be directly in proportion to the fineness of the dust, and to have little
or no connection with their chemical composition. * * * I may state my own
conviction that the finest dust of all kinds of coal, with the exception possibly of the
dryest kinds of anthracite, is inflammable or explosive when mixed with air and ignited
in large volumes.

As a further result of their tests, the Prussian commission declared
that black powder and all other slow explosives ought to be pro-
hibited in collieries containing fire damp, and that even dynamite
and other high explosives, though permissible in certain cases, ought
not to be used where accumulations of fire damp are possible in
sufficient quantity to give a clearly perceptible blue cap on a lamp;
and that in all cases it is desirable that the air should be tested
within a radius of 10 yards before igniting any shot. In consequence
of this report, shot firing was prohibited altogether in mines controlled
by the Prussian Government, where safety lamps were used.°

It is evident that by 1886 the serious danger of coal dust was
realized in Germany,-although the investigators were not quite
ready to believe that coal dust would explode without fire damp
being present. In another part of Germany, at Zwickau in Saxony,
a testing gallery had already been erected (1883), and thenceforward,
investigations in various parts of Germany went on more or less
continuously, both under government supervision and by various
mining companies.

EXPERIMENTS IN AUSTRIA BETWEEN 1885 anp 1891.

In Austria a commission on explosions in mines was appointed
in 1885, and in 1886 a testing gallery was established at Mahrisch-
Ostrau. A large number of experiments were conducted and in
1891 the Austrian commission made its report, the substance of which
is stated by the British royal commission as follows:

In all, 353 experiments were mado with 345 kinds of dust, generally without any
admixture of gas. Those experiments showed that, without any admixture of fre

4 First Rept. Roy. Comm. on Mines, 1991, p. 36.
2 Trans, Am. Inst. Min. Eng., 1894, vol. 24, p. 202.
«Second Rept, Roy, Comm., 1894, p. &


BIBLIOGRAPHY. 187

Hux, C. Jahrbuch Berg-, Hiitten-, und Salinenwesen im preuss. Staate, vol. 33,
1885, pp. 273-276. Summarizes tests with coal dust at the Kénig mine, Neun-
kirchen.

Hovey, H. C. Danger from coal dust in mining. Am. Jour. Sci., ser. 3, vol. 22, pp.
18-20. Refers to results of investigation of explosion at Albion mines, Nova
Scotia.

Hurcuinson, E. 8. Notes on coal dust in colliery explosions. Trans. Am. Inat. Min.
Eng., vol. 13, 1885, pp. 253-279. Reviews literature on coal dust; refers chiefly
to British investigations.

Jones, C. E. The explosive properties of coal dust, coal gas, and atmospheric air, with
special reference to mines, Jour. Gas Lighting, London, vol. 13, 1883, p. 358.
Concludes coal dust will not explode unless in a cloud so dense that particles touch.

Kuetock, Henry. Influence of coal dust in mines. Colliery Engineer, vol. 9, 1888~
1889, p. 56.

Le Cuarenier, H. Le grisou et les accidents. Rev. Gen. Sci., vol. 1, October 30,
1890, pp. 630-635. Minimizes danger from dust.

Mattaro, F. E., and Le Caarewrer, H. Du réle des pouisstres de houille dans les
accident de mines. Annales des mines, ser. 8, vol. 1, 1882, pp. 5-98.

Matzarp, F. E. Rapport sur l’étude des questions relatives & l'emploi des explosifs
en présence du grisou. Annales des mines, ser. 8, vol. 14, 1888, pp. 197, 376.
Mercier, MAUNSELL. Dust in mines. Colliery Engineer, vol. 10, 1890, pp. 152-
McLaren, Roserr. Mine gases, coal-dust explosions, ete. Colliery Guardian, vol.

60, 1890, p. 526.

McNett, Joun. Explosions. Report of State inspector of coal mines of Colorado,
1887-1888, pp. 24-51. Says Newcastle explosion caused by dust.

Pernoer, M. A., and Acon.on, L. Exploitation et réglementation des mines &
grisou. Paris, 1881, 335 pp. Discusses dust, p. 285.

Prussian Frre Damp Commission. Zeitschr. fiir Berg-, Hiitten-, und Salinen-
wesen im preuss. Staate, vol. 32, 1884, pt. 5, p. 575. Gives summary of experi-
ments made by Prussian Fire Damp Commission to end of 1884.

Rovat Commission oN Accrpents iN Mines. Preliminary report. London, 1881.
Concludes that proportion of fire damp required to make dust explosive ia too
small for detection by existing apparatus.

— -~ Final report. London, 1886. 219 pp. Report, minutes of evidence, and
appendix. Appendix 9 (pp. 150-159) and appendix 10 (pp. 161-166) describe
experiments by Abel.

Final report. Reprinted by Engineering News Company, New York, 1887.

Seauam Cotuery Exriosion. Blue book issued by Home Office, London, 1881.
Contains conclusions of F. Abel, p. 146, that coal dust and air without fire damp
will carry flame a short distance only. Describes tests at Garswood Hall colliery,
near Wigan.

Smo, A. Note relative & des essais faits aux mines de Liévin sur les explosifs de
sGreté. Annales des mines, ser. 8, vol. 18, 1890, pp. 580-607.

1891-1900.

Aguttion, L. Note sur la question des poussidres en Angleterre. Annales des mines,
ser. 9, vol. 52, 1895, pp. 535~559. The coal-dust question in England. Abstract
by W. N. Atkinson: Trans, Fed, Inst. Min, Eng., vol. 9, 1895, p. 474.

Asawonta, James. Colliery explosions and coal dust. Colliery Guardian, vol. 71,
1896, pp. 305~306.

Arginson, W. N. Coal dust and colliery explosions. Colliery Engineer, vol. 11, 1891,
p. 187. From Colliery Guardian.

~——- Report of the Austrian Fire-Damp Commission. Trans. Fed. Inst. Min. Eng.,
vol. 3, 1892, pp. 531-550.



52 THE EXPLOSIBILITY OF COAL DUST.

INFORMAL TESTS WITH ROAD DUST.

Some informal tests were made at intervals during the past year at
the request of various mining men. The results of a few of special
interest are given in the table below. The last three were with road
dusts, which had a large admixture of clay or shale. The total ash
ranged from 30 to 57 per cent. In two tests there was complete
propagation, but in one test, in which the combined material had a
total of 53 per cent ash, the flame died away, reaching only half the
length of the gallery.

With regard to road dust, it is important to bear in mind that
unless the shale or stone dust is very fine and is intimately mixed
with the coal dust its presence has very little deterrent influence on the
explosion. A concussion from a blown-out shot or a small explosion
of fire damp does not throw the pieces of rock into the air if they
are coarse, and therefore the dust cloud may consist only of the fine,
pure coal dust that rises from around the rock fragments. The same
is true of any large pieces of coal that are present. The question in
regard to any road dust is whether there is sufficient fine coal dust
among the coarser pieces of rock to rise and form a dust cloud of
sufficient density to permit a propagation of flame.

Special explosion-gallery tests with bone dust, road dust, and mixtures.

Flame showed

Black powder 2
| Dust on} Cindicating its
Used,“ Tponetamd engin) at— | Leng
Test | Date of test ‘shelves tn of flame | gn | ropa.
No. est. - ‘shelves inj —____ beyond | tion. | gation.
[AROS | oots [windows] 20%
Size, | Weight, | Nos-

\
F

4
1
4
12
| Souree of coal dust. | Analyses. &
Test | | Vols | 4
0. ‘ Gla” | Fixe
Location of | Character and source | Mots- Sule
| Name of mine. ‘mine. of sample, ture. Ash. toh

0
i | ih
G-608..| Bear Cresk No.5..| Boar Creek, | Subbituminous. coal | 8.04 30.87 (43.49 | 17.00{ 1.78
Mon and bone cuttings.
Gallup,'N.Mex| Sybbituminous tasen| 9.13 | 1.87 | 4142 | 27.58 |° «59
1 from roads. |
G-491..| Penn Gas Coal Co. | Irwin, Pa.....| Bituminous, taken | 2.50 26.06 | 53.43 | 18.01! 1.24
No.3. I from roads {
O-1481.) Elkins C, and ©, | Fikins,W. Va.| Bituminous, taken | 1.02] 12.76) 92.04 $8.98; 2.14
C from roadw:
.| Carbon, W, Va_| Coal dust and 1 bre clay 15.45 | 24.85 | 56.95! 1.48
from room 12 | |

G-1S..| Weaver mine.

0.
G-398._| Carbon mine.

Biturninous coal dust, | 10.66 | 29.44) 45.00 | 14.90 | 2.29
4 rent.
-2062.| Bunson Coal Co...] Georgetown cigs PSsratone, and | 6.41 | 19.45 | 27.18 | 46.98 | 1.40
coal, 30 per cent,

«Dust placed on floor in sections 1-3 and not on horse,
Size not given.

¢ Flame extended 40 fect beyond end of gallery.
@A.C, Fieldner, analyst.


BUREAU OF MINES BULLETIN 20. PLATE Xi)

|. TIMBERING AND STONE PACKING IN PRELIMINARY GALLERY AT ALTOFTS.

JB. STONE DUST ON HANGING SHELVES IN ALTOFTS COLLIERY.


92 THE EXPLOSIBILITY OF COAL DUST.

the igniter (cannon) being 360 feet from the downcast, or intake, end.
The explosion was notable for its violence, the result being thus
described: ¢

Three boilers forming the downcast were wrecked. [See Pl. VI, A.J Several
pieces of boiler plate were blown high into the air a considerable height and distance.
The flame shot out to great length from the downcast and the vibration of the explo-
sion was felt more than 7 miles away.?

In 29 experiments without the interposition of a stone-dust zone,
the flames projected from the gallery averaged 156 feet in length,

Experiments with stone dust continued, and in September a length
of coal dust (367 feet) was laid between two stone-dust zones of 210
feet each, which effectually extinguished the flame in either direction.
This experiment was witnessed by a number of the members of the
royal commission on mines.°

The first series of experiments was completed in 1909 and the
results were published in 1910, in a volume entitled ‘‘Record of the
First Series (1908-9) of the British Coal Dust Experiments.” The
experiments indicate that with a charge of 375 pounds of coal dust
distributed over 375 feet, the flame of the coal-dust explosion will be
extinguished by the stone dust after penetrating 22 to 125 feet into
it, the distance depending on the method of application. The most.
effectual method tried was to place stone dust on noninflammable
brattice cloth on the tops of timbers. When the explosions knocked
the timbers out the stone dust fell in a shower on the flame. Photo-
graphs taken of typical explosions are reproduced in Plate VT, B and C.

The pressures shown by the recording instruments varied widely
at different stages of the explosion and in accordance with other
conditions. The investigations into the pressures developed by an
explosion gave most interesting results. With a smooth or clear
gallery the pressures were very low; when the distances traveled by
the explosion from the pomt of ignition to the manometer were 125
to 375 feet the maximum pressure developed ranged only from 8.3 to
11.9 pounds per square inch.

On the other hand, when the gallery was lined with props and bars
9 feet apart and a small mine car (weighing 450 pounds) was placed
in the mouth of the gallery, great violence was shown and the pres-
sures ranged from 34 to 100 pounds per square inch.

Tn the clear gallery the pressures indicated by the manometer read-
ings did not rise with increased distances but remained uniform,
within about 10 per cent, but in the uniformly obstructed gallery the

Ghardian, August 28, 1908, p. 111.

S$ of hoiler weighed from 30 to 1,500 pounds and were scattered 1o a distance of 1,150 fect.

From certain observations and limiting angles, it was celeulated that some of the pieces had risen to a

hicight ofabout 500 fect. Although the hoilers were built to withstand a static pressure of 160 pounds, later

experiments indicated that the pressure suddenly applied was not more than 120 pounds per square ineh,
Colliery Guardian, July 30, 1908, p. 221.



EXHAUST STEAM AS A PREVENTIVE. 169

in keeping the entry moist was observed, and when the question of
watering the mine was more seriously considered a year or so later it
was decided to continue to utilize the means that had been acci-
dentally discovered.

RECORDING INSTRUMENT.

As no records of temperature and humidity of the atmosphere of
the vicinity were available, it was necessary to produce such records
extending over all the seasons of the year. Individual observations
taken periodically were obviously insufficient, considering the large
fluctuation in comparatively short times. For a recording instrument
a hygrothermograph, manufactured in Baltimore, Md., was used.
This instrument records both temperature and humidity for weekly
periods. No difficulty was anticipated with regard to the tempera-
ture, but the calibration of the instrument for humidity was attempted
with considerable misgivings, as the actuating part is a hair that
expands or contracts in direct proportion to the relative humidity of
the atmosphere. IHowever, the instrument was set up in a covered
box and checked with a standard psychrometer for temperature and
humidity at least twice a day for several weeks. It was considered
sufficient to test the instrument at the maximum and minimum
points of both temperature and humidity, which occurred usually
at 8a.m.and4p.m. After adjustment and thorough calibration
this instrument and two others that were bought later gave very
satisfactory results. While far from perfect, it is nevertheless the
best known to the writer for continuous record and gives results well
within the limit of error of other observations necessary for the
investigation.

RECORDS OF OUTSIDE TEMPERATURE AND HUMIDITY.

Tn figure 22 is presented, together with the results of the weekly
records from the instrument, the daily range with maximum and
minimum of temperature and humidity of the outside air at Fair-
mont, W. Va., from June 1, 1908, to June 1, 1909. In this chart the
water vapor has been calculated and recorded in gallons per 100,000
cubic feet. This is simply a convenient figure for comparison, as
100,000 cubic feet is ordinarily a practical unit for mine ventilation
and is one that makes the quantities of water whole numbers rather
than fractions. The chart shows at a glance the difference between
the quantity of water vapor held by the atmosphere in winter and in
summer.



156 THE EXPLOSIBILITY OF COAL DUST.

The file of boilers originally placed in line has been shortened so as
to leave an intake gallery of 600 feet only.

The number of experiments carried out to date amounts to 115,
about half of which have been ‘‘spectacular,” that is, repetitions of
phenomena regarding which those in charge were long ago satisfied,
but which it was considered necessary, or at least desirable, to repeat
in order to convince stanch unbelievers in coal-dust explosions,

EXPERIMENTS WITH PROTECTION ZONES AT ALTOFTS.

Apart from the crucial demonstrations of true coal-dust explosions
furnished there during two seasons, much attention has been given

Flare 160°

Coal dust 275’

. Dustless 150 16’
I WF tame
‘Coal dust 275"

_ Stone dust 1507
{ 2 —_— 7
Coal dust 275’ ‘55/

Dustless 100/ Flame 150"

Coal dust 275° Coal dust 50’

Stone dust 100’

Stone dust 100”
L =. mnmuinnwnn Beriame | a]
Cannon 227 .0. 50"

Ficur®, 16—Propagation of flame in coal-dust, dustless, and stone-dust zones.

to the question of the relative protection afforded by dustless and
stone-dust zones. Stone dust has been found to be the most effective.

‘The results of experiments typical of that particular investigation
are shown in figure 16.

Instructive as these tests undoubtedly are, they can at best serve
as a stimulus for gaining further knowledge, and must not be regarded
as exhaustive; nor will they help to discover what would happen
should the length of the coal-dust zone be doubled, or even trebled.
This can only be determined by future experiments on a still larger
scale.



REMEDIES FOR COAL DUST. 71

ordinary room-and-pillar system the fine coal and dust is seldom
wholly loaded out. Although the coal may be carefully shoveled up
at the face, the fine coal, thrown back into the “gob” by shooting,
usually becomes so mixed with dirt or rock that it would be difficult
to gather it and send it out in pit cars without undue expense.

In some sections of this country the miner is required to leave the
cuttings in the gob, particularly when the cutting is done in mixed
coal and shale bands. This is certainly not good practice. It may
save the quality of the screenings from injury at mines where there
is not a washery, but it leaves a dangerous condition within the mine,
increasing the chances of a dust explosion and the risk of gob fires.*

To clean up fine dust after the coarser small coal has been shoveled
out is far more difficult than to shovel out the latter and is practically
impossible on a rough uneven floor. If a broom is used, it merely
moves the finer and more dangerous dust to other settling points. A
possible method of sweeping which may be developed in future is the
use of a modified form of house vacuum cleaner, though recent pre-
liminary trials in England have not been successful except where the
passageway was lined smoothly with brick or concrete.

SPRINKLING FROM WATER CARS.

Sprinkling the roadways by means of water cars was the earliest
method of watering coal dust. At first the water was thrown out by
means of a bucket from a plain tank car or let dribble from the car
in the middle of the roadway. The latter plan is still used in many
mines. The next step was to put a perforated pipe on the rear of the
water car. Only the roadway floor can be sprinkled with the slight
head given by the tank, and though such sprinkling, if frequent, pre-
vents some dust from being raised by the traflic it does not reach the
dangerous dust on the walls and timbers.

The next advance was to place a force pump on the cars, or to use
air compressed in the top of the tank, to force the water out under
such pressure that the roof and sides could be sprinkled as well as the
floor. This method is much employed to-day at many of the leading
mines. If carried out systematically and constantly it is an effectual
method, but if used only occasionally, say once or twice a week, vory
little good is accomplished. Dust is extremely difficult to wet and the
drops of water are not absorbed by the dust unless it is already more
orlessdamp. If the drops remain exposed, they are quickly absorbed
by the air currents and the road becomes dry. There are practical
difficulties in using water cars efliciently; thus, to sprinkle each road.
one or twice a day would seriously interfere with the hauling of coal.
On the night shift the tracks and sidings are oceupied by “loads”
and “empties,” so it is difficult to get the water cars through the

@ One great.coaltnine explosion iavestizated by the enzincers of the Buren of Mines was probably started
by a partly blown-out shot projecting its flame into a heap of machine cuttings.


200 THE EXPLOSIBILITY OF COAL DUST.

The two following paragraphs supplement the footnote on
page 50:

Even when the density of the coal dust in the air is less than that
which would exhaust the oxygen in a given space, it is probable that
the burning of all the combustible matter is rarely complete. This
is instanced by the density tests described on pages 38 to 41. They
gave coked residues, although the densities were low (32 to 63 grams
per cubic meter). The incomplete combustion is probably due to
the rapidity with which the explosive wave passes a point.

From the ultimate analysis of the eoked dust G-2892 and the anal-
ysis of the original coal dust, it has been calculated that if the same
proportion of the combustible matter were burned to water and car-
bonie acid the combustion of 154 grams of this coal dust would exhaust
all the oxygen in a cubic meter of air. If some carbon monoxide
were produced, as is the case in explosions, a less density of the dust
would be required. On the other hand, in a mine the dust is rarely
pure and is more or less oxidized, so that a larger quantity or a greater
density of dust would enter into an explosion.

On pages 166 to 179 of this report Mr, Frank Hans describes the
use of exhaust steam for humidilfying mine air. In commenting on
the method in ‘Coal and Coke,” of May 1, 1911, Mr. Haas

The result covering some three years of experiments has developed a thoroughly
reliable method, Whatever may be the virtues of a wet mine, this method will dis-
tribute water uniformly and in any quantity desirable and with uo attention and
entirely iree from human opinion or direction. {t might be pertinent to remark also
that in the operation of some 40 coal mines in this State, the Consolidation Coal Com-
pany estimates that the exhaust-steam methods of introducing moisture into mines
has resulted in a saving of some $50,000 per year as compared with the water-car
method, To those who have not, as yet, tried this method of saturating their mines,
T would recommend it as the most eflicient where conditious and circumstances will
permit

xv





INVESTIGATIONS AT EUROPEAN STATIONS, 165

water pipe. (See fig. 21.) The pipe was inserted into the bore hole
and sledge-rammed home. The pipe was then connected by a hose
to the water main of the pit (now easily accessible in all dusty pits
in Germany) and the water was turned on.

After twelve minutes loud crackings were heard from several parts
of the coal seam, and presently the water had found an outlet some
10 feet above the bore hole and came rushing down the coal face.
It was stated that the one bore hole had loosened 36 half-ton cars
of coal, all of which would be got by the pick and at about half the
cost of blasting.

In reply to a question whether the method would prove practicable
in less favorable conditions, it was stated that practically all seams,
whether horizontal or perpendicular, were amenable to the treatment,
but that not every coal could be got by pick with equal facility.
But even if explosives had to be used afterwards, the effect of the
injection was said to be such as to eliminate danger of using them,
as far as coal dust was concerned. ‘The coal was rendered just moist
enough to prevent the formation of appreciable amounts of dust at

L. 4 gg

a ANN MATIN OTA THe

HLA

Ficune 21.—Deviee for dislodging coal by injection of water.

the face, and all watering of the face could be dispensed with. The
atmosphere in the workings never became dust-laden, hence there
could be no clogging of lamp gauzes.

On returning toward the shaft the writer found the coal in passing
ears clammy to the touch and haulage roads practically free from
coal dust.

The double cone collars on the insertion pipe are said to be an
improvement on Herr Meissner’s method, and it is understood that
patents have been applied for.

KRUSKOPF SPRAYING PROCESS.

Another method of staying accumulations of coal dust in mines
was mentioned to me while in Westphalia, namely, the Kruskopf
spraying process. The inventors, Messrs. IL. and E. Kruskopf, of
Dortmund, propose to wet the walls of underground roads with a
certain chemical solution, or to suspend similarly soaked cloths from
the roof of haulage and main roads, with a view to preventing deposits
of dust and to stopping coal-dust explosions.



202

Coal-dust explosions, experiments with... f
description of
fatalities from, in England...
history of, in England wo
in the United States............+.
prevention of.

30, 70-98, 103-107, 149-151, 164-183

views of cesses ceceecee eee B88
Coal mines, water in... oL
Coals, noneoking, explosive dust from us

Coke, character of... 4
Coked dust. See Coal dust, coked.

Colorado, explosions in. ceeesese 81-82, 108

Cotton mills, sprinklers in... 78
Cunynghame, Henry,on coal-dust explosion. 20
D.

Density of dust, degree of weve cess 38-42, 99

Desborough, A., on coal-dust explosion.
Du Souich, —, on coal-dust explosion...
Disasters, great, in 1907, descriptions of...

Incorrect reports on.....
Dust. Sec Coal dust; Stone dust.
Dustless zones, efficacy of

efficacy of, diagran

RE.

England, coallust explosions in, 11-14,
explosives in. . os
rogk dust in...
watering in...
See also Altofts.
Engler, C., apparatus of.......
‘experiments of. i
Entries, dust in, dangers of....-
eat radiation from.........

chart showing cee 8
See also Road dust
Europe, coaldust experiments in.......... 149-163
Exhaust ventilation, advantages of 183
Explosibility, cone 99-108
factors affecting. 99-101
Explosion gallery, description of............ 39-40 i
figure showing. oe 4]
plateshowing. 0.0.0.0... Sy
tests with... cee 51-88 |
|

See also Propagation
Explosives, regulation of. ...
tests of,
See ulso Explosives, permissibte. :
Explosives, permissible, tests of, . 83-84, 159, 102-163
Explosives, quick-flaming, use of.......-.-.. S2-84

19-20, 92-84, 107

Fr
Fans, preferable type of...

Fatalities in Great Britain, stati
in United States, statisties of.
Fire damp, explosibility of.
Flame, phenomena of...
Flour dust, explosion of.
Fog line, significance of. os
Fogs, production of, by steam...
water carried in...
Forstmann, —, on hair hygrometer

Page.
Frameries, Belgium, gallery at. 159-163,
gallery at, figures sho’ 159, 160, 161. 162
France, coal-dust explosions in.....-....-.-. 12,20
experiments in. : 137-140,

explosives in. 83
See also Liévin.

Frazer, J. C. W., invention of, ve 40
on coalaiust ignition....... cone MSL9
work of.......-. fee 0

G

Galleries, model, experiments in. 12-26

See also Aitofts gallery; Coal-dust explo
sion.
Galloway, William, experiments by....... 116,126

on coal-dust explosion. 12-13, 14, 16,116
Garforth, W. E.,experimentsof, onrock dust. 64,91
Gas after explosion, character of. 139-140
Geological Survey, U. S., investigation by... 32-33
coal-dust explosions in. = 16,19

explosives in. . 82
gallery at... 163
Grahamite dust, explosion of...0.0.00.0.0-.. 0 2
Greenwell, @. C., experiments by... 128
is

Haas, Frank, on exhanst steam as a pre-
ventive. 166-179
onsteamjets. + 90,106

work of...
Haldane, J. 8., on dust sampling. .
Hall, Clarence, work of ........ .
Hall, Henry, on calciuin chloride...

on coal-dust explosion - - 13,18
Hall, H., and Clark, G., experiments of..... 120
Hand cutting, dust produced b; 35-87
Health, effect of humidity ceeceseeess 17
Heat, manifestations of... eevee WUE
Hilt, C.,0n coal-dust explosion. 6

Holtzwart, R., and Meyer,

fee ceeeeeeeeees 130
experiments of... ceceeeeeees 1304132
Hosing, use of... 77-78, 104, 159

‘See also Sprinkling.
Beets OF ee ee LOOT

fouging from...
Humidity, effects of.
measurement of,
principles of........
records of..-....
relation of, to temperature
charts showing.
See also Saturation.
‘Hygrometer, deseription ot of.
‘View of...
Hygroscopie salts, use of.

L

Ignition, conditions for.
definition of.....
investigations of.
means of, experiments in

figures showing.

Illinois, Iong-wall system in...
shot firing in...



46 THE EXPLOSIBILITY OF COAL DUST.

have been made at various times and in various countries, both in
laboratories and on a larger scale. The earlier experiments of the
foreign investigators, Abel, Hall, Galloway, Marreco, and others,
and of the early European testing stations, have been mentioned on
pages 12-19. The small-scale experiments of Professors Peckham
and Peck, of the United States, have been referred to on page 27.

INVESTIGATIONS IN THE UNITED STATES BY CHAMBERLIN.

No large-scale systematic tests of the explosibility of coal dust had
been made in this country before the Pittsburg station experiments
were started; but some very interesting studies of explosive mine
gases and dust have been made by Mr. Rollin Thomas Chamberlin.*
The investigations relating to coal dust were made to determine
the part that dust took in explosions, particularly in the Monon-
gah, Naomi, and Darr disasters. Mr. Chamberlin observed the
enormous quantity of fine coal dust coating everything in the ex-
ploded mines. He noted that the dust was of two sorts, ‘‘uncharred
dust”’ and ‘‘charred dust,” and that each took certain positions with
reference to the obstructions in the passageways. He observed that
the charred dust in the Monongah and Darr mines was for the most
part on exposures facing away from the source of the explosion, but
adds that there were many exceptions to the rule. He concluded that
much dust was coked while in the air and deposited in a semiplastic
condition. Laboratory experiments were made by Mr. Chamberlin
on the loss of volatile matter in the charred dust. In these investiga-
tions he determined the amount of volatile matter contained in differ-
ent coal dusts, and the amount of gas given up in the process of crush-
ing coal to dust, and also made some investigations of the relative
inflammability of old and new dust. From the latter studies he con-
cluded that the oxygen absocbed by dust is mainly chemically com-
bined and that there is not enough free oxygen in the dust to play an
important part in an explosion. He therefore inferred that ‘‘fresh
dust is likely to prove more inflammable and more predisposed to
start and propagate a dust explosion.”’

EXPERIMENTS OF BEDSON AND WIDDAS.

Abroad, during the past few years, valuable tests of the compara-
tive sensitiveness of different dusts have been made on a laboratory
scale by Professors Bedson and Widdas at Newcastle University,
England. Preliminary results were given by them in two papers
read before the North of England Institute of Mining and Mechanical
Engineers, 1906-7. These results are discussed by Dr. J. C. W.
Frazer on pages 133-137 of this bulletin.

@ Chamberlin, R. T., Notes on explosive mine gases and dusts, with special reference to explosions tt the
‘Monongab, Darr, and Neots! eoal mines: Bull. U.. Geol. Survey No. 383, 1900,


MANIFESTATIONS OF COKED COAL DUST. 109

important in carrying an explosion into remote corners after the
active flame of an explosive wave has temporarily died away. Then
should any gas be present it would be greatly compressed, so that
when the red-hot particles penetrated the compressed gas at the head
of an entry or other closed place they would cause its ignition, and
thus a secondary explosion would be set up.

5. The fifth kind of coke is not a coke from dust. It is formed
where the flame of the explosion has lingered and the flame or
adhering coked dust has ignited the coal ribs, sufficient oxygen
being present for the combustion to go on. This sometimes occurs
in a room, and such a place, if a large amount of coke has been present,
has frequently been mistakenly considered the point of greatest inten-
sity of the explosion.

In few places has it come to the observation of the writer that coking
of the face or ribs has been due to the direct explosive blast; this would
appear to be an after-effect.* Generally coked dust has been caked
while in the air, and in the plastic or semiplastic state has been thrown
against exposed surfaces. Coke from dust is more likely to be found
upon the timbers and coal ribs than upon the roof or rock ribs where
such are exposed; but this is by no means invariably so. However,
there does appear to be a selective action. It was peculiarly notice-
able in a certain entry in the Franklin Slope mine, in which several
slate partings with a smooth fracture showed along the ribs; the coke
adhered conspicuously to the coal above and below each of the part-
ings, but not to the partings themselves.

The coke or caked coal found after explosions shows a marked
increase in ash and decrease in volatile matter as compared with the
average coal of the mine. Even when no coking is apparent to the
eye there may be a considerable loss of volatile matter in the dust.
This is indicated by a comparison of dust gathered near the shaft
bottom at Marianna with the standard coal of the mine, as shown in
the following tabulation:

Prorimate analyses of dust and of coal from Marianna mine.

[A. G. Fieldner, analyst]

eoal.2

As collected: t
Moisture. .

Volatile matter
Fixed carbon.
Ashe.

‘Moisture and ash free:
Volatile matter ..
Fixed earbon..

@Tn the Banner mine, Alabama, efter the explosion of April 6, 19U, large coke globules were found at
several points in one entry adhering to the roof and manifestly formed in place by the melting and coking
of splinters of the coal which formed the fool, "There was ite mechanical violence at these points
coking effects are rarely found,

® Suruple of coal full section of seam, as mined

Moisture undoubtedly absorbed after explosion; sample was gathered about ten days after ft,



EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS.

51

Explosion-gallery tests at Pittsburg station on dusts from representative coals.

Flame showed

‘indicating it
Dust on} fIBdtaihe 1S) Length
‘test | Dateot horse and| offiame | tons. | pr
Nest Explosive used. shelves in|————— beyond | {fn | baton,
| ai. sections } win | dust 7
‘Nos. | Doors | WI") zone.
Nos | Nos. —
G-700..| Jan. 30..| S00grams FFF blackpow-| 145] 1-6) 1-6
er.
e000... 415| (a) 3
5.) 600 grams C biack powder.| 1-15 |1-3,11-12{ 1-15
300 grams dynamite. 115 |.
-| 978 grams FF black pow-| 4-9
er.
G67... Son grams FFF blackpow-| 45} 1-9
er.
C465. spsngeee #6| siz] 14s
G26, pick pow} = 15] 5} LS
G-2156.] Apr. 24 ys| 4s] as,
G-2517.| June 19." wis! 1s} 5
{rate powder, (
G-1501.| Mar. 20. si grams FFF biackpow-| 1-15! 145 | 115
i
G-22,| Apr.17.,| 875 grams FF black pow-| 6/145) 45
er. i

Source of coal dust.
ye Nite’ | Ftxea
io. 5 le | Fixe
Location of | Character and place of | Mots- | {lle | Fixe Sule
Name of mine. | '°rtine. sample. ture. | eam: | eat | Ash. | phar,
bie.
G-700..| No.2 Bear Val-/ Wililamstown,| Anthracite from first | 2.36 | 4.22 | 83.44] 9.98] 0.49
fey shaft. Pa. heading in the Little
View at No. 2 shalt,
G-013,| Connell Anthra- | Bernice, Pa...| Subanthracite from in-| 1.40 | 8.32
cite MiningC terior of mine.
2389.) No. 37 B mine...] Windber, Pa.., Semibitaminous. -17| 13.96} 79.80] 5.47] .87
G-2365 |, do. feceeenn 177 | 13.96 | 79.80] 5.47) ¢87
Shamoida ise. 8 tabaci, Semubfominous “from } 84] 15.16 | 70.90] 4:10] $8
a. ple.
” from dry | 13.18 | 19.97 | 56.37 | 10.48] | .77
‘coal ele.
G467..| Mine No. 5,| Whitwell, | Bituminous) vator/
Whitwell| ‘Tenn, fom miain | 3.41 | 17.98 | 47.22 31.30 | 1.20
mines, entry.g
No. $ Tenn. romtipples] 2-07 | 26.49 | 8.01 | 18.23 | «82
and I.Co, from ribs | 3.22 | 24.18 | 49.34] 2.20]
4465.4 8G TCO. | Blocton, Ava...) Bituminous goal |
and T.Co. | i
{ tram tate | 1.52 a0.89 | 56.70 | 11.20] 2.00
G-2116,| Federal Shaft | Fairmont, Bituminous) rior |
mine. Ww. liromtipple.s, 1.25 | 31.70 | 7.34} a7] 24
G-2156, Grek | Lghger, Ww. | Bituminous from No. 21 164 | 31.54 | 6655 | 227]
me | Vat Kanawha gas seam. |
G-2517. Oak station, | Bitum uous (“stin- 1.81 ) 38.62 | $8.96) 6.31 | 1.00
dard” dust).
G-s01. Saline vil, | Bituminous. «| 2.03; 25.97] 57.00] 5.60] 2.38
G-2112,| Superlor Coal | Sweetwater, | Subbituminous trom} 9.63} 34.49] soot | 4.07] 1.05
Wyo. face of room 1 off first |
north, i i

@ Not recorded.

» This test was repeated with 40 per cont dynamite with same result.

¢ This test was repeated twice with black powder, slzes “CC” and “\CCC.”
ignition, but “CCC” did.

'é'This test was repeated with a similar result.

«Flame extended 50 feet beyond end of gallery.

J Dust placed on a horse in the tests.

Dust placed on shelves in the tests.

“CC” did not result In ao


186 THE EXPLOSIBILITY OF COAL DUST.

Acuitton, L. Note aur les expériences enterprisés par M. Abel pour étudier le réle
des poussiéres dans les explosions de mines. Annales des mines, ser. 7, vol. 20,
1881, p. 121.

American InsTITUTE oF Mininc Enoineers. The Pocahontas mine explosion.
‘Trans. Am. Inst. Min. Eng., vol. 13, 1884, pp. 237-249. Report of commiittee,
Messrs, Bramwell, Buck, and Williams.

Arison, W. N. Colliery explosions. Colliery Engineer, Jan. 14, 1887, p. 52.

Arxinson, W. N. and J. B. Explosions in coal mines. London, 1886. 144 pp.

Bramwew, J. H., Buck, 8. M., and Wuurams, E, H., Jr. The Pocahontas mine
explosion. Trans. Am. Inst. Min. Eng., vol. 13, 1884, pp. 237-249, Report of
committee on explosion that killed 114 men. Explosion due mainly to dust.

CHESTERFIELD AND Derpysinre Instirure or ENGINEERS. Report of committee on
dust. Trans., vol. 10, 1882, pp. 1-44. Report of committee on dust experi-
ments in wooden tube 82 feet long. Appendix to report contains reference to
early observations and experiments in England and France. An excellent
summary of literature.

Couuery Enarivrer. Explosiveness of coal dust. Vol. 4, November 29, 1884, p.
605. Reprint of article in Engineering. Article refers to experiments by Prua-
sian fire-damp commission.

Coal dust a cause of colliery explosions. Vol. 8, 1887-1888, p. 83. Notice of

lecture by Arnold Lupton, at Yorkshire colliery.

The Kansas mine disaster. Vol. 9, 1888-1889, p. 76, Notice of explosion at

Frontenac, Kans., which killed 45 persons.

Coal dust and colliery explosions. Vol. 9, 1888-1889, p. 80. Refers to explo-
sion at Frontenac, Kans.

———- Another explosion in which coal dust plays a prominent part, Vol. 9, 1888-
1889, p. 209. Quotes testimony of W. N. Atkinson regarding an explosion at an
English colliery.

Cotuery Guarpran. The coal-dust question. Vol. 51, 1886, p. 69.

ENGINEERING AND Mininc JouRNAL. Coal dust in the Mardy colliery explosion.
Vol. 41, 1886, p. 86.

‘The Pocahontas mine explosion. Vol. 38, 1884, p. 281.

——— The Prussian experiments on coal dust in colliery explosions. Vol. 39, 1885,
pp. 221-223. Translation of article in Zeitschr. ftir Berg-, Hiitten-, und Saiinen-
wesen im preuss. State, vol. 32, pt. 5, p. 575. Good summary of experiments
at Kénig mine.

Further results of experiments at Neunkirchen. Vol. 40, 1885, p. 201. Brief

account of experiments and results.

The Victoria mine disaster. Vol. 43, 1886, p. 343.

Gatoway, WILLIAM. On the influence of coal dust in colliery explosions (IV),
Proc. Roy. Soc. London, vol. 33, 1882, pp. 437-445. Describes 63 experiments
with coal dust in July, 1880.

On the influence of coal dust in colliery explosiona (III). Proc. Roy. Soc.

London, vol. 33, 1882, pp. 490-495. Describes new dust experiments at Liwynpia

colliery in September, 1880. Notes effect of moisture and shale dust in explo-

sion at Penygraig, December 10, 1880.

On the influence of coal dust in colliery explosions (¥). Proc. Roy. Soc.
London, vol. 37, 1884, pp. 42-46. Reasserts belief that a mixture of coat dust
and air is inflammable. Mentions explosion at Dinas Colliery, South Wales, 1879.

Hasstacurr, F. A. Hauptbericht der preussischen Schlagwetter-Commission. Ber-
lin, 1887, 259 pp. Five appendices issued separately. Appendix 4 contains
account of dust experiments at Neunkirchen.



130 THE EXPLOSIBILITY OF COAL DUST.

long and h 30.48 centimeters. The tubes a and fA are connected by a
collar (f) which holds in position the cotton gauze e, on which is
placed a quantity of dust (g). Into the other end of a is fitted a
stopper (6) through which passes the glass tube c, the
upper end of which (d) comes a short distance below e.
By means of an air blast blown through ¢, the dust is
blown from the gauze and disseminated as a cloud, which
is carried upward by the air blast to the open end (i)
of the tube h. When a naked flame is applied to i the
cloud of dust ignites and the flame of combustion travels
down the tube.

EXPERIMENTS OF HOLTZWART AND MEYER.

In 1891 the attention of Rud. Holtzwart and Emst
von Meyer was directed to an investigation of the cause
of explosions which had occurred frequently in factories Fievae s.—
where lignite briquets are manufactured. The principal Apparatus
result. of their work was a study of the explosive nd wia-
character of lignite dusts mixed with air. Their apparatus aan ihe
(fig. 9) consisted of an explosion tube (E) of 50 cubic tures.
centimeterscapacity, having two platinum wires sealed through its side
about midway the length of the tube. These wires (i i) are about 3
to 4 millimeters apart. The spark used as the source of ignition was
obtained from an induction coil operated by two
strong Bunsen elements. In one end of this tube
(k,) is fitted a one-hole rubber stopper, through
which passes a glass tube bent downward at a
right angle. The longer limb of this tube (m) is
immersed under water. A weighed quantity of
dust is placed against the stopcock H. A is a
glass bottle of 600 cu-
bic centimeters capac-
ity; B, a bottle of 3
liters capacity. Cisa
im reservoir of water
placed at aheight of 1.5
meters above the level
of the water in B. In
each of the experi-
ments performed 0.18 gram of the dust was used. Water from the
reservoir (C) is allowed to flow into B, compressing the air contained
in B to a pressure cqual to the difference in the level of the water in

@ Dingler’s Polytechnisches Journal, vol. 280, 1891, pp. 185 and 237.

¥iGuue 9.—Coaldust ignition apparatus of Holtzwart and Meyer.



EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS, 47

INVESTIGATION IN FRANCE BY TAFFANEL.

M. J. Taffanel, in August, 1907, published the results of his first
year’s experiments at the Liévin station. A large number of tests were
made with the coals from the several mines of the Pas de Calais dis-
trict. M. Taffanel, believing that a uniform density of dust cloud
was necessary to obtain consistent results, arranged a closed-circuit
gallery. (See fig. 12.) This consisted of two parallel sheet-iron pipes
2 feet in diameter. These pipes were 25 feet long and connected at
the ends. In one of the pipes there was a disk fan for propelling the
air current and mixing the dust. The four openings to the gailery
were closed by paper diaphragms. The inclosed volume was 152
cubic feet. In operation, the fan was started and the dust put in
gradually, and after time had been given for circulation four or five
times around the closed circuit at a speed of 13.16 feet per second, a
cannon charged with a half stick of dynamite, weighing 1.12 to 1.33
ounces (32 to 38 grams), and not tamped, was fired through one of the
paper diaphragms.

The dusts were always passed through a French 200-mesh sieve,
equivalent to English 190 mesh. The dust put into the gallery was
weighed and it was assumed that all was put into suspension.

The most sensitive dust was found to be that from the Courriéres
mine. In one instance, with as low a weight of dust per cubic foot as
0.023 ounce or 23 grams per cubic meter the flame traversed the tube
and came out about half a yard. TJowever, this was the only instance
in which a flame was produced, out of three experiments tried with
that density of dust. With this exception, it was only when as
much as double this density, or 0.046 ounce, was used that flame
was occasionally produced. With 0.070 ounce per cubic foot, or 70
grams per cubic meter, explosions were produced quite regularly with
almost all the coals except anthracite. With this, as high a dust
weight as 0.222 ounce per cubic foot (222 grams per cubic meter)
were tried without producing continued flame.

Taffanel’s conclusions were as follows:*

The experiments show, in the first place, that for most of the dusts tested it does not
require large quantities of fine dust, once put in suspension, to form an inflammable
cloud. A mine road where 0.1 ounce of fine duat per cubic foot [100 grams per cubic
meter] may be collected is generally regarded as [but a] little dusty. Jt is important
to observe that so far the experiments have been confined to screen dusts, which are
purer and without doubt more inflammable than those from the mine.

We see, in the second: place, that the small charge represented by half a cartridge of
gelatin dynamite is above the ‘‘charge limit” for most of the duaty tried. This, of
course, refers to the “charge limit” without stemming.

Finally, we remark that for the eight types of dust tested the increasing order of
inflammability is the same as the increasing percentage of volatile matter. Strictly

« Premiers essals sur VInflammabilité des poussiéres, p.20; Proc. South Wales Inst. Eng., vol. 26, No.
1909, p. 677.



BIBLIOGRAPHY. 197

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27, 333, 894.
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2

Ace

Pa

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198 THE EXPLOSIBILITY OF COAL DUST.

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January 2, 1909, pp. 17-19. Discusses chemical reactions of explosion; fineness of
“dust.”

An analygis of the coal-dust problem. Eng. and Min. Jour., vol. 89, June 18,
1910, pp. 1294-1297.

TarraneL, J. French coal-dust experiments. Proc. South Wales Inst. Eng., 1909.

Description de la station d’essai. Comité central des houilléres de France,

March, 1909, 19 pp. Description of Liévin station.

Les résul tata obtenus jusqu’ ace jour dansle galerie d’essaide Liévin. Extract

from Bull. and compt. rend. mensuels Soc. ind. min., Feb., 1909, pp. 18. Dis-

cusses experiments with dust of various coals; effect of stone dust.

Coal-dust experiments at Liévin. Colliery Guardian, vol. 98, July 30, 1909,
Pp. 22, Brief notice of translation, by W. N. Atkinson, of two reports, dealing
with work at Liévin.

—— French coal-dust experiments. Colliery Guardian, vol. 98, August 13, 1909,
pp. 315-818. Abstract from Proc. South Wales Inst. Eng., of translation by
W. N. Atkinson of report describing equipment and methoda at Liévin station.

‘Les expériences frangaises sur les poussiéres de houille, Comité central des

houilléres de France. Notes techniques, November 15, 1909, p. 347.

Expériences sur les poussidres de houille et aur les moyens de combattre

leurs dangers. Annales des mines, ser. 10, vol. 17, September, 1910, pp. 189-241.

Describes third series of experiments at Liévin and gives general conclusions.

Earlier experiments described in Annales des mines, July, 1910, pp. 14-66, and

August, 1910, pp. 73-187.

Enquéte sur les conditions de formation des dépota poussieux dans lea mines,

Annales des mines, September, 1910, pp. 242-264. A report to the Permanent

Committee of Scientific Research on Firedamp. Summarizes conditions at

various French coal mines.



74 THE EXPLOSIBILITY OF COAL DUST.

In a recent article * Mr. Joseph Virgin, the superintendent of the
Plymouth Coal Company, Plymouth, W. Va., says:

Believing that calcium chloride would act satisfactorily * * * on February 8,
1909, we placed 3 barrels (14 tons) * * * on about 500 feet of heading, the latter
being 8 feet wide; we distributed the salt like sowing seed broadcast. The dust on
the tracks was about 3 inches deep and on the débris one-eighth inch. All was covered
with salt * * * in twenty-four hours, the fine coal was moist, and in two days
the dust was quite damp and would stick to the hand like wet gunpowder. ‘The dust
remained damp for more thanamonth. On April 8, 1909, this heading was cleaned up.

Several mines in the Pocahontas region of West Virginia, at Mary-
town and near Elkhorn, and several mines in the Pittsburg district
of Pennsylvania used calcium chloride during the winters of 1908-9
and 1909-10 with reported favorable results.

Some tests with crude calcium chloride,’ a by-product of chemical
manufactories, were made in the winter of 1909-10, with the coopera-
tion of the writer, in the Catsburg mine of the Monongahela Con-
solidated Coal and Coke Company, working the Pittsburg seam, in
Washington County, Pa. Two adjoining “butt” entries, very dry
and dusty, about 2 miles in from the drift mouth, but on a split of
air drawn from an air shaft only 2,500 feet distant, were selected
for the experiments.

The reason for the dryness of these roads is apparent from the
hygrometric readings, which were made on January 14, 1910. The
calculated results follow:

Sy

Hygrometric readings in Catsburg mine

Water per
i | Relative

| Dry bulb. | Wet hulh. + 100,000 eu,
ad bamidity. | "fp, ‘of air,

Return of distriet

There is therefore absorbed from this one district 3.46 gallons of
water per 100,000 cubie feet of air circulated. The volume of the
split is 8,750 cubic feet per minute. The extraction of moisture from
this small district, assuming that the hygrometric reading repre-
sented average winter conditions, would be 187 gallons per twenty-
four hours.

Three areas were treated, each about 400 feet long, separated by
untreated areas.

Tn the first, the road had been cleaned up to the level of the top of
the ties and watered about one week before the application of calcium

@ Dust problamn in coal mines: Eng. and Min. Jour., October 9, 1909, p. 734.
> Composed, according to an analysis by 4. C. Fieldner, chemist, now of the Bureau of Mines, of 56

per cent CaCl, 11 per cent NaCl, and 32.70 per cent HO.



84 THE EXPLOSIBILITY OF COAL DUST.

By the use of ‘permissible explosives” the chance of disasters
developing from blown-out or overcharged shots is reduced to a
minimum. As a majority of the great mine disasters in this country
have been caused by blown-out or overcharged shots of black pow-
der, the general adoption of the “permissible explosives” should
result in a tremendous reduction in the number of such disasters.
There are, however, other initiating causes of great explosions—for
instance, the ignition of any small body of fire damp. Under some
conditions an electric arc may cause an ignition of coal dust. Although
no large-scale tests of the explosibility of coal dust by electric arc or
hot wire have been made at the Pittsburg station, the possibility of
such ignition is shown by the laboratory experiments conducted by
Messrs. Bedson and Widdas in England, already referred to, and by
the preliminary laboratory experiments of Dr. J. C. W. Frazer, an
account of which he gives as part of this bulletin (pp. 140-148).

ROCK DUST.

The British accident in mines commission in 1886 said:

‘The observation recently made in Germany, in some preliminary experiments, that
a thin layer of fine angular sand strewn over mine dust appeared to have the effect
of preventing the communication of flame from a blown-out shot to all but the most
inflammable dusts, is worthy of a passing notice.

Messrs. W. N. and J. B. Atkinson * suggested (1881), among other
remedial measures, that “bottom dust might be rendered uninflam-
mable by an adulterant like sand.”

Mr. W. E. Garforth, in giving testimony before the royal commis-
sion in 1891, in reply to a question about the Altofts explosion which
took place October 2, 1886, said: °

‘Those roads containing coal dust were affected, those containing dirt dust or only
a sprinkling of coal dust were not affected. * * * I think you should
some experiments on the different kinds of coal dust and dirt dust. I bel

dust will really be the means of preventing an explosion on some roads; more so
than water.

In a discussion following the reading of a paper before the Illinois
Mining Institute, May 16, 1893, on the Pekay mine explosion,° the
writer of this bulletin remarked to the following effect:

‘The mine was entirely dry and there was coal dust on all the roads * * * In
mines where there is plenty of fire clay this might dilute the coal dust and make it
loss explosive * + *. The Pekay mine was new * * *.

The miners were paid for Jump coal and they were not careful about loading up the
slack, which by the travel to and fro on the hard floor of the roads was ground up
quite fine, but not yet diluted with clay. Such, no doubt, were the circumstances

# Explosions in coal mines, py. 127.
® First Rept. Roy. Comm, 1881, p. 125
¢ Trans. Ill. Min. Inst., vol. 2, 1893, pp. 75-76.



EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 43

Tests of propagation of flame by different sizes of coarse coal dust.

[All charges of explosive tamped with clay.)

Flame showed (in-

\
| Explosive. Dust sed. | dleating ts Tength) Result.
Ste

i

Date of —-- ~;

No Gallery | Date ot | ]
test No.

(1909), | Wine

| Pounds.| Grams. | Weight. | Size, | Poors. gows | Tenttion. gee

Pounds.) Mesh

ib 7 10} 20- 40

ul Br 20| 20-40

i 567 10 | 40- 60

yy 567 20 )-

a] Bez 10] 60- 0

a] 57 20} 60- 80

ul ber 10} 80-100

HL B67 17| 60-80

Hh (567 14{ 60- 80

2} 1,135 10 | 60- 80 Yes,

ai] 13135 10 | 60- 80 :

2) 1135 12| 40-60 Yes.

ai] 1135 15| 20-40 +} Partial
1,135 23) 20 40 { Partial.

@ Dust was piaced on a horse in the first three sections, and on shelves In sections 3-6, except in tests 13
‘and 14, in which dust was placed on shelves in sections 3-0 and 3-11, respectively.
® Edge of door 3,

Analyses of dust samples taken before and afler tests shown in preceding tabi

Volatile | ized

No Gallery: Character of sample. Moisture combus-| ction, | ASH
1 | Dust before shot - 2.00
3| Ged) do. i 2.20
5 | 2580. 2:00
7} G-2804 ee
Dust before shot nn : 2.20
2 | Gast.) Coked dnst attr shot. aoe 2
‘Dust before shot... as
18 | @-2987.. {Ookod st ater shod :

A.C. Fieldner, analyst.
» Analyses of these coked dusts were not made until over a month after the test; it is probable that the
molsturé shown bad been absorbed In the meantime,

METHOD OF SCREENING.

The coal was of the kind used for standard tests at the station, the
average analysis of which is shown on page 35. After being crushed
and ground, it was passed through 20, 40, 60, and 80 mesh screens,
so that four sizes of dust remained over 40, 60, 80, and 100 mesh
screens. Difficulty was experienced in getting each size free from
the next smaller size, and particularly from the float dust, so that
great care was required in screening. The float dust was eliminated
by stirring small portions of the screened size in a deep pail, with
the end of a hose discharging compressed air. By this means each
size when finally finished was remarkably clean and free from other
sizes.


INVESTIGATIONS OF THE IGNITION OF COAL DUST. 121
EXPERIMENTS OF ABEL.

Abel * attempted to secure the explosion of coal dust on a small
scale by means of a charge of 26 grams of powder placed on the bottom
of a wooden box, which was used as the explosion chamber. He
judged the effect of the dust by the extent to which the flame of the
powder was elongated by the burning of the dust. His results were
negative, as the length of the flame was sometimes longer but some-
times shorter than the flame of the powder alone. But he concluded
that possibly with the large flame and violent agitation from a
blown-out shot dust alone would propagate a flame farther than the
experiments on a small scale seemed to indicate.

EXPERIMENTS OF MALLARD AND LE CHATELTER.

In 1882 Mallard and Le Chatelier * published the results of their
work. In the course of this work the authors undertook a study on a
laboratory scale of many of the important conditions influencing
the ignition and the explosive character of coal dust. This work is
of great historical interest, because of the conclusions reached by its
authors and the influence which these conclusions have exercised
in the development of the coal-dust theory. The work is also of great
scientific interest because of its scope and the number of problems
of a fundamental character which the authors have undertaken to
investigate. Their experimental work is prefaced by a summing up
of the evidence in support of the theory, both the evidence furnished
by laboratory experiments and that obtained from mine accidents
where coal dust had been assumed to be a factor.

Their own laboratory experiments are divided in the following way

Chapter I, The study of the phenomena presented by the mixture of coal dust and
air containing no methane.

Chapter IT. The study of the phenomena presented by mixtures of coal dust with
air containing an amount of methane too small to form an explosive mixture.

Chapter IIT. The study of the phenomena presented by mixtures of coal dust with
an explosive mixture of air and methane.

Our interest in this work, for the present, centers in Chapter I.
This chapter is subdivided into the folowing six sections:

. A study of the influence of the eize of the flame.

A study of the influence of the velocity of the air current.

. A study of the influence of the size of the dust particles.

Section 4, A study of the influence of the nature of the coal.

Section 5. A study of the influence of the relative proportions of dust and air.
Section 6. The velocity of propagation of the flam

@ Annales des mines, ser. 7, vol. 20, 1881, pp. 121-153.
> Idem, ser. 8, vol. 1, 1882, pp. 5-98,


TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 105

The same result could be accomplished by passing the steam through
a registering meter.

Disadvantages.—The disadvantage of steam sprays is that the
steam fogs the air current in cold weather, so that the sprays can not
be placed on the haulage roads without considerable discomfort and
danger of collision. It therefore seems requisite to employ a blowing
system of ventilation, placing the steam sprays on the air way at the
intake and throwing the return air on the main haulage road. This is
manifestly unsafe to do in gassy mines or in mines liable to an out-
burst of gas, particularly if the method of haulage is electrical. The
only alternative in such a mine is to have an additional entry for the
return air way, making the ventilation in the haulage way “neutral”’
or passing through it a very small but sufficient supply of fresh air.
In most old mines this is an impossible condition; therefore the
decision as to the use of the steam-spray system must depend on
whether the mine makes suflicient gas to prevent the return air being
passed through the haulage way. In much the greater number of
es, particularly in the Middle West, there is not sufficient gas to
prevent this being done; therefore in such mines the use of steam
sprays appears to be one of the best systems where the roof condi-
tions permit it. A compromise method is that used at the Schoen-
berger mine, described on pages 80-82, in which the steam sprays are
used in the haulage road at night only, water sprays being used on
the day shift when coal is being hauled.

Danger to roof.-—It has been held by many mining men that the use
of exhaust steam for humidifying would be especially severe on the
roof. In the opinion of the writer this is not generally true. The
condition of humidity obtained by its use is very uniform. Where
humidifying is not done it is the alternate drying out and wetting
due to the changes in weather that causes most of the trouble. The
roof is not subjected to any more severe conditions by steam or water
sprays than in spring when hot moist air enters the mine. Later in
the summer during the hot weather the same high degree of moisture
prevails, but the roof, becoming acclimated, as it were, to this condi-
tion, is not as likely to fall as during the spring, when the change of
temperature and humid y took place. If, when cold weather comes,
the humid condition of summer is maintained by introducing sprays,
the roof will not be subject to violent changes in humidity.

Heating intake air.—The plan of merely heating the incoming or
intake air to produce summer temperature without introducing
additional moisture has sometimes been proposed as a remedy. The
fallacy of the argument will be obvious to one familiar with the
principles of relative humidity and their application to mine air.

Teating the intake air as an aid to quick humidifying, where either
steam or water sprays are used, has been tried more or less, with



114 THE EXPLOSIBILITY OF COAL DUST.

not play any part in its propagation, except by the momentary
mechanical pressure required to overcome the inertia of the air cur-
rent, The fact that a dust explosion does usually seek the intake
entries is due to another cause, namely, that the fresh air has dried
the coal dust along the roads, whereas in the return air way of mines
of any size the air current, being saturated with water vapor, has
exercised no such drying effect.

The presence of the dust is the all-important thing. This was pecu-
liarly obvious in the Primero mine explosion, where certain intake
entries on which there was no haulage and which were free from dust
showed no manifestation of the flame having passed through them.

In general, dust explosions are apt to die away on long stretches
of wet ground, along which the ribs are alsodamp. However, if there
has been much dry dust in that part of the entry nearer the origin,
the blast may carry the dust through the wet zone and in this way
continue the explosion beyond the area where it is not fed with fresh
dust. Just what length of wet zone is essential to stop an explosion
depends upon the violence of the explosion wave and the amount of
dust carried in advance. Much is yet to be learned on this and other
points from the experiments now being made here and in other
countries. It should always be borne in mind that though coking
js a conspicuous result of a coal-dust explosion in coking-coal mines,
in mines producing coals that do not coke freely, such as those in
the interior fields, or that do not coke at all, such as the lignites of
the far West, few signs of coke or in the latter case none at all will
result from an explosion. In such mines the dust. will show a loss in
volatile matter and an increase in ash; the chemical analysis must
therefore furnish the clue as to the part played by dust.

Dust from black lignite or subbituminous coals, under some condi-
tions, has proved to very explosive. For instance, in the Gallup,
N. Mex., subbituminous field, violent explosions have resulted from
blown-out shots. Coals of this field do not coke at all, and the mines
are generally free from methane.

In the absence of the coking phenomenon, an explosion of con-
siderable magnitude must be traced by the effects of flame and of
violence. The former are particularly erratic in dust explosions, as
previously indicated, for often such explosions traverse long distances
without leaving signs of heating. This is probably due to several
causes—the speed attained by the flame, the excess of dust over that
needed for propagation, and the blanketing effect of the rock dust
that is present. It is probable that where extreme speed is reached
the flame darts only through the center of the dust cloud, borne by
the advance wave. When the explosive wave reaches an enlargement
of the passageway or where side passageways lead olf, giving a large


192 THE EXPLOSIBILITY OF COAL DUST.

Verner, J. The explosion at Cedar Mines, Report Iowa mine inspector, 1893, pp.
29-35.

Waxxer, Sipney. Ignition of fire damp and coal dust by means of electricity. Col-
liery Guardian, January 12, 1900, p. 64; January 19, 1900, p. 109; January 26,
1900, p. 161.

Waxxer, W. The coal-dust theory. Colliery Engineer, vol. 12, 1892, p. 268.

Winknavs, F, Die berggewerkschaitliche Versuchsstrecke zur Ergriindung der
Einwirkung von Sprengstoffen auf Schlagwetter und Kohlenstaub auf Zeche Con-
solidation Schacht bei Schalke in Westfalen. Glickauf, 1804, pp. 165L-1654;
1895, pp. 559-562, 577-580, 597-600.

—— Experiments with explosives at Schalke, Westphalia, Trans, Fed. Inst. Min.
Eng., vol. 9, 1895, pp. 250-280.

Zonner, RicHarn. Methods used for diminishing danger of coal dust in governmental
coal mines of Saar district. Trans. Fed. Inst. Min. Eng., vol. 14, 1894, p. 620.

1901-1906.

Apet, F. A. Accidents in mines, Proc. Inst. Civ. Eng., vol. 91, pp. 36-83. Dis-
cussions, pp. 84-185.

Asnworrn, James. Flameless explosive and coal dust. Colliery Guardian, vol. 82,
1901, p. 23.

Damping the air of coal-mines a safeguard against explosions. Iron and Coal

Trades Review, September 26, 1902.

Observation on water sprayed or damped air in coal mines. Trans. Fed. Inst.
Min. Eng., vol. 29, 1904, pp. 11-22. Discussion, p. 22; vol. 30, p. 125.

——- Spraying or watering problem of dusty mines. Mines and Minerals, vol. 24,
1903, p. 97.

‘The Clydach Vale explosion. Mines and Minerals, vol. 26, 1905, pp. 154-155.

Method of laying dust by watering.

The Courriéres disaster. Engineer, November 9, 1906, pp. 470-471.

Bearp, J.T. Mine explosions, excessive use of powder. Mines and Minerals, vol. 25,
1904-1905, p. 560.

Energy developed in the combustion of powder and coal dust. Mines and
Minerals, vol. 25, 1905, p. 509.

Benson, P. P. Gases inclosed in coal and coal dust. Trans. Fed. Inst. Min. Eng.,
vol. 24, 1902, pp. 27-40.

Buakemore, W. The Fernie explosion. Trans. Fed. Inst. Min. Eng., vol. 24, 1902,
pp. 450-461. Discussion, pp. 461-477.

Broockmann, K. Gases inclosed in coal. Trans, Fed. Inst. Min. Eng., vol. 24,
1902, p. 18. Discussion, vol. 25, p. 43.

Coutery GUARDIAN. Notes on the Llanbradach explosion. Vol. 83, 1902, p. 350.

—- —- Notes on the Talk-of-the-Hill explosion. February 14, 1902, p. 350; February
21, 1902, p. 389; March 14, 1902, p. 574.

ENGINEERING AND MINING JoURNAL. Coal duet as a factor in mine explosions, Vol.
77, 1904, p. 758. Editorial notice of Harwick disaster.

Coal-mine explosions in Kansas. Report of State commission, Vol. 79, 1905,
pp. 509-510.

-—— Electric lights and coal dust. Vol. 80, 1905, p. 496. Notice of paper by
Henry Hall, before Manchester Geological Society.

Watering coal dust in mines. Vol. 80, 1905, p. 355. Editorial.

Fautps, ALEXANDER. The spraying or watering problem of dust in mines. Mines
and Minerals, vol. 24, 1903-1904, p. 219.

Gattoway, Wituiam. Report on the Senghenydd colliery explosion, Colliery
Guardian, vol. 82, 1902, pp. 450-456; also p. 506.



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 119

The coke residues from a and ¢ were hard and brilliant, while those
from b and d, collected after the explosion, were found to be pulveru-
lent. A sample of reddish dust charred by an explosion in the mine
from which the dusts used in the experiments came gave the following
analysis:

Analysis of coal dust charred by mine explosion.

Volatile matter.......... 2.2.22 00 cc cece e eee ee cece eet e eens 27.2
Ash....-..-
Fixed carbon

100.0

The conclusions reached as the result of this and additional experi-
ments were:

(1) Certain finely divided dusts, rich in gas, take fire when brought
into the air by a blown-out shot. These dusts, being decomposed,
yield an explosive gas mixture which would take fire from the powder.

(2) The flame is instantaneous; it burns or alters the small amount
of coal dust raised in its path and goes out.

(3) The intensity of the phenomenon is intimately connected with
the character of the dust and becomes practically nil if the size of
the particles is increased to an appreciable part of a millimeter.

(4) Other things being equal, the violence of the explosion would
depend essentially on the physical conditions which determine the
raising of the cloud of dust and its subsequent conduct.

(5) The presence of an excess of free carbon in the powder facili-
tates the production of an explosion.

Certain experiments were performed by the Societé de |’Industrie
Minérale in a gallery used for testing lamps. During the experiments
an air current was kept circulating through the apparatus. The
inflammation was produced by igniting 50 grams of powder contained
in a lead cartridge, after coal dust had been placed in the gallery.
A second series of experiments was made in a gallery constructed
for the purpose, the length of which could be varied. In this set of
experiments the ignition charge was 30 grams of powder placed on
the bottom of the gallery in a paper or lead cartridge.

In the first series of experiments it was noticed that the flame from
the powder was elongated from 3 meters to 6} meters. In the second
series, when the gallery was 4 meters long and the ignition charge
was placed 2 meters from the orifice a large flame shot out of the tube
on the ignition of the charge; when the gallery was 8 meters long
the flame did not emerge. Thus they were able to secure the ignition
of the coal dust in this way, but the amount of such ignition must
have been small, as paper was not ignited at 3 meters from the cart~-
ridge.



204 INDEX.
Page. | Page.
Stokes, —, on use of calcium chloride. . 72 | Verpilleaux, ——, on coal-dust explosion.. ta

i
Stone dust, application of | Violenee, variations in. tty
application of, views on ! Virgin, Joseph, on caleium chloride u
cost of application of. Virginia, disasters in. a1
experiments with, at Altotts, England... 90-97 | Vital, —, apparatus of, figure showing..... 117
experiments with, at Liévin, France.... 86-90 | on coal-dust explosion... 213, 117-119
Stone-dust zones, efficacy of... 150,185,156, 157-158 | Volatile matter, necessary peroentage of...
efficacy of, diagrams showing......-... 150,156 | 124-195,137
Summer. See Seasons. 1 w.
: fect of.
Sweeping, eftect o 71 | Wales, sprinklers in Er
Washing down, Sce Hosing.
‘Taffanel, J., on coal-dust explosions. . ao, | Water, injection of, in mine faces:
GELB loo, 101 injection of, figure showing.
‘Taffanel’s methods, comparison of, with Pitts- ‘Water pressure, coal breaking By -
pure experiments 18-90 coal breaking by, figure showing. 165
Tamping with coal dust, effects of. < sicoa | Watering, See Spring ere ye
‘Temperature, effect of, on humidity. 58-60,61,65-09 ] VA  veasters it cares ree
effect of, charts showing........-...... 59,65,67 | West Vérginia, disasters in. :
dust experiments in... 35-56
records of.. 109 ; °
thant showin, srahamite-dust explosion in. 2
rn, : i paying methods in. . al
‘ermpeature ingly eliotn 154 | Wet zones, efieacy of. 198,104, 114,150, 155
Thermometer, wet and dry, theory of, Fo eer ee nga B.D apparstuset. 190,
Thorpe, T. E., apparatus of. wee yay | Widdas, Hand Beason, 2B. y SPPATROS ON 136
ents Of... eeveseceseeve 2 aed
experiments 0 experiments by. 46, 129-130, 153-137
u, Williams, E. H., jr, Bramwell, J. H., and
Undercutting, dust from. Boek, 8. M. on coaldlust expe
Utah, watering 71 ws 7
watering In 7 | winter. See Seasons.
v Wood, G. R., on dust experiments
Vacuum sweeper, use of, a
Vaporization, effects of. "
Velocity of flame, measurement of. 152 | Zones, protective. See Wet zones; Dustless
Ventilation, efficacy of. 9 zones; Slone-dust zones.



BUREAU OF MINES BULLETIN 20, PLATE Vi

A. COAL-DUST IGNITION APPARATUS USED AT PITTSBURG.

B. APPARATUS USED AT PITTSBURG, SHOWING IGNITION OF DUST.



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 145

Results of second series of experiments with explosive coal dusts at Pittsburg station—Convd.

Source and proximate analysis of coal dust used and pressure
developed in tests.

Results of tests.

Weight | Equivalent| Effect on steel
applied. | per sq. cm. all,
Grams, | Grams.
2, Bituminous free-burning domestic coal from Chandler mine, ;
Fremont County, Colo, (Lab. No. 9778): 260 675 | Not lifted.
Moisture. . 2 662 | Lifted,

Volatile matter.
Fixed carbon
ASH... clo i

Suiphit- : : “9
Pressure developed, 668 grams per square centimeter

258

0 ‘#649 | Lifted.
i

670 | Not lifted.

3. Bituminous, noncoking steam or domestic coal, with cubical |
of round fracture, from Maitland mine, Huetfano County,
Colo, (Lab. No, 9784):

Moisture.
Volatile matter a
Fixed carbon..717117 :
Ash.

4
1 38,

4, Noncoking, bituminous coal of “nigger head” or round forma-
tion from Ravenwood mine, Huerfano County, Colo. (Lab.

: 0.
Not lifted.
Lifted,

Not lifted

714 | Not lifted,
0151 Do.
519; De.
300} Do.

5. Bituminous coking coal from Delagua mine, Las Ani 20 649 ' Not lifted.
County, Colo. (Lab. No. 9785): 259 619 “Do.
Mol Bib 20 es Lited
DUUIIT ga a5 245 636: Do.
: 5 42 250 649 | Not lifted.
: ax 248 | 644 | Lifted
‘tg 248 H
Pressure developed, (47 grams per square centimeter. !
6. Bituininous coking coal from Bowen mine, Las Animas 250 649 | Litted,
County, Colo. (Lab. No. 9779): 701 | Not lifted.
Moisture. cece Me 675 Do.
Volatile matter, nore 662| Do.
Fixed carbon. 6 Do.

Ash... 2 eae

Sotphars 7200007. a:
Pressure developed, 652 grams per square centimeter.

7, Bituminous coking coal, high carbon, from Sun No. 2 mine, 250 {49 | Not titted.
Fayette County, W. Va. ‘lab. No 9783): 230
are. - nee 0696, 200 9
Volatile miter 21.08, 150 390 vate
Fixed carbon...” 338 10 45
Ash... AR x70 4a | wot ified,
SUR ee el 1 | 428| Do.
Pressure developed, 426 grams per square centimeter. 13 423 | Lifted.
T
8, Bituminous coking coal from Ansted mine, Fayette County, 320, 831 | Not lifted,
W. Va. (Lab. No. 9787): 310 | 05 | 0.
Moisture . 305 | 792 | Lifted.
Volatite matter: 307 Wi) Do.
300 802 Not lifted.

Figed carbon..200000002 INE

auipkar 4
Pressure developed, 800 grams per square centimeter.

88006°—J3ull. 20—11—10



CONTENTS.

Page.

Introductory statement... 9
The coal-dust problem. 9
Acknowledgments. . 10
Historical review of the coal-dust question in Europe. u
Observations in England prior to 1850 u
Observations by French engineers prior to 1890... 2
Experiments in England between 1850 and 1885 4
Experiments in Prussia uu
Experiments in Austria between 1885 and 1891. 16
Views of English authorities between 1886 and 1908... 7
German, French, and Belgian stations for testing explosives. 19
Altofts gallery, England, 1908 a
Second report of Royal Commission on Mines, 1909. 23
Recent Austrian experiments. 24
Historical review of the coal-dust question in the United States 27
Grahamite explosions in West Virginia, 1871 and 1873 a7
Flour-mill explosion at Minneapolis, 1878 27
Explosion at Pocahontas mine, West Virginia, 1884. 28
Explosion at Pekay mine, Iowa, 1892 29
Proposed remedies for dust... 30
Results of shooting off the solid. 30
Great disasters of 1907. 31
Inaccurate reports of accidents. 32
Fatalities in 1908 32
Inquiry by the United States Geological Survey. 32
Coal dust and its origin and distribution - 3
Definition of dust 33
Ignition and propagation 34
Coal-mining methods and dust production 34
Dust from hand and from machine undercutting. 35
Agencies that distribute coal dust. 37
Experiments with explosible coal dusts 38
Effect of quantity or density of dust. 38
Character of dust used.. 38
Method of procedure. . 39
Method of taking samples. 40
Results... 40

Coked dusts produced by explosions. - 42

Effect of degree of coarseness of dust... 42
Results of tests. 42
Method of screening. 43
Distribution of dust. - 44
Diecussion of resulta - 44
Character of coke produced. 45



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 137

The authors in concluding their paper call attention to the influence
which the proportion of volatile matter in the dusts exercises on
their inflammability and explosive character, and assert that the
method affords a ready means of judging the character of a coal
with respect to these qualities. They express the hope of being
able to contribute further results of a similar character.

In some of his work Bedson has made use of a different. method
for obtaining the relative pressures produced by the explosion of
coal dust. This is a modification of the method used by Vital in
his experiments.

EXPERIMENTS AT LIEVIN, FRANCE.

A series of interesting experiments carried out in a comparatively
small gallery at the Liévin station in France will next be considered.
These experiments have been mentioned in another portion of this

ELEVATION
£
8B A
[2 a a 5 a
z Fl Hi i
mt —o {r { Oe.
c PLAN

3
a Pa ea

Figure 12. Coal-dust ignition apparatus used at Liévin.

bulletin (pp. 47-48) but they can scarcely be passed over here, because
they embody the features of laboratory experiments together with
those of actual mining conditions. They are, therefore, doubly
interesting in this connection as bearing on both the quantitative
side of the problem and its practical side. The experiments were
performed in a small gallery (fig. 12), made of shect-iron pipe, 0.6
meter in diameter, and arranged so as to form two galleries parallel
to each other and connected at cach end, so that the two galleries
formed a closed circuit in which the air is made to circulate at regu-
lated speed by means of a ventilator (V) placed near the middle of
one of these galleries. The length of the gallery was about 7 meters.
At the points A, B, C, and D were openings, which were closed
during the experiment by means of paper diaphragms. The long
side of the gallery A-B had five observation windows, numbered
1 to 5. Ignition was brought about by firing a cannon into the end


98 THE EXPLOSIBILITY OF COAL DUST.

The cost of such linings is considerable, yet in a mine where the
roof is poor, requiring much timbering, and the mine is to be long-
lived, the saving effected in the maintenance of the roadways will
probably pay in a few years for the additional cost of the lining.
The managers of the Bethune mines state that the passageway
maintenance cost in the mine mentioned is only one-fifth of the aver-
age maintenance at their other mines in the same district.

The method of lining generally used has been to divide the mine
into sections and to make the length of lining sufficient to prevent
a flame of an explosion in one section from passing through to another
section—in other words, to create a ‘‘dustless zone.’’ Until the
Altofts experiments were begun there was little definite idea as to
what length a dustless zone should have. In earlier discussions
lengths of 100 to 200 yards had been suggested.

For prevention of dust explosions the importance of lining the pas-
sageways is not due to the lining as such, but to the ease of cleaning
and to the fact that it allows the free use of water without weakening
the roof, or the floor where there is an inverted arch as well.

Except at the Bethune mine mentioned above it has rarely, if ever,
been contemplated to completely line the passageways; the usual
thought has been to employ linings to divide the mine into sections.
In order to decrease the necessary lengths of dustless linings, water
curtains have been suggested and have been experimented with to
some extent in the gallery at Rossitz, in Austria. In experiments
there with water curtains the usual flame length of dry dust without
the curtains (147 meters) was shortened about 30 meters (97 feet),
but the flame still penetrated a wet zone about 21 meters (68 feet).
The conclusion was that a wet zone alone must be at least 60 meters
(195 feet) long, but that apparently a zone supplemented by water
curtains at either end could be shorter. These figures are somewhat,
below those indicated by the Atlofts and Liévin experiments, where
larger initial explosions were tried.

The recent experiments in the Altofts and Liévin galleries and the
investigation of recent mine explosions in this country have awakened
considerable doubt as to the efficacy of zones that are merely dustless,
unless such zones are of much greater length than formerly suggested,
and unless they are situated at frequent intervals, so that an explo-
sion may not spread by getting such headway that the dust in the
“pioneering cloud” carries the inflammation over the dustless zone
to untreated coal dust beyond.




50 THE EXPLOSIBILITY OF COAL DUST.

varies somewhat with the character of coal.t The gallery at Pitts-
burg is charged with dust much in excess of the theoretical amount
to insure the most severe conditions in testing explosives, but
repeated tests have shown that dust through a 100-mesh sieve can
be put in suspension by the concussion of 1} pounds of black
powder if the dust is merely placed on the floor of the gallery. For
the tests given in the table, the coal was ground until it would pass
through a 100-mesh screen, but when road dust was tested it was
used in the gallery as received.

No propagated explosion has been obtained with anthracite dust,
although several tests have been made with a low-volatile anthracite
(under 5 per cent volatile combustible matter) and with a higher
volatile anthracite (8.32 per cent volatile combustible matter). How-
ever, it must not be concluded that these tests are final; there may
be conditions under which propagation can be obtained.

Propagation did not take place with oue semibituminous dust when
dynamite was used for the firing charge, nor in one test when black
powder size CC was used, but in subsequent tests, with other sizes
of black powder, complete propagation followed. The failures to
propagate may have been accidental, but considered together with
the slowness of propagation observed in the other tests on this coal
they indicate that it is not so sensitive as most bituminous coals.

With other semibituminous coals and all bituminous and sub-
bituminous coals propagation of flame and explosion was complete.
As these dust tests could only be made occasionally, when the gallery
was not occupied by the more pressing testing of short-flame or so-
called safety explosives, quantitative results on the relative sensi-
tiveness of different bituminous dusts could not be attempted under
the circumstances. But these typical tests and numerous other in-
formal tests of the same character have demonstrated effectively the
explosibility of coal dust.

The explosion propagative results with bituminous dusts have been
so uniform that it is hard to understand the difliculty which carly
foreign experimenters had in obtaining consistent results, unless it
was due to the uncertain character of the mine dust, or possibly to
the very small charges of explosive employed.

@ The theoretical quantity of the standard coal used for tests in the Pittsburg station, required for the
complete exhaustion of the oxygen of a cubie foot of air by combination with all The combustible mat-
ter of the coal to produce carbon dioxide and water was 0.123 ounce per cubic foot, or 125 grains per euble
meter. ‘This is based on the ultimate analysis of a sample (10536 F) which was whined December 7, 1909,

and analyzed June 27, 1910, The exposure for six monihs probably inereasrd he oxygen contents an
decreased the efficiency of the coal. ‘The ultimate and proximate anulysrs of {his coal, analyzed by A.
Fleldner, are as follows:

Ultimate analysis.

Prorimate analysis
5.1 | Moisture. : 2.59

Yolatiie matter.
| Bixed carbon.

Hydrogen
Carbon. .

Suiphur --
Ash.



INVESTIGATIONS AT EUROPEAN STATIONS. 157

By means of the present equipment, however, it has been possible
to show that when once initiated in the presence of abundant and
inflammatory sustenance a coal-dust explosion will travel com-
paratively slowly for a hundred yards, when suddenly a high tem-
perature will develop, accompanied by corresponding concomitant
pressures. If, after this, conditions still remain favorable to propa-
gation, the maximum pressures and velocities will probably prevail
undiminished until opposed by tracts of nonsupporting or screening
material.

EXPERIMENTS AT ALTOFTS ON MEANS OF IGNITION.

In reference to the initiation of a coal-dust explosion it may here
be mentioned that although shot firing has hitherto been resorted to
in the galleries, the fact that a blown-out shot is but one of several
possible causes in practice has at last been recognized, and conse-
quently other means of ignition are about to be attempted. When
the writer visited Altofts he had an opportunity to see an apparatus
designed to produce a long gas flame of sufficient volume and duration
to ignite coal dust in suspension without setting up high pressures
such as are caused by explosives (Pl. XII, €).

It consists of a cylinder which is filled with gas. At the end of the
outlet tube there is a specially constructed valve operated by a long
turning bar carrying a weight at each end. One of the weights
suspended by means of a piece of wire which forms part of an electric
circuit with a current of suflicient tension to fuse it. When the
weight is released in this manner, the other weight causes the bar to
revolye and thus to open the outlet valve. A heavily weighted
piston drops to the bottom of the gas cylinder, causing the gas to
rush out at an adjustable pressure. The gas is simultaneously
ignited by an electric spark inside the gallery. Figure 17 is a rough
sketch of the apparatus.

DISTRIBUTION OF STONE DUST IN ALTOFIS GALLERY AND MINE,

In the majority of coal-dust experiments carried out at Altofts
props and tubs have been placed in the gallery and even stone packing
has been built in behind the timbering (Pl. XILI, A).

Hanging shelves carrying an extra supply of stone dust, as used in
the Altofts mine, were likewise provided along the stone-dust zones
(Pl. XIII, B).

Through the courtesy of Mr. Garforth, chairman of the Altofts
Colliery Company, the writer was given the opportunity of inspecting
the distribution of stone dust in the mine. The dust is thrown onto
the walls of the roadways by hand, the greater part of the coal dust
adhering to them being displaced by the process. Stone dust is also


REMEDIES FOR COAL DUST. 95

and the particles (aggregates of molecules) of coal dust on the other, so that anything
which tends to increase the number of collisions between the oxygen molecules and
the combustive dust will also increase the rapidity of combustion. It is for this
reason also that the fineness of the dust ia such an important factor in insuring rapid
propagation—greater fineness disposes greater surface to the bombardment by the
oxygen molecules. Looking at it from this point of view, it would appear that dust
can never, as is sometimes supposed, be stifled by too great an excess of dust. * * *,
‘The oxygen * * * willcombine with such coal as it requires and leave the remain-
der unburnt.

Subsequent to the passage of the explosion, no doubt the excessive dust will enter
into the chemical reaction with the products of combustion, but, though such reactions
may absorb heat, they will have no retarding effect upon the rate of propagation of
the flame, since it has already passed.

To support this view, a comparison is made of results of experi-
ments employing 275 feet of the gallery. In a test in which 0.2
ounce of coal dust per cubic foot of air space was used, the maxi-
mum pressure produced was only 11 pounds per square inch; on
the other hand, in experiment 54, in which twice this quantity of
coal dust was used, a maximum pressure of 50 pounds per square
inch and a mean velocity of propagation of 1,700 feet per second
were obtained.

The retarding effect of inert dust was shown in experiment 82.
In this experiment there was only 10 per cent of stone dust in
the mixture, and the same weight of coal dust was used as in experi-
ment 54, namely, 1 pound per linear foot of gallery, or 0.4 ounce per
cubic foot of space. The maximum pressure produced was only 4.8
pounds per square inch, and the mean velocity of propagation was
only 185 feet per second.

The committee considers—

that the effect of stone dust as a zone in the path of the coal-dust explosion would
seem to lie in its power of offering resistance to the projection of the flame of the explo-
sion. ‘That is to say, its action is mainly mechanical * * * fit] presents a denser
atmosphere, offering greater resistance, * * * it mingles with [the coal dust], and
in this way raises its ignition point. For stone dust to act in this way, however, it is
essential that it must be fine enough to be raised as a cloud in the path of the explo-
sion, and it has yet, to be proved whether its action would be sufficiently rapid when
dealing with an explosion that has traveled a longer distance and has attained its
maximum velocity of propagation. ‘The value of stone dust, would appear to lie more
in ils use as a diluent, thus preventing ignition, than in any specific action it may
have in stopping an explosion that has once started. It would therefore seem
advisable not to employ zones of any description, whether dustless, watered, or stone
dust, in spite of the good results that have heen given by the last named, when dealing
with an explosion that has traveled 275 feet.

The committce therefore considers it is better to use stone dust
wherever coal dust may accumulate and to prevent the ignition of
the coal dust than to attempt to stop an explosion after it has started

@ Record of the first seties (1906-9) of the British coal-dust experiments.
b Idem, pp. 106-108.


30 THE EXPLOSIBILITY OF COAL DUST.
PROPOSED REMEDIES FOR DUST.

The numerous accidents of this nature naturally led to a great deal
of anxiety in the interior fields, and a great many palliatives were
suggested and in some cases tried. There was considerable belief in
the explosibility of coal dust, and, as it was noted that the explosions
were usually more severe on the intake air way, it was proposed, and
in some States was carried out under the instructions of the mining
departments, that the fan should be slowed up or stopped at the
shot-firing time. This was on the theory that fresh air and pressure
increased the chance of ignition. To a small extent, sprinkling or
wetting the floors of the roads from a tank car once or twice a week
was practised.

An important change was then made in many of the States west of
the Mississippi by the passage of laws requiring the shot firing to be
done by shot firers, the miner still drilling and charging the drill
holes. The immediate results were not at all favorable, as the miners,
relieved of personal risk, transferred it to the shot firers. There was
an increasing tendency to do less ani less cutting to relieve the shot,
and to increase the already large charges of black powder. The
effect was to cause more accidents from blown-out and overcharged
shots, although the number of killed and injured men was decreased,
owing to the fewer number of men exposed to the hazard. Further
legislation followed in some States, compelling the inspection of holes
by the shot firers before they were loaded by the miner. This measure
very much improved the situation, resulting in a smaller number of
killed and injured from shot firing.

RESULTS OF SHOOTING OFF THE SOLID.

East of Mississippi River, in the castern region of the interior coal
province, the number killed from mine explosions was relatively very
small until a change came in the method of paying the miners, in 1897.
Before that time the miners had been paid on the basis of the amount
of lump or screened coal produced. After 1897 they were paid on
the basis of the amount of run-of-mine coal produced. This took
away from the miner the incentive for cutting the coal ‘and for using
small charges of powder, and put a premium upon shooting down the
coal in the cheapest and easiest manner. ‘‘Shooting off the solid,”
theretofore practiced only to a small extent, became very general,
and with it a large increase in the amount of black powder used in the
shots. As in the coal-mining States west of the Mississippi, this pro-
duced an immediate increase in the number of explosions and fatali-
ties therefrom. Fortunately, the explosions were usually of limited
character, because tho natural conditions were unfavorable to wide-
spread explosions. Nevertheless, the accidents were so frequent


26 THE EXPLOSIBILITY OF COAL DUST.

To investigate the effect of inert dust, the coal dust was mixed
with dry Roman cement; the proportions of cement varied between
13 and 63 per cent. The coal used contained 14 per cent ash. The
results of the experiments were regarded as justifying the addition
of stone dust to lessen the explosibility of coal dust, but the limit of
danger was not passed until the percentage of stone dust reached 57
per cent. This corresponds to an ash content of 63 per cent in the
mixture, whereas using the dust of high-ash coal alone explosibility
ceased when the ash content reached 47.9 per cent.

In the experiments on the influence of wet zones and water cur-
tains, the wet zones were formed by sprinkling in the usual way just
before shot firing; they were intensified at intervals by water cur-
tains. The results indicated that the wet zones shortened or extin-
guished the flame, thus confirming previous results recorded in the
first report of the Rossitz station.

When the dry coal dust zone was 50 meters long the flame died
away after penetrating 40 meters of the wet zone. Even when the
flame passed through the wet zone the dry dust beyond was not
ignited. The nonignition is explained on the ground of the lowered
temperature of the flame.

Water curtains used alone were reported to produce little effect in
checking the flame, but saturation of the air with moisture, natural
or artificial, had a retarding influence on the coal-dust explosions.

Experiments were made to ascertain the most dangerous density
of the dust clouds. In the open gallery the most violent explosion
was produced with dust containing an average of 120 grams of dust,
per cubic meter (0.12 ounces per cubic foot), the dust being partly in
suspension and partly at rest, but in a closed chamber the greatest
explosion was not obtained until the weight of the dust was 500 grams
per cubic meter (0.5 ounce per cubic foot), all of this dust being in
suspension. It is stated that further investigation will be made of
the cause for the maximum explosion in the open gallery occurring
with a less quantity of coarse dust, in comparison with the maximum
explosive force developed in the chamber with a much larger amount
of finer dust per cubic meter of air.

It would appear that the cause of the difference in the results may
be that in the open gallery, when the dust is ignited, if it is not too
coarse, the explosion accelerates in traversing the gallery, the heat
and pressure bringing into play all the dust for which there is avail-
able oxygen, whereas, in a closed chamber only the initial effects
would be obtained and probably only a small portion of the finest
dust would be involved. This is indicated by the large quantity of
dust employed in the test, 500 grams per cubic meter, which is much
in excess of the amount theoretically needed for combination with
the oxygen present.


REMEDIES FOR COAL DUST. 97

ledges, and as the angle of repose of the coal dust is less it falls to
the ground and is covered up by additional stone dust. The stone
dust must be renewed at intervals, depending on the rapidity with
which coal dust gathers.¢

Other methods of applying the stone dust are being tried in the
Altofts colliery. Where a roadway is wide enough, wooden shelves
are fastened to the posts along its sides, and on these the stone dust
is placed. In another method, where the height of a passageway
permits, the stone dust is loaded on planks that are placed across and
above the haulage road, or on wide longitudinal platforms hung from
the crossbars (Pl. XIII, B).

COST OF APPLYING STONE DUST.

At Altofts the cost of applying the stone dust is stated to be one-
eighth of a penny (4 cent) per ton (2,240 pounds) of coal raised. The
coal seams of the Altofts colliery are nearly horizontal. In the
inclined workings of the New Moss colliery (under the same manage-
ment as Altofts), at Ashton, where the average gradient is 19 degrees,
the cost is stated to be about one-tenth of a penny (4 cent) per ton
(2,240 pounds) of coal raised.”

Mr. Garforth states that the quantity of stone dust required for
the first dressing of level roads is 75 pounds and of inclines 125
pounds per yard.°

BRICK OR CONCRETE LININGS AND WET ZONES.

Lining sections of entries at regular intervals in a mine to limit
the extent of an explosion has received some attention abroad. The
ideal system is to line the passageways throughout with brick or
concrete, and this has been done systematically in a new mine of
the Bethune Company in the Pas de Calais district. In September,
1908 (when it was visited by the writer), 3,500 meters (11,000 feet)
of reinforced concrete lining had been constructed, so that a visitor
entering the mine passed through a concrete tunnel, clectrically
lighted up to within a few hundred yards of the face. The linings
are smooth and are easily kept clean and free from dust, so that it
would appear impossible for an explosion originating at the face
to penetrate any considerable distance through the gangways.

aColliery Guardian, Oet. 1, 1909, p. 676.

® Record of the first series of the Brilish (1905-9) coul-dust experiments.

British coal-dust experiments. Internatlonaler Kongress, Diisseldorf, 1910, Abtellung fir Bergbau,
Pp. 88-100.

88006°—Bull. 20—11——7


BUREAU OF MINES BULLETIN 20. PLATE x

B. CONTACT BREAKER, ALTOFTS EXPERIMENTAL GALLERY; AFTER FIRING.


BUREAU OF MINES BULLETIN 20. PLATE xt

B.
AFTER-DAMP SAMPLER, ALTOFTS EXPERIMENTAL GALLERY.


INVESTIGATIONS AT EUROPEAN STATIONS, 155
RESULTS AT ALTOFTS AND LIEVIN.
EXPERIMENTS WITH PROTECTION ZONES AT LYEVIN.

The following is a synopsis of results obtained at the Liévin gallery
with zones of protection against coal dust:

The gallery was divided into three zones, a, b, and c, 75, 100, and
60 meters long, respectively.

To test the effect of a watered zone of coal dust, zone a was
lined with fine Liévin coal dust, containing 30 per cent volatile
matter; b with watered coal dust (2 liters per meter); and ¢ with
coarse coal dust. The result’ was slow propagation of the flame,
visible 60 meters outside of the gallery.

In a second test a contained coal dust as before; b was dustless,
but watered as before; and ¢ contained coal dust as before. The
flame stopped midway of zone b.

To test the effect of stone dust, in a was placed 450 grams of coal
dust. per cubic meter, in b 450 grams per cubic meter of pure stone
dust, and in ¢ 900 grams of coal dust per cubic meter, As a result the
stone-dust zone stopped the flame about midway. If the stone dust
strewn in zone b is reduced to 225 grams per cubic meter, however,
the flame leaps over to c.

In another test of stone dust a and ¢ were arranged as before, while
b contained a mixture (450 grams per cubic meter) consisting of 25 per
cent coal dust and 75 per cent stone dust containing carbonate of lime.
As a result the flame leaped ss zone b.

Tn a few months Mr. Taffanel expects to publish'a full account of
the coal-dust experiments and recent research work carried out at
Liévin station.*

CONDITIONS

At the Altofts station, work in the gallery is discontinued during
the winter months. The foggy weather which generally prevails
during that part of the year obviously produces different working
conditions, which render uniform results difficult, and frequently
impossible. Moreover, the gallery is closely situated to three railroad
lines, and though a system of signaling has becn agreed upon with
a view to the safety of passing trains, any serious dislocation of
the railroad traflic in foggy weather would practically compel the
suspension of gallery work.

During such periods of adjournment the steadily accumulating
laboratory work and questions of equipment are attended to. As
already mentioned, the station now possesses a set of the finest
instruments yet produced for this particular work.

@A series of valuable reports was issued by Mr. ‘Tatfanel in 1640. 4 review of some of the results at
Tiévin is given on pp. 86 to 90 of this bulletin.



38 THE EXPLOSIBILITY OF COAL DUST.

4, By lumps of coal jolting off the tops of pit cars and then being
ground up by the traffic of men and mules or horses. This condi-
tion is found particularly at sidings and at the ‘‘main bottom,”
owing to abrupt stops while the cars are moved and switched.

5. By ventilating currents, which pick up the fine ‘‘float” dust at
the face, and more particularly from the tops of cars. The passing
of a trip of cars, partly blocking the air way, causes a very high
velocity past the cars, especially when they go through a single venti-
lation door. If the hoisting shaft is dry and is a downcast, and the
surface screens are near the top of the shaft, the ventilating currents
may draw considerable quantities of dust from the screens.

Dry coal dust along the passageways or entries of a mine is a great
menace. While in this country the great majority of dust explosions
have originated at the face from blown-out or overcharged shots,
the propagation has been through dusty entries. If the entries were
free from dry coal dust the explosion would be local. Again, some
explosions have originated on the entries from igniting pockets of
gas in poorly ventilated entries; or in shooting down the roof for over-
casts, or in brushing or grading. Firing shots on roadways has
been a frequent source of disaster in England.

The problem is not alone to treat the dust lying on the floor, but
the fine ‘‘float’”” dust that lodges on walls, roof, and timbers. Every
ledge and projection has a coating of more or less thickness of the
purest coal dust. In the opinion of many writers, what Mr. W. N.
Atkinson terms ‘‘upper’’ dust is more dangerous than the ‘‘lower”
dust, because it is more finely divided. This will evidently depend
on the characteristics of the dust—whether it is coal dust or rock
dust and whether the former retains its strength.

The ventilating currents have a sorting action, dropping the coarser
particles to the floor and lodging the finer higher up.

EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS.
EFFECT OF QUANTITY OR DENSITY OF DUST.
CHARACTER OF DUST USED.

A preliminary series of experiments have recently been made in
the explosion gallery at the Pittsburg station to observe the effect
of sizing fine coal, and to determine the quantity or density of the
finest size necessary to propagate an explosion.

All these tests were made with artificially prepared dust from a
certain mine working the Pittsburg seam, which provides coal of
uniform character and chemical composition for all standardizing
tests at the station.



INVESTIGATIONS AT EUROPEAN STATIONS. 159

INVESTIGATIONS AT FRAMERIES IN BELGIUM.
DIRECTION OF INQUIRY.

In Belgium investigations on coal dust have been chiefly directed.
to the degree of inflammability as compared with the volatile matter
contained in the dust, and also to the liability to ignition by explo-
sives in the absence of gas.

OBJECTIONS TO WATERING ROADWAYS.

The possibility of minimizing the coal-dust danger by watering the
roadways has had to be at least temporarily disregarded in view of
the prejudicial effect both on the health of the miners and on the
economical working of the mines which that measure would unques-

Fiaunr, 18.—Detachable section, Frareries gallery.

tionably entail. The Belgian mines are deep, depths of 800 meters
being quite common, and many workings reach a depth of 1,000 and
1,100 meters. ‘The temperature at that depth is about 45° C. (113° F.),
and if charged with humidity in addition the atmosphere obviously
would not be fit to work in. Besides, watering near the coal face,
where it is considered to be most. ne
found to cause serious disturbances in the coal-bearing strata, and
jon of coal, quite apart
from the increased risk of fatal accidents from falls.

“Tn tho face of such grave objections,” M. Watteyne explained,
“We have not yet felt justified in recommending compulsory [univer-
sal] watering in Belgium.

in some cases, has been

thus materially to raise the cost of produc

Coal is extracted mainly hy pick in the Belgian gassy collie Explosives (of permitted charac
fer) are used only in rock work. In brushing ba ssageways watering is generally done in tho
vicinity of the shot, before firing it—G. S. TR.



TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 107

mine at which this takes place when no artificial heating is done
necessarily varies with the temperature of the incoming air. The
sprays must therefore be arranged at intervals and turned on or
off according to the temperature. The important point is to keep
the air saturated as it rises in temperature. By either method of
humidifying steam or water sprays, with careful attention there
is no serious difficulty in keeping the dust moist and in a relatively
safe condition.

Effect of humid air on health—In England, where the mine tem-
peratures are 15° to 20° F. higher than in the mines of this country,
owing to the greater depth, fear is expressed frequently by the mining
men that a humid condition of the air is unhealthy and enervating.
The spreading of the intestinal disease called ankylostomiasis,
which at one time afflicted large numbers of the German miners, was
by some ascribed to the warm humid air of the German mines. Be
that as it may, sanitary precautions have now largely stamped out
the disease. Hard physical labor may be done in a saturated atmos-
sphere at 60° to 65° F. with much less discomfort than at 75° to 85°,
aside from that due to the greater heat, because the warmer air carries
twice the weight of water per cubic foot. Hence conditions in this
respect are very different in England and Germany from those in
this country. The writer has observed no discomfort in a saturated
or nearly saturated atmosphere at 65° F. The air of most mines in
summer is in this condition. Only when the air is supersaturated
or foggy does it become unpleasant.

STONE DUST.

The use of stone dust is the most recent suggestion for cither pre-
venting or limiting explosions of coal dust. As the method is only
in the experimental state, it is too early to express any decided
opinion. The results at Altofts appear very favorable. Not all
the mines in this country provide a suitable stone for grinding, but
burned dirt piles or clay or sand are nearly always available, and to
a limited extent thoroughly burned ashes from the boiler plant.

The method is not so adaptable to room and pillar workings as
to the long-wall system, but it may prove a valuable alternative
remedy for coal dust where the humidifying methods are considered
inapplicable on account of danger to the roof, or in those mines
in the arid parts of America where water for humidifying is not
available.

If in addition to wetting coal dust throughout a mine by one of
the foregoing methods “ permissible” explosives are used for shooting
coal at the face, or for brushing or grading the roadways, the chances
of starting a wide-sweeping mine explosion are reduced to a minimum.
As a means of prevention of dust explosions, the writer would place
the employment of permissibles at the head.



THuRaoAy
2eastoae +6 sto] 2esar

WEDNESDAY
aeoaioiae 1210

FuEsbAY
2sesiowrss 310

WoNDAY
meio

2

100

queo seg

yeyuesyey soodeg

hart of temperature and relative humidity with exhaust steam on and heater on.

a
#
g
&

THE EXPLOSIBILITY OF COAL DUST.

HEAT RADIATED FROM SURFACE
OF ENTRIES.

To investigate the effect of
radiation on the temperature of
intake air, we selected a mine
(Monongah No. 6) which had
two parallel intake headings
without a split for over 2,000
feet. Along one of these en-
tries at intervals of 200 feet
thermometers were hung, and
during a night when outside
temperature conditions were fa-
vorable observations of time
and temperature were fre-
quently taken at cach of these
thermometers. The average
velocity was determined by
vaporizing carbon bisulphide
at a certain time at the in-
take, and having another ob-
server record the time the scent
reached theend of the heading.
The area of exposed surface
and the volume of each 200-
foot section of the double entry
were calculated. Figure 28
shows graphically four sets of
the observations. The radia-
tion from the side walls 1s
greatest where the difference
in temperature is most. The
rate of increase of temperature
is dependent on so many quan-
tities and conditions that it
could hardly be attempted to
throw them all into one equa-
tion. The area exposed, the
velocity and the volume of air,
and the original temperature
are the principal factors. The
temperature of the side walls
is not uniform, however, and
is considerably, though tempo-
rarily, affected by changes in


128 THE EXPLOSIBILITY OF COAL DUST.

By the use of Lycopodium powder instead of coal dust, Thorpe
states, one can observe with this apparatus the phenomena of a dust
explosion. For example, it is possible to show how the charred dust.
is found lodged in greatest proportion behind obstacles and not on
the face presented to the advancing air wave, as frequently observed
after mine explosions. By putting small pegs in the floor of the
experimental gallery it can be shown that the lycopodium powder
is swept away clean from in front of the pegs and heaped up behind
them.

Thorpe says it is well known that dust explosions increase in violence
with the distance from the source of the explosion, At the point
of origin the disturbance is small, while a few hundred yards away
the violence of the explosion is remarkably greater. ‘This fact also is
useful in determining the point of origin of the explosion,

REDUCTION OF PRESSURE FOLLOWING EXPLOSIVE WAVE,

It has been said by some that mine explosions are frequently so
violent that the diminution in pressure at places is great enough to
«raw out methane inclosed in the coal. This statement has obtained
many believers. The only experimental evidence in regard to it was
obtained by Greenwell.*| The apparatus used for his experiment
was a box closed at one end and open at the other. The box is 3 feet
long, and at right angles to this and opening into it is another box
smaller than the first and fitted with a valve on which the outside
atmosphere acts. When a charge of dust was fired in this apparatus
the violent outrush of air drew out some of the air in the small box
connected to the side of the larger one, and the valve was driven in
because of the diminished pressure produced in the small box by the
withdrawal of a portion of the air which previously filled it at atmos-
pheric pressure. This does not show a diminution of pressure in the
main gallery, according to the author, as the position of the side box
would cause the withdrawal of part of the air it contained by the prin-
ciple on which an injector operates. By a special manometer, which
he devised to show that an area of low pressure exists around the
flame of a Bunsen burner, Thorpe was able to demonstrate that no
diminished pressure exists along the side of the gallery during an ex-
plosion, but that on the contrary there was always considerable
pressure against the sides and top of the box. Ilence the statement
that gas is brought into a mine from the face of the coal because of
diminished pressure produced in certain areas during an explosion
does not receive confirmation by this experimental work.

© Trans, Manchester Geol. Soe., vol. 10, 1870, pp. 20-27.


161

INVESTIGATIONS AT EUROPEAN STATIONS.

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6 THE EXPLOSIBILITY OF COAL DUST.

In the sixth experiment (G—-483) the relative humidity of the air
was still higher, 95 per cent, and the duration of the test the same,
forty-eight hours. More moisture was precipitated than in the
previous experiments, the average sample of dust on the shelves
showing 26 per cent. In this experiment there was practically no
propagation, only a slight ignition.

In the last experiment of this group (G-580) the experiment was
made of not raising the temperature of the intake air. This averaged
only 44° F. The relative humidity was maintained at 90 per cent,
and the duration of the test was seventy hours, but owing to the
low temperature practically no moisture was deposited on the coal
dust and complete propagation ensued, as would be expected.

Another group of experiments was made under the direction of
the writer during September, 1909. In these it was decided to mix
a definite quantity of moisture with the coal dust and to humidify
the air as far as possible with the limited volume of the sprays.
Owing to insufficient number of sprays, the humidity could not be
brought up to the point of depositing moisture upon the coal dust;
therefore the propagation or nonpropagation of the explosion epended
on the quantity of water mixed with the coal dust. The other
conditions were the same as in the previous series of tests
that the igniting charge was 2} pounds of black powder instead of
1} pounds. The ing v carefully done and oecupied con-
siderable time, as it is difficult to mix water directly with dust.
After a stirring and kneading by hand, the wet dust was forced
through screens to insure an even mixture. When the wet dust
had been placed upon the shelves of the gallery, a sample was gathered
from the dust at regular intervals through the gallery, and analyzed.
The results of these experiments are given in the following tables:

Explosion-gallery tests to determine effect of humidity upon explosibility of coal dusts.

. . Average | Flame showed (in-
rstgomnm | See | Flan sbaned rest
Gallery | Date of y alreureent., percent of| —lengthyat-- |
ars) Date Mergent _
Noe | cise) | ‘ineoal. |

ly
minute. | Nos — |
-l

Sept. 21 . 7S ‘Yes.

See af ge) YE
win te | ge) | ¥s
2 ses) Ns
Sept. 24 | 48 Tl No.
os Bi) #8 a
Be xe

,

4 In all tests. 29 pounds of Job mesh or sf was plued on the horse, and 1 pound per linear foot
of gallery on the shelves. ‘The explosive used was 2$ pounds (1,144 grams) of PFE black powder in first
thee tasts anid tie same amount of FF black powder in the otlver four tests.

test was made ty deteraine the length of flame when only the horse and the first 20 feet of shelves
were loaded with dust.

e Delayed flame showed also in windows 4 and $.

4 Delayed flame showed also in window 5.


104 THE EXPLOSIBILITY OF COAL DUST.
CLEANING UP DUST—WASHING DOWN WALLS.

Cleaning up coal dust and sending it out of the mine is a plan used
more or less under all systems, but applied only to large masses of
dust. The plan can not reduce the quantity below the danger point,

Thorough washing down of roof and walls with hose is required by
the mining laws in Germany, and in this country in Utah. If thor-
oughly and frequently done, it is undoubtedly most effective. The
difficulty is that usually it is not done systematically and thoroughly.
It is a system that can not be effectively applied to shaly or weak
roofs without resulting in many falls and great cost of timbering.

PERMANENT SPRINKLERS—ZONAL LININGS.

Using permanently located sprinklers, attached to pipe lines and
running continuously, but with a flow that can be varied according
to need, is very effective in saturating the mine air within a moderate
distance of each sprinkler, and through this means gradually wetting
the dust. One of the great merits of the system is that the sprinklers
can be distributed where most needed; that is, where there is a tend-
ency to produce the most dust or where the humidity of the air cur-
rents is lower than it should be. A disadvantage in some mines is
that the moisture causes falls of roof. Some of the evidence of this
fact is derived from trials of intermittent rather than continuous
wetting. Nevertheless, where there is roof material that will come
down, or fire-clay floor that will swell immediately on contact with
water, in order to use sprinklers it may be necessary to introduce
brick or arched linings, sometimes with concrete floor and sump, and.
to place individual sprinklers in the lined sections. The linings would.
serve two purposes—to catch any condensed water from the sprays
and to provide a damp and dust-free zone, limiting a possible dust
explosion from either side.

The use of more complete zonal linings is well worthy of considera-
tion for long-lived mines or long-lived entries (particularly the main
entries), not alune as a dust remedy, but also for fire protection.

USE OF EXHAUST STEAM SPRAYS.

Sprays —Humidifying the intake air current with exhaust steam
sprays is much the easiest and cheapest method of introducing mois-
ture into a mine where the ventilating fan is run by a steam engine.

Supplementing fan steam —The quantity of steam that it is neces-
sary to use in the fan engine for ordinary air-ventilating pressures is
sufficient to humidify the air in moderately cold weather, but in
extreme cold weather is insuflicient. Therefore it must be supple-
mented by live steam or, as suggested by Mr. Frank Laas, in order
to insure that it is used, by passing more steam through the engine.


72 THE EXPLOSIBILITY OF COAL DUST.

roadways, and particularly to water the partings or sidings, which
are usually the most dusty points. It therefore requires special
planning and efficient administration to obtain satisfactory results.

CALCIUM CHLORIDE AND OTHER DELIQUESCENT SALTS.

The rapid drying out of dust which had been sprinkled and the
damage wrought to some mine roofs and ribs by sprinkling inter-
mittently, led some of the early investigators to experiment with
hygroscopic salts.

In 1879, Professor Stokes suggested the use of calcium chloride.
Professor Abel, giving evidence before the accidents in mines com-
mission in 1881, said:

It might possibly be desirable to try for watering purposes a solution of caleium
chloride * * * which has been found very useful in keeping ground moist in a
current of air.

The commission, in its final report in 1886 (p. 49) stated:

The generally elevated temperature of mines combines with the desiccating effect
of the more or less rapidly circulating air currents to counteract the amount of pro-
tection obtainable even by frequent liberal watering. Hence attempts have been
made within the last six or seven years to promote the retention of water by coal dust,
by the application to it of hygroscopic or normally deliquescent bodies. de salt
was tried in the first instance, and in 1879 Professor Stokes suggested the watering of
the dust with a solution of calcium chloride, a highly hygroscopic salt which had been
successfully applied in connection with street watering * * * but its trial in
some dry deep mines in South Wales and also in the Jablin pits in France was not
attended with success; the highly deliquescent salt actually crystallized out, conse-
quent upon the rapid evaporation of ihe water in the warm air currents, Some
amount of success appears however to have attended the application, in mines in
North Staffordshire, of crude or refuse salt; this contains a very notable proportion
of the magnesium chloride, which is, if anything, more hygroscopic in its character
than the calcium salt. In an interesting discussion which followed Mr. Robert
Stevenson's communication of his favorable experience in this direction to the North
of England Institute of Mining Engineers, the view received some support that the
deliquescent salts would be most operative if used in admixture with sodium chloride,
as is the case in crude or rock salt. The proportion of crude salt which Mr, Stevenson
had found effective in maintaining the dust sufficiently moist to prevent ils flying
was 9 tons per 500 yards of 6-foot roadway, applied once weekly for the first month
and once a month afterwards.

The method was not mentioned in the report of 1894 of the royal
commission on accidents from coal dust in mines. It apparently
attracted very little attention until the last few years, when the dis-
cussion of the use of salts was revived.

Mr. Henry Hall, British inspector of mines, in a recent article «
says:

On February 22, 1908, a length of 285 feet of tunnel at St. Helens, England, was
treated with a 40 to 45 per cent solution of calcium chloride. The floor of the tunne!

9 Cual and Coke Operator. Pittsburg, Pa., Muy 27, 1909, p. 375.


32 THE EXPLOSIBILITY OF COAL DUST.

deaths; on January 26, at the Penco mine, W. Va., 12 deaths; on
January 29, at the Stuart mine, near Fayetteville, W. Va., 90 deaths;
on February 4, at the Thomas mine, Thomas, W. Va., 25 deaths; on
December 1, at the Naomi mine, Pa., 35 deaths; on December 6, at
Monongah mines Nos. 6 and 8, W. Va., occurred the greatest disaster
in the history of coal mining in the United States, 358 lives having been
lost; on December 16, at the Yolande mine, Ala., 56 men were killed,
and on December 19, at the Darr mine, Pa., 230 men were killed. In
this black month of December 648 men were sacrificed chiefly from
the effects of coal dust, which, if not the initial cause, in all cases was
the agent carrying death. Including the powder explosions and so-
called ‘‘windy shots,” there were 1,148 men killed by mine explo-
sions in the United States during 1907.¢

INACCURATE REPORTS OF ACCIDENTS.

Most of the so-called ‘‘powder explosions” and ‘‘windy shots”
are in reality dust explosions. It is true that the origin of these is
generally from blown-out or overcharged black-powder shots, but it
is without question coal dust that carries the flame, and death in its
trail. In certain States it is considered that legal responsibility
attaches, if the fatality is pronounced due to coal dust; and this fact,
together with the knowledge in many such instances that improper
use of powder was the initial cause has led to the use of inexact and
ambiguous terms in reports to the several state statistical bureaus.

FATALITIES IN 1908.

In 1908 the fatalities due to mine explosions of various kinds num-
bered 469, according to state statistics reported to Mr. E. W. Parker,
of the United States Geological Survey. This shows a marked
improvement over the previous year.

INQUIRY BY UNITED STATES GEOLOGICAL SURVEY.

On June 10, 1907, the Secretary of the Interior transferred the
supervision of the work of the coal-mine inspectors in New Mexico
and Indian Territory (now included in the State of Oklahoma) to
the United States Geological Survey. The Secretary suggested to
the officers of the Survey that the general mining conditions in the
Territories be investigated, with a view to lessening the number of
mine accidents. Under the direction of J. A. Holmes, expert in
charge of the technologie branch, an inquiry was begun into the
nature and extent of coal-mine explosions and the methods employed
to prevent them. In December, 1907, a brief summary of the results
of this inquiry was published as Bulletin 333.

2 Mineral Resources U. 8. for 1907, U. 8. Geol. Survey, 1908, pt. 2, p. 58.
‘eMineral Resources U. 8. for 1908, U. 8. Geol. Survey, 1909, pt. 2, p. 56.


90 THE EXPLOSIBILITY OF COAL DUST.

In a report issued in November, 1910, Taffanel states:

The methods of stopping coal-dust explosions that have been tried can be grouped
in two classes.

By the methods of the first group, which are watering and atone-dust treatment in
dispersed form, we find that it is more difficult to stop an explosion than to prevent
it from starting, and a large quantity of water and a strong proportion of shale dust are
necessary to obtain a stoppage.

‘The methods of the second group, which are schistification and watering in concen-
trated form, have been enccessful in causing the immediate extinguishment of the
explosion, cutting off the flame no matter what the nature of the coal dust “layer” or
loading may be.

In the same report Taffanel advises that caution should be taken to
employ safety explosives, with good tamping, and to water the workings
within a radius of 10 meters (33 feet) before firing shots. He also says
that wetting the dust with a weight of water equal to the weight of the
dust, or spreading a quantity of inert dust in the proportion of 40 to
50 per cent, will render the risk of an explosion almost nil.

In reference to widespread watering, Taffanel suggests the inconven-
ience of its having to be frequently renewed. He says: ‘‘The surest
way of watering is to wash the walls and maintain the dust in a muddy
condition.” He considers the use of rock dust more practical.

In reference to the percentage of inert matter in the dust of a mine
passage, Taffanel says: ‘‘It is not at all certain that the ash content
of the coal itself has as marked an effect as the same proportion of
inert particles,” and advises that ‘‘an excess of inert dust should be
used to insure successful treatment.”

“Concentrated schistification,”’ Taffanel considers, is the most efli-
cient method of stopping explosions, but he adds: ‘‘It is only by pro-
longed and large scale tests that we shall be able to judge whether
arresting barriers are more efficient than dispersed (general) watering
or schistification.”’

For practical application of arresting barriers, he recommends
‘placing the stone dust or inert matter on transverse shelves in
amounts of at least 4 hectoliters per square meter (1.31, cubic feet per
square foot) of cross section of gallery.”

The various questions that form the object of the investigations are
being pursued without interruption at the experimental station at
Liévin.

EXPERIMENTS AT ALTOFTS, ENGLAND.

The movement leading to the establishment, in the early part of
1908, of the experimental gallery at Altofts, England, by the Mining
Association of Great Britain, was initiated primarily to study the

@Taffanel, J, Practical Conclusions, November, 1910.


THE COAL-DUST QUESTION IN EUROPE. 13

dust and air did not form an inflammable mixture a small addition
of fire damp, which would not be inflammable alone, would become
inflammable when coal dust is added.”

In 1878 Prof. A. Freire-Marreco gave an account? of coal-dust
experiments made in conjunction with Mr. W. Cochrane and Mr.
Morison. They employed a box 8 feet long with a longitudinal par-
tition, with a circulating current of air actuated by a fan. They
arrived at the same general conclusions as Mr. Galloway.

Soon after making the experiments mentioned, Mr. Galloway
investigated an explosion that occurred in the Llan colliery, South
Wales, December, 1875, and reported that ‘‘coal dust had undoubt-
edly played the most important part in the explosion.” Subse-
quently Mr. Galloway made further experiments and investigated
the explosions at Pen-y-graig, Risca, and Seaham in 1880, and as a
result decided ‘‘that fire damp is altogether unnecessary for the
propagation of flame with explosive effect by a mixture of dry coal
dust and air.’’?

Mr. Henry Hall, English mines inspector, in 1876 made experiments
at St. Helens in an adit or drift which ran in from the outcrop of a
coal seam and which was 135 feet long. Coal dust was laid on the
floor and shots were fired at the face of the adit. Mr. Hall stated in a
paper read before the North of England Institute of Mining and
Mechanical Engineers that ‘‘flame traveled the length of the adit.”
The blast was very fierce ‘‘and would certainly have proved fatal to
anyone struck by it in its course.”

This was the first large-scale test of coal dust undertaken, but it
appears to have been received with skepticism at the time. The
prevailing impression was that some fire damp must have been
present.

Up to 1880 the theory of. the explosiveness of coal dust had made
little progress. The British accidents in mines commission began ita
sittings in 1879, but did not make its final report until 1886. In a
preliminary report issued in 1881 the evidence of practically all
the expert mining witnesses, except that of Mr. Hall and Mr. Gallo-
way, was to the effect that it was improbable that coal dust would do
more than increase the range of a fire-damp explosion. Even Mr.
Galloway testified (March 18, 1880) that it was necessary to have a
slight amount of gas present to explode coal dust.

On September 8, 1880, a terrible explosion occurred at the Seaham
mine, County of Durham, England, which attracted gencral atten-
tion to the subject of coal dust. Prof. Frederick Abel was commis-
sioned to make some experiments with coal dust. His experimental

Trans. North of England Inst. Min. and Mech. Eng., vol. 28, p. 85.
Second Rept. Roy. Comm., 1894, p. 5.


REMEDIES FOR COAL DUST. 73

was very dusty, the dust (chiefly stone dust) rising higher than the men’s knees as
they walked along. he solution was put on with a whitewashing machine, using
about 8 gallons of solution to 30 linear feet of road (road 9 feet wide). The surface of
the dust was thus dampened, but under the crust there was very little effect, and dust
raised by the traffic inby continued to travel, carried by the wind, over the treated
portion, Considering that the dust was not removed before the application, but lay
some 8 inches thick, the result was fairly satisfactory, and for three months the road
could be traveled with comfort. * * * On April 14, 1908, 225 feet in the main
return tunnel was treated with 90 gallons of 48 to 50 per cent solution of calcium
chloride, the dust having been previously cleaned off. This application kept the
road clear of dry dust for three months, and at the present time (August 22, 1908) the
effect is still visible. * * * The solution when applied to side or roof had the same
damaging effect as water. On May 28, 1908, 330 pounds of calcium chloride, previ-
ously ground to a fine powder, was sprinkled on the floor of the back brow for a distance
of 249 feet, no dust having been removed. It was reported as being wet and no dust
rising on the following day. The writer saw this road on July 6 and the effect was
still visible. Judging from this experiment, one application for every three months
would be ample. ‘The depth, from the surface, of this underground road is but 500
feet. The powdered calcium chloride was thrown on dry by hand, 350 pounds being
put on 2,241 square feet. On July 14, 282 square 4 feet was treated with 448 pounds
of dry powdered calcium chloride. The dust was cleaned away from 60 feet of this
road; the remaining 222 feet not being cleaned. This road was reported to be wet the
next day and the writer sawit on July 16. * * * The writer saw a team brought
out by the pony and no dust was raised. Previous to the application, dust traveled
some 60 feet ahead of the pony. The writer saw this part again on August 6 and
found it to bestill quite satisfactory and apparently likely to continue so for some time
longer. * * * The writer believes the cost to be about 50 shillings ($12.50) a ton
(dry powdered calcium chloride), but there would be a great saving in labor in its
application to the roads as compared with either plain water or any solution, and no
capital outlay for pipes, barrels, hose, sprinklers, etc., is needed. Probably the cost
per 100 yards by 9 feet wide would be something like 13 shillings ($3.25), but it must
be remembered that plain water would have to be applied almost daily, whereas the
calcium chloride would apparently be effective for three months.

Mr. Hall then comments on the superior hygroscopic property of
calcium chloride as compared with common salt.? In conclusion he
remarks that the tests would require to be carried much further than
he had carried them. The conditions vary much in different min
The impression left on his mind was that dust accumulated in the
main roadways at a much smaller rate than has been generally
observed. Te agreed with the observations of Mr. Rhodes, as to
the effect of occasional spraying with water: That 50 or 60 yards in
advance of the sprays the conditions were generally just as they were
before the spraying was done.

Mr. Hall gives a table of analyses of dust from the mine where the
tests were made, but he does not give the moisture content. The
ash content of the samples was high, ranging from 17 to 67 per cent.
It is evident that the coal dust was much diluted with rock or shale
dust.

@ Author probably intended tbis to be linear feet of roadway.
2 Common salt is nol deligueseent when pure, and must he considered an adufterant when mixed with
caleium chloride for absorbing moisture.



REMEDIES FOR COAL DUST. 79

produced. The spray heads are of the kind employed in cotton mills,
and are too small and fragile for mine use. In mines where com-
pressed air is available underground the system has much merit.

Plain water sprays have been much used in the coal mines of Wales.
In certain collieries they are used continuously day and night, and the
effect is excellent. In addition to the regular station sprays, special
sprays have been used at the ends of partings or sidings. When a trip
of cars leaves the siding, the spray is turned on and drenches the top
of the car. Sprays of this kind should throw a larger volume of water
than the station sprays. They serve a most useful purpose in wash-
ing fine dust that may have settled on top of the coal down into the
body of the car, so that the sweeping of the ventilating current over
the tops of the cars does not carry away fine coal.

In this country water sprays have been used only to a moderate
extent until quite recently. In the Rock Island Coal Company mines
in Oklahoma water sprays have been extensively introduced by Mr.
Carl Scholz, who has written a number of papers on the subject,
among others one on the effect of humidity on mine explosions.*
He has contributed a chapter in this bulletin on the use of steam and
water sprays in Oklahoma mines (pp. 179-183).

In the Alabama mines of the Tennessee Coal, Iron, and Railroad
Company sprays have recently been extensively introduced.

In the Shoenberger mine (see pp. 80-82) of the Pittsburgh-West-
moreland Coal Company, in Washington County, Pa., water sprays
supplement exhaust steam. The principal intake enters the mine by
the drift road or main haulageway. At night between 1 a. m. and
6 a.m. exhaust steam from three generator engines is allowed to enter
with the intake air. It thoroughly saturates the air, and in the early
morning the interior of the mine is said to be dripping with moisture.
As the cloud of steam is very dense it is impossible to use it during
the working hours. During this period a system of water sprays is
used. The sprays are located about 1,500 feet from the drift mouth.
There are 24 spray heads at intervals along a pipe about 450 fect in
length. These sprays throw a strong, fine spray by direct water
pressure. As they would drench men passing by, whenever an elec-
tric locomotive with a trip of cars is passing the sprays are turned
down by manipulation of a valve in charge of a trapper boy.

Though an observation made by the writer on a cold day indicated
that the air was saturated by the sprays, yet as the air had not yet
attained the degree of warmth of the mine it is a question whether
these sprays would have been sufficient but for the exhaust steam
supplied at night at the main intake and continuously supplied in
an independent split of air intaking at a back opening of the mine.

2 Fiflect of humidity on mine explosions: ‘Trans. Am. Inst, Miu. Eng., October, 1908,


THE EXPLOSIBILITY OF COAL DUST.

By Georer S. Rice.

INTRODUCTORY STATEMENT.

THE COAL-DUST PROBLEM.

This bulletin traces the growth in the belief in the explosibility
of coal dust, summarizes the experiments and mine investigations
that have established this belief, and gives the present status of pre-
ventive measures. It has been prepared in accordance with the pro-
visions of the acts of Congress authorizing investigations relating to
the causes of mine explosions, and contains references to and descrip-
tions of experiments made at the Federal testing station at Pittsburg,
Pa. This station was inaugurated under the United States Geo-
logical Survey, and was transferred to the Bureau of Mines on the
establishment of the latter on July 1, 1910.

Only within comparatively few years has the dry dust of bitumi-
nous and lignitic coals been generally recognized as an explosive
agent more insidious, threatening, and deadly to the miner than fire
damp. Fire damp carries its own flag of warning—the ‘‘cap” in the
safety lamp—but coal dust, though visible, does not attract attention
until present in large quantities. Fire damp is of local occurrence,
and except in notable and very exceptional cases is controllable by
careful manipulation of ventilating currents. If by mischance a body
of fire damp is ignited in a mine, the force of the explosion may be
terrific, but the effect is local unless dry coal dust is present, or unless
(as it very rarely happens) an explosible mixture of methane gas and
air extends through large areas of the mine. Ina dry mine dust accu-
mulates everywhere, and the blast from the ignition and combustion
of bituminous dust may traverse miles of rooms and entries and wreck
structures at the entrance to the mine. The comparative potential
destructiveness of gas and of bituminous dust is strikingly shown by
the history of the Pennsylvania anthracite mines. These mines not
infrequently have large inflows of gas, and the resulting mixtures of
gas and air have sometimes been ignited, yet no such wide-sweeping
explosions have taken place, despite the presence of dry anthracite
dust, as have happened in excellently ventilated bituminous mines.

9


TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 108
MIXTURE WITH INERT SUBSTANCES.

When the dust is abundant, the effect of high ash content, unless that
content is excessive, is apparently not noticeable. The upper limit
has not yet been closely defined by experiment. The effect of inti-
mately mixing coal dust with shale dust or stone dust has also not
been fully determined experimentally. The few tests in this direction
conducted at the Pittsburg station have been with ‘road dusts’’ or
other coarse mixtures, and the tests with these indicate that the amount
of the inert substance has to be very large, possibly equal to the amount
of pure coal dust. The tests with finely pulverized stone dust in the
Altofts experiments have been chiefly directed to supplanting or
covering up coal dust.

ADVANTAGES AND DISADVANTAGES OF PROPOSED REMEDIES.

In reviewing the methods for preventing coal dust explosions or
limiting them to certain zones the writer presents merely his own
views and conclusions, subject to change as the investigations proceed.
The remedial measures will be taken up in order as already given
(pp. 70-98). The writer believes that all have more or less merit, ex-
cept the water boxes or sprinkling cars of primitive type.

FORCE SPRINKLERS IN CARS,

Water cars with force sprinklers, in which the pressure is produced
by pump or air pressure, if used frequently and thoroughly, are good.
The great danger is that they will not be so used throughout all the
mine, owing to their interference with the haulage of coal, and fre-
quently owing to the lack of tracks in the air course or manways.
When used intermittently the water-car system is useless because
the dust is not wetted; as the drops of water do not mix with it, they
are exposed to the air currents and quickly dry up.

CHEMICALS.

The use of calcium chloride and similar salts has not yet been
sufficiently tested to permit a conclusion as to its effectiveness in
preventing explosions. If it renders the dust merely dampish—that
is, not sufficiently moist to prevent explosions—it may improve the
sanitary condition and lessen the quantity of float dust, It may also
prove to be effective in supplementing intermittent sprinkling,
enabling the dust to absorb drops of water that would otherwise be
taken up by the air current.


REMEDIES FOR COAL DUST. vid

there is a scarcity of water for wetting the dust and where an unusu-
ally large amount is needed on account of the dryness of the air.

Crude calcium chloride can be procured in granulated form. The
price in the leading cities in 1910 varied from $14 to $18 per ton, put.
up in wood barrels. If preferred it can be procured in a 40 per cent
solution in iron drums.

SPRINKLING AND WASHING DOWN WITH HOSE AND NOZZLE.

The method of using pipe lines through a mine with connections at
intervals for attachment of hose was introduced in England and used
to a slight extent after the report, in 1886, of the accidents in mines
commission. In the same year W. N. and J. B, Atkinson published
their book “Explosions in coal mines.’ In their suggestions for reme-
dies they anticipated some of the later developments. They state
that water tubs of the ordinary kind are ineffectual and that the use
of water pipes, with cocks at short intervals, and hose is a better sys-
tem; and they advise that where watering causes trouble by affect-
ing the roof or floor, the mine may be divided into sections by arching
entries, whitewashing the arched sections, and sweeping up the bot-
tom dust. They add: ‘Perhaps 100 yards (of lining) would suffice.”

In Germany in consequence of the report of the Prussian fire-damp
commission of 1885 watering, chiefly by hose sprinkling, was intro-
duced into mines. This system has grown to the exclusion of others.
Watering became compulsory in Germany in 1900. The mining
department now insists that the roof and walls of the gangways be not
merely sprinkled but washed by a stream from a hose.*

Jn England the use of the hose and nozzle has not become at all
general. The mining men generally consider that it is too severe on
the roof and walls; that heavy falls of roof and heaving of the floor
would be caused.

In the United States the system of watering by hose and nozzle has
been employed in the coal mines of Utah since the Scofield disaster of
May 1, 1900, and it is now required the Utah mining law. The
conditions for the use of this method in the Utah field are very favor-
able, as the floor and roof are generally sandstone and are therefore
not affected by the direct application of water. The method has been
used only to a very limited extent in a few mines in Pennsylvania
and other eastern States.

Wherever the method can be employed it is undoubtedly an effi-
cacious one, particularly if the water pressure is good, but it requires

@ About the time sprinkling was begun extensively in Germany the worm disease called angylostominsis
broke out widely among the mine workers of Westphalla, Tt had been known much carltor, butt the fact
that the severe outbreak occurred simultaneously with more extensive watering led to the belief that
that practice was the sole cause, Undoubtedly humid warm air fosters the disease, but by the adoption
of rigid sanitary precautions the epidemic was overcome and although the watering has been continied
the disease has been almost completely stamped out.



172 THE EXPLOSIBILITY OF COAL DUST.

1, 1908, to June 1, 1909, the minimum average temperature for
one day was 21° and the minimum average content of water vapor
per 100,000 cubic fect of air was equivalent to 1.3 gallons of water.
The lowest weekly average temperature was 34° with a concurrent
average humidity of 3 gallons, and the lowest monthly average
temperature was 39° with 3 gallons of water. As the deficiency
and excess of water in a mine are more or less cumulative, it
would be safe to take the weekly average as a basis for calculating the
quantity of heat and moisture to be supplied by artificial means.

According to the records, the temperature of the return air current
during the coldest weather of the year was 55°, and it carried 7.2
gallons of water per 100,000 cubic feet. If, then, sufficient heat were
constantly supplied to raise the intake temperature from 34° to 55°,
and sufficient water to raise the quantity from 3 to 7.2 gallons per
100,000 cubic feet (the rate per minute), the conditions would be
such as to provide an excess of water in the mine and keep the mine
airsaturated. Holding to a unit of 100,000 cubic feet per minute, we
find that it will require 39,900 B. t. u. per minute and 4.2 gallons
of water.

AMOUNT OF HEAT AVAILABLE,

Monongah No. 8 mine fan during these observations was making
about 135,000 cubic feet per minute with 14-inch water gage. By
the common formula this required about 30 horsepower; by indicating
the engine, however, it was found that 55 horsepower was actually
supplied. This difference is due to the great loss in efficiency in
running a large engine below capacity. If 55 horsepower is supplied,
with a steam pressure of 100 pounds, and consumes 35 pounds of
water per minute per horsepower, about 1,500 B. t. u. is used by the
engine per minute for power and about 31,000 B. t. u. is available for
heating the air if the exhaust steam is turned into the mine. This
amount of heat would be sufficient to increase the temperature 12°,
or from 34° to 46°. It would also furnish 3.85 gallons of water per
minute and would raise the water content of the air 2.8 gallons, or
from 3 to 5.8 gallons per 100,000 cubic feet of air.

EEF!

OF STEAM ON MINE AIR.

These figures are more or less theoretical, and though both the heat
and the water of the exhaust steam enter the mine it does not neces-
sarily follow that all of both are available for the saturation of the
mine air.


TENTATIVE CONCLUSIONS ON THE DUST PROBLEM. 99
TENTATIVE CONCLUSIONS ON THE DUST PROBLEM.«

FACTORS AFFECTING EXPLOSIBILITY.

VOLATILE COMBUSTIBLE MATTER.

That coal dust will explode under some circumstances, both in
the presence of fire damp and without it, is now generally accepted
by mining men. The writer fully agrees with this and takes the
following views of the explosibility of dust and the conditions neces-
sary for explosion.

Experiments at Pittsburg indicate that under ordinary conditions
the dust must be from coal having at least about 10 per cent of vola-
tile combustible matter, though in certain foreign experiments
explosions were obtained with charcoal dust.

Dusts with higher percentages of volatile combustible matter are
more sensitive, ash, moisture contents, and size being constant.
This view is based partly on the preliminary experiments at Pitts-
burg and on the results of experiments by Taffanel and other
foreign investigators.

STRUCTURE AND SIZE,

Physical structure and size of the dust particles are factors in the
relative sensitiveness. In coals approaching the border line of non-
explosibility, structure and particularly size are the more important,
and affect ignition. That is, the less readily the dust gives up its
gases the larger and more intense must be the igniting flame.

Whether or not concussion or compression of the air at the moment
of attack by the flame is required for the ignition of the less sensitive
dusts and the propagation of the flame is a question yet to be answered,
but it is self-evident that the larger and heavier the particles are the
more difficult it is for the air waves in advance of an explosion to
bring them into suspension where the flame can strike them.

DENSITY.

For continued propagation of flame, the dust particles must be so
close together that the burning gas enveloping one dust particle will
inflame the next particle. In other words, at each successive moment
of inflammation there must be a certain density of dust for each
character and size of dust.

Tt appears to the writer that the combustion of the fixed carbon of
an average-size particle of coal dust will not take place until the vol-

a Tt must be understood that the conclusions here slated are those of the writer and are of a tentative
character, subject to revision as further investigation is carried on at the Pittsburg testing station and
elsewhere,


88 THE EXPLOSIBILITY OF COAL DUST.

The station also has apparatus of high precision for recording the
variation of the pressure at a given point in the gallery. The instru-
ments are derived from Carpentier’s manograph. The movable
parts are reduced to a metallic membrane, which receives pressure de-
veloped within the gallery, and a little mirror which is deflected by
the flexure of the metallic membrane. * * * The mirror throws
a ray of light on a revolving cylinder covered with photographic
paper. * * * The apparatus has a special device by which the
explosion flame passing through the gallery throws a mark on the
margin of the sensitized paper, and thus the paper will show not only
the pressure curve, but also the position of the flame with respect to
the compression waves. The precision of the measurement is
about 0.001 of a second.4

Experiments were first made in the 230-meter gallery with coal
dust alone. Coal dusts containing different percentages of volatile
matter were tried. The effects of density of the dust cloud and size
of the dust particles were also studied. In some tests very high
velocities and pressures were recorded.

Taffanel states that in an experiment with a dust deposit of 225
to 450 grams per cubic meter (0.225 to 0.450 ounce per cubic foot)
the flame traversed the gallery in less than one and one-half seconds.
The velocity in the last 50 meters exceeded 1,000 meters (3,300 feet)
per second. The flame at the orifice was 80 meters long and 20 meters
high. * The air waves caused by the explosion were large. The effect
was noted for a distance of more than 10 kilometers (6.21 miles). In
every test of this kind, although the houses in the neighborhood are
scattered, there are always 10 to 50 window panes broken within a
radius of 2 kilometers (1.44 miles). Sometimes the ceilings come
down,

The pressure becomes higher and higher in proportion as the explosion approaches
the orifice. We have meagured pressures of 16 and even 19 kilograms per square
centimeter (227 to 270 pounds per square inch). Moreover, these pressures are instan-
taneous, as they are established in leas than 0.002 second and last but 0.02 or 0.08
second.

In one test, with dust a little finer than ueual, * * * the last 12 meters of the
gallery gave way; several pieces of shcet steel, the interior lining, and the embank-
ments were projected to distances up to 150 meters. The eteel gallery had an esti-
mated breaking strength of 40 kilograms per square centimeter (70 pounds per square
inch).

* * * We have verified the fact that the presence of a free orifice favors the
increase in violence of the explosion and the change to the stage of the shock or deto-
nation wave. If the orifice of the gallery is partly obstructed, the paradoxical result
is reached that the pressure of the explosion is lowered.

© Les expériences frangaises sur les poussiéres de houille. Iuternationaler Kongress, Diisseldorf, 1910.
Revichte der Abteilung fiir Bergbau, p. 226.
®1dem., pp, 230-231,



164 THE EXPLOSIBILITY OF COAL DUST.

SPECIAL PREVENTIVE MEASURES.

BREAKING COAL BY DIRECT WATER PRESSURE.

One of the recommendations contained in the report of the royal
coal-dust commission of 1894 was as follows:

The substitution for explosive agents of similarly efficient methods of bringing
down coal and stone which are quite {ree from the special dangers attending the use
of those agents.

Attempts have frequently been made, both before and after, to
give effect to this suggestion, but none of the methods proposed has
so far proved successful. Certain experiments made many years ago
at Saarbrucken at the suggestion of Herr Meissner, privy councilor
of mines, at that time in charge of one of the state collieries in that.
district, may be cited as offering an interesting exception. This
gentleman was, however, suddenly transferred to another sphere of
activity, and the trials were discontinued. But recently the method
has been again taken up in a Westphalian coal mine and put to
practical tests with considerable success.

As the process comes under the head of “means for preventing
coal-dust explosions,” it may fittingly be described in this report.
Indeed, as a preventive means, it may be said to start considerably
ahead of all other remedies proposed, inasmuch as it is directed
against the very source of coal dust, the solid coal itself. Briefly, it
may be described as hydrostatic injection of the coal face (in German
“Stosstrankung”),

Into a bore hole, preferably bored at right angles to traceable
divisions or slips in the coal, an iron water pipe is tightly wedged
so as to prevent any back flow. Water is then turned on and allowed
to permeate the coal face under a pressure of about 12 atmos-
pheres. Unless the coal is absolutely impermeable the forced endos-
motie action is so quick that in about fifteen to twenty minutes loud
“working” of the seam is heard, followed shortly afterwards by a
rush of water from some point offering the least resistance. The
operation is then finished and the water is turned off.

As a rule the impregnated area is about twice or three times the
cube of the depth of the bore hole, and where the coal is naturally
interstitial in structure the whole of the affected area may be got by
the pick.

In the Scharnhorst mine, near Dortmund, the writer saw the
method practically employed in a seam of schistose coal 24 meters
thick and dipping at an angle of 80° from the horizontal. A bore
hole was hand drilled in three divisions of different diameters, to
provide the necessary ‘‘grip” for two conical wedges fixed on the



EXHAUST STEAM AS A PREVENTIVE. 167
AMOUNT OF WATER ABSORBED BY COAL DUST.

Though the writers’ experiments along this line have not been com-
pleted, it has been determined that coal dust does, to a certain
extent, absorb moisture, which for gas coal (to be hereinafter con-
sidered) amounts to about 4 per cent.

In nominally dry atmosphere, the dust which was experimented
with contained about 1.5 per cent of water. In the return air way of
a mine in which the air was kept moist to the point of saturation,
dust was collected from the side walls of the entry where it had lodged.
on the small projections of the solid coal. The moisture determina-
tions obtained for this dust were extremely various, the minimum
moisture being 4 per cent, the maximum 42 per cent, and the aver-
age 25 per cent. As the atmospheric conditions surrounding each
particle were practically the same, the results should have been
uniform if the content of water so determined were one of the phys-
ical properties of the dust. As they were not uniform, however, it
was concluded that the minimum more nearly expressed the absorp-
tive power of the coal and that any additional water was merely
mechanically held in contact.

Now, 4 per cent is by far too little to be considered of much conse-
quence, hence additional water uncombined with the coal is neces-
sary for protection against ignition. From such of the writer’s
results as are available, however, it appears that the element of time
enters into the question, and it is apparent that the longer dust. is
exposed (within a limited period) to water or saturated air the larger
will be the quantity of water absorbed.

AMOUNT OF WATER REQUIRED IN MINE.

If the roof, floor, and sides of any entry are covered with a film of
water of sufficient thickness, it will not only prevent the addition of
fuel to an explosion, but will extinguish an explosion once started.
This latter action, as it depends largely on contact, would not be
instantaneous, but would be effective in a comparatively short dis-
tance if the wet conditions were maintained. ‘To demonstrate this,
let us assume that in an entry 10 feet wide and 6 feet high there is
a film of water 0.025 inch thick on floor, roof, and sides. In one
linear foot of such entry there would be 32 square feet covered by
this film, making in all about 115 cubie inches, or 4.25 pounds of
water. Let us suppose an explosive flame passes through this entry,
say, at a temperature of 4,000° F. and at a pressure of 3 atmospheres.
If the specific heat of the gases be taken at 0.3, the weight of a cubie
foot of the gases at normal pressure and temperature would be ap-


58 THE EXPLOSIBILITY OF COAL DUST.

These experiments, though limited in number, were consistent in
results, and indicate that slight dampness is not sufficient to prevent
flame propagation by an explosion; that with a high volatile and pure
coal such as that used, it is necessary to have a total moisture content
approaching 30 per cent to insure that there will be no propagation.
This amount of moisture does not make 100-mesh dust seem exces-
sively wet. It can be balled up in the hand, but water is not squeezed
out by pressure of the hand. If more moisture is added the critical
point is reached, and with about 40 per cent of water the 100-mesh
dust and water mixture becomes a coal mud.

These experiments, though they must be accepted as preliminary,
give » definite figure for the percentage of moisture that makes
coal dust relatively safe under ordinary conditions. Information
on this point has been strangely lacking, and it is very important
that experiments in this direction be continued.

As 2 pure 100-mesh coal dust was used in the experiments, a larger
amount of moisture probably was needed to render it inert than if it
had contained larger particles, or had been less pure, or had been mixed
with shale dust. The tests probably represeuted extreme conditions.

HUMIDITY OF MINE AIR.
NATURAL PRINCIPLES.
SATURATED AIR AT DIFFERENT TEMPERATURES.

The amount of moisture in mine air is of vital consequence in
relation to coal dust, as well as in other respects. Aqueous vapor is
everywhere present in the atmosphere, whether above ground or
in the mine, varying in amount within wide limits.

The term “relative humidity” means the percentage of water
vapor present with reference to complete saturation as 100 per cent.
When there is complete saturation of aqueous vapor for a given
temperature, the “dew point” is reached. Beyond this point of
complete saturation, with constant temperature, additional water
may be held mechanically in minute drops, as in fog. Hygro-
metric or psychrometric tables, prepared by Prof. C. F. Marvin, are
published and issued by the United States Weather Bureau, and are
entitled “Psychrometric tables for obtaining the vapor pressure,
relative humidity, and temperature of the dew point.” These
tables are calculated to small differences in temperature and relative
humidity, so that when the difference in the wet and dry bulb ther-
mometer readings is known the figures for the relative humidity and
the temperature of the dew point can be read directly with little or
no interpolation.

The variation in the amount of water vapor at different tempera-
tures is very striking. For example, at a temperature of 0° F. a



54 THE EXPLOSIBILITY OF COAL DUST.

A third set of experiments was tried with the same weight of coal
stemming, but with 24 pounds of black powder. The flame with the
wet stemming was still more increased, being over 50 feet in total
length, and with the dry stemming the flame was over 60 feet in
length, causing, in fact, a limited explosion.

The length of flame from black powder without stemming does not
appear to increase with size of charge, as far as tested (24 pounds),
but it appears from these tests that the flame from the coal stemming
increases with the chargg of powder used. In fact, it is possible that
a blown-out shot with a very large charge of black powder, such as
is sometimes used in shots in mines of the interior coal province, that
contains 8 pounds or more, and with coal dust for stemming, may
cause a local dust explosion without the presence of any external
dust. This may happen even in a wet entry. The tests with coal
stemming at Pittsburg were made during rainy weather and with
the gallery wet throughout by hose.

When very small charges of black powder are used wetting coal-
dust stemming may make the length of flame slightly less than that
with dry coal stemming, though the flame length would still be greater
than that resulting with clay stemming; but when medium-size charges
of black powder are used the heat is such that the water has little or
no effect.

It is a reasonable conjecture, in view of the results of the experi-
ments described above, that with larger charges of black powder
moistening or wetting the coul-dust stemming would cause no appre-
ciable decrease in the flame.

The conclusion is drawn from these experiments that the use of
coal dust or coal cuttings for stemming, whether wet or dry, is a most.
dangerous practice. With » blown-out shot in which coal dust has
been used for stemming, causing flame extending 50 to 60 feet or
more if there is any dust along the room or entry, the chances of an
extended dust explosion are enormously increased.

EXPERIMENTS WITH COAL DUST IN HUMIDIFIED AIR,

During the winter of 1908-9 experiments were made under the direc-
tion of Clarence Hall in explosion gallery 1 with standard 100-mesh
dust distributed on horse and shelves and a current of humidified air
drawn through the gallery. A Koerting injector used as an exhauster
drew the air from a relief doorway near the “face” of the gallery.
The intake air entering a relief doorway next to the outer end of the
gallery was warmed by steam coils and humidified by compressed air
and watersprays. The latter were of a type much used in cotton mills,
in which the water is mixed with compressed air to finely pulverize
the water spray. The gallery end was closed by a paper and cloth
brattice and the intake air from the heating and humidifying box


22 THE EXPLOSIBILITY OF COAL DUST.

The fan is inclosed with a steel-plate casing, but its evasée chimney is
constructed of light boards to give an indication of the force of the
explosion and of the “after-suck.”’

The drift connecting the casing to the gallery has two openings to
the outside, independent of the gallery. These openings are pro-
vided with doors hung horizontally, which may be closed from the
firing station. The arrangement is such that when the fan is started
it may draw air from outside, until brought up to the proper speed;
then the doors are closed. Closing the doors makes an electric
cireuit which causes a bell to ring in the firing station, thus giving
notice that the ventilating current has been established through the
gallery. Seven seconds later the ‘cloud raiser” is discharged, and
two seconds after that the “igniter” is fired.

A supplementary door hung at the entrance of the fan drift into
the gallery may be closed after an explosion to retain the afterdamp.

The coal dust used in the standardizing experiments is made by
pulverizing nut coal from the Altofts colliery. This pulverizing is
done in an impact machine revolving at high speed, the dust being
lifted to the storage bin by the air current developed by the moving
blades of the machine.

The coal dust has the following composition by proximate analysis:

Moisture . .. .. . 8.21
Volatile matter. 33. 68
Fixed carbon . 57. 60
Ash... a. G51
The ultimate analysis of the ash-free dust
Carbon... -- 80.50
Hydrogen . 5.45
Oxygen. 9.70
Nitrogen 142
Sulphur. . 2.98
The degree of fineness of the dust is found to be:
Per cent.
Remaining on a 100-mesh acreen....... a. 7.25
Through a 100 and remaining on a 150-mesh 6c 7.50
Through a 150 and remaining on a 200-mesh scree! 3.00
‘Through a 200 and remaining on a 240-mesh sere 9.15
Through a 240-mesh and finer. 73,00

The means of igniting the dust is the discharge of a shot of black
blasting powder from a cannon with a bore 3 inches in diameter and
2 feet 9 inches deep. The charge is 1} pounds with 8 inches of dry
clay stemming, properly tamped. The effect is.that of a blown-out
shot from an improperly placed drill hole in a mine.

The bore inclines upward 32 to 35 degrees, and the cannon is fired
against the air current. The dust is nearly always ignited. To
insure ignition for public demonstrations, a small cannon with a
charge of only 4 ounces of powder is employed to raise a cloud of dust,
into which the igniter discharges. These cannon are fired electrically


EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 45

charge of powder, increasing the concussion and heat of the initial
explosion, complete propagation would be produced. It may be
that in a mine still coarser sizes would propagate from very large
shots, in view of the fact that smaller sizes are present to sustain
the flame; but tentatively, until further tests can be made, the writer
has accepted 20-mesh as the dividing line between what may be
termed fine coal and what may be considered dust.

It must not be inferred that larger particles of coal may not be a
factor in a mine explosion once fairly started. On the contrary, the
writer believes that they are, and that in a strong explosion the coal
walls of the passageways where struck by a fierce blast will give up
their quota of volatile gases. The assumption as to the size (20-
mesh) therefore refers only to the initial stage of anexplosion. Here-
tofore such coarse dust has not generally been considered dangerous.

CHARACTER OF COKE PRODUCED.

The coke produced in these tests presented some interesting pecu-
liarities, as indicated in the photographs of coke from two typical
explosions, reproduced in Plates III and IV. The first (PL. ITI) from
test G-2894, is the product of the explosion of ‘‘dust”’ finer than 80
and coarser than 100 mesh. The globular pieces shown in the upper
part of the picture, which are from one-half to three-fourths inch in
diameter, resemble -the coke from float dust, though more irregular
and made up of a mass of smaller cells. The smaller particles in the
middle of the picture (obtained by screening) are largely spherical,
and many consist of a single cell. The finest particles, at the bottom
of the picture, are finer cells, also fragments of larger coke cells.

Plate IV shows coke and coal particles from test G-2987, in which
a partial propagation was obtained from ‘‘dust” finer than 20 and
coarser than 40 mesh. Particles of this ‘‘dust’’ which were not used
in the experiment are shown in the lower part of the picture. The
large crumbly masses of coke in the upper part of the picture con-
sist of individual coked and caked particles loosely stuck together
as they were swept into little piles at the flanges of the gallery.

The piece at the top which has the same thickness as width, three-
fourths inch, was formed in the corner of a flange. The piece on the
squares C-6 and 7 to G-6 and 7 shows the under side of such a mass
with the coal particles caked or fused only enough to stick together.

EFFECT OF CHEMICAL COMPOSITION.
PAST EXPERIMENTS.

The effect of the chemical composition of dusts upon their rela-
tive explosibility or nonexplosibility is a problem that has been
much discussed by mining men and by scientists from the time of
Faraday. Experiments with dust of different chemical composition


EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 49

space in the gallery ($2 grams per cubic meter), as reported in the
table on page 41.

M. Taffanel has recently written a paper on his tests in the larger
gallery at Liévin.t These tests confirm those made previously in a
smaller gallery. He has devoted much attention to the chemistry of
dust explosions. He finds that schist (shale) dust tends to blanket
the effects of the coal-dust explosions, but he states that his ex-
periments in this direction have not gone far enough to permit con-
clusions to be drawn therefrom. His aim, in this first series of
experiments, unlike that of the Altofts station, which will be men-
tioned hereafter (p. 90), had been to find the effect of mixing this schist
dust with the coal. (lor later experiments at Liévin, see pp. 86-0.)

INFORMAL TESTS AT PITTSBURG STATION.

There has not yet been opportunity at the Pittsburg station for
systematically testing in the gallery the relative explosibility of dusts
of different chemical composition; but Clarence Hall, in charge of
explosives testing at the station, has made a great many informal
tests of coal dust from different parts of the United States, and has
kept careful records of them. These records he has kindly put at the
writer’s disposal. Certain tests have been selected as typical, and
these are given in a table below. The materials range from anthracite
with little volatile matter to subbituminous coal with much moisture
and volatile matter. All shots were made with black powder, except
one with dynamite. The weight of the charge is specified in the table.
Clay stemming was used in all these tests, The amount of coal dust
was usually 120 pounds, of which 20 pounds was placed on a horse
and 100 pounds distributed on side shelves running along the full
length of the gallery, 1 pound per linear foot. When the full number
of shelves was not used, the loading was proportionately less. The
horse or center shelf is placed in front of and 9 inches below the
center line of the bore hole, so that the flame of the explosive would
touch but not directly play upon the dust. This arrangement simu-
lates the condition in a mine where a pile of coal with dust on it lies
in front of a blow-out shot.

The charge of coal dust averages 1.2 pounds pér linear foot of
the gallery, equal to 0.61 ounce per cubic foot, or 610 grams per
cubic meter. According to Taffanel, the theoretical weight of coal
dust necessary to produce a maximum explosion is about 0.111 ounce
per cubic foot or 111 grams per cubic meter.» Naturally this weight

Les résultats obtenus jusqu’a co jour dans Ia galerie d’essais de Liévin: Bulletin et comptes rendus
amensuels de la Société de l'industrie minérale, February, 1909.

> This Is figuring that “the total combustion of the carbon and volatile matter, with the exclusive
formation of carbonic acid and water vapor, would exactly absorb all the oxygen of the alr” (loc. cit.).
In reality only a portion of the volatile matter and fixed carbon is burned. Sec analyses of coked dusts
in reports of experiments, also footnote } to second table on p. 41 and footnote on p. 50.

88006°—Bull. 20—11-—~4


76 THE EXPLOSIBILITY OF COAL DUST.

dried. The moisture in the whole sample from the area treated
eight days before (first area) was 10.57 per cent, or about 8.5 per cent
excess over the normal moisture content of the air-dried coal. The
moisture in the sample for the area treated twenty-three days before
(second area) was 7.20 per cent, or about 5 per cent excess over nor-
mal. Of the former sample only 25 per cent passed through a 20-
mesh screen; of the latter, 12 per cent. Experiments with these sam-
ples indicated that the undersize retained after preliminary drying
three times as much water as the oversize. If this proportion also
holds in the preliminary drying, the undersize from the first area
contained 14 per cent of moisture and the undersize from the second
arca contained 21 per cent. The plastic condition of the samples
indicated at least these amounts of moisture. Tt was the moisture in
the finer sizes of dust, as well as the sticky nature of the salt, that
caused the adhesive quality,

It is evident that a determination of the humidity of the air in areas
treated with calcium chloride does not provide a test of the efficacy
of the latter in preventing the formation of loose, dry, dangerous coal
dust. The calcium chloride through its affinity for water draws the
water vapor from the atmosphere. The latter would therefore show
a deficiency (too small to be measurable) rather than an excess of
moisture. Hence the success or failure of the treatment must be judged
by the physical aspect of the dust or by chemical determinations sup-
plemented by tests in an experimental gallery.

The experiments in the Catsburg mine can not be considered con-
elusive, but it is interesting to compare the results obtained by the dry
and the wet treatments; the application of the dry calcium chloride
to the floor dust appeared to be very effective, under severe condi-
tions, inasmuch as rooms were turned off the butt entry and there
was a constant dribbling of fresh coal along the road. The condition
of the floor, however, was such that the new dust as it was crushed
under foot packed down into the general mass.

At first thought it appears singular that the application of the cal-
cium chloride in solution was less effective, The explanation may be
that on account of the dryness of the dust the solution quickly sank
down into the large mass of coal dust, which was deeper than the
thickness of the ties, and the effect on the surface was thus lost,
whereas the dry calcium chloride, being more or less coarse, re-
mained on the surface and absorbed tie moisture from the air,
causing a stickiness that ‘onded to pack the dust together. Tt will,
of course, be necessary to have more data before positive conclasions
can be reached as to the advisability of the use of calciam chloride
under varying mine conditions, Tf as successful as it promises to be
on the floor or gobs of mines it would seem to be a system peculiarly
adapted to the mines in the arid Rocky Mountain district, where



134 THE EXPLOSIBILITY OF COAL DUST.

metallic magnesium. The source of ignition used in each case was a
small gas flame, the amount of dust 1 gram. In every material
except dant and charcoal inflammation took place.

In a second paper the same authors record the results of further
experiments on coal dust with apparatus (fig. 11), somewhat different
from that described above. In order to secure better control of the
conditions of ignition they substituted a coil of platinum wire for the
gas flame and electric spark used in some of their earlier experiments.
They could in this way obtain a considerable range of temperature,
and could measure approximately the temperature of the coil during
any experiment by measuring the current passing through the coil.
Below is given the current that was found necessary to produce
inflammation of each of the dusts named:

Current required to produce ignition in specified dusts.

Ampere.
Brown coal. _ 10.5
Busty seam, bright coal 1.5
Hutton seam, coal. 1L5
Lycopodium... 1.5

Brockwell seam, cannel
Harvey seam, splint

A current of 17 amperes was insufficient to produce an ignition
with anthracite or dant. The samples used in these experiments
were passed through a 100-mesh sieve and were air dried. To show
the effect of drying on the temperature of ignition of those same
coals, experiments were carried out in the same way as those described
above, except that the coals were dried. The results were es follows:

Current required to produce ignition of dried dusts.

Amperes.
Brown coal 9. 8-10.6
Buaty seam, bright coal IL.OILS
Hutton seam, coal_.. 1LQ@11.5
Brockwell seam, cannel 11. 5-12.6
Harvey seam, splint. 13.0+15.0

Further experiments were made on the effect, of moisture by expos-
ing the coal dusts under a bell jar over water. Brown coal dust,
after seventy-two hours’ exposure, and Hutton seam coal dust, after
ninety-six hours’ exposure, required, respectively, 12.2 and 13.5
amperes. In another set of experiments, the freshly ground dust
was mixed with water to a thin paste and allowed to dry for six
days in the air. At the end of that time it was found to contain 3.1
per cent moisture, and to require 13.5 amperes for its ignition. The
coal was mixed with water the second time and left to dry, and on the
fifth day it was found to contain 3.77 per cent moisture, and to require

‘Trans. Inst. Min, Eng., vol. 34, 1908, pp. 91-97.


INVESTIGATIONS OF THE IGNITION OF COAL DUST. 127

have been discussed in another portion of this bulletin. Before
describing certain experiments carried out under conditions which
have been particularly well controlled attention will be called to
several demonstrations of the explosive character of coal dust made
on a laboratory scale as lecture experiments. A number of such
experiments have been described, and of these one described by
Thorpe,? with which it is possible to illustrate many features of a dust
explosion, will be taken up first.

The apparatus (fig. 6) consists of a long wooden gallery in two parts,
A and B, which together are 3.66 meters long, each 12.7 centimeters
square in cross section. These two parts fit into opposite sides of a
similar gallery (C) placed at right angles to A and B and intended to
represent a second gallery of a mine crossing the main one at right
angles. Each of these galleries is covered for its whole length by
a hinged top in two parts, which during the experiment are tightly
clasped down. The box should be made of 1-inch oak and screwed
together. A shutter (a) fits in the slot s. This end of A slips into

Fravee 6—Coal-dust ignition apparatus of Thorpe.

a quadrangle box D, 22.86 centimeters square, which is provided
with a door (6) and a small hole (c), through which a tube can be
inserted.

The coal dust is put into the box D and a blank cartridge is fired
from a small pistol through ce. The dust raised by the concussion
ignites from the flame of the powder, and the flame of the burning
dust goes several feet out of the ends of the box. To illustrate the
effect of a local explosion of methane, D is filled with an explosive
mixture of methane and air, with a in place; @ is then withdrawn
and a flame applied at c. The resulting gas explosion charges the
air with dust and ignites it, and the flame rushes along the gallery
and shoots out at the end, being propagated the length of the gallery
and 4 or 5 feet out into the air. ‘The success of the experiment
depends on the nature of the coal dust and the character of the initial
cause. Some dusts are not brought into the air by concussion and
the flame soon dies out. The condition of the coal dust with respect
to dryness and fineness of division has a great influence on the char-
acter of the explosion.

4 Jour. Chom. Sov., ¥ol. 61, p. 414.



THE COAL-DUST QUESTION IN EUROPE. 17

damp, nearly all kinds of coal dust were ignited by a cartridge of 100 gramsof dynamite
lying loose; while many notoriously dangerous dusts were less inflammable than other
inflammable dusts. It was further shown that a small admixture of fire damp
notably increased the danger and sensitiveness of coal dust, so that a dust which
is otherwise not dangerous may give rise to a disastrous explosion if thore is a little
fire damp present. The fineness of the dust, as well as its dryness, greatly increases
its sensitiveness and danger.

VIEWS OF ENGLISH AUTHORITIES BETWEEN 1886 AND 1908.

On March 15, 1886, the British accidents in mines commission,
which had been sitting since 1879, after reviewing the coal-dust
problem and experiments made in England and other countries,
reported the following facts as conclusively established : 4

(1) The occurrence of a blown-out shot in working places where very highly inflam-
mable coal dust oxistsin great abundance may, even in the total absence of firedamp,
possibly give rise to violent explosions, or at any rate be followed by the propagation
of flame through very considerable areas, and even by the communication of flame
to distant parts of the workings whero explosive gas mixtures, or dust deposits in
association with nonexplosive gas mixtures, exist.

(2) The occurrence of a blown-out shot in localities where only small proportions of
fire damp exist in the air, in the presence of even comparatively slightly inflammable,
or actually noninflammable, but very fine, dry, and porous dusts, may give rise to
explosions, the flame from which may reach to distant localities where either gas
accumulations or deposits of inflammable coal dust may be inflamed, and may extend
the disastrous results to other regions.

It will be observed that this report shows a great change of senti-
ment from the time of the preliminary report in 1881, when the
commission considered the explosibility of coal dust of itself as
improbable.

In the same year W. N. and J. B. Atkinson published a book
entitled ‘“‘Explosions in Coal Mines,” in which they made a special
study of five then recent English explosions and reviewed the history
of past explosions. They state, in unqualified language, that coal
dust was the effective agent in most of the great mine explosions.

The reports of the accidents in mines commission in 1886, and of
other investigations, led to an enactment by Parliament in 1887
requiring certain precautionary measures to be used in dusty mines,
as follows:

If the place where a shot is to be fired is dry and dusty, then the shot shall not be
fired, unless one of the following conditions is observed, that is to say: (1) Unless the
place of firing and all contiguous accessible places within a radius of 20 yards are at the
time of firing in a wet state from thorough watcring or other treatment equivalent to
watering, in all parts where dust is lodged, whether roof, floor or sides; or (2) in the
case of places in which the watering would injure the roof or floor, unless the explosive
is co used with water or other contrivance as to prevent it from inflaming gas or dust,
or is of such a nature that it can not inflame gas or du:

@ Final Rept. Accidents in Mines Comm., 1886, p. 48.
88006°—Bull, 20-112



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 129
EXPERIMENTS OF ENGLER.

In 1907 Engler* published a description of a form of apparatus
designed to demonstrate the explosion of coal dust on a laboratory
scale. He showed that substances like bituminous coal, meal, and
naphthalene, which are capable of giving gas, can be exploded by
an electric spark. He showed also that substances such as soot and
charcoal do not ignite in air alone, but will explode in a mixture of
air with a small amount of combustible gas, even a mixture that
would not ignite in the absence of the dust. Thus in air containing
2.5 to 3.5 per cent of methane the presence of soot or charcoal dust
brought about the explosion of the mixture, and this explosion was
increased in violence by the use of dust from bituminous coal. A
bituminous coal dust that does not explode when mixed with air
will do so if the air contain a small percentage of methane. The
apparatus which Engler used to demonstrate the explosion of coal
dust is shown in figure 7. A is a flask of 250 to
500 cubic centimeters capacity. A quantity of
coal dust is put into B, a small amount of
which can be introduced into A by elevating B.
The wires cc lead from an induction coil, the
spark gap being between the two platinum
wires at a. By blowing air into d in jets from
a rubber bulb the dust is brought into suspen- |

1

sion, and as the cloud passes (a) the ignition of
the dust takes place, if the dust is that of the
proper kind of bituminous coal. In a similar

. . . «-Figuae 7.—Coal-dust Igni-
piece of apparatus filled with a mixture of air {cn apparatus of Engler.
and 2.5 to 3.5 per cent of methane, or even less,
no explosion takes place when the mixture is sparked in the absence of
dust, but on introducing a small amount of a coal dust that has been
found to be nonexplosive, and blowing it into the air as before by
means of a rubber bulb, the contents of the vessel explode with
great violence, and the stopper is blown out of the vessel or the
glass flask is shattered. The same is true when soot or powdered
charcoal is used in place of the noncxplosive coal dust.

LECTURE EXPERIMENT OF BEDSON AND WIDDAS.

A simple lecture experiment to show the inflammable character
of finely ground coal dust is described by Bedson and Widdas.?
Their apparatus is shown in figure 8. Jt consists of two glass tubes,
a a and h, each 3.81 centimeters in diameter, @ being 7.62 centimeters

a Chem, Zeitung, vol. at, p. 388; Jour flr Gashelenchtamg und Wasserversorgumg, vol 50, p- 486.
> Trans. Inst. Min. Eng., vol. 32, 1907, p. $31.

88006°—Bull. 20—11—9


EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 53
EXPERIMENTS AT PITTSBURG WITH COAL DUST.

USE OF COAL DUST FOR STEMMING.

In various parts of the country the practice of using machine cut-
tings (“bug dust”) or other coal dust for stemming has become
very common. Some mining men have had a theory that if coal-dust
stemming was dampened or made wet it would be rendered harmless.
With a view to determining this point, a number of experiments were
made in gallery 1 at the Pittsburg station with black powder, using
machine cuttings, dry and wet, for stemming. The wet dust was wet
enough to pack in the hand, and in the tamping a little water was
squeezed out. The powder was protected from the damp dust by
a paper wad. A statement of the results is given in the following
table:

Explosion-gallery tests with machine cuttings (“bug dust’’) used for stemming.

Powder. Stemming. Flame showed
Date of
‘Test : _—|—________.--_____]. __ Length
Be | Ss, —| RE,
Size. | Weignt. Condition. Weight, | Bors eegow lows
Peet

13 1B

rs 30

1 8

14 a

M7 4

rs 50

1-10 of

a-The dust used for stemming was bituminous eoal from the Keystone tine, MeDowell County. WV
with the following analysis: Moisture, 1.24 per cent; volatile matter, 14.03; fixed carbon, 73.53; ash,
sulphur, 0.06, in all the tests with stemming the walls of the gallery were Kept wel:

> Length of flame measured from the mouth of the blown-out shot to the Yast. window showing. In

each test the flame may have extended 6 feet farther, to a point Just short of next successive window.

CNostemming used,” ‘The test was repeated with 507 and 1,701 grams of powder, and the fame showed
Jn the same number of windows. Wher clay was used, flame was seen in two windows, and occasionally
in thr

'é Not recorded,

The first experiments were made with 24 pounds of black powder
(1,134 grams) and 0.9 pound (400 grams) of machine cuttings. The
effect with wet coal stemming was nearly to double the length of the
flame from black powder alone, but with the dry stemming, for some
unexplained reason, the flame was not materially lengthened in this
test.

Experiments were then made with 1} pounds of black powder (567
grams) and 2.6 pounds (1,200 grams) of cuttings, wet and dry.
With a smaller amount of powder than in the previous tests, the length
of flame with the wet stemming was not quite so long as with the
larger charge of powder but smaller amount of dust stemming. With
the dry coal-dust stemming, the flame was two and one-half times as
long as that of black powder alone.


6 CONTENTS.

Exhaust steam as a preventive of dust explosions, by Frank Haas.
Moisture in coal dust... .....-
How moisture prevents explosion.
Resistance of coal dust to mixture. . .
Amount of water absorbed by coal dust.
Amount of water required in mine
Distribution of moisture.
Exhaust steam in operation. .
Value found by accident
Recording instrument. -
Records of outside temperature and humidity.
Moisture content of return air. .
Deficiency of water to be supplied
Amount of heat available. .
Effect of steam on mine air
Observations of mine air without effect of steam
Observations of effect of steam.
Effect of heating mine air... .
Heat radiated from surface of entries.
Moisture carried as fog. ........--
Quantity of steam needed for saturating mine air. .
‘Use of steam and water sprays in Oklahoma mines, by Carl Scholz
Purpose of inquiry......000....0000ecccseeeeeeeeeeees
Moisture and mine air. . .
Application of steam and water sprays.
Cost of water sprays.
Selected bibliography
Addenda.

Page.
166
166
166
166
167
167
168
168
168
169
169
170
170
172
172
173
Bee
174
176
178
178
79
179
180
181
183
184
200
201


158 THE EXPLOSIBILITY OF COAL DUST.

strewn on the floor. It was stated that every district in the mine
was isolated by stone-dust zones 600 fect in length. The dust
required but occasional renewal, and its application gave little or no
trouble. The cost was said to be about 1 penny (2 cents) per linear
yard of roadway with a section of 10 by 7 fect, exclusive of cost of
crushing and grinding,

Adjustable
‘weights

tamed into
igomont of

Leather packing}

Figure 17, ation of apparatus for igniting voal dust b

Experiments at the Altefts gallery will be resumed in May, 1910.
Meanwhile a full report on the work done to date is being prepared
and will be published shortly."

1 the first report on the work at Attotts,

4 For a revicw of some of the conclusions



180 THE EXPLOSIBILITY OF COAL DUST.

A tabulation of the accidents in mines of the Rock Island Coal
Mining Company resulting from explosions, mine fires, windy shots,
and roof falls drew attention to the fact that the accidents and
expense from roof falls diminished with the arrival of cold weather,
but that the number of accidents from the other causes mentioned
increased. The writer was prompted to continue his inquiry in
this direction with a view to determining means of preventing, if
possible, the disintegration of roofs in summer and the explosions
and mine fires in winter.

MOISTURE AND MINE AIR.

The roof falls were ascribed to the deposits of moisture or “sweat”
on the roof and ribs, at first near the intake, then slowly extending
farther into the mine. With the return of cold weather the moisture
gradually disappeared, the rate of appearance and disappearance
varying with the local climatic conditions.

A series of observations made with thermometer and hygrometer,
both inside and outside the mines, showed that during the summer,
when the temperature outside averaged 85° F. for twenty-four
hours, with a maximum of 95° or 100°, the mine temperatures
fluctuated between 70° and 78°; and that during the winter, with a
temperature of 40° to 50° outside, the mine temperatures ranged from
60° to 67°, the exact temperature necessarily depending somewhat
on the extent of the mine. In a new and less extensive mine the
fluctuations follow more closely the outside temperature; in an
older mine, with more extensive workings, the return air does not
show many degrees difference between summer and winter.

At about the time that some experiments were being conducted
in one of the mines of the Rock Island Coal Mining Company, water
overflowed from one of the adjoining mines and flowed down a slope
2,000 feet to the shaft of the mine under investigation. This slope
was the intake air way of the mine. Apparently the contact of the
air with the water tended to reduce in this mine the number of
local dust explosions and gas ignitions from black-powder shots,
without increasing the number of roof falls. The absence of effect
on the roof was attributed to the uniformity of the humid condition
of the mine air, in contrast to the former extreme changes from
winter to summer, or during shorter intervals.

This observation led to an investigation of the relation of the
humidity of mine air to dust explosions. Cold air entering a mine
has a low capacity for absorbing water. As it is warmed by contact
with the warmer mine walls its capacity for moisture increases
rapidly, so that it draws the moisture from the mine and leaves the
dust and timbers and faces of the coal dry. Hence in winter water
is carried from the mine by the air current, and in summer moisture
is deposited on the roof and walls of the mine, or the mine “sweats,”


INDEX. 203
Page. { Page.
Indiana, shot firing in 31 | Pekay mine, Jowa, coal-dust explosion in... 29

Towa, coal-dust explosions in 29

Jones, B. F., experiments
K.
Knopf, H. K., on steam jets. cee

Kruskopf process, description of........ 70.165
L
Larsen, Axel, on European experiments... 149-103
WOTK Of... eeseeeeenee
Le Chatelier, —, and Mallard, —, on coal-
dust explosion... --.-...... - B

Liévin, France, gallery at.
gallery at, experiments at.
figure showing.
instruments at.
Lignite, dust from, analyses of

dust from, experiments with er
Lignite-briquet factories, explosions in.... 130-132
Linings, brick or concrete, effects of.

Literature, lists of.
Long-wall system, employment of.

safety of .
Lupton, Arnold, on steam jets.

M.
‘Machine eutting, dust produced by se 35-38
Mallard, —, and Le Chatelier, —~, on coal-

dust explosion. 12,121-126,
Marreco, A. F., on coal-dust explosion... 13,24, 116
Martin, Henry, on sprinklers. 78
‘Methane, induction of, by reduced pressure... 128

Meyer, E. von, and Holtzwart, C., apparatus
of.
experiments of.
Mine air, effects of heat on.
humidity of
effects of heat on

charts showing. .

60-61, 170-175, 178-179
+ 61, 65-69, 180
66, 67,171, 173.174

See also Aix,
Minnesota, flour-dust explosion in....... z
Moisture, distribution of.....0..-.20 ce 168
efficacy of, in preventing explosions... 1ii-168
See also Humidity.
Monongah mines, W. Va.,coal-dust explosion
[renee cee 8
Morison, D. P., on coal-dust explosion... 13, 14,116
XN.
‘New Mexico, explosions im... TM
0.
Ohio, paying methods in al

Oklahoma, coal-dust explosion in... ”

coal-mine accidents in. : 180
use of steam and water in... ...... 79, 17)-183

P,
Paste, use of, on mine faces. 70

Payment, methods of, selation of, to acei-
dents.
‘Peckham, 8. F., and Peek, L. Woven dust ex-
Plosions

itm

Vennsylvania, comlcutting experiments in... 35
disasters in. 31-82, 108
‘experiments with caleium chloride in,
paying methods in.
watering in.

Permissible explosives.

ite,

“11,79, 0-82
See Explosives, per-

Pittsburg, experiments at. = 10,33
Pocahontus mine, W. Va., explosion in...... 28-20
Powder, black, danger from... - 83-84

| Pressure, duringexplosion, amount of. .... 143-148

effect of. 2178, 48-149
Primero mine, Colo., explosion in
Pressure in gallery, measurement of.
Propagation, definition of.
factors effecting
velocity of.
measurement of, figures showing... 150, 154
Prussia, coal-dust explosions in.............. M16
investigations in... cecceeeeeees 168
Psyehrometer, description of........0....-.. 62
Puncher, dust produced by cece BEB
R
Remedies for coal dust, discussion of. 70-98, 103-117

| Removal of dust, value of. cece 10-71, 108
Road dust, experiments with... » 52,103
Rock dust. See Stone dust.

Roof, effect of steam on...... 105
Rossitz, Austria, gallery nt, coaldust ex:
plosions in oo 288
s
Saturation, relation of, to temperature. 58-60
steam required for, amount of. .. 178-179
‘See also Humidity.
Scholz, Carl, on sprinklers a

on use of steam and waterin Oklahoma. 179-183

work of. - ve W
| Seott, C. E., on dust experiments. . 38
| Screening, methods of - 8
| Seasons, effect of, om mine air....... 61, 100-172, 160
| Shale dust, effect of, on cont dust - 49,64
‘Shoenberger mine, steam jets iu... - 8l
Shooting off the solid, dangers from. » 80-81
Shot firing, regulation of... 16,30
Solid. See Shooting off the solid.

Spraying. See Kruskopf process; Sprinkling,
i Sprinklers, cost of. 188
| Sprinkiers, permanent, experiments with... 7&78
| Yocation of. in Oklahoma, figure showing. 182
Fuse Of eeeeeeee 78, 103, 181

view of... .

| Sprinkling, effects of. . :
| use of. in Oklahoma. .....-

| See atso Hsing.
i
|

‘80-82, 104-107, 166-179
A789
174

Steam, dampening b:
dampening by, amount neoded for.
' apparatus for, plate showing,

ruse of gure showing..... - 15

in Oklahoma... + 181-183

Hl origin of. + 168-180
See also Mine air.

Stevenson, Robert, on deliquescent salts... R


INVESTIGATIONS AT EUROPEAN STATIONS. 154

the Altofts gallery, which, owing to the limitation of strength of the
gallery tube, have to be confined to about 367 feet, is inadequate for
complete solution of the problem.

APPARATUS AND METHODS AT ALTOFTS AND LI£VIN.

GENERAL STATEMENT.

The complex study of coal-dust explosions obviously involves the
use of delicate recording instruments. Both at Altofts and at Liévin
the equipment in this respect, most of which has been specially
designed, apparently leaves little to be desired.

At stations where observations have not yet been sufficiently
extended, the selection of instruments will now be greatly facilitated
by experience gained elsewhere. It is gratifying to acknowledge
that the benefit of such experience is freely and willingly offered to all
interested, both at Altofts and at Liévin.

INSTRUMENTS AT ALTOFTS.®

Measurement of pressure-~The B. C. D.* manometer (PL IX, B)
records the movement of a strong spring under the pressure of a coal-
dust explosion. In order to reduce error caused by the inertia of the
moving parts they are made as light as possible and the amount of
movement of the spring is as small as is convenient for accurate
measurement. The spring itself is triangular in form and clamped
at its base, the force acting vertically upward at its apex. With this
form the maximum strain is the same at all cross sections of the
spring and the inertia is also reduced, because the narrow lighter
part of the spring moves most and the wide heavier part leas

The pressure acts directly upon a surface of oil contained in a
hexagonal oil box and is transmitted to a light hollow cylindrical
plunger (closed at the bottom) moving in the oil box through a hole
in the top. This arrangement keeps the plunger well lubricated,
reduces leakage past it, and prevents the fine dust with which the
gas is charged from cutting and clogging the rubbing surfaces. It
also damps out any rapid vibrations due to sudden shock.

The natural period of vibration of the spring is one onc-hundred-
and-fiftieth of a second, and such vibrations do not mask the actual
fluctuations of pressure due to the explosion. The plunger makes
contact with the spring by means of a loose link, one end of which
rests in a conical depression in the bottom of the plunger and the
other in a similar depression in the face of the

pring.

2 The writer is indebted to Mr. W. ©. Garforth and Doctor Wheeler for the accompanying photographs
‘and the following cleseriptions of instruments used at Altotts.

©. C. D.,, the distinguishing mark used for these instruments by the makers, stands for “British coal
dust.”


68 THE EXPLOSIBILITY OF COAL DUST.

Gallons of water per 100,000 cubic feet of air for specified temperatures and percentages of
saturation.

| Relative humidity (per cent)—

Tempera-
ture. |

40.

]
8

0.170 0.227

ue}. 2179 238
1126 1158] 189 252
fi34 | lass | 1202 1269
1283

im) ae

149
1158
1166
1176
1188
1568
1599
— 5. 63 633
4 [067 1666
<3 070 T14
=2 074 S743
=i lo78 1782
0 -082 +823
865
908
1948
£996
ou
LL
1
1
tS
1

1 hoa
1 oo
i 1 1
L 2
| i 2
| 1 15 2
i 1 1 2
a 1 L 2
Korg] 1.37 1X 2
Loz | 1:328 | 1.85 2
f
. 1 1.390 | 1 a2.
1 1453 | 2 Bug} 2
: 1 T5iR 2 2 3
1 1.586 220 3
1 1.656 2. 3
'
3 M6 1 Lat) 2 aig! 3
32. 362 1 vam] 2 1 3
3B. 376 1 Liss) 2.25
35. 1405 t 2005 | 2 :
J azn} gat 1 2.103] 2 i
| lasz | 1873 L 213] 26 929
BRITE Tas] To06 | t 2265 | 2 4077 |
SO Lar 240 L 2as| 2 42a |
40, Tags) Lo7s Rago! 292 4390

# The table fs devised on the assumption that if the water vapor in 100,000 cubic feet of air at any given
temperature and pereentage of saturation were condensed, {l would be equivalent to a certain number of
allonsof water at that temperature. For temperatures of 32° or under, the Agures are given on the ussump-
Hion that the vapor is equivalent to a certain volume of water at 32".



THE COAL-DUST QUESTION IN THE UNITED STATES. 31

that legislation followed in Illinois requiring the employment of
shot firers* and inspection by them of the drill holes, and limiting the
charge of black powder. The amount of powder used in a shot was
difficult to control, and in some mines in Illinois the output of coal
per keg (25 pounds) of powder fell as low as 15 tons (of 2,000 pounds).

In the meantime mines opened in the deeper-seated coals in south-
ern Illinois found considerable gas (methane). Even where the coal
was undercut by machine, overcharges of powder were frequently
used, so that serious accidents resulted, in which some or all the shot
firers were killed. This condition still prevails (1909), but more
care is now exercised by the shot firers in condemning bad holes, and
a considerable number of operators are paying more attention to
dampening coal dust along the entries by sprinkling.

In Indiana the conditions have been somewhat similar to those in
Illinois, except that the employment of shot firers has not been com-
pulsory, so that explosions killing a considerable number of miners
have occurred, notably at Princeton. Very large charges of black
powder are used in the Indiana mines. The revised state act of 1907
fixed the limit at 6 pounds of black powder, but instances have been
reported in which as much as 10 to 12 pounds of powder has been.
used ina single shot. Where law and local regulations allow 25-pound
cans of powder to be in possession of the miner in the mine, and allow
him to charge and fire his shots, there is no way of effective control
to insure safe conditions.

In Pennsylvania, the chief coal-producing State of the country, and
in Ohio the method of paying the miner on the screened-coal basis
has prevailed to the present time; and in these States and in parts
of West Virginia the system of undercutting before shooting has
generally been adhered to except in the Connellsville coke region.

GREAT DISASTERS OF 1907.

Though numerous explosions occurred in the Appalachian field in
Virginia, West Virginia, and Pennsylvania up to 1907, the only ones of
the most disastrous order were those at Newburg, W. Va., in January,
1886, Red Ash, W. Va.,in 1900, Johnstown, Pa., in July, 1903, Cheswick,
Pa.,in January, 1904, and Pocahontas,Va.,in 1906, and in the majority,
including those cited, there was always a question whether fire damp
was not the initial cause. However, in the propagation through the
mine there is little question but that coal dust was the chief factor.
The same might be said of the explosions that occurred from time to
time in Alabama and Tennessee.

Tn 1907 occurred an appalling series of great. wide-sweeping disas-
ters. On January 23, at the Primero mine, Colorado, there were 24

‘@In mines where in shooting more than 2 pounds of black powder {s used in any one ahot,


THE EXPLOSIBILITY OF COAL DUST.

66

Figure 2 gives the curves resulting from taking the different weights

of aqueous vapor per cubic foot in grams as constants and considering
the temperatures and different percentages of saturation as variables.

J

mt

‘Temperature in degrees Fahrenheit

Fioure 3.—Curves of equal relative humidity for varying temperatures and depressions of wet bulb.

Figure 3 shows the curves derived from considering the different

relative humidity percentages as constants and the depression of the


188 THE EXPLOSIBILITY OF COAL DUST.

A or B, the muzzle of the cannon having first been placed against
the diaphragm closing the end. In this way the ignition could be
brought about either against or in the direction of the current of
air in A-B. The shot was always fired with the ventilator in opera-
tion. The dust was introduced through E during the circulation of
the current of air. The introduction was regulated by hand, so as
to secure uniform distribution of the dust throughout the gallery.
The time required to introduce the dust by hand was sufficient to
permit the circulation of the air from five to filty times around the
closed circuit formed by the two galleries. The dust used throughout
these experiments was passed through a 200-mesh sieve without
any attempt to screen it to a certain size. The velocity of the air
current used was from 4 to 5 meters a second, a velocity that was
relied on as sufficient to maintain in suspension all of the dust of
this degree of fineness. The total capacity of the apparatus was
4.5 cubic meters, and the density of the dust was determined by the
amount introduced considering the whole amount as suspended at
uniform density throughout the galleries.

When the cannon was fired into the gallery devoid of dust a rapid
flame was seen at the first two windows, and at the same time all four
paper diaphragms were ruptured. Identical results with a dust-laden
air in the system indicated no inflammation. When inflammation
occurred a red flame advanced at different velocities to various points
of the gallery, or in some tests projected out the end opposite the can-
non. Lacking the facilities for such work, the experimenters did not
attempt to measure the velocity of propagation of the flame, but,
judging by the eye, they were able to express the velocity as very slow,
slow, or rapid. After each experiment the tubes were carefully
cleaned.

In the course of this work eight different samples of dusts were
examined. By varying the density of the dust, beginning with
densities too low for inflammation to occur, they were able to arrange
the dusts in the order of their inflammability under these conditions.
The fact was brought out by this work that the order of inflammability
is the same as that of the content of volatile matter in the coal. The
same conclusion, as we have seen, was reached by other investigators,
namely, Vital, Mallard and Le Chatelier, Holtzwart and Meyer, and
Bedson and Widdas. Further factors considered by the author as
determining the inflammability of dust are the character of the vola-
tile matter and the percentage of ash in the coal; but the dusts as
prepared for use in this investigation were of somewhat similar com-
position with respect to ash, so that the content of volatile matter
was found to exercise a preponderating influence, and to determine
the order of inflammability. Attention is also called to the influence
which the ash exercises, both by increasing the weight of the particles,



HUMIDITY OF MINE IR. 61

less than 80 to 90 per cent is to dry out the walls of the passageways
through which they pass

Normally a coal bed is free from water. In many mines water
seeps from the surface through troubled ground or ‘‘faults,” and in
some mines artesian flows from the bottom are-encountered, but
ordinarily there is sufficient clayey matter in the roof and floor to
keep out water. In most coal mines, therefore, the presence of
moisture, except locally, depends on atmospheric conditions.

EFFECT OF SEASONAL CHANGES OF TEMPERATURE ON MINE AIR.

The warm or hot air of summer contains a large amount of moisture.
On entering the mine the air and water vapor are cooled, usually
below the dew point, so that precipitation takes place. The walls
and roof of the passageways become gradually more and more moist
as the summer progresses, and in parts of the mine the walls frequently
become beaded with the deposited moisture. In some mines the floor
becomes rather wet in the summer months.

On the other hand, in winter the air enters the mine at a tempera-
ture usually lower than the mine temperature, which ordinarily
ranges in this country from 60° to 65° F. In England and other
European countries* the outside winter temperature averages higher,
but the mine temperatures are also higher, owing to the greater
depth of the coal beds. Hence there is the same general contrast of
outside and inside temperatures and of relative humidi

When the air current enters the mine at a low temperature, it car-
ries only a small amount of moisture in the form of vapor, even
when the relative humidity is near saturation. As the currents go
through the mine and the walls heat up the air and vapor, the relative
humidity falls to such an extent that the moisture contained in the
walls of the passageways and in the dust lying along them is vapor-
ized and carried away by the air currents. This fact has been noted
for many years and by many observers. The danger of dry coal
dust has been so much commented upon that it will not again be
discussed here until the remedies are considered.

INSTRUMENTS FOR MEASURING ATMOSPHERIC MOISTURE.
SLING PSYCTROMETER,

In the field practically the only method that can be employed to
measure the amount of moisture in the air, or the relative humidity,
is by observing the temperature of evaporation, which is obtained by
noting the difference in temperature between wet and dry bulb

@ Since the body of this bulletin has been written an important series of papers entitled Investigation
of the drying out of mines and combating the dangers of coal dust,” by Bergasseseor Forstmann, has been
published in Gliickauf (January § to February 12, 910). ‘These papers treat of genetal investigations
and of an elaborate sories of observations recently made in mines of Germany by a government
commission.



24 THE EXPLOSIBILITY OF COAL DUST,

Figures are quoted from the British ‘“Annual Report on Mines and
Quarries” by five-year periods, of the death rates from accidents
underground in mines per thousand persons employed. The annual
death rate due to explosions of fire damp or coal dust shows a regular
decrease from the period 1851-1855, when it was 1.280 per 1,000,
until 1907, when it was 0.057. In other words, considering an equal
number employed, for 22 men killed in 1851-1855 by fire damp or
coal dust, but 1 was killed in 1907.

RECENT AUSTRIAN EXPERIMENTS.

The Vienna permanent fire-damp committee in 1908 decided to
continue experiments begun some years before with coal dust in its
gallery at Babitz, near Segengottes in the Rossitz district, Austria.
This gallery consists of part of an old mine level 293.7 meters (964
feet) in length, connected with the surface by three shallow shafts.
Coal dust is introduced sometimes on shelves and sometimes through
pipes leading from the surface, the dust being thrown into suspension.
by fans. The coal dust is distributed for distance of 10 to 90 meters
(33 to 295 feet) from one end, where there is an explosion chamber.
The dus ignited by blow-out shots from a cannon or cannons
charged with black powder, or by dynamite cartridges hung in the
explosion chamber. The flame, in these experiments, traveled from
50 to 180 feet beyond where the coal dust was laid, depending upon
the character of the dust, its purity, its fineness, and its dryness.
These experiments are still continuing, and as yet no conclusions
have been reached.

A description of this station is given in the Colliery Guardian for
September 24 (p. 635) and October 1 (p. 687), 1909.

A second series of tests is reported in the Colliery Guardian of
December 30 (p. 1294), 1910.*

In these tests the arrangements of the gallery were slightly modi-
fied from that of the previous experiments, by providing an iron door
for the middle upeast. This door, opening into the gallery, would
resist the shock of the explosion and open by the recoil,

A fourth dust distributor was erected 120 meters from the explosion
chainber, to permit the trial of another dust zone beyond the wet zone.

The recesses containing the electric lamps were provided with
sheet iron covers, and the conducting wires were laid in pipes.

A flame 200 meters (660 feet) in length was obtained in one experi-
ment in which an average weight of 129 grams of coal dust was
disseminated per cubic meter of air (0.129 ounces per cubic foot)
over a total length of 120 meters (394 feet) in the gallery.

‘The objects of the experiments, in which only Rossitz. dust was used, wete to deter-
mive the minimum amount which might be ignited and exploded by a charge of

910, pp. 295-298.


EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 39

The coal as prepared after grinding and screening has the following
average proximate analysis:

Proximate analysis of coal used for testa at Pittsburg station.

Moisture 1.94
Volatile combustible 35.11
Fixed carbon 57.73
5, 22

100. 00

Sulphur... 1.25

There is manifest advantage in using an artificially prepared dust
of uniform chemical composition and known size. The use of so-called
mine dust of unknown composition in the early experiments abroad,
was probably the cause of inconsistency in many of the results
reported.

The coal dust for the following density tests was made by grinding
in a ball mill the standard Pittsburg station coal until it would all
pass through a 200-mesh sieve (200 wires to the linear inch).

METHOD OF PROCEDURE.

In these tests, six sections (40 linear feet), of the explosion gallery
were used. The gallery 100 feet long and 6 feet 4 inches in diameter,
may be seen in Plate I, which shows the first stage of a dust explosion.
The near end is closed by a concrete block, in which is placed the
cannon for simulating blown-out shots. The gallery has 15 sections,
each 6 feet 8 inches long, with a window on the observation side in
the middle of each section and a relief door or flap at the middle of
the top of each section. For the density tests the following arrange-
ment was used: A paper diaphragm was placed at the farther end
of the sixth section. The space between the diaphragm and the
concrete block contained 1,260 cubic feet. Air was blown into the
bottom of the gallery and drawn out at the top by two blowers with
5-inch inlets and outlets. These blowers, one for each three sections,
were connected with the gallery by independent pipes. Each pipe
formed with the gallery and its respective blower a separate circuit.
The dust was placed in a short 6-inch pipe at the top of the gallery
near the concrete block. A blast of compressed air ejected the dust
from the pipe, which pointed toward the paper diaphragm and the
farther end of the gallery.

The fans were started at the moment of dust ejection, to cause
circulation of the air and so keep as much of the dust in suspension
as possible. Nevertheless, it was found, by taking samples at the
axis of the gallery, that the greater part of the dust fell quickly to
the floor. In eighty-five seconds only about 9 per cent remained in
suspension, and in two hundred and seventy-five seconds about 4 per

A.C, Fieldner, analysts


INVESTIGATIONS OF THE IGNITION OF COAL DUST. 147

Results of second series of experiments with explosive coal dusts at Pittshurg station—Cont’d.

| Results of tests.

Source and proximate analysis of coal dust used and pressure
developed in tests,

Weight |requivatent Brffect on steel
applied, | per sq. cm, ball.

Grams. Grams.
16. Subbituminous, noncoking coal from Weaver mine, N. Mex. 282 782 | Not lifted.
(Lab, No. 10039): 230 507 | Lifted
Moisture. . 12.14 240 | 623 | Not lifted.

Volatile miutter: 82 235 | 610) Do.
Fixed carbon. Be a} Do.

Ash. on CIID ns
Sulphin 52
Pressure developed, db grams por suave contimeter.

17. Subbituminous, noncoking coal from Superior mine, Wyo. ( 200
Lab. No. 10040): 325
Moisture. cecteeteceeseses 10.45 250
Volatile mutter. : 38,28 260
Fixed earbon 45.06 270
: a 6.2 280
i 215 Litted.
oped, 718 grams per suare veniimeter i 28 Not lifted.

noncoking coal from Superior mine, Wyo. 619 | Lifted

(Lab. No. 10041): 779 | Not lifted.
Moisture. veces ia | Lifted,
Votatile rninttee. 2000000200201 75a) "Do.
Fixed carbon..20.00 0022 ite | Do.

ASD vss 779 | Nos lifted,
phar.» mi” Do.

Pressure developed, Tt grains par square coniimeter.

19. Subbituminoue, noncoking coal from Weaver nine, N. Mex. a8 2 | Lited.
Cha, No, 10042 B00 719
- 306 Fe2 | Not hited.
: . 302 784 | Litted,

Ash.
Sutpinn
Pressure develop

Fixed earboa..170000007 :

ed, 782 grains per square centimeter.

The experiments recorded in the table were made on equal weights
of the dusts, and each sample was ground to pass through a 100-
mesh sieve. These results are interesting chiefly for two reasons,
First, they show what degree of accuracy may be expected from this
method of examining the explosive character of dusts. From expe-
rience it may be stated that the pressures developed in almost all of
the tests could be measured to about 3 per cent of the total pressure
developed. Second, the results are of most importance in showing
the care which must be taken in preparing the dusts in order that the
results obtained with different coals may be strictly comparable.
Each sample of coal was ground in a ball mill, so that the whole of
the sample passed through a 100-mesh sieve, and efforts were made
to have them ground as nearly as possible to (he same degree of fine-
vess. But this object was not attained by any means. It wi
shown that fully 90 per cent of those dusts which developed the
greatest pressures in the explosion vessel would pass through a 200-
mesh sieve, whereas of some samples only about 30 per cent would

s



EXPERIMENTS WITH EXPLOSIBLE COAL DUSTS. 55

was drawn into the gallery through the last relief doorway and a box
conduit by the Koeting injector. The results of the experiments are
given in the following table:

Erplosion-gallery tests to show effect of humidity.

{In all tests the explosive used was 1} pounds (587 grams) of black powder. Explosive tarmped with elay.]

| Fiome_|

g | ‘SH | showed (in-
Air current. 2 | =e Gicating its Result,
= | eB Uengunya—|
g | 54
Gal. > Sinema 262 OTTO
lery | pate of test. | Duration ‘Temper-| Relative} Z| 2S |
leg | Daweortes | Ryaton |Z. Tamper Rewee | BEE | | |
No. i i ait]! 18
| 2 2181
| Pi |eiels
| g|/2)2/4
a |e] &
Hrs, min. t
19, 1908 28 | 191 |
ae108} =a | 104 | Yes:
3 | | Yes_| No:

The first experiment (G-346) was made without humidifying, to
observe the effect of an explosion of dust in the face of a current of
air traveling 131 linear feet per minute. The explosion was propa-
gated through the gallery.

In the second experiment (G-348) the relative humidity of the air
was raised to 89 per cent, and the current was maintained for one
hour and forty-six minutes. Practically no moisture had been
deposited by this time, as indieated by the analysis of the coal dust,
a sample of which was gathered from all shelves in the gallery.
Complete ignition followed the shot.

In the third experiment (G-349) the average relative humidity
was 98.6 per cent, and the current was kept on for sixteen hours and
thirty-tive minut A considerable amount of moisture was pre-
cipitated on the dust, the analysis showing the total moisture to be
18.4 per cent, or about 16.5 per cent in excess of the normal content
of the coal dust. The result of the shot was a partial propagation,
the flame dying down before it reached the end of the gallery.

In the fourth experiment (G-350) the relative humidity was 82
per cent and the total moisture of the dust on the shelves 11.63
per cent. There was also partial flame propagation in this test.

In the fifth experiment (G-482) the relative humidity was some-
what higher, but the percentage of moisture precipitated very little
greater. The flame propagation, however, was much less, owing to
some cause not apparent.



THE COAL-DUST QUESTION IN THE UNITED STATES. 27

HISTORICAL REVIEW OF THE COAL-DUST QUESTION IN
THE UNITED STATES.

GRAHAMITE EXPLOSIONS IN WEST VIRGINIA, 1871-1873.

One of the earliest recorded dust explosions in the United States
was in a grahamite mine in Ritchie County, W. Va., on February 9,
1871, when 4 men were killed as the result of a very violent explosion.
The official report of the investigators was that an “explosion of
powder (184 cubic inches in the shot) pulverized a certain quantity
of mineral (grahamite—a hydrocarbon) and in that state it was
easiest decomposed. The indications are that gas burned along all
the air passages and exploded at the portal.’’¢

The management subsequently employed sprinklers, as much dust
was made in running the mined mineral through chutes, but a second
explosion, February 25, 1873, also from shot firing, killed 4 men.

FLOUR-MILL EXPLOSION AT MINNEAPOLIS, 1878.

On May 2, 1878, a tremendous explosion occurred in the Washburn
Flour Mills, at Minneapolis, completely wrecking the building and.
setting on fire 6 other flouring mills and a number of other buildings.
Professors Peckham and Peck were commissioned by the coroner’s
jury to investigate. They made experiments in closed boxes with a
variety of powdered substances to test their explosibility. Among
other things, they tested various flour mixtures and coal dust. The
powdered materials were blown into the box by bellows and ignited
by an open light. The findings of Professors Peckham and Peck
were to the effect that practically all finely divided highly carbona-
ceous material would explode under the conditions tried. Their
report was not made public at the time, but was published in issues
of the Chemical Engineer, March, April, and May, 1908, An ubstract
of it appeared in Mines and Minerals for September, 1908, page 55.

In an issue of the Scientific American Supplement, May 25, 1878
(p. 1985), there is printed an article entitled “Dust as an explosive.”
After a general discussion of the subject, it continues:

It has been well known for a long time past that it is not alone to mixtures of the
issuing gases with air that the explosions in colleries are to be ascribed. Finely
divided coal is always present to a more or less extent in the air of 4 mine, of, if not
present in suflicient quantity, is sure to be produced by the shock of an explosion,
This dust furnishes a material which gives the fire power to spread from gallery to
gallery should the mixed gases themselves be insufficient in quantity to permit
such a spread. Indeed, it would appear that coal dust itself, when mixed with
certain proportions of air, renders the air explosive withont the presence of any of
the gases usually evolved in coal mines; and there can be no doubt that the presence
of coal dust renders mixtures of coal mine gas and air explosive that would other-
wise be quite harmless,

Trans. Am, Inst. Min. Eng., vol, 24, 1894, p. 105.


136 THE EXPLOSIBILITY OF COAL DUST.

colored water. The third opening contains a glass tube, the upper
end of which is closed by a short piece of rubber tubing and a pinch
cock. Any sudden pressure generated in the explosion vessel pro-
duces a movement of the liquid in the manometer, the extent of
which is noted by means of a scale attached to its side.

Equal weights of the same coal dust gave practically the same
pressure in the apparatus.
Equal weights of different
dusts, when the same cur-
rent was used for ignition,
produced quite different
pressures. These pressures,
the authors consider, indi-
cate the explosive character
of the dust mixture. Sev-
eral samples of dusts were
examined in this way; some
of these were collected from
a mine, while others were
ground in the laboratory.
FIGURE 11. Later coal-dust ignilion apparatus of Bedson These are designated in the

and Widdas. table below as natural and
artificial dusts, and all were put through a screen of 100 meshes to
the inch. The weight of dust used in each experiment was 2 grams,
the pressure of the air used to project the dust into the vessel was 8
inches of mercury, and the wire was heated by a current of 15 amperes.
The results are given in the following tabl

Explosive character of coal dusts of stated composition as shown in experiments by Bedson
and Widdas

Composition of dust.

No.of | | | Ratfo of

Ratio of Pres:
experl-) Nature of dust, | | fixed care a
ment. | { Volatile Fixed fixed 8 yon and | SUF
Moisture. Ash. | bon to
| mutter. © carbon. pantie

matter.

&
2aee

SEER.

ton seam. 3, Ground coat from
(from Busty seam. 6. Dust, fro
. in roof of yard seam. 8. Dust from top and bottom
1 seam, 9, Dust from sides of baulage roads and pillar sides of Grey seam,

1. Ground brown coal.
4. Ground coal from yard seatn
‘ind haulage roads in yard seam.
of timber baulks and roof of G

@ The length of the sealed tinh of the U tnbe above the level of the water Iu the tube ls 12 inches. The
pressure of 5 inches, therefore, wonld represent s compression sulliclent to reduce the volutne of alt to
Seven-twellths of Its original volume, ete,



86 THE EXPLOSIBILITY OF COAL DUST.

As a final result of his investigations of the Monongah, Darr, and
Naomi explosions Mr. Chamberlin concludes that the proportion of
shale present in the dust exerts a marked influence on the degree of
coking, and suggests as a means of preventing or limiting explosions
the use of a mixture of shale, earth, or lime with water through the
mine. The inert material would lessen the inflammability of the
coal dust and would bind the particles together and to the walls and
timbers. If such a mixture were applied to the ribs and props it
would prevent the coal dust being swept up by the ordinary air
currents. He says:

Whether shale dust on the entry floors alone is competent to check a dust explosion

once under way when fine coal dust unmixed with shale or whitewash is present upon
the ribs and timbers, can be told only by experiment.

EXPERIMENTS WITH ROCK OR SHALE DUST AT LIVIN, FRANCE.

According to a paper entitled ‘A Word on the Question of Dus
by L. Aguillon, general inspector of mines of France, during the in-
vestigation of the Courriéres disaster it was observed that the explo-
sion had not propagated in levels or galleries where the coal was thin
and the rock or shale walls had been cut or blasted, making a deposit
of inert: dust on the ledges or floor.

Furthermore, the opinion of the General Council of Mines of France,
as published in the official journal, August 1, 1907,¢ was that there
were great difficulties and inconveniences in general watering as
practiced in Germany and doubtful results. The council, therefore,
considered that the ‘‘schistification of the coal dusts or their mixture
with other inert substance would perhaps constitute a practical
means of obviating the risk of inflammation,” and before prescribing
any administrative measures suggested that the fire-damp committee
proceed to a further study of this feature.

In consequence of this advice of the General Council of Mines, it
was proposed that a series of experiments with coal dust and shale
be made at the gallery at Liévin, which was established in the same
year, 1907. In some of the experiments made prior to November,
1908, it was shown that coal-dust explosions did not seem to be pro-
duced under the conditions of the experiments with a mixture of 40
per cent of shale dust. By August, 1909, according to Mr. Aguillon:

It was recognized that schistification by simple mixture, or scattered schistification,
was not sufficient to stop a dust explosion, which, on the contrary, could be stopped
by a transverse heap of clay. ‘This was the first idea of the condensed schistification
in the form of an arresting barrier (“‘arrét-barrage”’).@

a Op. cit, p. 56,

» Bull, Soc, ind. min., ser. 4, vol. 13, October, 1910, pp. 309-317.

© P. 5411; reproduced in Auuales des Mines, ser. 10, vol. 12, 1907, pp. 484-480.
4 Bull, Soc. ind. min., ser, 4, vol, 13, October, 1910, p. 314.





44 THE EXPLOSIBILITY OF COAL DUST.

DISTRIBUTION OF DUST.

In this series of experiments, the dust of the size to be tried was
distributed along the gallery on four narrow iron shelves on either
side. The gross amount distributed was 1 pound per linear foot of
gallery. This amount is much in excess of what is necessary to
produce an explosion, so that only a relatively small part of the dust
is active or loses its volatile matter. In addition to the dust placed
as just described, 20 pounds was placed upon a horse 20 feet long and
9 inches below the center line of the bore hole and the axis of the gal-
lery. The dust was placed in this way to obtain the most extreme
condition, such as would be found in a mine with a blown-out shot

Kosrting
exhauster

CROSS SECTION

Relief door

im

7 z
LONGITUDINAL SECTION
0 5 10 Feet

rr

Figure 1.— Diagrammatic sections of cannon end of gullery No. 1, Pittsburg station.

pointed toward a pile of coal dust. Figure 1 is a sectional outline
of part of the gallery, showing the location of the horse.

DISCUSSION OF RESULTS.

In the first tests a charge of 1} pounds of black powder was used,
tamped with 2} pounds of clay. With this charge dusts larger than
60-mesh did not even ignite (except for slight prolongation of powder
flame in tests 1 and 2), but 80 to 100 mesh dusts and also 60 to 80
mesh dusts in three out of four tests did ignite and propagate the
explosion. It may be assumed that finer sizes would propagate, so
no tests were made of them.

A series was then tried with double the quantity of black powder,
or 2} pounds, and with 2 pounds of clay stemming, which was all that
the depth of the bore hole would allow. The effect was notable; 60 to
80 mesh dust propagated the explosion and so did 40 to 60 mesh dust.
With 20 to 40 mesh dust, while there was ignition, there was only
partial propagation, but the indications were that with a still larger


REMEDIES FOR COAL DUST. 81

uniform condition of moisture rather than when the moisture in the mine varies as it
would do without having the moisture put into the air during dry, cold days.

At our Hazel Kirk No. 2 mine, which is also a shaft, we have steam from the fan
engine and 14-inch steam line from the boilers. At our Hazel Kirk No. 1 mine we
have the exhaust from the fan engine and about 30 sprays, separated about 50 feet apart
in the air way. During the daytime only a limited quantity of steam in addition to
the moisture from the sprays goes into the mine, but at night a full amount of steam is
tumed in from the engine. At this mine we have obtained an average of 95 per cent
moisture, and we have obtained 96 per cent of moisture even during the coldest days.
At our Dunkirk mine we exhaust steam from the fan engine into the air shaft and we
also have the exhaust from two or three pumps, in the mine, put into the air, All
of the above-mentioned mines have force fans. At our Shoenberger mine we have the
exhaust from three generator engines carried into the mine during the nighttime and
we have a system of sprays during the daytime. At night, after the men have gone
into the mine, the steam is turned on partially in addition to the sprays which work
all the time. Assoon as the fire bosses go into the mine in the morning, about 20’clock,
a full head of steam is turned in, and shut off whenever they areready tocomeout. In
addition to the steam at the front part of the mine, we also have the exhaust from the
fan engine to the back of the mine (on a separate split), together with the sprays which
operate substantially at the front.

Observations were made by the writer at the Shoenberger mine on
March 8, and except in one stretch of road about 3,000 feet from the
mouth of the mine the road dust was uniformly dampened and plastic.
The ribs and roof were free from dust and, though not dripping, were
damp. The relative humidities of the ventilating currents are shown.
in the following table:

Hygrometric conditions of ventilating current at Shoenberger mine, Washington County,
Pa., March 8, 1910.

Relative!

Dy. hum | Condition of floor and ribs.

Place of observation. wie. | aa. |
in

‘Main ventilating split: |
Intake air at entrance
1,500 feet from entrance.
2000 feet from entrant

‘water sprays).
t eross-exit, main entry, 7,000 | 55
feet from entrance, i
Ventilating split at back of mine:

92 | Damp from night exhaust jets.
96 | Very damp.

94 | Floor damp, ribs and toof dampish,
no dry dust.

Totake air at entrance 354) 314 ry
600 feet from entrance and’ dis- 4 4H] 100 | Alr_very foggy. Walls and ribs
charge of exhaust, | “dripping, floor wet.
‘Near inby end of split 58 32 4 | Floor very damp, ibs and roof
dampish.
Avother split... 534 53 %/ "De

It would appear from the readings in the main ventilating split
that the water sprays used near the main entrance were not sufficient
to humidify the mine at the observed temperature and humidity
of the entering air-—that it was the large steam exhaust at night that
supplied the chief quantity of water, the water sprays giving some
moisture during the day. ,

The exhaust steam used in the independent back split of air shows
the efficiency of this method where it can be applied. The exhaust

88006°-- Bull. 20—11—6


THE EXPLOSIBILITY OF COAL DUST.

160

suorsuayxe posodosd Bo} moys ‘Lua|j08 sapouesy Jo UeLE—"6l KADDLT
age.)
nett i ao
en
wo an

ssepuiko

engernddy

wey opens
s8y0ys UoITEAIEEAO, Buys | — onceoy,

ye

poys Teog

fone

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91 vorsusre pojejduze: ><



194 THE EXPLOSIBILITY OF COAL DUST.

Arxinson, W. N., AND Cunynaxans, Henry. Report on the disaster at Courrigres
mines, Pas de Calais, France. London, 1906. Report to Secretary of State for
the Home Department on the disaster. Issued as a bluebook (Cd 3171).

Armansoy, W. N., anp Hensaw, A. M. The Courriares explosion. Trans. Inst.
Min, Eng., vol. 32, 1907, pp. 439-492. Discussion, pp. 340-348; vol. 33, pp.
124-137.

Bacue, FRANKuIN. Dust explosions in coal mines. Trans. Am. Inst. Min. Eng., vol. 40,
1909, pp. 667-673. Abstract of paper printed in Mining World, October 23, 1909.

Bariow, J. E, Exhaust steam as a dust precipitant. Coal and Coke Operator,
February 11, 1909, pp. 115-116. Describes experiment with exhaust steam at
mine taking 75,000 cubic feet of air per minute.

Beano, J. T. Mine gases and explosions. New York, 1908, 402 pp. A descriptive
treatise on the various factors involved in explosions.

Bepson, P. P., anv Wippas, Hevry. Experiments illustrative of the inflammability
of coal dust and air. Trans. Inst. Min. Eng., vol. 32, 1906, pp. 529-531; vol. 34,
1907, pp. 91-97. Reprinted in Iron and Coal Trades Review, June 3, 1910.

Bonneau, ——. Suppressing coal dust at the Dourges collieries. Iron and Coal
Trades Review, November 26, 1909. From paper in Bull. Soc. ind. min.

Brevnaenr, F. Note sur la question des poussiares dans les mines anglaises. Annales
des mines, ser. 10, vol. 12, 1907, pp. 532-551. Review of dust problem and mine
explosions.

Capman, JonN. The ignition of coal dust by a naked light. Colliery Guardian,
vol. 98, 1909, p. 929. Abstract of paper before the North Staffordshire Institute
of Mining and Mechanical Engineers. Describes experiments with vertical
gallery 12 feet long and 8 inches square.

Some experiments to illustrate the ignition of coal dust by electric means.
Colliery Guardian, vol. 99, February 25, 1910, p. 382.

Cautot, Tony. The experimenting station at Liévin, France. Eng. and Min. Jour.,
vol. 88, 1909, pp. 1-5.

Cuamsernin, R. 'T. Notes on explosive mine gases and dusts, with reference to explo-
sions in the Naomi, Darr, and Monongah mines. Bull. U. S. Geol. Survey No. 383,
1909, 65 pp. Describes laboratory experiments to determine the gases in coals
and considers the action of dust in mine explosions.

CurwicaL Enaiveer. Report of S. F. Peckham on Minneapolis explosion. March,
1908, p. 97; April, 1908, p. 146; May, 1908, p. 194. Reprint.

Coriery GuarpraN, The Courriéres bluebook. Vol. 92, 1906, p. 801. Editorial
comment on British report on Courriéres disaster. Refers to experiments on coal
dust in France, Prussia, and England. Concludes that Courrigres explosion was
due to dust.

Need for coal-dust experiments. Vol. 93, 1907, p. 204. Editorial comment

on report of Taldane, Hall, and Atkinson to royal commission on mines; advo-

cates experimental investigations of value of watering and of dust-free spaces.

Tests at Altofts. Vol. 96, 1908, p. 407. Describes experiments at Altofts;

purpose of experiment station.

- The British coal-dust experiments. Vol. 98, 1909, pp. 217-221. Mentions

experiments at Altofts with stone dus

‘West Stanley colliery explosion. Vol. 98, 1909, pp. 318-819. Reprint of

official report by Redmayne and Bain.

West Stanley colliery explosion. Vol. 98, 1909, p. 363. Review of report of

yne and Bain.

ish coal-dust experiments. Vol. 98, 1909, pp. 673-678.

Darran colliery explosion. Vol. 99, 1909, p. 765. Describes a coal-dust explo-

sion in Wales. Review of report by W. N. Atkinson and F. A. Gray.



184 THE EXPLOSIBILITY OF COAL DUST.

SELECTED BIBLIOGRAPHY.
1800-1870.

Bax, Jonn. On the fires that take place in collieries. Edinburgh New Philo-
sophical Journal, vol. 5, 1828, pp. 101-121. Notes that gas explosion might fire
“the small dust of the roads in the mines” (p. 102).

Boroura, . Traité complet de mécanique appliquée aux arts, Paris,1818. On
p. 197 is a description of a Niepce engine, which had a piston impelled by the
the explosion of a mixture of coal and resin dust.

Buppie, JonN. Account of an explosion which took place in Jarrow colliery on the
3d of August, 1830, Trans. Northumberland Nat. Hist. Soc., vol. 1, 1831, pp.
184-205. Refers to ‘‘ charred coal dust.”’

Du Souren, ———. In a report in 1855 as government engineer of the St. Etienne
Department he noted the part played by dust in an explosion at the Charles pit,
Firminy, Loire, France, August 29, 1855. First notice in France of coked dust.

Farapay, Mictazt, and Lyext, Cuartes. Report on the explosion at the Haswell
collieries. Philos. Mag., ser. 3, vol. 26, 1845, pp. 16-35. Point out evidence of
coal dust taking part in explosion, First decided opinion on subject.

Greenweut, (i. C. Use of gunpowder in mines. Trane. Manchester Geol. Soc., vol.
10, 1870, pp. 20-27. Notes probability of blown-out shots igniting coal dust.

Hopeson, J. Fossil fuel, collieries, and the coal trade. 1820. Describes (p. 256)
dust cloud and coking of dust at Felling colliery explosion, 1812.

VerPuiteux, ———. Sur une systéme des portes destinées 4 limiter les accidents.
produits par le grisou. Bull, Soc. Ind. Min., vol. 9, 1864, p. 466. Annales des
mines, ser. 6, vol. 12, 1867, pp. 561-566, Says fine coal dust in some mines spreada
explosions; speaks of coked dust.

1871-1880.

Borat, A. Les houilléres en 1872, Contains notes from Jutier, chief mining en-
gincer of the Department of Sadne-ct-Loire, dated March 21, 1872, stating belief
-that blown-out shot can ignite fine dust like that of coal from Sainte-Marie seam.

Desmrer, P., and Cuanseite, J. De influence des poussitres charbonneuses dans
les explosions de grisou. Bull. Soc. Ind. Min., ser. 2, vol. 4, 1875, p. 205.
Review of discussions at mecting of society 1872-1875. Early observations of
Du Souich and other French engineers. Describes experiments made by society
in February, 1872, and March, 1875. Translation by W. Galloway in Iron,
January 26 to March 23, 1878.

Enaineerine anb Mixine Jounnat. Influence of coal dust on the explosiveness of
fire damp. Vol. 21, 1876, p. 199.

’. M. Notes on the West Virginia asphaltum deposits. Am. Jour. Sei.,
ser. 3, vol. 6, 1873, p. 409. Notes explosibility of grahamite dust.

Gatioway, Wiutam, On the influence of coal dust in colliery explosions (I). Proc.
Roy. Soc. London, vol. 24, 1876, pp. 354-372. Describes experiments with coal
dust and lamp flame. Concludes that less than 1 per cent of fire damp will make
fine dry dust inflammable.

——~ Influence of coal dust in colliery explosions. Eng. Min. Jour., vol. 22, Sept.
16, 1876, pp. 158-187. Reprint from London Mining Journal of abstract of paper
before the Royal Society of London.

Role dea poussires de charbon dans les explosions de grisou. Auuales dea
mines, ser. 7, vol. 11, 1877, pp. 229. Translation of paper before Royal Society,
London, 1876.

-—— De V’influence des poussitres charbonneuses sur lea explosions dans jes
houilléres, Bull. Soc, Ind. Min., ser. 2, vol. 6, 1877, pp. 799-830.



60 THE EXPLOSIBILITY OF COAL DUST,
AMOUNT OF MOISTURE IN MINE AIR,

The rapidity with which water throws off vapor up to the point of
the saturation of the adjacent space is remarkably demonstrated in
mines. Technically, the air has not a capacity for moisture, and
does not become saturated with it, the aqueous vapor filling a given
space with practically negligible reduction in the quantity of air in
the same space. The moisture may properly be spoken of as partly
or completely saturated, but for brevity it is usual to speak of the
“moisture carried by mine air’ or of the “relative humidity of the
air.”

Repeated observations of the amount of moisture carried by mine
air, as measured in percentages of the amount of saturation for
the observed temperature, have shown that the air current, after
traveling about the mine, has a relative humidity of 80 to 100 per
cent. In mines in this country the “return” air current near the
outlet rarely, except in the dry climate of the Rocky Mountain region,
shows less than 90 per cent of saturation, even in a mine that has
appeared dry.

A group of observations made in the mines of a considerable num-
ber of States and averaged for each State are shown in the follow-
ing table:

Average of humidity observations during March and April, 1909, in dry and more or tess
dusty coal mines,

i
Temperature. | Retative mumidity.| Water ex | Water exe
tracted 1 "tracted
Num. | Series of 7 trom due | ena
State. ber af | obsere { sal
mines.| Hons. | Triake, | Return. | Intake. | Return, | Bet 10000
tubteteet. |, i023,
of air.
oe [Pererat.| Percent.| Guttons, | cations
. 5 3 9 O34 237 3.300
3 3 ay 4.70 |
x i is 4
Q 4 5 4
Colorate i 1 70 “
West V 9 fy a 2
Virginia L 1 at 3.
Perinsylvania 1 4 4” L
‘otatl...f aa Wo
Average 0)... cts Es w
4 The last colnmn fs based on the assiimption thal the average volume of the ventilating eurrents of the

‘mines was 100,000 enbie feet per minute.

These observations were chiefly made in March and April, 1909,
when the conditions contrasted much less than they would in winter.
Tt will be observed that the relative humidity of the return air is
nowhere less than 90 per cent, except in the New Mexico and Colorado
mines, where the relative humidity of the outside air is normally very
low. Therefore the effect of air currents of a relative humidity


82 THE EXPLOSIBILITY OF COAL DUST.

steam in the main entrance was not used during the day because the
fog produced was so dense that it would not have been possible to
use the road for haulage—the main intake coming in on that road.

QUICK-FLAMING EXPLOSIVES.

The report of the Prussian fire-damp commission in 1885 stimulated
the research in Germany for the development of explosives which
would not ignite fire damp and coal dust under ordinary conditions.
Sir F. Abel in his paper on mining accidents and their prevention in.
1887, expressed the belief that the explosives then being introduced
in Germany, robuite, securite, and carbonite (in its original form),
were not flameless, and he did not consider them promising means.
He advocated inclosing the explosive in water cartridges and similar
devices. Nevertheless, the improvement and development of the
so-called nonflaming explosives proceeded so actively in Germany that
by 1890 they began to be regarded as the proper explosives to be used
in coal mines.

The report of the British royal commission in 1894 in mentioning
“flameless explosions”’ says (p. 25):

Many different patent explosives have been brought to the notice of the commis-
sion. The so-called “flameless explosives” are largely in use in all parts of the
country and as the result of practical experience are generally pronounced to be
effective substitutes for gunpowder, and certainly very much safer. Each of these
compositions has its advocates and each is said to be flameless or practically so. As
far as dust is concerned, the current opinion appears to be that. they are perfectly safe,
but there is considerable doubt as to how far the small flash or scintillation, which many
witnesses say they display, renders them dangerous in the presence of gas.

By 1896 the agitation for better mine explosives caused the passage
of a coal-mine regulation act in England, under which authority was
given to prohibit the use of dangerous explosives, and an explosives
testing station was established at Woolwich in 1897. Since that time
all explosives used in gaseous or dusty mines must pass the tests at
the Woolwich station. Those that pass are placed on the list of ‘‘per-
mitted explosives.”

In Germany a station for the testing of mine explosives in the pres-
ence of gas and dust mixtures had already been opened in 1894 at
Gelsenkirchen, Westphalia, under the direction of a government en-
gineer.* The German mining department does not allow the use of
long-flame explosives in coal mines.

A station similar to the German one was established by the Belgian
Government at Framerics in 1902. The Belgian mining department
publishes lists of explosives which have passed the required tests.

Austria has a station at Mahrisch-Ostrau in whieh explosives are
tested by discharge, not from a cannon, but while suspended in the
gallery. ThisGovernment also has a “permitted”

For deseription see p. 19. © For description sce,


SPECIAL FEATURES IN DUST EXPLOSIONS. 113

SPECIAL FEATURES IN DUST EXPLOSIONS.

At the face of headings or rooms what has been termed stalactitic
carbon is found hanging in long threads from the roof. This is
evidently the result of an insufficient-supply of oxygen to allow
complete combustion, and of subsequent deposition in still air.

In the typical explosion the great variation in the manifestation of
heat is one of the curious features. At one point the heat appears
very intense, at another there appears to be a complete dying away
of the flame. Every observer has noticed that at certain points,
where there can be no question that the flame has passed, blasting
powder in cans has not been ignited. In some instances the powder
has been upset on the ground and the grains scattered, but it has not
always been burned. The upsetting may have been done after the
passing of the flame by the subsequent rush of gases. It very fre-
quently happens that an explosion passes by brattice cloth or sight
strings (for alignment of entries) without igniting them. One obvious
reason is that such cloths are generally damp and the time of exposure
is momentary. Another reason is that immediately preceding the
flame there is undoubtedly an air wave, which throws any loose canvas
or string flat against the roof or ribs. In the majority of explosions
it appears that the flame rarely fills the entry from side to side, but
zigzags along, more or less in the center of the entry, striking the
walls only here and there. This is also the manifestation in the
Pittsburg gallery when mine road dust with high ash content is used
and the flame is partly blanketed by the excess of ash.

The belief has prevailed very generally among mining men that
because a dust explosion is usually manifested in the intake entries the
explosion “feeds on the fresh air” or advances against the air current.
When it is considered that the oxygen content of the return air of the
average mine in this country rarely shows a decrease of more than
one-half of 1 per cent of oxygen from the normal, and that the com-
bustion of coal dust would not be seriously affected unless the defi-
ciency excecded 2 or 8 per cent or possibly more, it is clear that there
can be little real basis for this impression, ‘The idea has also been
expressed that the action of the fan, blowing or drawing in fresh air
to support the flame during the progress of the explosion, accounts
for the greater destruction at the intake frequently manifested. But
since the speed of a dust explosion, measured over only a short dis-
tance from the origin, as indicated by the Altofts experiments, is
sometimes 1,400 feet per second,* a rate presumably less than when
the explosion is under greater headway, and since the speed of the
ventilating current would be at most one-sixtieth part of that rate,
it is obvious that the fresh air introduced during an explosion can

4 A velocity of 2,000 feet per second over a short, distanoe is indicated by a later experiment at Altofts,
and a velocity of 3.300 feot per second after 1,600 feet of travel Is reported from Liévin.

88006°—Bull. 20—11 8



EXHAUST STEAM AS A PREVENTIVE. 177

atmospheric temperature. The unknown factor makes the applica-
tion of an equation impossible.

The fact demonstrated by these observations is that radiation from
the side walls has considerable effect in raising the temperature of the
air. In this particular test in 4,000 feet of mine entry over 30,000
British thermal units had been radiated per minute, which would be
equivalent to heat derived from burning over a ton of coal per day.
It was the utilization of this radiated heat that led to the abandon-
ment of the preheater. This can be done in every mine where the
air travels over 3,000 feet at a velocity not to exceed 500 feet per
minute before it reaches the men to be served with ventilation. For
example, in the mine in which the observations were made, if suffi-

snonpetvecceeneetaae=

aan : i”

1 |

¥:

Volume in cubic feet.

Temperature of air current (Fahrenheit)

ve
i_| | | |

{ at. —.
FOO 400 G00 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 300032003400 360036004000
Distance from fan (blowing) in feet

Ty

20"

FIGURE 23.~Progressive change of temperature of air current due to radiation. Average velocity, 453
feet per minute; volume of air, 06,432 cubic fect per minute.

cient exhaust steam were introduced at tho end of the 4,000 feet the
additional heat would raise the temperature to or above the normal
mine temperature, even with an outside temperature of 25°. The
conditions for complete saturation would be continuously in force,
and the result would be a wet mine, not only theoretically wet, but
looking and feeling wet enough to satisfy the practical man. There
is, however, serious objection to carrying an exhaust-steam line 3,000
or 4,000 feet into a mine, on account of the back pressure on the
engine and the probability of adverse grades; in fact, the practical
difficulties in the way are sufficient to condemn the method. It is
possible, however, to avoid this objection by a sacrifice of part of the
moisture.
88006°—Bull. 20—11——.12



116 THE EXPLOSIBILITY OF COAL DUST.

experiments are mentioned because of their historical interest and
some of the most recent on account of their great importance in
furnishing quantitative data.

EARLY EXPERIMENTS OF GALLOWAY.

Galloway* was one of the first to study this question from the
experimental side. His experiments were carried out in a wooden
box 5.71 meters long and 0.305 by 0.0152 meters cross section, through
which a regulated current of air was passed. A hopper placed at
one end served to introduce the dust, which was then carried by the
air current 2 meters to a naked flame. Two kinds of coal dust were
used, of the following composition:

Composition of coal dusts used in Galloway's experiments.

Carbon (C),

Hydrogen (Hig)...0.0.7 an DIU
Oxygen (02)
Nitrogen (Ns).

Galloway’s first conclusion is thus stated by him:

The results of these experiments and others which T have since made indicate in
a conclusive way that a mixture of air and coal dust is not inflammable at ordinary
atmospheric pressure

However, on investigation he concluded that suspended coal dust
could cause the explosion of a mixture of air and amounts of methane
too small to be explosive in the absence of the dust.

IGNITION OF DUST FALLING ON FLAME.

Marreco and Morison? record certain crude observations made by
persons whose names are not given, in which the tendency of coal
dust to inflame was studied by allowing 5 liters of the powder to
fall from a height of 6 meters upon a strong gas flame and noting the
effect. Some of the dusts were ignited, and flame emitting much
heat rose at times to a height of 10 meters. Other dusts were less
inflammable, while still others failed to ignite at all. Professor Abel
made certain experiments on ten different samples of coal dusts in
an apparatus similar to that used by Galloway, with results entirely
negative.

# Proc. Roy. Soe, Londoa, 1876, p. 168; Annales des mines, ser. 7, vol. 11,18
tale, Sor, 2, vol. 6, 1877; vol. 7, 1878, p. G17; vol. 9, 1880, p. 157.
® North of England Inst, Min, and Mech. Eng., 1879, p. 92.

p22; Bull. Soe. ind. ming



ORIGIN AND DISTRIBUTION OF COAL DUST. 35

or machine and then shooting—we have no authoritative figures as
to their relative production of dust.

DUST FROM HAND AND FROM MACHINE UNDERCUTTING.

In the process of cutting coal by hand and by different types of
machines, some tests have been made by private interests and their
results made public.

Tests of the production of dust in undercutting by hand, by chain
machines, and by air punching machines in the Pittsburg seam were
made by the late B. F. Jones. Mr. Jones published his results in the
March, 1908, issue of Mines and Minerals (p. 397). The tests were
made in three adjacent ‘‘butt”’ rooms in the Westmoreland mine,
Pennsylvania. The undercutting by each process was conducted in
a separate room, and in each case was 4 feet 3 inches deep and as
wide as the room (15 feet). The height of undercutting with the
puncher was 11 inches at the front and 3 inches at the back, and with
the chain machine 4 to 4} inches throughout. The seam was 6 feet
thick.

The same total amount of coal was assumed to have been produced
from each room (15.68 tons of 2,000 pounds). ‘The results, reduced
to tabular form, are as follows:

Weight of cuttings and percentage of total coal mined by different methods, as determined
in experiments at Westmoreland mine, Pennsylvania.

—— ee T
1 Cuttings passed
‘Total euttings. 1 through 1emesh. | through 4-mesh.
‘Method. |

Cuttings passed

Pounds. | Per cent,| Pounds. | Per cent.| Pounds. | Per cent,

Puneber.._-

3,436 | 10.95 758 | - 2.40 304 2.280
Chain machin 1,836 5.86 233, 1.06 155 1494
Hand pick... 4/583 | 14.45 349 rete 128 1408

Evidently these figures did not include the dust produced in shoot-
ing down the coal and in loading it on pit cars.

With dust defined as coal that. will pass through a 20-mesh sieve,
these figures indicate that the amounts of dust made by the three
cutting processes would be slightly less than 2.40, 1.06, and 1.11 per
cent of the total coal to be produced by the undercuts.

Some tests * were made by the Fairmont Coal Company in one of
their mines working the Pittsburg seam in the Fairmont district,
West Virginia, The undercutting was done with electric punching
machine and breast chain machine. One working face in which the
coal was soft was cut by each machine, and in another part of the
mine where the coal was harder similar cuts were made. The

4 Described by ©. E. Scott in Mines and Minerals, May, 1908, p. 477.


146 THE EXPLOSIBILITY OF COAL DUST.

Results of second series of experiments with explosive coal dusts at Pittsburg station —Cont’d.

Source and proximate analysis of coal dust used and pressure
developed in tests,

Results of tests.

Weight [quivatent | Effect on stot
applied, | per sq. cm
Grams, .
9. Bituminous coal, coking, from Gem mine, Campbell County, 250 649 | Not lifted.
‘Tenn. (Lab. No. 9782) 370 ail] Do.
Moisture... . 358 Mo 303 Do.
Volatile matte 3418
Fised carbon : Til Bal 98
Ash... 7.26
Sulphur. 4
Pressure developed, less than 140 granis per square centimeter.
i
10. Bituminous coal, steam and domestic, from, Wooldrldge 20 | 649 | Lifted.
mine, Campbell County, Tenn, (Lab. No. $786): 300 791 "Do.
Moisture. : - 320 SL | Not lifted.
Volatile mnatter..2.220000020002 310) 805 | Lifted.
Fixed carbon : 32 B10 | Not lifted.
Ash.
Sulphar!
Pressure developed, a8 grams per square centimeter. i
i
|
11, Bituminous coking, hi carton coal trom fed mine, MeDow-| 250
. a. (Lab. No, 10084) 100
Volatile matter:
Rive carbon. 2002-2 77.65
Ash. : GR
Sulphur Tl
Pressure developed, Inss than 259 eramis per Sqptare centimeter
42, Bituyninons coking, high calm co from Ek TRkdge ste, 250
McDowell County, W. Va. (Lab, No, 10085 100
Moisture... . 20
Volatile matters) H 10
ised carbon i 105,
Ash... I 102
Sulphur. 58 !
Pressure developed, 242 grams per squire centimeter ;
13. Bituminous, noneoking coal from Woodside anine, Sanga- 230 aug | Not ifted,
mon County, Ill. (Lab. No. 974) 235 584
Moisture. 13.43 on 519 vated
Volatile matter 35.00 210 BAS
Bixod carbon. : 41.53 2 £50 | Not fitted.
Ashe... i 024
Sulphur, 3.48 {

Pressure dev eloped, ‘548 grams per Square centimeter.

14. Bituminous, noncoking coal iro
Vermilion'County,, IL (Lab. 5
Moisture... 2.
Volatile matter,
Fixed carbon. :

m Jie Vermilion mine,
3. 100371:

13.92
33.24

Ash...
Sulphar : a)
Pressure developed, 522 grams per square cenitmeter.

ing coal from Navaju mine, N. Mex.

15. Subbiturninous noncol
(Lab. No. 1003

Moistare.
Volatile matier,
Figed carbon.
Ash
Sulphar i a

Pressure developed, 730 grams per square cenfimeter

Not Hifte
Lifted,

Do.
Not lifted.



INVESTIGATIONS AT EUROPEAN STATIONS. 163

length of stemming is fixed at 20 centimeters. All cartridges must
have the exact composition printed on their wrapper. Other pre-
cautionary measures in connection with shot firing remain in force.

Speaking of results generally, the ‘‘charge-limite” of permitted
explosives fell in proportion to the increase of volatile matter con-
tained in the coal dust. When inert dust was added the ‘‘charge-
limite”’ rose.

EXTENSION OF GALLERY.

The gallery at Frameries has now been extended to a total length
of 80 meters in one direction. ‘The extension is connected with the
old gallery by a section detachably bolted to both (fig. 18). When
the full length of gallery is not required (for example, for testing
explosives), the connecting piece, which rests on rails, is transversely
run out of position. The annexed plans (figs. 19 and 20) show fur-
ther proposed extension and details of construction.

INVESTIGATIONS IN PRUSSIA.

According to a recent announcement, the Coal Mining Corporation,
of Westphalia, has decided to erect a trial gallery after the Liévin
and Altofts type for the investigation of coal-dust explosions. The
gallery will be built at Gneisenau, near Dortmund, where land has
been bought for the purpose, and will be under the charge of Berg-
assessor Beyling, the present director of the Gelsenkirchen explosives
testing station, which will also be removed to Gneisenau. The entire
works will be completed in the spring of 1910. The Gneisenau coal-
dust gallery will in all probability be of similar construction to that
recently adopted at Liévin--an upcast section of armored concrete
and a downcast gallery of 10-millimeter plate boilers, although for
the latter portion some mining engineers are in favor of wood con-
struction, which could be repaired more easily and at less cost.
There will be two parallel lengths of gallery with crosscut connections
at varying angles. A total length of 300 meters is mentioned.

Save such work as was feasible in the short Gelsenkirchen gallery
(34 meters), more particularly in respect to the testing of explosives,
no special study of coal-dust explosions has proved practicable at
Mr. Beyling’s station, but the matter will be taken in hand immedi-
ately when the new station is ready.

Preliminary tests with local coal dust have shown that while dust
containing 24 per cent of volatile matter and passing No. 150 mesh
was regularly ignited by 160 grams of gelatin dynamite, no ignition
of the same dust took place when the gallery had been previously
watered.


THE COAL-DUST QUESTION IN EUROPE. 11

HISTORICAL REVIEW OF THE COAL-DUST QUESTION IN
EUROPE.

OBSERVATIONS IN ENGLAND PRIOR TO 1850.

In the published account of an explosion in an English colliery,
Wallsend, on September 3, 1803, J. Buddle, chief of the Newcastle
coal miners, says: ‘The workings were very dry and dusty, and the
survivors who were most distant from the points of explosion were
burnt by the shower of red-hot sparks of ignited dust which were
driven along by the force of the explosion.”

Robert Bald, in Jameson’s Journal for 1828,¢ mentions the possi-
bility of the flame from a fire-damp explosion igniting the coal dust
strewn more or less thickly about the working places of a colliery.

In a book by W. N. and J. B. Atkinson, English inspectors of
mines, entitled ‘Explosions in coal mines” (1886), page 132, there
js a list of mine explosions in England prior to 1870, made from
contemporaneous newspaper reports and inquest records. In certain
explosions it was mentioned that coked dust was observed. Besides
the explosion above noted, it was reported to have been found at
the Jarrow explosion of August 3, 1830, at the Wallsend explosion
of June 18, 1835, at the Springwell explosion, December 6, 1837, and
at the Thornley explosion, August 5, 1843.

Professor Faraday, the famous chemist and physicist, remarked in
his report on the Haswell colliery explosion, September, 1844:

In considering the extent of the fire from the moment of explosion it is not to be
supposed that fire damp was its only fuel; the coal dust swept by the rush of wind
and flame from the floor, roof, and walls of the works would instantly take fire and
burn if there were oxygen enough present in the air to support its combustion; and
we found the dust adhering to the faces of the pillars, props, and walls in the direction
of and on the side toward the explosion, increasing gradually to a certain distance
as we neared the place of ignition. The deposit was in some parts half an inch, in
others almost an inch thick; it adhered together in a friable coked state. When
examined with a glass, it presented the fused round form of burnt coal dust, and
when examined chemically and compared with the coal itself, reduced to powder,
was found deprived of the greater portion of the bitumen, and in eome instances
entirely destitute of it. There is every reason to believe that much coal gaa waa
made from this dust in the very air itself in the mine by the flame of the fire damp
which raised and swept it along, and much of the carbon of this dust remained
unburnt only from want of air.

It may be remarked that many investigations of explosions since have
established that coked and caked coal dust is more generally, though
not invariably, deposited on the side of timbers and projections
opposite to the direction from which the explosive wave approached.
This is commented on by W. N. and J. B. Atkinson.>

a Final Rept. Accidents in Mines Comm., 1886, p. 30.
‘Explosions in coal mines, p, 25.



188 THE EXPLOSIBILITY OF COAL DUST.

AusrriAN Commission on Fire Damp. Report. Vienna, 1891.

Baumaartver, Kart. Coal explosionsat Haustram, Bavaria. Trans. Fed. Inst. Min.
Eng., vol. 19, p. 505.

Bearp, J.T. The explosion at Cedar mines, Iowa. Colliery Engineer, June, 1893,
p. 255.

Bevson, P. P., and McConnett, Wituta. Notes on gases inclosed in coal and coal
dust. Trans. Fed. Inst. Min, Eng., vol. 3, 1892, pp. 307-310.

-—— Contributions to our knowledge of coal dust. Trans. Fed. Inet, Min. Eng.,
vol. 7, 1894, pp. 3.

Bera- unp HiirrenmAnniscues Janrpucu. Uber die Ursache der Entstehung von
Explosionen in Braunkohlen Briquette-Fabriken. 1891, pp. 357-358. Conclu-
sions of Holtzwart and von Meyer.

Leackerr, W. C. Combustion of oxygen and coal dust in mines. Trans. Fed. Inst.
Min. Eng., vol. 7, 1894, p. 54.

Broockmany, K. Uber die in Steinkohlen cingeschlossenen Gase. Gliickauf, Aprii
1, 1899

Bexverr. Coal-dust explosions in mines. Report Kansas State Inspector of
Mines. 1895, pp. 171-195. Good review of literature.

Cuesyeau, G. Note sur les resultats des travaux ‘de la commission autrichienne de
grisou. Annales des mines, ser. 9, vol. 1, 1892, pp. 239-264.

Clowes, Frank. Coal dustin mines. Colliery Engineer, vol. 13, 1892, p.6. Abstract
of lecture at Nottingham, England.

Cotuery FE. ‘R. Report of the Prussian fire-damp commission, Vol. 11, 1890~
1891, p. 209. Reprint of report of A. Hasslacker from the Colliery Guardian.

The Roslyn disaster. Vol. 12, 1891-1892, p. 255,

The McAlester disaster. Vol. 12, 1891-1892, pp. 157-160.
—The dust theory. Vol. 12, 1891-1892, p. 59. Extract from prize paper of J. L.
Williams on the Prevention of accidents in mines.

-—— Cval-dust and colliery explosions. Vol. 12, 1891-1892, p. 151. Abstract of
lecture by HL. B. Dixon at Manchester, England.

I dust. Vol. 13, 1893, p. 251. Reprint from the Colliery Guardian of de-

scription of a sprinkling car.

-Coal-dust explosions. Vol. 15, 1894-1895, p. 86. Notice of report of royal

non explosions due to coal dust in mines.

——- Explosions due to cual dust in mines. Vol. 15, 1894-1895, p. 39. Refers to
finding of royal commission on explosions due to coal dust. in mines.

——- Will coal dust explode? Vol. 15, 1894-1895, p. 132. Refers to Galloway's

experiments in December, 1894.

An ignition of coal dust in the No. 7 Eureka mine. Vol. 16, 1895-1896, p. 208.
~ - Interesting experiments with coal dust. Vol. 15, 1894-1895, p. 68. From Coal
and Iron Trades Review. Refers to experiments by Cailyn Jones, at Lowe
Dutiryn collieries, Wales, August, 6, 1894.

-==- Colliery explosions produced by coal dust. Vol. 16, 1895-1896, p. 160. Com-
ment.en explosions cited by F. M. D, Stuart.

Effects of different explosives on fire damp and coal dust. ” Vol. 16, 1895-1896,

p. 39. Abstract of paper by Winkhaus before North of Englaud Institute of

Mining Engincers.

Mining methods, air coursing, and return to haulage—how the cars produce

coal dust. Vol, 16, 1895-1896, p. 138.

Colliery explosions and coal dust. Vol. 16, 1895, p. 204. Notice of paper by

Ashworth, in Colliery Guardian.

GUARDIAN. Method of preventing coal-dust explosions, Vol. 61, 1893,

comm

Vol. 61, 1891, p. 13.
otes by Henry Hall.

———~ Coal dust in mines. Vol. 61, 1891, p. 97:



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 131

the two vessels. The screw cock ¢ is then opened until the air con-
tained in A is compressed to a definite pressure indicated by the ma-
nometer D. This pressure was varied in the course of study of each
sample. After the proper pressure was secured in A and the apparatus
was connected up as indicated, the passage of the spark between the
terminals ¢ i is started. H is then quickly opened and closed and
the character of the explosion observed. The character of the ex-
plosion is indicated somewhat by the behavior of the water closing
the open end of m.

Eight samples of dust were tested. The results of these exper:
ments and the analyses of the dusts are given in the two following
tables. The samples were collected from various parts of the briquet-
ting plant, put through a fine sieve, and dried for a long time over
sulphuric acid. To remove the last of the moisture the samples were
heated to 60° or 70° before analysis.

Results of experiments by Holtewart and Meyer with explosions of lignite dust.

Results of tests for specified pressures of air in A in
‘contimeters of mereury.
Sample

Ne Remarks,

2 centimeters [3 centimeters |& centimeters. 8 contimeters

2negative,1 | Inegative, 1 | 2 negative...i Negative....| Tendency to explode small; in 8 ex-
very weak.| weak. periments 6 negative.

2 negative. | 2 negative...|.....do...-..|.....d0.... «| Noexplosion.

3 | 2negative,i|.... fa02 222) {| Dust'not inclined to explode.
very weak.

4/2 wots view) 2 very vio- [2 very vio-] 2 very vio |

4 lent Tent {

5 | ancgutive...| znegutive...| 2negative,1 | Negative....! In 7 experiments 6 negative.

6 | 2uegative,1/2 cather/2 rather! 2 rather | Sample inclined to explode; in 9 ex
weak. strong. strong. strong. perituents 7 positive,

1 gstong.... astrong.....] 2strang.....] 2strong.....| Dustexplosion very strong.

8] 2 strong, i |..-.do...2. 2. do, oo.

\

|
negative. *
i

Analyses of lignite dusts used in experiments by Holtewart and Meyer.

Ash. | 0. | Hs. | Nn On
-] 1608] so.09] 515) 9.93 16.92
ion ee era! 10 16
i465 473| 0 l74 19.60
- - 5.5 1 286 22.80
ny 9a Bet 115 31.43
seaeenren ee 5% 12r 23.67
. wee 6.12) 4.66 | 101 26.15
\Ash-lree. mn nae 496) 121 78
jComplete. 7.08 4.53 1,22 27.01
Ash-tree m asm | 1:53 29.04

A glance at the above table shows a great difference in the conduct
of the coals with respect to their inflammability. There is, however,
no apparent connection between their explosive character and their


INVESTIGATIONS OF tHE IGNITION OF COAL DUST. 1389

and by furnishing inert matter which must be heated up before
inflammation occurs. The results, summed up in a table, have been
given in an earlier part of this bulletin (p. 48). It is seen by inspec-
tion of this table, that of the eight dusts investigated, inflammation
was obtained in all but the anthracite and Lens 2. The inflamma-
bility of the others was found to be greater according as they con-
tained more volatile matter. The four types richest in volatile
matter ignited at low densities, and the violence of the inflammation
increased with the density of the cloud of dust. The point of greatest
interest in connection with this work is the fact that inflammation
and propagation of the flame throughout the available length of the
gallery took place with a comparatively low density of dust, such as
in mining conditions would be considered as indicating a compara-
tively dust-free gallery.

Since the publication of the preliminary bulletin containing the
results of work done in the small gallery, further work has been done
in this same gallery, and in one much larger. This work, however,
is considered in another part of this bulletin (pp. 86-90).

In discussing the results of his work, Taffanel enters somewhat
into the chemistry of dust explosions. No measurements of the
pressure produced in the gallery, or of the velocity of propagation
of the flame were obtained, because the necessary apparatus was
lacking, but analyses of samples of gas taken from the gallery during
the explosion have thrown much light on some of the problems
involved.

Attempts to obtain samples of the gas after the explosion gave
uncertain results because of the reentrance of fresh air. The method
that was found satisfactory was to introduce into the gallery a closed
glass tube, which communicated with an evacuated vessel outside of
the gallery. By means of a detonator and instantaneous fuse, which
was ignited by the passing flame, the closed glass tube was broken,
and the evacuated vessel was filled with gas from the gallery in a
fraction of a second. Analysis of this gas showed the presence of
nitrogen, carbon monoxide, carbon dioxide, oxygen, and at times
smal] quantities of methane. The distribution of the oxygen con-
sumed between the carbon and hydrogen of the dust was obtained
by deducting from the oxygen present in the beginning that con-
sumed by the carbon plus that remaining free. The amount of
carbon and hydrogen burnt per unit volume being known, and the
amounts of the various constituents to be heated by this combustion,
it was possible to calculate the theoretical temperature of the flame.
This calculation gave a temperature ranging from 1,000° to 1,700° C.

The amount of carbon dioxide found, except when large amounts
of dust were used, was much greater than the amount of carbon
monoxide, and the absorption of heat, which takes place in the


INVESTIGATIONS OF THE IGNITION OF COAL DUST. 143

Results of laboratory experiments with explosive coal dusts at Pittsburg station.

Distance |i | Distance
No. of i No.of |
Character of coal. exper: | Pall was | Character of eoat. expert | Pal was
ment. | 5 2rey. ment, | ;
om, |)
1 ‘ais |, 1
Pennsylvania bituminous. ..} 2 {| New Mexico bitumninous...... 2
3 5 E
| 1 ‘2 1
IMinols bituminous, nonooke | 2 Xentucky eannel ae
| 3 | Texas lignite N 3
Inns bituminous gas coat. nal 1 | 1
Montana bituminous + rf | Dakota lignite... e+ 3
1 5
West Virginia bituminous. ... 2 8
3
| Solorado ign af
Alabama bituminous A ra Colorado lignite... | 3:
{ i

In the above tabulation no account is taken of the moisture or ash
in the coals, nor of any deterioration of any of the samples that may
have taken place before or after powdering and storing in bottles.
As shown in the table, lignites generally exhibited greater irregu-
larity of results. The coals are not greatly differentiated here, prob-
ably because the heat supplied by the wire was too great in compari-
son with that supplied by the dust in burning, so that the differences
of the dusts were masked.

The photograph reproduced in Plate VIII, B, was taken during one
of the experiments. The flame observed has been in every test ap-
parently confined to the upper half of the 2-liter bottle, as shown
here. Consequently, the density of the mixture of dust and air at
which the ignition occurred is not 0.04 gram of ‘dust in 2 liters of
air, but greater than that, 0.04 gram in less than 1 liter. Further-
more, the phenomena can not be considered as indicating indefinite
propagation of the flame in an atmosphere containing the same
density of dust, but only indicate propagation in the available space,
and under the conditions of these experiments. It may be desirable
to add that the inflammation was in all tests practically instantane-
ous and similar in appearance to the ignition of a slightly explosive
gas mixture.

A great deal more work would have to be done before any positive
statement could be made concerning the relative behavior of differ-
ent coals. The same is true with respect to the effect of variations
in the current used, and in the pressure with which the dust is brought
into the bottle. A definite strength of current does, however, seem
to be required for complete ignition, and beyond that strength varia-
tion of current has no effect. The initial pressure of the ignition mix-
ture is probably of considerable importance.



BUREAU OF MINES AULLETIN 20° PLATE WV

COKED DUST PRODUCED FROM 20 TO 40 MESH DUST.

Unused particles shown at the bottom. Photographed on half-inch squares. Experiment G-2987,


190 THE EXPLOSIBILITY OF COAL DUST.

Grurritm, D. Special report on the Sunshine coal mine explosion. Report of State
inepector of coal mines of Colorado, 1897-98. Mine free from gas. Blown-out
shot ignited dust.

HAARMANN, C. Watering coal dust at the Mayback Colliery (Germany). Trans. Fed.
Min, Eng., vol. 9, 1895, pp. 90-95. Describes plant and cost of installation and
maintenance.

Hatpane, J. S. The causes of death in colliery explosions. Trans, Fed. Inst, Min.
Eng., vol. 11, 1896, pp. 602-513.

Haut, Henry. Coal dust. Fed. Inst. Min. Eng., vol. 2, 1891, p. 415.

| dust and colliery explosions. Colliery Engineer, vol. 11, 1890-1891, p. 174.

‘ome aspects of recent colliery explosions. Trans. Fed. Inst. Min. Eng., vol.

11, 1896, p. 526.

Coal dust in mines. Important experiments on its explosive properties.
Colliery Engineer, vol. 14, 1898, p. 241.

Hatteux, ARMAND. The coal-dust question. Trans. Inst. Min. Eng., vol. 14, 1897,
p. 619.

arze, R. Automatic sprayer for preventing accumulations of dust in mines. Trans.
Ints. Min, Eng., vol. 18, 1899, pp. 113-119.

Hayes, Jouy. Explosions in coal mines. Colliery Guardian, vol. 75, 1898, pp. 217
and 402.

Herse, Fritz, anp THe, . Experiments on the ignition of fire damp and coal
dust by means of electricity. Trans. Fed. Inst. Min. Eng., vol. 27, 1899, p. 88; dis-
cussion, vol. 18, p. 183. Paper translated and abridged from articles in Gliickauf,
vol. 34, 1898, pp. 1, 25, 45.

Hewitr, RicHARDSON. New method of laying coal dust. Trans. Fed. Inst. Min.
Eng., vol. 4, 1892, p.494. Description of spray nozzle. Discussion, vol. 6, p. 497.

Hourewarr, Rup., AND von Meyer, Ernst. Ueber die Ureachen von Explosionen
in Braunkahlen-Briquettefabriken. Dingler’s Polytechnisches Jour., vol. 280,
1891, pp. 185 and 237.

Jici¥sKy, JARostav. Removal of coal dust by water spraying in Westphalian coal
mines and in those of the Saarbruck coal field. ‘Trans. Fed. Inst. Min. Eng.,
vol. 10, 1895, p. 546.

Marruews, D. I. F. On damping dust in mines. Trans. Manchester Geol. Soc.,
vol. 23, 1895, pp. 90-95. Describes sprays and spraying. Abstract of Jecture.
Colliery Engineer, vol. 15, April, 1895, p. 208.

Mives anv Miverats. Sunshine coal-mine explosion (Utah). Vol. 18, 1897-1898,
p. 291. Extract from official report of mine inspector.

Coal dust in mines. Vol. 19, 1898-1899, p. 572.

Ignition of fire damp and coal dust. Vol. 20, 1899-1900, p. 13. From report

of Heise and Theim.

Dust explosions in coal mines. Vol. 20, 1899-1900, p. 40. Extract from paper
by John Hayes.

Morrram, Tuomas H. Explosions of fire damp and coal dust in the west of Seotland.
Trans. Fed. Inst. Min. Eng., vol. 18, 1900, pp. 186-193. Discussion, pp. 390, 393.

Norta, S. H. Explosions from coal dust in English mines. Eng. and Min, Jour., vol.
37, 1894, p. 273.

Nortn oF ENGLAND Istitute oF Mining AND MECHANICAL ENatrers. Report of
the flameless explosives committee, 1896. Discussion, Trans. Fed. Inst, Min.
Eng., vol. 8, 1895, pp. 593-608, 227-235; vol. 9, pp. 115-118, 206-221, 274-280; vol.
10, pp. 38-44, 197-201, 492-496, 503-512.

Nova Scoria Commisston on Mine Fires. Report on fires in Pictou coal mines.
Halifax, 1896, 104 pp.

Oaxzey, SamveL, An explosion ina coal box. Colliery Engincer, vol. 12, 1891-1892,
p. 212.



10 THE EXPLOSIBILITY OF COAL DUST.

This bulletin, as is emphasized in the body of it, should be regarded
as a preliminary study of the coal-dust problem. The pressure of
other work and the almost continuous use of the explosives-testing
apparatus at the Pittsburg station for the important work of investi-
gating the relative safety of explosives for use in coal mines have
limited the experiments that could be made dealing with methods
of lessening the danger from coal dust. However, it is expected that
opportunity will be afforded in the future to take up systematic test-
ing in an experimental mine or underground gallery near Pittsburg.

ACKNOWLEDGMENTS.

The writer desires to express his thanks to Dr. J. A. Holmes,
formerly expert in charge of the technologic branch of the United
States Geological Survey and now director of the Bureau of Mines,
for the inspiration of the studies undertaken, and to Mr. H. M. Wilson,
chief engineer, for advice in the preparation and editing of the paper.

He also desires to acknowledge the great assistance given by his
associates in the mine-accidents division, Messrs. Clarence Hall and
J. W. Paul, Dr. J. K. Clement, Dr. J. C. W. Frazer, and the writer’s
assistants, Messrs. A. C. Ramsay and L. M. Jones.

The account of the investigations under way at experiment sta-
tions in Europe is by the late Mr. Axel Larsen, explosives expert,
who, in connection with his work for the Survey, visited these stations
and examined their equipment.

The chapter on the use of steam as a preventive of dust explosions
was prepared by Mr. Frank Maas, consulting engineer for the Con-
solidation Coal Company, and that on experiments with sprays in
Oklahoma coal mines by Mr. Carl Scholz, vice president of the Rock
Island Coal Mining Company. Cordial acknowledgment is made
of the interest shown by both these gentlemen in the study of the
practical aspects of preventive measures, and of their kindness in
preparing for presentation in this bulletin the results of their
observations.

The chapter on laboratory investigations of the ignition of coal
dust, by Dr. J. C. W. Frazer, a chemist of the Pittsburg station, gives
a review of the laboratory and other small-scale experiments that
have been made in the past, and an account of the laboratory experi-
ments undertaken by him, and to be continued, on the relative explo-
sibility of different coal dusts collected by mining engineers in dif-
ferent parts of the country.

The author's indebtedness to various foreign investigators is
shown by the numerous quotations from their published works.


42 THE EXPLOSIBILITY OF COAL DUST.

Although the sampling showed that a very small fraction of the
coal dust remained in suspension, the propagation of explosive wave
was proportionate in each instance to the total amount injected into
the gallery, indicating that a considerable part of the dust that had
fallen to the floor before the shooting was thrown into suspension
by the concussion of the shot and in time to assist in the propagation.
of the flame. Not all of the dust was burned and portions of it had
not lost all of its original volatile combustible matter, but the greater
part was more or less coked.

COKED DUSTS PRODUCED BY EXPLOSIONS.

The coked dust produced in these tests developed some interesting
peculiarities, as shown in Plate II. There are three types of coked
dust. The first consists of large globular pieces, with large interior
air cells and thin glazed walls, from one-fourth to three-fourths inch
indiameter. The pieces of coke shown in Plate II were photographed
on paper divided into half-inch squares, so that the actual size may
be sealed from these squares. This type of coke was evidently pro-
duced by the flame striking a mass of floating particles, the concussion
and heat causing them to cohere and distill their gas, the expansion
of which within the melted mass blew it into the globular forms
shown at the upper part of Plate II. These had time to cool and
harden before they fell to the bottom of the gallery.

The second type of coke, shown in the middle portion of Plate IE,
consists of masses of loose particles, which have fallen while still hot,
sticking to other masses and flattening on the floor of the gallery.

The third type, shown in the lower left corner of Plate IT, is not a
true coke but’ scales of particles evidently caked while lying on the
floor of the gallery. The upper side of those on squares J-4, K-4,
show minute bubbles of coke. The lower surface on square K-3
shows dust apparently little affected by the heat. These scales of
caked dust are not thicker than one one-hundredth of an inch.

EFFECT OF DEGREE OF COARSENESS OF DUST.

RESULTS OF TE

A series of tests was conducted in the explosion gallery of the
Pittsburg station to determine how course a coal dust may be that,
if abundantly present, will propagate an explosion that has been
started by ignition from a blown-out shot. The results are shown in
the two following tables;


112 THE EXPLOSIBILITY OF COAL DUST.

attained, which carries along everything loose. This action is shown.
by the scouring of the walls of the passageway. Facing edges are
rounded off, sometimes as if by a sand blast. The coke particles
may be reduced to fragments, and it is possible that the intensity
of the heat may effect a more or less complete combustion of the
fixed carbon of the dust and resultant coke.

Following such an explosion there is a continued outrush of burned.
gases, which often carry surplus dust and deposit it on the lee side
of projections, sometimes covering the coke just deposited.

Succeeding this outrush there is-a return rush to fill the vacuum
caused by the cooling of the gases. The return wave if strong may
pick up dust and redeposit it on the lee side of projections, or that
side which faced the explosion.

It must be remembered that in nearly all extensive dust explosions
an immense amount of dust is subsequently drawn out of the work-
ings and also created by the violence of the explosion. Moreover,
there is usually a great surplus along the pathway. In the average
entry 6 by 9 feet in section about 7 ounces of pure coal dust per
linear foot will if completely burned give the maximum explosive
effect possible with the air present. (See pp. 49-51.)

Typical analyses of coke from dust explosions, compared with analyses of the coal as mined.

[A. C. Fieldner, analyst.)

| Franklin No.2 mine, |
Miller (B) seam, Johns-, Primero mine, Las Apimas County, Colo.

town, Pas

7 1 T

1 2. 3. jou %.

i i

t } ‘ -
Sample as received: H i

M eevee] 1.28] 0.71 1} 3.47] ssg! aa] 4.90) e62
olatile matter 19.88 | 11.00 421.93) 24.331 18.98; 12.68) 20.49
Fixed earbon . | 6S11 | 67. 31.17 | 42.97, 58.120 45,22 55. 66.
ASD eee eeeceee sie) 10:73 | 20155 4413 | 28.96! 937° 37.01) 17.33

| 199.00 | 100.00 | 100.00 |"100..00 | 700.00 | 10.00 , 100.00 , 100.00 | 109.00

and ash free: i
tile matter. 22.00] 14.09] 13.89, 36.06) 40.51] 36.34, 24.43 (e210) 26.91
Fixed carbon. 77.40 | 85.91 | 86.11 41 50.49] 63.66 ; Te

Fi eTsiO| 73.00

Samples taken following an explosion October 31, 1908.

> Samples taken after explosion January 41, 1910.

e1n this specimen of coke there appears to have been considerable combustion of the fixed carbon.

4 Probably contains water of crystallization of clay in ash, thus affecting carbor-volatite ratio as de-
termined by proximate method of analysis

¢ This carbon-volatile ratio is interesting as indicating more complete combustion where the explosion
died away. ‘The ash content is also

igher than that of coke samples near origin.

1. Coal from face, sample of full section as mined.
, Thick coke sale from car bumper.
Coke seale adhering to rib in tenth heading.
Coal from face of room 2, LI-A entry, sampie of full seetfon of seam as mined. (Lab. No. 10063.)
joad dust from room 47, 7-A entry (beyond ares affected by explosion). (Tab. No. 10052.)
ample of dust from large mass in Jast erosseut, between entries 11-4 and 12-A, close to their faces,
‘abably deposited by wave following the explosive wave. (Lab. No. 10051.)
7. Coked dust from prop in room 6, 11 A entry. (Lab. No. 9949.)
8. Coked dust from post in §-A entry about 1,600 feet from main slope. (Lab. No, 9947.)
8. Coked «lust from prop in last crosseut. between entries N-A and 12-A, (Lab, No. 9948.)



196 THE EXPLOSIBILITY OF COAL DUST.

Gauoway, Wint1as. Coal dust. Science and Art of Mining, June 12,1909, Abstract
of paper before Congress of Applied Chemistry. Discusses origin of duet, history
of inquiry, preventive measures.

Colliery explosions and rescue appliances. In Practical coal mining, London,
1907. Reviews coal-dust problem, pp. 92-107.

Garrorru, W. E. Colliery Guardian, vol. 98, July 30, 1909, p. 218. In account of

Altofts experiments, says of Silkstone explosion, 1886, that it was firet colliery
disaster on record in which a coroner's jury returned the verdict of “death from
an explosion of coal dust without gas.

British coal-dust experiments. Internationaler Kongress itr Bergbau,
Hiittenwesen, angewandte Mechanik und praktische Geologie. Dusseldorf,
1910. Berichte fiir Bergbau, pp. 88-102.

Grace, Zur Kentniss der Kohlenstaub Explosion. Braunkohl, May 38,
1909, pp. 125-129. Discusses explosions of dust in lignite-briquet planta.

Gurrermay, K. 8. Mining coal in southern Colorado. Eng. and Min. Jour., vol. 88,
November 20, 1909, p. 1009. Describes sprinkling methods at (okedale.

Haas, Franx. Is coal dust, as such, explosive; and if 80, what are the chemical
reactions and the most efficient preventives? Paper before Weet Virginia Min-
ing Association, October 17, 1908. Discusses preventive measures; advocates
use of steam. Printed under the title, “The problem of treating coal dust in
mines,” in Eng. and Min. Jour., October 24, 1908, pp. 814-817; also under the
title, “Is coal dust, as such, explosive?” in Coal, November 11, 1908, pp. 15-175
also in Mines and Minerals, December, 1908, pp. 227-229.

Hatpasg, J. 8. The investigation of mine air. London, 1908 (?).

HALt, CLARENCE, and SNELUNG, W. 0. Coal-mine accidents, their causes and pre-
vention. Bull. U.S. Geol. Survey No. 333, 1907. 23 pp.

Ha, Hevay. The coal-dust question in Great Britain. Eng. and Min. Jour., vol.
87, May 22, 1909, pp. 10841089. General review of progress of inquiry from
1844 to present time.

Calcium chloride treatment of mine dust. Fuel, June 23, 1909. Describes
experiment with CaCl, in a eection of tunnel 285 feet long.

Hansey, C. M. Dust explosion in the boiler room. Power and the Engineer, Decem-
ber 5, 1908, p. 1017. Mentions explosion of dust and soot on top of a boiler.

Hani, Ricnarp. Treatment of dust in mines, above ground and below ground.
Trans. Inst. Min. Eng., vol. 33, 1907, pp. 254-257. Describes a spray system.

Harnixcron, D. Spraying coal mines. Mines and Minerals, vol. 29, 1908, pp.
102-104. Describes sprinkler system at Sunnyside mine No. 4, Sunnyside,
Utah; cost of construction; efficiency.

—— Spraying coal dust ae a colliery safeguard. Eng. and Min. Jour., January 23,
1909, pp. 103-106. Refers to dust explosion at Winter Quarters mine, May 1,
1900, and Sunnyside (Scofield) explosion; describes spraying methods of Utah
Fuel Company, and cost.

Harzrexn, . Die Versuchsstation 2 Liévin. Glickauf, October 9, 1909, pp.
1484-1491.

Heise, Fritz, and Herssr, Fr. Berghaukunde, 1908, p. 448.

Herrick, R. L. The Primero disaster. Mines and Minerals, vol. 31, March, 1910,

Heurreav, ©. E. La catastrophe de Courriéres. Annales des mines, ser. 10, vol. 12,
1907, pp. 323-426, 429-444.

Hounauu, A. W. G. Some memorandwns concerning cual dust and the essential
principles of the coal-dust theory. Colliery Guardian, vol. 99, June 80, 1910,
pp. 1065-1066, Abstract of a paper read before the Institution of Mining
Engineera.

Tuurwors Coat Ovgrators’ Association. Report of committee, 1905. Contends
increased use of powder has greatly increased number of accidents.



THE COAL-DUST QUESTION IN EUROPE, 23

from a firing station in a cylindrical bomb-proof, which also serves
as an observatory. This is located 130 feet from the gallery.

Unlike some other galleries, the prime purpose of the Altofts gallery
is not the testing of explosives, but the study of the behavior of coal
dust in exploding and the discovery of some effective remedy as a
substitute for watering. The first tests were to demonstrate and
convince the few who still had doubt as to the explosibility of coal
dust. Some of the explosions produced were very violent. In one
test, in which a longer portion (450 feet) of the gallery had been
charged with coal dust than before or since, the resulting explosion
tore off the three end sections, threw heavy pieces of boiler plate
several hundred feet, blew out windows in houses for a mile or so
around, and, it is claimed, produced a concussion that was felt 7
miles aw:

After a series of preliminary demonstrations, the study of remedial
methods has been taken up. Several plans have been tried: Having
an intercepting zone free from coal dust, the employment of a zone
of stone dust, and completely covering the coal dust with stone dust
or mixing stone dust with the coal dust. These will be discussed
under other heads (pp. 90-96).

SECOND REPORT OF ROYAL COMMISSION ON MINES, 1909.

The second report of the royal commission on mines appeared in
September, 1909. The coal-dust question is discussed as well as
other dangers, and with regard to dust the commission says: *

‘The witnesses, who included those best qualified from scientific or practical experi-
ence to speak on the question, expressed opinions which were often widely divergent,
as to the best means of meeting ihe danger of explosions, but they were generally
agreed on two points—that coal dust is liable lo explosion with or without the presence
of fire damp, under conditions which are at present to be found in most coal mines in
this country and abroad, and that there is pressing need for the elucidation of the
problems involved by a series of exhaustive experiments on an adequate scale. With
regard to the first point, it was a matter of satisfaction to us that all the witnesses whom
we consulted expressed theroselves as adherent to the received opinion on the subject
ofcoal dust. In this respect we found ourselves in a better position than the commis-
sions who preceded us--the royal commission on accidents in mines (1879-1886) and the
royal commission on coal dust (1891-1894)—in that we were able to confine our attention
to the means of dealing with coal dust without having to prove the necessity for such means.
* * * Wedonot mean to convey the impression that all managoms and mining engi-
neers are fully alive to the danger of coal dust. Unfortunately, recent occurrences
have tended to show that this is not the case. 1f such is the position taken by some
managers in thiy country, it is the Jess surprising that. the workmen do notall appreciate
the danger of coal dust.

Tho commission, after speaking of the merits of the Altofts gallery,
the thoroughness of its equipment, and methods in carrying on the
tests, says:

Until these experiments are completed we are unable to make recommendation
covering the whole question of the means of preventing coal-dust explosions.

@ Second Kept. Roy. Comm. on Mines, 1909.


18 THE EXPLOSIBILITY OF COAL DUST.

Despite the foregoing affirmative report by the royal commission,
there was not a general acceptance among mining men of the explo-
sibility of coal dust in itself, so that in 1890 Mr. Henry Hall, govern-
ment inspector of mines, was commissioned to make some further
experiments on a large scale in certain disused shafts with coal dust
from various mines.

Some of these tests were very spectacular, notably several at the
Big Lady pit, which was 630 feet deep and was connected by a small
arched way with another shaft. The experimental shaft was the
upeast. The firing charge was 1} pounds of black powder in a can-
non placed 540 feet from the surface. In the seventh test—
dust. was ignited, followed by a continuous roar, and a rush of flame completely filled
the pit mouth and ascended 60 feet into the air. This was the most violent explosion
since the commencement of the experiment. It is difficult for anyone who did not.
witness this experiment to realize the extent of the explosion. The flame continued
to issue from the pit for five to six seconds, followed by dense smoke. The violence
carried away some of the woodwork 37 feet above the pit mouth.

Mr. Hall, in his summary, states: *

These experiments conclusively prove that blasting with gunpowder in dry and
dusty mines may cause serious disasters in the entire absence of fire damp, It is impos-
sible to explain why many of the experiments failed to cause explosions or to ignite
the dust, but the fact that at intervals these did occur perfectly justifies the above
conclusion.

In February, 1891, a royal commission on explosions from coal
dust in mines was appointed, and began hearing evidence in the fol-
lowing month. Its first report of evidence, without conclusions, was
published in July, 1891. In 1892 its sittings were adjourned, pend-
ing further experiments by Mr. Henry Hall, which were conducted
at intervals in that year and in 1893.

The commission made its second report in 1894, giving additional
evidence and their final conclusions. In reviewing the evidence they
state:?

‘The experiments made by Mr. H. Hall in 1890, 1892, and 1893 on a larger scale,
and in shafts of mines, appear to be conclusive in the vame sense, although they show
that an explosion is not a cortain consequence of every shot that blows out or emits
flame, but depends on many circumstances affecting the condition and quantity of
the dust, the nature and strength of the explosive, the sizo of the galleries orshafts, ete.

The Prussian commissioners reported that “if absolute immunity from blown-out
shots could be obtained, the dangers which are brought about by coal dust would be
almost entirely prevented.” In their experiments they found that no shots, other
than a blown-out shot, caused an explosion of the dust.

Tt is, however, the opinion of several witnesses that the danger is not confined to
blown-out shots, but that an overcharged shot which does not blow out, or one which
partially does the work for which it is intended, may exhibit flame and therefore
ignite the dust. In the opinion of Mr. W. N. Atkinson, the explosions at Seaham
in 1871 and 1880, at Elemore, at Usworth, and at Altoits were caused by shota which
did not blow out.

a First Rept. Roy. Comm., 1801, p. 153, 2 Second Rept, Roy, Comm., 1804, p. 1.


ILLUSTRATIONS.

Prats I. Explosion from coal dust in gas and dust gallery No. 1, Pittsburg
testing station.

II. Coked dust from Pittsburg gallery density test with 200-mesh dust...
III. Coke produced from 80 to 100 mesh dust...
IV. Coked dust produced from 20 to 40 mesh dust.
YV. Mine hygrometer with improvised sling arrangement
VI. A, Altofts experimental gallery after explosion of dust occupying 450
linear feet of gallery, August 11, 1908; B, Experiment 58 at Altofts

gallery, showing stone dust and smoke issuing from gallery as the

result of an explosion of the 275-foot coal-dust zone; C, Experi-

ment 99 at Altofts gallery, showing flame and smoke issuing to a

distance of 160 feet from explosion of 375 feet of coal-dust zone.

VII. Side of roadway in Altofts mine, showing method of applying stone
dust as a preventive of explosions. .

VIII. A, Coal-dust ignition apparatus used at Pittsburg: B, Apparatus used
at Pittsburg, showing ignition of dust.

IX. A, Time marker, Altofts experimental gallery; B, Manometer,
Altofts experimental gallery...

X. A, Contact breaker, Altofts experimental gallery, before firing;
Contact breaker, Altofts experimental gallery, after firiny

XI. After-damp sampler, Altofts experimental gallery
XU. A, British coal-dust contact maker, before firing; B, Same, after fir-
ing; C, Apparatus for igniting coal dust by gas flame, Altofts ex-
perimental gallery

XIII. A, Timbering and stone packing in preliminary gallery at Altofts;
B, Stone dust on hanging shelves in Altofts colliery..............

XIV. Radiator and steam pipe in use, Monongah No. 8 mine; B, A spray
in an entry.

Fraure 1. Diagrammatic sections of cannon end of gallery No. 1, Pittsburg

2. Curves of equal weights of water vapor per cubic foot for varying
temperatures and relative humidities when the barometric pres
sure is 30 inches.

3. Curves of equal relative humidity for varying temperatures and
depressions of wet bulb...

. Curves of equal relative humidity for varying temperatures and

volumes of water carried.

. Coal-dust ignition apparatus of Vita

. Coal-dust ignition apparatus of Thorpe

. Coal-dust ignition apparatus of Engler.

Apparatus of Bedson and Widdas for lecture demonstration.

i

Orme

92

96

142

0

150

152

152

156

174

58

66

67
n7
127
129
130


124 THE EXPLOSIBILITY OF COAL DUST.

have previously attempted to connect the inflammability of the dust
with the gaseous character of the coal from which it was derived,
without, however, giving any experimental evidence of such connec-
tion. The authors took up this question and employed for the inves-
tigation both forms of apparatus described above, after having
shown previously that the behavior of each dust was similar in both
forms of apparatus. As a result of this investigation the authors
were able to arrange the coals investigated into two groups, first,
those whose dusts were inflammable, second, those whose dusts were
noninflammable. These results are summarized as follows:

Percentage of volatile matter in inflammable and noninflammable dusts.

Inflammable dusts: | Noninflammable dusts:
Sample 1. Sample 1. wee 19.5
Sample 2 1. 24.6

19.0
18.0

Sample 3.
Sample 4.

Sample 4...

In stating their conclusion the authors say that a coal to yield
an inflammable dust must contain 30 per cent or more volatile
matter. The last sample investigated was a lignite, containing 50
per cent volatile matter. It was also found to be the most inflam-
mable of all.

In stating that a coal dust is noninflammable the authors do not
mean that the coal dust does not burn, but that under the conditions
of the experiment the dust suspended in the air is not capable of
propagating the combustion much beyond the confines of the source
of inflammation. The propagation of the flame they consider to
be a complex function of the temperature of combustion, of inflam-
mation, of distillation, ete. It is conceivable that this combustion
could be arrested under certain conditions and that the air and dust
mixture would not inflame, while in other circumstances it would
burn more or less easily. It is for an analogous reason that a mixture
of air with methane in amounts insufficient to form an explosive
mixture can be rendered explosive merely by raising somewhat the
temperature of the mixture. The dusts of all coals are certainly
combustible under the proper conditions, but only a certain num-
ber are inflammable under the conditions set by the authors. The
proportion of volatile matter, according to the authors, is not the
only cause of the infammuability of coal dust, as they consider that
those volatile constituents which have already been partially
oxidized would be expected to be more inflammable than those same
substances unoxidized, just as alcohol vapor is more inflammable
than vapors of petroleum. In other words, the authors believe that
the inflammable character of the coal dust depends not only on the
amount of volatile matter contained in the coal, but also upon its
character. A further influence on the inflammable nature of a



102 THE EXPLOSIBILITY OF COAL DUST.

propagation with as low a density as 23 grams per cubic meter (0.023
ounce per cubic foot), In the experiments at the Pittsburg station
with 200-mesh dust from the Pittsburg coal seam, in a much larger
gallery, but also with far larger charges of explosive, two propaga-
tions were obtained with as low a dust density as 32 grams per cubic
meter (0.032 ounce per cubic foot).

Density tests with the coarser sizes have not yet been tried in the
Pittsburg station.

MOISTURE IN DUST AND IN AIR.

The experiments with wetted dust at the Pittsburg station have
been very instructive. The first attempt has been made to define the
amount of water that must be present with the dust to prevent prop-
agation. It is true that these experiments were few and were made
with dust from the Pittsburg seam only, which is possibly more sen-
sitive than the average bituminous dust. On the other hand, the
igniting charge was only 24 pounds of black powder. In the inte-
rior coal fields it is not at all uncommon for charges of 5 to 6 pounds or
more to be used and for blown-out shots to occur with s charges,
Hence, despite the possibly less sensitive character of the coal dust in
these fields, the initiating cause of explosions may be greater, and it
would not be safe to assume that a less percentage of moisture than
that indicated by these preliminary experiments would render the
coal dust inert.

Where there is a large amount of dry coal dust, judging from the
Pittsburg experiments, a humid atmosphere has little effect on igni-
tion of dust or propagation of an explosion. A long continuance of
the humid conditions renders the coal dust moist and inert, but the
presence of moisture in the air at the moment of explosion is not
sufficient to prevent an explosion; that is, not enough moisture is
carried by the mine air to reduce materially the temperature of the
flame. Fully saturated vapor at 65° F., an ordinary mine temper-
ature in this country, weighs 6.78 grains per cubic foot (15.5 grams
per cubic meter), Coal dust suspended in such a saturated atmos-
phere in a cloud of moderate density weighs, say, 200 grams per cubic
meter. At the figures given the weight of vapor is but 7.8 per cent
of the weight of dust. The Pittsburg experiments with wetted dust
showed that several times this percentage of moisture in the dust, in
addition to a nearly saturated atmosphere, was required to prevent
propagation.

Probably with a low dust density the relative humidity of the air
would be an important factor in tending to prevent the initiation of
an explosion. However, the great purpose of artificially humidifying
mine air is that it may serve as a vehicle for carrying wuter to the dust.



HUMIDITY OF MINE AIR. 65

important that the cloth of the wet bulb be freshly wetted for each
observation.

On going out of the mine it is very important that the observer
make hygrometric and barometric readings at or near the station
where he made readings on going into the mine and use the average
of the two sets to compare with the underground observations or, if
the two differ widely, prorate according to the time intervals.

Notation should be made at the different underground stations, and
at other intervals, of the amount of dust present on floor ribs, roof, and
timbers, also the condition of the dust in the same places as regards
moisture. Particular note should be made of moisture drops beading
the roof or ribs.

In the light of the preliminary experiments with moistened dust
made at the Pittsburg station, as described on pages 54-58, it is advis-
able to take samples of the dust at certain points and have the mois-
ture and ash contents determined. Such samples should be placed in
air-tight receptacles, like glass jars with screw tops and rubber
gaskets, at the point of taking, or in special cans, such as are used
by the Bureau of Mines, sealed with insulating tape. Care will have
to be exercised in gathering the samples, to have them representative
of only that dust which is likely to be thrown into suspension by a
violent concussion.

RELATION OF MOISTURE CONTENT TO TEMPERATURE AND
PRESSURE OF MINE AIR.

The psychrometric tables issued by the Weather Bureau have
already been referred to. The method of using them is explained in
connection with the tables as published. One table gives the tem-
perature of the dew point in degrees Fahrenheit for various atmos-
pheric pressures and various depressions of wet-bulb thermometer.
This table will nét ordinarily be consulted by the mine observer. The
tables of more immediate use to him are those giving the relative
humidity percentages for different. temperatures, pressures, and de-
pressions of the wet-bulb thermometer and the table giving the
‘‘weight of a cubic foot of aqueous vapor at different temperatures
and percentages of saturation.”

The last-mentioned table has been supplemented by one appended
below, which gives the number of gallons of water equivalent to the
same weight of aqueous vapor in 100,000 cubic feet of air at differ-
ent temperatures and different degrees of saturation. This unit,
100,000 cubic feet of air, passing in one minute, represents an ordi-
nary mine condition. The other unit (gallons) gives a convenient
measure for calculating the amount of water that must, be introduced
artificially in winter to offset the amount carried out by the return
currents.

88006°—Bull, 20—11—5


BIBLIOGRAPHY. 189

Coutery GuARDIAN. Coal dust in connection with colliery explosions. Vol. 61,
1891, p. 202.

—— Explosions, gob fires, and coal dust. Vol. 63, 1892, p. 851.

- Coal-dust explosions. Vol. 71, 1896, p. 558.

- Jolliery explosions produced by coal dust. Vol. 70, 1895, p. 1168.

~ Rationale of colliery explosions from coal dust. Vol. 72, 1896, p. 1159.

Brancepeth colliery explosion. Vol. 72, 1896, p. 597. Abstract from official
reports.

Coal-dust explosions. Vol. 75, 1898, p. 571. Notice of lecture by H. B. Dixon
at Stoke-on-Trent, March 28, 1898.

—-~— Methods of dealing with coal dust. Vol. 76, 1898, p. 737. Describes spraying
and sprinkling methods.

—— Rendering coal dust nondangerous in the Saar district, Germany. Vol. 76,
1898, p. 1057. Abstract of official report by Bergassessor Drige.

Cunynoname, I. I. Report of the departmental committee appointed to inquire
into the testing of explosives in coal mines. 1897. 14 pp.

Day, D. T. Coal dust in mine explosions. Trans. Am. Inst. Min. Eng., vol. 24, 1894,
pp. 908-911. Discussion of Stuart’s book.

Donpar, C. Coal dust in mines and its relation to colliery explosions. Trans. Fed.
Inst. Min. Eng., vol. 6, 1893, p. 372.

Durree, W. T, Coal dust in mine explosions. ‘Trans. Am, Inst. Min. Eng., vol. 24,
1894, pp. 911-913. Discussion. Mentions explosion at Washburne Mills, 1878,
and investigations of L. W. Peck.

ENGINEERING AND MINING JouRNAL. Coal dust and colliery explosions. Vol. 5:
1891, p. 738. Notice of Hall’s experiments.

~~. Ignition of coal dust by the sun’s heat. Vol. 63, 1897, p. 234.

~~~. Precautions against coal-dust explosions. Vol. 63, 1897, p. 446. Refers to
cost of sprinkling at Hibernia mine, Germany.

——- The mine explosion at Scofield, Utah. Vol. 69, 1900, p. 552. Editorial notice
of disaster, by S. Sanford.

Evrarp, A. L’explosion de grison du puits Verpilleux. Le génie civil, vol. 15, 1889,

pp. 264-268.

Feperaten Instrrumion oF Minin Evainrers. Influence of the ventilation current
and of coal dust on gas testing, Trans., vol. 4, 1892-1893, p. 452. In paper by
Frank Clowes describing a hydrogen-oil safety lamp

Explosions of fire damp and coal dust. Trans., vol. 9, 1895, p. 300. In presi-

dential address of W. N. AUsinson.

Coal dust rendered harmless. ‘Trans., vol, 10, 1895-1896, p. 546.

Experiments with explosives. ‘Trans., vol. 12, 1896, p. 32.

-—~~- Damping coal dust at the Merthyr Vale colliery. ‘Trans., vol. 12, 1897, p. 411.

-——~ Explosions of fire damp and coal dust. Trans., vol. 19, 1900, pp. 22-75.

Fow.er, Gorse. How a mine may be dry but not dusty, Trans. Fed. Inst. Min.
Eng., vol. 11, 1896, p. 128.

Guin, Epwin. Explosions in Nova Scotian coal mines. Trans. Fed, Inst. Min. Eng.,
vol. 8, 1894, pp. 143-158. Proc, Nova Scotia Inst. Sci., sor. 2, vol. 1, pp. 58-70.
Mentions more important explosions in Nova Scotia since beginning of coal min-
ing. Thinks no important explosion duc to dust. alone.

Guewn, WitLiam. Mine explosions generated by grahamite dust. Trans, Am, In:
Min. Eng., vol. 24, 1894, pp. 195-207, p. 898. Describes explosions of grahamite
dust in mine at Richie, W. Va., February 9, 1871, and February 25, 1873.

Grey, René. Résumé des conclusions du rapport final de la commission autrich-
ienne de grivou. Bull. Soc. ind. min., ser. 3, vol. 5, 1891, pp. 663-711.

Gaurrrmm, D. Dust explosions. A peculiar explosion on a tipple at the Crested Butte
mine, Colorado. Mines and Minerals, vol. 18, 1898, p. 496. Dust ignited by
lamp.



28 THE EXPLOSIBILITY OF COAL DUST.

Then follow remarks about the Haswell mine explosion report of
Lyell and Faraday, and some quotation from Galloway’s papers.
In view of the definite statements in this article, it is surprising how
delayed the general acceptance of the coal-dust theory was in this
country.

EXPLOSION AT POCAHONTAS MINE, WEST VIRGINIA, 1884.

On March 13, 1884, occurred the first great mine explosion of the
bituminous fields of this country, at the Pocahontas mine, West
Virginia. There were 114 men killed, all who were in the mine. At
the request of the operating company, a committee was appointed
by the American Institute of Mining Engineers, consisting of Messrs.
J. UH. Bramwell, Stuart M. Buck, and Edward H. Williams, jr. As
soon as the mine workings were accessible, they made a careful
examination of them. A summary of contributing causes found by
them is as follows: 4

1. The unusual dryness of the mine.

2. The very large quantity of dust in an extremely fine state of division.

3. The constant working of the mine day and night, allowing no time for clearing
air [of powder smoke].

4. The uve of excessive quantities of powder, largely increasing the amount of dust.

5, The probable existence of small quantities of fire damp slowly given off from
the coal.

6. The employment of incompetent and inexperienced men.

7. The almost complete stagnation of the air on the east side of the entry, owing
to the fact that the main doors were untended and fastened open, allowing the ait to
pass up the main entry direct to the fan.

8. The failure to recognize and appreciate the previous wanings of danger given
by occasional flashings of unusual extent, when shots were fired, indicating the need
of special precaution.

The investigators say further: ‘The existence of fire damp is 8
disputed point.” They obtained no evidence of the previous
existence of fire damp from the workmen of the other shifts, except
that a miner claimed that once, when his light was in an undercut-
ting, he observed a lengthening of the flame. The investigators com-
ment that in general the evidence given by the former workers
appeared to be prejudiced and therefore unreliable.

On reopening the mine after the explosion and partial flooding, no trace of fire

damp was discovered, and none showed at the time of inspection, although the
ventilation had been only partly restored, especially to the rise.

Their conclusion was:

We believe that the explosion was due mainly to dust, and that it originated either
in the (3d) east headings (‘at D”) or very possibly in one of the rooms (‘‘eouth of
D”—south of the 8d east headings). The evidence of a short northward current
being obliterated by the stronger reaction from the close heading. We can not
determine the initial cause, whether a blast or the accidental ignition of a small
accumulation of fire damp.

Trans, Am, Inst. Min, Eng., vol, 13, p. 237,


INVESTIGATIONS OF THE IGNITION OF COAL DUST. 185

13.8 amperes for its ignition. At the end of eight days it contained
1.78 per cent moisture, and required 13.8 amperes for its ignition.
The conclusion of the authors regarding the effect of moisture on the
inflammability of coal dust is that in order to prevent an ignition of
an inflammable dust it must be made so damp that it can not be
blown into the air as a cloud by a jet of air, but that an increase of
moisture tends to raise the temperature of inflammation.

It was also found that exposure to air rendered freshly ground dust
less inflammable. A sample of dust which in the beginning required
12.5 amperes for ignition required 14 amperes at the end of seven-
teen days.

Experiments were also made to test the effect of incombustible
dusts on the inflammability of coal dust. The result of these experi-
ments, summed up in the table below, was to show that the tem-
perature of ignition of such a mixture was higher than that of the
coal dust alone.

Effect of mixture of sand with coal dust on current required for ignition.

Amount of Current |
sand to , required |
gram of

coal.

Character of coal. i
ignition.

Brown coal.
Do 6 trials, 4 ignitions.
13.5 | 4 trials, 3 ignitions.

sb
+ 15 | Ne inflammation.
i i

While these results afford evidence of the difference in conduct of
different coals regarding their temperature of ignition, they give
no measure of the relative inflammability of the dusts, as the only
means available of judging the results was by the eye, and they
could only be classified as no ignition, a slight puff, or a violent
inflammation. An attempt was made by these authors to gain more
exact information on this point with the use of the piece of apparatus
shown in figure 11. It consists of the explosion vessel a, of 2 liters
capacity, and provided with 3 tubulures, 6, £, and o. In 6 is inserted
a stopper, permitting connection to a coil of platinum wire (f). The
dust is introduced through & in much the same way as in their first
experiments, while o is attached to the apparatus used for registering
the pressure developed in a by the inflammation of the dust. The
apparatus constructed to register the pressure consists of a three-
necked Wolff bottle, one opening of which is connected with the
explosion vessel and the second with a closed manometer containing


14 THE EXPLOSIBILITY OF COAL DUST.

apparatus, a long, narrow explosion box or flue, was similar to that. of
Galloway’s. In his report he said:*

In the complete absence of fire damp, coal dust exhibits some tendency to become
inflamed when passing a very large lamp flame at a very high velocity. Ifexposed to
the action of a large volume of flame, as from the explosion of gunpowder, it exhibits
a decided tendency to propagate flame. But eo far as can be determined by experi-
ments on a moderate scale, this tendency is of a limited nature.

Professor Abel, in giving evidence at the Seaham inquest, said that
“if coal dust alone would have exploded every colliery would have
been wrecked long ago.”®

The Chesterfield and Derbyshire Institute of Engineers appointed
a committee in 1880 to conduct some experiments with coal dust.
The committee included Professor Marreco and Mr. Morison. The
experiments were made in a miniature gallery 82 feet long, 16 inches
wide, and 18 inches deep, connected with a chimney to produce an
air current. Coal dust was introduced at the open end of the chamber
and carried in by the current. A horse pistol was used to simulate a
blown-out shot. The charge was one-half ounce of gunpowder. It
was fired into the open end. Out of 134 tests with coal dust alone,
ignition was obtained in 36 cases. Even when 6 per cent of gas was
tried, no violent explosion resulted. In the opinion of the observers
it was more of an inflammation than an explosion.

The dust for these experiments was gathered from the floor, timber,
and sides, and in all probability was more or less mixed with stone
dust. This may have been the cause of the inconsistency in the
results.

In 1884 Mr. William Galloway took a more positive stand than in
April, 1879, when he appeared before the accidents in mines commis-
sion. In his fifth paper on the subject of coal dust, communicated to
the Royal Society in May, 1884,“ he states that no earlier author than
himself had credited coal dust with being a principal factor in mine
explosions, relegating fire damp to a secondary place.

EXPERIMENTS IN PRUSSIA.

The Prussian fire-damp commission in 1884 conducted a series of
experiments with coal dust and with coal dust with gas in a gallery
which had been built at the Koenig mine at Neunkirchen, Saar-
brucken. This gallery was partly constructed under a refuse pile.
It was 51 meters (167 feet) long and elliptical in cross section, 1.72
meters (5.6 feet) high by 1.20 meters (3.9 feet) wide. Twenty-eight
varieties of coal dust were tested and compared, each separately tried

a Final Rept. Accidents in Mines Comm., 1886, p. 158
® Blue book on Seaham colliery explosion, 1881,
Trans. Chesterfield and Derbyshire Inst. Eng.,
4Proc. Roy. Soc. London, vol. 37, 1884, p. 42.



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 133
LABORATORY EXPERIMENTS OF BEDSON AND WIDDAS.

Convinced of the utility of the method adopted by Holtzwart and
Meyer in their investigations of the explosive character of lignite
dusts, Bedson and Widdas® undertook a similar investigation of
mixtures of coal dust and air. The apparatus they used for this
work differed in certain respects from that used by Holtzwart and
Meyer. In place of the electric spark used by those authors as the
source of ignition they substituted in certain experiments a gas flame
or a spiral of platinum wire heated electrically. The apparatus
shown in figure 10 consists of a bottle (a) of about 1,900 cubic centi-
meters capacity, closed by a three-hole rubber stopper, through
which pass three glass tubes (6, ¢, and ¢). The tube 5 was con-
nected with a foot bellows, ¢ with an open manometer (d), and e with
the chamber in which the explosion takes place. This chamber in
the first form of apparatus is a cubical tin box (f) of 10.16 centimeters
dimension, provided with mica windows (g) at the front and back. On
two opposite sides of the
box are openings 3.81
centimeters in diameter,
provided with collars
permitting the attach-
ment of the glass tubes
landm. The glass tube
e, communicating with
the ‘bottle a, is provided
with a stopcock (p) and
was bent downward (in-  ¥##8® 10—Fist coal-dust iguition apparatus of Bedson and

Y Widdss.

side of the glass tube m)

at n, in front of which is placed the weighed sample of dust. Two
other openings (f and ¢) into the top and bottom of f are for the
introduction of the gas flame or other source of ignition.

The operation is carried out in the following way: A weighed
quantity of dust is placed in front of n, in the glass tube m, The air
in the bottle a is compressed to the desired pressure by means of the
foot bellows connected to b. After placing the gas jet. (g) in position
the stopcock p is quickly opened. The outrush of air from ¢ blows
the dust into the air and carries it to the source of ignition, where the
behavior of the dust is observed through the windows. The first
series of experiments was made on finely ground samples of lignite.
The sources of ignition used were an electric spark, electrically heated
platinum wire, and a small gas flame. The second series of experi-
ments was a study of finely ground dust of cach of the following
materials: Brown coal, bituminous coal, dant (slack), charcoal, wheat
flour, wood sawdust, lycopodium powder, metallic aluminum, and

@ Traus. lust. Miu. Eug., vol. 32, 1907, p. 529.


168 THE EXPLOSIBILITY OF COAL DUST.

proximately 0.1 pound. At normal pressure and a temperature of
4,000° F,, (absolute) the water vapor would weigh roughly “Pi” or
0.011 pound per cubic foot. At 3 atmospheres pressure the weight
would be 0.033 pound per cubic foot. The heat units in 1 linear
foot of entry 10 by 6 feet would be 2,376 B. t. u., since the tempera-
ture (4,000) times the weight (0.033 x60) times the specific heat
(0.3) equals 2,376.

It requires 756 B. t. u. to evaporate 1 pound of water, hence 2,376
B. t. u. would evaporate about 3 pounds of water. If, then, a film
of water 0.025 inch thick is maintained, which is equivalent to 4.25
pounds of water per linear foot, to vaporize this water would absorb
all the heat of the explosion and drop the temperature well below
the ignition point of the coal dust.

It may be noted at this point that the smaller the area of the entry
the less is the thickness of the film of water necessary. Ience open
spaces in a mine should be avoided as much as possible. Mines that
have idle rooms or unpillared sections under ventilation introduce
an unnecessary element of danger in spite of the fact that the force
of an explosion may be dissipated in a large opening.

DISTRIBUTION OF MOISTURE.

It is difficult or impossible to maintain or even establish a uni-
form film of water over the surface of the coal. Coal dust and solid
coal so resist the contact of water that it can not be applied to them
in better form than as ‘‘drippers’”’ on roof and side walls. It is
possible to provide in this form an amount of water equivalent to the
film, but its effectiveness is not so complete. To establish such a
condition in a mine is merely a matter of mechanical labor, but to
maintain it requires vigilance with constant labor, or else an atmos-
phere either neutral or supersaturated with moisture.

EXHAUST STEAM IN OPERATION.
VALUE FOUND BY ACCIDENT.

In connection with the following account of experiments and obser-
vations the reader should have in mind the nature of relative humidity
and the general relations of air aud water vapor.

The introduction of steam into the air current in the Fairmont
Tegion began about three years ago. At that time the danger from
coal dust was not so seriously considered, and the steam was not
introduced for the purpose of moistening the coal dust. 1t was rather
for convenience to get rid of the exhaust steam from a pump and
hoist engine rather than carry it up a shaft. The effect of the steam


ORIGIN AND DISTRIBUTION OF COAL DUST. 33

The coal-dust question in this country can not be said to have
awakened widespread interest among mining men until the terrible
disasters of December, 1907. In response to a demand by those
interested in coal mining throughout the country, Congress in 1908,
made an appropriation for the investigation of mine explosions, which
became available July 1, 1908. The United States Geological Survey
was charged with the investigation. A testing station was at once
decided upon and was established at Pittsburg, Pa. The station was
officially opened December 3, 1908, and testing of nonflaming explo-
sives was begun soon after. Field investigations of mine conditions
and of mine explosions were carried on, especially of the explosions
at Marianna, Pa., and Lick Branch, W. Va., in 1908; Rend, Ill., Weh-
tum, Pa., Eureka, Pa., Johnstown, Pa., and Herrin, Ill., in 1909; and
Primero, Colo., Drakesboro, Ky., Stearns, Ky., Mulga, Ala., and
Palos, Ala., in 1910. Special attention has been paid to the humid-
ity of the mine air and the condition of the dust. At the Pitts-
burg testing station some experiments have been made with coal
dust, described hereafter, and this work will be actively pursued in
the future.

While it is probable that for several years the Jeading mining
men in this country have believed in the explosibility of coal dust
without the presence of fire damp, yet until the public demonstrations
were given at the testing station at Pittsburg, during 1908-9, and
reports were received of similar tests made abroad, a large pro-
portion disbelieved. These tests were so convincing to those who
saw them, and such general publicity has been given to them, that it
is now exceptional to find a mining man who does not accept the
evidence of the explosibility of coal dust. The question of the day
no longer is ‘‘will coal dust explode?” but ‘‘What is the best method
of preventing coal-dust explosions?”

COAL DUST AND ITS ORIGIN AND DISTRIBUTION.
DEFINITION OF DUST.

There is a diversity of opinion as to what the term ‘“‘coal dust”
means; that is, how finely must coal be divided to be termed dust.
Some writers base the distinction on the point whether it can be
carried to considerable distances by air currents. Coal that will pass
through 100-mesh screens (100 wires to the linear inch) is frequently
accepted as representing mine dust. For testing explosives at the
Pittsburg station coal passed through 100-mesh is taken as standard.
In the foreign galleries the practice varies between this size and coal
that passes through 200-mesh.

For the consideration of coal dust as it effects mining, the writer
proposes tentatively a definition based on the capacity of the dust to

88006°—Bull. 20—11 3


EUREAU OF MINES BULLETIN 20. PLATE xi

A. Before firing. B. After firing.

CONTACT MAKER USED AT ALTOFTS EXPERIMENTAL GALLERY.

(APPARATUS FOR IGNITING COAL DUST BY GAS FLAME, ALTOFTS EXPERIMENTAL
GALLERY.

Opened Fy detacoment of lever weight,



170 THE EXPLOSIBILITY OF COAL DUST.

1909
MARCH

JANUARY FEBRUARY

5 tons 20 25

1908

4y09j b19n2 000'001 sed suoIIE &

Fiauke 22—Atmospherle temperature and water-vapor chart.

MOISTURE CONTENT
OF RETURN AIR.

Concurrent with
those of outside tem-
perature and humid-
ity, observations of
the temperature and
humidity of the return
air of certain large
mines of the Fair-
mont Coal Company
were taken. These
observations were free
from daily fluetua-
tions—-in fact were so
regular and uniform
that monthly aver-
ages, as shown in
figure 23, give the
information in suffi-
cient detail. In this
chart, it will be noted,
arethe daily averages,
also calculated in gal-
lons per 100,000 cubic
feet, of the vapor
content of the outside
atmosphere and of the
air in the return air
way.

DEFICIENCY OF WATER
TO BE SUPPLIED.

Such a chart shows
at once the excess and
deficiency of water in
amine air current at
different periods of
the year. It indi-
cates that an ordi-
nary mine ventilated
with 150,000 cubic
feet of air per minute




132 THE EXPLOSIBILITY OF COAL DUST,

elementary composition. Coal No. 4 is chemically very closely
related to No. 5, but their conduct with respect to their explosive
character is entirely different. It is probable that the imflammable
character of the dust is related to the condition of the surface as well
as to the bituminous matter of the coal. Coals Nos. 4, 6, 7, and 8
are seen by inspection of the analyses to be very explosive, while No. 5,
chemically very similar to these, is not explosive. Nos. 2 and 3
were found to be nonexplosive, and No. 1 exploded only once. The
character of the explosion could be judged by the eye. With Nos. 1
and 3, as propagation of the flame was very slow, its passage through
the tube could be readily followed by the eye, appearing to have a
velocity very much like that of propagation of a flame in a mixture
of carbon monoxide and oxygen near its explosive limit; but in
Nos. 4, 7, and 8 the explosion was sudden, and the whole tube filled
with a flash of light. In case of such violent explosions much gas
escapes from the tube (m), while in weak explosions no gas escapes.
The experimenters failed to secure an explosion of lignite dust except.
when the dust was blown in as indicated above. When the dust
was placed in the tube E, and the tube was shaken while the spark
was passing, no explosion was obtained even with the most explosive
dusts. This shows the great importance which the method of
introducing the dust can exercise on the character of the explosion.
To the authors the character of the explosion of lignite dust under
these conditions appeared very similar to that of an explosive gas
mixture.

In one experiment, A and E were filled with a mixture composed
of 10 per cent carbon monoxide and 90 per cent air. This amount
of carbon monoxide and air was just below the explosive limit for
these gases. A sample of coal No. 4, which was one of the most
explosive coals investigated, was exploded in this mixture. When
the coal was blown into the apparatus the explosion which resulted
was not noticeably stronger than when the coal was used with air
alone.

Their study was confined entirely to lignites, but they considered
that a similar study of bituminous coals would be of greatest import-
ance in furnishing data regarding the explosive character of such
coals.

They further investigated the gases which were evolved from
lignites when heated. Even at 400° C. the gases which were given
off were found on analysis to be in such small amounts and of such
nonexplosive nature that they could not be considered as a source
of the explosions which so frequently occur in briquetting plants;
the real cause of the explosions, according to the authors, must be
the coal dust.


REMEDIES FOR COAL DUST. 87

On pages 47 and 48 of this bulletin a review is given of the first series
of Liévin experiments in the small preliminary gallery. These experi-
ments chiefly dealt with the explosibility of different coal dusts.

A second series of similar experiments was carried on under the
same conditions; the results were published by Mr. Taffanel in April,
1910,

In 1908 a gallery of large cross section, 2.80 square meters (30.1
square feet) was started, and was completed for a length of 230
meters (755 feet) by 1909. The first portion of this gallery, 30 meters
(98.5 feet) long, is built of concrete. The following portion is made
of a steel tube 10 millimeters (0.4 inch) thick. The tube has a diame-
ter of 2.10 meters (6.9 feet) and the inside is lined with wood, It is
strengthened externally by embankments. The last 19 meters (62
feet) is built in the same manner, but is of soft tempered steel 20 milli-
meters (0.8 inch) thick. A part of this portion is made square to
allow a side gallery to enter. Smal] port holes are placed at intervals
in the gallery to permit observation of the flame. One end of the
gallery can be closed or both ends can be left open. A passage lead-
ing from the fan is usually protected at the moment of the explosion
by a heavy door.

The ventilation is produced by a helicoid Rateau fan of 3 horse-
power. This fan can deliver, at 525 revolutions, 18,000 cubic feet
of air per minute under a pressure of 0.58-inch water gage, and can
yield an air current with a velocity of about 600 feet per minute, or
one-half the velocity obtainable in the Altofts gallery.

The crushing plant for preparing coal dust comprises a ball mill,
which produces what are termed ‘‘grains”’ of coal, and an improved
Alsing pulverizer, in which small steel cylinders do the grinding,
that yields dust of different degrees of fineness.

To measure the pressures Taffanel states that it is essential to have
instruments in which inertia does not play any réle. For this reason
the apparatus for determining the maximum pressure have been
based on the principle of the crusher gages that are used in artillery
investigations.

In order to study the form of the compression waves and their
velocity of propagation, a series of pressure indicators, which act at a
pressure known in advance, break or reestablish an electric current at
the exact moment when the pressure in the gallery attains that at
which the instruments were calibrated. Interruptions and reestab-
lishments are inscribed on a chronograph with which 0.001 of a
second can be estimated. The same registrating chronograph
measures the propagation velocity of the flame. For this purpose
electric wires are so placed at points in‘the gallery that they are
broken by means of detonators which are ignited as soon as reached
by the flame.



INDEX.

A. Page,
Abel, Frederick, experiments of. = 116,121
on coal-dust explosions... 31d
on explosives . 92
on permanent sprinklers... 8
on steam jets... : 80
Acoidents, incorrect reports of. ee’)
Acknowledgments to those assisting...... 10
After-damp, sampling of. » 152-138, 154
sampling of, apparatus for, gure show-
cesses 152
40
v2
‘See also Mine air.
Air, return, moisture in......... 170-172
moisture in, chart showing.......0.0..-. IML
‘Air supply, relation of, to dus explosions. 118114
Alabaina, explosions in..... cee BR
Altofts, England, conditions at.. -. 185-160
gallery at... cecesesees 21-28, 84
coahdust use at, ss. 2-88
experiments at... 3, 135-158
cee 158
3, 156
instruments at = 151-153
views of. - 150,152
Jimitations of. 151
Altoftsmine, 157-158
stone dust in, application of, views of... 86,156
Ankylostomiasis, relation of, to watering... 77,107
Anthracite dust, explosibility of........--.. 60,100
Ash, effects of. ....... : - 101,108
Atkinson, W. N., on coakdust explosion..... | 20
Atkinson, W. N. and J. B., on coal-dust ex-
plosion. .. ur
on hosing. : 7
on rock dust. : 84
Austria, coal-dust explosions in212017) 1617, 21-26
explosives in. . cee 8
B.
Bald, Robert, on coal-dust explosions....... U1
Bedson, P. P., and Widdas, H., apparatus
of. +--+ 180, 133,136
experiments of, 46, 129-130, 133-137
Belgium, coal-dust explosions in 19
explosives in... - 8
investigations in. co. 1594160, 163
. ~ 184199
coal, dust from. cee 9
dust from, explosion of - m0
Bramvell, J. H., Buck, 8. M. and Williams,
E. H., Jr, on dust explosion..... 28
Branck, Otto, on coal-dust sampling........ 40

Page.
Buck, 8. M., Williams, E. H., jr, and Bram-
well, J. H., on coal-dust explo-

sion. 7 . 28
Budile, J., on coal-dust explosion... n
co
Caleium chloride, use of = 7217, 108

Catsburg mine, Pa., experiments with cal-
cium chloride i ET
Chain machine, dust produced by. = 35-37
Chamberlin, R. T., investigations of. . 4
Chareoal dust, explosion of........+..+0 99
Charge limit, definition of - BB
Charred dust, character of. .... ~ 46,119
Clark, G., and Hail, H., experiments of...... 120
Clement, J.K.,on dry and wet thermometers. 63
Coal dust, absorption of water by ce 167
analyses of. ~ 109,118, 119
chemical character of, effect of = 45-53
definition of... = B84
distribution of, .....- = 87-38

explosibility of, comparison of, with fire
damp - 9
conelusions on. . “goto?

‘ignition of. See ignition.

moisture in. - 166-168,
origin of. w- 8487
removal of. 70-71, 104
size of... 133-34, 45,00-100
resistance of, to moisture. 166
tamping with, effects of. Beit
Coal dst or experiments), analysts of. 39,57, 109
character of...... 38-39

distribution of.
precipitation of. .
preparation of.
sereening of, method of.
Coal dust (in suspension), coarseness of, ef-
fects of. 42-45, 99-100, 101
density of, effects of. .... 38-42, 100,101-102,124
humidifying of, effets of. -- 4-58, 102
measurement of. 0
Coal dust, coked, analyses of. ma
character of. Tos-110
deposition of. = 11, 110-112
description of
position of....--.
views of...
Coal-dust explosions, eauses of.

conditions of. 148-153
experiments in. 24-28,81, 38-81, 140-149
apparatus used in. aerieers

description of...



EXHAUST STEAM AS A PREVENTIVE. 175

These curves, showing plainly that disturbing elements of consider-
able magnitude did exist, led to a separate study, which resulted in
important conclusions, to be noted later in this paper. The principal
fact brought out was that there was not sufficient heat supplied to
establish a normal temperature of 55° during this season of the year.
To supply this deficiency of temperature it was then decided to put
in an air preheater. This was done by placing 1,200 feet: of 2-inch
pipe in nine coils around a coal pillar, which happened to be con-
veniently situated behind the fan, and between the fan and the point
where the exhaust steam was allowed to escape into the air (fig. 26).
In Plate XIV, A, is reproduced a photograph showing one corner of
this radiator and the exhaust-steam pipe in operation.

An endeavor was made to measure the heat supplied by this radi-
ator in order to get a practical figure for the size or length of pipe
required to heat a unit volume of air. This was found very difficult

Jan course

Figure 26—Plan of intake at Monongah No. 8 mine, showing arrangement of live-steam heater and
exhaust-steara pipe.

to accomplish, and while several methods were tried they were not
pursued far enough for satisfactory results.

Figure 27 shows the difference in temperature and vapor contents
between the outside air and the air 400 feet from the fan, when both
the exhaust steam and the heater were used. The air shows com-
plete saturation, while the temperature was raised on an average 19° F.
A disturbing element was noted in this experiment, as in that in
which only the exhaust steam was used. There was evidently another
source of heat present which affected the results more than either the
exhaust steam or the heater. It was noticed that the difference in
temperature was less when the instruments were moved nearer the
intake and greater when they were moved farther away. The item
of radiation of heat from the side walls of the entry, which at first was
considered inappreciable, developed into the most prominent factor.


THE COAL-DUST QUESTION IN EUROPE. 15

by placing about 15 kilograms (3.3 pounds) of it along 10 meters
(32.8 feet) of the gallery. Several means were tried of distributing
the dust, but scattering on the floor was practically as efficient as
any other way. The igniting charge consisted of 230 grams (0.51
pound) of black powder placed in one of several cast-iron blocks
or cannons at the inner end of the gallery. Clay and coal dust were
separately used for tamping the shot. With clay for tamping, the
flame from the explosive itself was 3 to 4 meters (64 to 10 feet) long,
but with the coal tamping it was from 9 to 16 meters (30 to 524 feet)
long. The coal used in each test was analyzed and the resultant coke
was also analyzed. In one instance the volatile matter was reduced
from 21.8 to 13.6 per cent.
The conclusion of the commission was as follows:4

1. The presence of coal dust with or without small quantities of fire damp always
increases the length of a blown-out shot.

2, When fire damp is fully absent, the prolongation is usually limited, not exceeding
6 to 15 meters for most varieties of dust, when clay tamping is used and when the
sides of the bore hole do not themselves yield coal dust and gas, or 9 to 21 metera
when dust is used for tamping or is produced from the hole itself. But there are
coal dusts which, once ignited by a shot, burn or spontaneously give flame far beyond
the locality strewn with the dust, and sometimes actually produce explosions when
no fire damp is traced.

The conclusions drawn by Mr. Hilt, a member of the Prussian
commission, were submitted to the British commission as follows:

1. The prosence of coal dust in more or less abundance in the immediate vicinity
of the working face gives rise to more or less considerable elongation of the flame
projected by a blown-out shot, whether small quantities of fire damp be present in
the surrounding air or not.

2(a) In the complete absence of fire damp the elongation or propagation of fame
ia generally of limited extent, however far the deposits of dust may extend in the
mine ways.

(8) There are, however, certain descriptions of coal dust which, if ignited by a
blown-out shot, will not only continue to carry on the flame, even to distances oxtend-
ing considerably beyond the confines of the dust deposits, but will also give rise to
explosive phenomena or results, in the complete absence of any trace of fire damp,
which in character and efiects are similar to those produced with some other dust
in air containing 7 per cent of fire damp.

3(a) All the phenomena produced by the burning of, and propagation of flame
by, coal dust are intensified by the presence in the air of small proportions of fire
damp, but such dusts as will per se only favor to a limited extent the propagation
of flame from a blown-out shot, give rise only to moderately increased volumes of
flame, in the presence of even as much as 3 per cent of gas, and are not at all capable,
under those conditions, of carrying on flame throughout the length of a dust-atrewn
area; the latter result, will, however, be produced, even with such dusts, if the pro-
portion of fire damp in the air amounts to 4 per cent.

@ Rept. Prussian commission; Preuss. Zeltschr., vol. 32, 1884, 1885; also Eng, and Min. Jour., 2885, p.
221; also Trans, Am. Inst. Min. Eng., vol. 24, 1895, D. 201.
» Final Rept. Accidents in Mines Comm., 1886, p. 43.


BUREAU OF MINES PULLETIN 29. PLATE VI

A. ALTOFTS EXPERIMENTAL GALLERY AFTER EXPLOSION OF DUST OCCUPYING 450 LINEAR
FEET OF GALLERY, AUGUST 11, 1908,

The vibration of the explosion was felt at a distance of 7 miles. (From Coltiery Guardian.)

|

See Se as SS iS |
B. EXPERIMENT 58 AT ALTOFTS GALLERY, SHOWING STONE DUST AND SMOKE ISSUING

FROM GALLERY AS THE RESULT OF AN EXPLOSION OF THE 275-FOOT COAL-DUST
ZONE.

The flame penetrated only 54 feet into a stone-dust zone of 100 feet, therefore not igniting another zone:
of coal dust at the outer end of the galley. (From Colliery Guardian.)

EXPERIMENT 99 AT ALTOFTS GALLERY, SHOWING FLAME ANO SMOKE ISSUING TO A
DISTANCE OF 160 FEET FROM EXPLOSION OF 375 FEET OF COAL-DUST ZONE.

Fiame shows white in tre view. (From Colliery Guardian.)


EXHAUST STEAM AS A PREVENTIVE.

will show an accumu-
lated deficit of water
amounting to 2,000,-
000 gallons per year.
Two months during
the yearthe quantity
of water taken into
the mine by the air
is in excess of that
taken out. This
period is approxi-
mately from the
middle of June to
the middle of August.
Hence it appears
that artificial means
of watering are neces-
sary during the
greater part of the
year—from August
15to June15. Dur-
ing that time at least
2,000,000 gallons of
water must be sup-
plied. This figure,
of course, is based
only on one year’s
observations, and
may be greater or
less from year to year,
yet the indications

are that the observa- 5

tions in the second
year will practically
coincide with those
of the first year.

In supplying the
deficiency of water,
the aim should be to
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deficiency for any
period rather than
the minimum at any
one time. During
the year from June

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96 THE EXPLOSIBILITY OF COAL DUST.

and traveled some distance and inflammable gases have possibly
formed by the partial combustion of the coal dust in an untreated
zone.

In a summary, the Altofts committee states:

* * * The existence of a pioneering cloud at the front of the explosion has been
established, and evidence has been obtained that the true flame of the explosion has
a length of from 60 to 80 feet, or possibly less. Lengths of flame outside the gallery,
150 feet and upward, that have been recorded, are shown to be due to a subsequent
burning of the cloud of coal dust which issues in advance of the flame * * *,

It would appear that the presence of a zone of incombustive dust in the path of a
coal-dust explosion that has traveled 275 feet checks the continued propagation of
the explosion.

The experiments in which stone dust has been intimately mixed with coal dust
algo tend to show that as the percentage of incombustible dust is increased, it becomes
increasingly difficult either to originate an explosion in the mixture or to cause an
explosion to be propagated. * * *

The results of the preliminary experiments made so far have given insight into the
manner of propagation during the initial stages of the explosion; but it is essential
that the phenomena occurring after a much greater distance of travel should be studied
before any definite statement can be made regarding the lessening of the destructive
effect possible.

Of the fi that have been established the most important are, the increase in the
pressures developed with increased distances of travel of the explosion, the marked
influence of obstructions in causing the explosion to be propagated with greater vio-
lence, and the possibility of propagating an explosion through a cloud of wood-charcoal
dust and air, * * *

It is also of importance that experiments should be made on a large scale with air
currents containing a small percentage of firedamp, such as is generally present in
the ventilating currents of most mines. This is necessary in order to determine
whether any remedies which may suggest themselves can overcome the additional
violence that the presence of a small percentage of gas will cause.¢

APPLICATION OF STONE DUST IN BRITISH MINES.

The earliest experiments with stone dust in the Altofts gallery
having, in the opinion of the committee, given “unmistakable indi-
cations of its possible value,” the management of the Altofts colliery
was asked to try its use in the mine to ascertain the cost of application.

The first scheme adopted was to isolate various parts of the mine
by stone-dust zones 600 fect in length. “Further consideration led
to the abandonment of zones and the institution of the principle of
scattering stone dust wherever there was coal dust.”

The stone dust is obtained from the roof material, a shale, which
is ground fine and applied dry,

Plate VII shows part of the wall in its natural condition, the other
part treated with stone dust. ‘The Altofts management state that
stone dust by reason of its greater density displaces the.coal dust on

@ Record of the first series (1908-9, of the British coal-dust experiments, pp. 169-175.



USE OF STEAM AND WATER SPRAYS. 183

Observations on air in mine of Rock Island Coal Mining Company in Oklahoma.

‘Total water con

)- | tents, 24 hours.
oy Relative | Volume Quan rents, 24 hot
em. | humtd- | of air per| tity OF
perature) “ity. | minute. p

minute. | Down-
Meat | Upeast.

Date, Location. Time.

°F. | Percent. \Cubicfeet.| Gallons. | Gallons. | Gallons.
48 0 {000 | 0.0576

65 & 4,976] 9,180
a 85

38 34

55 6 I} 2,629} 9,603,
68 89 i

82 36

sa 95 I 6,498} 13,275,
a 95

i

«= Sprays in operation; roads well sprinkled. § Weather very dry. ¢ “Sweat” disappearing rapidly.

It may be observed from the above tabulation that the method of
exhaust ventilation was employed in this mine, the hoisting shaft
being the intake. It is the writer’s opinion that gassy or dusty mines
are preferably ventilated with an exhausting fan. By this method
the haulage roads have fresh air, and the following marked advantages
result: (a) Electricity and lights are kept out of the return-air current,
which is important if the mine makes gas; (b) the intake is under
inspection, so that falls will be taken care of promptly; (c) in case of
mine fires or explosions fresh air comes into the main entrance, where
there are usually the best facilities for quick escape.

COST OF WATER SPRAYS.

Objection has been made to the spraying system on account of
cost of installation. While no general estimate of the necessary
outlay can be made, as each mine has its own peculiar conditions, an
average of 5,00u feet of 1}-inch pipe, with 6 to 10 spray heads, should
be sufficient to saturate the air current in a mine producing 500 to 800
tons per day. The cost of operation is slight. The labor charge is
limited to that required for the examination of the spray heads to
see that they are not clogged. This may be made one of the duties
of the mine foremen.

The chief cost is in the extension of pipe lines and sprays and in
supplying water. If the mine makes water that is not too acid to
use, the cost of supplying water is insignificant.

A test will readily convince a mine management of the improvement
in the atmosphere of a mine in which sprays have been introduced,
It is purified and free from dust, and by dampening the coal dust
one of the great sources of danger of an explosion is minimized.




110 THE EXPLOSIBILITY OF COAL DUST.

Where there is actual coking the loss of volatile matter and
increase in ash is more noticeable. The high percentage of ash
shown in the above dust analysis is presumably due to inclusion of
foreign matter and not to complete combustion, although that may
have played some part.

POSITION OF COKED DUST AFTER AN EXPLOSION.

Tho observation of the writer has been that at the originating
point of a coal-dust explosion, and near by, the coked particles are
projected directly upon the exposed surfaces of props, caps, collars,
and walls, particularly upon the upper portions toward the roof. In
other words, the coked dust faces the originating point.

As found in mines in which the coal cokes strongly, the coked dust
near the source of explosion is usually in thick loosely cohering
masses, and where the dust is abundant this coke scale may be as
much as half an inch or even an inch thick. The coking or rather
caking through an individual scale is uniform, but the coking process
has been carried only so far as to render the individual grains plastic
enough to cohere and to lightly stick to surfaces. A slight touch
will detach and break up the scale. Such coke is dull in luster and
presents a rough granular appearance. It often contains foreign
matter, pieces of shite, or fragments of timber.

A few loose grains or globules may adhere to the roof, but there is
rarely a scale of coke, though such a scale is often attached to the
bottom side of a collar.

Near the point of origin, on the reverse side of props or collars
(facing away from the source of explosion) there are usually only a few
scattered particles of coke, unless some reflex action has had effect.

The above-mentioned effects are those usually noted in room and
pillar workings, in the room or in the entry where the explosion
originated. After the explosive wave has passed from the room into
the entry, er, if it originated in the entry, has traveled along it a
few hundred feet, it gathers headway, and, provided it still has dry
and pure enough coal dust to feed upon, forms thinner and more
scattered coke sc As the velocity of the explosive wave increases
it no longer depe coked dust on the facing side of props or posts,
collars, and rib projections, except occasionally as scattered particles,
but forms thin scales, often bright, first on the under side of collars,
where there are any, then on the reverse side of timbers or projections.

At this stage coke particles may be driven into facing crevices in
the ribs or cracks in timbers.

It is quite usual for the projections facing the origin to be coated
with unburned dust brought out from adjacent workings, after the
explosive wave has passed, by the suction created by the depression
that follows the wave.

Jes.



BUREAU OF MINES AULLETIN 20. PLATE V

MINE HYGROMETER WITH IMPROVISED SLING ARRANGEMENT.

‘Showing nie:nad of holding for whieling.


HUMIDITY OF MINE AIR. 67

wet-bulb thermometer and the temperature as variables when the
barometric pressure is 30 inches.
Figure 4 shows the curves resulting from taking different percent-

35)

Cort

30)

25)

per 100,000 cubic feet

8 of wats

i r :
0 7 +00
‘Temperature in degrees Fahrenheit

Figure 4.—Curves of equal relative humidity for varying temperatures and yolumes of water carried.

ages of saturation as constants and the temperatures and gallons of
moisture per 100,000 cubic feet of air as variables.


182



20 THE EXPLOSIBILITY OF COAL DUST.

In France, as already mentioned, the effect of the early investiga-
tion, and particularly of the French fire-damp commission, was to
prevent acceptance of the theory of the explosiveness of coal dust
when fire damp was not present. The effort of the French engineers
was to prevent ignition of fire damp, and every precaution was taken
in the French mines to this end. It was felt that if this danger could
be guarded against, that there was practically no danger from coal
dust. Captain Desborough, of England, in a ‘“‘Report on bobbinite”
(1907), states:

The French were, I believe, the pioneers in placing restrictions upon the indis-
criminate use of explosives in gassy mines. After many valuable experiments had
been carried out on a laboratory scale, it was decided that in gassy mines no explo-
sives should be used whose calculated theoretical temperature of explosion exceeded
1,500° ©., which is considerably above the ignition point of a fire damp and air
mixture.

The general good care exercised in the mines of France and the
excellent ventilation gave France comparative freedom from the
large mine disasters that were occurring in other countries, until the
terrible disaster at the Courriéres mines in 1906. Although there
was no official French report attributing the cause to coal dust, such
was the opinion of the English investigators, Sir Henry Cunynghame
and Mr. W. N. Atkinson, who examined the mine. They ascribe the
initial cause to a blown-out shot in a heading, igniting coal dust,
and state further that the propagation through the mine was
probably through the agency of coal dust.*

As a result of the disaster the central committee of mines of France
(comité central des houilléres de France) established station at
Liévin, in the Pas de Calais district, in 1907 for the study of the relative
explosibility of different coal dusts with various percentages of fire
damp and without fire damp. A small-scale experimental gallery
was first erected to determine on plans for a large-size gallery. After
aseries of tests with the former, the large permanent gallery, or the first
section of it, was erected in 1908. As at the other European stations
there is no difficulty in causing explosions of coal dust without the
presence of fire damp, at will, by discharging either black powder or
dynamite from a cannon at one end of the gallery.

Some of the conclusions of M. Taffanel, the government engineer
in charge of this station, are given in subsequent pages of this report
(pp. 47-48). The plans are to gradually extend this gallery to alength
of 500 meters and to investigate means for preventing or of limiting
the explosion of coal dust.

The results already reached by the Liévin station and by the testing
stations of other countries have fully convinced the French engineers
of the dangers of coal dust.

@Home Office report on Courriares disaster, . 11.


150 THE BXPLOSIBILITY OF COAL DUST.

Watered zones are probably more effective provided the watering
is sufficient. But such sufficiency appears to depend greatly on
local conditions and on the character of the dust to be dealt with.
In German mines, more particularly in the Westphalian and Saar-
briicken coal fields, systematic*watering has been made compulsory
by law, and in spite of the numerous drawbacks attending its instal-
lation and upkeep, both owners and men have accepted the measure
with growing favor. In Belgium, on the contrary, extensive water-
ing has been considered impractical, owing to the damage said to
be eaused to walls and roof. The same is true in many English
mines, although in Wales the watering system i extensively pr acticed.

Stone dust has in the experimental ‘galleries so far given the best
results, and its use entails but few of the disadvantages of the two
other methods. Its efficacy as a stopping agent has been experi-
mentally demonstrated both in England and in France, although
the results are not entirely concordant. The dissimilarity, for
instance, between the results in the tests depicted in figure 13 is
remarkable, considering that the two galleries are practically alike
and that the conditions of the tests are apparently analogous.

LIEVIN:

Flame stopped

ALTOFTS: (tenet! 1

Coal e275"
FIGURE 13.—Relative effect on flame of stoue-dust zones at Ligvin and at Allofts.

Such, at Jeast, is the impression received at the ‘first glance. But
it is, of course, quite possible that the numerous factors influencing
an explosion may produce apparently discrepant results by acting
in different order in different tests, and that when properly under-
stood and accounted for such results may yet be brought into harmony.
Indeed, if this were not credible, all attempts to determine adequate
lengths of protection zones in mines by extrapolation would appear
futile.

At the time of writing this report no information could be obtained
at cither station as to any existing ratio of increase between varying
lengths of coal dust and stone dust. But as the recording instruments
at Altofts have shown that the pressure increases but slowly over a
distance of 200 to 300 feet, and then suddenly rises to the maximum,
it may be assumed that if a coal-dust zone of, say, 600 feet were
employed for originating and propagating an explosion, the pressures
obtained in an adjacent stone-dust zone would be very different
from those obtained by shorter lengths of the propagating zone.
Hence the employment of the relatively short propagating zones at



REMEDIES FOR COAL DUST. 93

pressures rose with the distances traveled. The maximum distance
tried was 375 feet from the point of ignition.

At 125 feet from the point of ignition the pressure usually developed.
was about 35 pounds per square inch. In certain experiments the
development of pressure was very rapid; this was notably true in
experiments 55 and 62. In the latter the investigators state a
change impressure of 40 to 90 pounds must have occurred in a dis-
tance of 20 feet; the distance was figured from the velocity deter-
minations and the time interval, namely, +}, of a second, as shown
on the pressure curves.

When stone dust was used the pressures showed a drop in pro-
portion to the rapidity with which the explosion was extinguished
by the stone dust.

No observations on the speed of propagation of explosions are
reported for the first part of the series of experiments. A few
observations are reported in the later experiments. In experiment
91 the reported velocity over a distance of 70 feet, beginning at a
point 200 feet from the point of ignition, is given as 1,400 feet per
second; in experiment 114 the velocity given is 700 feet per second.
In experiment 54 the mean velocity of propagation is reported at
1,700 feet per second. In experiment 62 a distance of 200 feet,
between one contact breaker 175 feet from the point of ignition and a
second at manometer ‘‘A,”’ gave a value representing a mean speed of
2,014 feet per second for the distance. In experiment 53 the velocity
between the point of ignition and a point 275 feet distant was 475
feet per second. ‘‘Many determinations have shown the velocity
at which an explosion travels for the first 175 feet is only about 350
feet per second, so that the speed during the next 100 feet was about
1,300 feet per second.””

In comparing the pressure curves attached to the record of a con-
siderable number of experiments, the writer of this bulletin notes
that the curves shown by manometers ‘‘B” and ‘‘A” give a time in-
terval of #3; to #%; of a second. The distance separating these
manometers is 100 feet, ‘‘B” being 125 fect and ‘‘A”’ being 225 feet
from the shot, so the record would indicate that the speed of the
preliminary wave between these points was 1,000 to 1,085 feet per
second. In a test in which the igniting shot was fired without the
presence of dust, the air wave registered by the manometers showed
an interval of 4%; of a second, or a velocity of 1,085 feet per second.
The pressures shown by the manometers in this test were light. At
“B” the registered pressure was 24 pounds and at ‘‘A” 1 pound per
square inch,

When the gallery was clear of obstructions, the velocities of the
explosions, like the pressures, were much less than when the gal-


THE COAL-DUST QUESTION IN EUROPE, 25

dynamite; to study the influence of the moisture and ash contents of the coal dust on
its explosibility; the influence of inert dust; and, the effectiveness of water curtains
and wet zones in limiting coal dust explosions. An exploding charge of 250 grams
(9 ounces) of dynamite was used throughout, except where otherwise stated.

In the experiments to determine the lowest limit of explosibility,
three methods of disseminating the coal dust were employed:

Strewing it around cartridges.

Suspending it in the air of the gallery.

Combining the above methods.

The coal dust used contained 13.3 per cent ash, 0.45 per cent
moisture, and 19.2 per cent volatile matter. In the tests with the
first method, using quantities of 2} to 11 pounds of dust, correspond-
ing to 250 to 1,250 grams per cubic meter of air, no ignition was
produced in any of the 25 experiments, even by using 250 grams
(9 ounces) of dynamite.

With suspended dust in quantities of 2} to 8? pounds, or 250 to
1,000 grams per cubic meter of air, some ignitions occurred with 100
grams (34 ounces) of dynamite, and with 150 grams (5 ounces) of
dynamite explosions resulted in nearly every case.

In the third method, using a combination of strewn dust (2} to
43 pounds) and suspended dust (2} to 3} pounds) there were no
explosions in 10 experiments, even with 150 grams of dynamite.
From these results it must be assumed that the coal dust strewn in
the immediate vicinity of the cartridges has a retarding rather than
a stimulating effect on the explosions in the chamber.”

In the experiments to determine the influence of moisture in the
coal dust, light or fine dust was collected from the screening plant
or from the timbering in the mine. The dust contained 12 to 14
per cent ash and 19.7 per cent volatile matter; its moisture content
varied from 0.3 to 10.17 per cent. Violent explosions were obtained
with dust containing only 1 per cent or less of moisture. The violence
diminished with the increase of the moisture content, until with 6
per cent moisture the violence was much less. With dust containing
7.55 per cent no explosion took place, nor was there one with dust
containing 10.17 per cent moisture.»

In the experiments used to determine the effect of ash content,
dust containing 14 to 60.5 per cent of ash was employed, the moisture
content being below 1 per cent. The results showed that with an
increase in the ash content the violence of the explosion and the
length of flame diminished, until with 47 per cent ash no explosion
was produced.

@-The writer of this bulletin questions this deduction; but if it is true of ignition from a suspended stick
of explosive, he believes it would not apply to ignition of dust from a blown-out shot or a gas explosion.

The marked effect with so small a quantity of external moisture would seem lo be due to the relatively
small igniting charge (9 ounces) of dynamite. ‘The experiments at Pittsburg, as cited hereafter, show that
‘the ignition of damp dust, up toa degree of wetness at which it coheres, depends upon the size of the leniting
charge. Using 1,134 grams (24 pounds) of black powder, both ignition aud propagation were obtained
with pure dust (4.50 per cent ash) which contained 19.20 per cent moisture. (See pp. 55-68.)


48 THE EXPLOSIBILITY OF COAL DUST,

speaking, it may be considered that the dusts differentiate not only by their percentage
of volatile matter, but also by other elements of their composition, particularly by the
percentage of ash. But the dusts tested, coming nearly all irom the screens, have &
somewhat similar percentage of ash, which causes the factor ‘volatile matter” to pre-
dominate. The ash intervenes in two ways: First, by its weight; the cloud densities
indicated in the above tables are gross densities; it would be more just to compare the
densities by reckoning only the combustible portion, after deduction of the ash and
moisture; in the second place, the ash intervenes as an inert matter absorbing a part
of the heat of combustion of the dust; it would be too hazardous to try to calculate this
latter influence, which might without doubt be determined by experiment. But in
the following table account is taken of the first influence by showing, alongside the
gross densities, the densities calculated by deducting the ash and the moisture. This
table places clearly in evidence the influence of the percentage of volatile matter.

Cloud densities from | Cloud densities from
which inflammations | which inflammations

Percen commence. always occur.

Calculated
(ash anid
moisture

deducted),

t
Caleulated

ducted). | Gross.

02, pereu.ftJOz. percu.ft Oz. per cu.ftlOe. per eu. ft
Anthracite. a! re !

No inflammation.

By the aid of these numerical results, which, it must not be forgotten, are approxi-
mate, may be drawn the conclusion that there are great differences in inflammability,
under the conditions of the experiments, between the three following groups: Firat,
anthracite and Lens 2, not ignited; sccond, Dourges and Lens 1, inflammable, but
without great effects of flame, and with a marked tendency to stifling; lastly, the four
types richest in volatile matter, which were ignited at low densities and which pro-
duced increased flames as the cloud density increased.

COMPARISON OF TAFFANEL'S METHODS WITH THOSE USED AT
PITTSBURG GALLERY.

The few density tests made at the Pittsburg station (described on
pp. 38-41) were all made with the high-volatile coal from the Pitt:
burg seam. While they were not numerous enough for a direct com-
parison with M. Taffanel’s results, as given above, it would appear
that the initiating charge of explosive was a most important factor.

M. Taffanel, in the experiments described above, used but 1.12 to
1.33 ounces of a low-grade nitro-explosive, while in the Pittsburg
density tests, in a much larger gallery, 1} pounds of black powder
was used. With this charge dust explosions were produced with as
low a density of coal dust as 0.032 ounce of dust per cubic foot of



REMEDIES FOR COAL DUST. 91

effect of dustless and stone-dust zones in preventing or limiting
explosions of a mixture of coal dust and air; but the first experiments
were intended to establish beyond doubt the explosibility of such
mixtures without the presence of inflammable gas and to obtain
data upon which to make comparisons with subsequent experiments
in which dustless and coal-dust zones were employed.

The first series of tests began May 12, 1908, and no difficulty was
experienced in demonstrating the explosibility of a mixture of coal
dust and air. The unusual size of the gallery (see p. 21) and the
heavy explosions of coal dust attracted wide attention. In all ex-
periments the “return” end of the gallery was employed for the ex-
plosions. Dustless zones beyond the coal-dust zone were tried.
They did not appear to be effectual, as the excess dust thrown up
by what the English term “the pioneering cloud” was swept over
a dustless zone and was inflamed by the explosive wave that followed.

The use of stone dust had been suggested to the committee by
Mr. W. E. Garforth, the suggestion being the outcome of his personal
observations at the Altofts’ Silkstone pit after the explosion in 1886.
At that time he noticed that the explosive blast had traversed all
yoads containing a preponderance of coal dust and had caused great.
destruction therein; but the indications of flame and force disap-
peared when the stone-dust roads were reached.*

On June 13 an experiment (test 13) was made with a stone-dust
zone, 158 feet long, placed on the return side of the coal-dust charge,
369 feet long. On the intake side there was a 175-foot dustless zone.
The flame traveled only 44 feet into the stone dust, but 110 feet in the
dustless zone, and at this point the force was so great that it burst
two of the boiler plates of which the gallery was built, the flame
finding relief upward.

The first trial of stone dust on the intake side of the cannon (with
which the explosions were started) was carried out on July 18, 1908
(experiment No. 22). The results were such as to cause the officials
at the Altofts’ colliery to regard the application of stone dust as a
practical undertaking.’

Test 24, August 8, 1908, showed a penctration of flame into the
dirt dust (ground shale) of only 155 fect, while on the opposite (return)
side the explosion was very violent.

In test 25, August 11, 1908, a heavier loading of coal dust than
that previously used was tried, 450 pounds over 450 feet of gallery,

¢ In his evidence before the royal commission on coal dust in mines, July 2, 1901, Mr, Garforth said:
“What are the particular points upon which you think further experiments ara neces: L think we
should conduct ¢xperiments on different. kinds of coal dust and dirt dust. T belleve dirt dust will really
Le the means of preventing explosions in some roads—more so than waler.’"-Finst Rept, Roy, Comm.,
1891, p. 125
> Record of the first series (1908-9) of the British coal-dust experiments. 1910.



ORIGIN AND DISTRIBUTION OF COAL DUST. 37

relative to the total amount mined, in compiling the following table
the coal seam for each test was arbitrarily assumed to be 6 feet
thick. The Fairmont percentages are refigured accordingly.

Comparative amounts of machine and hand cuttings passed through a 40-mesh sieve, in
percentages of total coal produced, assuming a 6-foot seam.

Chain

mghait, | Puncher) Hand.
Westmoreland... 49} 3.25
Fairmont ‘soft art “70 |.
Fairmont “hard” coal, cor} xin |:
Washington Coal and Goke Gomipay. 2230 193
Pittsburgh Coal Company, Midland No. 1. { caf Lah

Average... |

50 7 1.03

@ Chalo with plek potnts,

The figures for the chain machines are fairly close together, also
the two tésts of hand-pick undercutting, but the results of the puncher
tests are too divergent, even after due allowance is made for the phys-
ical character of the coal and ability of puncher machine men.

Judging from the Fairmont figures the quantity of coal dust pass-
ing through a 20-mesh sieve is double what will pass through a 40-
mesh sieve. If we assume the limit of dangerous coal dust as 20-mesh
(the reason for this assumption will appear later), by doubling the
above averages we get 1.00, 2.06, and 0.78 per cent of the total coal
as dangerous dust. If we accept these figures for a mine producing
1,000 tons of coal per day, there would be from 15,000 to 41,000
pounds of dust produced daily from the undercutting, besides a
certain additional amount from shooting down, picking, and shovel-
ing the coarse coal. Tf only a small fraction of the coal dust daily
produced in the ordinary mine is left exposed in rooms and along the
entries, and not rendered inert by natural or artificial means, the
mine will soon contain more than sufficient dust for propagating an
explosion.

AGENCIES TITAT DISTRIBUTE COAL DUST.

While coal dust mainly comes from breaking down coal at the
face of the mine, it is distributed through the mine in several ways:

1. By the force of the explosive used.

2. By the shoveling of coal along the face and into pit cars.

3. By the fine coal running through cracks and holes in pit cars,
and particularly under the car door, which usually fits more or less
loosely, and thus being distributed along the haulage ways.


154 THE EXPLOSIBILITY OF COAL DUST.

INSTRUMENTS AT LIEVIN.

Measurement of pressures.—The recording instruments for meas-
uring pressures at Liévin comprise: (1) Spiral spring gages graduated
to indicate 4, 2, and 5 kilogram pressures per square centimeter; (2)
copper-disk crusher gages of known pattern; and (3) “Thomson’s
tubes,” as used for taking deep soundings. The last consist of thin
glass tubes about 20 inches long, open at one end and filled with
chromate of silver. When placed in an iron tube containing salt

Dismantled section

Present section,

OTM

Figure 14.~Dismantled and present scetions of Liévin gallery.

water and inserted into the gallery, the pressure causes the water to
mount into the glass tubes, <liscoloring the chromate. Although the
pressure records obtained in this manner are not invariably trust-
worthy, the method is inexpensive.

Measurement of rate of propagation.—The rate of propagation of
flame is obtained by means of a number of electric circuits which are
broken by the passing flame. The interruptions of current are
recorded on a chronograph. The connecting wires enter the gallery
at regular intervals through iron tubes fixed under the roof, as shown

in figure 15. The circuit is
“¢ broken at the point marked
i

x through the explosion of a
fulminating cap.

Measurement of tempera-
ture—For measuring the
temperature of explosion a
thermocouple and a Le
Chatelier galvanometer have
been used, but for very
violent and rapid explo-
Frovre 15.—Device for breaking circuit inexplosion gallery gions they are not satis-

at Ligvin, factory.

Taking samples—The contrivance used at Liévin for taking sam-
ples of the combustion gases is a simplified adaptation of the more
elaborate instrument at Altofts, and consists of an evacuated glass
retort ending in a long-drawn closed bent tube at the end of which a
detonator is fixed. The flame fires the detonator and the gases rush
into the glass vessel. By filing an indention into the glass tube at a
suitable distance above the detonator the tube is made to break at
that point and the entrance of fulminate combustion gases is thua
supposed tobe obviated.



INVESTIGATIONS OF THE IGNITION OF COAL DUST. 125

coal dust would be the ease with which the volatile matter is
expelled.

The authors confirm the conclusions of Galloway that the amount
of dust suspended in the air must be considerable to render the
mixture inflammable—that the dust clouds should be very dense,
such that a thickness of 50 centimeters of the mixture in bright
daylight intercepts completely the light from a candle placed in it.
The authors made no special measurements in this connection, but
conclude from their experience that Galloway was correct in assum-
ing that the amounts of suspended dust most likely to give an
inflammable mixture would be 1 kilogram per cubic meter of air.

Berthelot has stated that such an excess of dust is necessary
because the only part of the dust particle that enters into action
is its surface, whereas in gases the mixture exploding most vio-
lently contains the constituents in proper proportions for complete
combustion.

The authors consider that to put in suspension such a quantity
of dust and keep it suspended would require a violent agitation in
the air, because the density of such a mixture is nearly double that
of the pure air, and hence only a considerable force can overcome
the tendency of the two to separate; besides, the dust would be
deposited soon after the cause of agitation ceased. As previously
mentioned, the authors show that according to their experiment a
velocity of 1 meter a second is not sufficient to keep the air charged
to the point of inflammation.

In studying the velocity of propagation of the flame the authors
attempted to use the same method by means of which they meas-
ured the velocity of propagation of the flame in gas mixtures, but
they found that in mixtures of coal dust and air not much agitated
there was no appreciable velocity of propagation of flame, and
conclude that if it exists it must be less than 1 centimeter. The
propagation appears to be effected by the internal movements of the
air instead of by conductivity or radiation.

When the air and dust mixture is agitated by considerable internal
movements, the velocity of propagation is still small, less than 1
meter, which shows the great difference between the velocity of
such a flame and that in an explosive mixture of gases. In con-
firmation of this statement the authors call attention to the fact
that when coal dust was ignited in their long apparatus a shect of
paper which covered the hole in the side of the gallery was not
broken and was scarcely puffed out by the pressure -within.

In applying their results to mining conditions the authors say
that the accidents that can be attributed to dust alone are very
rare, not. dangerous, and that the flame does not extend farther
than 50 meters. The dangerous explosions occur mostly in gaseous


THE COAL-DUST QUESTION IN EUROPE. 21

ALTOFTS GALLERY, ENGLAND, 1908.

In England a new royal commission on mines was appointed in
1906, which began hearing evidence in June of that year. This com-
mission, while taking up all questions relating to mines, has given a
great deal of attention to coal dust and remedial methods. It has
issued four volumes of evidence, one in 1907, two in 1908, and one in
1909, in which many methods for solving the coal-dust question have
been suggested.

The general interest in the subject led the Mining Association
of Great Britain to establish in 1908 a testing gallery of unusual
dimensions at the Altofts colliery in Yorkshire.

With all extensions connected this gallery has a total length of over
900 feet. It is circular in cross-section. The downcast or ‘‘intake” end
is 74 feet in diameter and 400 feet or more long. It is built of ,5-inch
boiler plate, the sections readily separable, so that different lengths
of intake can be used in different series of experiments. To strengthen
it, the intake part has external ribs and it is also wrapped with heavy
chains. The upcast or “return” end is 6 feet in diameter and is
built of $-inch boiler plate. The gallery has six right-angle turns,
including the connection to the intake and the connection to the
upcasting fan. The aggregate length of the return from the con-
nection at the intake gallery to the fan is 295 feet. For the pro-
tection of the fan, each right angle bend has two relief valves. These
valves are the full cross section of the gallery, except the one oppo-
site the main intake, which is reduced by a conical connection to
one-half the area. A concrete floor extends through the gallery; also,
a pit-car track.

Props and bars similar to timbering in a mine heading are set up at
regular intervals in the intake portion of the gallery. These are
wedged in position and numbered, so that if they are blown down, as
generally happens, the distance they are carried by the explosion may
be determined. Some of the props and bars are more securely
fastened, by iron clamps to the boiler shell, so that the position of the
deposits of coke and dust may be noted.

The coal dust required for an experiment is placed on wooden
shelves, which extend as far as required. These shelves are 5 inches
wide and three-fourths of an inch thick. There are five rows of
them on either side of the gallery, placed close to the boiler shell and
supported on iron brackets. When an explosion of the dust is
obtained, the shelves are more or less splintered and the pieces are
blown down or blown out of the gallery.

‘The shelf surface is intended to correspond to the ledges and inter-
stices of the walls of an underground road,

The air current is produced by a fan acting as a suction fan (not
reversible), having a capacity of 60,000 cubic feet of air per minute at
a water gage of 3 inches. It is driven by an 85-horsepower engine.


HUMIDITY OF MINE AIR, 59

cubic foot of completely saturated aqueous vapor weighs 0.481
grain; at 32° the same saturated volume weighs 2.113 grains; at 65°,
an ordinary mine temperature in this country, it weighs 6.782 grains;
and at 90°, the summer temperature, it weighs 14.790 grains. This
is shown in a graphic way in figure 2, which gives the curves of differ-
ent weights of aqueous vapor per cubic foot at different temperatures
and relative humidities.

100,

i
aoe

iil

20

70

Saenne ree

sof EN

Percentage of saturation

30 a
b
es
cI ott
oN
ne A)

10

o 10 20 x 40 100

Temperature in degrees Fahrenheit,

Ficure 2.—Curves of equal weights of water vapor per eubie foot for varying temperatures and relative
huridities when the barometric pressure is 30 inches.

It will be seen, therefore, that when the air and water vapor enter
the mine at 0° temperature and are raised to 65° temperature in their
course about the mine, unless moisture is picked up on the way the
effect is to reduce the relative humidity to a remarkable degree. For
instance, if a given space is completely saturated at 0° and contains
0.481 grain of vapor at 65° this weight of water would correspond
with only 7 per cent of saturation. This effect is strikingly shown
by the curves in figure 2.


BIBLIOGRAPHY. 199

Tarranet, J. Les expériences frangaises sur les poussiéres de houille. Internationaler
Kongress fiir Bergbau, Hiittenwesen, angewandte Mechanik und Praktische
Geologie. Diisseldorf, 1910. Berichte der Abteilung far Bergbau, pp. 224-233.

Essais sur les inflammations de poussiéres exécut la Station d’essais de

Liévin. Bull. Soc. ind. min., ser. 4, vol. 13, September, 1910, pp. 263-304;

December, 1910, pp. 553-599

Abstracts of the reports on the French coal-dust experiments, conducted

at the Liévin experimental station, 1907 to 1910, by J. Taffanel. London. The

Colliery Guardian Company. 1910.

anp Duxaime, Por. Les catastrophes miniéres américaines de Monongah,
Darr, et Naomi. Annales des mines, ser. 10, vol. 16, July, 1909, pp. 1-873
August, 1909, pp. 75-210. Describes mines and mining methods and discusses
causes and courses of explosions. Summarized in Mines and Minerals, vol. 30,
May, 1910, pp. 595-597.

Trornton, W.M., anv Boropey, E. Ignition of coal dust. by single electric flashes.
Colliery Guardian, April 22, 1910, p Account of experiments.

‘Trivpe, Frirz. Stosstrinken und hydraulische Kohlensprengung in Steinkolhlen-
flézen, Gliickauf, June 25, 1910, pp. 977-983. Describes breaking down coal by
injecting water into the face

Ueber Stosstriinken und hydraulische Kohlensprengung in Steinkohlenflézen
nach dem Verfahren des Geheimen Oberbergrats Meissner. Internationaler
Kongress. Diisseldorf, 1910. Berichte der Abteilung fiir Bergbau, pp. 234-245.

Verner, J. Physical action of air a factor in dust explosions. Black Diamond,

7, 1909, pp. 12 Considers dust. a pai factor; says records of Iowa

enty years show no dust explosions between March 12 and October 21.
Concludes heating of mine air and control of its velocity will prevent explosions.

Viren, Josern. Origin of coal-mine explosions. Coal, December 17, 1908, pp. 15-16.
Abstract of paper before West Virginia Coal Mining Association, Gives dust first
place as cause of explosions.

———- Facts disproving recent statement relative to mine fatalities. Eng. and Min,
Jour., vol, 87, January 2, 1909, pp. 12-13. Advocates plenty of air and moistening
of air.

‘The dust problem in coal mines. Eng. and Min. Jour,, vol. 88, October 9,
1909, p. 734. Discusses use of salt and calcium chloride, and experiments at
Plymouth, W. Va.

Warreyne, Victor; Metssver, Cars; anp Desnoroucn, ArtHur. The prevention
of mine accidents. Bull. U. 8. Geol. Survey No. 369, 1908, Ll pp.

Warreyne, Victor, anp Stassart, 8. Courriéres et La Boule; Examen comparatif
de deux grandes explosions. Annales des mine de Belgique, ser. 3, vol. 13, 1908,
p.785. Comments on Courritres and La Boule explosions. Brief abstract of thie
paper in Coal, November 12, 1908, pp. 16-17.

‘Les mines et les explosiis au septi¢me congrés international de chimie appli-

quée. Annales des mines de Belgique, vol. 4, 1909, pp. 1221-1444, Review of

papers and discussion at the congress. Coal-dust experiments (pp. 7]-74) by

P. P. Bedson. Use of sprays in German mines (pp. 75-81) by Forstimann, Report

on coal-dust experiments at Rossitz gallery (pp. 183-207) by Czaplitiski and

Jicitisky.

STANLEY, G. H, Some causes and the prevention of colliery explosions, Tron and

Coal Trades Review, September 30, 1910
Woon, G. R. Electricity in coal mines. Coal Min. Inst. America, June, 1909.



122 THE EXPLOSIBILITY OF COAL DUST.

The experiments were made in two forms of apparatus. The
first resembled that previously used by Galloway, Morison, and
Abel. It consisted of 2 wooden box, 4 meters long, 0.4 meter high,
and 0.15 meter wide. One extremity communicated with a ventilator
capable of giving a pressure of 5 centimeters of water. At 50 centi-
meters from this end was a device to regulate the flow of air, the
velocity of the ventilator being maintained uniform. At a point
25 centimeters farther there was placed on top of the main box or
gallery a second box, perforated for the introduction of coal dust.
The arrangement of the regulator with reference to the point of intro-
duction of the dust was such that the eddy produced at the regulator
served to disseminate the dust through the air. At 2 meters farther
a removable glass window was placed, which permitted the intro-
duction of a lamp and the observation of the results. The other
end of the gallery was open to the outside air, 50 centimeters beyond
this window. When the dust burned it gave a large flame, filling
the whole section and extending out of the orifice.

The second form of apparatus used was simply a cubical wooden
box of 50-centimeter dimensions. At the center was placed a gas
flame directed downward in order to spread it out. In testing the
dust in this form of apparatus a double handful of the dust was held
about 14 meters above the box, and was allowed to fall between the
fingers in such a way as to subdivide it as much as possible. In fall-
ing the columns of descending dust carried along a considerable
amount of air by the time the dust reached the flame, and the eddy
produced in the box by this air kept the atmosphere charged with the
dust. If the sample was inflammable, it ignited at the gas flame.

The sources of heat investigated by the authors were, first, the
normal flame of the Davy lamp; second, the same after regulating
its flame to a height of 5 centimeters; third, a large gas flame; fourth,
a large roll of burning paper.

With finely powdered coal of an inflammable character it was
found that in the first form of apparatus described above inflarnma-
tion took place instantly when the last three sources of heat were
used. With a normal flame of the Davy jamp flashes occurred, after
which the whole was inflamed, the duration of this phenomenon
being only about two seconds.

Coal dust collected in the gallery of the same mine, but less finely
divided, took fire immediately on contact with the gas flame and roll
of burning paper, and after the end of some seconds it ignited from
the flame of the Davy lamp, burning 5 centimeters high. But with
the normal flame of the Davy Jamp, ignition occurred only after
some time, or not at all.

The coarser dust collected from the floor of a gas works ignited
after some seconds from the third and fourth sources of heat, but not



106 THE EXPLOSIBILITY OF COAL DUST.

some diversity of opinion as to results. Mr. Frank Haas’s experiments
with heating the intake at the Monongah mine, as described by him
on pages 174-177, indicate that there is no need of such heating. The
walls of the passageways effectively heat the air in cold weather, so
that the expense of artificially heating a large volume of air does not
appear necessary, if the intake is kept humidified to the point of
saturation as the temperature rises, Some mine operators have con-
sidered heating of great advantage.

In the use of steam sprays the steam raises the temperature of the
incoming air to some extent, depending on the relative temperatures
of the steam and air as well as on their relative weights for equal vol-
umes. The lower the temperature of the external air the greater
the weight of steam necessary to be introduced; hence the greater
the temperature rise of the incoming air. Practically, this rise will
range from 8° to 15° F., depending on a variety of conditions, Theo-
retically, if we should disregard the conductivity of the walls of the
passageway and assume that all the steam in excess of that imme-
diately required for saturating the incoming air is condensed, the
rise would be very much greater. There are so many variable fac-
tors and the influence of the walls is so great that it is impossible to
determine the rise by calculation.

Vaporization.—If the steam sprays are placed at the entrance of
the intake of the mine, when the external air is considerably colder
than the normal temiperature of the mine, the difference being
greater than the rise resulting from the heating by the steam sprays,
the steam in excess of the vapor capacity condenses, and some water
falls to the ground, but as the air current moves rapidly most of it
is carried along mechanically in the form of fog. As the air current
travels along the mine passage and absorbs the natural heat from
the walls, its vapor capacity increases and the fog is gradually
tevaporized, thus keeping up saturation until there is total disap-
pearance of the fog or visible moisture. If at this point the heat
of the air current has reached that of the strata or walls, the air will
remain practically saturated throughout the mine, but if the tem-
perature still rises the air current no longer remains saturated, but
has a relative humidity that decreases as the temperature rises.

Cooling effect of vaporization.—When steam or water sprays are
used, the vaporization of water or the revaporization of fog absorbs
heat with the result of lowering or keeping down the temperature
of the air. This result is only temporary, as the passage walls
impart the difference in heat in a relatively short time. The
amount of the temporary reduction or retardation of tempera-
ture under mine conditions is practically impossible to calculate on
theoretical grounds, owing to the undetermined heating effect of
the passage walls. Water sprays can not well be employed until
the air has risen in temperature to about 32° F. The point in the



108 THE EXPLOSIBILITY OF COAL DUST.

OBSERVATIONS ON MANIFESTATIONS OF COKED COAL
DUST IN MIDS EXPLOSIONS.

CHARACTER OF COKED DUST.

The mining engineers of the Bureau of Mines or the technologie
branch of the United States Geological Survey have investigated all
the greater explosions that have occurred since July 1, 1908.

Of those which have been personally investigated by the writer,
and in which dust played the most important part (though not neces-
sarily at the origin), the most serious were those at Marianna, Pa.,
November 28, 1908, in which 156 men were lost; at the Franklin
slope, Johnstown, Pa., October 31, 1909, in which 13 men were killed
and 2others seriously burned; at Primero, Colo., January 31, 1910, in
which 75 men died; at Mulga, Ala., April 20, 1910, in which 35 men
died; and at Palos, Ala., May 6, 1910, in which 84 men died.

In these explosions the coke manifestations were strong and very
characteristic. From a study of these and previous explosions inves-
tigated by the writer, there appear to be five phases of coke developed
in a mine explosion:

1. Bright splashes of coke on the open exposures, adhering to the
ribs and to a less extent to the roof, indicating an abundance of dust
and an intense heat, but not much movement. Such coke was found
near the heads of entries.

2. Less friable coke or caked dust, in some places over an inch thick,
sometimes found on the exposed surfaces of the walls and posts of
rooms and to a lesser extent on entries facing the source of explosion.
Such coke is found near the origin of explosions or where there have
been secondary explosions. It indicates an abundance of dust and
not much movement.

3. Individual particles of coke, generally bright, and in some places
close enough together to form a thin scale. This is sometimes found
driven into crevices facing the approaching explosive blast, but
usually is on the reverse side of timbers, projections, or rib corners.
Such coke indicates a violent sweep of the explosive blast too strong
to allow deposition on facing exposures, but which whips around the
projections and deposits the semiplastic coke on the lee side.

4. Minute globules of coke as large as j, inch diameter and smaller.
Many of these are perfectly round, and on the interior nearly hollow,
with one or more cells. They are to be found on top of cars at the
face of entries or on other surfaces on which they can be seen. Those
globules falling to the floor are diflicult to observe. Such spheres of
coke are like tiny balloons. They do not adhere together, but have
evidently been cooled in transit through the atmosphere. Their
occurrence, so far as observed, is only as the result of explosions in
mines in which the coal is of a distinctly coking nature or in which the
bitumen is considerable, as coal of the Pittsburg seam. It would
seem that these glowing float globules, or other particles, might be



Fiavure 9.
10.
i.
12,
13.
4.
1b.
16.
V7.
18.
19.
20.

21

22.
23.
24.
25.
26.
27.

28.

ILLUSTRATIONS,

Coal-dust ignition apparatus of Holtzwart and Meyer
First coal-dust ignition apparatus of Bedson and Widdas.
Later coal-dust ignition apparatus of Bedson and Widdas.
Coal-dust ignition apparatus used at Liévin.. :
Relative effect on flame of stone-dust zones at Liévin’
Dismantled and present sections of Liévin gallery .
Device for breaking circuit in explosion gallery at Liévin.
Propagation of flame in coal-dust, dustless, and stone-dust zon
Elevation of apparatus for igniting coal dust by gas flame
Detachable section, Frameries gallery...
Plan of Frameries gallery, showing proposed extension
Constructional details of extension to Frameries gallery
Device for dislodging coal by injection of water...
Atmospheric temperature and water-vapor chart.
Chart of water content of outside air and return air of mine
Chart of temperature and relative humidity of intake air with ex-
haust steam off and heater off...
Chart of temperature and relative humiity with exhaust steam on
and heater off
Plan of intake at Monongah No. 8 mine, ehowing arrangement of of
live-steam heater and exhaust-steam pip
Chart of temperature and relative humidity with exhaust steam on
and heater on......2.21222 0.2 02e2ec eee eee eeee eee
Progressive change of temperature of air current due to radiation...

and at Altofts.

Page.

137

165

176
tT


REMEDIES FOR COAL DUST. 89

The reason for this is that the air waves are not produced freely
and do not raise sufficient dust.

Taffanel reports that dust containing only 12 per cent of volatile
matter did not prove to be inflammable under the conditions of the
tests. Dust containing 15 to 18 per cent of volatile matter, although
proving inflammable, did not propagate explosions; the initial flame
advanced slowly and died away. The effect of shale dust is remark-
able. If quantities of incombustible dust are mixed with coal dust,
the inflammability of the latter is decreased. When the proportion
of the shale dust exceeds 50 per cent, it is difficult to cause inflamma-
tion, but if, on the other hand, an explosion of pure coal dust is devel-
oped through a distance of 75 meters (246 feet), a mixture of even 75
per cent of shale dust with the coal dust in a “stopping zone” of 150
meters (493 feet) is not sufficient to prevent the flame from passing
through this zone.

More favorable results in arresting explosions were obtained by the
employment of what has been termed “concentrated schistification”’
(sometimes called a “dust curtain’). Under this plan inert mate-
rial, like ground shale, clay, slag, or cinders, is placed on platforms
or shelves for a distance of 5 to 20 meters (15 to 60 feet).

‘The material is placed on these boards, which are arranged either against the lateral
walls or against the roof. * * * The arrangements have proven effective, even
when the coal-dust zone was 100 to 150 meters (300 to 500 feet) in length. For exam-
ple, we placed at 150 to 160 meters (500 to 530 feet) from the point of ignition, 10
double boards making platforms 12 inches wide and 5 feet long, spaced 3.3 feet center
to center. On these there was deposited an 8-inch thickness of inert material, boiler
cinders. When the entire length of the gallery was loaded with 450 grams per cubic
meter (0.45 ounce per cubic foot) of very fine coal dust containing 30 per cent of vol-
atile matter, the inflammation was stopped. ‘The air waves which precede the flame
blow off the stored material, thus precipitating the coal dust in the air to the floor,
and at the same time so loading the air with incombustibles that the flame is choked.
We have never yet observed any passage of flame through such an area.

Not less encouraging results have been obtained by putting tanks
filled with water on platforms so constructed as to be easily over-
turned, Witt 10 tanks of 30 liters (8 gallons) each, no matter what
the intensity of the explosion developed along a distance of 150
meters (492 feet), the flame is immediately extinguished by the body
of water precipitated on the overturning of the tanks.*

Following the third series of experiments, the Liévin Gallery was
extended to a total length of 300 meters (984 feet) and a fourth series
of experiments was made on lines similar to those made in the 230-
meter gallery.

eTaffanel, J, Op, cit., p. 232



40 THE EXPLOSIBILITY OF COAL DUST.

cent. If followed out, the curve showing the rate of fall made by
platting the several results makes it probable that after two hundred
and ninety seconds, the average time before the shots were fired, thera
was not in suspension at the middle of the gallery over 24 per cent of
the original amount of dust injected.

METHOD OF TAKING SAMPLES.

The samples of the dust in suspension were gathered by a special
device consisting of a small tube in which dried cotton served as a
filter. This filter tube was attached to a long, thick glass tube, which
was inserted into the gallery through a hole in a paper diaphragm
placed over the third top relief valve of the gallery, 17 feet from the
firing end, so that the filter tube could be placed to draw air and dust
from the center or axial line of the gallery, and at a point where the
end of the flame from the blown-out shot would impinge. Suction
was produced by emptying water from a bottle of 4 liters capacity.
The long glass tube was connected with the top of the bottle by a
rubber hose. The water from the bottle was discharged downward.
through a rubber hose into a similar bottle below. The filter tube
was dried and weighed before insertion and after gathering the sample
was again dried and weighed, the difference in weight giving the
amount of dust in suspension in 4 liters of the gallery atmosphere,
at the average time of taking the sample. Check samples were
taken simultaneously with duplicate apparatus. This apparatus,
designed by Dr. J. C. W. Frazer, was found to work admirably.
Some inconsistency in the amounts of dust in suspension was evi-
dently due to the irregularity of the air currents and the method of
injecting the dust, rather than to the method of sampling. Similar
devices for obtaining the amount of dust in mine air are described by
Prof. Otto Brunck, of the Royal Saxon Mining School, Freiberg ;*
and a more portable form, in which the filter tube is attached to a
brass exhausting syringe of 200 cubic centimeters or more capacity,
is described by Dr. J. S. Haldane in his valuable little book, ‘“The
investigation of mine air” (p. 57).

RESULTS.

Five tests of dust were made under the conditions named, with
amounts varying from 2 to 5 pounds. The results are shown in the
table below. As already stated the fans were started at once after
the dust was injected into the gallery by the blast of compressed air.
One minute later the first sampling of dust in suspension, in duplicate,
was begun, and lasted approximately one minute, After an interval of
another minute, a second sample was taken, also in duplicate. Then

‘Die chemische Untersuchung der Grubenwetier, p. 01.


148 THE EXPLOSIBILITY OF COAL DUST.

pass through the same sieve. To obtain comparable results it will
be necessary to impart to all of a sample such a degree of fineness
that the whole amount introduced into the explosion yessel will take
part in the explosion. A series of experiments is being conducted
on the same coals that were used in the tests described above. The
samples used in this series were ground so that the whole passed
through a 200-mesh sieve. The following results of experiments
are given for comparison of the pressures developed in the previous
experiments with the pressure developed by the same samples
ground to pass through a 200-mesh sieve.

Comparison of pressures developed by 100-mesh and 200-mesh coal dusls of like composition.

Grams per sq. om.
[00-mesh.. 2. eee eee eee Less than 454
549

Coal No. 9780 {559 mesh,

{100-mes
200-mesh

Coal No. 9784 Von. TM

Coal No. 9778

Less than
Coal No. 9781 (ones
100-mesh.

200-mesh .

Coal No. 9785 {

If it is not possible to obtain dust sufficiently finely divided to get
comparable results it will be necessary to screen the samples used for
the tests with more than one sieve and to use in each test only dust
whose particles are between certain sizes. This process may change
somewhat the composition of the dust from that of the original coal
and will not be used except as a last resort.

SIGNIFICANT POINTS IN EXPERIMENTS.

In closing this short summary of the laboratory experiments on the
ignition of coal dust, it may be well to call attention to certain facts
which they show. In the first place, the phenomenon of ignition is
very complex, and for that reason it is necessary to have the proper
conditions in order to demonstrate the ignition of coal dust on a
laboratory scale. It has been pretty well demonstrated by these
experiments that the order of inflammability of a coal dust is a fune-
tion of the amount and character of the volatile matter which is
expelled, the ease with which it is given up, the fineness of division
of the dust particles, the density of the cloud, the character of the
source of ignition, the amount of water and ash, and, finally, the
pressure prevailing in the neighborhood of the flame. It does not
seem that sufficient attention has been given to the last condition.
Several facts brought out in the experiments support this statement.

Unless there is an exceptionally large amount of dust in the air,
experience shows that ignition does not take place from a naked flame.



INVESTIGATIONS OF THE IGNITION OF COAL DUST. ews

EXPERIMENTS OF VITAL.

While investigating the cause of a certain mine explosion Vital
concluded that coal dust had been an important factor in the acci-
dent, and he accordingly began certain laboratory experiments to
see if it were not possible to ignite coal dust.

His apparatus (fig. 5) consisted of three parts—an explosion gal-
lery, a gas burner of special construction, used as the source of ignition,
and a device for measuring the violence of the explosion. The
explosion gallery was a straight glass tube (g) 3.5 centimeters in diame-
ter and 2 meters long. The end of this tube at which the ignition
took place was somewhat enlarged, the opposite end somewhat con-
stricted. Along the outside of this glass tube was pasted a strip of
paper marked in 2-centimeter divisions in order to measure the
distance to which the flame was propagated. Inside of the tube, at
distances of 1.5 to 1.75 meters from the larger end, were placed small

ieces of lead wrapped in paper to serve as indicators of the character
of the flame traversing the tube. The ignition was brought about by

¥icurs 5.—Coal-dust ignttion apparatus of Vital.

means of a specially constructed gas burner (6) situated at the larger
end of the gallery tube. The gallery was movable, so that the flame
from the gas burner could, at the proper instant, be directed momen-
tarily into the larger end of the glass tube along its axis. This gas
burner was operated by a foot bellows (f). Intervening between the
bellows and the lamp was a glass reservoir into which the air entering
from the bellows was directed toward the bottom. By this arrange-
ment the gas burner could be operated by pure air by direct connec-
tion with the bellows or it could be fed by a dust-laden atmosphere
by placing dust on the bottom of the reservoir beneath the opening
from the bellows. At the opposite end of the gallery was placed
the arrangement used for estimating the violence of the explosion in
the gallery. This consisted of a light pith ball (A) 2 centimeters in
diameter, the surface of which was coated with a layer of ivory black.
This ball was placed against the open end of the gallery and rested
against the front of a graduated circle (4), the divisions on which
were 2 degrees cach.

4 Annales des mines, ser. 7, vol. 7, 1875, p. WW.


94 THE EXPLOSIBILITY OF COAL DUST.

lery was timbered. In experiment 110, on South African coal dust,
the velocities, recorded at 50-foot intervals from the point of ignition,
were as follows: 39.7, 52.5, 72.5, 119, and 222.6 feet per second,

Concerning the obtained differences in pressure and velocity
between a clear gallery and one obstructed by props and bars, the
Altofts committee states that experiment will be needed to determine
the reason for this difference. The committee suggests—

that the timbers by offering a certain amonnt of surface at right angles to the direction
of inovement of the explosion enable a compression wave to be formed, thereby
causing heat to be generated and combustion of the dust to be more rapid. Another
possible explanation is that each prop presents a surface upon which the coal dust
can be driven by the advancing heated gases and distilled, the coal gas produced then
propagating with greater violence. Such a distillation, however, takes
time, compared with the rate at which the explosion is traveling, so that it is very
doubtful whether actual propagation of the explosion occurs by any other means than
combustion of the dust as a whole; distillation may and, in fact, does occur, but there
is more reason to believe that it is effected by the heat products of combustion, and is
subsequent to the passage of the explosion. A third explanation can be found in the
mechanical action of the props in forming eddies and enabling a better mixing of the
dust and air to take place than would otherwise oceur.¢

A series of experiments was conducted in which stone dust. was
mixed in various proportions with the standard coal dust from the
Altofts collieries; the quantity of coal dust used was varied also.
The results of these experiments indicate that if thequantity of coal
dust present in a given area is increased, the proportion of stone dust
in the mixture must be increased to prevent propagation of an
explosion. For example, with 0.2 ounce of a mixture of stone dust,
with coal dust per cubic foot of air space of the gallery, propagation
was prevented when only 10 per cent of the mixture was stone dust.
With 0.6 ounce of the mixed coal dust and stone dust, propagation was
obtained when 20 per cent of the mixture was stone dust, bul only
ignition occurred when 30 per cent was stone dust. With 1 ounce of
a mixture of coal dust and stone dust containing 40 per cent stone dust
there was propagation, but when 50 per cent of the mixture was
stone dust evidence of flame was found only 10 feet from the
cannon,

The theoretical quantity of Altofts Silkstone coal required for the
complete combustion of the oxygen in 1 cubic foot of air at 15° C.
is 0.1185 ounce.” The committee states that at first sight the theo-
retical amount of coal dust required to exhaust all the oxygen in the
air should produce a more explosive mixture than one containing a
great excess of coal dust, us the excess might exercise a retarding
effect by cooling the flame, but on consideration, they think it is-~

more likely that the presence of the excessive coal dust would favor the propagation
of the flame; for the reaction takes place between molecules of oxygen on the one hand

@ Record of the first series (1008-9) of the British coal-dust experiments,
> Compare with figures for Pittsburg coal, p». 50,


BUREAU OF MINES AULLETIN 20. PLATE It

3 Ge 5 6 7

ce

~

COKED DUST FROM PITTSBURG GALLERY DENSITY TEST WITH 200-MESH DUST.

Photographed natural size on paper divided into half-inch squares. Experiment G-2892.