THE GREAT TUNNEL OF THE ALPS—TUNNEL VENTILATION—VENTILATION IN THE
METROPOLITAN RAILWAY.
By some authorities, the great tunnel of the Alps is called the “Mont
Cenis Tunnel.” But this appellation is a misnomer, as the tunnel is
as far as 15 miles distant from the Cenis Mountain. It is in reality
carried through the Great Vallon Mountain, the narrowest of the Alpine
range which separates France from Italy. Nevertheless, between the spot
where the tunnel enters the mountain at Modane, on the French side, and
makes its exit at Bardoneche on the Italian, there is an intervening
distance of more than 7½ miles. It is opposite to Fourneaux, a village
1½ mile from the village of Modane, that the Modane entrance of the
tunnel commences. It is 3,709 feet above the level of the sea, and it
is at an elevation of about 150 feet over the roadway of the Mont Cenis
Pass, between St. Michel and Lanslebourg. It is visible on the right
hand side as a traveller is going from France towards Italy.
The Bardoneche entrance is not visible, as it is in the midst of the
mountains, far away from any roadway, and 426 feet higher above the
level of the sea than the Modane entrance.
At Lanslebourg, the road which has, for all the distance from St.
Michel, run nearly due east, makes a sudden turn to south-west and
continues in this direction to Susa. The course of the tunnel is
south-west throughout its entire length. It is consequently parallel or
nearly parallel to the Mont Cenis Road, between Lanslebourg and Susa;
although, as just stated, they are about 15 miles apart.
The following little outline will convey to the reader an idea of the
relative positions of tunnel and railway.
[Illustration]
We have drawn a straight line between Lanslebourg and Susa, solely
for representing the general direction of the road; but in reality
the road is a cork-screw with fully as constant deviation from the
straight line as is exhibited by that useful article of domestic
economy, and perhaps we could not find a better manner of illustrating
the difference between an ordinary road on the level, and one on or
through a mountain passway. If the iron of a cork-screw went straight
from where it is fastened to the handle, to its point or extremity,
it would measure about three inches, but its convolutions extend it
to ten. It is precisely the same with the road between Lanslebourg
and Susa. If it were on the plain it would measure about seven miles;
but its convolutions, its twists and its turns, its zig-zags, and its
_lacets_ convert seven into twenty-five. The length of the tunnel when
completed will be 12,220 metres, or 7½ English miles and 242 yards. It
consequently exceeds by about 4½ miles, the next longest railway tunnel
on the continent of Europe, that of Lanerthe, on the Paris, Lyons and
Mediterranean Railway already referred to.
The Tunnel of the Alps has a double nationality, it is half, exactly
half, French, and exactly half Italian. By the convention of 1856,
between the Governments of Sardinia and France, 6,110 metres of
perforation and of lining were to be made at the expense of each
country, but the whole of the works were to be done by Italy
exclusively. They were commenced on each side of the mountain in 1857.
For the first 3½ years, that is, until the end of 1860, the process
of perforation was performed by manual labour only; in 1861 and 1862
it was partly by manual labour and partly by machinery; since 1862,
machinery has been exclusively adopted.
The following Table sets forth the progress made on each side since the
commencement of the work.
THE TUNNEL OF THE ALPS.
————————————————————————————┬—————————————————————┬———————————————————
NORTHERN ENTRANCE. │ SOUTHERN ENTRANCE.│
—————┬———————————┬——————————┼——————————┬——————————┤ GENERAL TOTAL.
Year.│ Progress. │ Total. │ Progress.│ Total. │
—————┼———————————┼——————————┼——————————┼——————————┼——————————┬————————
│ M. C .│ M. C.│ M. C. │ M. C. │ M. C. │ M. C.
│[135] [136]│ │ │ │ │
│ │ │ │ │ │
By Hand Labour. │ │ │ │ │
1857 │ 10 80 │ │ 27 28 │ │ 38 8 │
1858 │ 201 25 │ │ 257 57 │ │ 459 82 │
1859 │ 132 75 │ │ 236 35 │ │ 369 10 │
1860 │ 139 50 │ │ 203 80 │ │ 343 30 │
1861 │ 193 00 │ │ 00 00 │ │ 193 0 │
1862 │ 243 00 │ │ .... │ │ 243 0 │
├———————————┤ 921 0 ├——————————┤ 725 0 ├——————————┤1646 0
│ │ │ │ │ │
By Machinery. │ │ │ │ │
1861 │ .... │ │ 170 0 │ │ 170 0 │
1862 │ .... │ │ 380 0 │ 380 0 │ │
1863 │ 376 00 │ │ 426 0 │ │ 802 0 │
1864 │ 466 65 │ │ 621 20 │ │1087 85 │
1865 │ 458 40 │ │ 765 30 │ │1223 70 │
1866 │ 212 29 │ │ 812 70 │ │1024 99 │
1867 │ 317 98 │ │ 456 60 │ │ 774 58 │
[137]│ │ │ │ │ │
├———————————┤ 1831 32 ├——————————┤3631 80 ├——————————┤5463 12
│ ├——————————┤ ├——————————┤ ├————————
│ │ 2752 32 │ │4356 80 │ │7109 12
—————┴———————————┴——————————┴——————————┴——————————┴——————————┴————————
The rate of progress given in the foregoing Table is very different
from what was expected previous to the commencement of the works. It
was then anticipated that the tunnel would be excavated from end to end
before the close of 1864, but it was not until the 15th of October,
1866, or 9¼ years after operations had been begun, that exactly
one-half was perforated. On the 1st November, 1867, the half had been
exceeded by 1,958 metres, still leaving 4,152 metres to be excavated.
The amount of perforation accomplished on the two sides of the mountain
has always been unequal, for of the 4,152 metres yet to be excavated,
2,905, equal to about 1⅞ mile, have to be accomplished on the French
side, whilst on the Italian there are two-thirds of a mile. This will
be understood by an explanation of the strata through which the tunnel
is to be carried. Commencing at Modane, there are 2,140 metres of
schist, then 363 of quartz, followed by 2,706 of compact limestone, and
finally 901 of schist. This completes one half; the other, or Italian
half, is all schist. The only rock comparatively easy in working is the
schist, but from the commencement the schist on the French side was of
a more resisting character than that on the Italian. The miners came
upon the quartz exactly where they expected to find it, but instead of
its being a stratum 400 metres thick, as was anticipated, it turned out
to be only 363 metres; nevertheless, it required two years, less two
months, to bring it into subjection, that is, from the 15th of June,
1865, until the 20th of April, 1867,—the progress forward during all
that time, not much exceeding half a metre (about 20 inches) a-day. The
compact limestone nearest to the quartz having been partly decomposed
by the action of this latter, was very workable. Hence, during May and
part of June 1867, the advance was very considerable, but since June
the compact limestone has proved to be harder but not so difficult to
work upon as the quartz. For six weeks the engineers were hopeful that
they could go on at the rate of three metres a-day. If such progress
could have been unflinchingly maintained, the excavation on the French
side could have been accomplished by August 1870. With two metres a-day
it will require until March 1872; but if, the advance do not exceed a
metre and a-half a-day for two-thirds of the whole distance, the tunnel
cannot be perforated under six years, which brings the date to July,
1873.
But the perforation of the rock is not the only serious impediment to
progress. All things that live and breathe, miners among the number,
require air for their sustenance; and, in order to supply it in
sufficient quantities for the support of the human moles within the
interior of the tunnel, it has been necessary to resort to special
appliances for this purpose. Immense machinery, moved by water-power
of an aggregate force for each end of about 400 horses, erected at
both entrances of the tunnel, works not only the boring machines,
but, at the same time, furnishes the miners with the necessary
ventilation. The air is compressed to five atmospheres by means of
the water-power just referred to; and the double application of the
air is the ingenious contrivance of Messrs. Someilier, Grandis and
Grattoni, the distinguished Italian engineers, under whom the works
are conducted. Until recently the ventilation, although indifferent
except at the site of the boring machines, was excellent in their
vicinity; but with each metre that the works progress farther into the
mountain, the difficulties of ventilation are added to; especially so
on the French side, and for a reason that will at once, on a moment’s
explanation, be evident to the reader. When the boring machines have
made the usual holes in the rock about three feet deep, they are
filled with gunpowder, and exploded. Now, if the excavation of the
mountain had been made partly by adit and partly by shaft, as soon
as one of the latter had been made, the smoke from each explosion
beyond it would have found vent through it to the outer air, and in
a few minutes the forward face of the tunnel would be ready for the
fresh action of the boring machines. But as there is no shaft in the
Cenis Tunnel, the whole of the smoke created by each explosion has
only one means of exit—that is, through the tunnel’s mouth. Smoke, in
its escape, wants to ascend (as we know by our everyday experience),
but it cannot do so for the want of a shaft; it cannot get out even on
the level, for the gradient in the tunnel on the French side is, on an
average, 1 in 45, or 117 feet 4 inches per mile. As the perforation
had, on the 1st November last, been accomplished to the extent of 3,205
metres, the face of the tunnel was about 226 feet higher than the
entrance,—consequently, the smoke of each explosion at the present time
is not only not able to come out on the level, but it has actually to
descend the number of feet just stated before it can commingle with the
outer air; and the number of these feet of elevation wall continually
increase, until, at the end of the French perforation, there will be
429. We believe it is a matter of fact, that the ventilation is every
day becoming worse, and the means of supplying the requisite air are
becoming more difficult with each metre of advance made, and so it must
continue until the final perforation has been (for no doubt it will
be) accomplished.[138] On the Italian half, the rock is throughout,
schist, and the gradient, being only one in 2,000, or 2-8/25 per mile,
all the elements for progress will continue to be, comparatively, as
favourable as they have hitherto been; and even with a much less rapid
rate of advance than on the French side, it requires no great gift of
prophesy to “forecaste” that the boring machines from Italy will be
ready to embrace those from France long before the latter shall have
arrived at the midway point. But let it be understood that the works
from the Italian side cannot go on a yard beyond midway,—first, on
account of the gradient, which would dam up all the water percolating
into the tunnel; second, because it would be impossible to keep the
line of the tunnel, owing to the absence of all the external landmarks
required for ensuring its correct direction. The embrace we have just
referred to will take place 4,138 feet above the level of the sea,
1,645 above the level of St. Michel, 429 above the Modane entrance of
the tunnel, but only 2-8/25 above that at Bardoneche, 2,360 above the
level of Susa, about 5,360 feet _below_ the highest point of the Great
Vallon Mountain, and 2,520 feet below the summit of the Mont Cenis
Railway.
What might have proved a source of great trouble and expense—water—has
fortunately not as yet on any one occasion presented itself in a manner
to cause alarm or even uneasiness. We need not therefore refer to
this subject in any detail, but before proceeding to as important an
element as any with which the tunnel is encompassed—cost—we had better
state that the arch of the tunnel is a semicircle 25 feet 3½ inches at
its base, 26 feet 3 at its broadest part, and 24 feet 7 inches high.
(See diagram.)
Captain Tyler in his report of 1866, sets down the total cost of the
tunnel and its 34½ miles of approaches at £5,400,000, or £128,500 per
mile. Now we know that up to the present time each metre of tunnel
excavated and lined (for it is to be lined throughout from stone
quarried near to each entrance, with an occasional introduction of
brickwork) costs 7,000 francs, or £280. This would bring its total cost
exclusive of permanent way, which would be, say £30,000, to £3,421,600,
but we believe that the farther the tunnel is penetrated, the expenses
will increase rather in geometrical than arithmetical proportion,
and that the average cost of the tunnel will not be 7,000 francs or
£280 “_per metre courant_,” but 10,000 francs or £400. If this be so,
the cost of the tunnel, without permanent way, would be £5,188,000.
To this sum has to be added the cost of the 34½ miles of approaches.
The nature and the probable cost of the works can be appreciated from
the fact that they are now about to be let, and the contract time for
their completion is to be four years and a-half from the date of their
commencement. These 34½ miles of double railway cannot be estimated at
less than £60,000 a mile or £2,070,000, making the total cost of the
tunnel and of the railways which connect it with the railways of France
to the north, and with those of Italy to the south, £7,258,000, or at
the rate of £172,800 per mile. Possibly, if the construction were in
the hands of a railway company instead of those of two governments, a
saving of a million or so might be effected, but in any case the cost
would be upwards of £6,000,000, or nearly £142,850 a mile.
In connection with the subject of cost, a calculation of Captain
Tyler’s gives the following results. The difference, says the Captain,
of elevation between the outer summit of the Mont Cenis Pass and the
summit of the railway through the tunnel is 2,520 feet. The excess of
working expenses in consequence of this difference of height, estimated
on a traffic ten times as great as that which passed over the Mont
Cenis in 1865, and the cost of traction per horse power and per hour
being taken at 2¼d. (the cost on the Sœmmering and the Giovi), an
additional capital of £650,000, or £13,000 a mile, with interest taken
at 6 per cent., is represented. If then £13,000 a mile be added to
the £21,000 actual cost per mile of a permanent Alpine railway, the
total cost of a railway _on_ the mountain becomes, for the purposes of
comparison, £34,000 a mile, as against whatever may be the cost per
mile for the Tunnel Railway and its approaches. If they cost £142,850 a
mile, the comparison will be as 31 to 142; but, if, as we believe, the
cost will be £172,800, then the proportion will be at 31 to 172.
A few years ago people could think or speak of nothing else for the
Alps but tunnels; there was to be a tunnel railway through the Simplon,
one through the St. Gothard, and as immediately to the eastward of the
Great St. Gothard range, there is a rapid diminution of elevation of
the Alpine mountain, no less than three passes were named as suitable
for tunnels, the special advantage of each being that they could be
constructed by means both of shaft and of adit. These three passes
commencing near Dissentis, run from north to south, and each, as it
were, starting from one root, branches off and follows its own course
through its own system of valleys, but the three unite in a common pass
about two miles to the south of Olivione. They are called respectively
the Cristillina (the easternmost), the Greina (the centre), and the
Lukmanier (the westernmost). The length of tunnel suggested for the
Cristillina was the most modest of all, only seven miles; for the
Greina it was to be twelve and a-half miles, whilst that for the
Luckmanier was proposed to be fifteen miles, nearly but not quite
double that now constructing under the Great Vallon Mountain. But
if the tunnel of the Lukmanier was to be the longest, its advocates
were able to assert in its favour, that not only could the shafts be
numerous, but that not one of them need be at a greater depth from the
surface than two hundred yards. Well, notwithstanding these supposed
advantages, these long tunnel railways have ever since remained a dead
letter, and have long ago been consigned to rest in the wide laying
burial ground of Utopia. We shall one of these days (_probably_, in
four or five years) have _one_ tunnel through the Alps; we are not
likely in this or the succeeding generation to have a second.
At a very early period in the history of English Railways, the
ventilation of tunnels came to be considered a very important question,
and as usual on such occasions, ignorance furnished an immense number
of facts and realities which experience showed to be nothing but
fictions. It was in deference to the highly wrought popular feeling
on the subject, when every manner of evil was prognosticated for
travellers going through tunnels, that the late Mr. R. Stephenson was
induced to construct the large ventilating shafts on both the Kilsby
and the Watford tunnels of the London and North-Western Railway. There
are two shafts in each of these tunnels, the diameter of each of the
four being sixty feet. They may be said to divide the tunnels into
three distinct parts, the periods of going along each space of sixty
feet being perfectly appreciable by the traveller. The ventilation
is no doubt better in consequence of the execution of these gigantic
shafts; but experience has long since shown that shafts nine to twelve
feet in the clear, are quite sufficient for all ventilating purposes,
no matter how much the tunnel may be below the earth’s surface.
We are indebted to Mr. Charles S. Storrow, an American engineer of
reputation, for a great deal of very interesting information upon
the subject of the ventilation of tunnels, and the state of the
atmosphere in them during and subsequent to the passage of trains. Mr.
Storrow was sent to Europe in 1862, by the commissioners of the State
of Massachusetts, which had been appointed by legislative action,
in relation to the construction of the Great Hoosac tunnel already
referred to. The tunnel first visited by Mr. Storrow, in England, was
the Box Tunnel, of which in his report he furnishes a section. Its
length is 3,227 yards; its gradient throughout is 1 in 100. It has
five shafts, each being twenty-five feet in internal diameter. But
this diameter is, as just stated, now considered to be unnecessary.
The deepest shaft is 300 feet.[139] Mr. Storrow experienced no
inconvenience as regards ventilation when going through the tunnel in
passenger trains. On one occasion he proceeded through the tunnel in
a hand car—“a passenger train passed us” says Mr. Storrow, “on the
other track to that which we were on. It filled the tunnel with smoke
and produced perfect darkness, so that the other ends of the tunnel
(which had been seen most distinctly previous to the passage of the
train) could not any longer be seen, and on removing the lights we were
carrying, the person who sat at my side talking with me and touching
me, was absolutely invisible. With all this, however, there was nothing
troublesome to respiration. As we proceeded and successively passed
the large shafts, a ray of light appeared directly under them, which,
a moment afterwards was lost in intense darkness, and this continued
until we reached the other end of the tunnel, after an interval of
fifteen or twenty minutes from the passage of the express train.”
Mr. Storrow was informed that “the ventilation of the tunnel depends
a good deal on the weather. Whenever a strong clear wind blows, the
smoke disappears very readily, but in fogs it is quite troublesome to
the workmen. I could not find, however, that it seriously interfered
with their work. Indeed there never was a time when it could not be
done, if required. No artificial means had ever been used to ventilate
the tunnel, but the passage of quick trains going through it in the
ordinary course of the operations of the road, is a powerful agent
for this purpose. With the steep grade of 1 in 100, the steam, on the
descent of the tunnel, is nearly or quite shut off, and the train
passes quickly through. The first engine which passed us, moving
down the grade, produced no sensible effect upon the air, but in
ascending the tunnel there is a very great expenditure of steam;
the trains moving slowly, and heavy trains are assisted by a second
engine. All this of course vitiates the air. The quick passage of a
train always produces a current in the direction of its motion, and
if made by a train running downward, and therefore using but little
steam, its effect in clearing the tunnel is very marked. This effect
is said, however, to be rather impeded than assisted by the presence
of the shafts, and I found that the persons in charge of the tunnel,
taking this circumstance, and the water admitted into the tunnel by
the shafts, into consideration, would be pleased to have them closed
altogether, and to depend for ventilation upon a natural current from
end to end being caused by difference of temperature, or prevailing
winds, and by the artificial current produced by the passage of quick
trains.”
“Its most dangerous enemy is frost. In winter enormous icicles are
sometimes formed by the gradual accretion, and if not removed would be
very dangerous.”
Of the Sapperton tunnel on the Birmingham and Gloucester section of the
Midland railway, 1,760 yards long,[140] Mr. Storrow says, “the grade is
very steep, 1 in 70, or 75½ feet to the mile. Hence, in running up the
tunnel a great deal of power is required, and an assistant locomotive
is kept constantly in use. This, of course, creates a large additional
development of smoke and steam, so that after the passage of a single
heavy freight train up, the smoke would fill the tunnel for hours, and
be quite offensive. Formerly coke was used on English railways, but
latterly coal (which, as we know, produces a much greater volume of
smoke) is now universally used. All agree that this change has been
very injurious in tunnels. At the Sapperton tunnel the assistant engine
is usually run down the tunnel immediately after the train has passed
up, and thus assists in clearing away the smoke, but a quick passenger
train running down the steep incline at great speed is found to be far
more effectual, and is indeed the only effectual ventilation.”[141]
“The inspector of the road, who accompanied me, thought the opening in
the shaft of some use, and said the men wanted it. The superintendent
thought it of no use whatever, and that it was something of a nuisance
from the water which dripped from it. He was of opinion that after a
tunnel was constructed, it would he better to close all shafts, and to
trust to quick trains for ventilation. As the tunnel now is, the men
continue in it all day, whenever necessary, though they do not like it,
but if two freight trains should follow each other without the smoke
being cleared away, it would be very difficult for them to work, and if
four trains followed each other, it would be impossible.”
In confirmation of the view that tunnels are better for ventilation
without shafts, than with them, Mr. Storrow gives the particulars of
interesting conversations he had with Mr. Brotherhood and Mr. Brassey
upon the subject. Both say that numerous shafts are unnecessary for
ventilation. They make eddies and currents, and interfere with each
other. Mr. Brassey particularly says, that the passage of a train at
quick speed is the best ventilator.
On the whole, although opinions are divided in England, as to the use
of shafts for ventilation after a tunnel is completed, it leans rather
to the side, that unless in very long ones, shafts are of no use and
had better be closed, as they are rather an interference with the
natural current which difference of temperature, or prevailing winds,
generally occasion; they also interfere with the great ventilating
agency of quick trains. A tunnel is compared by many engineers to an
_inclined_ chimney; and, as in the upright chimney, the draft would be
impaired if there were several openings in its side, interfering with
the direct currency of air for ventilation.
The Hauenstein Tunnel (already mentioned in our list of tunnels) is
2,731 yards long; it is straight throughout, and has a uniform gradient
of 1 in 139. Three shafts were commenced in the construction of the
tunnel—two only were completed, of which one, by a fearful accident
through fire, that caused the death of between fifty and sixty persons,
became irremediably choked up. The third shaft was used until the
completion of the works, but it was closed immediately afterwards,
and has not since been opened; the tunnel, therefore, is without
ventilating shaft. We have, in the last three years, passed through
this tunnel eight or nine times, and, notwithstanding the slowness of
the pace, never experienced any inconvenience from want of effective
ventilation. Mr. Storrow, who rode on the outside platform of the
carriages (they are on the American plan), expresses the same opinion.
The conductors of both the trains informed him that there is usually
a current of air through the tunnels, and that the smoke disappeared
in from fifteen to twenty minutes. Both complained of its being very
wet from the dripping of water—a fact that we can fully confirm from
personal experience.
Even with goods trains, drawn by two heavy locomotives, which burned
coals, although the tunnel was filled with smoke, Mr. Storrow did not
find respiration so difficult as what he had often experienced when
sitting in a room with a smoky chimney; and he remarked on several
subsequent trips the same day, how quickly the tunnel became free of
smoke.
The greatest danger to travelling in the Hauenstein, is the falling
down, either of portions of the rock, through which the tunnel is
pierced, or the giving way of portions of its lining, owing to the
water, which is constantly falling, forming into ice. To exclude the
cold, as far as possible, a wooden screen, during winter, covers the
upper part of the arch at each entrance, descending as far as possible,
but allowing sufficient room for the funnel of the locomotive; there
are also canvas curtains which may be drawn across the entrance at
pleasure, and they are invariably so drawn in winter, except at the
very moment of the passage of trains.
The chief engineer of the line is doubtful as to whether there ought
not to be a shaft. At times the current of cold air through the tunnel
is so strong, that it would be an inconvenience to the trains if not
checked by the curtains. They also have the effect of keeping up a
temperature in the tunnel sufficient to prevent the water that drips on
to the rails becoming frozen in winter. Great trouble and inconvenience
were experienced from this cause in the first instance. The freezing of
water, lodged on the rails, has scarcely ever happened during the last
few years.
The time that a train will take to pass through the tunnel of the Alps
must now be considered. If it had been constructed throughout on the
level, or with every favourable gradients, and that a train would be
permitted to run throughout at express speed, it might be conveyed from
entrance to exit in about twelve minutes. This gives a speed of say
thirty-eight miles an hour. But with a gradient, the average of which
is 1 in 45, anything approaching this rate of speed would be simply
impossible.
Length, however, is not the only element that has to be taken into
account.
M. Auguste Perdonnet, in his “_Traité Elémentaire des Chemins de
Fer_” (Paris 1858-60), says with great truth: “Les fortes pentes sont
plus nuisibles dans les souterrains que dans toute autre partie, d’un
chemin de fer. L’humidité empechant la boue, qui impregne les rails,
de secher, l’ascension de fortes rampes y devient tres penible. Il
faut, donc, s’appliquer a les eviter plus encore dans les tunnels qu’a
ciel ouvert.” No matter how stoutly the tunnel of the Alps may be
lined, and no matter how impenetrably the tunnel may act as a barrier
against infiltration of water, it never can be free from moisture;
not the moisture of a downfall of rain, which washes the rails and
“makes things pleasant,” but it will be one in which will be conbined,
unchemically and therefore loosely, the steam of the engines condensed
into water, minute particles of grease, and smoke; all three will,
_inter alios locos_, find a resting place upon the rails, and they
will thus create on them a thick, clammy, _pasty_ moisture, which will
sensibly diminish the engine’s adhesion, and act as a most serious
impediment to its progress. It will therefore be impossible with the
foregoing elements, and with a gradient of 1 in 45, to calculate on a
higher rate of speed from the Modane entrance to the centre than ten
miles an hour, or six minutes to the mile—twenty-two minutes; and our
belief is that to maintain even this rate of speed it will be necessary
to have a fiercely burning fire in the fire-box and tubes, together
with a plentiful fall of sand from the sand boxes on to the rails. As
soon as the train has arrived at the centre, which is also the summit
of the tunnel, the engine will get relieved, and with the gradient
almost level the second half of the tunnel can, as a simple question
of speed, be run at the highest possible rate. But although it may be
safe, it certainly will not be expedient to do so. At twenty-four miles
an hour the time required would be nine minutes; total, with twenty-two
minutes for the ascent, thirty-one minutes. As regards the journey
from Italy to France, Can a higher rate of speed be permitted for the
descent of the 429 feet in 3¾ miles than was allowed for the ascent?
There appears to us to be but one answer—Certainly not. As regards
danger, we believe that with efficient and powerful engines and proper
brakes, in the hands of steady and competent men, the transit will
not be attended with a particle of danger; but the question arises,
Will travellers generally be of this opinion? Many of both sexes will
undoubtedly consider that they are as safe in the tunnel as during any
other part of their journey; but it is to be feared that the majority
of persons who go through it will not only have vividly present in
their minds a sense of actual danger from material causes, but also a
belief that if they escape any damage from these causes, suffocation
must be a natural result of going through seven and a-half miles of
foul, fetid, and polluted atmosphere, in a long hole never less than
three thousand, and for a tolerable distance five thousand six hundred
feet, below the upper and outer surface of the mountain. Death, if
it do occur, will be caused, not by actual suffocation, but from
some action upon the nervous system, that will produce all the fatal
symptoms of suffocation.
We have had no less than three very recent illustrations of death from
such a cause, no later in fact than in August 1867; for during that
month three inquests were held on three persons who had been taken out
in a dying state from the London Metropolitan Railway. In each case
the suspension of animation took place between Lisson Grove and King’s
Cross Stations, yet the distance (all in tunnel) between them only
slightly exceeds two miles, and there are abundant means of ventilation
at the three intermediate points, Baker Street, Portland Road, and
Gower Street Stations. The verdict in the first case was “accidental
death from natural causes, accelerated by the suffocating atmosphere
of the Underground Railway.” “Death from effusion of serum on the
brain” was the verdict in the second case—in other words, apoplexy;
but as the medical gentleman who made the _post-mortem_ examination,
could not state at the inquest that the atmosphere of the railway had
accelerated death, no reference to it was made in the wording of the
verdict.
The third case, happening almost immediately afterwards, excited a good
deal of alarm in the public mind; and the alarm was not lessened in
consequence of the publication of several sensational articles in two
or three London newspapers. Therefore, at the opening of the inquest
held upon Elizabeth Stainsley, on the 28th of August, Mr. Myles Fenton,
the General Manager of the company, requested an adjournment until time
had been afforded to obtain analyses of the atmosphere of the tunnels.
Professor Julian Rodgers, of the London Medical School, was engaged by
the Coroner; Drs. Bachhoffner, Letheby and Whitmore by the company.
At the adjourned inquest, held on the 30th of October, Professor
Rodgers submitted his report, in which he stated that he had analysed
and tested the air contained in the tunnels of the railway between
Bishop’s Road and King’s Cross Stations, and he had made comparative
experiments in other tunnels. “The atmosphere in a pure condition,”
continued Professor Rodgers, “consisted of a volume of 79·19 measures
of nitrogen, and 20·81 of oxygen; and every 10,000 measures of air
contained from 3·7 to 6·2 measures of carbonic acid. On the 4th of
September he found that, in 17 cubic inches of air taken from each of
the tunnels between the hours of 3 and 5 p.m., tested for carbonic
acid, with the exception of the air from the Gower Street and King’s
Cross tunnel (which contained a more notable quantity), only a slight
trace of the acid was indicated. On the 10th of September, between 10
and 11 p.m., he determined the quantity of carbonic and sulphurous
acids contained in 17 cubic inches; and during his transit backwards
and forwards from King’s Cross to Bishop’s Road he found 13 measures
of carbonic acid in 10,000 of air, and one measure of sulphurous acid
in 40,789. Carbonic acid was evident in 17 cubic inches of the air
taken from the Gower Street and King’s Cross tunnel. On October 2, in
the same tunnel, he found 18·7 measures of carbonic in 10,000, and one
measure of sulphurous acid in 23,913. On October 28, between 8 and
9 p.m., he found traces of carbonic evident, in 17 cubic inches in
all the tunnels. On the 4th of September he found that the following
were the per centages of oxygen in the tunnels:—Bishop’s Road, 20·48;
Edgware Road, 20·60; Baker Street, 20·30; Portland Road, 20·10; Gower
Street, 18·7. In the Blackheath tunnel, on September 28, it was 20·0.
The air of Pimlico on September 21 contained 20·9. On October 24 the
per centage was as follows:—Box Tunnel, 20·3; Birkenhead Tunnel, 20·1;
Wolverhampton Tunnel, 20·5; at Wellington Barracks, 22·42, at 2 feet 6
inches from the floor.”
Replying to the Coroner, Professor Rodgers said he did not think the
deficiency of oxygen would act injuriously upon a delicate person
passing through the tunnels; and he considered that the amount of
carbonic and sulphurous gases in the tunnels could not have been
injurious to the woman. There was not a sufficient accumulation of
these gases to be of injury to the public health. The woman had eaten
heartily, was laced tightly, and had a diseased heart; he, therefore,
did not think the deficiency of oxygen could have hastened her death.
The joint report of Drs. Bachhoffner, Letheby, and Whitmore was then
read and put in evidence. It stated that the analysers collected
samples of the air on three separate occasions:—First, immediately
after the trains had ceased running at night; second, just before
they commenced running in the morning; and third, in the afternoon,
between four and five o’clock, a period of the day when there was
generally the largest amount of traffic. The samples, twenty-eight in
number, were analysed for sulphurous acid, carbonic acid, carbonic
oxide, coal gas, and oxygen. The presence of sulphurous acid having
been sought by the most delicate chemical test—namely, its action upon
iodic acid and starch, which was capable of showing the presence of
one part by volume of sulphurous acid in 100,000 parts of air, but by
such test the presence of that acid could not be detected; and from
this the analysers concluded that its volume was less than the above
in the tunnels. The mean proportion of carbonic acid was about 6 in
each volume of 10,000. The amounts of coal-gas and of carbonic oxide
were so small as to be barely discoverable. The amount of oxygen in
the tunnels and stations was not in any case deficient. These results
proved that in no instance was the air found to be vitiated to any
material extent, although the air taken in the afternoon was less pure
than that taken at night. The presence of sulphurous acid gas in the
tunnels and stations, which at times was appreciable to both taste and
smell, must not be taken as an indication that this gas existed in
dangerous quantities, for as little as one part of this gas in 100,000
parts of atmospheric air was strongly perceptible both to taste and
smell. The partial combustion of the wood forming the breaks, when
acting upon the tires of the wheels, also produces a pungent smell. The
analysers were of opinion that, having regard to the cubical volume of
the trains, the short time occupied by them in passing through the
tunnels and stations, the large volume of air they displaced, and the
increased impetus given to the horizontal movements of the air by the
rapidity of their transit, the vitiation of the atmosphere could not
be of a serious character, and this accorded with the results of their
analysis. The tunnels were dry and free from infiltration of liquid
or other matters prejudicial to health. The general health of the
_employés_ of the company was such as to afford unquestionable proof
of the sanitary condition of the air in the tunnels. The report ends
thus:—“From the foregoing facts, we are enabled confidently to state
that the atmosphere of the Metropolitan Railway is not unwholesome or
injurious to health.”
Mr. Fenton, general manager, and Mr. Driscoll, an inspector of
the company, having been examined as to the improvements made in
the ventilation of the tunnels, and the absence of complaint from
_employés_ of the company, or from passengers with respect to the
atmosphere, the jury, almost without hesitation, returned a verdict of
“Death from natural causes.”
The singular fact was elicited at the inquest that the peculiarly
“pungent smell” of the tunnel is due rather to the friction of the
brakes, than to any other cause. The partial combustion of the wood
produces a pyroligneous carbo-hydrogen, as Dr. Letheby styled it,
together with a small amount of sulphurous acid gas. These the nose
and lungs will detect sooner than the most delicate chemical tests,
and they are the real producers of the coughing and unpleasant feeling
experienced by some passengers. Such vapours, however, only affect
delicate people. This will account for the fact that people, travelling
through ordinary tunnels, are free from irritation and coughing. The
Metropolitan Railway is the only tunnel in which, owing to stoppages
at intermediate stations, it is necessary to put the brakes on.
The efforts made by the company to ensure the best ventilation and
purest atmosphere possible, are unremitting. Before the opening of the
line an extended series of experiments was made with various specimens
of coke supplied by all the leading coke manufacturers in the kingdom.
That which best bore the crucial tests, to which the specimens were
submitted, is the coke supplied by Messrs. Straker and Lowe from
their Brancepeth Collieries near Durham. Coke for locomotives, and
other purposes, is usually burned seventy-two hours. When coke of a
very superior quality is required (so that all sulphurous and noxious
vapours may, as far as possible, be consumed) it is burned ninety-six
hours, but all coke used on the Metropolitan Railway is burned
twenty-four hours more—that is 120 hours. Special ovens have been built
for burning it, and when the process of combustion is completed, the
coke is, what is well known in railway locomotive phraseology, “hand
picked.” Thus, only the bright coke of each burning is allowed to be
sent to London; any outside or dirty coke, however good it may be in
reality, being kept back. It is, therefore, impossible to procure,
in the whole range of fuel, any more free from ingredients likely to
produce unpleasant smell, or to affect respiration.
A few words must be said with respect to the peculiar construction
of the engines. In the first place the parts are so arranged that
no steam whatever escapes into the tunnel. This is accomplished by
having a large tank on each side of the engine. These tanks together
contain about 1,000 gallons of water. The exhaust steam is turned into
them, instead of through the funnel in the ordinary way. The second
peculiarity of the engines is that they are constructed with large
heating surface. The steam is raised to a pressure of about 130 lbs.
at starting, and by the time the journey through each tunnel, between
station and station, is performed, it has been reduced to about 80. The
damper is kept on during the entire journey. It will thus be seen that
the combustion of fuel in each tunnel must be very small indeed, the
fire being simply kept in, without any draft through the fire box.
Recently, the directors of the company, with the view to satisfying
public feeling in every possible way, forwarded to the Vestries of
St. Marylebone and St. Pancras, applications for permission to effect
openings to the external air at several points of the Marylebone and
Euston Roads—where important roads cross this thoroughfare—by means of
handsome and ornamental hollow columns, which should be connected with
the railway, and would support street lamps similar to those now placed
at frequented crossings in various parts of the town.
It is a fact beyond all question that, unvaryingly, there are fewer
persons belonging to the staff of the Metropolitan Railway, in
proportion to their numbers, absent from duty on account of illness,
than on other railways. We have seen returns, fully confirming the
statement to this effect. We believe they were published by Mr. Myles
Fenton, in the newspapers a few months ago.
During the year ending the 30th of June, 1867, the enormous number of
22,458,067 passengers[142] were conveyed by the Metropolitan Railway
Company without accident, injury, or (as far as the world knows) ill
effects to any one of them.
There is a source of danger in connection with travelling through a
long tunnel with a bad gradient, that a recent occurrence in the Dove
Hole tunnel of the Midland Railway (a tunnel to which special reference
is made at page 372), suggests. The accident is so extraordinary in
its character that a brief account of it at present will not he out of
place. It appears that on the 9th of September last, a ballast train
had gone into the tunnel with the intention of the permanent way men
supplying it with ballast. Whilst it was at a stand-still and the
men were at work, a cattle train, consisting of twenty-seven trucks,
and drawn by two powerful goods’ engines, was permitted to enter the
tunnel. This cattle train came into collision with the ballast train,
when, among other results, one was that the coupling chain which
connected the cattle trucks to the engines broke. The trucks thus freed
began to descend the incline, which, as already stated, is 1 in 90;
their _impetus_ increased each moment, and by the time they emerged
from the tunnel, on the wrong line, they were travelling at express
speed. Notwithstanding a slight change in the gradient, they went
on at that rate for eight miles, continuing always, of course, _on
the wrong line_. At that point the trucks came in collision with the
engine of an express train from Manchester, which had been standing on
its own proper line waiting for the signal it should receive before
proceeding onwards. The driver of the express train engine perceiving
in a moment what was occurring, reversed his engine, put on full steam,
and then jumped off, very unfortunately for himself. But the engine
had not sufficient speed upon her to prevent a collision with the
cattle trucks. The greater part of these latter were literally crushed
to atoms; and, perhaps, fortunately, the cylinders of the express
train engine were burst by the collision. This allowed a great escape
of steam, and it was ultimately, combined with the presence of mind
of a pointsman, the means of the engine not doing more mischief than
shaking some and frightening all the passengers travelling in the train
belonging to it. Not so five drovers who were in the brake-van of the
cattle train: they were killed, and, apparently, their deaths were
instantaneous. Such an accident as this is not likely to happen in the
tunnel of the Alps; but, suppose a coupling iron broke, and with it the
coupling chains, on the French or ascending side, would the brake power
attached to the carriages be enough to check their downward speed? At
all events, it must not be forgotten that the average gradient on the
French side of the tunnel is 1 in 45 (117 feet in the mile), or exactly
double as steep as that of the Dove Hole Tunnel, and that the Modane
entrance of the tunnel of the Alps is 1,216 feet above St. Michel,
consequently there is an average fall per mile during the whole twelve
miles of 1 in 101, or at the rate of 50 feet in the mile, and as there
will be no intermediate station, carriages if they came to be detached,
and had not sufficient brake power to arrest their progress, might
continue to run the whole of this distance at high speed, and _on the
wrong line_.
[For minute details relating to the construction of the Tunnel of the
Alps, up to 1862, and to the means of supplying ventilation during
its progress, the reader is referred to the interesting report of
Mr. Storrow, embodied in that of the Commissioners of the State of
Massachusetts on the Troy and Grenfield Railroad, and of the Hoosac
Tunnel, dated the 12th of March, 1863; also, to an article on the
Tunnel, in the _Edinburgh Review_ for July 1865, No. 249.]