296 TUNNELING 



In a long tunnel excavated through hard rock the number 

 of workmen all together may be assumed at 400 at each end, 

 and each workman is supposed to be furnished with a lamp. 

 No less than ten horses are employed, and the average quantity 

 of dynamite consumed is 600 Ibs. per day. From the data given 

 the consumption of air by workmen and lamps would be : 

 240x400 = 96,000 cu. yds. ; the consumption of air by horses 

 would be 850 x 10 = 8,500 cu. yds. ; the consumption of air by 

 dynamite would be 150 x 600 = 99,000 cu. yds. ; making a total 

 consumption of air per day of 197,5.00 cu. yds., or about 8,000 

 cu. yds. per hour. 



To obtain good ventilation, then, it will be necessary to 

 furnish every hour a quantity of fresh air amounting to not less 

 than 8,000 cu. yds. Since, however, a large quantity of pure 

 air is expelled with the foul air, it is necessary greatly to in- 

 crease this quantity. 



It may be observed, in closing, that the water having its 

 particles divided, as in a fog or mist, rapidly precipitates the 

 gases produced by explosions. Now, when hydraulic machines 

 are used, there is a hollow ball pierced by holes that are almost 

 imperceptible, from which the compressed water spreads in very 

 subtile particles, and this causes the fall of the gases from 

 explosions. Such a method of precipitating gases is very good, 

 but does not have the advantage of supplying new oxygen to 

 replace that consumed by the men, animals, lamps, and ex- 

 plosions; besides, it has the defect of increasing the quantity of 

 water to be removed. In tunnels the pipes used either for con- 

 veying the fresh air or for carrying away the foul air, are of 

 iron, having a diameter of about 8 in. ; they are fixed along the 

 side walls about 3 ft. above the inverted arch. 



