CHAPTER IV. 



VENTILATION . 



The ventilation of a colliery is of vital importance to those 

 working Underground- Air is made up of approximately 79 

 per cent, of nitrogen by volume and 21 per cent, of oxygen; 

 but in nature it also contains a small amount of moisture and 

 from 0.03 to 0.04 per cent, of carbon dioxide. A cubic foot of 

 air is 773 times lighter than water. At 32deg. F. it weighs 

 0.080721b. : it expands 1 volume in 460 for every degree Fah- 

 renheit. 



1000 cubic ft. of air weighs 811bs. 



1000 cubic ft, of CO, weighs 1241bs. 



1000 cubic ft. of CH 4 weighs 45-221bs. 



The amount of oxygen in the air diminishes more rapidly 

 in coal than in metal mines, as there is a larger surface ex- 

 posed to oxidation in proportion to the ventilation current. 

 The amount of air required by law in New South Wales is 100 

 cubic feet of air per minute for each man, boy and horse. 



Air should not contain less than 0.5 per cent, of the nor- 

 mal amount of oxj^gen. 



A man inhales about three times as much air when in 

 motion or at work than when at rest. 



Carbon dioxide (CO A) has neither taste, colour nor smell. 

 Among miners it is known as "choke damp" or "black 

 damp," but in mines the gas is never pure, and is said to have 

 a smell; this, however, is due to the presence of hydrocarbons. 

 According to most authorities air containing more than 0.1 per 

 cent, of CO 5 is unfit for respiration; the effects of it, however, 

 are not very noticeable until the proportion reaches 3 per 

 cent., when the depth of respiration is slightly increased. At 

 5 per cent, there is a marked panting while at rest. At 7 to 8 

 per cent, there is great oppression and painful panting. With 

 10 per cent, the difficulty becomes severe, while a slight in- 

 crease of CO 9 produces unconsciousness and death. When 

 the air extinguishes a lighted candle one should take it as an 

 indication that the air is unfit to support life- The amount of 

 C0 2 - that is sufficient to extinguish a flame depends partly on' 

 the nature of the illuminant and partly on the amount of 



