The concentration of oxygen in the air is reduced by injecting inert gases into the air to avoid coal combustion.The most common way to prevent fire in coal mines is to fill them with nitrogen. Mainly because of the characteristics of nitrogen: colorless, tasteless, non-toxic, non-corrosive, very good stability (especially under the action of vibration, heat and electric spark).Nitrogen is simple to produce, low economic cost, and basically does not pollute the environment.

The role of filling nitrogen into coal mines to prevent fire is:

(1) )After filling nitrogen into coal mine, the oxygen concentration in the goaf decreases. Nitrogen partially replaces oxygen into the fissure surface of coal and exchanges and adsorbs with the microscopic surface of coal, thus reducing the adsorption of oxygen on the surface of coal and inhibiting or slowing down the oxidation of coal to a large extent.

(2) For the fire prevention area with certain closed conditions of nitrogen injection, after long-term continuous filling of nitrogen in the coal mine, a large amount of nitrogen can form positive pressure in the goaf, thus reducing the amount of air leakage in the goaf, so that the coal remains in an anoxic environment and is not easy to oxidize.

(3) When the lower temperature nitrogen flows through the coal body, it absorbs part of the heat generated by coal oxidation, which can slow down the rate of coal heating and reduce the temperature of the surrounding medium, so that the oxidation of coal is delayed or terminated due to the destruction of heat accumulation conditions.

(4) When the combustible and explosive gas in the goaf is mixed with nitrogen, the explosion range is gradually reduced with the increase of nitrogen concentration. When the mixture ratio of inert gas and combustible gas reaches a certain value, the upper and lower limit of explosion of the mixture coincide, and the mixture loses its explosive ability.