GENERAL DESCRIPTION OF EXPERIMENTS. 45

the atmosphere, and thus the explosion may have been started with
greater strength. In the main entry the flame was 552 feet in length,
and therefore passed 262 feet beyond the end of the zone of loading,
as compared with 175 feet in the previous test. There was also much
more physical manifestation of violence at the mouth of the mine.

The pressure wave between stations E 650 and E 550 had a velocity
of 1,136 feet per second, and between stations E 550 and E 450 of
1,116 feet per second. This wave was probably that produced by the
shot of the cannon and did not represent the explosion wave which
followed it. The flame circuit breakers at the 100-foot stations
between E 650 and E 250 showed velocities of 220, 254, 398, and 51
feet per second, thus indicating that the inflammation was relatively
slow, and was dying away when it reached station E 250. (See fig. 10.)
The last evidence of flame as shown by tufts of guncotton was 58
feet outby station E 250. Manometric pressure readings were not
obtained, except for pressures below atmospheric, following the ex-
plosion. The curve obtained is shown in figure 21. The maximum
depression was about 1 pound per square inch, and the total period
of depression was one-fourth of a second only. The details of this
test are given on pages 91 to 95.

EXPLOSION TESTS 9, 10, AND 11.

In test 8, pressure circuit breakers set to release at a pressure of 2
pounds were seemingly operated by the pressure wave from the
blown-out shot from the cannon. Further tests were required, there-
fore, to determine the minimum pressures at which the circuit breakers
might be set without risk of being operated by the wave from the
cannon. In test 9, made February 8, 1912, and in tests 10 and 11,
made February 9, 1912, no coal-dust load was used, and the entry was
wet down with hose. The cannon was loaded with 2? pounds of
black blasting powder, with 4 inches of clay stemming. In test 9
there was one circuit breaker at each station, and all were set to re-
lease at a 2-pound pressure; all were operated on the discharge of
the shot. In test 10 two circuit breakers were installed at station
E 650, one set to release at a 3-pound pressure, and one at a 4-pound
pressure; both were operated by the shot. In test 11 the two circuit
breakers installed at station E 650 were set, one to release at a 5-pound
pressure and the other at a 6-pound pressure; neither was affected
by the pressure from the shot.

As a result of these tests it was decided that in future tests when
the coal dust was to be ignited by a shot from the cannon the pressure
circuit breakers should be set to release at a pressure of 5 pounds.
The tests demonstrated what has been suspected—that a blown-out
shot from a cannon causes a higher air pressure than a shot of the
same weight of charge placed in the coal face, even when a pipe liner


DETAILS OF EXPLOSION TESTS. 101

Analysis of stone dust.—
Organic hydrogen. 0.39
Organic carbon. .- 7.59
Moisture (at 105° C.) 3.94
Inorganic volatile matter (combined water, CO», ete _ 5.42
Ash... 2... eee e eee eee eee eter reer eee ee 82. 66
100. 00

OUTSIDE MANIFESTATIONS.

The steel sheets of the explosion-door section were disarranged.
The smoke and coal dust shot out of the main opening for a distance
or 100 to 150 feet.

INSIDE OBSERVATIONS.

Little violence was manifest. The curtain in the air course was
blown down; a few of the bags in the cut-through were disarranged.
The shelves of the Taffanel barrier were not disturbed.

LENGTH OF FLAME.

None of the guncotton tufts not affected by the preceding test was
affected by this test, so that the length of the flame was manifestly
not greater than in the preceding explosion. No recording instru-
ments were used in this test.

TEST 14.

Date.—February 19, 1912.

Purpose.—To study the propagation of coal-dust explosions, and
the efficiency of Taffanel barriers.

Point of origin of explosion.—F ace of main entry, at E 744.

Method of ignition.—Blown-out shot from cannon.

Ignition charge——Two and three-fourths pounds of FFF black
blasting powder, tamped with 4 inches of damp shale dust.

COAL DUST.

Source.—The coal dust was ground from bituminous coal from the
Pittsburgh bed at Willock, Pa.
Size.—Over 95 per cent passed through a 100-mesh screen.

Analysis.—
Moisture 3.30
Volatile matter.

Fixed carbon


BUREAU OF MINES BULLETIN 58 PLATE I

A, REINFORCEMENT OF PORTAL.

@. EXTERNAL EXPLOSION GALLERY,


SL 4S31L ‘W1¥Od WOH4 ONINSS! NOISOTEX3



DETAILS OF EXPLOSION TESTS. 97

Ignition charge-—Two and three-fourths pounds of FFF black
blasting powder tamped with 4 inches of damp clay.

Coal dust.—None used.

Inert zone.—The entry was sprinkled for its entire length.

Instruments.—Two circuit breakers were installed at station E 650,
one adjusted to operate at a pressure of 5 pounds and the other at a
pressure of 6 pounds.

Results.—Neither of the pressure circuit breakers operated.

Conclusions.—In tests 9, 10, and 11 circuit breakers set to release
at pressures of 4 pounds or less were operated by the pressure from
the blown-out shot, whereas those set to operate at a pressure of 5 and
6 pounds did not operate. As a result of these tests it was decided
in future tests in which the igniting shot was from the cannon with
the usual charge and stemming to set the pressure circuit breakers to
operate at a pressure of 5 pounds.

TEST 12.

Date.—February 10, 1912.

Purpose.—Study of the propagation of coal-dust explosions and
the efficiency of Taffanel barriers.

Point of origin of explosion.—F ace of main entry, E744.

Method of ignition.—Blown-out shot from cannon.

Ignition charge-—Two and three-fourths pounds of FFF black
blasting powder, tamped with 4 inches of damp shale dust.

COAL DUST.

Source.—The coal dust was ground from bituminous coal from the
Pittsburgh bed at Willock, Pa.

Size.—95 per cent passed through a 100-mesh screen.

Analysis.—

Moisture......

Volatile matter.
Fixed carbon.

Sulphur.

Zone.—From E 744 to E 34, or 710 feet.

Position.—E 742 to E 726 on a bench placed just below the level
of the bore hole of the cannon; E 733 to E 34 on permanent side
shelves on both sides of the entry.

Quantity—Four hundred and eighty-two pounds. The first 290
feet was loaded at the rate of 1 pound per linear foot; the outer 420
feet was loaded at the rate of 0.457 pound per foot.



54 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

The B. C. D. pressure manometers do not register pressures below
atmospheric pressure on the same instrument that records the posi-
tive pressures. In several of the experiments one of the manometers
was arranged to record pressures below normal atmospheric pressure.
In each case the instrument was placed in the station 50 feet from
the entrance. In test 15 the maximum depression registered at this
point was about 1.80 pounds, sustained for one-tenth of a second,
the entire period of depression being three seconds.

MAXIMUM-PRESSURE GAGE RECORDS.

On account of imperfections in the copper cylinders of the maxi-
mum-pressure gages used in the later tests of the first series, the
results obtained were not reliable. It is hoped that with improve-
ments in making the cylinders the maximum-pressure gages will fur-
nish as reliable a check on the records obtained with the recording
manometers as that reported in the Liévin tests.

GAS SAMPLING.

The difficulties that were experienced in getting samples with the
B. C. D. automatic samplers have been discussed in detail on page 38.
No samples of afterdamp were obtained except those gotten by hand
at a considerable interval after the explosion. In addition to the
improvements planned on the B. C. D. instrument, it is proposed to
employ other gas samplers arranged in groups of three at one station,
to be automatically actuated by the flame so that three gas samples
may be taken at predetermined intérvals during and after the passage
of the flame.

Two samples of afterdamp, gathered by men wearing breathing
apparatus 15 minutes after explosion test 15, are of much interest.
They were taken at points only 150 and 200 feet from the mouth of
the main entry; consequently they were largely diluted by the air
that entered immediately after the explosion. The most striking
feature of the analyses (see page 113) is the high ratio of carbon
monoxide to carbon dioxide (1:1.51 in the first instance and 1:1.36
in the second instance), which seems to indicate that at the time of
explosion there was a great excess of carbon in the air.

VENTILATION.

In all of the experiments, except in test 8, there was employed a
ventilating current with a velocity of about 100 linear feet per minute,
the current traveling in the same direction as the explosion. Test 8
was made in still air. In other words, the explosion traversed the
return-air passageway. In the next series of experiments it is


MEASUREMENT OF VELOCITY AND PRESSURE. 63

FLAME CIRCUIT BREAKERS.

The method of obtaining the velocity of the flame is the same as
that for obtaining the velocity of the pressure wave, except that a
different form of circuit breaker is used. The breaker must be sensi-
tive to heat but not affected by pressure.

The first form of flame circuit breaker tried was simply a detonator,
such as is used for “setting off” dynamite, placed in a wooden block,
so that its open end would be exposed to flame passing through the
entry and having a small wire wrapped a couple of times around it.
The ends of this wire were carried back through separate holes in the
wooden block and connected in the automatic commutator circuit.
Each detonator was made extremely sensitive to heat by coating the
inside and the open end of the brass capsule with silver carbide,
which explodes at a lower temperature than the fulminate. This
carbide coating was suggested by W. O. Snelling, chemist, formerly
connected with the bureau.

In a slight modification of this form of circuit breaker the silver
carbide was placed on a match stick instead of directly upon the brass
cap. The advantage of the modification was that the match stick
could be put in the detonating cap a few minutes before the explosion
and not have as much time to collect moisture from the damp mine
air as did the cap, which had to be in place two or three hours earlier.

The detonator form of flame circuit breakers, however, was not
entirely satisfactory. It was finally replaced by the tin-foil circuit
breaker, which consists simply of a small strip of tin foil that is fused
by the heat. Each strip is about one-fourth of an inch wide and 14
inches long, and is placed in a groove (about three-sixteenths of an
inch deep) in a wooden block, for protection against mechanical
injury. Wires fastened to either end of the strip are carried back
through the block and make connection with the instruments in a
manner similar to that described for the pressure circuit breakers,
except that circuit breaker 1 is connected to stud 2 (fig. 14) on the
automatic commutator. The first point on the commutator is con-
nected to a fine wire stretched across the entry in front of the igniting
shot. The wire is similar to the “ignition wire” connected to one
indicator of the B. C. D. manometers.

The pressure circuit breakers and flame circuit breakers, in the
series of tests here described, were placed at intervals of 100 feet along
the main entry of the mine in the stations already described, the first
one being about 100 feet from the igniting shot.

72322°—13——5


INTRODUCTION. 15

small quantities of methane are present without the large wreckage
that would be liable to result in a surface gallery. The study of the
effect of the presence of small quantities of methane is of great
importance; probably more often than has been suspected, methane
has been present in an amount too small to be detected by a safety
lamp yet has been influential in the first ignition and propagation of
a dust explosion.

Among other possibilities offered by the experimental mine when
equipment suitable for each class of experiments has been installed
is that of testing the relative dust production of different kinds of
undercutting machines, and of investigating the safety features of
underground electrical installations, including tests of devices for
greater safety in the use of the electric-trolley locomotive, and of
studying problems of mine ventilation, such as the efficiency of fans,
doors, and stoppings, and the determination of the frictional resistance
to the passage of air currents offered by the ribs, roof, and timbering
of mine entries and rooms. The figures currently used as coefficients
of friction of air passing through underground passageways are
approximations, and the wide range of values of the coefficients given
by different authorities shows the need of more positive determina-
tions. Altogether, the possibilities for usefulness of the experimental
mine are limited only by the appropriations that may be available
from year to year.

The scientific study of coal-dust explosions in the experimental
mine has been only begun. The most important results of the pre-
liminary series of experiments described in these pages have been:
(1) To convince the mining public that coal-dust explosions can be
produced at will in a mine as well as in a gallery, and (2) to show
that relatively violent explosions of coal dust can be produced by a
violent means of ignition in a comparatively short length of passage-
way. The second result is of importance because it shows the neces-
sity of preventing an ignition of coal dust rather than of attempting
to limit an explosion by zonal treatment except as the latter is made
a secondary safeguard.

ACKNOWLEDGMENTS.

For assistance rendered in developing the experimental mine the
writer of this introduction, who was placed in general charge of the
investigations, desires to express appreciation of the inspiration and
guidance received from Director Holmes, and the hearty and efficient
cooperation of his associates, L. M. Jones, mining engineer; H. C.
Howarth, mine foreman; J. K. Clement, physicist; and W. L. Egy,
assistant physicist. Many others connected with the bureau, but not
directly connected with the experimental-mine work, contributed
valuable assistance, among whom are H. H. Clark, electrical engineer;

72322°—13—2,


106 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
COAL DUST.

Source.—Coal dust was ground from bituminous coal from the Pitts-
burgh bed, some of which was obtained from the Oak mine, near
Pittsburgh, and the remainder from the mine at Willock, Pa.

Size.—Over 95 per cent passed through a 100-mesh sieve.

Analysis.—An analysis (No. 13389) of the coal dust from coal from
Oak mine was made with the following results:

Moisture . . 2 248
Volatile matte: 36.73
Fixed carbon. . 56. 16
Ash........ . 4.68

100, 00
Sulphur... c0eceeececeeeeeeeeeeceeeeeeecececececsnseeeeeeees -99

Zone.—In entry, E747 to E 34, or 713 feet; in cut-through 50 feet;
in air course, A 654 to A 427, or 227 feet, and A 347 to A 290, or 57
feet; total, 1,047 feet.

Position. —E 747 to E 731 on bench just below the level of the hole
containing igniting shot; E 733 to E 34 on permanent side shelves,
also on the floor; in cut-through and air course, on floor, and on three
transverse “‘book”’ shelves,

Quantity—Two thousand two hundred and thirty-two pounds, or
an average of 2.13 pounds per linear foot; equivalent to 0.568 ounce
per cubic foot or 568 grams per cubic meter.

Inert zones.—Air course, A 290 to opening; gallery slant.

TAFFANEL BARRIER.

Location.—A 427 to A 347.

Length.—Kighty feet.

Number of shelves.—Thirteen.

Distance between shelves.—Six to seven feet from center to center.
Width of shelves.—Twenty inches.

Thickness of shelves.—One inch.

Depth of stone dust.—Six and one-half inches.

Obstruction.—10.4 per cent of total cross section.

Analysis of stone dust.—

Organic hydrogen. 0.39
Organic carbon. . 7.59
Moisture (at 105° ¢.) 3.94
Tnorganic volatile matter (c ombined water, ©, etc.) - 5.42
Ash. cece ete eeee eee ceveees 82.66

100. 00


112 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

barrier remained standing after the explosion; all the rest of barrier
was blown down and the shelves destroyed. The posts and side
supports were scattered along the entry for 150 feet outby.

One of the track ties at A 330 was broken at the middle and the
east end moved outby. Ties at A 290 and A 281 were also broken
in like manner. These breaks were probably due to blows received
from the flying posts of the stone-dust barrier.

COAL DUST AND COKED DUST.

No coke or coked dust was noted in the entry from the opening
to E 550. Practically all of the coal dust had been swept from the
shelves throughout this length, so that the blast was probably too
great to allow deposition of coked dust. From E 550 to the face
there were increasingly large deposits of soot on the shelves. There
was a deposit of coked dust on the outby side of a post at E 648;
also heavy deposits on the inby corner of the third cut-through and
the entry. At E 656 there were smaller deposits on the inby side
of a post on the east side of the entry, and on the outby side of a
post on the west side of the entry.

The coal in the entry near the cut-through and through the cut-
through had many new blisters. The east rib of the air course
opposite the third cut-through and for a short distance outby this
point was badly blistered.

In the air course there were still large quantities of coal dust remain-
ing on the floor from A 650 to A 450 but in decreasing amount as
A 450 was approached. The coal dust overlaid the shale dust from
A 450 to A 350. There was considerable coal dust still remaining
on the floor for 75 feet outby this point but very little beyond.

A sample of the coked dust from the inby corner of the main
entry and the third cut-through was analyzed with the following
results:

Moisture. . 1.10
Volatile matter. 15.40
Fixed carbon 43.19
40.31
100. 00
Sulphur 2.000000... 0ceceeececccee eee eceecee cece eee eneeeeeeeeees 1.54

The ratio of volatile matter to fixed carbon shows a large decrease
in the percentage of volatile matter over that in the original coal

dust.
EFFECT OF BARRIER.

It is not known precisely how far the flame extended beyond
the Taffanel barrier. A guncotton tuft 30 feet inby the mouth of
the air course was not burned, whereas at 55 feet inby the air-course






DETAILS OF EXPLOSION TESTS. 81
TEST 4.

Date.—Sanuary 31, 1912.

Purpose.—To determine the possibility of an explosion from the
same dust as was used in preceding test.

Point of origin of explosion—Face of main entry, E 738.

Method of ignition.—Blown-out shot from 1}-inch pipe in the coal.
The hole in which the igniting charge was placed was 2 feet 4 inches
above the bottom, and 16 inches from the west rib. The axis of the
hole intersected the floor 16 feet from the face.

Ignition charge—Two pounds of FFF black blasting powder,
tamped with 5 inches of damp clay stemming.

COAL DUST.

Zone.—E 738 to E 654, 84 feet.

Position.—E 738 to E 732 on bench placed just below the level of
the hole containing the igniting charge; E 733 to E 654 on permanent
side shelves on both sides of the entry.

Quantity.—Twenty-six pounds of fresh dust was placed on bench
in front of shot; dust on the shelves was that remaining from the
preceding test in which 105 pounds had been used.

Inert zone.—Preceding the previous test the main entry had been
watered from E 650 to the opening. Some coal dust had been blown
from the shelves onto the floor of the entry from E 650 outby, so
that this zone was not as inert as it had been in test 3. The air
course, for a like reason, had a thin coating of coal dust on the floor.

TAFFANEL BARRIER.

Location.—In the air course, extending from 5 to 85 feet outby the
third cut-through.

Number of shelves—Eleven.

Distance between shelves.—About 8 feet from center to center.

Width of shelves.—Twenty-four inches.

Depth of shelves.—Two inches.

Depth of stone dust—Seven and one-half to 8 inches.

Obstruction.—13.81 per cent of the total cross section.

Analysis of stone dust.—

Organic hydrogen. . . 0.15
Organic carbon. 1.98
Moisture (at 105' 2,87
Inorganic volatile matter (combined water, CO», etc. 8.42

86,88


DESCRIPTION OF MINE AND EQUIPMENT, 33

replacement after each experiment would be too slow and too
expensive.

For the experimental mine it was decided to use fixed and some-
what permanent wooden shelving (Pl. II, A) which could be kept
reasonably dry and be easily cleaned. The shelving is made heavy,
of 3 by 4 inch hard-pine material, in order to lessen breakage. It was
thought that if the shelves were set close to the ribs and were con-
tinuous and smooth, like the rifling of a gun, they would not be
seriously damaged. This generally has proved to be the case, except
that shelving in front of an opening is liable to be broken down.
The shelving is placed with the 3-inch side horizontal. In the lined
sections bolts were set in the concrete wall during construction, so
that each 16-foot length of shelving is supported by three §-inch
bolts, which pass through the timber; the bolts are drawn up, pressing
the shelving tightly against the concrete. (See fig. 5.) In the unlined
portions of the entry 8 by 8 inch posts are used to support the shelves
(Pl. II, A); they are recessed into the ribs so as to present little or
no projection for the pressure wave to strike. However, in a few
tests some of the posts, in spite of being wedged, have been drawn
out of the recesses, presumably by the depression wave following the
explosion waves. It has therefore been necessary to anchor the
posts to the ribs by bolts set into drill holes in the coal rib and
cemented,

At the time of the first two official tests the shelving arrangements
had not been completed, so that it was necessary to set up temporary
props and place the shelving without fastenings. The result was that
in the tests all the shelving throughout the mine was thrown down;
some of it was broken, and many pieces were blown out of the mine
to the hillside opposite.

INSTRUMENTS USED IN THE FIRST SERIES OF TESTS.

In the study of coal-dust explosions it is desirable to have flame
and pressure records at as many points along the course of the explo-
sion as practicable. It is important that each record should show
the rise and fall of each pressure or depression wave that passes the
recording instrument; it is equally necessary that each record should
have the same time intervals marked upon it, so that the records
made at successive points may be compared; and it is of the utmost
importance that the position of the forward point of the flame and its
duration with reference to the curves of the pressure waves shall be
obtained at the various stations. The instruments used at Liévin
photograph the flame directly on the manometer films on which the
pressure records are photographically recorded. The instruments
used at Altofts and at the experimental mine in this series of tests


50 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

on a single-stylus chronograph (time marker) and an intermediate
automatic commutator which, under the arrangement of the instru-
ments, did not act quickly enough for the higher velocities, was not
satisfactory, as a failure of any one of the circuit breakers to operate
prevents obtaining records beyond that point. Therefore, it has been
decided that in future tests there is to be a chronograph with as many
recording pens as there are circuit breakers, so that each may be

T
an

ce

T
26 t
¥

22

2.0)

S

‘TIME, SECONDS
&

Es

o CT)
DISTANCE FROM FACE, FEET

FIGURE 9.—Relative positions of flame and pressure wave, test 15.

independent in registration although marking on the same drum;
the registration will then be referable to the same time intervals.
When a blown-out shot has been fired the shock wave raises the
coal dust in the vicinity into the air, and the flame ignites the dust.
At first it would seem there is merely quiet combustion, but if
the coal dust is inflammable, pressure is gradually developed and
the pressure waves start. In test 15 the period of developing pres-
sure, including time of traversing the first 300 feet, occupied 2}


DESCRIPTION OF MINE AND EQUIPMENT. 29

tube during the first series of tests. It will be returned to the air
shaft when the larger fan has been erected.

There has been much contention among mining men as to the effect
of a ventilating current on the initiation and propagation of a dust
explosion. Some claim that a dust explosion always ‘‘goes against
the air”; that is, advances toward the intake air on account of the
additional oxygen it meets in an opposing current of fresh air. They
claim further that this condition has most effect in wintertime when
the intake air is colder than the return air and hence has greater
density and contains more oxygen per cubic foot. Others have
thought that the reason that coal-dust explosions are more apt to
traverse the intakes than the returns is that the intake air, cold and
carrying little moisture, dries the coal dust, whereas the return air is,
as a rule, nearly saturated, and the coal dust in the return passageways
is apt to be damp. Many have believed that it was a case of the
explosion seeking the dry coal dust, whether this is to be found on
intake or return. Further, some have suggested that a high velocity
of the air current greatly increases both the risk of a dust explosion
and its violence. By conducting identical tests except for the direc-
tion of the air current, one set of tests with the air moving in one
direction, with different velocities, and another set with the air
moving in the other direction but with similar velocities, the influence
of the direction and the quantity of air current can probably be
determined within reasonable limits.

POWER PLANT.

The power plant consists of one 60-horsepower boiler of locomotive
type, placed in a galvanized-iron boiler house sufficiently large to
permit the erection of a duplicate boiler. There are the necessary
steam appliances, hot-water heater, pump, and other fittings. The
engine plant is in an annex to the boiler house, and consists of an
8-horsepower steam-generator set, the speed regulation of which is
close with change of load.

The generator set is for the purpose of supplying electricity for the
recording instruments and for lighting the mine, stations, and build-
ings. It is expected that in the future a sufficiently large generator
set will be installed to enable experiments to be made with electric
machinery, electric motors, and electric coal cutters. Since the first
series of tests, a single-stage air compressor with a capacity of 174
cubic feet of air per minute at atmospheric pressure and capable of
compressing to 100 pounds has been installed for the immediate
purpose of running a “puncher” air machine. In the next series of
experiments compressed-air jets assisted by the fan will be tried for
cleaning the dry dust and soot from the shelves and the walls of the
entries.


COMMENTS ON THE DATA OBTAINED. 53

From the evidence of test 15 alone, the flame would appear to
travel at the start more slowly than the front of the pressure wave;
at 2.3 seconds after ignition the curves (fig. 9) indicate that the flame
was 225 feet behind the front of the pressure wave; at 2.4 seconds
after ignition it was 250 feet behind; at this point it began going
faster than the pressure wave. The precision of these registrations
is admitted to be somewhat uncertain. As stated, the pressure cir-
cuit breakers indicate only the front of the pressure wave; the flame
circuit breakers do not act until the tin foil has melted, so that
there is an appreciable lag, although this lag should be the same at
each circuit breaker. From observations of issuing flame and rec-
ords obtained from surface gallery explosions and from Taffanel’s
records of the Liévin station, it would seem that the flame is pointed,
the point being in advance of the body of the flame, which fills the
passage and melts the tin foil. If this is so, it is probable that the
point of the flame may be much closer to the front of the pressure
wave than is indicated by the curves of figure 9.

In future experiments the relation of the flame to the pressure
wave will be made a special study. Manometers like those used by
Taffanel will be tried. As the manometer drums carry sensitized
paper the pressure curve will be photographed through the medium
of a ray of light thrown on a mirror attached to a deflecting dia-
phragm, and simultaneously, through a glass-covered opening, the
light from the flame will be photographed on the same paper, so that
the exact time relation may be obtained.

RECORDS OF PRESSURES.

The B. C. D. manometers proved to be fairly satisfactory for the
conditions to which they were subjected. Unfortunately, the motors
supplied with the manometers were too small, with the result that
in several tests no records were obtained. For the last test (test 15)
stronger motors were installed. Although the instruments were
designed with a view to reducing to a minimum the inertia of the
moving parts, this inertia is large enough to introduce considerable
errors in the records of pressures that rise with the rapidity of those
resulting from explosions. In future tests it is planned to supplement
the B. C. D. manometers with instruments of different design, in
which the inertia of the moving parts will be much less.

As already commented, it is probable that the manometric curve
(fig. 15) for station E 150 in test 1 does not show the maximum pres-
sure. The highest point registered was 50 pounds, but it is quite
possible that the peak of the curve was considerably higher. The
same is true of both the manometric curves (fig. 27) in explosion 15,
in which the highest point of the curve registered by the manometer
at station E 150 was 103 pounds, and at station E 50, 60 pounds.


82 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
INSTRUMENTS AND RECORDS.
No instruments were used in this test.
OUTSIDE MANIFESTATIONS,

The steel sheets over the explosion-door section rattled, but were
not moved to any great extent by the explosion. The second puff
blew open the east door on top of the air shaft. Eight well-defined
puffs of smoke were seen to come from the shaft. The only indica-
tion of an explosion at the main entry was a flurry of snow and dust
from the opening to the end of the dump.

INSIDE OBSERVATIONS.

An examination of the face of the entry showed that the pipe in
which the charge had been placed was split its entire length, and the
coal was broken for 18 inches back from the front of the hole.

Shelves from E 650 to E 350 had a fine coating of coal dust. which
had been blown from the dust zone. A deposit of coked dust was
found on the east shelf outby the third cut-through.

The shelves from E 738 to E 610 were coated with soot deposited
from the smoke of the explosion. A small deposit of coked dust was
found on the shelves inby E 670.

LENGTH OF FLAME.

None of the strips of guncotton unaffected by the preceding explo-
sion was affected by this explosion. It is probable that the length
of flame of the two explosions was about the same.

TEST 5.

Date.—February 2, 1912.

Purpose.—In test 3 of January 31, the circuit breaker at station
E 650 operated, but none of the other circuit breakers was acted on
by sufficient pressure to break the circuits. It was thought that had
the circuit breakers in the preceding explosion been so adjusted that
they would have been operated by less pressure, more records would
have been obtained. Therefore, this test was made to determine
what was the least pressure to which they could be adjusted and
still not be operated by a blown-out shot in the coal face.

Point of origin of explosion.—Face of main entry, E 744.

Method of ignition —Blown-out shot from 14-inch pipe in the coal,

Charge.—Two pounds of FFF black blasting powder tamped with
5 inches of damp shale dust:

Coal dust.—No coal dust used in this test.

Inert zone.—Main entry watered the entire distance.


104 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,
INSIDE OBSERVATIONS.

A curtain packed in the crevices above the door frame inby the
shaft was sucked inby 15 feet from its original position. An electric-
light wire extending from the end of the concrete section in the air
course to the first crosscut was blown outby so that it stretched from
the end of the concrete to the intersection of the gallery and the air
course.

Most of the dust on the Taffanel shelves was blown off. The first
shelf outby the cut-through was blown down, and the second
was swung around until it was

following the explosion wave.
ew The bags of the top 2 feet of

the sandbag stopping in the

second cut-through were blown

x
P| *TM parallel with the side of the

entry.
y 3 l=s4 2 | In the main entry the mine
post-4 t 4 track at E 530 seemed to have
| [| been raised slightly, as the bal-
Mened eT ecing 7] 2s0 last was very loose. This was
ee ee of EA possibly caused by the suction

ess ony EE

SYMBOLS USED
‘Taffanel barrier

‘uit Coah dust

= Frame

SEP Flame outside of ming fez] °°" out. Some bags were thrown
28 toward the entry, but many
se more were thrown toward the
rye air course. Many of these

bags were upset and the sand
20.99.50 1g 200 eu SPilled.
At E 390 the east end of one
of the ties was bent forward 45°.
es This tie was broken where the
Faeliel doce i rail was spiked to it. The rail

had probably been slightly frac-
tured at this point preceding
the explosion. The post hold-
ing the shelves at E 294 was
Figure 5,~Test 14, extent of fame and conditions Pushed into the groove in the
of test. rib 1} inches. The floor from
E 220 to E 160 was raised several inches, the ballast between the ties
being rather loose.
LENGTH OF FLAME.

The flame extended through the full length of the entry (fig. 25).
In the cut-through air-course branch it extended 130 feet, but did
not pass the Taffanel barrier.


BUREAU OF MINES BULLETIN 56 PLATE Vi

@. RUPTURE OF LINING OF MAIN ENTRY.


DETAILS OF EXPLOSION TESTS. vel

of the shot-firing lines in the mine disclosed a short circuit in the
lines where they had been trampled by some of the visitors. A
second trial resulted in a second failure. As the place of short-cir-
cuiting was not found by a second inspection, an entire new shot-firing
line was installed. It was evening before the warning signals were
given for a third time, when the button was pressed and an explosion
resulted.

INSTRUMENTS AND RECORDS.
MANOMETERS.

Location.—-Manometer A at station E 150; manometer B at station
E 50.

Spring.—Thirty-pound springs were used in both manometers.

Records.—As the motors which drive the drums of the recording
manometers did not run during the explosion, the records showed
the maximum pressures only. Maximum pressure of manometer
A, 26.5 pounds; manometer B, 21.3 pounds.

PRESSURE CIRCUIT BREAKERS.

Pressure circuit breakers were installed at station E 150 and
station E 50.

Records—No velocity records were obtained. When new shot-
firing wires were installed after the second failure to obtain the
explosion, the batteries used to operate the recording apparatus
were disconnected from the apparatus and connected to the shot-
firing line.

OUTSIDE MANIFESTATIONS.

LENGTH OF FLAME.

The flame burst out of all openings almost simultaneously and
seemed to fill the valley from the main opening to the opposite hill (fig.
17). It was estimated that the flame from the main opening extended
horizontally nearly 500 feet, and from 200 to 300 feet vertically.
The vertical estimate is probably much too great, the glare on the
clouds making the height seem greater than it really was. A tree
153 feet from the main opening was ignited at a point 46 feet above
the level of the ground at the mine opening.

INDICATIONS OF VIOLENCE.

Before the explosion a mine car containing several hundred pounds
of material had been on the mine track in the line of the entry 40
feet from the opening. Twenty-five feet beyond the car mentioned
had stood a car loaded with coal, the total weight of which was


8 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

making arrangements for the lease of the property and subsequently
in the opening of the mine.

Immediately on completion of the development of the mine to the
extent considered desirable for experimental work, the first series of
tests was begun.

The number of experiments embraced in the first series, here
reported, was comparatively small. The tests chiefly served to try
out the mine and apparatus; apart from this end, there was valuable
educational service accomplished by certain tests before large audi-
ences of mining men. The fact that coal dust in air containing no
inflammable gas may explode is now almost universally conceded in
this country. This was not the case prior to the first public test of
October 30, 1911, when many still doubted even after having wit-
nessed explosion tests in the Pittsburgh surface testing gallery.
However, as a result of the mine test mentioned, those who had
previously doubted expressed themselves as convinced.

This explosion test seriously damaged the mine equipment, neces-
sitating considerable delay before repairs could be completed. Then
followed further experiments, which were limited in number by lack
of funds.

PHENOMENA OF A DUST EXPLOSION.

When a source of heat, for example, an incandescent platinum
wire, an electric arc, or the flame from a blown-out shot, is intro-
duced into a cloud of coal dust, combustion takes place between the
particles of dust and the oxygen of the air. If the quantity of heat
transferred to the dust cloud is relatively small, the combustion may
proceed only in the immediate vicinity of the heating agent. If, on
the other hand, sufficient heat is available, the temperature of the
dust cloud is raised to such an extent that combustion takes place
rapidly, developing more heat than can be conducted away. Conse-
quently the adjacent part of the dust cloud is heated to a tempera-
ture sufficient for rapid combustion, and by its combustion develops
heat, which in turn raises the temperature of the next dust layer.
This process continues, and the flame travels through the dust cloud
with rising temperature and increasing velocity.

In this report the term “‘ignition” is used to describe the propa-
gation of the flame beyond the immediate influence of the igniting
agent.

When the conditions are favorable, the flame is propagated through
the dust cloud with rapidly increasing velocity and rising pressure.
A true dust explosion then results, and the velocity of the flame rises
rapidly to over 2,000 feet per second and great pressures are pro-
duced.


CONTENTS.

Introduction...

Phenomena of a dust explosion. 8
Objects of dust-explosion investigations. a
Inflammability factors properly included in laboratory studies. . 12
Factors partly under control in experimental explosions in the mine. re
Variable explosion characteristics for determination in each test. 13
Problems to be investigated after determination of stated variable 13
Outlook for solution of coal-dust problems. u
Outline of various tests made in the experimental mine. u
Acknowledgments. 15
Description of mine and equipment. VW
Selection of a mine... iv
Underground development. 19
Reinforced-concrete lining 19
The Pittsburgh coal bed. 24
Surface equipment of the mine. 26
External explosion gallery. 26
Cannon for ignition shots. 27
Ventilating system. 28

Power plant. _
Coal-dust and rock-dust grinding plant
Coal-handling equipment.

Water supply and fire protection.

Observatory and control station
Underground equipment.

Coal-dust shelving. .
Instruments used in the first series of tests. .

Recording manometers.

Maximum-pressure gages

Velocity-recording instruments.

Electric cables,

Firing circuits.
Chemical analyse
Afterdamp sampling.

General description of experiments
Preliminary explosion trials.
Explosion test 1.
Explosion test 2.
Explosion test 3.
Explosion test 4.
Explosion test 5.
Explosion test 6.
Explosion test 7.
Explosion test 8.
Explosion tests 9, 10, and 11
Explosion test: 12
Explosion test 13.
Explosion test 14
Explosion test 15.





B. B.C. D. TIME MARKER,


DETAILS OF EXPLOSION TESTS.

The most important details of the 15 experimental-mine explo-
sion tests that constituted the major part of the investigation here
reported are given below in condensed form.

TEST 1.

Date.—October 24, 1911.

Purpose.—To determine the possibility of obtaining a large coal-
dust explosion at the mine and to obtain records of the resulting
pressures and velocities.

Point of origin of explosion.—Face of main entry, 722 feet from
mouth.

Method of ignition —Blown-out shot from a 13-inch pipe in the
coal.

Charge.—Two pounds of FFF black blasting powder, tamped with
24 inches of damp clay.

COAL DUST.

Source.—Dust was ground from bituminous coal from the Pitts-
burgh bed at Oak mine, near Pittsburgh.

Size—-Over 98 per cent passed through a 100-mesh sieve.

Analysis. —

Moisture. ...-----22------+
Volatile matter
Fixed carbon.

Zone.—Main entry, E 722% to E 300, or 422 feet; gallery slant:
Some old coal dust remaining on side shelves from previous gallery
tests.

Position.—E 722 to E 702 on bench just below the hole containing
igniting charge; E 712 to E 472 on temporary side shelves; EK 472
to E 300 on transverse “book’’ shelves.

Quantity. —500 pounds of coal dust, or a little more than 1.18 pounds
per linear foot of entry. The load was equivalent to 0.315 ounce
per cubic foot of space or 315 grams per cubic meter.

Inert zone.—E 300 to opening, no coal-dust load; air course, no
coal-dust load.

@ An expression consisting of a number preceded by the letter E refers to a point in the main entry
distant from the end of the buttress wall at the mouth of the entry by the number of feet indicated.

66





86 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,
RECORDS.

Manometers.—Pressure too small to be recorded (less than 1 pound
per square inch).

Pressure circuit breakers.—Operated at station E 650.

Flame circuit breakers.—Operated at stations E 650 and E 550.

Velocity of flame propagation.—The flame reached station E 650,
1.8714 seconds after ignition and station E 550, 2.6617 seconds after

ignition; the time between

ie those stations was 0.7903 sec-
ond, and the velocity 127 feet

# “AV } we per second.
38
Method of placi fst OUTSIDE MANIFESTATIONS.
segue §
‘across entry ia AL} B50 Violence—The steel sheets
| . .
# of the explosion-door section
SYMBOLS $5 i
nen SSMBOLS USED EE were rattled by the explosion,
eee Coal dust 7\{ }®* and some of them were moved

Flame
Bottom wet slightly toward the steel gal-
lery. The only other outside
evidence of an explosion was
the swirl of snow and dust from
ems the opening to the end of the

SCALE IN FEET dump.
10.3059 100 20

Ea

uF

Concrete

stoppini

INSIDE OBSERVATIONS.
E1bo
The curtain hanging across

the air course inby the shaft

nso wascarried inby 26 yards. The

board door outby the shaft was
broken outward.

Length of flame.—The length

Figure 19.—Test 6, extent of flame and conditions of flame in the main entry was

ore indicated by the guncotton

tufts suspended along the entry to be 265 feet long (fig. 19). The
branch flame in the cut-through and air course was 72 feet long.

Relief door die

EFFICIENCY OF BARRIER.

The flame extended farther into the barrier than it did in test 3, in
which the length of the coal-dust loading in the main entry was 100
fect less than in this experiment. The stone dust was not disturbed
very much by the explosion, so that its effect in quenching the flame
was probably not great. A sample of the coal dust left on the shelves


109

DETAILS OF EXPLOSION TESTS.

85 TIME, SECONDS
22 0 Ee) 80 100 «1014.00.80 00).
ee
28
ger ‘Fiaure 26—Manometrie curve, test 15, pressure below atmospheric.
ae

120

100)
Bn
Ze 8)
64 ;
i eo) t
gs a

g 40} i
ts ;
Ho
0 cr) “08 2 16 2 7 3B 2 36 “40 mr) 48 Be
TIME, SECONDS

Figure 27,—Manometric curves, test 15, pressure above atmospheric,


First edition. April, 1918.



DETAILS OF EXPLOSION TESTS. 87

after the explosion was taken, the analysis of which gave the following
results:

Moisture. . .. - 2.85
Volatile matter. 33.02
Fixed carbon 54. 31
9.82

100.00

1.24

A comparison of the ratio of volatile matter to fixed carbon (37.81:
62.19) with the ratio of volatile matter to fixed carbon in the original
coal dust (37.55: 62.45) shows that the percentage of volatile matter
was not materially changed.

Of the 200 pounds of coal dust used in this test, 76 pounds remained
on the shelves after the explosion.

TEST 7.

Date.—February 5, 1912.

Purpose.—Study of the propagation of a coal-dust explosion and
the effect of Taffanel barrier with a coal-dust zone of 290 feet.

Point of origin of explosion.—F ace of main entry, E 744.

Method of ignition —Blown-out shot from 14-inch pipe in the coal.

Charge.—Two pounds of FFF black blasting powder, tamped with
5 inches of damp clay.

COAL DUST.

Source.—The coal dust was ground from bituminous coal from the
Pittsburgh bed at Willock, Pa.
Size —Over 95 per cent passed through a 100-mesh screen.
Analysis.—
Moisture. -.-

Volatile matter.
Fixed carbon.

Zone.—From E 744 to E 454, or 290 fee

Position.—¥rom E 744 to E 728 on a bench placed just below the
level of the hole containing the igniting charge; from E 733 to E 454
on permanent shelves along both sides of the entry.

Quantity —Twenty-six pounds of coal dust was placed on the bench
and 324 pounds was along the side shelves. This is equivalent to an
average loading of 1.21 pounds per linear foot.

Inert zone.—The main entry was watered from E 450 to the opening;
the air course was also sprinkled to render it inert.


26 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

The average ultimate analysis is as follows:

Hydrogen.
Carbon.

SURFACE EQUIPMENT OF THE MINE.

The surface equipment of the experimental mine consists of an
external explosion gallery, ventilating fans, a power plant, a coal-dust
and rock-dust crushing and grinding plant, an observatory and con-
trol station in which recording instruments are placed, an incline, a
coal tipple and chute for loading railroad cars, a reservoir, pump
house, blacksmith shop, barn, tool house, and a water-tank and
hydrant system for fire protection.

EXTERNAL EXPLOSION GALLERY.

The explosion gallery (Pl. III, C) consists of a steel tube 6 feet 4
inches in internal diameter and 122 feet long, set in line with the
diagonal heading, or ‘gallery slant,” and 20 feet from its mouth.
Between the tube and the mine portal there is a U-shaped passage
(fig. 6) of heavily reinforced concrete; it has the same diameter (6 feet
4 inches) as the steel tube and the diagonal heading. The roof of this
passage is closed by flat plates resting loosely on 23-inch round tie
rods (connecting the tops of the concrete walls) and when necessary
is weighted down with sandbags. This loose covering is 20 feet long
by 6 feet 4 inches wide and serves as a great relief valve for the pro-
tection of the tube and ventilating fan in case of a very violent
explosion in the mine.

In order to make the external steel gallery available for small
explosion experiments outside the mine itself, the inner 20-foot
section, adjacent to the U-shaped passage, can be rolled to one side;
then, after the mouth of the diagonal heading has been closed, the
steel gallery is isolated from the mine and tests can be conducted in
it without interfering with work in the mine. During such periods
mine ventilation is carried on by means of a fan set at the top of the
air shaft. The steel gallery when thus isolated is 102 feet long and
has practically the same dimensions as the gallery for testing explo-
sives at the Pittsburgh station. There is, however, one difference.
The outer end of the steel gallery at the mine is left open except for a
board or plank stopping which can be slid into place in the con-
crete framework. This stopping is to provide for relief of violent
pressure and therefore is made comparatively thin (of 2 to 4 inch


DETAILS OF EXPLOSION TESTS. 73

to the northeast. A telephone pole 5 inches in diameter, which stood
northeast of the tool house, was struck by a flying timber from the fan
drift and was broken square off at a point 4 feet 9 inches from the
ground. A second piece of the fan drift was found 100 feet northeast
of its original position. Two windows on the south side of the tool
house fell out toward the fan drift; this was no doubt due to a suction
following the pressure wave of the explosion. Two lights in a window
on the south side of the blacksmith shop were broken. The 1-inch
board door and stopping at the end of the steel gallery was blown
into small pieces and scattered over the dirt backstop. Flame also
issued from the end of this gallery. Many sandbags from the explo-
sion-door section fell to the south of the gallery, some as far as 100
feet up the hill. One bag became caught on a limb of a tree, 42 feet
from the ground and 110 feet from the explosion-door section, A
piece of corrugated iron was found on the upper side of a fence at a
point 110 feet south from its original position. Many pieces of board
were found in this field, some as far distant as 235 feet from their
positions before the explosion.

INSIDE INDICATIONS OF VIOLENCE.

The action of great force was indicated in the concrete section of
the main entry by numerous fractures of the concrete, particularly
along the springing lines, and by the exposure and bending of many
of the vertical reinforcing rods. The concrete arch had manifestly
been lifted by the explosion, thus causing the vertical reinforcing
rods to be thrown in tension. The rods tended to become straight
where they curved around the arch at the springing line, and this
tendency caused the breaking out of the concrete between the rods
and the face of the concrete. A crack in the concrete at the springing
line on the east side of the entry extended from a point 44 feet from
the opening to a point 118 feet inby. On the west side the springing-
line crack extended 44 feet to a point 117 feet inby. A large trans-
verse crack (Pl. VI, C) was opened in the concrete arch at this point;
for some distance inby this point the arch seemed to have been lifted
bodily out of its place, and at this point it did not return to its former
position but still remained 11 inches higher up. When the concrete
lining was originally put in at this point a fall of roof occurred, and
after the concrete lining had been put in, loose dirt was tamped into
the hole in order to fill it as completely as possible; later the mate-
rial settled, as there probably was a cavity above the concrete at
this point. Practically all of the posts of the coal-dust shelving sets,
from the concrete section in to E 612, were blown out. Inby this
point the shelving sets seemed to have been merely upset. There
had been 2 7-foot sandbag stopping in the second cut-through. Prac-
tically all of the stopping bags were moved out of place; most of


68 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

A car that stood 50 feet from the opening and was filled with small
boards was blown over the side of the slate dump and fell across a
wire fence 90 feet from its first position.

A 5-ton gasoline locomotive that had stood just beyond the car
was moved 15 feet, and its top plate, pivoting on the rear bolts, was
bent through 180°. A car dump which had been at the end of the
slate dump was blown 30 feet over the west side of the slate dump.

A steel-plate door weighing about 60 pounds was blown from a
point a short distance within the main entry over the dump and

em Was half buried in the ground in
the valley beyond the dump, 200
ul zoo feet from the opening.

INSIDE OBSERVATIONS.

E550
Violence—The concrete wall

over the top of the steel-plate

E«0 door at station E 50 was cracked
through into the station. The
concrete lining was cracked along
the springing line on both sides of
the entry for 50 feet inby E 50.
e%0 The concrete arch was cracked
from side to side at three points,
18, 30, and 54 feet from the
opening. All the steel rails and
timbers which had held up the
zs roof at the intersection of the first
Bl; cut-through and the main entry
were thrown down. Some of the

4 timbers were carried out the entry

and some through the air course,

but the rails had simply dropped

out of place. The sandbag stop-

Figure 16.—Test 1, extent offlameand conditions. ping in the second cut-through
of test. was piled against the inby rib.

Some bags were blown into the entry and some into the air
course. All the posts and shelves outby the last or inner cut-
through had been blown down with the exception of three posts
on the east side of the entry. The stopping in the air course
outby the intersection with the gallery slant had been blown
down and some of the bags had been carried through the air
course to the opening 117 feet distant. The concrete arch in the
air course just inby the stopping was cracked from side to
side, as was also the arch of the gallery slant at the intersection.

SYMBOLS USED
x Origin of explosion
Weite Soak dust

Flame
<P Flame outside of mine

=
ear ree

Eso

SCALE IN FEET
00 2

fandba
Bool )) Curtain

inch plank
stopping



12 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

INFLAMMABILITY FACTORS PROPERLY INCLUDED IN LABORA-
TORY STUDIES.

Factors affecting inflammability that are properly included in
laboratory investigations are as follows:

(1) The chemical composition of typical coal dusts.

(2) The relative inflammability of dusts containing different per-
centages of volatile matter, ash, sulphur, and moisture, as tested by
different laboratory methods and apparatus and as influenced by:

(a) Character of ignition coil, induction spark, electric arc, or flame.

(b) Size of coal-dust particles.

(c) Method of putting coal dust into suspension.

(@) Method of mixture with inert dusts and chemically unstable
compounds to give extinguishing effects.

(e) Presence of methane and other gases.

(f) Size and shape of explosion chamber.

(3) The physical nature, composition, and affinity for oxygen of
each of the component substances that make up the coals from which
inflammable dusts are derived (microscopic and chemical investi-
gation).

(4) The nature and composition of gases distilled from the coal dusts
at different temperatures and during different periods of exposure to
heat.

FACTORS PARTLY UNDER CONTROL IN EXPERIMENTAL EXPLO-
SIONS IN THE MINE.

Factors more or less under control in experimental dust explosions
in the mine are enumerated below. ‘The bureau is investigating the
effect of each in connection with its study of dust explosions.

(1) Source, composition, and relative inflammability of dust.

(2) Size and character of dust particles.

(3) Admixture of inflammable dust with inert dusts.

(4) Quantity of dust per linear or cubic foot of space.

(5) Method of loading dust—on shelves, on floor, ete.

(6) Moisture adhering to dust and not part of its normal composi-
tion.

(7) Moisture on walls, roof, or floor, and not in contact with dust.

(8) Humidity and temperature of air.

(9) Air movement in passageways—velocity and direction with
reference to proposed explosion path.

(10) Character of walls, roof, and timbering.

(11) Turns and curves in path of proposed explosion.

(12) Proposed branching of the explosion into other entries by
prearranged loading.

(13) Coming together of two explosions by prearranged loading.






MEASUREMENT OF VELOCITY AND PRESSURE, 59

instant the weight begins to fall. The strength of the spring is such
that the support is rotated well out of the way of the knife edges on
the weight rod. While the weight is falling, the opposite end of the
support flies up and closes the circuit again. As soon as the weight
hits the platform at the bottom of its fall the circuit is again broken.

By means of suitable electrical connections, the catch is released
by an electromagnet operated by the same switch that fires the ignit-
ing shot, so that the time interval recorded begins at the moment the
explosion is started.

B. C. D. MEASURING APPARATUS.®

: The smoked paper records, after being removed from the manom-
eter and fixed in a bath, are placed on a special drum (PI. VI, B) and
are examined under a microscope. The circumference of the drum is
graduated into millimeters, so that the distance between any two
points on the chart can be measured by rotating the drum and bring-
ing the points on the chart in turn under the cross hairs of the micro-
scope. Since the 5-second interval marked on the chart is always
over 50 mm. long, 0.1 mm., which may be read on the chart, would
correspond to one five-thousandth of a second.

By means of a micrometer screw with a divided head, the drum can
be moved axially in the direction of motion of the pressure spring.
By this means the pressure ordinates may be measured accurately to
0.01 mm.

The manometer springs are calibrated by applying known pressures
to the manometer with a Schaeffer and Budenberg dead-weight pres-
sure-gage tester and a standard gage.

SUCTION MANOMETER.

One of the three B. C. D. manometers used in this work is so made
that it may be converted into a suction nanometer; it was used as
such during the tests of January and February, 1912. A much lighter
spring is used for this purpose and is placed so that its zero position
is higher on the drum than that of the pressure springs, thus allowing
room for a downward deflection. The plunger, by means of a light
framework, makes contact upon the upper face of the spring. Any
suction applied to the manometer pulls the plunger downward,
deflecting the spring in this direction. The spring is calibrated by
means of a vacuum pump and a mercury manometer.

MAXIMUM-PRESSURE GAGES.

The maximum-pressure gages are of the ‘‘crusher” type used in
ordnance work to measure the pressures in the chambers of large
guns, and are similar to the gages used by Taffanel.

See Pl. VI, B.


30 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
COAL-DUST AND ROCK-DUST GRINDING PLANT.

For extensive coal-dust experiments such as have been planned, a
large quantity of coal dust will be required. For example, if 2,000
feet of entry is to be loaded with coal dust to an extent of 2 pounds
per linear foot, 4,000 pounds or more will be necessary. Sufficient
coal dust made in the ordinary way can not be easily obtained, nor
is it uniform when procured. Therefore the dust is made artificially
from the coal mined at the face. In order to obtain comparable
results when making coal-dust explosion tests, the coal after having
been crushed is uniformly ground until 95 per cent of it will pass
through a 100-mesh sieve, as determined by frequent tests of sam-
ples. During the first series of experiments the crushing and grind-
ing machinery had not been completed, and the coal dust had to be
ground at the Pittsburgh station. For the second series all of the
dust will be ground in the mine plant.

The crushing and grinding plant is housed in a building, the first
story of which is concrete, the upper part being of galvanized iron on
wood framing.

The coal, or the rock if rock dust is desired, is transported in
mine cars to the second floor of the building and shoveled on a bar
sereen with 4-inch spaces, and the larger pieces are broken by sledge
until they pass through; a hopper receives the screened material and
delivers it to a hammer crusher which breaks it into smaller pieces
three-eighths of an inch in diameter and finer. From the crusher
the coal is taken by an elevator to a bin that feeds the pulverizer.

The pulverizer is an impact machine. _ Its essential part is a beater
with two blades, which revolves in a steel-lined box at a speed of 2,700
revolutions per minute. The blades break and pulverize the material,
and act as fans, the effect of which, assisted by the suction from a
large fan above, is to lift the finely ground material through a conical
separator provided with deflectors. The air current rising through
the separator with a lessening velocity, caused by the enlarging cross
section, has a sorting action; the coarser particles drop back and the
finer dust is drawn upward to the fan. There are dampers at the top
of the separator which can be adjusted to control the air current and
cause the coarser dust to fall back to the beaters for finer grinding.
On passing through the fan the dust is blown into a large upright
pipe which connects above to a “cyclone” collector which gathers
all but the lightest dust. The lightest dust and the excess air from
the top of the collector are blown into an adjacent collector con-
sisting of a large number of cotton tubes or “stockings,” by means
of which even the finest dust is strained out as the air discharges
through the fabric. The dust gathered by the ‘“‘cyclone” and the
tubular collectors drops through pipes into a tight steel-plate bin.


38 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

CHEMICAL ANALYSES.

In order to study the chemical processes accompanying an explo-
sion, analyses of the coal dust used and of the residual solids left
after the explosion—that is, cooked dust and condensed hydrocarbons—
are required so that the changes in the composition of the dust and
the loss in gaseous constituents may be determined. Representative
samples of the coal dust may easily be taken previous to an experi-
ment, but it is not so easy to obtain average samples of the solid
residues of the explosion, and it is practically impossible to recover
the total quantity of the residues.

AFTERDAMP SAMPLING.

Samples of the afterdamp may be obtained some minutes after the
explosion by men wearing oxygen helmets such as are used in rescue
work. It is important, however, to obtain gas samples at intervals
during the explosion as well as immediately after the explosion.

This can be accomplished only with the use of automatic appara-
tus, like that used in the investigations at Altofts and at Liévin.

The B. C. D. automatic sampler * (Pl. VII, A) used in the first
series of tests at the experimental mine was opened by a circuit maker
operated by pressure. On account of the difficulty in predetermining
accurately the relative velocities of the pressure wave and the flame,
the attempts during the first series to obtain gas samples during the
passage of the flame were not successful. Also, in some tests the
projecting pipe connections were carried away by the force of the
explosion. It is planned in future experiments to have gas samplers
operated by means of the flame circuit makers, to have no projecting
parts, and to use devices for quickly closing the sampling bottles after
the sample has been admitted.

A new type of automatic gas sampler is being developed at the
Pittsburgh station for taking a set of three successive samples during
or following the passage of the flame. The sampler is set in operation
by a flame circuit breaker. The first sample is taken instantaneously ;
the others are taken at predetermined intervals by means of clockwork
mechanism.

See full description under “ Description of Instruments for Measurement of Velocity and Pressure.”


DETAILS OF EXPLOSION TESTS. 95

explosion, it would seem that the higher pressures developed caused
more of the dust to be thrown in suspension.

A sample of dust that had settled out on the surface of a side
support on which the shelves of the Taffanel barrier rest was taken
and analyzed with results as follows:

3.21

Volatile matter. 12. 24
Fixed carbon 11. 20
73, 35

100. CO

Sulphur.....eceeeeeeeeeeeeecceeeeeeeeeeeeeeeeeeeenetseeeeeeeeeees 64

The material of this sample had been in suspension immediately
following the explosion, and the analysis indicates that the material
was a mixture, probably of stone dust, coal dust, and soot.

TEST 9.

Date.—February 8, 1912.

Purpose.—In tests 6 and 8, pressure circuit breakers set to release
at a pressure of 2 pounds were operated, seemingly by the pressure
wave produced by the blown-out shot from the cannon. This test
was made under the same conditions as those of the preceding test
except that no coal-dust loading was used, so as to ascertain whether
the same circuit breakers would be operated.

Point of origin of explosion—Face of main entry, E 744.

Method of ignition —Blown-out shot from bore hole of cannon.

Ignition charge.—Two and three-fourths pounds of FFF black
blasting powder tamped with 4 inches of damp clay.

Coal dust.—No coal dust used in this test.

Length of flame—The guncotton tufts at E729 and E704 were
ignited by flame or flying pieces of burning powder.

INSTRUMENTS AND RECORDS.
INSTRUMENTS.

Location.—Pressure circuit breakers were located at stations E 50,
E 150, E 250, E 350, E 450, E 550, and E 650.
Adjustment.—All the circuit breakers were adjusted to operate at
a pressure of 2 pounds.
72322°—13-——7


BUREAU OF MINES BULLETIN 56 PLATE VII

A, RESULTS OF TEST 1 AT JUNCTION OF SLANT AND AIR COURSE.

B. BENT j-INCH STEEL BAR, SHOWING LIFT €, REINFORCING ROD PULLED OUT OF CON-
OF ROOF. CRETE IN ROOF OF MAIN GALLERY.




BUREAU OF MINES BULLETIN 56 PLATE vit

A. B.C, D. AUTOMATIC GAS SAMPLER.

B. B.C. D. AUTOMATIC COMMUTATOR,



62 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

electromagnet on the chronograph, the commutator electromagnet,
the brush g circuit breaker 1 (as at E 650), and back to the battery.
If the explosion breaks the circuit at cireuit breaker 1 (as at E 650)
the chronograph electromagnet releases its armature and the pen
makes a mark on the moving surface; at the same time the armature
d of the commutator electromagnet is released and the anchor
escapement @ attached to the armature is moved. This allows the
spring s to pull the scape-wheel 6 around by the cord k, which is
wound on a drum, attached to the axis of the scape-wheel. The
brush then moves part way to stud 2; the current immediately begins
to flow through circuit breaker 2 (as at FE 550), the chronograph
electromagnet, and the commutator electromagnet; the armatures
of both magnets are again attracted; and then the pen on the chrono-
graph is moved back to its former position. On the commutator, the
armature d and the escapement a move back to their former position
and the brush g moves a little farther on to stud 2. When the
explosion operates circuit breaker 2 (as at E 550) the brush moves
to stud 3, the same cycle being repeated, and so on, for as many
points as may be fixed, all the breaks in the circuits being recorded
by the one pen on the chronograph so long as they occur in the proper
order. It will be readily seen, however, that if any one circuit breaker
fails to operate properly, no records will be obtained at the circuit
breakers following, since the armature on the automatic commutator
will not be released, and consequently the brush will not be free to
move to the next stud.

CHRONOGRAPH.

The laboratory chronograph (Pl. VI, B) used in connection with
the automatic commutator and circuit breakers traces a record in
ink on a long riband of paper. It comprises three electromagnets
to the armature of each of which is attached a brass recording pen
that moves with the armature when the electric circuit is made or
broken. The pens rest lightly on the strip of paper which is drawn
along at a uniform rate by an electric motor. One of the electro-
magnets is connected in series with a storage battery and a “contact
clock”’ which breaks the cireuit every half second, thus giving the speed
at which the paper travels. A second electromagnet is connected as
described above, and its pen records the various breaks in circuit due
to the pressure wave of the explosion. From the breaks the velocity
of the wave may be determined. The third pen is used to record the
travel of the flame during an explosion.


12 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

about 2 tons. The partly filled car was hurled over the loaded one
and thrown a distance of 184 feet into the ravine beyond the dump.
It bounded four times after the first landing and came to rest at a
point 45 feet beyond the first landing place; the total travel, meas-
ured horizontally, was, therefore, 229 feet. The loaded car first
mentioned, even with the brakes
ew set, was driven along the track
and finally derailed 70 feet beyond
its original position. The hill op-
posite the mine was strewn with
pieces of shelving and posts (Pl.
V, B). Posts 5 to 6 feet long and
6 inches in diameter were found
Eso 413, 354, and 250 feet from the
mine opening.
A sandbag from the sandbag
stopping in the air course at the
intersection of the air course and

B60

Dinu |
‘stopping 8 feet
wd

= Flame
EB Mame outside of mine

Esto

re
i
é
SCALE IN FEET. 1 exo gallery slant was found 45 feet

30,3050 100 200

from the air-course opening.
Many other bags were found be-
tween this point and the opening;
many of them had been torn and
the sand spilled out. The sand-
bag farthest from the explosion-
door section that was blown to the
north was found 115 feet distant.
Many bags were found scattered
between this point and the explo-
sion-door section. A consider-
ablenumber of the bags were blown
high in the air and a rain of
sand resulted from their becom-
ing broken and torn. One of the
bags was caught in a tree near
the explosion-door section at a
height of 72 feet above its original
position.
The “danger” signboard nailed
Fiaune 17—Test 2, extent of flame and conditions. on the cap at the air-course open-
ores ing was blown off and was found
140 feet to the northeast. A piece of corrugated iron 2 feet wide and
7 feet long, which had been placed over the bags at the explosion-
door section, was found 110 feet to the north. A second sheet of
corrugated iron from the explosion-door section was found 260 feet



DESCRIPTION OF MINE AND EQUIPMENT,

Give shelf a bearing
in concrete

[<p Cast-steel plate

rods 4 i fy f - sl
& y ty

ZH
squares 6apart
B

Heme Y Conerete

x’squares.
6’apart

at

-Cast-steel door

i

Seas a
SS
=
SS

100 feet to next/station "100 feet to next station

|
ie
L

A WW  “—"F°’’lE.

Freure 7.—Construction of instrument chamber: A, front elevation; B, vertical section; C, plan.

35


DETAILS OF EXPLOSION TESTS. 107

VENTILATION AND HUMIDITY READINGS.

Ventilation —At station E 540, where the cross section was 6 by
9 feet, the velocity of the air was 101 feet per minute, and the volume
5,445 cubic feet per minute.

Humidity readings, test 15.

Station. Dry bulb, | Wet butb. | Humidity.
. | Fagg | Pereent,
E50. 44 43
E 250. 6 | 434
F 550. 44 | 2 85
Airco 38 | 36 8

ANALYSIS OF SAMPLE OF AIR.

A sample of air was taken at face of entry just before firing the
igniting shot. An analysis was made with the following results:

0.04
20. 95
- 00
+. Trace.
79.01

100. 00

INSTRUMENTS AND RECORDS.

MANOMETERS.
Location.—B. C. D. manometer A (suction) at station E 50; B.C. D.
manometer B (pressure) at station E 50; B. C. D. manometer C
(pressure) at station E 150.
Springs.—Manometers B and C were equipped with springs having
a rating of 200 pounds.

PRESSURE CIRCUIT BREAKERS.

Location.—Pressure circuit breakers were installed in all stations
from E 50 to E 650, inclusive.

Adjustment.—All pressure circuit breakers were adjusted so as to
be operated by a pressure of 3 pounds.

FLAME CIRCUIT BREAKERS.

Type.—Tin foil. (See p. 63.)
Location.—At all stations from E 50 to E 650, inclusive.
SAMPLING BOTTLES.
Two types of sampling bottles were used in this test. The B.C. D.
automatic sampling bottle was installed at station E 150, its circuit

maker being installed at station E 250. A special sampling bottle
was installed in a groove in the rib at E 374.


DETAILS OF EXPLOSION TESTS. 91

TEST 8.

Date.—¥ebruary 7, 1912.

Purpose of test—Study of propagation of a coal-dust explosion
and the effect of Taffanel barrier with a coal-dust zone of 290 feet.

Point of origin of explosion —Face of main entry, E 744.

Method of ignition—Blown-out shot frgm a cannon placed near
the face.

Charge.—Two and three-fourths pounds of FFF black blasting
powder tamped with 3 inches of damp shale dust.

COAL DUST.

The coal dust was ground from bituminous coal from the Pitts-
burgh bed at Willock, Pa.

Size —Over 95 per cent passed through a 100-mesh screen.

Analysis. —

Moisture... L294
Volatile matter. 33. 98
Fixed carbon 54. 36
Ash. . 8.72

100. 00
Sulphur........0ce-coceeeeeseeceeeeeseeeeceeeeenreeeeceeeeeenseeee 1.32

The sample analyzed was taken from the dust on the shelves just
preceding the explosion.

Zone.—From the face at E 744 to E 454, or 290 feet.

Position.—E 742 to E726 on a bench placed just below the level
of the bore hole of the cannon; E 733 to E 454 on permanent side
shelves along both sides of the entry.

Quantity—Thirty pounds of coal dust on the bench and 270
pounds scattered along the shelves. This is equivalent to an average
loading of 1.03 pounds per linear foot.

Inert zone-—The main entry from E 450 outby to the opening,
the last cut-through, and the air course were watered to render
them inert.

TAFFANEL BARRIER,

Location.—In the air course, extending from 5 to 85 feet outby third
cut-through.

Number of shelves.—Eleven.

Distance between shelves.—About 8 feet from center to center.

Width of shelves —Twenty-four inches.

Depth of shelves —Two inches.

Depth of stone dust.—Seven and one-half to eight inches.

Obstructions.—13.81 per cent of total cross section.


100 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

TEST 13.

Date—February 10, 1912.
Purpose.—To ascertain whether an explosion could be produced
from dust that had been exposed to the previous explosion.
Point of origin of explosion.—F ace of main entry, E 744.
Method of ignition —Blown-out shot from 14-inch pipe in coal.
em Charge—Two pounds of
‘ ass FFF black blasting powder,
Pot ‘ oH tamped with 4 inches of damp
isl fe shale dust.
Method of place
sua

‘waren ontey

COAL DUST.
e0
Source. —The dust was
ground from bituminous coal
— ati pan pct ao tion the Pittsburgh bed at
errlanyoned illock, Pa.
Beton sens To wet yi Size-—Ninety-five per cent
es passed through a 100-mesh
sereen.
Zone —From E 744 to the
£0 main opening, 744 feet.
eo Hl Position —E 742 to E 726
on bench placed just below
“| | © the level of the hole contain-
ing the igniting charge; E 733
to the main opening on side
shelves or on the floor.
ac Quantity. — Twenty - five
pounds of fresh coal dust was
placed on the bench at the
Ficune 24.—Test 12, extent of flame and conditions face. Throughout the re-
mf Wet mainder of the coal-dust zone
the coal dust remaining after the preceding test was left as the
load for this experiment.

TAFFANEL BARRIER.

SYMBOLS USED

CALE IW FEET.
x

Location.—In the air course, extending from 5 to 85 feet outby the
third cut-through.

Number of shelves.—Thirteen.

Distance between shelves.—Six feet from center to center.

Width of shelves.—Twenty inches.

Depth of shelves—One inch.

Depth of stone dust.—Four to five inches.


DETAILS OF EXPLOSION TESTS. 105
COAL DUST AND COKED DUST.

A thin layer of coal dust and soot was observed in the air course as
far out as 36 feet inby the first cut-through. The whitewashed ribs
inby this point were very much blackened and coated with dust
and soot.

The first two posts of the Taffanel barrier on the east side outby
the third cut-through had large crusts of coked dust on the inby side.

The coal was blistered slightly on the north side of the last cut-
through.

There was a heavy crust of coked dust on the outby side of the
first post on the east side of the entry outby the third cut-through.

A heavy crust of coked dust was found on the outby side of a post
at E 658 on the east side of the entry.

A heavy coating of soot covered the shelves inby the third cut-
through.

Scattered patches of coked dust were noted on the outby exposures
of the coal and posts from E 650 to E 550.

There were crusts of coked dust on the outby sides of posts at E 550
west and E 540 east. There was some coked dust on the outby
exposures of the ribs and posts from E 530 to E 440. There was a
small deposit of coked dust on the outby side of the shelves at E 350.
Slight quantities of coked dust were noted on the outby ends of the
shelves at E 250.

ANALYSIS OF AIR SAMPLE.

A sample (No. 2251) of mine air was taken in the last cut-through
as soon as it was possible for persons to enter without helmets. The
sample was analyzed with results as follows:

- 0.08
20. 85

It is to be noted that there
monoxide in the air at the point where this sample was taken, yet
the odor had been very irritating.

TEST 15.

Date.—February 24, 1912.

Purpose.—Public exhibition of the explosibility of coal dust and
influence of a Taffanel barrier on the advance of the flame from an
explosion.

Point of origin of the explosion.—Face of the main entry, E 747.

Method of ignition.—Blown-out shot from a 14-inch pipe in the coal.

Charge.—Three pounds of FFF black blasting powder, tamped with
5 inches of damp shale dust.


Bulletin 56
DEPARTMENT OF THE INTERIOR
BUREAU OF MINES

JOSEPH A, HOLMES, Drrucror

FIRST SERIES
OF

COAL-DUST EXPLOSION TESTS

IN THE

EXPERIMENTAL MINE

BY

GEORGE S. RICE, L. M. JONES, J. K. CLEMENT

AND

W. L. EGY

WASHINGTON
GOVERNMENT PRINTING OFFICE
1913


84 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

Charge.—Two pounds of FFF black blasting powder, tamped with
5 inches of damp shale dust.

COAL DUST.

Source.—The coal dust was ground from bituminous coal from the
Pittsburgh bed at Willock, Pa.

Size.—Over 95 per cent passed through a 100-mesh screen.

Analysis.—

Sulphur... eee ceeeeseeeceeeeeeseeeeeeeeceeeevecseeeesereeens 44

Zone.—E 744 to E 554, or 190 feet.

Position —E 744 to E 728, on bench placed just below the level of
the hole containing the ignition charge; E 733 to E 554, on perma-
nent side shelves on both sides of the entry.

Quantity —Twenty-five pounds of coa] dust on the bench; 175
pounds on the side shelves; loading equivalent to 1.05 pounds per
linear foot of entry.

Inert zone.—Main entry, from E 554 outby, was sprinkled. Air
course also was sprinkled before the explosion.

TAFFANEL BARRIER.

Location.—In the air course, extending from 5 to 85 feet outby
third cut-through.

Number of shelves.—Eleven.

Distance between shelves.—About 8 feet from center to center.

Width of shelves.—-Twenty-four inches.

Depth of shelves—Two inches.

Depth of stone dust.—Seven and one-half to eight inches.

Obstruction.—13.81 per cent of total cross section.

Analysis of stone dust.—The coal dust that had settled on the sur-
face of the stone dust after explosion tests 3 and 4 was scraped off,
and ground shale dust was heaped on the shelves until they would
hold no more. A sample of the dust was taken from various parts
of a carload of shale. Its analysis follows:

Organic hydrogen. .
Organic carbon. :
Moisture (at 105° C.) 3.94
Inorganic volatile matter (combined water, CO,, etc.



52 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

were obtained from the B. C. D. manometer record; the other points
were obtained from the chronograph record. The curves in figure 9

Test 6 S
Test 7 S
Test 3 SS
‘Test 12 S

‘Test 15} S

COAL DUST

4

LOADING WITH|

TT TT

g

g

g

g

g

8
HV
F

‘est 7.

FLAME VELOCITY, FEET PER SECOND

o rest 6 | iis
7 20050 ~~ SCC
DISTANCE FROM FACE, FEET
F1ouRe 10.—Flame-velocity eurves obtained in tests 6,7, 8,

and 15,

show the relative position of the flame and that of the pressure wave,
as obtained from the data from test 15. The horizontal distance

2400

g

g

&
ct
i

VELOCITY, FEET PER SECOND.

s

°

10 200 300 400 500 00 700
DISTANCE FROM FACE, FEET
Ficure 11.—Pressure-velocity and flame-velocity curves obtained in test 15.

between the two curves indicates the distance that the front of the
pressure wave is in advance of the flame.


40 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

decided on October 24 to see whether a blown-out shot at the face
of the main entry would start an explosion. The result was sur-
prisingly successful. Flames shot from every opening, and there
was a loud report. A car standing 50 feet from the mouth of the
entry was blown off the dump, evidently being lifted over a gasoline
locomotive, as indicated from certain marks on the locomotive.
The locomotive was moved 15 feet. The details of the experiment are
reported .on pages 66 to 69. The intensity of the explosion was a sur-
prise to the observers. Considerable damage was done to the mine,
including cracking of the concrete in the main entry and in the air
course at the junction of the diagonal heading. There had been a
6-foot sandbag stopping in the air course at this point, the sandbags
being tightly wedged in. As the explosion came outward on the air
course, the rush of the gases was momentarily arrested by the stop-
ping, which probably acted like a water hammer to produce great
increase in pressure, causing the concrete roof to be lifted and to lift
up with it the upper part of the corner pier. A piece of board and
some brattice cloth were blown into the break as the roof lifted, and
when it dropped it nipped the cloth and stick, as shown in Plate
VIII, A. Meantime the sandbag stopping had been thrown outward,
some of the bags to the outside of the mine. After the rush of the
hot gases to the outside, there was a return wave to fill the partial
vacuum; this carried a few of the sandbags inby their former position.

The pressure manometers at stations 150 and 50 feet, respectively,
from the mouth of the mine indicated a velocity of the pressure wave
between these stations of 1,954 feet per second. In this test the
manometers were equipped with 30-pound springs. The pressure at
station E 1504 exceeded the capacity of the spring, and the record was
interrupted by the stylus being thrown off the smoked paper. The
actual pressure at station E 150 was probably greater than 50 pounds.
The highest pressure recorded at station E 50 was 40 pounds.

The chief lessons to be learned from this first formal test were:

(1) That an explosion could be obtained by a single blown-out shot
at the face;
_ (2) That the reinforced-concrete lining was not sufficiently strong
In itself to prevent rupture when an explosion approached the deto-
nating stage;

(3) That the instrument stations were satisfactory in their con-
struction;

(4) That the general arrangement of the mine was very satisfactory;

@ Text and figure references to stations E 50, F 150,etc., and to stations G 200, G 300, ete., refer to stations
placed in the entry or in the gallery at pointsdistant from the mouth of either the number of feet designated
by the figures attached to the initial.


DETAILS OF EXPLOSION TESTS. 79

TAFFANEL BARRIER.

Location—In the air course, extending from 5 to 85 feet outby
third cut-through.

Number of shelves —Eleven.

Distance between shelves—About 8 feet from center to center.

Width of shelves.—Twenty-four inches.

Depth of shelves.—Two inches.

Depth of stone dust.—Seven. and one-half to eight inches.

Area of obstruction.—13.81 per cent of total cross section.

Analysis of stone dust.—

Organic hydrogen. 0.15
Organic carbon. 1.98
Moisture (at 105° C. 2.57
Inorganic vo volatile matter (combined water, CO,, etc.) 8.42
Ash... ween eee eee eee e eee ee eee eee ee 86.88
100.00
Ventilation and humidity readings.
Wet {parom-| Humid-| cross |yetoeity |v.
Station bab. | ab {Veter. | ity. | section. | Velocity-| Volume,
| | Feet per | Cubic feet
or_| °F. |Inches.|Percent.| Feet. | minute. | per minute
G 3100. 26] “9 | 28.80 67 | 64 by 6} 193 7,488
E650. : 43/45 | 28.85 Josraeerze4 . wee
850.0000 AL) 82 28.875 92/9 bya 6 4388

@ 310 feet from mouth of gallery

INSTRUMENTS AND RECORDS.
MANOMETERS.

Location.—Manometer A (suction) at station E 50; manometer B
(pressure) at station E 50; manometer C (pressure) at station E 150.
Springs.—Manometers B and C were equipped with 200-pound
springs.
Records.—Pressure too small to be recorded.
+ PRESSURE CIRCUIT BREAKERS.

Location.—At stations E 50, B 150, E 250, E 350, E 450, E 550,
E 650.

Adjustment.—Set to operate at a pressure of 5 pounds.
Records.—Pressure circuit breaker at station E 650 operated.

FLAME CIRCUIT BREAKERS.

Type.—Detonator, coated inside and outside with silver carbide
(see p. 63).
Location.—Stations E 50 to E 650, inclusive.
Records—F lame circuit breaker at station E 650 operated.
72322°—13-—6






DETAILS OF EXPLOSION TESTS. 83

Ventilation—In order to determine whether the mine was pro-
ducing any gas, the fan was shut down for 14 hours preceding this
test and two samples of gas were taken; one at the face of the air
course and one at the face of the entry, with results as follows:

Analysis of air-course sample.

0.07
20.59
00
06
79. 28

100. 00

Analysis of entry sample.
0.06
20.58.
.00
204
79.32

100.00

The above results of analyses show that very little methane had
accumulated during the time the fan had been shut down. On the
basis of the analysis results no perceptible amount of gas would be
found with the ventilation in normal condition. After the samples
had been taken the fan was started so that the ventilation conditions
of this test would be similar to those of test 3.

INSTRUMENTS AND RESULTS.

Pressure circuit breakers.—Two pressure circuit breakers were
installed in the station at E 650; one was adjusted so as to be oper-
ated by a pressure of 1 pound and the other by a pressure of 2 pounds.

Length of flame—Guncotton tufts at E 704 and E 729 were ignited
either by the flame from the shot or more probably by a flying particle
of burning powder.

Results.—Only the circuit breaker set at 1 pound operated. It was
concluded, therefore, that circuit breakers set at 2 pounds would not
be operated by the pressure from a blow-out shot from a 13-inch pipe,
with the charge and the stemming of this test.

TEST 6.

Date.—February 3, 1912.

Purpose.—Study of the propagation of a coal-dust explosion, and
of the effect of Taffanel stone-dust barrier with coal-dust zone of 190
feet.

Origin of explosion —Face of the main entry, E 744.

Method of ignition.—Blown-out shot from 14-inch pipe in the coal.


28 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

the steel tube, so that the cannon can point into it through a hole in
a heavy plank stopping. The truck has the same gage as the mine
tracks, so the cannon can also be used in the mine for making a test
in which the equivalent of a blown-out shot is desired. Although
long-flame explosives like black powder or dynamite, when used in
coal-face shots and so prepared that they will blow out, will readily
ignite bituminous coal dust of sufficient purity and quantity, it was
found best for experimental purposes to start experimental explosions
by means of a blown-out shot from the cannon in order to obtain
uniform initial pressures. Another advantage gained by the usc of
the cannon is that coal-dust explosions can be originated at any pre-
determined point along an entry or heading of the mine, thus giving
conditions similar to those that may occur when a “brushing” shot
is fired in an entry or airway.

VENTILATING

SYSTEM,

It is intended to have the ventilation at the mine such that it will
be possible to duplicate almost any condition liable to occur in an
ordinary mine. The entries are double, thus allowing a regular
coursing of the air. In future some stub entries will be driven to
permit experimenting in a stagnant atmosphere.

The fan, which is now (March, 1912) on hand but not yet in-
stalled, is a centrifugal fan of standard make. It is designed for a
capacity of 80,000 cubic feet of air per minute at a pressure of 2
inches water gage, or 15,000 cubic feet of air per minute at a pressure
of 6 inches water gage. It will be driven by a 100-horsepower steam
engine; a belt connection, instead of direct connection, will be used,
as the former provides greater flexibility in case of a serious concus-
sion or a sudden stoppage of the fan through violence. The fan is
reversible and will be mounted at the end of the branch of the exter-
nal steel gallery. There will be several relief doors in addition to the
protection afforded the fan by its being set to one side of the gallery.
Unlike the practice at foreign testing galleries, at which the fan is
cut out by valve arrangements a few moments before an explosion
is started, it is proposed to run this fan during an explosion in order
to parallel conditions that occur in mine disasters.

Unfortunately, sufficient funds were not available for erecting the
large fan before the first series of explosion tests, so that a small fan
was temporarily set up in place of the large one. The small fan has a
capacity of 5,000 to 10,000 cubic feet of air per minute at pressures
of 1-inch and 3-inch water gage and is run by a gas engine. It was
originally placed near the top of the air shaft and connected therewith
for the ventilation of the mine under ordinary conditions, as in entry
driving. It was removed from the air shaft and connected with the


DETAILS OF EXPLOSION TESTS. 93

Velocity of propagation of explosion, test 8.

Pressure wave. | Flame.

Station. Total time | | “ime

“from. | between
ignition. | stations.

Velocity | Total time| ‘Time | Velocity
between irom | between | between
stations. | ignition. | stations. | stations.

| Feet per Feet per
Seconds. | Seconds. | second. | Seconds. | Seconds. | second.
-| 0.0885 0.6216
0.0880 1,136 0.4555 220
+1565 4.0771
= 0896 1,6 8044 254

= 2461 | 1.4715

1.7226

| 3.6857

2511 308
1.9631

MANIFESTATIONS.

Outside —The only outside evidence of an explosion was a rattling
of steel sheets over the explosion-door section, and a cloud of dust
and smoke and flurries of snow swirling from the main opening to
the end of the dump. The brace on the west side of the car dump,

TIME, SECONDS
12 16 20

°
2
ZB

2 28 82

S

SUCTION, POUNDS
PER SQUARE INCH

Ficure 21.—Manometric curve, test 8, pressure below atmospheric.

which was standing at the edge of the slate dump, was broken by a
flying board from a concrete form that had been resting against the
concrete wall at the opening. Other pieces of the same concrete
form were sucked into the entry to station E 50. The top bar of
the entry gates was broken into two pieces; one piece was found
on the dump 120 feet from the opening, and the other on the east
side of the slate dump. One part of the board “Danger” sign on
the air course was blown 54 feet and the other 72 feet in from the
opening. The last four sheets on the explosion-door section were
lifted completely out of place, and fell on the movable section of the
steel gallery.

Inside—There was considerable coke on the inby and outby
exposures of the shelves at E 240, E 340, and E 440; the rib was
soot covered from E 300 to the face; at E 304 the coal was blistered,
and many other small blisters were noted between this point and
the face. The roof was badly blistered at E 440. A deposit of
coked dust was found on the shelves at E 479. There was some
coked dust on the outby end of the shelf at E 550. At E 590 there


PUBLICATIONS ON MINE ACCIDENTS AND TESTS OF
EXPLOSIVES.

The following Bureau of Mines publications may be obtained free
by applying to the Director, Bureau of Mines, Washington, D. C.:

BuLETIN 10. The use of permissible explosives, by J. J. Rutledge and Clarence
Hall. 1912. 34 pp., 5 pls.

Buzetin 15. Investigations of explosives used in coal mines, by Clarence Hall,
W. O. Snelling, and 8. P. Howell, with a chapter on the natural gas used at Pittsburgh,
by G. A. Burrell, and an introduction by C. E. Munroe. 1911. 197 pp., 7 pls.

Buisetin 17. A primer on explosives for coal miners, by C. E. Munroe and Clarence
Hall. 61 pp., 10 pls. Reprint of United States Geological Survey Bulletin 423.

Buietin 20. The explosibility of coal dust, by G. 8. Rice, with chapters by J. C.
W. Frazer, Axel Larsen, Frank Haas, and Carl Scholz. 204 pp., 14 pls. Reprint
of United States Geological Survey Bulletin 425.

BuL.erin 44. First national mine-safety demonstration, by H. M. Wilson and A. H.
Fay, with a chapter on the explosion at the experimental mine, by G. 8. Rice. 1912.
75 pp..7 pls.

BUuLteTin 46. An investigation of explosion-proof mine motors, by H. H. Clark.
1912. 44 pp., 6 pls.

Butetin 48. The selection of explosives used in engineering and mining opera-
tions, by Clarence Hall and 8. P. Howell. 1913. 50 pp., 3 pls.

Buttetin 52. Ignition of mine gases by the filaments of incandescent electric
lamps, by H. H. Clark and L. C. Isley. 1913, 31 pp., 6 pls.

Tecanicat Parer 4. The electrical section of the Bureau of Mines; its purpose
and equipment, by H. H. Clark. 1911. 12 pp.

‘TECHNICAL Paper 6. The rate of burning of fuse as influenced by temperature and
pressure, by W. 0. Snelling and W. C. Cope. 1912. 28 pp.

‘Teounrcat Paver 7. Investigations of fuse and miners’ squibs, by Clarence Hall
and S. P. Howell. 1912. 19 pp.

‘Trcunicat Paper 11. The use of mice and birds for detecting carbon monoxide
after mine fires and explosions, by G. A. Burrell. 1912. 15 pp.

‘Tecuntcat Paver 12. The behavior of nitroglycerin when heated, by W. 0.
Snelling and C.G. Storm. 1912. 14 pp., 1 pl.

‘Tecurcat Parer 13. Gas analysis as an aid in fighting mine fires, by G. A. Burrell
and F. M. Seibert. 1912. 16 pp.

‘Taounicat Parer 17. ‘The effect of stemming on the efficiency of explosives, by
W. 0. Snelling and Clarence Hall. 1912. 20 pp.

‘TECHNICAL PapER 18. Magazines and thaw houses for explosives, by Clarence Hall
and 8. P. Howell. 1912. 34 pp., 1 pl

TeEcHNICAL Paper 19. The factor of safety in mine electrical installations, by H. H.
Clark. 1912. 14 pp.

TecuNicaL Paper 21. The prevention of mine explosions; report and recommenda-
tions, by Victor Watteyne, Carl Meissner, and Arthur Desborough. 12 pp. Re-
print of United States Geological Survey Bulletin 369.

14


44 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

EXPLOSION TEST 6.

In test 6, made February 3, 1912, the coal-dust load was 190 feet in
length, or over double that used in tests 3 and 4. A stone-dust
barrier like that described under test 3 was erected in the air course
immediately outby the open crosscut. The main entry was left open.
The results were that the flame, after having passed through the cut-
through into the air course, died away after having passed the first two
or three shelves, but the ground rock dust on these shelves was little
displaced; and it is questionable how far the flame was checked by
reason of the presence of the barrier. In the main entry the flame
traveled about 70 feet beyond the coal-dust zone, but there was no
indication of local violence.

In this test a record of the flame velocity between stations E 650
and E 550 was obtained, and showed that the distance of 100 feet was
traversed in 0.7903 second, or at the rate of 127 feet per second. (See
fig. 10.) For details of this test, see pages 83 to 87.

EXPLOSION TEST 7.

Test 7 was made February 5, 1912, with an increased length of coal-
dust load, the length being 290 feet, or 100 feet more than in the previous
test. Determination was desired of the effect of the rock-dust barrier
when the length of the coal-dust zone was increased. The results
showed that while the flame died away in passing through the barrier,
the rock dust was little disturbed, except on the first shelf or two. In
the main entry the flame traveled 465 feet, or 175 feet beyond the end
of the coal-dust zone. The humidity of the air at the mine in this
test, as well as in the previous one, was rather high, ranging from 93
at station E 450 to 100 per cent at station E 650 opposite the inner
cut-through. The velocity of the flame between stations E 650 and
E 550 was 160 feet per second. (See fig. 10.) For details of this
test, see pages 87 to 91.

EXPLOSION TEST 8.

Test 8, made February 7, 1912, was virtually a repetition of the
previous experiment. The coal-dust load and other conditions were
the same, except that the relative humidity of the air was considera-
bly less, being 85 per cent at station E 450 and 83 per cent at station
E 650 opposite the inner cut-through. It should also be noted that
the fan was shut down two minutes before the test was made, although
this may not have affected the results. Perhaps the most influential
cause of difference was that instead of making the blown-out shot in
the coal face, as had been done in the previous tests, the ignition was
gaused by a blown-out shot from the cannon, which was placed at the
face. The cannon probably produced a greater local concussion of


90 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

Comparison of the ratio of volatile matter to fixed carbon (39.23:
60.77) with the ratio of volatile matter to fixed carbon in the original
dust (37.55: 62.45) indicates again an increase in volatile matter and
a corresponding decrease in the fixed carbon. It is probable that
this change was again due to a mixing of the original dust with some
soot from the explosion.

One hundred and thirty pounds out of the 350 pounds put on the
shelves for this test remained after the explosion.

ROAD bust.

A road-dust sample (No. 13295) from the air course between the
second and third cut-throughs was taken after the explosion, and was
analyzed, with the following results:

Moisture. 16. 02
Volatile matter. 17.10
Fixed carbon. 13.91
52.97
100. 00
SD ae 84

The high content of ash and moisture would render this road dust
nonexplosive, and might possibly even have a quenching effect on
the flame of the explosion.

MINE AIR.

A sample of mine air (No. 2079) was taken at the face of the main
entry as soon after the explosion as it was possible to reach this
point without a helmet. The analysis showed the following results:

0.04

This sample showed a surprisingly small percentage of black
damp and no carbon monoxide; the smell and the presence of smoke
indicated worse conditions than were shown by this sample.

A sample of mine air (No. 2081) was also taken inby station E 650
about the same time as the preceding sample, its analysis showing
the following results:

CO,. 0.08

20.91

00
. Trace,
79.01

100. 00
This analysis is almost a duplicate of that of the preceding sample.


60 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

A cross section of one of the gages is shown in figure 13.

‘The value of the maximum pressure is determined from the shorten-
ing of a small copper cylinder under pressure. A light hollow plunger
(p) fits into one end of a cylinder (6), the other end of which is open
to the mine entry. Grooves cut around the outside of the plunger, or
piston, are filled with heavy grease or tallow to prevent corrosion and
reduce leakage past the plunger. The copper cylinder, which is
about 0.063 inch in diameter and 0.1023 inch long, is set on end in the
bottom of the plunger, and a cap (c) with a projecting pin (a) in the
center is screwed down against it.

The length of the copper cylinder is measured with a micrometer
caliper before and after the test, and the pressure is determined from
the amount of shortening of the cylinder.

Eight of these gages and a large number of copper cylinders were
made at the naval gun factory, Washington, D.C. The calibration
curve for the copper disks was furnished by the maker.

VELOCITY RECORDERS.

The method of measuring the velocity of the
pressure wave is to allow it to break a series of
electrical circuits, at regular intervals along the
mine. The breaking of each circuit is recorded
by the release of an electromagnetic pen which
makes a line on a suitable surface traveling at a
known speed.

B. C. D, PRESSURE CIRCUIT BREAKER.

Fate aoe nc. ~The breaking of the circuits at the various
tin of maximum. points is accomplished by means of the B. C. D.
Pressure gage. circuit breakers, which are adjusted so as to

operate circuit only when a definite pressure has been exceeded. Tho
breaker (Pl. VI, A) has a tube opening at one end into the mine
entry and connected at the other end to a cylinder containing a
plunger, which is held down by a lever and heavy spring. By
varying the tension of the spring the pressure required to lift the
plunger may be fixed at any value from 2 to 20 pounds per square
inch. A pin projects from the side of the plunger, and when set this
pin rests on two aluminum plates completing an electric circuit
between them. A small spring acts on the outer end of this pin
and tends to rotate the plunger; rotation is prevented by the alumi-
num plates, their shape being such that the downward pressure of
the plunger holds the pin on both of them. As soon as the explosion
raises the plunger, the contact is broken and the small spring pulls
the pin to one side, thus preventing any remake of the circuit when
the plunger falls again.


24 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

lapsible type which could be moved from point to point as the work
advanced. These forms were similar to those designed by Lombois.*

While the concreting material of the lining was being placed,
bolts were inserted for the support of five shelves on each side to be
used in coal-dust explosion experiments. There was also laid behind
the wall a 4-inch steel pipe in which were placed electrical cables, a
2-inch pipe for a compressed-air line, and a 2-inch water main with
hydrant boxes every 100 feet. The arched lining, which is finished
smooth, is 8 feet wide in the clear, and 7 feet 6 inches high from the
top of the track ties to the arch; near the entrance the roof has a
slight rise and the floor descends, so that the arch is 8 feet high at
the portal. The diagonal heading or gallery is smaller, being 6 feet
4 inches wide and 6 feet 4 inches high (fig. 5).

In constructing the lining in the outer part of the main entry and
in the diagonal heading or gallery, the preliminary timbering had
to be left in place above the arching as the roof was too weak to
allow its removal. Adjacent to the portals the arches were con-
structed in the open; they were afterwards covered with dirt, which
was filled in to the top of the retaining walls. During the first series
of experiments the concreting was extended into the main entry,
making its total length 169 feet; the entire diagonal heading, 198
feet long, was lined, and in the air course there was a lining from a
point 20 feet outby the connection with the diagonal heading or
gallery to a point 65 feet inby the junction. At the wide space at the
junction the roof had been supported with railroad rails which were
left in to supplement the strength of the reinforced lining.

THE PITTSBURGH COAL BED.

The Pittsburgh bed, in quality, extent, and uniformity, is one of
the most remarkable coal beds in the United States, if not in the
world. It extends southwestward from the vicinity of the city of
Pittsburgh to the middle of West Virginia, where there are scattered
areas in the hilltops, a distance of about 125 miles; on the west it
extends into Ohio; the width is 75 to 100 miles, but not all of this
area is underlain with the Pittsburgh bed, as in places the coal is
cut out in the valleys of the larger streams and on some of the anti-
clines that separate the several basins. Although varying in different
basins, in any one basin the coal is remarkably regular in quality
and thickness. In certain areas the bed produces the highest grade

@Lombois, J., Revetement en béton armé des bouvettes et des bures aux mines de Béthune: Bull. Soc.
Ind. Min,, ser. 4, vol. 6, 1907, pp. 195-205. The reinforcement was placed in the concrete arch to help sup-
port the roof. Tt was thought that the weight of the roof, together with its resistance to shear, could be
‘overcome by the upward pressure of an explosion. This proved not to be true; the arch and roof lifted,
causing the arch tods to break through the facing (see Pl. VIII, ). In future construction the arch
reinforcement will be placed farther from the face of the concrete, and the arch thickened to resist the
force of an explosion.




INTRODUCTION. 9

When an explosive gas mixture is ignited at the closed end of a tube
that is open at the opposite end, the flame travels with rapidly
increasing velocity toward the open end. In the early stage of the
gas explosion the flame is usually propagated in the way just de-
scribed for a dust explosion; that is, the heat evolved by the com-
bustion in one layer of gas raises the temperature of the adjoining
layer above the temperature at which ignition takes place. In cer-
tain gas mixtures, for example, a mixture of hydrogen and oxygen,
after the flame has traveled a certain distance from the point of
ignition an ‘‘explosion wave,” or so-called ‘detonating wave,” is set
up, and from this point the explosion is propagated almost instanta-
neously. .

The term ‘detonation wave” has been defined by Prof. Harold B.
Dixon? as follows:

The expression “I’onde explosive” coined by Berthelot, and its English equiva-
lent, ‘the explosion wave,” signify that flame which passes through a uniform gaseous
mixture with a permanent maximum velocity. The rate of the “explosion wave”
is a definite physical constant for each mixture; the explosion wave travels with the
velocity of sound in the burning gas, which itself is moving rapidly forward en masse
in the same direction, so the explosion wave is propagated far more quickly than sound
travels in the unburned gas. * * * In the explosion wave, each layer of gas is
compressed so suddenly that it is raised beyond its ignition point by the heat of com-
pression. * * * I use the word “detonation” to express the burning taking
place in the explosion wave, since a “detonator” when struck burns in this way itself
and sets up an explosion wave in explosive gases around it.

As the phenomena of coal-dust explosions are in many respects
similar to those of gas explosions, it is not impossible that an ‘“‘explo-
sion wave” or “‘detonation wave’? may be produced by a dust
explosion in a tube or gallery of uniform cross section under certain
conditions. A mine heading or entry never presents the uniformity
of a tube or an artificial gallery, because in a mine passage there are
irregularities due to projections of roof and ribs, to turns, to side
openings, to timbering, and to great variation in the amount and
quality of dust present. Therefore it does not seem probable that
in a mine explosion a detonation wave of permanent maximum
velocity can occur, although in some localities the disruptive force of
an explosion may be so great that in popular language it might be
termed ‘‘detonation.”

When a coal-dust explosion is caused by a blown-out shot, a
pressure wave is started that travels at a rate of a sound wave;
this wave, which in this bulletin has been termed the ‘‘shock wave,”
gradually becomes less and less in amplitude as it travels from the
origin. Near the originating blast, if several pounds of black powder

@ Report of Committee on British Coal Dust Experiments, Record of first series, 1910, p. 150.
> Nearly 1,100 feet per second in a mine passage, varying slightly according to the temperature of the air
‘and the velocity of the ventilating current.


MEASUREMENT OF VELOCITY AND PRESSURE. 61
AUTOMATIC COMMUTATOR.

Any variation in the lag of the electromagnetic pens used to
record the breaks of the circuit breakers, although short in itself,
might constitute a comparatively large percentage error since the
time interval to be measured is so very short.

Such an error is avoided in this apparatus by using an instrument
termed an “automatic commutator” (Pl. VII, B, and fig. 14), which
enables each successive break to be recorded by the same electro-
magnetic pen. This instrument is used in connection with the
recording instrument (chronograph) described on page 62. The

Chronograph Battery
ag vUU

E650

,

E550

E450

E350

‘Main entry

E250

E150

E50

Leg, et Ugh gh et

Figure 14.—Wiring diagram of automatic commutator.

current from the battery (fig. 14) goes through the electromagnet
on the chronograph so that its armature is attracted, and then
through the electromagnet of the commutator to the brush (g,
fig. 14). The other terminal of the battery is connected to one
terminal of each of the circuit breakers (at E 650, E 550, etc.,
fig. 14). The second terminals of the circuit breakers, in the order
in which the explosion reaches them, are connected by separate
wires to the studs on the commutator (1, 2, 3, etc., fig. 14).

Assume that the brush g rests on stud 1 (the position it occupies
before the explosion); the current then flows in order through the


DETAILS OF EXPLOSION TESTS. 67
VENTILATION AND HUMIDITY READINGS.

Ventilation.—5,000 cubic feet of air moving through last cut-

through. PRESSURE, POUNDS
Humidity. — PER SQUARE INCH,
° 8 5 s
Station, wet bulb. | Dry bulb. | Humiaity. | 7 cH =
oF oR, Percent. § H
Outside mine. . ... 44 52 | 52 5
Third cut-through - 56 574 | 91 , 2
5 if
Barometer.—28.88 inches. g cory
INSTRUMENTS AND RECORDS. 8 :: 2
MANOMETERS. a
Location —Manometer A at station E 150; g
manometer B at station E 50. Rok 4
Spring.—Thirty-pound springs were used
in both manometers. 2
Records.—See figure 15. 3 Ht
B & H
g t t
Location —At stations ©150 and E 50, * g i t
100.25 feet apart. a HH
Recorded time between stations.—0.0513 sec- 2 ss Ht
ond. 33 Hf
Recorded velocity between stations.—1,954 —£ ” i
feet per second. 2 tet
Adjustment.—Could be operated bya pres- 2 — Hit
sure of 5 pounds. & -
a
OUTSIDE MANIFESTATIONS. 5 gif
i
Length of flame.—Huge masses of flame 2
burst out of the openings. Flame from the @
main opening estimated to have extended 200 = a
to 300 feet (fig. 16). S
Violence of explosion.—The roof of the fan = t
drift was blown off and landed on the tram- =
road track, 25 feet distant. The 2-inch plank 2 % H
stopping at the end of the steel gallery was g
blown out. The sandbags on the explosion-
door section were thrown high in the air, and
the board framework beneath them was 8

destroyed.


ILLUSTRATIONS.

Page.
Puare I. Explosion issuing from portal, test 15 . - Frontispiece
IL. A, Dust shelves in main entry; B, Finished portal 20

IIL. A, Reinforcement of portal; B, Observatory and other buildings;
, External explosion gallery . - 2
IV. A, Undercutting a break-through; B, Coal brought down by shot... 26

V. A, Interior of instrument. station, showing B. C. D. manometer; B,
Débris on hillside opposite mine entrance. 34

VI. A, Circuit breakers in small stations; B, Observatory wiring connec-
tions; C, Rupture of lining of main entry ...........-22200000+- 36
VII. 4, B.C. D.automatic gas sampler; B, B.C. D.automaticcommutator. 38
VIII. A, Results of test 1, at junction of slant and air course; B, Bent -inch
steel bar, showing lift of roof; C, Reinforcing rod pulled out of

concrete in roof of main gallery. 40
IX. A,  B. C.D. pressure manometer; B, B. C. D. time marker. 58.
x. 16
XI. Coke bubbles formed along bedding planes of coal, test 2. 76
XII. A, Coked dust, test 2; B, Coating and filaments of soot, test 2. 7
Fraune 1. Profile of main entry of experimental mine 18
2. Plan of experimental mine, also surface contours, at time ‘of explo-
sion of October 30, 1911, showing path of mine car thrown by
explosion... 20
3. Cross section of reinforced-concrete portal of experimental mine. 21
4, Plan of reinforced-concrete portal of experimental mine 22
5. Cross-sectional views of mine gallery... 23
6. Sections of passage between steel gallery and diagonal entry. 27
7. Construction of instrument chamber. 35
8. Electric wiring of mine 37
9. Relative positions of flame and pressure wave, test 15 50
10. Flame-velocity curves obtained in tests 6, 7, 8, 12, and 15. 52
IL. Pressure-velocity and flame-velocity curves obtained in test. 15. 52
12. Section of B. C. D. manometer.......- 57
13. Cross section of maximum-pressure gage. 60
14. Wiring diagram of automatic commutator. . . 61
15. Manometric curves, test 1, pressure above atmospheric. 67
16. Test 1, extent of flame and conditions of test. . 68
17. Test 2, extent of flame and condi 72
18. Test 3, extent of flame and conditions of test. 80
19. Test 6, extent of flame and conditions of test. 86
20. Test 7, extent of flame and conditions of test. . 89
21. Manometric curve, test 8, pressure below atmospheric 93
22. Test 8, extent of flame and conditions of test. 94
23. Manometric curve, test 12, pressure below atmospheri 99
24. Test 12, extent of flame and conditions of test. 100
25. Test 14, extent of flame and conditions of test. 104
26. Manometric curve, test 15, pressure below atmospheri 109
27. Manometric curves, test 15, pressure above atmospheric. 109
28. Test 15, extent of flame and conditions of test. 110



DETAILS OF EXPLOSION TESTS. 89

station E 650, 1.4917 seconds after ignition and station E 550, 2.1149
seconds after ignition. The time between stations was 0.6232 second,
and the velocity 160 feet per second.

MANIFESTATIONS.

Outside.—The only evidence of an explosion outside was the

rattling of the steel sheets of
eu

the explosion-door section, and h
the appearance of aslight cloud
of dust at the mouth of the £3 |= Eee
main opening. y ES

Inside-—The door ‘in the air Method of plain EA
course had been previously ‘Tafanel barrier = ewe
removed and the curtains re- By
placing it were not torn down SYMBOLS USED 5
by the explosion. There were Bema Teffanc! barrier Law) ao
no signs of violence in any ae wet
part of the mine. tom nidecaand eee wet

LENGTH OF FLAME. ee

The flame in the main entry
extended from the face to E soaue In peer ea0
279, or 465 feet (fig. 20). In 2 Ei ed
the cut-through air-course
branch,the flame extended 135 Bue
feet or to the outby end of the
Taffanel barrier. The stone Eo
dust on the barrier was dis-

Relief door de

turbed only slightly and it is
uncertain just how much of a
quenching effect the barrier rune 2—rest 7, extent of flame and conditions
may have had on the flame. Of test.

ANALYSES MADE AFTER THE EXPLOSION.
COAL DusT.

A coal-dust sample (No. 13297) was taken from the dust remaining
on the shelves after this explosion and was analyzed, the results
being as follows:

Moisture... 3.01
Volatile matter. 32. 64
50.57

13.78

100.00

Sulphur.......eecceceeeeeeeeeceeeeeeeeceeeceeeeeeseereeeeeeseees 1.18


MEASUREMENT OF VELOCITY AND PRESSURE. 65

the two automatic commutators, the chronograph, the half-second
clock, the batteries, and the operating switches are placed in the
observation room. (See PI. VI, B.)

The connections necessary for operating these instruments are
made through two cables which run from the observatory to all the
stations in the mine (see fig. 8) through a pipe embedded in the rib
and faced with concrete (see Pls. II, A, V,.A, VI, A, VII, A). The
smaller cable contains three wires and supplies electrical power at 110
volts for the manometer motors, the gas sampler, and lights in the
mine. The larger cable contains 1 No. 10 wire and 30 No. 16 wires
(B. & S. gage) and carries low-voltage current from the storage
batteries only. This cable supplies the two shot-firing lines, the
tenth of a second and the ignition lines to the nianometers, and the
circuit breaker lines, besides a number of spare wires for special use.
The No. 10 wire is used as a common return to the observation room
for all circuits,


DETAILS OF EXPLOSION TESTS. 85
VENTILATION.

Air and humidity readings taken‘at two points just prior to the
explosion were as follows:

Air and humidity readings, test 6.

cross. |
section.
i

Wet

i Dry
Station. Aa

bulb,

Barom- | Humid-

aoe iy Volume.

Velocity.

Feet per | Cubic feet

°F | °F | Inches. | Percent.| Feet. | minute. | per minute.
45) 46h | 28.96 80 | Gi by 9 4, 680
39 I 40 28.96 92| 6Eby9 60 3,330

Analysis of mine air—A sample of mine air (No. 2078) was taken
at the face of the main entry just before firing the shot in order
to determine whether any methane was present. The results of
analysis were as follows:

- 0.06

19.86
00
02
- 80.06

100.00
The analysis shows 0.02 per cent of methane, and as the possible
error would not exceed 0.01 per cent, one may be assured that there
was only a slight trace of gas present, too little to affect the result of
the shot. It is also probable that even a trace could not be found
near the cut-through.

INSTRUMENTS AND RECORDS.

MANOMETERS.

Location —Manometer A (suction) at station E 50; manometer B
(pressure) at station E 50; manometer C (pressure) at station E 150.

Springs.—Manometers B and C were equipped with 200-pound
springs.

PRESSURE CIRCUIT BREAKERS.

Location.—Stations E 50, E 150, E 250, E 350, E 450, E 550,
E 650.

Adjustment.—Set to operate at a pressure of 2 pounds.

FLAME CIRCUIT BREAKERS.

Location Stations E 50, E 150, E 250, E 350, E 450, E 550,
E 650.


76 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
ANALYSES OF SAMPLES.

Samples of coked dust, blistered coal, stalactitic carbon, and
road dust were obtained and analyzed after the explosion.

The results of a proximate analysis of a combined sample of
blistered coal from the west rib of the air course and the north rib of
the last cut-through are given below. For purposes of comparison
the results of an analysis of a representative sample of the unaltered
coal are given also.

Results of analyses of blistered and of unaltered coal.

Constituent.

Blistered | Unaltered
coal. coal.

Moisture......
Volatile matter
Fixed carb

‘Ash.

‘Tots

[Proportion for blistered coal—Volatile mation fixed carbon :: 36.36 : 63.64; proportion for unaltered
coal—Volatile matter ; fixed carbon :: 39.59 : 60.41.)

A comparison shows that the percentage of volatile matter as com-
pared with fixed carbon is less in the blistered coal than in the unal-
tered coal. The low ash content of the blistered coal undoubtedly
is not significant of change. By accident the layer of coal had a
much lower content than normal.

Two other samples of blistered coal were taken in the third cut-
through. One was taken by cutting off as thin a slice as possible from
the blister; the other represented a second thin layer beneath the
first. It was thought that the analysis of the first sample, because
of the blistering that caused the curved surfaces on the face of the
coal, might show different results than did the analysis of the
unaltered coal. The results of both analyses were as follows:

Results of analyses of two layers of blistered coal.

constituent. Biot | Spo
Moisture... . 1.73,
Volatile matt 37.83
Fixed carbon. 67.25
Ash. 3.17
Tote 100.00

{Proportion for first layer—Volatite matter : fixed carbon :: 39.48 : 60.52; proportion for second layer~
Volatile matter : fixed carbon :: 39.79 : 60.21,]


46 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

is used, because some of the energy of the exploding powder is ex-
pended in breaking the liner and the surrounding coal.

In tests 5, 9, and 10 tufts of guncotton were suspended at intervals
along the entry. All of them within a distance of 40 feet from the
cannon were ignited, probably not by flame but by burning particles
of powder projected by the shot. This conclusion was reached as
the result of tests in the Pittsburgh station gallery.

EXPLOSION TEST 12.

In test 12, made February 10, 1912, a lighter coal-dust load was
used than previously, the quantity being 1 pound per linear foot for
the first 290 feet, and less than one-half pound (0.457 pound) per linear
foot for the outer 420 feet.

The flame did not travel to the outside of the mine, but stopped at
about 465 feet from the origin, or at 175 feet beyond the end of load-
ing of 1 pound per linear foot. Judging from the one experiment of
this character, it would appear that under the existent conditions
0.457 pound of dust per linear foot was not sufficient to propagate an
explosion. The quantity mentioned is equivalent to about 0.122
ounce per cubic foot (122 grams per cubic meter) of air space. The
humidity was high, but not extremely so, being 91 per cent at station
E 650. In this test the flame did not pass beyond the barrier.

As the explosion in the main entry died away before reaching the
manometer stations, the pressure produced had dropped so low that no
pressure record was obtained; but following the explosion the suction
manometer at station E 50 showed a depression wave lasting 0.6 sec-
ond, the maximum depression being only 0.5 pound per square inch
see fig. 23). The velocity of the flame between the circuit breakers
at the 100-foot stations between stations E 650 and E 350 indicated
velocities of 153, 161, and 225 feet per second (fig. 10), showing that
the explosion was relatively slow and feeble. The details of this test
are given on pages 97 to 99.

EXPLOSION TEST 13.

Test 13 was made on the same afternoon, February 10, 1912, as
test 12. The same dust was used except that 25 pounds of fresh dust
was spread in front of the blown-out shot, which was prepared in the
coal face, instead of using the cannon as in the previous test. The
result was practically the same, the flame, as indicated by the tufts of
guncotton, not extending further than in the previous test. Detailed
description is given on pages 100 and 101.

EXPLOSION TEST 14.

In test 14, made February 19, 1912, the coal-dust load in the outer
part of the mine was increased over that used in the previous tests;


42 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

be overcome, but also the weight and resistance to shearing of 6 to 12
feet of natural strata, shale and clay, overlying the arching.

The breaking of the lining of the diagonal heading was a temporary
misfortune, as it prevented resumption of experiments in originating
explosions at the mouth of that heading, both because of the weakness
of the cracked lining and because the breaks allowed ground water to
run in freely, keeping the gallery wet. So much damage was done in
the mine that several weeks was needed to make repairs. While the
repairs were being made, the permanent shelving was put in place,
the small stations installed for the circuit breakers, and the permanent
wiring put through a line of 4-inch pipe to the head of the main
entry. For safety, the pipe was set in a groove in the rib. With
the small force of laborers permitted by limited funds, these repairs
and improvements were not completed until the latter part of Janu-
ary, 1912, when the mine was put in readiness for further tests.

EXPLOSION TEST 3.

In order to test the new permanent shelving it was decided to first
try explosions limited in length and, if these were successful, to in-
crease successively the length and intensity of the explosions. The
coal-dust zone in test 3 was therefore made only 84 feet long—meas-
ured from the face in which was the blown-out shot to the outer
end of the zone.

It was also thought advisable in this series of experiments to make
some preliminary tests of stone dust placed on shelves. Such experi-
ments were made at the Altofts gallery, England, also independently
and more fully by Taffanel at the Liévin gallery, where a special
arrangement of them is termed l’arrét-barrage (‘‘arresting barrier’).
In consequence of the success of Taffanel’s tests, the plan of using the
barriers has been generally adopted in French mines. The ‘‘arresting
barrier” is composed of 10 or more shelves about one-half meter (20
inches) wide. Finely ground rock or shale dust is heaped upon
them. The shelves are placed sufficiently high to give clearance for
the cars, but a small space is left between the heaped-up dust and
the roof, each shelf and the heaped-up dust occupying about 10 per
cent of the cross section of the entry. The arrangement is such that
when an explosion strikes the barrier the shelves are knocked down
or demolished and the dust thrown into the air, forming what has
sometimes been termed ‘‘a dust curtain,” which in the Liévin gallery
has been found to check or stop the explosion.

For test 3, made January 31, 1912, a set of ‘“‘arresting-barrier”
shelves was placed in the air course immediately outby the inmost
cut-through, which was left open for ventilation. As the coal-dust
loading was limited, the explosion or inflammation was small and with-


18 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

(5) A natural-gas pipe line should pass near enough to the mine
to make feasible the laying of a branch line that would furnish a
supply of gas (methane and ethane) for experiments in combination
with coal dust and air in varying proportions, or with mixtures of
gas and air only.

(6) A good water supply should be available both for boiler use
and for fire protection as well as for experiments.

(7) The location should be accessible to a railroad so that the coal
produced could be loaded on railroad cars, yet should be so isolated
from houses or other buildings that violent explosions would not
endanger them.

After much search these requirements were all met by a site near
Bruceton, Pa., 13 miles southwest of Pittsburgh, on the Baltimore
& Ohio R. R. Here, the well-known Pittsburgh coal bed outcrops
along the sides of the valley of Lick Run. In a side ravine, in which
there is a small stream, a place in the outcrop was found sufficiently

15
150]
125
190}

ce)

E
a

Ggnerete por Z ‘Dat

BRo®

400 300 200 100 0 100 200 300 400 500 600 700 800 900 1000 1100 1200

FIGURE. 1—Profile of main entry of experimental mine,

back from the main frontage to allow entrance into the middle of an
extensive area of the coal. At the place selected for the drift open-
ings the bed dips gently to the north, and as the opening entries are
driven to the southwest they are self-draining. Many samples of
mine air have been taken and no appreciable amount of methane
has been found; even after the mine has been sealed for 14 hours a
maximum of only 0.06 per cent was found at the face of a heading.
The drift openings are high enough above the ravine bottom to
provide space for a convenient refuse dump and for other features
connected with the development of a mine. The hillside above the
outcrop rises steeply, so that there is a good cover over the main
headings. The crest of the hill is 132 feet vertically above the mine
(fig. 1). Across the ravine in front of the mine openings there is a
hillside that provides a natural barrier for catching material thrown
out by a violent explosion and deflects the air waves upward, a
protective feature of great importance in a populated district.


DESCRIPTION OF MINE AND EQUIPMENT. 37

FIRING CIRCUITS.

Among the other wires of the cables are a pair of firing wires that
can be connected to form a circuit in the observatory and thus dis-
charge the igniting shot. In the first two official experiments this
wiring was temporary, but subsequently when the flame and pressure
circuit wires were installed the shot-firing wires formed a part of one
of the cables passing through the pipe in the rib.

The shot-firing wires are separated from the other wires at the
mouth of the mine and enter a locked switch box.* This box contains
switches, which are always open until everyone has left the mine.

Observatory
Instrument cable,
‘BI wires

Power cable,
3 wires

SCALE OF FEET
80 6040 29 0 100 200
eee a

1g Water tank
Air course 8, $0°52'W.

cntout
box rd Doors Concrete )) ; i" ») Sandbag Lf |
sat OpPine? Main p_ ents ping

_
a a \ a a a
1 inadhument station

vument cable, 31 wires Power cable, 3 wires

station B50
Large instrument
‘stution E160
Eu

Large instrument

Figure &—Electric wiring of mine.

At the observatory there is another switch, also in a locked box.
This switch is closed by the engineer in charge of the experiment after
he has thrown in the switch at the mouth of the mine; that is, he car-
ries the keys to both boxes, so that he may make sure that everyone
has left the mine before he throws in the switches. When the switches
are both in, the firing circuit is completed by pressing a button that
causes the shot in the mine to be discharged. The details of the wir-
ing are given in a subsequent section of this bulletin and a diagram of
the wiring is shown in figure 8.

@ After the first series of explosions had been completed, with a view to greater safety the installation
was changed. Now all the wires enter the locked box and are arranged so that all the circuits are cut
by switches when men are in the mine.


GENERAL DESCRIPTION OF EXPERIMENTS.
PRELIMINARY EXPLOSION TRIALS.

The original plan was to make explosion experiments at intervals
while the mine was advancing, the explosions being originated in the
exterior gallery. In other words, the ignition of coal dust was to be
accomplished in the gallery in a manner similar to that employed at
the Pittsburgh gallery, namely, by simulating a blown-out shot of
black powder or dynamite at the closed end. However, the farther
end of the Pittsburgh gallery was open, whereas at the experimental
mine the farther end of the gallery, although unobstructed, pointed
directly into the mine. The cannon for simulating the blow-out shot
was placed against a plank stopping that closed the outer end, and a
hole was cut through the stopping opposite the bore of the cannon.

Coal dust was placed along the floor of the gallery. When the large
relief opening, or the movable section for connection to the mine
was rolled to one side, there was no difficulty in obtaining ignitions
similar to those at the Pittsburgh gallery. When, however, the
large openings were closed, the effect was striking. The plank stop-
ping was burst outward by the effect of the shot and the dust was
inflamed only in the first half of the gallery. On strengthening the
stopping, the flame was projected feebly through the gallery, but
died away on entering the mine. Force was manifested in the vicin-
ity of the cannon, breaking some of the heavy planks of the stopping
and throwing down a sandbag stopping in the branch to the fan, but
the force in the direction of the mine diminished rapidly. Seem-
ingly the concussion of the blown-out shot did not bring the coal
dust into suspension at a distance from the cannon, and the pressure
developed by the ignition of the dust near the cannon, being relieved
by the breaking out of the stoppings, was not sufficient to cause
pressure waves large enough to continue to raise in advance coal
dust in quantities sufficient to sustain propagation.

EXPLOSION TEST 1.

Several attempts of the foregoing sort were made and resulted in
considerable damage to the temporary fan casing. As the time was
getting short for preparing a public demonstration in connection with
the first national mine-safety demonstration on October 30-31, it was

39


64 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
B. C. D. AUTOMATIC GAS SAMPLER.

The apparatus used to obtain a sample of gas during the explosion
is of the B. C. D. automatic type (PI. VII, A), and is designed to meet
the following conditions:

(1) The exact moment at which the sample is taken with reference
to the explosion must be known and must be capable of alteration at
will.

(2) There must be no air in any of the connecting pipe between the
sampling bottle and the mine entry.

(3) The time during which the sample is being taken must be very
short if a sample from only one stage of the explosion is desired.

A steel sampling bottle is connected to a short pipe that just
reaches into the mine entry. The inner end of this pipe is closed by a
glass cap and the whole (bottle and pipe) is exhausted to a pressure
of about 3 mm. of mercury.

A circuit maker, which is similar to the B. C. D. circuit breaker
except that its operation closes an electric circuit instead of opening
one, is placed at any desired location in the mine. The pressure
wave causes the circuit maker to close an electric circuit through a
fine fuse wire that holds back a hammer over the glass cap of the
sampler. The current fuses this wire and allows the spring to pull
down the hammer and break the cap; then gas rushes through the
pipe and into the exhausted bottle.

The current also passes through an electromagnet in parallel with
the fuse wire, so that at the same time the wire is fused the armature
of the magnet is pulled down and releases a trigger which in turn
allows a small weight to fall, Gas enters the bottle during the time
this weight is falling. To the weight is attached a cord which, after
the weight has fallen a short distance, suddenly jerks a pin that
releases a heavy weight. This weight, by means of a cord and pulley,
turns a valve that closes the bottle. The length of time that the
bottle remains open is regulated by the length of the cord attached to
the small weight.

The instant of taking the gas sample is fixed by the location of the
circuit maker. Thus, if the circuit maker is located alongside of the
gas sampler, the time of sampling will coincide with the passage of the
front of the pressure wave. By placing the circuit maker between
the gas sampler and the point of ignition, the gas sample may be taken
in advance of the pressure wave.

ARRANGEMENT OF APPARATUS.

Of the above instruments, the pressure-measuring instruments, the
circuit breakers, and the gas sampler and its circuit maker are placed
in thevarious stations in the mine. The tenth of asecond time marker,


DETAILS OF EXPLOSION TESTS. 113

mouth neither the tuft nor the wire that had held it could be found.
The flame had burned the guncotton at a point 80 feet from the
mouth, so that the flame must have extended past A 80 but not
beyond A 30. Although the barrier did not stop the flame immedi-
ately, it had such an effect that the flame extended a much shorter
distance than previous experiments indicated it would have gone.

ANALYSES OF GAS SAMPLES TAKEN AFTER THE EXPLOSION.

Two samples of air were taken by a helmet party that entered the
mine at the main opening about 15 minutes after the explosion and
while the smoke was still issuing.

The analysis of a sample (No. 2249) taken 150 feet inby the main
opening showed the following results:

1.59
18. 38
1.05

42

- 78.86

100. 00

The analysis of a sample (No. 2250) taken 200 feet inby the main
opening showed results as follows:

- 147
18.30
1.08

100.00

The results of the two analyses are very similar. The oxygen
content is high and would be capable of supporting life if no carbon
monoxide were present, but the carbon. monoxide content is so
great that a person not protected by a helmet would retain con-
sciousness only a few minutes in such an atmosphere.


INTRODUCTION. 13

(14) Local widening of explosion passage.

(15) Number of side openings, such as cut-throughs, not dust laden.

(16) Dustless zones of various lengths in path of explosion.

(17) Watered zones of various lengths in path of explosion.

(18) Stone-dust zones of various lengths and kinds in path of
explosion.

(19) Means of ignition of coal dust, such as:

(a) Blown-out shots of various intensities with various explosives.

(b) Explosion of fire damp.

(c) Electric arcs or glowing wires or blowing out of fuse.

(d) Open flame when dust is already in suspension in air.

(20) Length of mine passage used in test.

(21) Character of mine passage—double or single or closed at one
end, that is, ‘‘in the solid.”

VARIABLE EXPLOSION CHARACTERISTICS FOR DETERMINATION
IN EACH TEST.

Variable explosion characteristics subject to determination in each
test are as follows:

(1) Velocity of flame at different stages of explosion.

(2) Velocity of pressure waves at different stages of explosion.

(3) Relative position of flame and of pressure waves.

(4) Rise and fall of pressure, above and below the atmospheric,
at different points in the course of an explosion.

(5) Composition of gases at various stages of an explosion, the
samples being gathered automatically.

(6) Temperature of explosion at different stages, as determined by
thermocouples, or by strips of metal of different melting points.

(7) Composition of coke and ash residues from explosion, and their
position with reference to direction of explosion.

(8) Manifestations of violence.

PROBLEMS TO BE INVESTIGATED AFTER DETERMINATION OF
STATED VARIABLES.

Below are enumerated problems that the bureau will investigate
after having determined satisfactorily the influence of the variables
mentioned above:

(1) Length of dust-laden zone (of given cross section) measured
from a blown-out shot (of certain strength) that, through the ignition
of its dust, creates sufficient pressure waves to raise dust beyond,
and thus permit propagation of the explosion beyond the influence of
the blown-out shot.

(2) Length of a dust cloud, which, when ignited by an arc or open
flame, will cause pressure waves to stir up the dust beyond and cause
@ propagation of the ignition or inflammation.


PUBLICATIONS ON MINE ACCIDENTS AND TESTS OF EXPLOSIVES. 115

‘Tecunicat Parer 23. Ignition of mine gas by miniature electric lamps, by H. H.
Clark, 1912. 5 pp.

‘TecHNIcaL PaPer 24. Mine fires; a preliminary study, byG.S. Rice. 1912. 51 pp.

TECHNICAL Parer 28. Ignition of mine gases by standard incandescent lamps, by
H.H. Clark. 1912. 6 pp.

‘Tecunicat Parer 29. Training with mine-rescue breathing apparatus, by J. W. Paul.
1912. 16 pp.

Tecunicat Paper 40. Metal-mine accidents in the United States during the calendar
year 1911, compiled by A. H. Fay. 1913. 54 pp.

Tecunicat Paper 46. Quarry accidents in the United States during the calendar
year 1911, compiled by A. H. Fay. 1913. 34 pp.

‘TecunicaL Paper 47. Portable electric mine lamps, by H. H. Clark. 1913. 12 pp.

TecunicaL Parer 48. Coal-mine accidents in the United States, 1896-1912, with
monthly statistics for 1912, compiled by F. W. Horton. 1913. 72 pp. 10 figs.

Mrvers’ Circutar 3. Coal-dust explosions, by G. 8. Rice. 1911. 22 pp.

Mrvers’ Crrcutar 4, The use and care of mine-rescue breathing apparatus, by
J. W. Paul. 1911. 24 pp.

Mrvers’ Circunar 5. Electrical accidents in mines; their causes and prevention,
by H. H. Clark, W. D. Roberts, L. ©. Isley, and H. F. Randolph. 1911. 10 pp.,
3 pls.

Miners’ Circuzar 6. Permissible explosives tested prior to January 1, 1912, and
precautions to be taken in their use, by Clarence Hall. 1912. 20 pp.

Miners’ Crecutar 9. Accidents from falls of roof and coal, by G. 8. Rice. 1912.

16 pp.
Miners’ Circuzar 10. Mine fires and how to fight them, by J. W. Paul. 1912.

M pp.
Muvers’ Circutar 11, Accidents from mine cars and locomotives, by L. M. Jones

1912, 16 pp.
12)


GENERAL DESCRIPTION OF EXPERIMENTS. 41

(5) That temporary shelving for coal-dust load was unsatisfactory
because its replacement causes serious delays in conducting consecu-
tive experiments.

EXPLOSION TEST 2.

Although it was a rainy day, probably 1,500 people visited the mine
to witness explosion test.2 on October 30,1911. Nearly 1,200 people
went through the mine previous to the test. Unfortunately delay
was experienced in discharging the igniting shot prepared at the face
of the main entry. This delay was due to some short circuits in the
shot-firing lines, probably caused by visitors accidentally trampling
on the wires. Eventually a temporary line was carried into the mine
and the blown-out shot was fired. The resulting explosion was most
spectacular, happening as it did on a dark, rainy night. The flame
was of great extent and most vivid, and the concussion was felt in
villages 4 miles distant; it is claimed to have been heard at Monon-
gahela City, 12 miles distant.*

Details of this test are given on pages 69 to 78.

The motors driving the manometer drums failed to start when the
switch was thrown in at the observatory, so that no record of the
pressure wave was obtained; only the maximum pressures were indi-
cated, which were 26.5 pounds per square inch at station E 150 and
21.3 pounds at station E 50. There is great doubt whether these
values represent the maximum pressures. The demonstrations of
violence were apparently greater than in the previous test, in which
the manometer readings showed higher pressures.

The lessons to be drawn from this experiment are:

(1) Coal-dust explosions may occur when the atmosphere is nearly
saturated (the relative humidity within the mine was over 90 per cent)
and the floor, ribs, and walls are damp, but not wet, provided the
coal dust is dry and sufficiently abundant.

(2) Temporary shelving, being easily wrecked, is too expensive.

(3) There were too few recording instruments to obtain the infor-
mation necessary to study satisfactorily the phenomena of a dust
explosion.

(4) The magnitude of the lateral pressure of the main explosive
wave of a coal-dust explosion was demonstrated by the 13-inch lift
of the concrete arching in the main entry near station E 50, and
by the lift of the arching in the diagonal heading, which for its
entire length of over 200 feet was lifted bodily, the reinforcing rods
being pulled through the concrete. This lift was about 12 inches,
judging from one piece of reinforcement that was doubled back on
itself (PI. VIII, B). Not only did the strength of the lining have to

@ An account of this explosion is given in Bull. 44, Bureau of Mines, entitled “First National Mine-

Safety Demonstration, Pittsburgh, Pa., Oct. 30 and 31, 1911,” by H. M. Wilson and A. H. Fay, with a
chapter on “The Explosion at the Experimental Mine,” by G. 8. Rice, 1912, pp. 20-41.



2 CONTENTS,

Commenis on the data obtained
Records of pressure velocities.
Records of flame velocities.
Records of pressures...
Maximum-pressure gage records

Humidity.
Description of instruments for measurement of velocity and pressure.
Pressure recorders. ..
B.C. D. manometer.

B. C. D. time marker

B. C. D. measuring apparatu:
Suction manometer.....
Maximum-pressure gages.
Velocity recorders.........
B. C. D. pressure circuit breaker.
Automatic commutator.

Flame circuit breakers
B. C. D. automatic gas sampler
Arrangement of apparatu:

Details of explosion tests.

Ventilation and humi
Instruments and records.
Manomete:
Pressure circuit breakers.
Outside manifestations. .
Inside observations.

Ventilation and humidity readings.
Attempts to fire igniting shot.
Instruments and records..
Manometers..
Pressure circuit breakers.
Outside manifestations. .
Length of flame...
Indications of violence.
Inside indications of violenc
Coke and coked dust
Soot ccating..
‘Analyses of samples.

Coal dust.
Taffanel barrier.
Instruments and records,
Manometers.
Pressure circuit breakers.
Flame circuit breakers...
Outside manifestations.



58 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

The pressure of the explosion is transmitted from the mine entry
to the manometer through a piece of heavy hose, as short in each
case as conditions will permit, usually 1 foot to 24 feet long.

in order to compare one pressure record with another record of
the same explosion it is necessary to know the relative position of
each manometer drum at the instant the explosion started, and the
speed of revolution of each drum. Two Deprez indicators attached
to each manometer are used for this purpose. The Deprez indicator
is a small electromagnet that holds down, against the pull of a weak
spring, a light aluminum style resting against the smoked surface
of the manometer drum. As soon as the electric circuit is broken
the style moves in a direction perpendicular to the direction of rota-
tion of the drum.

An indicator on one manometer is connected in series with one on
the next, and the circuit goes through a fine wire stretched in front
of the igniting shot. At the instant this wire is broken by the shot,
each style makes a mark on the smoked paper on its drum.

The second indicator on each manometer records the speed of
revolution of the drum. These indicators are connected in series
with each other and with the “tenth of a second time marker,”
known as the B. C. D. time marker.

B. C. D. TIME MARKER.

The B. C. D. time marker (Pl. IX, B) has a weight so arranged
that when suspended at rest an electric current passes through it;
when the weight falls, the circuit is broken. While the weight is
falling, a circuit is again made, but is broken when the weight comes
to rest. Consequently, when the time marker is connected in series
with the Deprez indicators on the manometers, a break, a make,
and a break are successively traced on the drums by the styles.

The space between the two breaks recorded on the drum is equiva-
lent to the time required for the weight to fall from rest through the
given distance. This distance, S, is calculated from the dynamic
formula S = 4g¢’, so as to represent a time interval, ¢, of just one-tenth
of a second. The space between two breaks, instead of between a
break and a make, is measured so as to eliminate any error from the
lag of the indicator. This lag would, of course, be the same for two
breaks, but might be different for a break and a make.

The two breaks in the circuit are obtained in the following manner:
The weight rests freely ori brass knife edges in a V support pivoted
at the middle. When the weight is thus supported the circuit is
complete and the current can pass through the electromagnets on
the manometers. As soon as a catch is released a spring rotates
the support from under the weiglit and the circuit is broken at the


DESCRIPTION OF MINE AND EQUIPMENT. 23

inches apart farther in. The arches were made in two halves, each half
extending from the foundation to the center of the crown, where they
were joined together by a bolt passing through a loop in the end of

——
[einfersing-anches
}‘squareivon 32'sparts
fox und pipe for
‘wiring madJights.

[Longitudinal reinforouamant
rx@ round bare apart,

Housiiation blocks ve 18 deep
neconling to kurduess of

Ditan

3" aber held by anshow toler
“in the comerete,
‘Tasaporary timbering dining Sxiving

lowed 19 seuss: —____———+J

GALLERY TUNNEL NEAR ENTRANCE
Froure 5.—Cross-sectional views of mine gallery.
each half arch. The horizontal reinforcement consists of }-inch rods

placed 12 inches apart (see fig. 5) and wired to the arch rods at the
intersections. The concrete lining was put in place over forms of col-


DESCRIPTION OF INSTRUMENTS FOR MEASUREMENT
OF VELOCITY AND PRESSURE.

In order to devise means for the prevention of coal-dust explosions.
as well as for the arrest of explosions that have started, a knowledge
of the nature of such explosions and of the accompanying phenomena
is necessary. It is essential to ascertain the physical laws governing
the propagation of the explosions and the chemical processes that
take place, as well as the means by which ignition of the dust is
brought about. A study of the propagation of a coal-dust explosion
requires the use of instruments for recording the pressures developed
at various stages of the explosion, for recording the velocity of prop-
agation of the explosion, and for taking samples of the gases pro-
duced by the explosion.

Instruments especially adapted for this purpose have been designed
in England for the experiments of the British Coal Dust Commission
at Altofts, and in France for the investigation at Liévin. Most of
the instruments used in the preliminary experiments described in
this report are the same as those used at Altofts and were fur-
nished by the English manufacturers.

As the experiments at Altofts were made in a steel gallery above
ground, recording instruments used could be mounted outside the
gallery, no special precautions being necessary for their protection.
The protection of instruments for recording the results of explosions
in an underground gallery is more difficult. In the experimental
mine of the Bureau of Mines, protection is afforded by rooms cut
in the rib at intervals along the entry and closed by steel doors (Pl.
V, A). The instruments connect with the entry through openings
in the doors. A description of these instrument stations appears
in a preceding section of this report.

PRESSURE RECORDERS.

Two types of instruments are used for the measurement of pressure,
one to obtain a continuous record of the pressure and the other to
record the maximum pressure.

56


COMMENTS ON THE DATA OBTAINED.

Although the tests were too few, and the data obtained too meagor,
to admit of final conclusions being formed concerning the phenomena
of coal-dust explosions, the results are of value in an educational way
in demonstrating to the mining public the explosibility of coal dust
when fire damp is not present, and the violence and destruction that
accompany extensive coal-dust explosions, even when fire damp was
not present. They were also useful in furnishing information to those
conducting the investigation concerning the conditions under which
coal-dust explosions may be brought about in the experimental mine,
the kind of equipment required, and especially the character of
instruments and apparatus necessary for properly recording and
studying the phenomena of such explosions.

RECORDS OF PRESSURE VELOCITIES.

In the course of the experimental tests there were obtained records
of five pressure waves in three experiments that were clearly “shock”
waves started by the igniting shot. Two of these: were registered
when coal dust was not used, so that there is no question as to the
correctness of the interpretation of their being waves started by the
shot and not by the explosion of coal dust.

The velocities recorded were: Test 8, 1,136 and 1,116 feet per
second; test 9, 1,111 and 1,099 feet per second; test 15, 1,139 feet per
second; average, 1,120 feet per second.

The ventilating current at the time of the passage of the shock
wave had in each case a velocity of about 2 feet per second in the
same direction; deducting this, the net average velocity of the shock’
wave was therefore 1,118 feet per second, as shown by the combi-
nation of circuit breakers, automatic commutator, and chronograph.

The temperature of the air in the passageway during these tests
averaged 42° F. A sound wave travels through air at this tempera-
ture at the rate of 1,096 feet per second. A “shock” or impulse
wave from the cannon, transmitted through the air, is equivalent to,
or has practically the same longitudinal velocity as, a sound wave
under the conditions through a tube or gallery. The difference, only
22 feet or 0.02 per cent, indicates the substantial accuracy of the
pressure-velocity instrument system; on the other hand, dependence

Landolt-Bérnstein, Physikalisch-chemischo Tabellen, 1905, p. —, results of Ciccone and Campanili.
49


20 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

The reinforcement consists of 4-inch, $-inch, and 1-inch round
rods of mild steel placed vertically, diagonally, and horizontally.
The vertical rods are set in drill holes in the limestone. The stresses

osnoy 22110
Josnoy auiaug

Claws

Eni —

Manometér}
station 50

a
4
ea
a i q
Esso FE De 2
2 Es

Boo

0

in
S shots at face

originating explosion

FIGURE 2.—Plan of experimental mine, also surface contours, at time of explosion of October 30, 1911,
showing path of mine ear thrown by explosion,

Bus

considered were (1) those due to forces directed outward from the
mine, and (2) a bursting pressure acting at right angles to the axis of
the entry or tunnel. The wing walls were also designed as retaining


DESCRIPTION OF MINE AND EQUIPMENT. 81

There is practically no loss of dust. The steel bins are covered in
order to lessen the danger from an explosion of dust in the house, and
to save the float dust, which, when pure, is probably very dangerous
in mines, so that its inclusion with the coarser dust is essential in
making tests of the explosibility of coal dust.

On the second floor of the house there is a mine-car track which
runs out on the level of the yard sidings. The dust bin is above the
track, so that cars can be loaded and taken into the mine with little
labor. The crushing and grinding plant will also prepare rock or
shale dust to be mixed with coal dust, or placed on shelves, or used
in other ways in the tests for preventing or checking coal-dust
explosions.

COAL-HANDLING EQUIPMENT.

When entries or rooms are being driven, the loaded coal cars are
hauled from the mine by mules or by gasoline motors. The track
has a slight down grade from the mine to passing tracks in the
vicinity of the boiler house, grinding house, and blacksmith shop,
into each of which cars may be run for the easy handling of timber
and other material. At the lower end of the yard there is a gas-
engine hoist for lowering the mine cars down an incline to the tipple
and pulling back the empty cars.

As coal is mined only in extending the headings and in preparing
for experiments, the tipple structure is simple, and there are no
screens.

WATER SUPPLY AND FIRE PROTECTION.

There is a rivulet in the ravine in front of the mine. An earth dam
has been thrown across to make a reservoir. The water is of good
quality for boiler supply. A steam pump discharges the water into
a 5,000-gallon tank on the hillside above the mine, at an elevation
that gives a pressure head suitable for fire fighting —40 pounds per
square inch at the mine hydrants.

OBSERVATORY AND CONTROL STATION.

Situated on the hillside, commanding a view of the three entrances
to the mine, is the observatory and control station (Pl. III, B). It is
built of reinforced concrete, the roof being constructed of railroad
rails covered with concrete. The front wall, the one facing the mine,
is 2 feet thick, and has small windows through which the external
evidence of the experiments can be watched in safety. The ex-
ternal recording instruments, the chronographs, time markers,
circuit-breaker recorders, and other instruments, as well as the
shot-firing connections and firing buttons, are in this building. A
detailed discussion of the instruments is given in the section of this

72322°—13-—3.


GENERAL DESCRIPTION OF EXPERIMENTS. 43

out violence. The effects on guncotton tufts suspended at intervals
along the entry indicated that the flame traveled over 159 feet from
the point of origin, or nearly double the length of the coal-dust zone.
The branch flame that extended through the open cut-through was 63
feet long, and did not extend through the barrier. The latter result,
however, was not conclusive, as the stone dust was very little dis-
placed. There were no indications of violence. For details of this
test see pages 78 to 80.

EXPLOSION TEST 4.

Test 4 followed test 3 on the same day (Jan. 31, 1912), the object
being to determine whether there was sufficient unaffected dust left
from the previous explosion to reignite and propagate the ignition.
It was noted that the bulk of the dust had not been displaced from
the shelving. No new dust was placed on shelves, but some fresh
dust was placed in front of the igniting dust, and the experiment was
made under practically the same conditions as present in test 3. The
results were practically identical, the flame probably going about
the same distance.

EXPLOSION TEST 5.

The object of test 5, made February 2, 1912, was to determine what
pressures should be placed on the circuit breaker so that the record of
the pressure wave from the dust explosion would not be influenced or
affected by the wave from a blown-out shot of 2 pounds of black
powder.

As the pressure resulting from a coal-dust explosion is at first low, it
is desirable that the circuit breakers be adjusted to operate at low
pressures. If, on the other hand, they are adjusted to release at too
low a pressure, they will be operated by the pressure wave set up by
the blown-out shot. In test 5 no coal-dust load was used, and the
entry was thoroughly wetted. In order to be assured that the result
would not be influenced by the presence of methane, the fan was shut
down for 14 hours preceding the test, and samples of air were taken.
at the face before the fan was started. The samples contained only
0.06 and 0.04 per cent of methane. The sample of mine air taken at
the face the following day, under normal conditions of ventilation,
contained only 0.02 per cent of methane. Two pressure circuit break-
ers were installed at station E 650, one being set to release with a
1-pound and the other with a 2-pound pressure. Only the one set
for a 1-pound pressure operated, and it was therefore concluded that
circuit breakers set for a 2-pound pressure would not be operated by
the pressure from a blown-out shot of the size mentioned from a
cased hole in the coal.


DESCRIPTION OF MINE AND EQUIPMENT. 21

walls for the roof shale and dirt cover over the arching of the tunnel.
Some of the reinforcement: at. one stage of construction is shown in
Plate III, A. The arrangement at the entrance provides for the
future addition of a counterweighted door, sliding vertically in
grooves, for use in special experiments requiring a perfectly quiet
atmosphere.

It was intended that a similar entrance should be placed at themouth
of the air course. Owing to the lack of funds this was not completed
for the tests of the first series, but has since been erected. The air-
course entrance was not intended to be used for explosion tests during
the first series. A reinforced-concrete portal is provided for the

i
rt (Msquare rods
i {Sto horizontal
2) H
x be found rods} SECTION B-B, 8 FEET, |
3 INSIDE PIT MOUTH ||,
HAL i
j round) onl or ical ||
snbritbata, ahi diagonal Font ‘ Zz z if
b skoda “
yor |* 3a !
71 |
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ets
SECTION THROUGH WING aie
WALL A-A EU
te
18
SSS H
pester nt Ls or x]
Anchorage holes drilled SFT SOMEIN TERT,

Fr@uRE 3.—Cross section of reinforced-conerete portal of experimental mine,

diagonal heading similar to that of the main entrance except that the
walls are not so heavy, the heading being smaller in cross section.
It was necessary to line the outer parts of the entries on account
of the poor roof; indeed this had to be supported by heavy timber
while the entries were being driven. It was manifest that timber for
lining would not be satisfactory in explosion tests, as the timber would
be likely to be blown out. As the best material for lining seemed
to be reinforced concrete, a type of lining was adopted similar to that
so extensively used in the Béthune mines, Pas de Calais district,
France, as designed by J. Lombois, principal engineer. The con-

@ Lombois, J., Revetement en béton armé des bouvettes et des bures aux mines de Béthune: Bull. Soc,
Ind. Min., ser. 4, vol. 6, 1907, pp. 195-205.


74 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

them were thrown against the inby rib, and some were scattered out
into the entry and air course. The inby rib was coated with a layer
of sand from the broken bags.

The center hole at the face was enlarged or ‘‘cratered” for several
feet. The west shot merely ‘‘cratered” the front of the hole slightly,
while the east shot cracked the coal vertically. The hole from the
center shot was partly filled with dirt and broken pieces of wood
which seemed to have been blown back into the hole by an air move-
ment rushing back toward the face to fill the vacuum following the
pressure wave of the explosion.

There had been a sandbag stopping across the air course just outby
its intersection with the gallery slant. This was thrown down and
the bags scattered along the air course to a point 55 feet outside of
the opening. After the explosion the inrushing air carried inby
some of the sandbags to the intersection with the gallery slant and
some were thrown by the blast into the gallery slant to points 15 to
54 feet from the intersection.

The concrete pillar at the intersection of the two entries was
cracked horizontally about 3} feet from the bottom and while the
upper half was raised by the pressure of the explosion, a piece of
brattice cloth and a stick were caught in the crack when the concrete
descended (Pl. VIII, A). The wooden doors in the air course
were blown open and the hinge posts moved outby 3 to 4 inches.
The lifting of the arch of the concrete section of the gallery slant caused
longitudinal cracks along the springing lines almost the entire length
of the entry. There were numerous exposures of the vertical rein-
forcement near the springing line, and in some cases the short diagonal
braces from the crossbars to the posts of the temporary timber sets
behind the concrete lining were exposed.

At G 1684 one of the vertical reinforcement rods was exposed for
34 feet and the middle portion was bent 7 inches outby the original
position. At G 164° the roof in rising pulled the reinforcing rod up
and when it settled again the rod became buckled (Pl. VIII, B);
measurements of the buckled portion indicated that the roof had
lifted 1 foot. The cover at this point was 8 feet. At G 161° the con-
crete was cracked across the arch. The roof seemed to have settled
slightly inby its original position.

COKE AND COKED DUST.

There were coke deposits on the inby corner of the entry and
second cut-through and some coked dust on the west rib opposite

@ One hundred and sixty-eight feet from outer end of iron gallery or 26 feet irom mouth of gallery slant.
® One hundred and sixty-four feet from outer end of iron gallery or 22 feet from mouth of gallery slant.
¢ One hundred and sixty-one feet from outer end of iron gallery or 19 feet from mouth of gallery slant.


36 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

tional instrument stations will be constructed, probably at intervals
of 200 feet.
MAXIMUM-PRESSURE GAGES.

In the later tests of the series the recording manometers were sup-
plemented by maximum-pressure gages.* They are similar to those
used by Taffanel at Liévin, being of the type employed in this country
and abroad in gunnery tests. The maximum-pressure gages are
placed in boxes with iron-plate fronts, into which the gages are
screwed, and are set in the side of the entry at 100-foot intervals.
The explosion pressure acts through a steel plunger upon a small
copper cylinder or column, the relative compression or shortening of
which measures the maximum pressure at that point. As the copper
cylinders or columns furnished with the pressure gages had not been
made with sufficient care, the records obtained in the first series of
tests were unreliable. It is expected that gages of better construc-
tion will be used in the future.

VELOCITY-RECORDING INSTRUMENTS.

The velocity of the flame and that of the pressure wave of the
explosions were measured by the automatic recording on the chrono-
graph of the respective times at which the flame or the pressure wave
passed each station. The stations were at 100-foot intervals. The
recording was accomplished by placing in the stations pressure circuit
breakers and flame circuit breakers. The former operate by the
action of pressure on a plunger, breaking a circuit. Two different
types of flame circuit breakers were used—the detonator type and the
tin-foil type. They are fully described in a subsequent section, en-
titled “Description of Instruments for Measurement of Velocity and
Pressure.”

The circuit breakers above described are placed in the rib in air-
tight concrete boxes with hinged steel doors (PI. VI, A). The circuit
breakers are attached to the doors, so that when the doors open they
may be readily inspected and connections made to wires leading to
the outside observation station.

ELECTRIC CABLES. ?

The cable carrying the wires to the various electrical instruments
runs through an iron pipe set in a deep groove in the coal. The
groove is faced with concrete to provide protection for the pipe and
support for the coalrib. The cable is cut at each instrument chamber,
and the wires are connected to binding posts on the switchboard at
the back of the chamber.

 Deseribed on pp. 59, 60.
} Seo also discussion under section entitled “Description of Instruments for Measurement of Velocity
and Pressure.”



DETAILS OF EXPLOSION TESTS, 69

Cracks in the gallery concrete along the springing line extended for
54 feet outby the intersection with the air course.

Coked dust.—Very little coked dust was noted. There was a deposit
on the north rib of the first cut-through near the air course on ex-
posures facing the air course. Some coked dust was deposited on
the inby side of the cap of the first timber set in the air course outby
the first cut-through.

Soot filaments.—In the main entry inby the last cut-through were
found many soot filaments hanging from the roof and ledges on the
ribs. Some of these were 2 inches in length. A sample of these
filaments was analyzed with the following result:

Moisture.

Volatile matter.
Fixed carbon

-  LbL
~ 27.15

{Volatile matter : fixed carbon :: 42.77 : 57.23.)

It is possible that the high ash content was due to impurities having
gotten into the sample when the soot filaments were scraped off
the slate roof.

NOTES.

It had been planned to cause this explosion by firing two shots,
one from the pipe embedded in the face of the entry and another
immediately afterwards from a cannon 18 feet from the face. It
was thought that the first shot would blow up a cloud of coal dust
and the second shot would ignite this cloud. However, the first
shot ignited the dust and caused the explosion. The explosion
disarranged the firing wires for the cannon and its charge was not
fired.

TEST 2.

Date.—October 30, 1911.

Purpose.—Public exhibition of the explosibility of coal dust and
a determination of the resulting pressures and velocities.

Witnesses.—Representative mining men from all parts of the
United States. Attendance, about 1,500 persons. Over 1,200 per-
sons passed through the mine and inspected the coal-dust distribution
and the position of the shot.

Point of origin of explosion—Face of main entry, E 725. (The
face had been advanced 3 feet since the first explosion test.)

Method of ignition—Four blown-out shots; three from 14-inch
pipes in the coal and one from a 14-inch pipe lying on the bottom.

Charge.—A total of 94 pounds of FFF black blasting powder in four
holes; each charge tamped with 4 inches of damp clay stemming.


48 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

Interesting, though incomplete, information as to the velocity of
the pressure wave and of the flame was obtained from the instrument
records. The pressure circuit breakers between stations E 650 and
E 350 indicated velocities of 1,139, 48, and 980 feet per second. The
first value, 1,139, probably represented the speed of the wave from
the blown-out shot, and not of the explosion itself; the second value,
48, obtained by difference between the registration of the shock
wave and the next registration by the explosion wave, must be disre-
garded; the record between stations E 450 and E 350 indicates that
the pressure wave from the explosion had fairly started. (See figs. 9
and 11.) Farther out the pressure circuit breakers failed to work.
The manometers at stations E 150 and E 50 indicated that the
pressure wave had moved between the stations at the rate of 800 feet
per second. The maximum pressures shown by the manometers
were higher than previously obtained, the manometer at station E 150
indicating 103 pounds per square inch, and at Station E 50, 61
pounds. It will be noted in figure 27 that the pressure curves are
incomplete, so that it is possible that higher pressures were attained
than shown by the marks of the recording stylus. Following the
explosion, the suction manometer at station E 50 recorded a depres-
sion lasting 3 minutes, with a minimum depression of 1.8 pounds per
square inch. (See fig. 26.)

From the instant of ignition at the face until the pressure wave
reached station E 350 the time interval was 2.367 seconds; the flame
traveled the same distance (397 feet) in 2.537 seconds. The instru-
ments indicated (if their relative lag be disregarded) that the flame at
station E 350 was only 0.17 second behind the front of the pressure
wave that acted on the pressure circuit breaker. (See fig. 9.) The
successive readings of the flame circuit breakers between stations
E 650 and E 450 were 408 feet and 1,351 feet per second; between.
stations E 450 and E 250 the tremendous velocities of 2,273 and
2,128 feet per second were indicated by the apparatus. Outby sta-
tion E 250, on account of the failure of the automatic commutator
to operate, records were not obtained. It would appear that the
explosion was slow at the start but that by the time it had reached
station E.450 it had approached a ‘‘detonating stage.”

The most striking features of this experiment were the compara-
tively slow development of the explosion, the relatively slow speed
of the pressure wave, and the rapid overtaking of the pressure wave
by the flame of the explosion.


10 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

COAL DUST.

Source —The coal dust was ground from bituminous coal from
the Pittsburgh bed at Oak mine, near Pittsburgh.

Size.—Over 98 per cent passed through a 100-mesh sieve.

Analysis —

Moisture . 194
Volatile matter. 35.11
Fixed carbon 57.73
Ash....--.-. : 5.22

100.00
Sulphur. ........ 0... eee eee eee ec eeeeeeeee tere e eee 1.25

Zone.—Main entry, 691 feet from face; first cut-through, air course
between first cut-through and gallery slant, and gallery slant, 481 feet.
Total length of coal-dust zone 1,172 feet.

Position. —E 725 to E 709 on bench below the hole containing the
igniting charge; E 712 to E 34 on temporary side shelves, and on
12 ‘‘book”’ shelves placed at intervals; first cut-through on four
transverse ‘‘book” shelves; air course and slant on temporary side
shelves.

Quantity—Six hundred and twenty-seven pounds in the main
entry (average cross section 60 feet), or 0.907 pound per linear foot,
which is equivalent to 0.242 ounce per cubic foot (242 grams per
cubic meter) ; 225 pounds in the branch from the entry to the gallery
slant (average cross section 48 feet), or 0.468 pound per linear foot,
which is equivalent to 0.156 ounce per cubic foot (156 grams per
cubic meter).

Inert zones.—No coal-dust loading in the air course inby the first
cut-through or outby the stopping at the gallery slant.

VENTILATION AND HUMIDITY READINGS.

Ventilation —The fan was furnishing to the gallery slant 10,600
cubic feet of air, and 5,000 cubic feet was passing through the last
cut-through.

Humidity—About 11.30 a. m. a drizzling rain began which con-
tinued the rest of the day, so that the air throughout the mine was
probably in a nearly saturated condition at the time of the explosion.

ATTEMPTS TO FIRE IGNITING SHOT.

After all the visitors who wished to inspect the mine had done so,
the shot-firing lines were connected to the lead wires of the electric
igniters in the charge, and after all persons had withdrawn to positions
of safety, and the prearranged warning signals given, the firing button
was pressed, closing thecircuit. Noexplosionresulted. An inspection


DETAILS OF EXPLOSION TESTS,
RECORDS.

Pressure.—Too low to be recorded by manometers
B and C. The record obtained on the suction ma-
nometer is reproduced in figure 23.

99

SUCTION, POUNDS
PER SQUARE INCH

2

Velocity.—Pressure circuit breaker at station E =
650 operated; flame circuit breakers at stations E
650, E 550, E 450, and E 350 operated. Tabulated 8
results were as follows:
Velocity of flame, test 12. is
‘Total time ‘Time | Velocity .
Station. from between between es
ignition, | stations. | stations.
7 3
‘Seconds. ‘Seconds, mone 3 8
0.5972 g
wel 1.2512 hae 8 og
| 7 6210 161 | ig
al el] mw E
2.3170 3
i Ry
: Pa
OUTSIDE MANIFESTATIONS. 5 3
The steel sheets of the explosion-door section were g Bg
thrown out of place. No flame was noted at the main ©
opening, but a cloud of smoke shot out 100 to 150 3 ig
feet. 3
INSIDE OBSERVATIONS. z is
g
Little violence was noted. No shelves were thrown 3
down. Only three bags of the stopping in the second 2 ie
cut-through were displaced. It was estimated that 4 z
to 5 inches of the stone dust remained on the shelves *
of the-barrier. to
LENGTH OF FLAME.
ig

The flame extended from E 744 to E 279, or 465
feet (fig. 24). Thelength in the air course was 85 feet.
It was noted that the flame did not extend beyond the
Taffanel barrier.

AFTERDAMP.

The mine was filled with smoke and afterdamp;
clearing it for the next explosion took 45 minutes.



102 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

Zone.—E 744 to E 34, or 710 feet.

Position.—E 742 to E 726 on bench placed just below the level of
the bore hole of the cannon; E 733 to E 34 on permanent side shelves
on both sides of the entry.

Quantity —Six hundred and sixty pounds; loaded 0.93 pound per
foot; equivalent to 0.248 ounce per cubic foot, or 248 grams per
cubic meter.

Inert zone.—No watering was done for this test, but as there was a
very large proportion of shale dust and clay in the road dust on the
air course this was probably an inert zone.

TAFFANEL BARRIER.

Location.—In the air course, extending from 5 to 85 feet outby the
third cut-through.

Number of shelves.—Thirteen.

Distance between shelves.—Six feet from center to center.

Width of shelves.—Twenty inches.

Depth of shelves.—One inch.

Depth of stone dust-—Six and one-half inches.

Analysis of stone dust—
Organic hydrogen.......0....-0000eccceceeeecceeeeeeceeeeeeeeeees 0.39
Organic carbon. :
Moisture (at 105'

Inorganic volatile matter (combined water, COz, etc.

100.00

VENTILATION AND HUMIDITY.

At station E 550, where the cross section was 64 by 9 feet, the
velocity of the air was 104 feet per minute, the quantity being 6,084
cubic feet per minute. The humidity readings were as follows:

Humidity readings, test 14

Station. Wet bulb. | Dry buib. | Humidity.
—_| j-———+|
oF, oF, Percent,
Outside. , 48 49 4
E 250. 4B rr 86
E 560. a7 48 93

INSTRUMENTS AND RECORDS.

MANOMETERS.

Location.—Manometer A (suction) at station E 50; manometer B
(pressure) at station E 50; manometer C (pressure) at station E 150.
Springs.—Manometers B and C were equipped with 200-pound

springs.


BUREAU OF MINES BULLETIN 68 PLATE IV

B. COAL BROUGHT DOWN BY SHOT

Note characteristic cleavage.



FIRST SERIES OF COAL-DUST EXPLOSION TESTS IN THE
EXPERIMENTAL MINE.

By Georce S. Rice, L. M. Jonzs, J. K. Clement, and W. L. Eey.

INTRODUCTION.

By Gzonce S. Rice.

This report has been prepared, not only for the purpose of recording
the results of the first series of coal-dust tests conducted in the experi-
mental mine of the Bureau of Mines, but also to place before the min-
ing public a description of the mine and an account of the objects
sought in its establishment.

Soon after the organization of the technologic branch of the United
States Geological Survey, J. A. Holmes, then chief of the branch,
concluded that for the solution of various problems relating to the
causes and prevention of mine explosions it would be best to carry
on large-scale tests in a mine rather than in a surface gallery.

The idea of utilizing the underground passage of a mine for making
explosion experiments did not at first meet with general approval
among investigators in this country or abroad. Many thought a
mine passage was not a proper place in which scientific tests could be
conducted, as great difficulty in controlling conditions was expected.
However, after all arguments for and against such an investigation
had been carefully considered, plans for opening an experimental
mine were definitely adopted by the Bureau of Mines in 1910, and an
allotment of funds was made to carry out the project. The first
endeavor was to find an existing mine suitable for the purpose, but
the mines offered by owners were either worked out, were wet, had
poor roofs, or presented complications of various kinds, so that it
was finally decided to open a mine if a site could be obtained having
natural conditions that would fill the various requirements.

A most desirable location was found on property of the Pittsburgh
Coal Co., near Bruceton, Pa. The president of this company, Mr.
W. K. Field, the general manager, Mr. G. W. Schluederberg, and the
chief engineer, Mr. E. J. Taylor, rendered every possible service in

7








34 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

record the position of the flame by a separate apparatus; therefore,
to obtain a comparison it is necessary that the flame records have the
same time intervals as are registered on the pressure manometer
records. The French method has the obvious advantage of the
records being made by the same instrument.

It was intended before the first series of tests was started to have
all the various kinds of instruments used in the foreign testing gal-
leries, and, if possible, to design and make new instruments better
adapted for the particular conditions at the experimental mine, but
circumstances prevented getting any but the British coal-dust instru-
ments, like those used at Altofts. The investigations at Altofts and
at Liévin were conducted in galleries above ground, so that there was
little difficulty in the attachment or placing of delicate recording
instruments, which could be set up on the exterior of the gallery and
connected through openings in the walls. In using instruments in
the experimental mine it is necessary to protect them from the action
of the pressure and the flame from an explosion by placing them in
special chambers (Pl. V, A, and fig. 7) as nearly gas-tight as possible,
lined with reinforced concrete, and located in the side of the entry.

RECORDING MANOMETERS.

For recording the pressures three B. C. D.* manometers similar
to those designed for the experiments at Altofts were purchased.
Two of these were used for high pressures and one for pressures
below atmospheric pressure. These manometers are somewhat
similar in principle to a steam-engine indicator and are described in
detail in the chapter entitled ‘‘Description of Instruments for Meas-
urement of Velocity and Pressure.” The connections from the
instruments to the main entry are made through a heavy ribbed steel-
plate casting 1} inches thick, which is designed for a pressure of 500
to 600 pounds per square inch. The casting is set in the concrete
wall of the chamber flush with the side of the entry. The instruments
are placed on a wide shelf, with sufficient space behind them to allow
manipulation. The cables carrying the wires for the electric circuits
are in a 4-inch pipe behind the concrete lining of the entry and enter
the instrument chamber under the shelving. Access to the chamber
from the entry is had through a side passage. The entrance door is
a heavy steel casting, designed to withstand a pressure of 500 to 600
pounds per square inch. The construction of a station is shown in
figure 7.

Four instrument stations of the kind described were constructed,
two in the diagonal heading and two in the main entry. These sta-
tions are at 100-foot intervals. For the next series of tests addi-

© See p. 57, footnote.


98 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

Inert zone.—The third cut-through and the air course were sprinkled ;
the floor of the main entry was also sprinkled to render the road dust
inert.

TAFFANEL BARRIER.

Location.—In the air course, from 5 to 85 feet outby the third cut-
through.

Number of shelves.—Thirteen.

Distance between shelves.—Six feet center to center.

Width of shelves.—Twenty inches.

Depth of shelves.--One inch.

Depth of stone dust—Six and one-half inches.

Area of obstruction.—-12.1 per cent.

Analysis of stone dust.—

Organic hydrogen. 0.39
Organic carbon. 7.59
Moisture (at 105° C.) 3.94
Inorganic volatile matter (combined water, CO,, etc. . BAR
Ash . 82.66

100. 00

VENTILATION AND HUMIDITY.

At the time of the explosion about 5,000 cubic feet of air was
moving through the last cut-through. A sample (No. 2252) of mine
air, taken at the face of the main entry just prior to firing the shot,
did not show any methane.

At the third cut-through the dry-bulb thermometer registered
35° F., and the wet-bulb thermometer 34° F., the humidity being
91 per cent

INSTRUMENTS AND RECORDS.

MANOMETERS,

Location.—Manometer A (suction) at station E 50; manometer B
(pressure) at station E 50; manometer C (pressure) at station E 150.

Springs.—Manometers B and C were equipped with 200-pound
springs.

PRESSURE CIRCUIT BREAKERS.

Location.—At stations E 50, E 150, E 250, E 350, E 450, E 550,
and E 650.

Adjustment.—Set to operate at a pressure of 5 pounds.

FLAME CIRCUIT BREAKERS.

Type.—Detonator type with silver-carbide stick.
Location.—At stations E 50, E 150, E 250, E 350, E 450, E 550,
and E 650.


DESCRIPTION OF MINE AND EQUIPMENT. 19

UNDERGROUND DEVELOPMENT.

Drift openings were started in December, 1910, and entries were
driven into the coal bed. Drifting proceeded intermittently up to
October, 1911, when the first series of coal-dust tests was begun.
The underground passages then consisted of two main parallel entries
a little more than 700 feet long, each 9 feet wide, with a 41-foot
pillar of coal between them. There are crosscuts or ‘‘cut-throughs’’¢
between the entries every 200 feet. A diagonal heading 198 feet
long connects the air course with a third opening (fig. 2); it enters
the air course at an angle of 55° at a point 117 feet from the mouth of
the air course. Fifty-five feet from the mouth of the air course there
is a fourth opening, an air shaft that is offset 6 feet from the entry.

This shaft is intended for ventilating purposes only, while the
mine is being developed, or as an auxiliary opening in case an experi-
mental explosion should wreck the other openings. The diagonal
heading was made in order to provide an opening for ventilation
purposes; it was turned off from the main air course, with the expec-
tation that the chief force of an explosion wave would pass directly
out of the air course.

The main entries were driven in the coal bed ‘on the faces,” that
is, at right angles to the principal vertical cleavage. These entries
are of the usual width employed in working the Pittsburgh bed, nomi-
nally 9 feet, but ranging between 9 and 9} feet. It was first intended
to place the cut-throughs 100 feet apart, but owing to the expense of
constructing tight stoppings strong enough to resist explosions, the
distance was changed to 200 feet. In driving the entries, line brat-
tices are carried from the last cut-through up to the face of each
entry. Fortunately the natural roof inby the concrete lining is
sufficiently strong so that only a few cross timbers have as yet been
necessary. Side posts have been put in, not to support the roof but
for attachment of the side shelves on which to lay coal dust. In the
first two tests these posts were exposed, and hence were blown down;
subsequently they were recessed (Pl. II, A) into the coal rib, so as
not to be exposed to the violence of the explosion. Ordinary mine
tracks of 42-inch gage are laid in each entry for handling coal cars
and for use in making tests of gasoline and electric locomotives.

REINFORCED CONCRETE LINING.

The main entry is provided with an arched portal of heavily
reinforced concrete (Pl. TI, B, and figs. 3 and 4) with retaining wall,
wing walls, and buttresses built “en masse;” the walls are carried
down to the solid formation, and the buttresses to a limestone 3}
feet below the coal.

© This term is employed in the bituminous coal mining laws of Pennsylvania of 1911.


14 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

(3) The circumstances under which the ignition or inflammation
becomes a strong explosion, productive of violence.

(4) Possibility of producing a coal-dust “explosion wave” or “de-
tonating wave” of permanent maximum velocity.

(5) The presence, origin, and character of reflex waves thrown off
frem the main explosion pressure waves and traveling back toward
the point of ignition.

(6) Chemical reactions taking place at different stages of an
explosion.

OUTLOOK FOR SOLUTION OF COAL-DUST PROBLEMS.

The solution of all the problems connected with coal-dust. explo-
sions, as outlined above, will not be simple, but with the systematic
prosecution of the investigations it is probable that the determina-
tions will be sufficiently complete to enable satisfactory planning of
adequate means of preventing explosions and the development of
valuable secondary safeguards.

Meantime testing stations in France, England, Belgium, Germany,
and Austria are prosecuting similar investigations, and through
friendly interchange of information it is expected that the advance
will be more rapid than would be made by the bureau’s investiga-
tors alone.

OUTLINE OF VARIOUS TESTS MADE IN THE EXPERIMENTAL
MINE.

In addition to the explosion experiments described in this report,
a considerable number of tests was conducted in the exterior gallery
to determine the conditions under which ignition of coal dust by an
electric arc could be obtained. Subsequently, while the mine head-
ings were being extended, tests were made to determine the relative
efficiency in blasting coal of different kinds of permissible explosives,
also of black powder, under the natural conditions offered by the
mine. With a view to determining the vitiation of mine atmosphere
by the use of these explosives, samples of their gaseous products were
obtained and analyzed. Some experiments with the treatment of
coal dust by calcium chloride for prevention of ignition were made.
An important series of tests of two types of gosoline locomotives was
conducted with a view to testing mechanical control, and to deter-
mining to what extent the exhaust vitiated the mine atmosphere
under different conditions of use and of engine adjustment. To
repeat, then, although only a small number of large coal-dust explo-
sion tests was made, the mine was constantly used for experiments.

In making explosion tests, one of the most important advantages
connected with the experimental mine as compared with a surface
gallery is the possibility of experimenting on coal-dust ignition when


CONTENTS,

Details of explosion tests—Continued.
Test 3—Continued.
Inside observations.

‘Taffanel barrier......
Instruments and record:
Outside manifestations.

Instruments and records.
Manometers.
Pressure circuit breakers.
Flame circuit breakers.
Records.

Outside manifestations.

Inside observations.

Efficiency of barrie

Taffanel barriers.
Instruments and records.
Manometers...
Pressure circuit breaker:
Flame circuit breakers.
Records. . .
Manifestations.
Length of flame
Analyses made after the explosion

Taffanel barrier...
Ventilation and humidity readings.

Flame circuit breakers.
Records.



110 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

An empty mine car that had stood on the track 33 feet in front of
the opening was blown over the dump and landed in the valley
beyond at a point 220 feet distant from its original position (Pl. V, B).

The gates at the end of the buttress wall at the main opening were
broken and all but the upper portion of the west gate was demolished.
The post from which the east gate had been hung, notwithstanding
that it was recessed at the end of the buttress wall, was torn from
position and carried 33 feet
from the opening. All of the

lights in the south and west
lm side windows of the pump house
were broken outward.

By eu

E60

INSIDE INDICATIONS OF VIO-

‘Method of placi Esso LENCE.
‘shelf (13 used) of
‘Teed sau In the conerete-lined portion
ew of the main entry the same
SYMBOLS USED effect was observed after this ex-
(seers Taffanel

plosion as had been noted after

so previous violent explosions, in

that the arch of the section

had been lifted, the consequent

exo straightening of the vertical

reinforcing rods having forced

cave eter off pieces of concrete lying

O10 e10 between these rods and the face

it of the concrete at the springing

line. With one or two excep-

2 tions the effect was less than

‘Relief door bey after the explosion of October

30, probably because the con-

crete had a much more solid

backing over the arch, where a

large quantity of cement grout-

ing had been run in from the

surface through holes. A piece

Fic. 28.—Test 15, extent of flame and conditions gf concrete 30 by 18 inches,

or test with a thickness of from 2 to 3

inches, was forced off at the springing line just over the door at E 50;

this piece of concrete was hanging from a }-inch round rod in front
of the door after the explosion.

At E 61 a j-inch square reinforcing rod was buckled by the settling
back of the arch, the extent of buckling indicating a raise of at least
3 inches.

At E77 a crack 14 inches deep had opened between the original
arch and the repair arch put inside the original one after the explosion

barrier
‘Witt, Coal dust,2 pounds per foot,
DW Flame outside of mine

‘Taffanel barrier
1Sshelves, 6’apart
T
Concrete ‘Sandbag LI
_— » sopping 5. ) stopping



88 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
TAFFANEL BARRIERS.

Location.—In the air course, extending from 5 to 85 feet outby cut-
through.

Number of shelves.—Eleven.

Distance between shelves.—About 8 feet from center to center.

Width of shelves —Twenty-four inches.

Depth of shelves—Two inches.

Depth of stone dust.—Seven and one-half to eight inches.

Obstructions.—13.81 per cent of total cross section.

Analysis of stone dust.—

Organic hydrogen. 0.39
Organic carbon. 7.59
Moisture (at 105° C. . 3.94
Inorganic volatile matter (com| 5.42
82. 66
100. 00
Humidity readings.
Station. Wet bulb. | Dry bulb.| Humidity,
°F. oF ‘Per cent.
Outside. 12 1: 63
E 250. 45 45 100
45 46 93

INSTRUMENTS AND RECORDS.
MANOMETERS.

Location.—Manometer A (suction) at station E 50; manometer B
(pressure) at station E 50; manometer C (pressure) at station E 150.
Springs.—Manometers B and C were equipped with 200-pound
springs.
PRESSURE CIRCUIT BREAKERS,
Location.—Stations E 50, E 150, E 250, E 350, E 450, E 550, E 650.
Adjustment.—Set to operate at a pressure of 2 pounds.

FLAME CIRCUIT BREAKERS.

Type.—Detonator with silver-carbide stick (p. 63).
Location.—Stations E 50, E 150, E 250, E 350, B 450, E550, E 650.

RECORDS,

Manometers.—Pressures were too small to be recorded.
Velocity—No pressure circuit breakers operated. Flame circuit
breakers at stations E 650 and E 550 operated. The flame reached


COMMENTS ON THE DATA OBTAINED. 55

planned to use ventilating currents of higher velocity and to dupli-
cate certain explosions, except in one test to have the air travel with
the explosion and in the other test against it.

HUMIDITY.

It happened that in the majority of the experiments the humidity
of the air was high. This was especially the case in the public demon-
stration on October 30, 1911 (test 2). Therefore, it would appear
from these tests that the humidity of the air itself has no appreciable
effect upon a strong explosion. In almost all the experiments the
floor was kept.moist in order to prevent the dust of the track ballast
from being brought into the air and affecting the explosion. The
coal dust in all cases was dry and had been placed only a few hours
previous to the experiment.


22 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

crete on the side walls is 7 to 9 inches thick, and thicker in places
where irregularities in the natural walls required the filling. The
arch is made 7 inches or more thick. As it was necessary to have

gi
bs :
in ie!
a Eg seyahe By oo ee
fda! ine
5 we SN ee pares _
zg gee “7 f. BE ae g
H ik a |: i d | i
| ead of
g f i 2
a3 | 3
4
z g
: 3
i 3
a i
aE 4
a
i i
a)

Lol

a

the lining strong, the concrete mixture was made relatively rich,

being 1 part Portland cement to 2 parts sand and 4 parts gravel.
The reinforcing bars of the arch are 3-inch square steel rods, placed

6 inches apart in that part of the entry close to the mouth and 32


10 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

or dynamite has been used, the concussion may be strong enough to
raise near-by coal dust into suspension and thus expose the dust to
ignition from the flame; but the blast concussion alone can probably
not raise dust sufficient for propagation of the flame under the con-
ditions present in the experimental mine for more than about 100
feet. Following the shock or shot wave are other pressure waves
which are started by the expanding gases from the burning coal
dust thrown into the air by the concussion from the shot. The
fact must be emphasized that unless the dust is raised into the air in
a cloud it can not explode. If the dust cloud is dense and other
conditions are favorable for intense combustion there is a corre-
spondingly rapid production of hot expansive gases with resultant
high pressure, causing the pressure waves and the flame to attain
high velocities.

The pressure waves started by the explosion are transmitted to the
air ahead, and doubtless travel through it at the rate of sound
waves. The body of air is forced ahead of the explosion, and as
the pressure waves travel through this, the total velocity of any
one of the almost infinite number of successive pressure waves with
reference to a fixed point is therefore greater than that of a sound
wave. When the combustion is relatively slow the advance air
waves may get considerably ahead of the combustion or exploding
zone. On the other hand, if the conditions for propagation are
favorable, the distance that the air waves are in advance will lessen
proportionately.

The existence of the advance air-pressure waves is an all-important
factor in the propagation of a dust explosion, for if there were none,
the coal dust would not be brought into suspension in the air and
thus furnish fuel for continuance of the combustion; the English
have popularly termed the advance pressure wave the ‘‘pioneering
wave”’ and the dust cloud “‘the pioneering cloud.”

There is no doubt that a dust explosion will die away, if a dustless
zone is reached, just as soon as the coal dust carried forward in sus-
pension and its unburned gases have been consumed. Similarly,
coal-dust explosions can be prevented from starting by so wetting
the dust that it can not be raised into the air by concussion. A
dustless condition would be equally good, but can hardly be attained
in the average mine.

The French (Liévin) experiments indicate that the maximum
pressure is exerted in the zone of combustion. This fact is deter-
mined from the automatic photographing of the flame itself on the
same revolving film as that on which the pressure curve is photo-
graphed. The pressure curve is obtained through the agency of a
ray of light reflected from a mirror attached to the back of a dia-


DESCRIPTION OF MINE AND EQUIPMENT. 25

of coking coal, the coal from the Connellsville district making the
standard coke of the country; in other basins or districts the bed
produces gas and steam coals. The thickness ranges from 5 to 10 feet,
but in any one basin the thickness varies little.

At the experimental mine, which is in the so-called “gas-coal”
district, the bed is 5 to 6 feet thick, averaging about 5} feet. Above
the coal there is a layer of soft shale (‘draw slate”) a few inches to
2 feet in thickness, averaging about 14 feet. This “draw slate”
falls or is pulled down with the pick as soon as the coal has been
removed. In some places it has to be brought down by light shots.
Above the “draw slate” there is a “top coal” or roof coal 1 to 2
feet thick; it in most places is shaly, and in the district in which
the experimental mine is located it is not sufficiently pure to be
regularly taken down and used for fuel purposes. This top coal,
when not broken by blasting, makes a good roof, except near the out-
crop. The main roof above the top coal consists of shales of little
strength; in some places, but not in the vicinity of the experimental
mine, the Pittsburgh bed is overlain with a strong sandstone. The
floor is clay, which is hard when first mined, but subsequently air-
slacks. At the mouth of the experimental mine the clay is 2 to 3
feet thick and is underlain with a limestone stratum.

The coal bed proper at the experimental mine is free from continuous
partings except for two thin bands of shale about 3 inches apart, a little
below the middle of the bed. The upper band is one-eighth to three-
fourths of an inch thick and the lower three-fourths to one and one-
fourth inches thick. The “faces” or “butts” of the coal (Pl. IV, A) are
strongly marked throughout the whole Pittsburgh coal bed and are of
great importance in mining. The coal itself is fairly hard, but owing
to the planes of cleavage it tends to break to cubical pieces (Pl. IV, B)
in blasting and in subsequent handling. The regular method of
mining in the Pittsburgh district consists of undercutting the coal
either by hand or with machines, generally the latter, and then
blasting down with two shots in entry work, or two to three shots
in the rooms. In general, through the gas and steam coal districts
about one-third of the coal produced is nut coal or finer, and two-
thirds is “lump.”

The average proximate analysis of coal from the Pittsburgh bed
from face-section samples gathered in the experimental mine is as
follows:

ae 27

- 36.0
. 55.0
6.3

100.0





DETAILS OF EXPLOSION TESTS. 15

the second cut-through. At E 560 there were coked-dust deposits
on the outby exposures of both the east and the west ribs, also in the
inby cracks on the entry rib near the third cut-through. At E 635
on a shelving post still standing there was a deposit of coked dust
on the inby side.

In the third cut-through the coal on each rib was blistered very
badly (Pl. X). Coked-dust deposits began to appear about 20 feet
from the entry in going toward the air course on the inby side of the
cut-through on the exposures facing the air course and increased in
amount toward the air course. Practically all coked dust on the
outby side of the cut-through was on the exposures facing the entry.

At A 654 ¢ there were heavy deposits of coked dust in the crevices
at the corner of the cut-through.

Twenty feet inby the cut-through on the west side of the air course
were deposits of coked dust on the outby exposures and coke bubbles
along the bedding planes of the coal (Pl. XI). This coking effect
has been termed ‘‘coke in situ.”

There were frequent deposits of coked dust (Pl. XII, A) on both
sides of the air course from the third cut-through to the second
cut-through, principally on the outby exposures. From the second
cut-through to the first the deposits were smaller and less frequent.

On the north rib of the blind cut-through at A 550 near the corner
of the air course the rib was considerably blistered, and particles of
coke were formed in place, grouped along the bedding planes of the
coal bed.

SOOT COATING.

In the entry inby the third cut-through, the walls, roof, and floor
were coated with soot, and threads or filaments of soot up to several
inches in length were hanging from the roof (Pl. XII, B). The un-
burned hydrocarbons were seemingly deposited from the quiet atmos-
phere after the explosion, the ventilation not being reestablished
until the following day. The analysis of the hanging filaments was
as follows:

Moisture - 225
Volatile matter. 41. 48
Fixed carbon. 49. 60
6. 67

100. 00

[Volatile matter : fixed carbon :: 45.54 : 54.46.)

The ash content was slightly higher than the ash content of the
original dust, but the percentage of volatile matter in the ratio of
volatile matter to fixed carbon increased considerably.

A point in the air course nearly opposite E 644.


INTRODUCTION. 11

phragm which is exposed to and is deflected by the pressure. The
pressure curve indicates that the greatest pressure of the explosion is
exerted in the zone of combustion. This maximum pressurewave may
be termed the ‘‘main pressure wave.” The records of the European
experiments have shown that as the main pressure wave travels
ahead it throws off reflex pressure waves that travel back toward
the origin, and that if the origin is at the closed end of the gallery,
the pressure may be raised above what it was at the time of ignition.

Following the passage of the pressure waves there is a depression
below atmospheric pressure, which is caused by the cooling of the
gaseous products of the explosion and by the ejectment of the gases
by the violence of the explosion. The depression causes a violent
movement or inrush of air from other parts of the mine, or from the
outside, to fill the partial vacuum.

The pressure waves and their movement are very complex even
in a single gallery closed at one end, but become more complicated
in a mine with two or more passageways. Taffanel, in reports? on
his third and fourth series of coal-dust experiments conducted at
Liévin in a single main passageway 300 meters (1,000 feet) long,
has contributed most important information relative to waves
developed in a gallery by simple explosions of dust and the arresting
of the explosions in various ways.

OBJECTS OF DUST-EXPLOSION INVESTIGATIONS.

A thorough knowledge of the nature of coal-dust explosions, and
of the accompanying phenomena, is necessary in order to devise
means for the prevention of such explosions, and for the arrest, or
rather, the stoppage of explosions if by mischance explosions start.
It is therefore necessary to know how coal dust ignites and the
various means by which it may be ignited, or inflamed, the chemical
processes that take place, the circumstances under which an inflam-
mation becomes a true explosion, and whether detonation some-
times takes place.

In endeavoring to discover the natural laws underlying ignitions
and explosions, the bureau considers the factors or variables men-
tioned below. Some of these are properly subjects for laboratory
investigations, and the others for investigations at the experimental
mine. The laboratory investigations of several, in particular those
relating to the relative inflammability of the different dusts, have
been pursued in the laboratories of the bureau at Pittsburgh and in
other laboratories, especially in England and France.

© Taffanel, J., Troisbme série d’essais sur les inflammations de poussitres; production des coups de
poussidres, April, 1910; Quatrieme série; theorio des explosions, August, 1911.


BUREAU OF MINES BULLETIN 56 PLATE x

A, COKED DUST, TEST 2.

B. COATING AND FILAMENTS OF SOOT, TEST 2.


80 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
OUTSIDE MANIFESTATIONS.

A cloud of dust blew out the explosion-door section first. The
doors at the top of the shaft blew open and a cloud of light-colored
dust came out. At the main entry a little dust blew out the opening.
The most noticeable feature outside the mine was the swirling up of
the snow from the main opening to the end of the dump.

INSIDE OBSERVATIONS.

Few indications of violence were noted. The first door in the air
course was blown open 2 feet. A board from the door was found in
Ay ume the air course 6 feet outby.

The second door was cracked
in the middle and the iron
straps on it were bent inby.

‘Taffanel barrier

11 shelves 2/ wide
») Sandbag LI
stopping {

Moti ot lacing qhere was more or less coal
"Taffanel barvieg ust scattered throughout the
across entey ®° air course, there being heavy
deposits of coal dust on the

SYMBOLS USED

shelves of the Taffanel barrier.

Black damp.—The doors were
closed so that the black damp
could be cleared out. Three

fons Taffane! barrier
‘@azee Coal dust
= Fame

——= Bottom wet

Esto

[3 = minutes after the doors had
FE been closed a heavy cloud of
as exo smoke started to come out and
ee ao continued for 15 minutes.
Length of flame —The length
zwo Of the flame was indicated by
guncotton tufts that had been
suspended from the roof at
es intervals of 25feet. The flame
Relief door 4 in the entry was 159 feet long,

and the branch flame in the
third cut-through and in the air
FIGURE 18—Test 3, extent of flame and conditions of course was63 feet long (fig. 18).

fest. Efficiency of barrier.—It is to
be noted that the flame did not extend through the barrier. The flame
might or might not have extended farther if the barrier had not
been there. The barrier probably did not have much of a quenching
effect as the stone dust was only slightly disturbed.


96 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
RECORDS.

The circuit breakers at E 450, E 550, and E 650 operated, the records
being as follows:

Velocity of pressure wave, test 9.

‘Total time| ‘Time be- | Velocity

Station. from igni- | tween sta- | between
tion. tions. | stations.
Feet per
‘Seconds. | Seconds. | second.
| 0.0683
0.0900 itty
+1583
0910 1,099

+2493

It was now necessary to make further tests to ascertain the mini-
mum pressure to which the circuit breakers could be adjusted and
still not be operated by the pressure from a blown-out shot similar to
the one fired in this test.

TEST 10.

Date.—February 9, 1912.

Purpose.—Determination of minimum pressure to which pressure
circuit breakers could be adjusted and still not be operated by a
blown-out shot from a cannon with the usual charge and stemming.

Point of origin of explosion.—Face of main entry, E 744.

Method of ignition —Blown-out shot from cannon.

Ignition charge—Two and three-fourths pounds of FFF black
powder tamped with 4 inches of damp clay.

Coai dust.—No coal dust used in this test.

Inert zone.—The entry was sprinkled throughout its entire length
in order that the road dust might be rendered inert.

Instruments.—Two pressure circuit breakers were installed at sta-
tion E 650. No. 6 was adjusted to operate at a pressure of 3 pounds
and No. 10 at a pressure of 4 pounds.

Results.—Both circuit breakers operated.

Length of flame.—Guncotton tufts at point E 704 were burned by
flame or flying pieces of burning powder.

TEST 11.

Date.—February 9, 1912.

Purpose.—Determination of minimum pressure to which circuit
breakers could be adjusted and still not be operated by a blown-out
shot from a cannon with the usual charge and stemming.

Point of origin of explosion.—Face of main entry, E 744.

Method of ignition —Blown-out shot from cannon.


COMMENTS ON THE DATA OBTAINED. 51

seconds from the time of ignition. When the pressure wave reached
the 300-foot point it was far behind the shock wave caused by the
blown-out shot. The pressure-velocity curve obtained from the
records of test 15 is shown in figure 9. Although the data are incom-
plete, sufficient details were obtained to make apparent the slow
development of pressure and velocity to the 300-foot point, where
the pressure wave started off at a higher rate but less than the
velocity of a sound wave. At the 600-foot point the manometers
indicated a slowing up between the stations at 600 feet (EZ 150) and
700 feet (E 50) from the origin. It is possible that the indicated
decrease in velocity is due to the lag of the manometer at the 700-foot
point. Much additional information from further experiments must
be obtained before conclusions can be drawn as to the normal pres-
sure-velocity curve resulting from uniform dust loading in a given
size and shape of passageway, and other known controlling factors.

RECORDS OF FLAME VELOCITIES.

The data of indicated flame velocities in the first series of tests-are
more satisfactory than those of the pressure velocities. There are
fewer difficulties with the flame circuit breakers than with the pres-
sure circuit breakers, since there is only one flame record to be made;
but there was difficulty with the automatic commutator and single-
point chronograph, since failure of any breaker meant loss of all
subsequent records.

Figure 10 shows the curve plotted from the flame-velocity records
from tests 6, 7, 8, 12, and 15. These curves indicate that for the
first 200 feet the velocity is relatively low, averaging less than 200
feet per second. In the case of explosions showing the least violence,
the velocities did not materially increase with distance, though in
test 8 the velocity reached 400 feet per second. This velocity was
attained about 60 feet beyond the end of the coal-dust zone; but, as
a large amount of coal dust would be carried forward by the wave
itself, there would be no lack of fuel for considerable distance.

Test 15 was most complete and satisfactory, although unfortu-
nately the velocity records were not obtained as far as the mouth of
the mine. A feature of great interest in the flame-velocity curve
(fig. 11) plotted from the record is the seeming attainment and passing
of a maximum velocity between the points 350 and 400 feet from the
origin. However, as there was only one registration beyond this
apex, it would not be safe to assume that a normal flame-velocity
curve drops after a maximum has been reached.

In figure 9 are shown the time intervals from the moment of ignition
of the blown-out shot to the instant of passing the various stations of
the flame and the pressure wave, respectively. The last two points
on the pressure curve, corresponding to time ordinates 2.48 and 2.605,


MEASUREMENT OF VELOCITY AND PRESSURE. 57
B. C. D, MANOMETER.®

The B.C. D. manometer (PI. IX, A, and fig. 12) is of the former type,
and records the movement of a strong, tempered-steel, triangular
spring (s, fig. 12) under the pressure of the explosion. The spring
is clamped at its base; the force of the explosion acts vertically
upward at its apex, which carries a fine steel point or scribing style.
In this form of spring the maximum strain is the same at all cross
sections, and the inertia is lessened, since the narrow light part of the
spring moves most and the wide heavy part least.

The pressure is transmitted by an oil cushion to a cylindrical
plunger (p, fig. 12), which can move freely in a vertical direction in
an open cylinder. The oil keeps the plunger well lubricated, reduces

SSK

Figure. 12.—Section of B. C. D. manometer.

leakage past it, and prevents the fine dust with which the com-
pressed gases are charged from cutting or clogging the rubbing sur-
faces; the oil box also acts as a dash pot, damping any rapid vibra-
tions. The plunger is hollow for the sake of lightness. It makes
contact with the spring by means of a loose connecting rod (;, fig. 12),
one end of which rests in a conical depression in the bottom of the
plunger, the other end resting in a similar depression in the lower
face of the triangular spring (s, fig. 12). A secondary weak spring
(s’) acts upward on the plunger, holding the connecting rod in place
when there is no pressure acting on the oil box. The scribing style
on the end of the triangular spring (s) presses lightly against a
smoked-paper band, which is lapped around a revolving drum.
The drum is driven at a constant speed by an electric motor. After
an experiment the smoked paper is removed and the surface fixed
by immersion in a bath of transparent varnish.

B.C. D.,” the distinguishing mark used for these instruments by the makers, refers to the British
Coal Dust Commission, for whom they were designed.


16 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

J.C. W. Frazer, chemist; J. W. Paul, mining engineer; J.J. Rutledge,
mining engineer; H. I. Smith, assistant mining engineer; Clarence Hall,
explosives engineer; and O. P. Hood, chief mechanical engineer.

The driving of the mine headings or entries, their lining with con-
crete, the outside and inside construction of the mine, and the prep-
aration of the mine for each test were under the immediate charge
of L. M. Jones, mining engineer, and H. C. Howarth, mine foreman.

The setting up of the instruments, their wiring, their operation,
and the interpretation of their records were in charge of J. K. Clement,
physicist, and W. L. Egy, assistant physicist.

The analyses of coal, coal dust, shale, and rock dust were made by
A. C. Fieldner, chemist; and the analyses of mine atmospheres and
mine gases were made by G. A. Burrell, chemist.


DETAILS OF EXPLOSION TESTS. qT

The results of the analyses show practically no change in com-
position as compared with the results of analysis of unaltered coal.
The low percentage of ash shown by the second analysis is not
significant on account of the small size of the sample.

The bright conchoidal surfaces of a blister were exposed when a
thin scale dropped from the blister. As both the scale and the
blistered coal were included in the above analyses, the results would
indicate that a change in physical appearance does not seem to be
accompanied by any great change in chemical composition.

The results of an analysis of the standard dust used in this experi-
ment were as follows:

194
35.11
87.73

5.22

100. 00

Moisture. .

{Volatile matter : fixed carbon :: 37.82 : 62.18.

A sample of coked dust from the outby exposures on the inby
corner of the last cut-through and the air course was analyzed with
results as follows:

Moisture
Volatile matter

Fixed carbon.
Ash... ...---

-» L5b

~ 22.32
42. 39
33. 78

00. 00

[Volatile matter : fixed carbon :: 34.49 : 65.51.)

This analysis shows a decrease of the percentage of volatile matter
in the ratio of volatile matter to fixed carbon, and a large increase
in the percentage of ash, probably caused by partial combustion of
the coal dust and to a mixing of the coal dust with some high-ash
material from the roof or floor.

Analysis of a sample of the road dust showed the following results:
Moisture. ....
Volatile matter
Fixed carbon.

[Volatile matter : fixed carbon :: 42.32 : 57.68.)

This analysis shows a large increase in the percentage of ash, as
might be expected, because the sample was taken from the entry
bottom where the coal dust might have become mixed with incom-
bustible material and because a large proportion of the combustible
material in the coal dust had been consumed. In regard to the
increased proportion of volatile matter to fixed carbon the possible
explanation is that the sample contained a quantity of highly volatile


‘BUREAU OF MINES BULLETIN 56 PLATE IL

B. FINISHED PORTAL,




BULLETIN 86 PLATE XI

BUREAU OF MINES

COKE BUBBLES FORMED ALONG BEDDING PLANES OF COAL TEST 2.


DESCRIPTION OF MINE AND EQUIPMENT. 27

plank) in order that it may break and thus lessen the strain on the
tube. Twenty-five feet from the outer end of the gallery there is a
branch (fig. 2) 6 feet 4 inches in diameter, set at an angle of 60°.
This branch is for connection to a fan for use in producing a venti-

Lonarropina SECTION SHOWING RELIEF VALVES
wD AIR Lock, a.
asp ar x" plate

_Center line of steel gallery _

0 Yi,

Sectiox C-D

food 6x 4”

256""tie rod

3”shelves held by
anchor bolts in
‘the concrete

yi),
et
4,

Sxcrion A-B

Arch ‘Wood 4"x 6

Front View or Arr Lock

FIGURE 6.—Sections of passage between steel gallery and diagonal entry.

lating current either at the time of an explosion or in the ordinary
mine operations.

CANNON FOR IGNITION SHOTS.

For testing explosives or for coal-dust ignition a special cannon
similar to those used at the Pittsburgh station is employed. The
cannon has a bore hole 2} inches in diameter and 18 inches deep;
it is mounted on a truck which can be wheeled to the outer end of


DETAILS OF EXPLOSION TESTS. lll

of October 30. Many of the small cracks caused by the explosion of
October 30 were enlarged by this explosion.

The track from E 150 to E 170 seemed to have been raised by the
suction following the explosion wave. The ballast was loose and
springy throughout this length.

The shelving at the end of the concrete section on the west side
of the entry was disarranged by the explosion. The first shelf at
the top was broken 2 feet outby the post; the third shelf was broken
5 feet outby the post; and the fourth and fifth shelves were broken
loose from the supporting posts at their outby end.

On the east side the third and fifth shelves were unfastened from
their supports in the concrete.

Three shelving sets on the east side of the entry extending across
the first cut-through were thrown down and moved out of place.
The pressure wave seemed to have swept around the inby corner of
the cut-through and carried the shelves that extended across the
open space against the north rib of the cut-through. When the
resulting pressure in the blind cut-through was relieved, a wave
swung the shelves of the next set across the main entry and carried
the supporting post across to the west rib.

Previous to the test a j-inch square iron clamp, the ends of which
were embedded in concrete in the rib, had held the post inby the
cut-through in the groove in the rib. When this post was carried
out of the groove the j-inch bar was broken off where it passed
around the post.

The posts and shelves at a dead end opening on the east side of the
entry at E 350 were disarranged in like manner to those at E 250.
The post on the inby corner was torn out, its clamps broken, and
the shelves and post carried across the entry and outby 15 feet.

The sandbag stopping in the second cut-through was partly blown
down, the bags of the upper 2 feet of the stopping having been car-
ried in about equal proportion toward the entry and the air course.
A cap piece, supported by braces to strengthen the sandbag stopping
on the air-course side, was thrown down.

A straw dummy that had been set up at E 650 was torn apart and
part of it thrown to the air-course end of third cut-through and
another part to E 550. “

The igniting charge at the face of the entry had cratered the hole
30 inches back from the front. The front of the hole was 4 feet wide
by 44 feet high.

Some of the temporary track at the face was torn up by the
explosion.

The “book” shelves that had been placed at intervals in the
third cut-through and the air course were torn to pieces. Only the
third, fourth, and seventh posts on the east side of the stone-dust

72322°—13-—_8


DESCRIPTION OF MINE AND EQUIPMENT.

There was no precedent to follow in developing an experimental
mine of the magnitude desired. At Segengottes, Austria, in the
Rossitz coal-mining district, there is an underground testing gallery,
the main passage of which was an abandoned drainage tunnel lined
with stone throughout. It is 293.7 meters (964 feet) long, but it is
narrow, being only 1.3 to 1.44 meters (4} to 43 feet) wide, and the
outer end terminates in a group of houses. Tests of the inflamma-
bility of coal dust are carried on in the inner portion of the gallery,
but owing to the surrounding conditions large-scale, violent tests
are not attempted. Birmingham University, England, has for the
instruction of mining students in the use of breathing apparatus and
lamps some underground passages in an old mine, but these are not
used for explosion tests. Henry Hall, an inspector of mines in Great
Britain, experimented with coal dust in 1876 in an adit that was 135
feet long; subsequently, in 1890 to 1893, he conducted series of coal-
dust explosion tests in disused shafts about 200 yards in depth.

The many surface galleries erected in the past for experimenting
with coal dust are described in Bulletin 20 of the Bureau of Mines.¢

SELECTION OF A MINE.

The requirements considered by the bureau in planning for an
experimental mine were:

(1) The mine should be in a coal bed that produced dust of inflam-
mable character and the other conditions of which favored the
possibility of dust explosions.

(2) The mine should be naturally dry and preferably self-draining
so as to allow experiments with dry coal.

(3) The main openings of the mine should be drifts, so that com-
plications from possible wreckage of a shaft would be avoided, thus
keeping down the expense and permitting a quick entrance to the
mine after explosions.

(4) The mine should be as free as possible from methane; that is,
the mine atmosphere should contain less than 0.1 per cent, in order
that experiments might be made in an atmosphere practically free
from inflammable gas.

@ The explosibility of coal dust, by G. S. Rice, with chapters by J. C. W. Frazer, Axel Larsen, Frank
‘Haas, and Carl Scholz, 1911. 204 pp. Revision of U. 8. Geological Survey Bull. 425.

17


GENERAL DESCRIPTION OF EXPERIMENTS. AT

throughout the mine it averaged about 0.93 pound per linear foot, equal
to 0.248 ounce per cubic foot (248 grams per cubic meter). No pre-
liminary watering was done.

The result was a sharp explosion, the flame issuing from the mouth
of the entry with manifestations of violence. In the air course the
explosion entered from the inner cut-through with considerable force,
dislodged most of the shelving, and blew off the rock dust. This
barrier, as in the previous tests, was located immediately outby the
inner cut-through. The striking feature was that the flame did not
pass beyond the barrier.

The motors driving the drums for the manometer failed to run, so
that maximum pressures only were recorded at stations E 150 and
E 50, the records being 14.7 pounds and 5.6 pounds per square inch,
respectively. The relatively small load of coal dust was seemingly the
cause of the pressures not being higher. Both the pressure and the
flame circuit breakers failed to operate at some of the stations and
thus prevented velocity records from being obtained. For details of
this test see pages 101 to 105.

EXPLOSION TEST 15.

As test 15, made February 24, 1912, was the last test of the series,
a public demonstration had been planned; consequently a number of
State inspectors and other mining men were present. The coal-dust
load per linear foot was double that previously used, averaging 2.13
pounds per linear foot, equal to 0.568 ounce per cubic foot (568 grams
per cubic meter). It was also more extensively distributed than in
any other experiment except test 2; it was spread throughout the
main entry and two-thirds of the way in the air course. The rock-
dust barrier shelving was changed from its position in the previous
experiments to a point in the air course about halfway out in order to
give it a more thorough test.

The result of the experiment was that the flame following the cloud
of dust shot out of the main entrance accompanied by a loud, sharp
report, and with manifestations of great violence. No flame appeared
from the air-course entrance; the rock-dust shelves were demolished;
the flame passed through the barrier, and traveled about 200 feet be-
yond, as shown by the ignition of tufts of guncotton suspended at in-
tervals along the entry. It probably ignited the coal dust in a 50-foot
zone that laid outby the barrier. In view of the great pressure exist-
ing within the air course, as demonstrated by the demolition of the
barrier, it is quite probable that the flame might have reached the out-
side but for the rock dust dislodged from the barrier. However, the
result as to the efficacy of the barrier must be considered inconclusive.
A graphic representation of the probable extent of the flame is shown
in figure 28.

72322°—13-——_4


108 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.
GUNCOTTON TUFTS.

Guncotton tufts were hung on wires from pegs in the roof at inter-
vals of 25 feet throughout the length of the main entry and the air
course.

RECORDS.

Manometers.—-Records were obtained on all three manometer
cylinders, which are reproduced in figures 26 and 27.

Pressure circuit breakers and flame circuit breakers.—All circuit
breakers operated, but on account of the failure of the automatic
commutators, records from only four stations were obtained from
the pressure circuit breakers and from five stations from the flame
circuit breakers. (See figs. 9, 10, and 11.)

Velocity of propagation of explosion, test 15.

Pressure wave. Flame,
Station. Total time| Time | Velocity | Total time! Time | Velocity
from between between from between between
ignition. stations. | stations. ignition. | stations. | stations,
Feet per Feet per
Seconds. Seconds. second, Seconds. Seconds. second.
E650... 0.0823 214
60, 0878 1,139 0.245 408
1701 2.419
2.095 foe 074 1,351
2.265 2.493
102 980 084 2,273
2.307 2.537
cece 087 2,128
ceed 2.584
2.480
2.605,
@ Due to shock from shot. > B,C, D. manometer records.

Sampling bottles—The pipe of the B. C. D. automatic gas-sampling
device at E 150, which projected from the plate to the center of the
entry, was broken off at the plate and blown to some other place not
known. An automatic gas-sampling device had been set in a recess
in the rib at E 370; when the shelves at this point were thrown down,
the pipe connection between the bottle and the valve was broken off,
and this destroyed the automatic sampling device.

OUTSIDE MANIFESTATIONS.

The first indication of the explosion was the projection of a huge
cloud of dust from the opening (Pl. I). When the advancing
front of the cloud had reached a point about 100 feet from the open-
ing a spear of flame (fig. 28) from the opening shot into the cloud and
disappeared.

There was no manifestation at the other openings except the dis-
placing of the steel sheets on the explosion-door section.


92 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

Shale dust—A sample of the ground shale and limestone on the
Taffanel-barrier shelves before the explosion was analyzed, with the
following results:

Organic hydrogen.........-..cescececeseee 0.41
i 7.48

4, 28

Inorganic volatile matter (combined water, CO;, ete.) 7.25
Ash. 80.58
100. 00

VENTILATION AND HUMIDITY READINGS.

Ventilation.—The fan stopped two minutes before the explosion,
so that the explosion probably occurred in still air.
Humidity.—

Station. Wet bulb. | Dry bulb. | Humidity.
oF. oF. | Percent.
‘Third cut-through. 365 384 33
E450... 405 2h 5
Outside. 18 2 7

INSTRUMENTS AND RECORDS.
MANOMETERS.

Location.—Manometer A (suction) at station E 50; manometer B
(pressure) at station E 50; manometer C (pressure) at station E 150.

Springs.—Manometers B and C were equipped with 200-pound
springs.

PRESSURE CIRCUIT BREAKERS.

Location.—At stations E 50, E 150, E 250, E 350, E 450, E 550,
E 650.

Adjustment.—Set to operate at a pressure of 2 pounds.

FLAME CIRCUIT BREAKERS.

Type.—Detonator type with silver-carbide stick.
Location. —At stations E 50, E 150, E 250, E 350, E 450, E 550,
E 650.

RECORDS.

Manometers.—The pressure was too low to operate manometers
B and C. The record obtained on suction manometer A is repro-
duced in figure 21.

Velocity.—Pressure circuit breakers at stations E 650, E 550, and
E 450 operated.

Flame circuit breakers from station E 650 to station E 250, in-
clusive, operated.


94 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

were large quantities of coked dust on the outby exposures of the
posts and bolt ends; at FE 640 there was coked dust on the outby
side of the posts and bolt ends; at FE 654 there was coked dust on
the outby corner and coke bubbles on the inby corner of the third
cut-through.

LENGTH OF FLAME.

The length of flame, as indicated by guncotton tufts suspended
along the entry, was 552 feet from the face to E 192 (fig. 22). The
branch flame on the air course extended for 225 feet outby the third

eut-through. About 4 to 5

fi®TM inches of stone dust remained
on the shelves of the barrier
a geo aftertheexplosion. The flame
Y; £y did not seem to be much
Method of placing $2 checked by the barrier.
Tattane! barrier a2
across entry E60
Fey SAMPLES ANALYZED.
Bal
procs Taft EA A sample of the coal dust
Witten Coal dust E450

remaining on the shelves after
the explosion was taken and
analyzed, with results as fol-

—— Bottom wet
‘Bottom and sides wet,
SE5= Bottom, sides,and roof wet

(ss lows:

iB Moisture ....... 2. 88
SF Volatile matter, 32. 43,

Exo of e
ceavt m reer Fixed carbon 51. 88
100 20 ASM eee 12.81
100. 00
Bio Sulphur... 0.20... 1.27

A comparison of the ratio

eso of fixed carbon to volatile mat-
ter (38.47 :61.53) with the
ratio of fixed carbon to volatile
matter of the original sample
FIGURE 22.—Test 8, extent of flame and conditions (38.47 : 61.53) shows that the
OF test. dust remaining on the shelves

after the explosion was practically unaffected by the explosion.
The increase in ash in the sample after the explosion was probably
due to a mixing of ash from the consumed dust or road-dust
material with the dust remaining on the shelves. Out of the 300
pounds put on the shelves for this test 87 pounds still remained
after the explosion. As the quantity remaining on the shelves after
this explosion was smaller than that remaining after the preceding



4 CONTENTS.

Details of explosion tests—Continued.
Test 11.
Test 12.

Coal dust.
Taffanel barrier.
Ventilation and humidity.
Instruments and records.
Manometers, wees
Pressure circuit breakers.
Flame circuit breakers.

Outside manifestations.
Inside observations.
Length of flame.

Taffanel barrier...
Outside manifestations.
Inside observations.
Length of flame.
Test 14.....
Coal dust.
Taffanel barrier.
Ventilation and humidity.
Instruments and records
Manometers
Pressure circuit breakers.
Flame circuit breakers.
Tin-foil strips.
Records... .
Outside manifestations.
Inside observations.
Length of flame
Coal dust and coked dust
Analysis of air sample.
Test 15.
Coal dust.
Taffanel barrier.
Ventilation and humidity readings.
Analysis of sample of air.
Instruments and records.
Manometers. .
Pressure circuit breakers.
Flame circuit breakers.
Sampling bottles...
Guncotton tuits.

Outside manifestations.
Inside indications of violence.
Coal dust and coked dust.
Effect of barrier.......
Analyses of gas samples taken after the explosion.
Publications on mine accidents and tests of explosives. ..



BUREAU OF MINES BULLETIN 58 PLATE x

BLISTERED COAL RIB, TEST 2.

Note rounded faces where the outer shel! of soot-coated coal spalled off after cooling,



32 FIRST SERIES OF COAL-DUST EXPLOSION TESTS.

report entitled ‘‘Description of Instruments for Measurement of
Velocity and Pressure.”

UNDERGROUND EQUIPMENT.

It has already been mentioned that tracks are run through the
entries to allow easy handling of materials, as well as the transporta-
tion of the coal mined at the face. The mine is now equipped with 24
coal cars and one car for concrete work. For coal cutting there is a
supply of hand augers, picks, shovels, and other tools. Recently, since
the end of the first series of tests, an air compressor has been added,
also an air ‘‘puncher” machine with which a 5-foot undercut can be
made.

A 2-inch water line is installed along the main entry, and another
line through the diagonal heading into the air course. These pipe
lines are placed in grooves behind the concrete lining, or where there
is no lining, in grooves in the coal, the grooves being faced with con-
crete. The pipes are thus protected to prevent damage during ex-
periments. There are hydrant boxes every 100 feet for attaching
hose for fire protection and for washing down or wetting the coal
dust.

COAL-DUST SHELVING.

Before making coal-dust explosion experiments it was necessary
to plan adequate arrangements for loading the mine headings with
coal dust. It is important that the test conditions can be duplicated
from time to time. In the surface galleries there is an iron, wood, or
concrete floor, which can be swept clean after an explosion test. In
the Liévin gallery, in France, the dust is spread on the floor (con-
creted at the inner end, wood covered at the outer end), and the
cleaning is accomplished by increasing the speed of the fan and then
raising the dust with a compressed-air jet from a hose, the cleaners
beginning at the inner end of the gallery and with the jets and
ventilating current sweeping the dust before them. In mine entries
or headings it is much more difficult to arrange for placing the dust,
because frequently the floor, ribs, and roof are damp. The roof and
ribs are uneven except in the concreted sections, which form a small
part of the whole mine. The floor is naturally rough on account
of the track and ballast.

In the Altofts gallery, in England, the coal dust was placed on
light temporary shelving of one-half by 5 inch boards, which rested
on brackets without fastenings. Whenever there was an explosion
the shelving was torn down and broken to pieces. This shelving,
however, was inserted along only 500 to 600 feet of gallery. In
much longer passageways, like those of the experimental mine,


DETAILS OF EXPLOSION TESTS. 103
PRESSURE CIRCUIT BREAKERS.

Location.—At stations E 50, E 150, E 250, E 350, E 450, E 550, and
E 650.
Adjustment.—Set to operate at a pressure of 5 pounds.

FLAME CIRCUIT BREAKERS.

Type.—Detonator type with silver-carbide stick.
Location.—At stations E 50, E 150, E 250, E 350, E 450, E 550, and
E 650.

‘TIN-FOIL STRIPS.

In order to determine their suitability for use in flame circuit
breakers, in this test four strips of tin foil of different thicknesses
were placed on the shelves opposite stations E 50 to E 650, inclusive.

RECORDS.

Pressures—The motors running the drums of the manometers
failed to run; therefore only the maximum pressures were recorded.
The records showed a pressure of 14.7 pounds at station E 150 and of
5.6 pounds at station E 50.

Velocity records.—The pressure circuit breakers at stations E 650,
E 350, E 150, and E 50 operated; flame circuit breakers at stations
E 650, E 450, E 350, and E 250 operated. The failure of the pressure
and flame circuit breakers at station E 550 to operate prevented the
obtaining of records of the circuit breakers at the stations outby this
point. All tin-foil strips, except the two thickest at station E 50,
were fused by the flame.

OUTSIDE MANIFESTATIONS.

A great cloud of dust swept out the main opening 13 seconds after
the igniting shot had been fired. When the cloud had seemingly
extended 50 to 75 feet from the opening, the flame shot through it,
accompanied by a sharp crack, due probably to detonation of coal
dust. The wave coming out of the gallery entry raised the steel
sheets of the explosion-door section and piled them one upon another
at the end of that section. The car dump standing at the top of the
slate pile was blown over and landed down at the dam, one footboard
having been broken. A barrel containing some ice was blown from a
point 75 feet in front of the main entry to the fence near the slate
dump. The “Danger” signboard on the air course was blown 100
feet distant. A piece of brattice cloth from the air-course curtain
75 feet inby the opening was blown outby to the air-course entrance.


18 FIRST SERIES OF COAL-DUST EXPLOSION TESTS,

soot which settled out of the smoke after the explosion, rather than
that more fixed carbon than volatile matter had been burned in the
explosion, but may be due to the water of combination of the in-
cluded shale or limestone dust.

TEST 3.

Date.—January 31, 1912.

Purpose of test—Study of the propagation of coal-dust explosions
and the effect of a Taffanel stone-dust barrier.

Special conditions.—Subsequent to October 30, 1911, permanent
shelving had been installed throughout the length of the main entry;
5 new circuit-breaker stations had been installed at points E 250,
E 350, E 450, E 550, and E 650; and a reinforced-concrete stopping
had been built in the first cut-through.

Point of origin of explosion.—Face of main entry, E 738.

Method of ignition —Blow-out shot from a 14-inch pipe in the coal.

Ignition charge—Two pounds of FFF black blasting powder,
tamped with 5 inches of damp clay stemming.

COAL DUST.

Source—The coal dust was ground from bituminous coal from
the Pittsburgh bed at Willock, Pa.
Size.—Over 95 per cent passed through a 100-mesh screen.
Analysis.—
3.13
32. 71

Moisture... .-.
Volatile matter.
Fixed carbon

Sulphur. .

Zone.—Main entry, E 738 to E 654, or 84 feet.

Position.—E 738 4 to E722 ona bench placed just below the level of
the hole containing the igniting charge; E 733 to E 654 on permanent
side shelves on both sides of the entry.

Quantity—One hundred and five pounds of coal dust: 26 pounds
on bench and remainder on side shelves, distributed 1 pound per
foot.

Inert zone-—The main entry was watered from E 650 to the opening.
The air course was also sprinkled throughout its length.

a ‘The main entry face was advanced from E 725 to E 738 in the interim between tests 2 and 3.


BUREAU OF MINES BULLETIN 56 PLATE V

A, INTERIOR OF INSTRUMENT STATION, SHOWING B. C. D. MANOMETER.

B, DEBRIS ON HILLSIDE OPPOSITE MINE ENTRANCE.