Many ore mines that have an active aerodynamic connection of underground workings with the surface through the caving zone are ventilated by the injection-suction method. In this method, by regulating the operation of the suction and discharge fan, it is possible to create in the area adjacent to the caving, the so-called zone of zero depression. In this zone, the effective depression is extremely low, so there should be neither air suction from the surface nor air escape from the mine to the surface. The actual large size of the caving area and the occurrence of local natural draughts do not allow for the complete elimination of air movement through the caving. Air may move upward in one part of the caving and downward in another, but in much smaller quantities than with a single fan. Thus, the zero-depression zone created by the blower-suction method of ventilation serves as a measure to control air suction through the caving zone. At mines in the northern regions, the position of the zero depression zone plays an important role in improving the atmospheric conditions of these mines, reducing the entry of cold air from the surface ...

Methane emission within the excavation area depends on the operation of mining machines, atmospheric pressure fluctuations, collapse of rocks of the main roof, irregularity of air supply, etc. Regardless of the influence of these factors, the methane content in the outgoing jet of the site should not exceed 1%. Consequently, it is necessary to supply to the site such amount of air Qpred that would ensure compliance with the requirements of Safety Rules at any combinations of these factors.

Topics of research work of the Department of Mine Ventilation and Safety Engineering of the Leningrad Mining Institute is aimed at ensuring normal ventilation of mines, creating in mine workings safety conditions and such sanitary and hygienic working conditions that would allow to achieve maximum productivity.

The question of the dependence of local resistance coefficients k on the roughness of the walls of air ducts is one of the little studied issues of practical aerodynamics. Most aerodynamics courses provide values, sometimes very detailed, of coefficients k for a number of local resistances – bends, sudden contractions and expansions – but usually do not indicate how to use these coefficients: whether to take them as constant, independent of the roughness of the walls of the air duct, or, conversely, to consider them as variable quantities related by some dependence to the coefficient of friction on the walls of the air duct. The work done by the authors made it possible to clarify the relationship between the coefficients of local resistance k and the coefficients of friction α of air on the walls of the air duct. The previously accepted dependence turned out to be incorrect and must be replaced by another (see the article). The turning resistance coefficients given in various courses should be increased for rough concrete support by 8–10% and for workings supported with staggered door frames by 25–30%. The correctness of formulas (11) and (12) for other types of local resistance requires verification.

This work gives the definition of the coefficient of resistance of the ventilating ducts as well as of the influence on the value of this coefficient of the curve of the interior and exterior angles of bending, of the grade of widening and of the sloping of the interior angle. It contains also the curves for calculating the coefficient of resistance of all kind of bending. The meaning of coefficients of resistance with the simultaneous expansion of air should be taken on the base of curves represented on fig. 2 and 3. Interior and exterior angles of turns should have rounded edges. The coefficients of resistance in this case also can be seen on the curves shown on fig. 2 and 3. It is recommended to the interior angles of turns. The size of the cut and the coefficients of resistance for this case should be taken on the curve, given on fig. 6. If the shaft is used for the purpose of ventilation only and is not used for hoisting then it is rational to lock the part of the shaft located above the air channel of ventilator.