VOLUME V - COAL MINES
PART 75 .... MANDATORY SAFETY STANDARDS - UNDERGROUND COAL MINES
Subpart C .... Roof Support
Subpart C .... Roof Support
75.209 Automated Temporary Roof Supports (ATRS) Systems
The purpose of the ATRS standard is to minimize hazards associated with miners working beyond permanently supported roof during the installation of roof supports. When this purpose is served, ATRS systems are required to be used. The use of an ATRS system is not necessary in the following three situations as miners are working in supported areas and are not exposed to unsupported roof:
- installing roof bolts in an unsupported area with a remote-control roof bolting machine, where the operator does not proceed beyond the last row of permanent support;
- placing truss supports in areas where permanent support is already in place, and where no adverse roof condition exists; and
- on a longwall face when the face is within 5 feet of the longwall supports.
Fatal roof fall accidents have occurred during pillar recovery operations. Investigation of a few of these accidents revealed that miners were occupying work locations inby the mining machine while coal was being mined or loaded. This practice should be discouraged, recognizing that recently mined coal pillars reduce the amount of support in these areas.
Work procedures and location of miners while coal is being mined or loaded should be incorporated into the roof control plan as part of the description of the mining system utilized during pillar recovery.
Subpart D .... Ventilation
30 CFR 75.301 defines return air as:
- Air that has ventilated the last working place on any split of any working section or any worked-out area, whether pillared or nonpillared. If air mixes with air that has ventilated the last working place on any split of any working section or any worked-out area, whether pillared or nonpillared, it is considered return air. For the purposes of existing Section 75.507-1, air that has been used to ventilate any working place in a coal producing section or pillared area, or air that has been used to ventilate any working face if such air is directed away from the immediate return, is return air.
Title 30 CFR 75.507-1(a) states that "All electric equipment,other than power-connection points, used in return air outby the last open crosscut in any coal mine shall be permissible except as provided in paragraphs (b) and (c) of this section."
For multiple entry setups with intake entries on one side, return entries on the other side, and conveyor belt and other common entries in the center, problems have arisen in determining whether or not return air is being coursed in the outby direction over non-permissible electric equipment in the conveyor belt entry. An acceptable method for making this determination is to measure air quantities at a location three crosscuts outby the working face in both the intake and return air courses. Taking into consideration standard anemometer error, if a comparison of these readings indicates a significant variance, a violation of 75.507 may exist.
Sulfur hexaflouride (SF6), tracer gas, should not be used as the primary means for determining compliance with this standard. If after analyzing appropriate intake and return air measurements,tracing clouds of chemical smoke, and examining the section ventilation system, a determination is made that there is a violation of 75.507-1, tracer gas may be used to substantiate the violation.
75.302 Main Mine Fans
Main mine fans shall be installed and operated as soon as possible after the first crosscut is made at drift mines and as soon as connections have been made between shaft and/or slope openings at shaft or slope mines.
75.310 Installation of Main Mine Fans
The purpose of paragraph (b)(1) is to ensure that the mine fan is provided with a dependable power supply that will not be affected by short circuits, ground faults, or overloads occurring in mine power circuits. Transformers or other power sources supplying mine fan circuits may also supply power to other circuits,provided that such circuits are protected in a manner ensuring that any malfunction in the other circuits will cause automatic deenergization of the affected circuit and will not affect the mine fan circuit.
75.323 Actions for Excessive Methane
Sections 75.323(b) and 75.323(c) specify actions to be taken when methane is 1.0 percent or more and when methane is 1.5 percent or more in working places, in intake air courses, and in return air splits. Section 75.323(d) specifies the requirements for using a return air split alternative and the actions to be taken when 1.5 percent or more methane is present in a return air split between a point in the return opposite the section loading point and where that split meets another split of air or where the split or air is used to ventilate seals or worked-out areas. In these cases, the mere presence of methane equaling or exceeding the applicable percentage is not, per se, a violation. A violation would exist if a mine operator, upon becoming aware of the presence of methane equaling or exceeding the applicable percentage, failed to perform the required actions.
Section 75.323(e) specifies that the concentration of methane in a bleeder split of air immediately before the air in the split joins another split of air, or in a return air course other than those described in Sections 75.323(c) and 75.323(d), shall not exceed 2.0 percent. In this case, a methane concentration in excess of 2.0 percent at the specified location would constitute a violation of Section 75.323(e). A bleeder system includes the area from which pillars are wholly or partially recovered, bleeder entries, bleeder connectors, and all associated ventilation control devices that control the air movement through the area. Bleeder entries are air courses designed and maintained as part of the bleeder system. Air from separate bleeder systems are separate splits of air.
The required 2.0 percent methane concentration limit in the bleeder airflow immediately before the bleeder split joins another split of air provides for a specified measure of dilution of the methane within the bleeder system. This 2.0 percent methane limit impacts the dilution of methane throughout the bleeder system. The air course downstream of the location where the bleeder split joins another split of air is a return air course.
Air that passes through a ventilation control that is intended to be reasonably air tight and that separates adjacent air courses is leakage. Leakage from another split that enters directly into the pillared area does not impact the location of the Section 75.323(e) 2.0 percent methane limit, but may impact the effectiveness and/or evaluation of the bleeder system. Leakage from another split that enters the bleeder split can decrease the dilution capacity of the bleeder system and impact the specified measure of dilution of methane quantified by Section 75.323(e). When evaluating the significance of the impact of leakage air on the methane concentration at the location specified in Section 75.323(e), the effect of the total leakage air must be considered. Factors to consider include the effect the leakage air from another split entering the bleeder split has on the air quantity and air quality within the bleeder split it enters. If the cumulative amount of leakage air that enters the bleeder split from another split or splits exceeds 15 percent of the air quantity in the affected portion of the bleeder split, a determination will be made as to whether the leakage is significant. MSHA's experience has been that leakage from another split in excess of 15 percent may have significant impact. This leakage may have an effect on the methane concentration in the bleeder split that is equivalent to another split of air joining the bleeder split at or before the location specified in Section 75.323(e). If this leakage is determined to be significant, the district manager may require, as specified in Section 75.371(z), methane limits at additional locations within the bleeder system be included in the ventilation plan in order to evaluate and to assure the effectiveness of the bleeder system.
A small split of intake air used to ventilate electrical installations that is directed into the bleeder split, that MSHA has determined to be insignificant, would not affect the location of the 2.0 percent methane limit prescribed in Section 75.323(e).
Considerations relative to the significance of the small splits of intake air used to ventilate electrical installations that are directed into the bleeder split should be similar to those related to the impact of leakage air on the air quantity and air quality of the bleeder split. In addition, these small splits should also be considered significant if they adversely impact the performance of the bleeder system, decreasing the ventilation of the pillared area by reducing the available ventilating pressure or airflow quantity. Multiple small splits of air that are used to ventilate electrical installations may have a cumulative impact on the bleeder system that is significant. This cumulative impact should be considered when determining the significance of each individual small split of air used to ventilate electrical installations directed into the bleeder split.
A small split of intake air used to ventilate a longwall set-up face that is directed into the bleeder split, that MSHA has determined to be insignificant, would not affect the location of the 2.0 percent methane limit prescribed in Section 75.323(e). Considerations relative to the significance of the intake splits used to ventilate a longwall set-up face that are directed into the bleeder split should be similar to those related to the impact of leakage air on the air quantity and air quality of the bleeder split. These splits should also be considered significant if they adversely impact the performance of the bleeder system, decreasing the ventilation of the pillared area by reducing the available ventilating pressure or airflow quantity. When evaluating the significance of longwall set-up face splits relative to the location of the 2.0 percent methane limit prescribed in Section 75.323(e), factors to consider include the effect air from the longwall set-up split that enters the bleeder split has on the air quantity and air quality within the portion of the bleeder split it enters. Approved ventilation plans sometimes set limits restricting the quantity of air that is permitted to ventilate a longwall set-up face such that it does not affect the location of the 2.0 percent methane limit prescribed in Section 75.323(e).
The location in the bleeder split where the concentration of methane shall not exceed 2.0 percent is immediately before the air in the split joins another split of air. When air from the bleeder split is directed to the surface, the bleeder split ends at the surface. In this case, the location where the methane concentration is to be measured for compliance with the Section 75.323(e) 2.0 percent methane limit is in the bleeder split immediately before the air in the bleeder split reaches the surface. When air from the bleeder split is directed to the surface through a vertical shaft, factors influencing air quality within the shaft should be considered in determining whether the bottom of the shaft provides an appropriate measurement location. When air from the bleeder split exits through an exhaust fan, consideration should be given to the significance of air from the surface entering the fan housing in determining whether the exhaust of the fan provides an appropriate measurement location.
Nothing stated above abrogates, alters, or diminishes mine operators' responsibility under Section 303(z)(2) of the Mine Act and 30 C.F.R. Section 75.334(b)(1) to ensure that bleeder systems are effective and maintained so as to continuously dilute, render harmless, and carry away methane and other explosive gases within areas that have been wholly extracted, partially extracted, or abandoned, such that the active workings of the mine are protected from the hazards of methane and other explosive gases. Section 75.334(b)(1) specifically requires that bleeder systems continuously dilute and move methane-air mixtures and other gases, dusts, and fumes from the worked-out area away from active workings and into a return air course or to the surface of the mine. A determination that the quantity of leakage air entering a specific bleeder split does not exceed 15 percent, or the fact that there has not been a determination to include an additional measurement point location in the ventilation plan, does not mean that the bleeder system is in compliance with Section 303(z)(2) of the Mine Act or 30 C.F.R. Section 75.334(b)(1).
75.325 Air Quantity
(a)(3)The name plate quantity of the machine mounted dust collector or diffuser fan is acceptable to meet the requirements of 30 CFR 75.325(a)(3) and 75.371(j). If the operator submits the nameplate quantity in the approved ventilation plan as the operating volume, this is the minimum quantity that must be maintained at all times. If this quantity is not maintained, if the measured operating capacity reveals that the name plate quantity is not indicative of actual conditions, or if respirable dust samples indicate that this quantity is not sufficient, appropriate enforcement action shall be taken and plan revisions shall be necessary.
Paragraph (f) requires that the minimum ventilating air quantity for an individual unit of diesel-powered equipment must be provided. This requirement includes entries under paragraph (f) (3) where diesel-powered equipment is being operated outby the loading point in areas of the mine developed on or after April 25, 1997. Such entries include crosscuts, dead-end spurs and any other area where such equipment is positioned to allow passage of other equipment or personnel, or entering an area to place or retrieve supplies.
The minimum ventilating air quantity for a unit of diesel-powered equipment is established based on the quantity of air specified on the unit's approval plate. The approval plate quantity is based on testing of the diesel exhaust gas concentrations of carbon monoxide (CO) and Oxides of Nitrogen measured as nitrogen dioxide (NO2). The approval plate quantity is the quantity of air that is required to dilute the concentration of CO and NO2 at the tailpipe to the Threshold-Limit-Values (TLVs) specified in 75.322. The TLVs are established to protect persons from adverse health effects from exposure to the specified contaminates. The TLV for CO is 50 parts per million (ppm) and the TLV for NO2 is 5 ppm and is noted as a "ceiling limit" which cannot be exceeded for any amount of time. Since the nameplate air quantity is the quantity of air necessary to dilute the engine exhaust to the TLV limit, it is imperative that this minimum air quantity be provided where the unit of diesel equipment is operating so as to ensure miners are not exposed to hazardous concentrations of CO and NO2. It should be noted that the testing of the diesel engine to determine the nameplate air quantity is performed on a new engine set to the manufacturer's specifications which represents the best operation of the engine.
75.327 Air Courses and Trolley Haulage Systems
The air in the trolley haulage entry, when separated from the belt haulage entry, may be used to ventilate the active working places.
Should conditions develop that necessitate an increased velocity in trolley haulage ways in excess of 250 feet per minute, the mine operator should apply to the district manager for an exception through the ventilation plan, Section 75.371(v), giving in detail the reason for the request.
75.330 Face Ventilation Control Devices
The "area of deepest penetration" referred to in Section 75.330(b)(2), in conventional mining sections, is considered to be the solid surface of the coal bed at the advancing end of the working place, in both uncut and undercut faces prior to blasting. After blasting, the "area of deepest penetration" is the toe of the coal fall before loading starts, and advances with the toe as the fall is loaded.
75.340 Underground Electrical Installations
Underground electrical installations shall be considered to be in a noncombustible structure if the enclosure provides protection against flame spread for at least 1 hour when subjected to a fire test incorporating an ASTM E119-88 time/temperature heat input or equivalent.
The following types of installations, if acceptable prior to November 16, 1992, will be accepted as meeting the requirements for a noncombustible structure required by 75.340:
- Installations that are manufactured as packaged units fully enclosed in a metal housing such as:
- power centers;
- rectifiers and transformer stations that use dry-type transformers; or
- transformers filled with nonflammable fluid or inert gas.
- power centers;
- Battery charging stations that:
- are enclosed in substantial metal housings;
- are used to charge batteries that are also enclosed in substantial metal housings; and
- remain on the machine during charging.
- are enclosed in substantial metal housings;
75.341 Direct-Fired Intake Air Heaters
A carbon monoxide sensor placed at the bottom of the shaft,slope, or in the drift opening which provides continuous monitoring of the affected area and causes the heater to shut down when the carbon monoxide (CO) level reaches 50 parts per million will verify that CO is not entering the mine and that the heater is operating properly. The sensor will satisfy the examination requirements of this section.
75.342 Methane Monitors
On cutting machines, continuous-mining machines, and loading machines (including scoops and diesel-powered machines used to load coal from inby the last open crosscut but not including clean-up scoops), the methane monitor power-shutoff relay shall be connected into the machine's controls circuitry so that all electric motors on the machine (including auxiliary fan motors),all electric lights on the machine (except headlights that are evaluated by MSHA under Part 18 and are installed on diesel-powered machines), and all power take-off receptacles on the machine (except intrinsically safe receptacles) are automatically deenergized when the methane concentration reaches a maximum of 2.0 percent or the monitor is not operating properly. The methane monitor may remain energized.
When a methane monitor is required on a diesel-powered machine,the methane monitor shall also shut off the diesel engine when the methane concentration reaches a maximum of 2.0 percent or the monitor is not operating properly. The methane monitor power shutoff relay shall be connected into the control circuitry of an electrically-operated machine so that it is not possible to defeat the methane monitor by holding or blocking the machine's reset switch in the start position.
When a machine is operated by remote control, a warning device shall be installed in the remote control unit or on the machine in such a location that the warning device can be readily seen or heard by either the machine operator or by the machine operator helper at all locations from which the machine is operated. This does not, however, permit the machine operator to be positioned under unsupported roof or where he or she could be endangered by a sudden movement of the machine.
The sensing device for methane monitors required at the return air end of the longwall face shall be installed in the air current ventilating the longwall face near the return end of the longwall face where it will not be affected by a secondary intake if one is used. The methane monitor power shutoff relay shall be connected so that all electric motors, lighting circuits, and power take-off receptacles associated with the longwall mining installation are automatically deenergized when the methane concentration reaches a maximum of 2.0 percent or the monitor is not operating properly. The methane monitor and approved permissible telephones, however, may remain energized.
Methane monitor deficiencies should be cited under this section or Section 75.503, as applicable. Checks for operating accuracy shall be conducted with the sensor head filter or screen in place. Hand-held methane detectors shall not be used to check the operating accuracy of methane monitors. Enforcement personnel should test methane monitors with a known methane air test mixture when it is suspected that the monitor is defective or improperly calibrated.
Methane monitor readings shall not be used to meet the requirements for methane examinations. Such examinations are required to be made with approved methane detectors or atmospheric monitoring systems if used as specified in Section 75.351. Enforcement personnel shall not use methane monitor readings as a basis for issuing citations or orders.
75.350 Air Courses and Belt Haulage Entries
A district manager may not grant exceptions to these provisions to operators of mines opened after March 30, 1970. The operator should be advised that such requests should be submitted under the provisions of Section 101(c) of the Act (petition for modification of a mandatory safety standard).
Exceptions to this provision may be granted by the district manager in mines opened on or before March 30, 1970, and extensions of belt haulage entries in mines opened on or before March 30, 1970, only when an investigation determines that the conditions in the entries, other than the belt haulage entries,are necessary to provide adequate ventilation to the working places.
75.360 Preshift Examination
Roadways and track haulage ways must be examined 3 hours immediately preceding each shift. This examination must include tests for methane in all high cavities where methane could accumulate.While traveling haulage roads, travel ways, or belt conveyors, if high cavities in the roof are observed, the inspector should look for some method that has been provided for the preshift examiner to make such tests. Examples are ladders, tubes, methane detectors with probes, etc. Lack of some method to safely make such tests would be a good indication that tests were not being made or not properly being made. This could require issuing appropriate citations or orders.
75.371 Mine Ventilation Plan; Contents
Questions have been raised concerning whether the angles at which water sprays are directed must be included in the mine ventilation plan. As stated in the preamble to the final rule, this information is necessary for plan approval. It is not intended that enforcement personnel use engineering instruments to measure precise angles during inspection activities. Rather, the general spray direction and orientation and other parameters such as number of sprays, orifice size, and operating pressure would be determined by comparison with the requirements of the approved ventilation plan.
75.380 Escape ways; Bituminous and Lignite Mines
"The most direct, safe and practical route," as used in paragraph(d)(5) will be determined on a mine-by-mine basis. If the inspector believes that a particular escapeway is not the most direct, safe, and practical route, he or she must specifically inform the operator that another route is more direct, safe, and practical. This should be done by the inspector at the time of issuing a citation by orally notifying the operator of the preferred escapeway route and by noting in both the citation and inspector's notes, the escapeway route which the inspector believes to be more direct, safe, and practical.
Serious consideration should be given to the inherent hazards related to rehabilitation of fallen areas. In addition to the hazards of exposure related to such rehabilitation, other factors affecting whether the operator has set out the most direct, safe and practical route include roof conditions, traveling height,fan location, physical dimensions of a mine opening, and similar factors.
For example, if bad roof conditions are present along the shortest direct route and those roof conditions are beyond reasonable control, then an alternate safest route, as designated by the mine operator, may be acceptable. The presence of roof falls does not necessarily indicate that the passageway would not be suitable for evacuation.
Where coal seam thickness varies to the extreme, the shortest route may be through lower coal, making travel relatively slow and difficult, whereas an alternate route through a high passageway may permit faster and easier travel. Such an alternate route, although longer, may be acceptable. Similarly, an old mine shaft may not be safe for travel because of badly deteriorated shaft lining, timbers, etc., even though it is still suitable for mine ventilation purposes.
Standard development projections will not have to be altered to drive additional rooms, entries, or crosscuts for the sole purpose of providing a passageway to the nearest mine opening.However, the construction of ventilation controls such as stoppings, overcasts, and under casts, or installation of an escape facility, may be required to provide the most safe, direct, and practical escapeway.
75.385 Opening New Mines
The total number of 20 miners allowed in any mine at any one time shall be interpreted to mean that no more than 20 miners (including supervisory personnel) may be permitted to work in any individual shaft, slope, or drift opening until a connection is made. In determining the total number of persons in the mine before a connection is made, the number shall not include State or Federal inspectors, representatives of the miners, or equipment manufacturing representatives.
Only the work necessary to make connections between the mine openings shall be permitted, and any development or other extraction of coal shall be prohibited until the connections are completed.
75.386 Final Mining of Pillars
The instructions outlined in Section 75.385 apply to this provision except that the limitation of 500 feet between the mine opening and working face shall be measured from the bottom of a shaft or slope or from the portal of drift mines to the working face.