1 INTRODUCTION 

Medical studies have shown that prolonged inhalation of excessive levels of respirable coal mine 

dust can lead to coal workers’ pneumoconiosis, a 

disease that is irreversible and can be progressive, 

disabling, and ultimately fatal. Thousands of underground and surface mine workers who are potentially at risk of developing adverse health effects from breathing respirable coal and silica 

dusts. The Coal Mine Health and Safety Act of 

1969 included a Black Lung Benefits Program. 

Over 104,000 beneficiaries received benefits in 

2004. The Black Lung Disability Trust Fund provided over $292 million in monthly benefits to 

beneficiaries while the Division of Coal Mine 

Worker’s Compensation administered another 

$380 million in monthly benefits (Office of Workers’ Compensation Programs 2004). Research and 

development in the measurement and control of 

mine dust will help reduce the number of pneumoconiosis cases as well as minimize worker compensation expenses. 

The assessment and sampling of dust levels can 

be challenging because of the variable composition 

of the dusts and the constantly moving work area 

(Hearl & Hewett 1993). Currently, dust levels in 

mining are either measured gravimetrically (Raymond et. al. 1987), using filters and the accumulated dust mass in a given quantity of air, or 

through the use of instantaneous electronic or direct-reading dust monitors (Cantrell et. al. 1993). 

The filter method can take several weeks to process before results are reported to the mine, which 

creates a delay in identifying and correcting the 

problem. Current available instantaneous or directreading monitors are not practical for routine personal monitoring because of their complexity, size 

and expense (Volkwein et. al. 2000). 

The U.S. Department of Labor’s Advisory 

Committee on the Elimination of Pneumoconiosis 

Among Coal Mine Workers recommended the development of both fixed site and portable continuous respirable dust monitors that could be used to 

enhance their compliance monitoring program. In 

response to this request, NIOSH examined several 

approaches. A personal dust monitor (PDM) has 

been designed, built and at present is proving to be 

an accurate and reliable dust monitor (Volkwein et. 

al. 2000). However, when the PDM becomes 

available to industry, it will cost several thousand 

dollars (present estimates range from $7,000 to 

$15,000). A more affordable, person-wearable, 

Evaluation of SKC Inc. Dust Detective 

E.E. Hall, R.P, Vinson, and J.C. Volkwein 

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA, USA 

ABSTRACT: Assessment of workplace exposures is an important tool for helping to minimize dust-related 

occupational illness and diseases. Real-time particulate monitoring can effectively locate areas where dust 

controls are needed and determine how well they are working. An affordable, person-wearable, real-time dust 

monitor is needed. The SKC Inc. Dust Detective (SKCDD) fulfills those requirements (Disclaimer: Mention 

of any company or product does not imply endorsement by NIOSH). The SKCDD consists of a disposable 

sampling tube (DST) connected to a small hand-held sampling pump. The SKCDD was developed through a 

Cooperative Research and Development Agreement (CRADA) between the National Institute of Occupational Safety and Health (NIOSH) and SKC Inc. The relationship of dust concentrations measured by personal 

gravimetric samplers to those measured by the SKCDD was determined in a laboratory aerosol chamber. A 

comparison of the means and the relative standard deviation of triplicate measurements of each type of sampling device demonstrated the SKCDD to be a viable alternative means for measuring dust. While it provides 

accurate measurements for specific coal types, it requires correction factors (those correction factors still need 

to be calculated) for other coal types. 
real-time dust monitor is now available that will 

provide the coal miner with a good estimate of 

his/her exposure to dust. The monitor is called the 

SKC Inc. Dust Detective (SKCDD) and will be 

less than $1,000 to purchase. The SKCDD empowers miners to self-assess their exposure to respirable dust in real time. 

The PDM is a quantitative instrument while 

the SKCDD is a qualitative tool. The PDM is a 

more expensive instrument yielding greater accuracy and more user options, while the SKCDD 

provides fewer options and still maintains accuracy 

at a lower cost. Both instruments will be very useful in providing mine operators the information 

they need to make control technology and administrative changes to reduce miner exposure when 

needed. 

2 DESCRIPTION OF INSTRUMENTS 

2.1 Personal gravimetric samplers 

Flow-controlled coal mine dust personal sampler 

units (CMDPSU) are currently used in mines; they 

are mandated by 30CFR part 74. A CMDPSU consists of a Mine Safety Appliances (MSA) Escort 

Elf pump operated at 2 lpm, connected to a sampling head by a section of 1⁄4-in inside diameter 

(ID) flexible tubing. The sampling head consists of 

a 37-mm diameter MSA filter cassette connected 

to a 10-mm diameter Dorr-Oliver cyclone size preselector. The CMDPSU were used to sample coal 

dust aerosols from the Marple chamber, a laboratory dust exposure chamber designed to evenly 

disburse dust throughout the chamber (Marple & 

Rubow 1983). Filters were pre- and post-weighed 

at the Pittsburgh Research Laboratory (PRL) in a 

controlled atmosphere. NIOSH receives filters unassembled; therefore the filters were prepared 

without the tamper-resistant backflow valve or the 

inner stainless steel support wheel since they were 

not necessary for laboratory testing. Pump flows 

were checked weekly with a Gilian Bubble Flow 

Meter, a primary standard flow measurement device. Twelve personal samplers were arranged for 

each test in groups of three, so that each grouping 

was evenly spaced about the central portion of the 

chamber at about the same elevation. 

2.2 SKC Dust Detectives 

One of the main components of the SKCDD is the 

dust detector tube. The dust detector tube was developed to provide inexpensive, short-term measurement of the cumulative personal dust exposure 

of a worker during a shift. The dust detector tube 

models itself after the concept of a radiation dosimeter or, more precisely, after sorbent detector 

tubes used to measure exposure to various gases. 

The SKCDD software converts differential pressure to cumulative respirable dust exposure and 

short term exposure. 

The SKCDD consists of a disposable sampling tube (DST) connected to a small hand-held 

sampling pump. Flow-controlled sampling pumps 

manufactured by SKC Inc. (Dust Detective) were 

operated at a flow rate of 0.250 lpm to draw coal 

dust aerosols into the dust detector tubes. The 

sampling pump consists of programmable microprocessor, flow sensor, pressure sensor, air pump, 

control switches, and a digital display. The DST 

dimensions are 1⁄2-in in ID by 4 inches in length. 

The tube contains two cylinders of porous foam 

that are particle size pre-separators at the inlet end 

and a glass fiber filter at the outlet end. The outlet 

end of the DST is connected to a sampling 

pump/monitor with a section of 1⁄4-in ID flexible 

tubing. The disposable single-use tube contains a 

respirable size classifier and the pressure drop filter media and can be assembled for a few dollars 

per tube (Volkwein et. al. 2000). 

Figure 1. SKC Dust Detective disposable sampling tube 

As the respirable dust collects on the glass fiber 

filter there is a corresponding increase in pressure 

drop across the filter. The pressure drop and air 

flow through the pump are continuously monitored 

and used by the pump’s programmable microprocessor to calculate the dust concentration. The back 

pressure increases linearly with dust particle 

buildup on the filter. The instruments are equipped 

with only three buttons, which allow for simplicity 

in programming the units, entering a calibration 

factor, and test parameters (Fig. 2). 
Figure 2. SKC Dust Detective 

3 METHODS AND MATERIALS 

Dust concentrations were measured by personal 

gravimetric samplers and by SKC Dust Detective 

(SKCDD) in a laboratory aerosol chamber. By 

comparing the means and the relative standard deviation of triplicate measurements of each type of 

sampling device, a correlation could be determined. A regression analysis was done to obtain 

the relative standard deviation (RSD), slope, and 

regression coefficient (R2

) values. 

3.1 Test aerosols 

Tests for this study were conducted in the Marple Chamber. They were comprised of three separate trials of five different coal types for a total of 

fifteen coal dust samplings, where MMD is the 

mass median diameter and GSD is the gravimetric 

standard deviation. The coal types were: 

• Keystone Black, 4.66 MMD, 3.04 GSD 

• Illinois #6, 5.72 MMD, 3.15 GSD 

• Pittsburgh Coal 18 μm, 11.01 MMD, 2.79 

GSD 

• Pittsburgh Coal 10 μm, 4.05 MMD, 1.98 

GSD 

• Pittsburgh Coal 5.77 μm, 3.68 MMD, 2.59 

GSD 

The size distribution measurements were made 

in the Marple Aerosol Chamber using Marple Personal Cascade Impactors 290 Series. 

3.2 Test procedure 

The guidelines for each set of three tests are as 

follows: 

Test 1: The Marple Aerosol Chamber was 

brought to an MRE equivalent (MRE is a multiplier of 1.38 required to meet federal standards 

(30CFR)) concentration of 2.0 mg/m3

. Three 

SKCDDs and 12 CMDPSUs were started at the 

beginning of the test. The SKCDDs ran for 8 

hours. Three CMDPSUs were turned off at each of 

the MRE equivalent concentrations of 0.3, 0.5, 1.0, 

and 2.0 mg/m3 to compare concentrations at different mass loadings. 

Test 2: The Marple Aerosol Chamber was 

brought to an MRE equivalent concentration of 2.5 

mg/m3

. Three SKCDDs and 12 CMDPSUs were 

started at the beginning of the test. The SKCDDs 

ran for 8 hours. Three CMDPSUs were turned off 

at each of the MRE equivalent concentrations of 

0.6, 1.2, 1.8, and 2.5 mg/m3 to compare concentrations at different mass loadings. 

Test 3: The Marple Aerosol Chamber was 

brought to an MRE equivalent concentration of 4.0 

mg/m3. Three SKCDDs and 12 CMDPSUs were 

started at the beginning of the test. The SKCDDs 

ran for 8 hours. Three CMDPSUs were turned off 

at each of the MRE equivalent concentrations of 

1.0, 2.0, 3.0, and 4.0 mg/m3 to compare concentrations at different mass loadings. 

The sampling inlets for both the SKCDD 

and CMDPSUs were positioned so that they were 

all facing the center of the chamber. The dust concentrations in the aerosol chamber were monitored 

with a TEOM1400a operated at 2.0L/min. The 

inlet of the TEOM was connected to a 10-mm cyclone with a 5-ft section of 1⁄4-in diameter tubing. 

4 RESULTS AND DISCUSSION 

Tests were run using concentrations as a 

guide for comparison with federal standards however for simplicity in data analysis dust mass was 

used. Data was analyzed and the standard deviation and relative standard deviation for both the 

CMDPSUs and the SKCDDs were calculated and 

are shown in Table 1. 

Table 1. Summary of laboratory correlation data 
Keystone 

Illiniois #6

Pittsburgh 10um

Pittsburgh 18um

Pittsburgh 5.77um

R2 = 0.98

R2 = 0.99

R2

 = 0.89

R2

 = 0.94

R2

 = 0.96

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Reference filter (mg)

Dust Detective (mg)

Figure 3. Dust Detective responses to coal types 

Figure 4. Dust Detective responses optimized for calibration factor

The RSD for the CMDPSU for all coal types, except Pittsburgh 18 μm, was lower than that of the 

SKCDD, but the differences were generally minimal. The regression coefficient was 0.86 or greater 

for all coal types. 

The averages of the three SKC Dust Detective instruments were compared with the CMDPSU data. 

The SKCDD dust masses were plotted against the 

CMDPSU dust masses. Linear regression was used 

to find the RSD, slope and R2

 values. As shown 

above in Figure 3, the Dust Detective response for 

each coal type was linear. The slopes for the coal 

types varied. The Illinois #6 and Pittsburgh 

5.77μm had similar slopes as did Pittsburgh 18 μm 

and Pittsburgh 10 μm. This is attributed to the differences in how each coal type loads the filter and 

changes the pressure drop. 

A regression analysis was performed for the data 

for all coal types. Based on the slope of the line 

that was derived from the data from all coal types, 

a range of ±50% is shown above in figure 4. The 

±50% is the European Standard criteria for survey 

instruments (EN 1994). Four of the five coal 

types fall within the parameters, therefore suggesting that one calibration factor would adequately 

represent those coal types. Keystone Black was the 

only coal type whose slope was out of the range. 

This could be due to that it is a manufactured 

product and not naturally occurring; it is a more 

finely ground coal material with size distribution 

less than naturally occurring coal. Based on the R2 

values, the SKCDDs can be programmed for coal 

seams specific to mine operations. 

5 CONCLUSIONS 

Initial work indicates that the SKC Dust Detective will be a reliable instrument that will provide a 

low cost alternate means for estimating dust concentrations. The instrument can be calibrated for 

specific coal types and is easy to program. Laboratory comparisons to CMDPSUs show good correlation for individual coal types. These instruments 

will be most applicable when big differences in 

size distribution are not expected. Future work will 

include water spray response (for longwall operations), determining correction factors, and conducting underground mine studies. The instantaneous 

feedback on dust level exposures that the SKC 

Dust Detective provides will help empower the 

worker and mine management to improve the min-
ing conditions and protect the worker’s respiratory 

health. 

6 DISCLAIMER 

The findings and conclusions in this report are 

those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. 

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Aerosol Measurement, Aerosol Measurement: Principles, 

Techniques and Application, Chap. 26, pp.591-611. K. 

Willeke and B.A. Baron, Eds. Van Nostrand, New York 

(1993). 

European Standard. EN 482 (1994). 

Hearl, F.J.; Hewett, P.: Problems in Monitoring: Dust Levels 

Within Mines. Occupational Medicine: State of the Art 

Reviews 8(1):93-109 (January-March 1993). 

Marple, V.A.; Rubow, E.L.: An Aerosol Chamber for Instrument Evaluation and Calibration. American Industrial Hygiene Association Journal 44(5):361-367 (1983). 

Office of Workers’ Compensation Programs: Black Lung 

Benefits Act 1996. DOL, Washington, D.C. (1997). 

Raymond, L.D.; Tomb, T.F.; Parobeck, P.S.: Respirable Coal 

Mine Dust Sample Processsing. MSHA IR 1156 (1987). 

U.S. Department of Labor: Report of the Secretary of Labor’s Advisory Committee on the Elimination of Pneumoconiosis Among Coal Mine Workers, recommendations 8 and 17. DOL, Washington, D.C. (October 1996). 

Volkwein, J.C.; Schoeneman, A.L.; Page, S.J.: Laboratory 

Evaluation of Pressure Differential Based Respirable 

Dust Detector Tube. Applied Occupational and Environmental Hygiene 15(1):158-164 (2000).