ACTIVE GASES (EN: active gases; DE: Aktivgase; FR: gases actifs; ES: gases activo; RU: активные газы) are the gaseous components of the mine air, which are changing the diffusion properties of the ventilation flow. The most common active gases are the methane and carbon dioxide.
The active gases cause the decrease of the turbulence of the flow, decrease its mixing ability and, as the result, facilitate the forming of the local accumulations of the gases of the increased concentration, often in the form of the hard to find layers at the roof or soil of the mine working.
The active gases may change the field of the velocities of the air flow: in the horizontal working as the consequence of the dependence of the profile of the velocity on the distribution of the density in the flow, and in the inclined working as the consequence of the appearance of the longitudinal component of the force of the gravity, which is acting along the flow or against it.
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