TRANSACTIONS OF SECTION G. 891 
The rapid extension of tunnel construction for railway purposes, both in towns 
and elsewhere, is one of the remarkable features of the period under review, and 
has been greatly assisted by the use of shields, with and without compressed air. 
This brings into considerable importance the question of mechanical ventilation. 
Amongst English tunnels, ventilation by fan has been applied to those under the 
Severn and the Mersey. The machinery for the latter is, probably, the most 
complete and most scientific application up to the present time. 
There are five ventilating fans, two of which are 40 feet in diameter, and 
12 feet wide on the blades; two of 30 feet, and 10 feet wide; and one quick- 
running fan of 16 feet in diameter, all of which were ably instailed by Messrs. 
Walker Brothers of Wigan. They are arranged, when in full work, to throw 
800,000 cubic feet of air per minute, and to empty the tunnel between Woodside 
and St. James’s Street in eight minutes ; but, unfortunately, it is found necessary, 
for financial reasons, not to work the machinery to its full capacity. 
The intended extension of electrical underground railways will render it neces- 
sary for those still employing steam traction either to ventilate by machinery or to 
substitute electro-motive force. 
Great improvements have been lately made in the details of mechanical venti- 
lators, especially by the introduction of anti-vibration shutters, and the driving 
by belts or ropes instead of direct from the engine. The duties now usually 
required for mining purposes are about 300,000 cubic feet of air per minute with 
a water-gauge of about 4 inches; but one installation is in hand for 500,000 cubic 
feet of air per minute, with a water-gauge of 6 inches. Water-gauge up to 10 
inches can now be obtained with fans of 15 feet diameter only. 
An interesting installation has been made at the Pracchia Tunnel on the 
Florence and Bologna Railway. 
The length of the tunnel is 1,900 metres, or about 2,060 yards; it is for a 
single line, and is on a gradient of 1 in 40, When the wind was blowing in at the 
lower end, the steam and smoke of an ascending train travelled concurrently with 
the train, thus producing a state of affairs almost unimaginable except to those 
engaged in working the traffic. 
Owing to the height of the Apennines above the tunnel, ventilating shafts are 
impracticable ; but it occurred to Signor Saccardo that, by blowing air by means 
of a fan into the mouth of the tunnel, through the annular space which exists 
between the inside of the tunnel arch and the outside of the traffic gauge, a 
sufficient current might be produced to greatly ameliorate the state of things. 
The results have been most satisfactory, the tunnel, which was formerly 
almost dangerous, under certain conditions of weather, being now kept cool and 
fresh, with but a small expenditure of power. 
In an age when, fortunately, more attention is paid than formerly to the well- 
being of the men, the precautions necessary to be observed in driving long 
tunnels, and especially in the use of compressed air, are receiving the consideration 
of engineers. In the case of the intended Simplon Tunnel, which will pierce the 
Alps at a point requiring a length of no less than 123 miles, a foreign commission 
of engineers was entrusted by the Federal Government of Switzerland with an 
investigation of this amongst other questions. 
During the construction of the St. Gothard Tunnel, which is about 10 miles 
in length, the difficulties encountered were, of necessity, very great; the question 
of ventilation was not fully understood, nor was sanitary science sufficiently ad- 
vanced to induce those engaged in the work to give it much attention. The 
results were lamentable, upwards of 600 men having lost their lives, chiefly from an 
insidious internal malady not then understood. But the great financial success of 
this international tunnel has been so marked, as to justify the proposed construction 
of a still longer tunnel under the Simplon. 
The arrangements which are to be adopted for securing the health of the 
employés are admirable, and will surely not only result in reducing the death rate 
to a minimum, but also tend to shorten the time necessary for the execution of the 
undertaking to one-half. 
The quantity of air to be forced into the workings will he twenty times greater than 
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