ENVIRONMENT MONITORING IN UG MINES

 

ENVIRONMENT MONITORING IN UG MINES

 

 

Normal ambient air is a mixture of gases containing 78.10 % nitrogen, 20.93 % oxygen, 0.03%  carbon-dioxide, 0.94% argon, traces of hydrogen, helium and other rare gases together with a variable amount of water vapour. It picks up other contaminant gases often produced in mines under normal conditions, namely, carbon dioxide, carbon monoxide, oxides of nitrogen, sulphur dioxide, hydrogen sulphide etc. When the mines gives off methane, large and small amounts of it may also be liberated into mine air. Under abnormal conditions such as during mine fire and explosions, the composition of the mine air may, however undergo significant changes.

Oxygen(O₂)content in mine air decreases due to breathing of men, burning of safety lamps, and gradual oxidation of organic and inorganic substances such as mine timber, coal and pyrites.The oxygen content,however,decreases considerably immediately after a mine-fire or explosion or due to appearance of other gases in higher concentration. In most cases the reduction of oxygen is attended with increase of carbon dioxide content.

It is advised not to enter a workplace with less than 18% oxygen. When it falls from 18to15 %,the breathing becomes labored and muscular skill is diminished;when it falls from 14 to10 %,a man is still conscious but has faulty judgment and he becomes fatigued very quickly. With a further fall from 10 to 6 %, he collapses due to inadequate supply of oxygen to the brain but can be revived by of fresh air or oxygen.The threshold limit value is given as 19%.The adequacy of oxygen in mine air may be ascertained by means of a flame safety lamp, the flame of which becomes dim and small and finally goes out when the oxygen content falls to about 16%.Ambient air oxygen concentration can be measured by use of an oxygen indicator,analyzer, meter or detector.

Nitrogen(N₂)undergoes no alteration in the process of breathing and is not poisonous but it suffocates due to lack of oxygen when present in an amount greatly in excess of that normally found in air.        

Carbon dioxide (CO₂)is not combustible and does not support combustion nor sustain life. It is produced in mines from the causes like burning of flame, breathing of men, decay of mine timber, slow oxidation of coal, blasting etc. CO₂ is not poisonous in the real sense but is asphyxiating. At even 0.5 % or 5000 rpm, breathing becomes a little deeper and faster; at 2 %, the rate and depth of breathing increases by 50 % and at 4 % breathing becomes much faster and with physical exertion over several hours, palpitation of heart results. The threshold limit value of CO₂is given as 5000 rpm.