Mining Topic: Explosions
What is the health and safety problem?
Explosions in underground mines and surface processing facilities are caused by accumulations of flammable gas and/or combustible dust mixed with air in the presence of an ignition source. While much progress has been made in preventing explosion disasters in coal mines, explosions still occur, sometimes producing multiple fatalities.
What is the extent of the problem?
In the years from passage of the landmark 1969 Federal Coal Mine Health and Safety Act to 2001, the number of fatalities due to underground coal mine explosions had exhibited a general downward trend. From 2001 onward, however, the industry has recorded 59 fatalities and 7 injuries from these occurrences. And, from 2006 to 2011, mine explosions accounted for nearly one-quarter of mining-related deaths. Many of these recent explosions have been due to methane ignitions in abandoned workings that breached the mine seals and extended into the active areas or a deficiency in rock dust related to poor rock dusting practices.
How is OMSHR addressing the problem?
The Office of Mine Safety and Health Research (OMSHR) conducts research to identify and then mitigate the causes of underground coal mine explosions. Research strategies include eliminating ignition sources, minimizing methane concentrations and coal dust accumulations, applying proper dispersible rock dust in sufficient quality at all locations, using supplemental protection such as passive and active barriers to suppress propagating explosions, understanding the science of explosions, properly designing and evaluating the strength of ventilation structures, and properly managing sealed areas.
Four key components of this explosions research program include:
- intramural engineering control research;
- technology transfer and information dissemination;
- funding of extramural research projects; andimprovements to rock dust specifications, rock dusting practices, and
- sampling methods.
OMSHR's ongoing intramural research addresses methane and coal dust explosion problems in the coal mining industries. Laboratory and/or mine-site research is conducted to identify and evaluate improved rock dusting practices and sampling methods and new technologies and structures to mitigate underground coal mine explosions. Control technologies proven to be successful then undergo final evaluation at operating mine sites.
OMSHR is also conducting research to advance the understanding of methane sources, migration and control strategies, interactions of sealed and active gobs with working sections, and improved ventilation methods through a complete understanding of longwall bleeder system effectiveness. A combination of field studies and numerical modeling methods are being used to identify gas migration pathways into working areas, sealed and active gobs, and to mitigate gas emissions using effective engineering controls.
What are the significant findings?
Publications include two documents: “Recommendations for a New Rock Dusting Standard to Prevent Coal Dust Explosions in Intake Airways” and “NIOSH Hazard ID (16): Non-Conforming Rock Dust.” Based on results of an extensive coal dust particle size survey and large-scale explosion testing, NIOSH recommended a new standard of 80% total incombustible content be required in the intake airways of bituminous coal mines in the absence of methane. After NIOSH research revealed that there are finer coal particles in intake airways, the Mine Safety and Health Administration (MSHA) revised the Title 30 Code of Federal Regulations 75.403 for maintenance of incombustible content of rock dust by increasing the incombustible requirement from 65% to 80% in intake airways. Likewise, after NIOSH published its Hazard ID, rock dust manufacturers, suppliers, and mine operators each implemented, as necessary, quality control measures to ensure that the rock dust used in the mines for explosion suppression met the size specifications detailed in the rock dusting standard.
Current research is focusing on identifying possible shortcomings of dust assessment and procedures for detecting and abating explosible accumulations. Highlights include:
- The Coal Dust Explosibility Meter (CDEM), which gives a real-time reading of the explosibility of mine dust so operators can maintain adequate levels of incombustible content (rock dust) to prevent propagating coal dust explosions.
- An online “Webinar and Workshop on Preventing Coal Dust Explosions in Underground Coal Mines.”
What are the next steps?
OMSHR funds extramural research in areas that can have a direct impact on the reduction of explosions in mining operations. These extramural research activities include advanced numerical modeling to determine the potential for methane deflagration-to-detonation transitions (DDT) in sealed and active areas of the mine; the strength of mine seal designs and materials; the design and manufacture of a MEMS component (micro-electro-mechanical system) into specialized electronics to measure methane levels, and development of a remote methanometer for detecting and mapping potentially explosive methane accumulations.
OMSHR has identified a dispersibility problem involving the effectiveness of rock dust within the mine entries when that rock dust has become wet and then dried; i.e., the rock dust forms a hardened cake that will not disperse. In order to prevent rock dust from caking, OMSHR is investigating the use of additives that would enable the rock dust to maintain its dispersibility. These additives allow the rock dust to maintain dispersibility, but must not contribute to the explosion or introduce a health hazard to the mine personnel. The additive-enhanced rock dust should also be able to be distributed using the existing rock dusting equipment.
OMSHR will continue to evaluate new rock dusting techniques as they evolve with the industry. Techniques, such as foamed dusting, will be assessed to ensure that the new methods provide at least the same level or better explosion prevention as the currently accepted practices.
Noteworthy Publications & Products
- A Centennial of Mine Explosion Prevention Research (2010-02)
This paper provides a brief historical overview of full-scale mine explosion research conducted primarily at the USBM, now the National Institute for Occupational Safety and Health (NIOSH).
- Alternative Methodologies for Evaluating Explosion-resistant Mine Ventilation Seals (2003-10)
Discusses the evaluation of a seal evaluation method, based on a hydrostatic pressure loading concept, for in-situ testing of seals in an operating mine.
- Coal Dust and Methane (2008-06)
This article describes the Coal Dust Explosibility Meter (CDEM), a hand-held instrument developed by NIOSH, which uses optical reflectance to measure the explosibility of a rock dust and coal dust mixture, which is now commercially available.
- Composition Change Model for Sealed Atmosphere in Coal Mines (2010-06)
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.
- Design and Analysis of a New Method to Test Mine Seals (2009-10)
This report describes a new seal testing program that will provide essential validation data for mine seal analysis and design methods.
- Explosion Effects on Mine Ventilation Stoppings (2008-11)
A joint MSHA and NIOSH study simulated actual coal mine explosion accidents to evaluate blast effects on typical U.S. mine ventilation stoppings, and presents construction and testing methods, explosion test data, and post-explosion conditions.
- Explosion Pressure Design Criteria for Seals in U.S. Coal Mine - An Update on Work at NIOSH (2009-11)
This paper seeks to encourage scientific discussion among international peers since preventing explosions within sealed areas is of interest to underground coal operators and regulators.
- Methods for Controlling Explosion Risk at Coal Mine Working Faces (2007-09)
This paper reviews how simultaneous application of three basic elements reduces the methane explosion hazard at coal mine working faces: (1) adequate ventilation, (2) regular monitoring of gas concentrations, and (3) elimination of ignition sources.
- NIOSH Hazard ID 16 - Non-Conforming Rock Dust (2011-10)
In September 2011, as part of an ongoing investigation, NIOSH determined that rock dust not conforming to the requirements in 30 CFR Part 75.2 for particle size and caking properties is being used in U.S. underground coal mines.
- Recommendations for a New Rock Dusting Standard to Prevent Coal Dust Explosions in Intake Airways (2010-05)
This NIOSH report presents the results of extensive in-mine coal dust particle size surveys of dust samples collected from intake airways in 61 U.S. coal mines, representing all 10 MSHA bituminous Coal Mine Safety and Health Districts.