508

THE COLLIERY GUARDIAN.

March 17, 1916.

HAULINC COAL IN STREET
SUBWAYS.*

In Chicago, coal is being delivered to office buildings
within the “ loop ” by an underground system of rail-
way, devoted solely to hauling coal, refuse and mer-
chandise. The Chicago Tunnel Company transports
about 1,700 tramcars of coal a month, or about 60,000
tons a year, and 27 of the most modern and largest office
buildings have connections for thus receiving coal and for
the disposal of ashes.

The coal is received from the Chicago and Eastern
Indiana Railway at the Eighteenth Street Yards, where
it is dumped into large and submerged concrete hoppers.
Hopper bottom cars are the most desirable for such an
arrangement, but coal can be handled from “ shovel ”
and side-dump cars as well, though the latter requires
considerably more time and labour.

The hoppers being situated directly over a coal-
receiving point in the tunnel, the coal is loaded into
tunnel cars by gravity, the flow of coal being governed
by large valves, which are under the- control of the
operator. The valves and loading arrangement are
shown in fig. 1.

As the cars are loaded they are weighed either by a
representative of the coal company selling the coal, or

Fig. 1.—Loading Tunnel Cars from Bins.

by an employee of the tunnel company, and then made
up in trains of eight cars each, this being the
average number to a train. Most of the coal is hauled
after six o’clock in the evening, as the deliveries are
chiefly to large department and mercantile stores where
the tunnel connection is liable to be congested during
the day in the movement of general merchandise.

The cars are made of heavy sheet steel, with side
dumps. Each will contain about 3-J tons; but new cars
of wood are being put into service.

The unloading and storing equipment at the above
railroad connection consists of six concrete hoppers, with
a total capacity of about 900 tons. That at the Chicago
and Alton Railroad connection has only three hoppers,
one of a capacity of about 250 tons, and the other two of
about 150 tons each.

Receiving equipment at the different buildings which
get coal by the underground system varies in design.
For instance, the arrangement used by one of the large
department stores, is as follows :—The coal is dumped
into large hoppers, which have a total capacity of about
350 tons. It is taken from the hoppers by a large bucket
conveyor, which elevates it to the large coal bunkers
above the boilers. Another arrangement is that the

Fig. 2.—Side-dump Cars Discharging into
Consumers’ Hoppers.

boilers are located below the tunnel levql, and the coal
is fed directly into the bunkers from the hoppers by
gravity.

The tunnel company makes a charge of 40c. per ton for
coal handled in this manner, including everything from
taking the coal out of the railroad car to the final dump-
ing into the hoppers of the building. Considering the
congestion of Chicago’s “ loop,” the time gained, the
saving in labour, the cost of equipment, and the more
satisfactory service, this method of delivery must prove
more profitable to the retail coal companies than any
alternative method of delivery they might employ.

Though the tunnel reaches all the railroads coming
into Chicago but one, coal-handling facilities are only
provided at the two mentioned above. However, plans

* Black Diamond.

are on foot for the erection of coal-handling equipment
on at least two more railroads.

The tunnel itself lies at an average depth between 42
and 45 ft. below the kerb. It resembles a large horse-
shoe in shape, being 6 ft. in width and 7| ft. high. The
walls, roof, and bottom are of solid concrete. Drainage
is effected by 71 electric pumps distributed throughout
the system discharging into the city sewers above. There
is very little evidence of seepage water through the floors
or walls; the temperature is even—55 degs. in winter
and summer—and ventilation is by the natural draught,
set up by the frequent passage of trains. This provides
a circulation of clean, fresh air through the vertical shafts
to the surface.

On the floor of the tunnel is a railroad track of 2 ft.
gauge. Near the roof is the trolley wire for supplying
the electric current to the locomotives. There are over
60 miles of tunnel, all equipped with track and trolley.
The lighting system consists of tungsten lights.

By means of a block and crossing signal at the busiest
points, the operation of trains, is conducted with a
minimum of delay and in absolute safety.

CARBON DIOXIDE IN EXTINGUISHING
MINE FIRES *

By E. C. Evans, B.Sc., F.I.C.

The subject of mine fires is one that has always
attracted the attention of mining engineers in this and
other countries; and yet, despite the enormous mass of
data that has been collected and the researches of mining
technologists, chemists and microscopists, our know-
ledge of the phenomena of mine fires is in many respec.s
imperfect. This is especially the case—from a scientific
point of view—when the action of inert gas on mine
fires is considered. At first sight the extinction of .a
mine fire by the action of some such gas as carbon
dioxide would appear to be quite a simple and practical
operation; and i. seems only reasonable to suppose that
carbon dioxide injected into a walled-off area in a mine
would accumulate to such an extent as to produce an
atmosphere absolutely extinctive to combustion. Never-
theless, the general consensus of opinion among mining
engineers is against the adoption of carbon dioxide, and
this opinion is thoroughly justified by the number of
failures that have been recorded in oases where it has
been tried. Consideration of the theoretical aspects of
the question shows that the matter is not so simple as
it appears at first sight. Prof. Clowes (Proceedings of
the Royal Society, vol. 56) and Dr. Haldane
(Proceedings of the Fed. Inst., vol. 8) have shown that
the addition of 14 per cent, to 16 per cent, of carbon
dioxide to atmospheric air, a quantity sufficient to
reduce the oxygen content to between 17’5 and 18 per
cent., creates an atmosphere extinctive to an oil flame,
an alcohol flame and a. candle flame. To extinguish a
hydrogen flame, however, it is necessary to add 58 per
cent of CO2 to atmospheric air—involving a reduction of
oxygen to 8’8 per cent.—whilst it has been -shown by
Dr. Harger (“ Coal and the Prevention of Explosions
and Fires in Mines,” p. 27) that an acetylene flame is
not extinguished until the oxygen is reduced -to 9-5 per
cent. When the question of the oxidation of coal (apart
from combustion) is considered, the matter becomes still
more complicated. It has been shown by Messrs.
Haldane and Meachem (Transactions of the Fed. Inst.,
vol. 16, p. 457) and later by Mr. F. Winmill (Trans-
actions of the Fed. Inst., vol. 46, p. 573) that coal
continues to absorb oxygen from atmospheres containing
percentages of that gas far below the limits required for
combustion, and the probability is that -such absorption
would continue-—with consequent evolution of heat—as
long as any oxygen remained in the atmosphere sur-
rounding the coal. When to these considerations is
added the influence of temperature, the effect of the
composition of -the coal, the effects of such impurities
as moisture and sulphur in its different forms, the effect
of the size of the coal particles, etc., it is evidence that,
even from a purely laboratory point of view, the problem
is a complex one; whilst when the venue of operations
is transferred to the mine, with -its entirely new -set of
conditions, with leakages, changes of ventilation,
fluctuations of pressure and temperature, factors con-
tinually varying both in extent and in their mode of
influence, then inconsistencies and discrepancies
between theory and practice are certain to be inevitable.

Fire at Senghenydd Colliery.

The fire at the Senghenydd Colliery occurred as the
result of the disastrous explosion of October 14, 1913.
This explosion was confined to the west side of the
colliery, and as a result the timbers in the main intake
on this side were set on fire, but these were soon buried
beneath falls, and the fire continued under these.
Attempts were made to extinguish it with water, with
the aid of chemical extinguishers, and by digging it out,
but these had to be given up, and ultimately the fire zone
was sealed off by 11 bashings ” (stoppings). The
stopping in the main intake was constructed entirely of
sandbags, and was 34ft. high; the second stopping,
called the Pretoria bashing, was 35 ft. high, built of
sandbags, and faced with concrete; while the Klondyke
stopping, closing the exit of the Klondyke stables into
the main return, was built of concrete. The whole of
the length of roadway was filled up with rubbish, and
the mouth sealed up with concrete. Previous to, and dur-
ing, the erection of these stoppings, analyses of samples
of air were taken on the in-bye side of the fire, and these
gave the results recorded in Appendix A, under the dates
October 21, October 25, and November 10. It will be
noted that, with the exception of the sample of
November 10 (which contained a considerable quantity
of air, and was evidently not representative), that there

* From a paper read before the Manchester Geological
and Mining Society, on March 14.

was a considerable amount of carbon monoxide present,
showing considerable combfistion, whilst the high per-
centage of hydrogen is evidence of high temperature.
After the creation of these bashings, temperature
measurements were taken hourly at the air bridge, and
in one of several cavities near the roof of the Klondyke
bashing. The air bridge, which is frequently mentioned
in the subsequent remarks, consisted of a disused boiler
shell. Holes had been bored in this, and several
thousand bags of sand had been poured into it, whilst
water was pumped continuously into it, day and night,
in the hope that it would penetrate into the fire area. It
was in direct communication with the fire area, and
therefore analyses of samples of gas taken through holes
in the out-bye side of the boiler shell gave an excellent
indication of what was taking place in the fire area. After
the installation of the C02 plant, a water gauge was also
placed here, and the readings of this instrument gave
some most valuable results, which will be found referred
to later.

The cavities in the Klondyke return were of a some-
what extensive character, and, for a considerable period,
emitted large volumes of steam and blackdamp from the
fire. It proved a task of considerable difficulty to keep
these airtight, and ultimately it was found necessary to
arch the roadway for some considerable distance on
either side of the entrance to the Klondyke stables. The
“ breathing action ” so often mentioned in the case of
mine fires, was especially noticeable in the gases emitted
from these cavities. This phenomenon is, of course,
due purely to the chemical actions producing the
phenomenon of combustion. Thus, in the case of
methane, the following reaction occurs :—

CH4 +2 ()2 = CO2 + 2 H2O.

2 vols. + 4 vols. = 2 vols. + 4 vols.

The process of combustion causes an increase of tempera-
ture, which produces a considerable increase in the
volume of the resulting gases. A large amount of the
steam produced, however, becomes condensed, thus
causing a contraction in volume; and, in order to
equalise the -drop in pressure thus formed, air is drawn
in through the crevices in the strata surrounding the
fire area. This, in its turn, occasions a fresh outburst of
combustion, and the fire continues to provide itself, by-
means of alternate expansion and contraction, with the
air required for its combustion. This breathing action
was especially noticeable during the earlier stages of the
fire, and a thermometer inserted in one of these cavities
gave a steady rise and fall of about 6 degs. in two
minutes.

It was hoped, with the erection of the bashings, that
the fire would become gradually extinguished, but the
temperature measurements gave no indication that this
result was being achieved, and it became evident that
further measures were necessary.

To relieve, as far as possible, the pressure-of the air
against the out-bye bashing, regulators were placed in
the cross cut, and a considerable quantity was short-
circuited in this way, whilst walls were erected running
half across the roadway between the downcast and the
outbye bashing. The pressure of air, however, against
the outbye bashing was still excessive, and produced con-
siderable leakage, and therefore the ventilation was
changed to another direction, the air travelling along
the main east level, and down the No. '1 north. This
produced an immediate improvement, and the tempera-
ture of the thermometer in the air bridge dropped about
6 degs. in a few hours. This improvement, however, did
not continue. A new condition of equilibrium set in,
and both analyses and temperature measurements
showed that combustion was still proceeding. The
following two analyses made during this period give an
indication of the state of the air inside the fire area :—•

Date and description Nov. 25.

of sample.	Air bridge.
Methane 		0-58
Carbon dioxide		13-08
Carbon monoxide...	0-72
Hydrogen 		0-48
Oxygen 		6-43
Nitrogen 		78-71

Dec. 6.

Air bridge.

0-56

12-66

0-51

0-30

6-13

79-84

These analyses show -a marked improvement over the
previous ones. The oxygen had decreased and the
carbon dioxide increased, showing that leakage had con-
siderably diminished, whilst the reduction in the
percentage of carbon monoxide—as is shown later-
pointed to a decrease in the combustion. Progress,
however, was -so slow that, in order to accelerate matters,
it wa-s decided to try the effect of inert gas, and arrange-
ments were consequently made for this purpose.

Installation of Carbon Dioxide Plant at Senghenydd Colliery.

When it had been decided upon to use inert gas as
an extinctive agent, consideration had to be given to
■the method of production advisable to adopt, and a
chemical method was finally selected. It was estimated
that there was an air space of 100,000 cu. ft. inside the
various bashings, and provided that -these were reason-
ably airtight, it was -hoped, with an hourly discharge
of 400 cu. ft. of CO2, that within three or four weeks,
the percentage of CO2 in the fire area would have risen
to such an extent as to completely extinguish all com-
bustion. This expectation seemed all the more reason-
able when it w-a-s seen that the air in the fire zone (on
the inbye side of the fire) showed a percentage of oxygen
amounting only to 6-0 to 6-5 per cent. It was considered,
therefore, that a small plant capable of producing from
400 to l,000eu. f.. an hour would be quite sufficient for
■the purpose required. The particular type chosen was
the “ No. 4 CO2 generator ” made by the Riley Manu-
facturing Company Limited, of South Lambeth, for use
in mineral water factories. This plant consists
essentially of a cast iron cylinder lined with sheet -lead,
and charged with finely ground limestone or bicarbonate
of soda and a definite quantity of water and sulphuric
acid. The supply of acid is initially regulated by a cock,
but once the generator is started the flow of acid is
governed automatically by the pressure of CO2 in the