VKNTlI.ATloN AND LIGHTING Dl'KIMJ mNSTKlVTlON 295 



ing purposes, it is better to have a number of small fans acting 

 independently of each other, conveying the fresh air where it is 

 needed through independent pipes. 



Compressed Air. In the excavation of tunnels in hard rock 

 a number of rock drilling machines are employed which are 

 moved by compressed air at a pressure of not less than fhe 

 atmospheres. At each stroke about 100 cu. ins. of compreaieU 

 air is set free, and at an average of 10 strokes per minute there 

 would be 5,000 cu. ins. of air at five atmospheres or 25,000 

 cu. ins., or a little more than 175 cu. ft. of fresh air at normal 

 pressure set free every minute by each of the machines employed. 

 But the air exhausted from the drilling machine is foul. 



Regarding ventilation by compressed air, Mr. Adolph Sutro, 

 in a lecture delivered to the mining students of the- I'niversity 

 of California, said : 



"I will note a curious fact which I have never seen explained, and which is 

 worthy of close investigation by means of experiments. In the Sutro tunnel we 

 found that the compressed air used for driving the machine drills, after havim: l>ccn 

 compressed and expanded and discharged from the drills, was not wholesome t<> 

 breathe, and the men and mules would all crowd around the end of the blower pi|H> 

 to get fresh uir. Whether the air in being compressed has parted with some of its 

 oxygen or because vitiated from some other cause. I do not know, and I hope that 

 this subject will at some future day be carefully examined into." 



In the Deceml>er, 1901, number of the "CWy /<**></ .1 >'/." a 

 in ;iL r :i/ine especially devoted to the useful application of com- 

 pressed air, is read : 



Compressed air wasted from power drills is so contaminated with oil from 

 the exlinders that it cannot be taken into consideration as ventilation. It is OH 

 important to displace it with pure air as it is to drive out or draw off other vitiated 

 air. The ventilation should be an independent supply provident by fan or blower, 

 delivering by pi|>c at the point where miners are working. 



Quantity of Air. The quantity of air to be introduced into 

 tunnels must be in proportion to the o\\-o;rn c(.ii>umed by the 

 mm, the animals, and the explosions. It is allowed that the 

 quantity of air required for breathing pur|M,- ;md explosions is 

 as follow.- : 



1 workman with lamp needs 240 cu. yds. of fresh air in 24 boon. 

 1 horse " 880 " " ' " 



1 Ib. gunpowder 100 " ' " 



1 Ib. dynamite 180 ' " " 



2070 64 



