December 3, 1915.

THE COLLIERY GUARDIAN.

1145

THE GASES IN COAL.*

By N. H. Darton.

The following account is a digest of the information
collected from the reports of various investigators in
Europe and America, and constitutes an introduction to
the discussion of the conditions governing the occurrence
of inflammable gases in coal beds which forms the body
of the report.

Nature of Gases in Coal Beds.

Many analyses have been made of the gases given off
in the mine by coal and by “ blowers ” and “ feeders.”
Methane is the predominant gas in most places, but its
proportion is exceedingly variable, in general ranging
from 75 to 99 per cent, of the gases as given off. Carbon
dioxide is an almost invariable constituent, and the
proportion, although usually less than 2 per cent., may
be much greater in certain places. Nitrogen and
oxygen are also present. Carbon monoxide, hydrogen
■sulphide, and various hydrocarbon compounds are of
much less frequent occurrence.

Composition of Blower Gas.

Chamberlin compared the composition of gas extracted
from coal samples in vacuum with gas from “ feeders ”
in mines and boreholes, and found that although the
feeder gas bore a close resemblance to the gas extracted
from lumps of coal and from finely crushed coal during
the first few weeks, under reduced pressure, it was,
however, quite different from gas extracted from finely
crushed coal that had lost most of its free gas by
exposure to air for a few months. The samples he
examined were from the Monongah mine, West
Virginia.

Analyses of inflammable gas found in different coal
beds in .the North of England were made by de la Beche
and Playfair in 1846 showed the methane content to
range between 77-5 and 98-2 per cent.; nitrogen 1-3 and
21-1 per cent.; oxygen, 0-6 and 3 per cent.; carbon
dioxide, 0-3 and 2-1 per cent.; and hydrogen (in one
sample), 3 per cent.

Le Ch atelier, from an extensive experience in mines
in France and Belgium, gives 78 to 99 per cent, as the
usual proportion of methane in gas from coal, and less
than 1 per cent, as the usual proportion of carbon
dioxide.

A sample of gas taken in 1893 from a blower at the
Hebburn Colliery had the following composition :—
Methane 78*8 per cent., nitrogen 18’6, oxygen 1’7, and
carbon dioxide 0*9. The gas continued to blow for
a long time, and analyses made at intervals showed but
little variation in the percentage of methane. Gas
from a blower in the Dunraven mine, South Wales, is
reported to contain 96’7 per cent, methane, 2’8 per cent,
nitrogen, and 0’47 per cent, carbon dioxide.

The Austrian Firedamp Commission analysed many
samples of gas from coal mines in Austria, with the
following average result:—Methane 91*0 per cent.,
carbon dioxide 0’8, nitrogen 7’1, and oxygen 0’5 per
cent. A sample from a blower in lignite at Trifail con-
tained 1-4 per cent, hydrogen and 7-7 per cent, carbon
dioxide. In a mine at Ear win, a sample of gas from
one blower contained 99’10 per cent, methane. Inflam-
mable gas from a dip drift in Gluckhilf Colliery,
Waldenburg, analysed by Poleck, contained :—Methane
32’65 per cent., ethane 3’99, carbon dioxide 41’49,
carbon monoxide 1’87, and oxygen and nitrogen 20 per
cent. This is, however, a most unusual combination,
and the carbon monoxide may be the result of some
special reaction.

In 1882 to 1884, Schondorff made a series of analyses
of gases from coal for the Prussian Firedamp Com-
mission, with the following result : — Methane
4’75—90’94 per cent., ethane 0’32—37’62, hydrogen
0’09—5*84, carbon dioxide 0’10—2’56, and oxygen and
nitrogen 3’61—92’32 per cent. The large proportion of
ethane (37’62 per cent.) in a blower in the Schaumburg
mine at Obernkirchen is a notable feature. The return
air from certain levels in this mine was found to carry
0’22, 0*19, 0’35, and 0’10 per cent, of ethane, with
0’96, 1’20, 1’02, and 1’11 per cent, of methane, and the
air had a strong odour of petroleum.

In the anthracite region of Pennsylvania some of the
holes bored into the coal measures near Wilkes-Barre
and elsewhere in Luzerne County, have tapped gas in
considerable volume. One notable example is found a
few rods south-east of Luzerne, where a pipe in a 98-ft.
hole sunk 11 ft. into coaly shale has been giving off gas
for years. A sample of this gas, collected and analysed
by Chamberlin, showed :—Methane 91’31 per cent.,
olefins 0’49, carbon dioxide 1’59, carbon monoxide 0’04,
hydrogen 0’82, air 1’10, and nitrogen (excess) 4’65 per
cent. A sample of gas from a borehole in coal at the
foot of No. 11 slope in the Dorrance mine contained :—
Methane 90’65 per cent., olefins 0’09, carbon dioxide
0’05, carbon monoxide 0’00, hydrogen 0’77, air 2’73, and
nitrogen (excess) 5’71 per cent.

Gas from French mines was found by Schloesing to
contain :—Methane and other hydrocarbons 78’6—96’9
per cent., carbon dioxide 0—4’1, oxygen 0—9’5, nitrogen
2’2—39’8 per cent. The nitrogen is believed to have
been derived from outside air, from which part or all
of the oxygen had been absorbed by the coal, the pro-
portion of argon to nitrogen being nearly the same as in
air. The oxygen may also have been derived from
outside sources. The methane in some of the samples
was associated with ethane, and possibly other hydro-
carbons.

Conditions Under which Gas is Given Off by Coal.

Gas escapes from coal mostly by percolating through
the minute spaces or pores between the coal grains, and
also in part through fissures, most of which are minute.
The pressure of the gas in the coal varies, and the
permeability of the solid coal is slight, and also variable,

* From Bulletin 72 of the United States Department of
the Interior, Bureau of Mines.

two factors that greatly affect the volume of gas given
off. Where coal is shattered or pulverised by pressure
and movement, gas is freed in large volume as soon as
the enclosing solid material is penetrated. Such gas
emissions are known as outbursts. Gas accumulates in
fissures rapidly if the fissuring is open and so far-reach-
ing as to drain a large surface of coal. Very often, in
mining gaseous coal, the gas issues from the fresh
working face through many small fissures with a hissing
or whispering sound, but some of the outflows are noisy,
especially if the gas bubbles through water. Movements
of roof or floor in coal mines and shattering of coal in
ribs or pillars increase the general emission of gas.
Some of the special conditions under which gas is given
off by ” blowers,’’outbursts, and squeezes are described
in the following paragraphs.

“ Blowers ” or “ Feeders.”

The term ” blower ” or “ feeder ” is used by coal
miners to denote a flow of gas from a crevice. Usually
the flow is from an orifice, and the emission is noisy.
More blowers occur in or near the roof or floor than in
the solid coal, and some are in strata containing no coal.
Many blowers are of great volume and of long duration,
but most of the stronger ones are short lived, and nearly
all of them cease in time. A blower at Wellesmeiler,
Saarbrucken, has been blowing for more than 50 years.
The volume of gas given off by different blowers differs.
One persistent blower in the Pelham mine in 1847 dis-
charged for a short time a volume estimated at 47,000
cu. ft. a minute, and one in a mine on the Tyne w.as
reported as giving off 6,000 to 7,000 cu. ft. per minute.
A blower in the Wallsend Colliery gave off 120 cu. ft. of
gas per minute. The pressure of some blowers is as
high as 501b. per square inch.

Blowers or similar noticeable gas emissions are not
always an evidence of unusually gaseous coal, for
blowers .are found in mines where no great volume of
methane is emitted by the coal, while, on the other
■hand, some gaseous mines have no large blowers. In
a few mines in France, Belgium, and Germany blowers
of carbon dioxide have been found. Blowers undoubt-
edly have their origin in crevices in which gas
accumulates, or in fissures that lead from reservoirs in
which gas has accumulated, such as porous sandstone,
bodies of crushed coal, or a network of fissures. A
strong blower in the Garwood mine, described by
Smethurst, began in a shaft at a point more than 300 ft.
above the coal bed, and had to be piped off as sinking
progressed. It burned from the pipes for more than
nine years, and at night the light could be seen for
10 miles.

Gas Outbursts.

Sudden outbursts of methane in mines indicate some-
what the conditions under which the gas occurs in the
coal. They appear to be due to one of two causes, or
a combination of them. One cause is a run of coal,
which may be produced either by gas or roof pressure,
or both, or by mining into a body of shattered coal.
Such a run exposes a large area of fresh coal surface,
for usually, if the coal is not already much broken, it
is greatly shattered by the movement, and thus a large
volume of gas is rapidly liberated. The other cause
is the opening of a fissure filled with gas under pressure,
resulting in a sudden outburst of the gas. The ordinary
gas outburst occurs when the pressure of gas exceeds
the resistance of the coal, and this condition generally
is found w’hen workings in hard coal approach a body of
softer or more porous coal containing a large volume of
gas under high pressure.

Some very heavy gas outbursts are on record. An
outburst at the Otto Colliery, six miles west of Pottsville,
Pennsylvania, liberated a body of gas estimated at
50,000 to 200,000 cu. ft. It seemingly came from a
great run on a 35 degs. dip in the Mammoth bed, and
filled an airway for 225 ft. It was carried out by the
ventilation without ignition, except in one small area,
where some of it exploded, killing one man and burning
several. A notable outburst in the Knickerbocker mine,
near Mahonoy City, Pennsylvania, in August 1908, dis-
lodged about 150 cars of coal, and gave off a great
volume of gas, which suffocated several men. It
occurred in a stope of rather steeply dipping beds near
the crest of an anticline; the space from which the coal
nan was about 6 ft. by 8 ft. in cross section, and 66 ft.
long. An outburst in one of the mines near Connells-
ville, Pennsylvania, filled the workings with such a great
volume of gas that 100,000 cu. ft. of fresh air per minute
for three days was required to reduce the proportion of
gas in the mine air to a safe limit.

Probably some of the great coal dust explosions in
mines have been started by ignition of a gas outburst.
These outbursts occur when the mining has progressed
to the vicinity of the gas reservoir, and neither their
occurrence nor their ignition can be connected with
atmospheric or seismic influences.

At the Agrappe Colliery in Belgium, in 1879, an out-
burst occurred at a depth of 2,000 ft. About 85,000
cu. ft. of gas was released so quickly that it reversed
the air current, and came to the pit mouth, carrying
wfith it a large quantity of fine coal; 121 men were
killed, and several others were injured. In the outburst
of gas at Besseges, in Belgium, in 1890, 131 men were
killed. In these outbursts 28,000 cu. ft. of gas issued
rapidly, and the overflow continued until, in 12 hours,
180,000 cu. ft. of gas had escaped. From 1850 to 1908
there were 357 serious outbursts in Belgian mines, 32
per cent, of them being fatal, and causing the death of
447 men.

An outburst at Morrissey, British Columbia, in 1904,
emitted a volume of gas estimated at 5,000,000 cu. ft.,
and the great mass of fine coal thrown out, amounting to
about 3,500 tons, extended 450ft. from the face; 14 men
were suffocated, but all the lights went out suddenly,
and there was no explosion.

A great outburst in the Black Vein coal at the
Abercarn mine, South Wales, occurred in a gangway
driving through compact coal, when it approached a

zone of softer coal. The face blew out, and a volume
of more than 1,000,000 cu. ft. of gas was estimated to
have been given off in a short time.

Crushed Coal a Cause of Gas Outbursts.

Certain gas outbursts in mines have been found to
be closely related to zones in which there has been
extensive crushing of the coal, caused by earth move-
ments, especially lateral thrust resulting in folds,
buckles, and small faults. In such zones the coal is
traversed by numerous < crevices, which serve as a
reservoir for gas given off by the large area of surface
exposed by the crushed coal. In an Australian mine
the outbursts occurred near such cracks or zones of com-
pression, where the coal was found to be extensively
shattered. However, most gas accumulations resulting
from such conditions, are found only in deep workings,
for, if the beds are near the surface, the gas escapes
through the broken strata. In one of the numerous
outbursts in the mine at Besseges, in France, 50 tons of
coal were thrown out; and it is estimated that 28,000
cu. ft. of methane were given off in the first 2J minutes,
and 175,200 cu. ft. in 12 hours. Most of the outbursts
were in soft, coals, and in coal either normally gaseous
or showing less gas than usual, in some instances with
harder coal behind. Several occurred in mines where
there were small breaks in the coal measures, but most
of them were in solid coal. Test holes were not found
efficacious either for warning or for decreasing pressure,
and they gave a false sense of security.

Outbursts in Belgian Coal Fields.

According to Roberti-Lintermans, these sudden out-
bursts occur in only a few beds, mostly at depths of
1,200 to 2,000 ft., but a few at depths of 2,000 to 3,500 ft.
The general dip of the measures has no relation to the
accumulations of gas, as the outbursts are as numerous
in horizontal as in inclined parts of the same bed. The
gas accumulations are, however, closely connected with
local disturbances of the strata, such as sudden upturns
or faults, folds, or thinnings out of the coal bed; for of
131 outbursts studied only 22 occurred in places where
the beds were undisturbed. Most of the outbursts have
been .sudden, and only a few gave premonitory signs.
The majority occurred in places where no appreciable
volumes of gas had previously been noticed.

The great outbursts in the Agrappe mine were in
horizontal measures where no large quantities of gas
had been observed before. An outburst in October 1880
threw 1,650 bushels of coal and coal dust into the
passages. In June 1886, in the same vicinity, after four
test holes had been bored 16 ft. without showing signs
of extra gas, 13,750 bushels of coal were suddenly thrown
out, and gas filled the stope for 109 yds. In April 1885,
in a coal mine at Marcinelle-Nord, with several 23 ft.
boreholes in advance, and no signs of extra gas, 3,437
bushels of dusty coal were thrown out, and 18 men
suffocated. All the gas and coal came from a face only
6| ft. by 6| ft. At the Produits Colliery, in April 1891,
in a crosscut that had just reached coal, four advance
holes through the bed showed so little gas that shots
were fired. The shots were followed by a great out-
burst, in which the gas came to the downcast shafts.
From one bed in this mine there were 23 small outbursts,
at the rate of about two a month. In several instances
the methane emanation at the place of outburst notably
diminished or ceased for a while before the outburst.

The outbursts of greatest intensity were in crosscuts;
they became more frequent and serious as the depths
increased, none of importance occurring above a depth
of 1,000 ft. In most outbursts the gas is seemingly
stored in bodies of permeable coal enclosed in more
compact coal; barriers or dams of this character were
noted in the Agrappe mine. The high pressure of gas
in solid coal noted by various observers indicates that
this enclosing material must be almost impervious in
order to retain the gas, which is under considerable
pressure. When the outbursts take place the shattered
coal quickly gives off most of its gas. That gas in solid
coal cannot be drained by boreholes is generally believed,
for such holes do not break down enough coal to give
outlet to any great volume of gas and, therefore, relieve
the pressure only in their immediate vicinity. Gas is
given off slowly from compact coal, even when the pres-
sure is high, but, in approaching zones of shattered
coal, boreholes in advance of the face might drain some
gas. This measure was tried in some of the French
and Belgian mines, and although in several instances
the holes did not even indicate an approaching outburst,
in others they delivered a large amount of gas.

The detailed investigations of outbursts in Belgian
mines by Stassart and Lemaire verified most of the con-
clusions of previous observers, and also brought out
various additional facts of interest. They found that
the upper series of coals with the largest percentage of
volatile combustible matter were the least gaseous, ami
that beds that were very gaseous in one place wore much
less so in others, and below a certain stage the occurrence
of gas was without relation to depth. They found also
that, in some places, outbursts were much" more likely
to occur under the overturned folds and along over-
thrust faults, especially in overthrust blocks, in all of
which the coal was so shattered that gas was given off
rapidly. In general, the more gaseous coal was in
zones and masses irregularly distributed; this condition
is believed to be due largely to areal variations in the
amount of gas developed in the original vegetal deposits,
or kept in them by impervious cover.

Outbursts Due to Roof Fall or Movement of Face.

Some outbursts are due to roof falls, many of which
are caused by the pressure of the gas; in others the
falling rock may disclose a gas-filled crevice, or a large
block of coal may be detached from the face, leaving an
opening from which gas flows in large volume, either
from crevices or from a mass of- shattered coal behind.
An outburst in the Jarrow mine, in August 1830, came
from the face of a drift that was 9 ft. wide and 5 ft.
high. The whole block of coal was forced forward with