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Subpart E .... Combustible Materials and Rock Dusting

75.400 Accumulation of Combustible Materials
Experience and tests have shown that accumulations of coal dust can contribute greatly to the propagation and severity of mine explosions.  Such accumulations are also potential fire hazards since they are more readily ignitable and, once ignited, are more difficult to control and extinguish.  The intent of this Section is to prevent the accumulations of the specified combustible materials in order to reduce the dangers of mine fires and explosions.

Coal dust means particles of coal that pass a No. 20 sieve.
It is this fraction of the coal that participates in the dust explosion reaction.  Loose coal means coal fragments larger in size than those passing a No. 20 sieve.

Tests have shown that intermittent piles of coal dust are more hazardous than smooth layers because the irregular piles are eroded more readily by the air movement generated during an explosion.  As little as two 300-pound piles, under experimental conditions, caused an explosion to propagate when the entry otherwise was adequately rock-dusted.

Coal dust or coal and loose coal accumulations present a fire as well as an explosion hazard.  The broken coal has considerably more surface area per unit mass than solid coal.  For example, should an electric cable fail and cause an arc, the probability of igniting accumulations is greater than igniting solid coal.  Also, when broken coal is ignited, fire propagates faster than in solid coal. As another example, if hydraulic oil is spilled into broken coal, the broken coal would ignite more easily and propagate flame faster than a similar spill on the smooth floor or against the coal rib.
Accumulations of coal dust, loose coal, or the combination of the two offer serious fire and explosion hazards and must be removed from the mine if, in the judgment of the inspector, they would lead to an intensification or spreading of a fire or an explosion.  In evaluating whether the coal dust and loose coal would lead to an intensification or spreading of a fire or an explosion, the inspector should consider all the facts concerning the deposit.  For example, float coal dust, loose coal and/or coal dust deposited near working faces and in active haulage entries, where sources of ignition are likely to be, are more hazardous than similar deposits in back entries.  However, the remoteness of back entries is not necessarily a safeguard.

Stoppings that normally isolate back entries may be destroyed by the force of an explosion, and accumulations of float coal dust, loose coal or coal dust in the back entries would add fuel to the flame.
In citing a violation, the inspector should describe fully the conditions and practices, such as the location, dimensions, etc. Imminent danger conditions normally can be considered to exist when accumulations of coal dust, float coal dust, loose coal, and other combustible materials are exposed to probable explosion and fire ignition sources, and the conditions observed could reasonably be expected to cause death or serious physical harm to a miner if normal mining operations were permitted to proceed in the area before the dangerous conditions are eliminated.  There may be times when the inspector's interpretation of what is an accumulation of float coal dust, loose coal and coal dust and/or other combustible materials will differ with the opinion of others.  However, the inspector should base his decision upon the facts surrounding each occurrence, and document such facts as the dimensions, type, specific location, and all other related factors.  The inspector's decision as to what is an accumulation must be an objective one based on the facts or circumstances surrounding each occurrence.

Experience has demonstrated that the loading of loose coal caused by sloughing ribs creates a hazardous condition in that the pillar size can be substantially reduced and the width of the entry or room dangerously increased; therefore, such loose coal shall not be considered accumulations of combustible material if such material is rendered inert by heavy applications of rock dust.  However, such loose coal shall not be permitted to accumulate in the roadways or outby timberlines.

75.400-2 Cleanup Program
The program referred to by this Section shall be outlined in written form and shall be available to the Secretary or his authorized representative.  Consideration shall be given as to whether the program is effective, systematic, and is adequate under normal circumstances to control dangers from float dust, dust and loose coal along beltways, and dust and loose coal in the area between the face and loading point.  Observance of quantities of inadequately inerted loose coal or coal dust throughout various areas of the mine during a single inspection, or from shift to shift, or from day to day, should be taken into consideration and is a strong indication that a systematic and effective cleanup program is not in operation.

75.402 Rock Dusting
If worked-out areas which are not rock-dusted are near active working areas and the rock-dusting can be done safely, they shall be rock-dusted in accordance with this Section.  It would be unwise for an inspector to require rock-dusting of worked-out areas if miners would be exposed to potentially serious hazards such as bad roof, poor ventilation, etc.  Nevertheless, where high-pressure rock-dusting machines are available, inspectors shall require that these machines be used at the outby edges of abandoned areas to rock-dust as much of the area that can be done safely.

75.403 Maintenance of Incombustible Content of Rock Dust
Section updated July 2015\ Release V-51
Provided the percentages of incombustible content specified in this Section are maintained, rock dust may be applied wet (including foam rock dust). Wet rock dust shall be limited to rib and roof surfaces in the face areas and shall not be used for redusting mine surfaces. In such applications, only limestone or marble dust which meets the specification contained in Section 75.2(d) shall be used.
The application shall be at the rate of not less than 3 ounces of dust per square foot of surface, and shall be by a mixture of not more than 6 to 8 gallons of water with 100 pounds of dust, whether by premixed slurry or by mixing at the nozzle of a hose to assure that the mixture is not too fluid and that sufficient dust adheres to the surfaces. After the wet rock dust dries, additional dry rock dust shall be applied to all surfaces to meet applicable standards. Wet rock-dusting of ribs and roof does not eliminate the necessity for dry rock-dusting the floor.

Subpart F .... Electrical Equipment - General

75.503 Permissible Electric Face Equipment; Maintenance
Splices shall not be made in external wiring of permissible equipment except in connection boxes as originally approved. However, splices may be made in cables of intrinsically-safe circuits, provided the splices are made in splice boxes (not necessarily explosion-proof) or the cables are joined together by proper connecting plugs. Longwall motor and shearer cable policy is located in Volume II under 18.20. Pump motor cables' policy is located in Volume II under 18.20.

Flame-resistant cable repair sleeves are acceptable for repair of conduit hose under the following conditions:

1. Minimum wall thickness of conduit and sleeve must be 1/4 inch. If a section of damaged conduit is missing, this wall thickness may be achieved by placing a section of conduit under the sleeve before shrinking.

2. If a sleeve is used to join two pieces of conduit, the conduit ends must be cut at an angle between 30 degrees and 45 degrees from the center line of the hose and butted together tightly.

All circuit breakers and other overload-protection devices shall be maintained in proper working condition. (Opening the circuit breaker on board the machine should deenergize the complete machine, except the methane monitor.)

An approval plate should be attached to the machine; however, a missing approval plate does not constitute a violation.

Where it is determined that a unit of equipment was shipped after January 1, 1981, and the load-locking valves are not maintained, enforcement action should be taken under this Section, for failure to maintain the electric face equipment in permissible condition. Load-locking valves provided on equipment shipped from the manufacturer prior to January 1, 1981, shall also be maintained. Appropriate enforcement action under Section 75.1725(a) should be taken if these load-locking valves are not being maintained.

75.507 Power Connection Points
This Section does not prohibit the installation of high-voltage cables, control cables or telephone cables in return air.Furthermore, splices may be made in such cables if they are made in accordance with the applicable requirements of Sections 75.514, 75.603, 75.604, 75.804, and 75.810. However, unless high-voltage couplers are certified as explosion-proof,this Section prohibits their use in return air.

75.507-1 Electric Equipment Other Than Power-Connection Points;
Outby the Last Open Crosscut; Return Air; Permissibility Requirement

"Return air," for the purpose of this Section, means air that has been used to ventilate any working face 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. "Permissible," as used in this Section, means equipment to which an approval plate, label, or other device is attached as authorized by the Secretary and which meets requirements prescribed by the Secretary for the construction and maintenance of such equipment and are designed to assure that such equipment will not cause a mine explosion or a mine fire. Consequently,this Section prohibits the use, in return air, of any unit of equipment or any device which has not been approved as permissible or certified as explosion-proof by MSHA. This Section also prohibits the use in return air of approved or certified equipment which is not maintained in permissible condition. Furthermore, this Section prohibits nonpermissible-type electric equipment on the return air side of a permanent stopping, even if it is placed directly against the stopping with a block removed.

An approved or certified component which is maintained in permissible condition may be installed in return air if all nonpermissible components are installed in intake air. For instance, a certified explosion-proof motor that was formerly used on a permissible machine may be installed in return air if the motor is installed and maintained in permissible condition and all nonpermissible components, such as open switches and controllers, are installed in intake air.

Section 75.1105, provides that air currents used to ventilate structures or areas enclosing electrical installations, including battery charging station, "...shall be coursed directly into the return." To comply with 75.1105, all components of battery-charging stations at stoppings or regulators that separate intake and return air courses must be located on the intake side of the stoppings or regulators. In addition, the intake split of air ventilating battery-charging stations must be coursed over the equipment and directly into the return.

Sections 75.507 and 75.507-1(a) also address the location of electric equipment in intake and return air. Section 75.507provides that "except where permissible power-connection points are used, all power-connection points outby the last open crosscut shall be in intake air." Section 75.507-1 further provides that "all electric equipment, other than power-connection points, used in return air outby the last open crosscut...shall be permissible...." Electric equipment,such as a battery charger, which is not permissible must be used in intake air.

75.508 Map of Electrical System
Stationary electric equipment in connection with the mine electrical system shall be shown on the mine map by the use of symbols, print, or well-defined overlays, and shall be kept at the mine in a location that is accessible to the miners in the mine.

Equipment being used on the working section is not considered stationary equipment and need not be shown on the map; however,the circuit supplying power to the section should be identified.

75.508-2 Changes in Electrical System Map; Recording
"Completion of such changes" means when the equipment is energized and returned to service.

75.509 Electric Power Circuit and Electric Equipment;Deenergization
A violation of this Section shall be cited only when electrical work is being performed on an energized machine. A violation of Section 75.1725(c) shall be cited if mechanical work or lubrication work is being performed on an energized machine.

For the purpose of this Section, troubleshooting or testing includes the work of locating electrical, hydraulic, or mechanical problems on a machine and the work of verifying that proper repairs have been performed. Troubleshooting or testing does not include the repair of the electrical, hydraulic, or mechanical problems. When troubleshooting and/or testing an energized machine, extreme caution must be taken to prevent inadvertent contact with energized parts in close proximity and assurance that equipment will not be accidentally started.Examples of tests which may be performed with equipment energized are:

  1. Voltage and current measurements;

  2. Pressure and volume measurements on hydraulic systems; and

  3. Mechanical clutch setting.
Sections 75.1720(c) and 77.1710(c) require that protective gloves be worn by miners when they are performing work "which might cause injury to the hands," unless the gloves would create a greater hazard by becoming entangled in the moving parts of equipment. As the accident and injury data associated with working on energized circuits and equipment clearly indicate,this type of work presents a significant risk of hand injury.Therefore, gloves, in accordance with Sections 75.1720(c) and 77.1710(c), are required whenever miners troubleshoot or test energized electric power circuits or electric equipment. Work gloves in good condition are acceptable for troubleshooting or testing energized low- or medium-voltage circuits or equipment.

This Section does not prohibit installation of temporary guarding on an energized trolley wire provided:

  1. It is not necessary to remove the trolley wire from the clips or hangers to install the temporary trolley guarding;

  2. It is not necessary to wrap the guarding material around trolley wire;

  3. The temporary trolley wire guard is specifically designed for the purpose so that it can be easily and safely installed without exposing the miner to a shock hazard; and

  4. The miner who installs the temporary wire guard has received training in the hazards of energized trolley wires and in the safe method for installing the temporary trolley wire guards used at the mine. All miners who perform tasks in proximity to energized trolley wires (e.g., motormen, brakemen, supply crewmen, trackmen, wiremen, and miners who rock dust and roof bolt in the track entry) should receive this training as part of the training they receive under the applicable provisions of Part 48.
When permanent guarding is to be installed on a trolley or trolley feeder wire by wrapping guarding material around the conductor or when it is necessary to remove the trolley or trolley feeder wire from the hangers or clips for installation of the guarding material, the circuit shall be deenergized before such work is performed.

75.510 Energized Trolley Wires; Repair
This Section contains exceptions to Section 75.509 and Section 75.511. These exceptions permit a miner who is properly trained(see Section 75.510-1) and who wears approved and tested insulated shoes and wireman's gloves to repair energized trolley wires, even though the miner is not a qualified electrician within the meaning of Section 75.153.

For the purpose of this Section, the term "trolley wires" would also include trolley feeder wires and cutout switches used in trolley circuits. For the purpose of this Section, the word"repair" includes work such as straightening kinks in trolley wires and replacing trolley wires and trolley feeder wires in the clips or hangers, but does not include work such as installing or removing trolley wires, trolley feeder wires or trolley cutout switches.

Wiremen's gloves used to satisfy the requirements of this Section shall have a manufacturer's rating of at least 750 volts. Rubber boots satisfy the requirements of this Section, provided they are maintained free from cuts, holes and excessively worn places.Leather footwear rated for electrical hazards should not be used to satisfy the requirements of this Section because leather shoes can become highly conductive in the normally damp or wet environment of underground coal mines. Insulated footwear and wireman's gloves shall be closely inspected for damage and defects before each period of use. Damaged or defective gloves and footwear shall be replaced before repairs are performed on energized trolley wires.

75.510-1 Repair of Energized Trolley Wires; Training
The training required by this Section shall be provided in accordance with the applicable provisions of Part 48.