Rambles on Railways

by Sir Cusack P. Roney

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.