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Engineering Controls Database

Best Practices for Dust Control in Coal Mining – Continuous Mining Operations – Blowing Face Ventilation

Respirable dust exposure has long been known to be a serious health threat to workers in many industries. In coal mining, overexposure to respirable coal mine dust can lead to coal workers’ pneumoconiosis (CWP). CWP is a lung disease that can be disabling and fatal in its most severe form. In addition, miners can be exposed to high levels of respirable silica dust, which can cause silicosis, another disabling and/or fatal lung disease. Exposure to coal mine dust may also increases a miner’s risk of developing chronic bronchitis, chronic obstructive pulmonary disease, and pathologic emphysema.

Once contracted, there is no cure for CWP or silicosis. The goal, therefore, is to limit worker exposure to respirable dust to prevent development of these diseases.
CWP contributed to the deaths of 10,406 U.S. miners during 1995–2004 [NIOSH 2008]. Pneumoconiosis continues to be a very serious health threat to underground coal mine workers.

The velocity and quantity of face ventilating air are important factors for controlling respirable dust exposure of the continuous miner operator. A good ventilation plan consists of sufficient mean entry air velocity to confine dust near the face and/or direct it toward the return entry with high enough quantity for diluting generated respirable dust. The two ventilation schemes most widely used for underground coal mining are blowing and exhausting. There are advantages and disadvantages to both systems as they relate to face worker dust exposure.
Blowing Face Ventilation. When blowing ventilation is used, intake air is delivered to the face of the working entry by blowing it from behind line brattice or tubing. The clean air is blown toward the face and sweeps the dust-laden air toward the return entries. This system allows the continuous miner operator to be positioned in the clean discharge air at the end of the blowing curtain or tubing. Although this method effectively sweeps dust and methane from the face, it also positions mobile equipment operators (e.g., shuttle car operators) and roof bolter operators working downwind in return air. Continuous miner operator movement is restricted due to the need to be positioned in the discharge air at the end of the curtain or tubing. The following best practices will reduce dust exposure on blowing ventilation sections:

• The operator should be positioned in the mouth of the blowing line curtain with intake air sweeping from behind (see Figure 1). The operator should not proceed past the end of the line curtain. If the operator must be on the return side of the curtain, some of the intake air should be bled over the line brattice to provide fresh air to the operator. Good communication with shuttle car operators is essential because visibility can be a problem depending on where the continuous miner operator is standing.

• According to MSHA, when it is necessary for the operator to move from the clean air position (end of the curtain), the operator should allow the dust-laden air to clear the entry and stop the scrubber before moving.

• According to MSHA, when aligning the continuous miner to square a face, the operator should position the machine and then return to the end of the curtain before coal cutting resumes. This reduces the potential for injury.

• Brattice discharge velocities exceeding 800 feet per minute (fpm) have better penetration to the face and thus better dilution of dust and methane. When brattice discharge velocities are less than 400 fpm, there is little difference in performance between blowing and exhausting ventilation [Luxner 1969].

• Scrubber discharge must be on the opposite side of the line brattice to allow scrubber exhaust to discharge directly into return air.

• The air quantity provided by the line curtain should be limited to 1,000 cubic feet per minute (cfm) over the scrubber capacity. Air quantities exceeding 1,000 cfm over the scrubber capacity can overpower the scrubber and push dust-laden air past the scrubber inlets [Schultz and Fields 1999]. Therefore, MSHA typically requires that the airflow entering a cut be equal to or exceed the scrubber airflow by no more than 1,000 cfm and must be measured with the scrubber off.

• Excess air velocity may be reduced by flaring out the line curtain at the end to lower the velocity of the air emerging from behind it or by pulling the line curtain back slightly to prevent overpowering the scrubber [Schultz and Fields 1999].

Figure1 - Schematic of a blowing ventilation system.

Figure1 - Schematic of a blowing ventilation system.
NIOSH [2010]. Information circular 9517. Best practices for dust control in coal mining. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2010-110.

Luxner JV [1969]. Face ventilation in underground bituminous coal mines. Airflow and methane distribution patterns in immediate face area: line brattice. Washington, DC: U.S. Department of the Interior, U.S. Bureau of Mines, RI 7223.

NIOSH [2008]. Work-related lung disease surveillance report, 2007. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2008143a.

Schultz MJ, Fields KG [1999]. Dust control considerations for deep cut mining sections. SME preprint 99-163. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc.
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