When air flows through the mine environment, its composition changes due to addition of different kinds of impurities along its path. These impurities are Classification of impurities Nontoxic but explosive gases Examples Methane, Acetylene, Hydrogenate. Toxic gases Examples Carbon dioxide, Radon and its daughter products, etc. Acutely poisonous gases Examples Carbon monoxide, Nitrous fumes, Sulphur dioxide, hydrogen sulphide, Arsine, Phosphine, etc. Miscellaneous impurities like Vapours of water, Fuels and lubricants, Metals like mercury and lead etc. Solid impurities, like dust, Smoke and organisms. Suspended fine liquid droplets, Such as fog due to condensed water- vapour or Mist of fine oil droplets from drills etc. In mines where cooling plants are used, the mine air also picks up Freon Some amount of water vapour is also present in the form of moisture in mine air. The management of mine ventilation is critical to the maintenance of a comfortable atmosphere for workers working in underground coal mines.