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One of the commonly present gas hazard in hard coal mines methane hazard. The most endangered region by this hazard, during ventilation of longwall in ?U from boundaries? system is the crossing with ventilation roadway (so called ?upper corner of longwall?). Accumulation of methane in this place results from its release from goaf. Therefore, in order to decrease methane concentration in this region, auxiliary ventilation devices are used. They are aimed to supply to this place such an amount of fresh air, as to di...