(1) The return air flow generally contains gas. When it enters the local ventilator again, due to the high-speed rotation of the fan blades, friction will occur with the dust in the wind flow to generate sparks, which may ignite the gas.
(2) As part of the cycle of polluted air to the heading face, so that the concentration of gas and dust heading face increasing may cause gas, coal dust accidents.
(3) Deteriorating the climatic conditions of the excavation face and damaging the health of the staff. The main reasons for the circulation of wind are:
(1) The local ventilator is improperly installed, that is, it is too close to the return air inlet of the heading face. Due to the diffusion of the wind flow, part of the return air enters the fan.
(2) The amount of suction of the local ventilator is greater than the amount of air supplied to it by the full wind pressure. The measures to prevent circulating wind are:
(1) The pressure local ventilation fan and starting device must be installed in the air inlet, not less than 10 meters from the return air outlet.
(2) The suction air volume of the local ventilator must be less than the air volume supplied by the full wind pressure.
(3) Always check whether circulating air is generated. The simple method of inspection is to stand on the side of the fan and smash the chalk end by hand. If the chalk end is observed to float toward the fan suction port, it means that the circulating wind has occurred. Otherwise, Indicates no circulation wind.
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