New York Paper - Coal-mine Ventilation

Ventilation within a coal mine is essential to the welfare of those employed therein, from the standpoint of health, safety, and efficiency. While the saving of life and the preserving of health are the chief reasons for ventilation, efficiency and production are increased. In spite of the fact that we speak of air as having a certain composition, the proportions of oxygen, nitrogen, and carbon dioxide are not fixed, but vary between small limits. The different elements are not chemically united, they are merely mixed and each is free and can be separated with little energy. For this reason air in the mine workings is seldom found in a pure state. Factors that necessitate ventilation in coal mines are those that change the composition of pure air. Contamination of mine air results from the burning of oil-fed flames, the use of explosives, the oxidation of coal, and the liberation of gases by the coal. The extent to which these factors exist governs the size and general plan of the ventilating applianccs required. An efficient ventilating system is one that will furnish air at the working faces in sufficient volume to dilute and render harmless noxious gases and at the same time maintain an oxygen content closely approaching that of pure air. In a well-ventilated mine, the oxygen seldom falls more than 0.5 per cent. below normal. The carbon-dioxide content of the air in the average coal mine will vary from 0.1 to about 0.8 per cent., which amounts are not harmful. Three per cent. of carbon dioxide in air doubles the frequency and the depth of breathing; it is plainly noticeable and if breathed continuously for several hours its effect would probably be harmful. Slight reductions in the oxygen content of the air, such as occur in well-ventilated mines, have no debilitating effect on the worker. A person not exerting himself would fail to observe any unusual physical effect in an atmosphere: containing 17 per cent. of oxygen. This condition, however, or even a condition showing an oxygen content below 20 per cent., would indicate poor ventilation and that the elements which tend to reduce the efficiency of the worker are present, namely water vapor and a high wet-bulb temperature.