Section 75.310 - Installation of main mine fans(a) Each main mine fan shall be-(1) Installed on the surface in an incombustible housing;(2) Connected to the mine opening with incombustible air ducts;(3) Equipped with an automatic device that gives a signal at the mine when the fan either slows or stops. A responsible person designated by the operator shall always be at a surface location at the mine where the signal can be seen or heard while anyone is underground. This person shall be provided with two-way communication with the working sections and work stations where persons are routinely assigned to work for the majority of a shift;(4) Equipped with a pressure recording device or system. Mines permitted to shut down main mine fans under § 75.311 and which do not have a pressure recording device installed on main mine fans shall have until June 10, 1997 to install a pressure recording device or system on all main mine fans. If a device or system other than a circular pressure recorder is used to monitor main mine fan pressure, the monitoring device or system shall provide a continuous graph or continuous chart of the pressure as a function of time. At not more than 7-day intervals, a hard copy of the continuous graph or chart shall be generated or the record of the fan pressure shall be stored electronically. When records of fan pressure are stored electronically, the system used to store these records shall be secure and not susceptible to alteration and shall be capable of storing the required data. Records of the fan pressure shall be retained at a surface location at the mine for at least 1 year and be made available for inspection by authorized representatives of the Secretary and the representative of miners;(5) Protected by one or more weak walls or explosion doors, or a combination of weak walls and explosion doors, located in direct line with possible explosive forces;(6) Except as provided under paragraph (e) of this section, offset by at least 15 feet from the nearest side of the mine opening unless an alternative method of protecting the fan and its associated components is approved in the ventilation plan.(b)(1) If an electric motor is used to drive a main mine fan, the motor shall operate from a power circuit independent of all mine power circuits.(2) If an internal combustion engine is used to drive a main mine fan-(i) The fuel supply shall be protected against fires and explosions;(ii) The engine shall be installed in an incombustible housing and be equipped with a remote shut-down device;(iii) The engine and the engine exhaust system shall be located out of direct line of the air current exhausting from the mine; and(iv) The engine exhaust shall be vented to the atmosphere so that the exhaust gases do not contaminate the mine intake air current or any enclosure.(c) If a main mine fan monitoring system is used under § 75.312 , the system shall- (1) Record, as described in paragraph (a)(4) the mine ventilating pressure;(2) Monitor bearing temperature, revolutions per minute, vibration, electric voltage, and amperage;(3) Provide a printout of the monitored parameters, including the mine ventilating pressure within a reasonable period, not to exceed the end of the next scheduled shift during which miners are underground; and(4) Be equipped with an automatic device that signals when- (i) An electrical or mechanical deficiency exists in the monitoring system; or(ii) A sudden increase or loss in mine ventilating pressure occurs.(5) Provide monitoring, records, printouts, and signals required by paragraphs (c)(1) through (c)(4) at a surface location at the mine where a responsible person designated by the operator is always on duty and where signals from the monitoring system can be seen or heard while anyone is underground. This person shall be provided with two-way communication with the working sections and work stations where persons are routinely assigned to work for the majority of a shift.(d) Weak walls and explosion doors shall have cross-sectional areas at least equal to that of the entry through which the pressure from an explosion underground would be relieved. A weak wall and explosion door combination shall have a total cross-sectional area at least equal to that of the entry through which the pressure from an explosion underground would be relieved.(e) If a mine fan is installed in line with an entry, a slope, or a shaft- (1) The cross-sectional area of the pressure relief entry shall be at least equal to that of the fan entry;(2) The fan entry shall be developed out of direct line with possible explosive forces;(3) The coal or other solid material between the pressure relief entry and the fan entry shall be at least 2,500 square feet; and(4) The surface opening of the pressure relief entry shall be not less than 15 feet nor more than 100 feet from the surface opening of the fan entry and from the underground intersection of the fan entry and pressure relief entry.(f) In mines ventilated by multiple main mine fans, incombustible doors shall be installed so that if any main mine fan stops and air reversals through the fan are possible, the doors on the affected fan automatically close.61 FR 9829, Mar. 11, 1996, as amended at 61 FR 20877, May 8, 1996