Mining Topic: Ventilation Overview

Airflow measurements in mines.

What is the health and safety problem?

Accumulations of explosive methane gas in active and inactive workings constitute the greatest safety risk to the underground coal miner. A mine's primary ventilation system is designed to dilute and control these accumulations. However, increased production from larger longwall panels is challenging the limits of modern and accepted ventilation system designs to maintain safe working conditions.

What is the extent of the problem?

Adequate control of methane is particularly acute in longwall operations using bleeder ventilation systems, especially at the tailgate corner where methane accumulations are most likely to occur. Also, severe changes in atmospheric pressure may cause increased interaction with sealed areas of the mine that can overwhelm the normal ventilation system.

How is OMSHR addressing this problem?

The Office of Mine Safety and Health Research (OMSHR) developed models to predict methane emissions at underground coal mines and the effects of various methane drainage techniques on emission rates. In addition, ventilation models were used to investigate the effects of larger panels and increased production rates on bleeder ventilation system designs to control methane accumulations on the longwall face and at the tailgate corner.

OMSHR also conducted underground field tests to identify airflow paths in the inaccessible portions of a longwall gob and its associated bleeder system. This work provided critical knowledge on the movement of methane gas and airflow, particularly at the longwall tailgate corner, during various phases of panel extraction. Finally, monitoring of outgassing events from a large sealed gob was used to determine seal leakage rates and changes in gas concentrations in the ventilation air during periods of low barometric pressure.

What are the significant findings?

The research demonstrated that the movement of ventilation air and methane gas through a longwall bleeder ventilation network can vary significantly depending upon the configuration of the network. A bleeder utilizing an offset design to handle differing panel lengths was able to maintain bleeder and airway continuity and keep methane concentrations at safe levels as longwall panel length changed. However, use of this design can greatly increase the complexity of the ventilation system.

OMSHR research also identified the importance of preventing the complete closure of the tailgate entry closest to the gob. If sufficient standing support is installed in this entry, then methane can more effectively move into the bleeder entries, preventing methane buildup at the tailgate corner of the face.

The research also showed that face advance rates should be limited for specific face ventilation airflow quantities and degasification efficiencies, depending on methane emissions into the active longwall area.

What are the next steps?

Research will continue to quantify the effect of ventilation system design on the control of methane, particularly at the longwall tailgate corner. Work will also evaluate support methods to maintain the integrity of the tailgate entry closest to the gob and to assess the robustness of the ventilation system to handle fluctuations in gob gas emissions during periods of low barometric pressure.

Noteworthy Publications & Products

• A CART Technique to Adjust Production from Longwall Coal Operations under Ventilation Constraints (2012-09)
  The CART-based model that is given in this paper can be used to predict methane emission rates and to adjust operation parameters under ventilation constrains in longwall mining.
• A New Leak Test Method for Enclosed Cab Filtration Systems (2012-08)
  AbstractA new test method has been developed by the National Institute for Occupational Safety and Health (NIOSH) and Clean Air Filter (CAF) for quantifying the outside air leakage into environmental cab filtration systems.
• An Analysis of Reservoir Conditions and Responses in Longwall Panel Overburden During Mining and its Effect on Gob Gas Well Performance (2012-08)
  NIOSH conducted a cooperative research study to provide direct measurements of changing reservoir conditions in longwall panel overburden.
• Development of a Gas Monitor Simulator and Mine Rescue Contest Field Trials (2012-08)
  NIOSH researchers completed field trials during coal mine rescue contests using simulated gas detectors in place of placards, and demonstrated that the newly developed GMS device may be used with no adverse impact on team contest performance.
• Field Study of Longwall Coal Mine Ventilation and Bleeder Performance (2012-08)
  To assess the effectiveness of commonly applied ventilation strategies for improving air distribution and ventilation controls to meet statutory requirements.
• Guidelines for the Control and Monitoring of Methane Gas on Continuous Mining Operations (2013-03)
  This NIOSH publication demonstrates how existing and new engineering controls can be used to reduce face methane levels.
• Guidelines for the Prediction and Control of Methane Emissions on Longwalls (2013-03)
  In this report, several practical guidelines are recommended for controlling longwall coalbed methane. All predictions are based on determinations made for the Pittsburgh Coalbed in southwestern Pennsylvania.
• Predicting Methane Emissions from Longer Longwall Faces by Analysis of Emission Contributors (2012-08)
  NIOSH conducted a longwall methane emission and mining time study at a Pittsburgh Coalbed mine to predict emissions from a longer face, and developed and applied mathematical formulas and constants to characterize four emission contributors.
• Prediction of Longwall Methane Emissions and the Associated Consequences of Increasing Longwall Face Lengths: A Case Study in the Pittsburgh Coalbed (2012-08)
  NIOSH conducted a study with the goal of characterizing methane emissions from increasing face lengths in the Pittsburgh Coalbed and providing a method of predicting emissions increases from longer faces and of planning for more methane control.
• The Borehole Monitoring Experiment: Field Measurements of Reservoir Conditions and Responses in Longwall Panel Overburden During Active Mining (2012-08)
  This paper describes the results of a NIOSH borehole monitoring experiment (BME) on an active longwall panel.
• The Effect of Ventilation on Spontaneous Heating of Coal (2012-08)
  Study results of the role of various ventilation rates in the spontaneous heating of coal in underground mines found that there is an optimum ventilation flow to produce the maximum rate of temperature rise at the critical ambient temperature.