NIOSH Research in Coal Dust and Explosions 


*Giirhmca R, CashdollarK, Volkwein J, **RupprechtE 


*Pittsburgh Research Laboratory, NIOSH 


**Rupprecht&Patashnick Co., Inc. 


Abstract: The National Institute for Occupational Safety and Health (NIOSH) mining research program at the Pittsburgh 

Research Laboratory (PRL),includes the areas of coal mine dust control and monitoring, and explosion prevention. One 

very important project at PRL is development of a continuous recording person-wearable respirable dust monitor. This 

Personal Dust Monitor (PDM) is a respirable dust sampler and gravirnetric -equivalent analysis instrument that is part of a 

belt-worn mine cap lamp battery unit. Prototypes were successfully t ested in the laboratory and in four underground coal 

mines. The PDM testing demonstrated that it was convenient to wear and use, robust, and provided accurate and timely data. 

NOSH is also conducting research in the program area of coal mine explosion p revention, suppression, and mitigation. 

Aspects of this research program include: full scale explosion research, laboratory scale research, 6ictional ignition of 

methane, mine ventilation seal construction, prediction of coal mine methane emissions, mine monitoring systems, flame 

cutting and welding operations, spontaneous combustion, and emergency preparedness. 

Introduction 

In 1996 the U. S. Bureau of Mines (USBM) was closed, however, the mining health and safety research 

function was absorbed into the National Institute for Occupational Safety and Health (NIOSH). NIOSH has an 

extensive research program in mining health and safety at the Pittsburgh Research Laboratory (PRL), including 

coal mine dust and explosion research. The focus in dust research is on the development of dust control and 

dust monitoring technologies to reduce and measure worker exposure to respirable coal and silica dust. The 

ultimate goal of this dust research is to eliminate pneumoconiosis in miners. The first part of this paper will 

discuss the current development of a continuous recording person wearable respirable dust monitor. The 

remainder of the paper will describe the current NIOSH coal mine explosions research program, which aims to 

eliminate fatalities from explosions in underground coal mines. 

Personal Dust Monitor (PDM) 

The PDM is a respirable dust sampler and a gravimetric-equivalent analysis instrument that is integrated in a 

belt-worn mine cap lamp battery. The main components of the device include a cap lamp, sample inlet located 

on the end of an umbilical tube, a belt-mounted enclosure containing the respirable dust cyclone, sampling, and 

mass measurement system, and a charging and communication module used to transmit data between the monitor 

and a PC while charging its lithium ion batteries for the next shift. Figure 1 illustrates the components typically 

carried by the miner. The PDM is designed to withstand the harsh conditions found in the mine environment and 

meets MSHA intrinsic safety type approval requirements. 

At the heart of the TEOM mass sensor is a hollow tube called the tapered element that is clamped at its base 

and is free to oscillate at its narrow end. An exchangeable filter cartridge mounted on its narrow end collects the 

respirable particles contained in the air stream that passes from the entrance of the mass sensor through the 

tapered element. Electronic components positioned around the tapered element cause the tube to oscillate at its 

natural (or resonant) frequency. As additional mass collects on the sample filter, the natural oscillating frequency 

decreases as a direct result. This approach uses first principles of physics to determine the mass change of the 

filter, and is not subject to uncertainties related to particle size, color, shape or composition of the collected 
aerosol. 

Fig1 : Major components of the PDM. Fig 2: Miner Wearing PDM. 

Built-in sample conditioning to remove excess moisture minimizes the PDM response to airborne water 

droplets. The PDM determines the mass concentration of respirable dust in the mine environment by dividing 

the mass (as determined by the frequency change) collected on its filter over a given period of time by the volume 

of the air sample that passed through the system during the same time frame. 

Laboratory dust chamber testing was conducted at the PRL. We first detded if the PDM mass 

measurement was accurate when compared to the filter mass measurement method using a defined accuracy 

criterionl. We also compared the PDM to the existing personal sampler method of dust measurement using a 

more complex study design that accounted for the PDM's use of a different cyclone to define the respirable dust 

fraction2. This bias analysis procedurei was used to determine if the Higgins-Dewell (HD) cyclone used in the 

PDM had less than or equivalent bias compared to the Don -Oliver (DO) cyclone, used with the current sampling 

system, when using either the Mining Research Establishment (MRE) or International Standards Organization 

(ISO) definition of respirable dust. 

The average mass of 3 individual gravimetric samplers in each time group was used to determine the dust 

mass during a specific test-time interval. We selected test-time intervals to achieve filter mass target loadings 

over the range of about 0.5 to 4 mg. As mass loaded onto the samplers with time, groups of gravimetric 

sampling pumps were turned off at predetermined mass loadings. The mass loading then determined the 

test-time interval. This procedure resulted in 4 test-time intervals with averaged dust mass that was compared to 

the measured mass, recorded in each PDM data file. This test was replicated 3 times with various mass loadings 

to yield a total of 12 measurements. A total of 5 different types or sizes of coal dust were tested in this manner. 

A total of 316 laboratory comparisons of PDM to reference samplers were conducted. In addition, 60 

laboratory determinations of cyclone bias to IS0 and MRE definitions were conducted. Bias, precision, accuracy, 

and confidence limit calculations for the overall data showed that there is a 95% confidence that the individual 

PDM measurements were within +25% of the reference measurement according to Kennedy's method. From the 

confidence interval data we can predict that 95% of hture random samples will be within *25% of a reference 

sampler measurement. All laboratory data for various coal types and size distributions are combined in the plot 

in Figure 3. The linear regression of individual pairs of data supports the accuracy analysis. 
0 5 1.O 1.5 2.0 

Reference concentration (ng/ni3) 

Fig 4. All mine data. 

0 1 2 3 4 5 6 7 

Reference mass (mg) 

Fig 3. All laboratory data. 

The laboratory work specifically assessed the performance of the new dust monitor by comparing the 

performance to currently used personal samplers in a two-step manner. The first step demonstrated that the PDM 

accurately measured mass according to accepted criterion. The second step showed that the HD cyclone was 

better than the DO cyclone in meeting both the IS0 and MRE def~tionsof respirable dust. The combination of 

these two results leads to the conclusion that the PDM is equivalent or better than the currently used personal 

sampler in measuring coal dust in the laboratory. 

In-mine testing used pair-wise testing to partially take into account the increased variability associated with 

personal sampling in mining conditions and examined the mine worthiness issues of the instrument when worn by 

miners performing their normal duties. Limited testing was conducted for 5 shifts in each of four coal mines. 

This testing compared the end-of-shift gravimetric concentration measured by the PDM to the end-of-shift 

gravimetric concentration measured with a single reference filter sampler using a HD cyclone and an analytical 

balance. 

Mine testing was conducted in 4 coal mines in different coal producing regions of the U.S. A total of 72 

in-mine comparisons of PDM to reference samplers and 40 companion determinations of cyclone bias to IS0 and 

MRE definitions were conducted. While additional shifts of data were successfully measured with the PDM, not 

all were paired with valid reference comparison samples. Figure 4 shows the regression analysis for the paired 

data. 

An intraclass correlation coefficient (ICC) statistical test for absolute agreement was computed for the 

overall mine data. The ICC between the PDM and reference sampler was found to be equal to .93 [F-value for 

two-way mixed effects model = 29.99, p < .0001; 95% CI (.90, .96)]. An ICC of .80 is considered good 

agreement, thus these data demonstrate excellent absolute agreement between the PDM and reference sampler. 

These results suggest that the two samplers could be considered interchangeable. 

The timely PDM dust exposure data provides information that can result in quicker recognition of the failure 

of engineering dust controls. This type of information enables both miners and management to prevent 

overexposure to coal mine dust. The information also showed how actions and equipment effect a miner's dust 

exposure. Miners quickly learn how to better reduce their dust exposures by minimizing certain actions and by 

better positioning themselves during given activities. 
USA Coal Mine Explosion Research at NIOSH 

Due in large part to the hlgh number of miner fatalities and incidents of disastrous coal mine explosions early 

in the twentieth century, the government of the United States formed the U. S. Bureau of Mines (USBM) in 

1910. These research findings and implementation of those findings, most notably those related to generalized 

application of rock dust for explosion suppression, along with the implementation of many explosion prevention 

practices and enforcement of explosion prevention and suppression laws and regulations by states and later 

nationally by the Mine Enforcement and Safety Administration (MESA- later the Mine Safety and Health 

Administration, MSHA), led to the significant decline in incidents and fatalities from coal mine explosions 

through that century as shown on figure 5. Indeed, near the end of the 20" Century, it had appeared that coal 

mine explosions had nearly been eradicated from the US coal mining industry (Figure 5). 

However, as can also be noted on figure 6 , recently there has been an alarming reappearance of deadly coal 

mine explosions in the U.S. Bracketed around the September 2001 sentinel event of the explosion at Jim Walter 

Resources (JWR) No. 5 Mine in Alabama (13 fatalities and 3 injuries) was the July 2000 explosion in at the 

Willow Creek Mine in Utah (2 fatalities and 8 injuries) and the McElroy Coal Mine explosion in West Virginia (3 

fatalities and 3 injuries) in January 2003. These events are stark reminders that coal mine explosion incidents 

still take an unacceptable human toll and clearly demonstrate that not all of the problems that can result in US coal 

mine explosions have been solved. Equally disconcerting is that a number of events and changes affecting the 

US coal mining industry that indicate that the risk of mine explosions may increase in the near future. These 

eventslchanges include an ongoing high level of frictional ignition incidents (621yr the last 5 years); the 

impending exodus of high numbers of highly experienced miners, mining professionals, and mining enforcement 

personnel; the depletion of "easy-to-mine" reserves and resultant movement into "difficult", deeper reserves with 

increased amounts of methane; technological and operational changes such as higher mining productivity rates 

and longer and wider longwall panels that compound methane issues; and the persistence of various potential 

ignition sources. 

3.-

@c A 

C <

2 2,000 W 

I

si 

Total fatalities 

2 

4 

0 

0 

n 

z 1.000 3 

2 

z 

w 

0 

z 

=I 

0 

1960 lalo lS20 la30 1940 lS50 1960 1970 1980 

Fig5: Underground U.S. Coal Mining Fatalities 19 -1980 

he successful prevention and mitigation of explosions in mines requires highly efficient programs in all of 

these 7 areas: 1 .) prevention of accumulations of flammable gasesldusts; 2.) isolation and elimination of potential 

ignition sources; 3.) understanding of mine explosion mechanics and parameters; 4.) employment of suppression 

methods and systems; 5.) foolproof examinations and monitoring of mine conditions; 6.) development of 

applicable systems to keep pace with industry changes; and 7.) understanding and knowledge of mining industry 
personnel of all of these factors so that proper actions and reactions are routinely made. The continued 

occurrence of US coal mine explosion events indicates that the systems currently in place to prevent and mitigate 

mine explosions in these areas are either not totally adequate, not keeping pace with the evolving changes in the 

industry, or are disregarded. 

To investigate these issues, the Pittsburgh Research Laboratory (PRL) of NIOSH formed a panel of its 

premier coal mine explosion experts to study the recent mine explosions and identify any areas where the 

explosion prevention, mitigation, or response systems were non-existent or deemed lacking and to propose 

research that could address those areas identified. This study focused on the recent fatal mine explosions noted, 

as well as other non-injury mine explosion and frictional ignition events. The panel examined all aspects of the 

explosion issue to identify the most important and common thread areas which, if addressed successfully, could 

provide a systematic, holistic approach to lowering the risk of mine explosions and resultant fatalities. The results 

of the analyses concluded that, while in retrospect these explosions might not have occurred had certain actions or 

individual reactions been different, many of the prevention, mitigation and response systems were not robust 

enough to reduce the risk to the desired near-negligible levels. The specific areas where knowledge or systems 

were non-existent or lacking were identified and research approaches and methodologies defined to address the 

problem aspects. These results then formed the basis for current NIOSH research in the program area of coal 

mine explosion prevention, suppression, and mitigation. Brief descriptions of selected aspects of this current 

research program area follow. 

INJURIES 

Fig 6: Fatalities and Injuries in U.S. Coal Mines due to Methane Explosions 1980-2004 (YTD) 

Full-Scale LLEM Gasmust Explosion Research 

Full-scale explosion research is conducted by NIOSH at its world class Lake Lynn Experimental Mine 

(LLEM) located 90 km south of the Pittsburgh Research Laboratory. The LLEM is a former underground 

limestone mine and surface quarry which has been developed fo; various mining research activities, but 

principally for explosion research in typical US coal mining geometries and configurations. Current full scale 

explosion research is focusing on key parameters that can influence the transition from a small gas explosion near 

the face to a full-scale propagating dust explosion. Another area of interest is the combustion of large volumes 

of non-uniformly mixed methane, which may present a different risk than the typical face ignition. These 

methane volumes may exist in gob (worked-out) areas of mines through a slow accumulation of methane or in 

working areas due to a more rapid methane outburst. In conjunction with these LLEM full scale explosions tests, 

various aspects of explosion effects on mine structures and objects are being studied to assist in explosion forensic 

investigations. Accurate forensics is an important factor for accurate accident interpretation and follow-up 

recommendations to prevent future occurrences. 
Laboratory Explosion Research 

To supplement and complement the full scale research at LLEM, laboratory scale research is conducted in 

20-liter, 1000-liter, and 1-m3 explosion chambers. This laboratory research is currently providing a better 

understanding of the interactions of coal dust as fuel source and rock dust as a suppression. agent. These 

laboratory studies are also fiu-ther assessing the sizes of coal dust particles that participate in mine dust explosions. 

The laboratory research investigates a much wider range of coal dust types and sizes than can be studied in the 

full-scale research. 

Frictional Ignition Studies 

Frictional heating is the primary cause of methane ignition in coal mines and additional basic research is 

being conducted to understand some key aspects of this source to reduce its occurrence. Laboratory research is 

currently centered on the measurement of the hot-spot temperatures (using infrared technology) and surface areas 

necessary to ignite flammable gases, liquids, dusts, and hybrid mixtures. In addition, the role of adjacent strata in 

contributing to frictional ignitions is being studied. Samples of adjacent and included rock are undergoing analyses 

to assess chemical and mineralogical variations and their relative incendivity potential, using a newly developed 

incendivity apparatus. 

Rapid in-situ method to determine the rock dust content and explosibility of coal and rock 

dust mixtures. 

Currently in the US, assessment of the adequacy of rock dusting for explosion preventions is done by 

sampling which can take weeks for the analysis to return. A portable handheld rock dust meter which is based 

partly on earlier Bureau of Mines research has been developed to provide on-the-spot assessment of the adequacy 

or hazard. Reliability assessment and implementation methodologies are being conducted for the potential 

induction of this device into the US coal industry. 

Development of improved methodologies to characterize streneth properties of mine seals 

Mine seals capable of withstanding explosion overpressures are used in the US to isolate active areas where 

miners work from abandoned areas of coal mines and the hazard of explosions that may occur in these areas. 

Being developed are acceptable, performance-based criteria for seal designs and construction methods that will 

ultimately reduce the potential exposure of US miners to explosion hazards. 

Investigations of the interaction between methane and mining induced caving/subsidence 

Coal room and pillar retreat mining, as well as longwall mining, cause the ground to cave and subside. This 

results in increases in permeability of the surrounding rocks and ground and causes fluids, such as methane gas, to 

flow into coal mines from previously isolated methane sources above, below, and adjacent to the mined coal bed. 

Caving and subsidence extent and mechanics are being studied via modeling techniques using field data for input 

parameters and model verification to lead to better predictive methods of coal mine methane emissions and to 

assist the design of better methane control procedures and techniques. 
Improved Ventilation Monitoring Strategies 

Recent coal mine explosions in the US have occurred in the large mines, many of which are longwall mines 

and, as expected, the most gassy. These mines usually employ mine monitoring systems which can assist to 

monitor for hazardous conditions. Currently, few of these systems fully monitor key ventilation and air quality 

areas which can provide early warning of system malfunctions. NIOSH is developing monitoring strategies and 

assessing hardware that will provide the means for a more robust use of these systems to assess these key mine 

conditions. 

CuttinfrJWeldinp hazards in underwound coal mines: 

Flame torch cutting and welding are permitted in US coal mines under certain conditions. Analyses of fires 

in the US coal mining industry for the period 1990-2002 indicated that 20% (110 fires) of the total number of 

reported fires (560 fires), resulting in 70 injuries (41% of total reported injuries) and 2 fatalities, were the result of 

either flame cutting or welding operations. In the recent shaft explosion at the McElroy Mine, flame cutting was 

the most likely cause of the explosion that resulted in 3 fatalities and 3 injuries. The root causes of the fires and 

injuries caused by flame cutting or welding operations will be determined and new and improved methodologies 

and technologies are being evaluated to prevent such fires and explosions. 

Spontaneous combustion hazards in gassy mines: 

Spontaneous combustion continues to be a problem for many western US mines, as well as several gassy 

mines in Alabama and the Eastern U.S. Dilution is the principal ventilation control technique to contro1,methane 

concentrations in US coal mines. Current ventilation dilution techniques can aggravate spontaneous combustion 

control measures. The specific aim of this research is to develop ventilation methodologies to minimize 

spontaneous combustion as an ignition source in mines with appreciable methane. 

Initial Explosion ResponseWiultiple Explosion Events 

The most recent coal mine explosions were glaring examples of the critical nature of the initial response to an 

explosion event. In both the JWR #5 and Willow Creek events these initial responses were deemed inadequate 

by MSHA which contends that these poor responses led to the fatalities. Interventions will be developed and 

transferred to the industry in the form of training aids and mechanisms to address other issues such as inadequate 

personal communications at the onset of an emergency, faulty assessment issues, and general emergency 

preparedness. 

Technical Transfer, Education, and Training 

It is clear that additional education and training is needed to provide mine inspectors, safety personnel, and 

underground miners with a better understanding of the factors and conditions contributing to explosion hazards in 

mines. The large influx of inexperienced personnel into these positions over the next few years in the US 

dramatically underscores this need. Training materials using various media, as well as workshops and other 

educational means, are being developed to address this requirement for new and updated explosion hazard and 

prevention materials and educational methodologies. 
Summary 

PDM prototype units were successfully tested in the laboratory and in four underground coal mines. Under 

these specific test conditions the PDM demonstrated that it was convenient to wear, robust, provided accurate data, 

provided timely data that could be used to prevent overexposure, and was easy to use. Overall successes 

documented in this work have lead to an early commercial version that promises to correct many of the minor 

problems identified in the prototype. Further in-mine trials will determine the long term durability, stability and 

maintenance requirements for this new dust monitor. 

The occurrence of an explosion in the underground workplace is in many instances the unfortunate, but 

preventable coalescence of multiple causative or contributing factors. Current explosion prevention and 

mitigation research by NIOSH in the US is aimed at providing the research tools that can lead to a systematic and 

holistic approach to address gaps in the coal mine explosion "safety shield". 

REFERENCES 


11 Kennedy, E. R., T. J. Fischbacb, R. Song, P. M. Eller, and S. A. Shulman, 1995. Guidelines for air sampling and analytical method 

development and evaluation, DHHS (NIOSH) Publication No. 95-1 17. 

1 Vohein, J.C., R.P. Vison, L.J. McWilliams, D. P. Tuchman, and S.E. Mischler. Performance of a New Personal Respirable Dust 

Monitor for Mine Use. US Dept. of Health and Human Services, CDC, NIOSH RI 9663. June 2004. 20 pp. 

(ht~://www.cdc.aov/niosh~minin~~ubs/Dublist.html) 


1 Bartley, D. L., C. Chen, R. Song, T.J. Fischbach, 1994.Respirable aerosol sampler performance testing. AIHAJ 55:11:1036 -1046.