Mining Topic: Monitoring Ventilation Parameters and Accumulations of Combustible Gas

Ultrasonic anemomemeters placed in a mine entry to measure air flow.

What is the health and safety problem?

The proper control and distribution of ventilation air in working areas of underground mines is crucial to the health and safety of mine workers. Many underground coal mines cover vast areas where workers are not located. Continuous knowledge of the ventilation system status, along with information on the presence of methane or products of combustion from fires, is critical for detecting and correcting problems in the mine atmosphere in their earliest stage.

To this end, monitors can be used in targeted areas of the mine to collect environmental data on levels of combustible gas or products of combustion that may provide an early indication that heating is in progress. In addition to levels of combustible gas, monitoring airflow velocity and direction continuously can improve the safety of the underground workforce. However, continuous measurements of air velocity may not always provide accurate assessments of ventilation conditions, as these values can change rapidly depending on measurement location and airflow conditions.

What is the extent of the problem?

Under MSHA regulations for atmospheric monitoring systems, monitoring in active mining areas usually involves methane and products of combustion around electrical and belt installations. Monitoring of ventilation airflow velocity is less common, with little information gathered on airflow direction. Large portions of many underground operations may not be continuously monitored for airflow velocity and methane accumulations.

How is OMSHR addressing the problem?

The Office of Mine Safety and Health Research (OMSHR) is investigating the use of ultrasonic velocity instrumentation in the underground mine environment. Ultrasonic anemometers are known for their accuracy, capability to measure low airflows, continuous measurement characteristics, and ability to provide a directional sign to the air velocity. This can be especially beneficial in situations with low air velocity in that airflow reversals may occur.

Current OMSHR research efforts are focused on the installation of integrated airflow and methane monitors in active areas of underground coal mining operations. This work is identifying specific sampling protocols for these devices and is assessing the behavior of these instruments in relation to the presence of airway obstructions such as personnel and equipment. OMSHR is also identifying potential applications and limitations of integrated air velocity and methane monitoring systems and developing guidelines to interpret air velocity and methane monitor outputs.

What are the significant findings?

OMSHR laboratory testing showed that air velocity readings from continuous recording instruments correlated well with those obtained using standard measurement techniques. Obstructions upstream of a continuous recording anemometer led to noticeable impacts on air velocity readings, suggesting that movement of these obstructions in the ventilation airstream could be correlated to changes in instrument readings. In conditions with steady airflow, recorded velocities showed little variation over time, whereas turbulent conditions produced greater variability. This work also identified the minimum number of instrument readings needed to obtain an accurate assessment of ventilation air velocity in both steady and turbulent airflow conditions.

What are the next steps?

Future work in this area will deploy sensors in underground coal mine environments to collect long-term data on airflow velocities and directions and on methane levels. This information will be analyzed for any trends that suggest the development of ventilation conditions conducive to accumulations of methane gas.

Noteworthy Publications & Products

• Composition Change Model for Sealed Atmosphere in Coal Mines (2012-08)
  This paper presents a mathematical model based on the conservation of mass principle describing the flow of air (nitrogen and oxygen), methane, and carbon dioxide into and out of a sealed atmosphere and time-dependent changes in gas concentration.
• Methods to Determine The Status of Mine Atmospheres - An Overview (2012-08)
  This paper serves as an overview to remind and/or instruct readers about gas-sampling methodologies and gas analyses to assist in determining the status of underground atmospheres.