Pittsburgh Mining Research Division

Rock Dust Partnership Meeting

December 5, 2017

NIOSH Mining Program
Agenda

Welcoming Comments

Opening Comments

NIOSH – Progress to Date

• NIOSH Health Effects Laboratory Division

• NIOSH Pittsburgh Mining Research Division

Comments and Discussion – Future efforts

Concluding Comments
Opening comments

• NIOSH – Dr. Jessica Kogel & Dr. R.J. Matetic

• MSHA – Stan Michalek

• IMA-NA – Mark Ellis

• NSSGA – Emily Coyner

• NLA – Hunter Prillaman/Bradford Frisby

• NMA – Bruce Watzman

• BCOA – Ed Green

• UMWA – Josh Roberts
Action Items from Last Meeting

• Silica and toxicity data

• Engineered rock dust

• In-mine studies

• Foamed rock dust
Initial Partnership

Inconsistencies in available rock dust supply

• Particle sizing

• Dispersibility

Rock Dust Partnership 

• IMA-NA

• NSSGA

• National Lime Assoc.

• MSHA

Test methods to assess rock dust quality

Improving rock dust performance
Expanded Partnership

Potential health effects

• Respirable silica

• Toxicological

Perceived respirable dust issues

Industry

• National Mining Assoc.

• Bituminous Coal Operators Assoc.

Labor

• United Mine Workers of America
NIOSH Mining – Progress to Date

• Rock dust toxicity – NIOSH/HELD

• Large scale testing at Polish Central Mining Institute

• Wrap-up of engineered rock dust

• Foamed rock dust work
Rock Dust Toxicity
Toxicity Studies

of Rock Dust Samples.

(In vitro Assessments)

Dr. Anna A. Shvedova

NIOSH / HELD

Dec 5th 2017
What Do We Know about Health Outcomes 

Elicited by Calcium Carbonate Dust ?

• Eight cases of suspected pneumoconiosis following

inhalation of limestone dust with low silica content were

described by Doig et al. (1953).

• Granulomatous lesions containing limestone particulates were

reported in lungs of quarry worker (Crummy et al. 2004).

• Limestone quarry workers had increased prevalence of

respiratory symptoms, e.g. various coughs, wheezing and

shortness of breath (Bwayla et al. 2011).

• Pulmonary alveolar proteinosis observed in marble-cutter in

Turkey (Case study: Yildirim et al. 2015).

• Erasmus syndrome (pneumoconiosis) in marble worker, most

likely exposed to high silica concentrations (Bello et al.

2015).
What Do We Know about Health Outcomes 

Elicited by Calcium Carbonate Dust ?

• Increased IL-8 level (inflammation marker) in serum was

associated with limestone dust concentration and the duration

of exposure in limestone miners (Tolinggi et al. 2014)

• Calcium carbonate dusts are not considered fibrogenic dusts,

but rather irritants (NIOSH guideline, 1995).

• Co-exposure with silica is most likely responsible for COPD,

pneumoconiosis and fibrosis seen in limestone/marble

workers:

• Even though the level of silica is very low – it may still cause the

adverse outcomes in susceptible individuals (Doig et al., 1954,

Crummy et al. 2004, Angotzi et al. 2005).
Need for Developing Anti-caking Rock Dust

Coating with hydrophobic Stearate

• Limestone-based rock dusts are used to prevent explosions

caused by high coal dust content in the air.

• Treating limestone will provide better dispersion of the

materials.

• Under humid conditions, limestone-based rock dusts have a

tendency to cake.

• Treated limestone particles can fill the empty spaces

between the larger untreated limestone particles, preventing

or inhibiting the migration of water throughout the blend.
Need for Developing Anti-Caking Rock Dust 

NIOSH 2014 Study

• Objective: To develop modified limestone based rock dust

blend(s) that are capable of :

• Effectively dispersing (NIOSH dust dispersion chamber after being wetted, then

dried)

• Increasing the inertness of coal dust (NIOSH 20-L explosibility chamber).

• Recommendations: 20 – 25 μm untreated rock dust blended

with 10% + 2.5% of a 3 μm treated component (e.g.,

stearate).
Anti-Caking Rock Dust 

Treatment Details

Hydrophobic Tail

Hydrophilic Head

Stearic Acid 

Cao, Z. et al., 2016 

During the treatment, stearic acid is adsorbed on the surface of CaCO3

particles by covalent bond between the stearic acid “head” group and Ca2+, 

forming a monolayer of hydrophobic molecules.
Particle Characterization

Representative TEM images of respirable rock dust

Particles Investigated in the 

Current Study

UL

• Untreated Limestone

TL 

• Treated Limestone

UM

• Untreated Marble

TM

• Treated Marble

J-C Soo et al., 2016

Details of Collection: Respirable fractions of rock dusts were collected with FSP10 cyclones 

loaded with polyvinyl chloride filters (PVC, 5 μm pore size, 37 mm). The collected particles on 

PVC filters were washed with a mix of phosphate buffered saline and isopropyl alcohol. Then 

samples were centrifuged and dried.
Particle Characterization

Aerodynamic particle size distribution of airborne rock dust

J-C Soo et al., 2016

Respirable fractions of rock dusts were collected with FSP10 cyclones loaded with polyvinyl chloride filters 

(PVC, 5 μm pore size, 37 mm). The collected particles on PVC filters were washed with a mix of phosphate 

buffered saline and isopropyl alcohol. Then samples were centrifuged and dried.

The mass median aerodynamic diameter (MMAD) of treated marble (TM) 

sample is lowest compared to other rock dust samples investigated.
Particle Characterization

Average hydrodynamic diameter of respirable fraction of rock dust 

UM

Zavg: 863 ± 31 nm

TM

Zavg: 1209 ± 64 nm

The average size/distribution of rock dust samples were determined using DLS measurements. The hydrodynamic diameter (Zavg) from 

DLS were represented as mean ± SD. The reported Zavg values correspond to a mean of six different measurements. 

The average size of treated marble (TM) rock dust sample was higher compared 

to other rock dust samples investigated.
Hydrodynamic size measured of treated 

marble by DLS is highest between all 

samples. Since the DLS measurements were 

in aqueous solution – could it be due to the 

agglomeration of treated rock dust 

(through hydrophobic surfaces)? 
Other Particles: What we have seen?

Uncoated and Lignin-coated Nanocellulose Crystals and Fibers.

Particle Characterization

Agglomerated Dispersed

Figure: Characterization of nanocrystalline and microcrystalline cellulose samples. (A−E) AFM amplitude and (F-J) TEM images of CNC

(A,F), L-CNC (B,G), CNF (C,H), L-CNF (D, I) and MCC (E,J). Scale bar in all AFM and TEM images corresponds to 500 nm and 200

nm, respectively.

Depending on the cellulose nanomaterial type and/or its morphology, lignin 

coating can lead to differential agglomeration/aggregation influencing their 

physicochemical properties in aqueous media.
Other Particles: Toxicity Evaluation

Uncoated and Lignin-coated Nanocellulose Crystals and Fibers.

Experimental Details

CNC, LCNC, 

CNF, LCNF, MCC 

or asbestos 

exposures

THP-1 cells

PMA stimulation

24h/72h post 24h/72h post 

A549 cells

Cellular Viability

Inflammatory cytokines/chemokines 

(Human 27-plex kit from Bio-RAD)

Viability Responses
Other Particles: Toxicity Evaluation

Inflammatory Cytokine Responses

L-CNC < CNC

L-CNF > CNF

The overall inflammatory responses in cells upon exposure to various 

concentrations of different NC materials investigated were in the order: 

CNC > L-CNF > CNF ≥ L-CNC ≥ MCC.
Does Exposure to Different Rock Dust 

Samples Trigger Variable Biological 

Responses In Vitro? If so, what is the 

effect of treatment with stearic acid?
In vitro Evidence for Discriminating between 

different Respirable Rock Dust

Similar Approach as Nanocellulose Materials

Untreated 

Limestone

(or) Treated 

Limestone

(or) Untreated 

Marble

(or) Treated 

Marble

Cellular Viability/Damage

Inflammatory cytokines/chemokines

(human 27-plex kit from Bio-RAD)

24h/72h

A549 

Human pulmonary 

alveolar epithelial 

cells

Particle Concentration’s:

• 0 mg/ml

• 0.025 mg/ml

• 0.050 mg/ml

• 0.100 mg/ml

• 0.200 mg/ml

• 0.500 mg/ml

• 1.0 mg/ml
In vitro Evidence for Discriminating between 

different Respirable Rock Dust

Cytotoxicity (viability) of various respirable rock dust samples

0

20

40

60

80

100

120

Viability, % of Control

Exposure (mg/ml)

UL

TL

UM

TM

LPS





24 h



0

20

40

60

80

100

120

Viabiliy, % of Control

Exposure (mg/ml)









 



72 h

LC50 (mg/ml, 72h) 

UL 0.41

TL 0.49

UM 0.46

TM 0.48

LPS 0.108

A dose- and time-dependent cytotoxicity was observed in A549 cells upon 

exposure to different respirable rock dust samples.
In vitro Evidence for Discriminating between 

different Respirable Rock Dust

Cytotoxicity (cell damage) of various respirable rock dust samples

0

100

200

300

400

500

LDH (% of Contrlol)

Exposure (mg/ml)

UL

TL

UM

TM

24 h

0

100

200

300

400

500

LDH (% of Contrlol)

Exposure (mg/ml)

UL

TL

UM

TM

72 h

Representative TEM macrographs of A549 cells exposed to respirable rock dust (72h, 0.1 mg/ml)

Red arrows indicating particle uptake. 
In vitro Evidence for Discriminating between 

different Respirable Rock Dust

Inflammatory Cytokine/Chemokine Responses

A Venn diagram presenting the 

responses in inflammatory 

mediators upon exposure of A549 

cells to respirable rock dusts 

(0.1 mg/ml) for 72h.

Fold Change : ± 1.5

TM

UL

TL

UM

IL-13

G-CSF

PDGF-bb

IL-17

FGF basic

IL-8

IL-1ra

IL-6

TNF-a

Eotaxin

MIP-1b

IP-10

Some cytokines are unique to 

treated marble (TM) samples. 

Treated limestone (TL) revealed the lowest inflammatory response 

compared to other rock dust samples.
In vitro Evidence for Discriminating between 

different Respirable Rock Dust

Hierarchical cluster analysis of cytokine profiles in A549 cells after 72h

The samples of A549 cells exposed to different concentrations of rock dust for 72h were clustered based on the Euclidean distance metric and ward.D2 clustering

method. The samples corresponding to different rock dust and several cytokines measured in supernatants were reordered based on their (dis-)similarities

according to the dendrogram on the top and left, respectively. Each branch in the dendrogram shows the similarity between samples, i.e., the shorter the branch,

the more similar. The heat map colors represent log2 transformed fold change values of cytokines relative to the minimum and maximum of all values, increasing

from red to green, in each case. A key showing the range of values is also shown in the figure.

Log2

(fold change)

Clustering analysis of the inflammatory cytokines/chemokines revealed an 

overall stronger effect of marble compared to limestone samples. A clear 

separation of marble rock dust from limestone samples was also observed.
Summary

• The results showed a dose-dependent cytotoxicity and

cell damage at 72 h in A549 cells, with the least effect

upon exposure to treated limestone (TL).

• The extent of inflammatory responses evaluated by the

number of cytokines released, increased with the

concentration of tested materials.

• Clustering analysis of the inflammatory

cytokines/chemokines revealed an overall stronger

effect of marble (i.e., UM,TM) compared to limestone

samples (i.e., UL,TL).
Summary (cont....)

• Furthermore, untreated rock dust induced an overall

greater inflammatory response as compared to treated

samples.

• Similar to the cytotoxic and cell damage results, treated

limestone (TL) revealed the lowest inflammatory

response compared to other samples.

• Similar to what we have seen before in nanocellulose,

treatment related differences between limestone (TL)

and marble (TM) samples were observed.

Overall, our results unveiled treatment related differences as well as 

material dependent changes in biological responses.
Pulmonary Deposition

Respirable Rock Dust Samples

MMAD ~ (1 – 2) MMAD ~ (3.1 – 4.5)

Bronchial and Conducting Alveolar Deposition

Airways Deposition

* MMAD: Mass Median 

Aerodynamic Diameter

Fold Change : ± 1.5

Under In vivo conditions, allergic 

immune responses are characterized 

by the production of IL-13 and 

other cytokines.

There is strong need for animal studies to adequately address

pulmonary toxicity responses of (un-)treated rock dust.
Disclaimer: The findings and conclusions in this presentation are those of the

authors and do not necessarily represent the views of the National Institute for

Occupational Safety and Health. The mention of any company names or

products does not imply an endorsement by NIOSH or the Centers for Disease

Control and Prevention, nor does it imply that alternative products are

unavailable, or unable to be substituted after appropriate evaluation.
Thanks To My Collaborators:

E. Kisin

T. Lee

N. Yanamala

T. Khaliullin

S. Guppi

D. Weissman

M. Harper

Funding: ???
Large-Scale Testing
Large-scale Testing

Central Mining Institute Located in Mikołów, 

Poland

Personnel

• Experimental Mine Barbara

• NIOSH PMRD

Objective

• To determine whether an anti-caking 

treatment would hinder the effectiveness of 

the rock dust
Why Poland?

• Length of entry – 400 m

• Ignition method – methane/air mixture

• Testing history and experience
Lake Lynn Experimental Mine

• Length of entry – 490 m

• Ignition method – methane/air mixture

Test Setup
Test Basis

Testing at EM Barbara was conducted on a 

comparative basis

• Shipment of dust to Poland

• Estimates of $26,000/ton of material

• Insufficient d99 Polish coal dust for 

large-scale testing

• d38 coal dust ≈ medium coal dust (RI 

9679)

• Polish rock dust ≈ Reference rock dust 

(RI 9679)
The Polish coal dust and the Pittsburgh coal have similar properties

Pittsburgh 

Coal

Barbara 

d38

Moisture, % 1.7 2.9

Volatility,% 36.5 36.7

Ash, % 6.2 7.9

The Polish treated and untreated rock dusts perform similar to the Reference rock dust in 

the 20-L chamber

Rock Dust Coal Dust % Rock Dust 

Inerting

% TIC

Reference d38 Polish 60 70.8

Polish untreated d38 Polish 60 70.8

Polish treated d38 Polish 60 70.8
Tests conducted at EM Barbara

TIC Rock Dust Type NIOSH Test #

50% TRD 4-6-8

50% NTRD 5-7-9

60% TRD 1-3-11

60% NTRD 2-10
Explosion Pressure Time Histories
Explosion Intensity

Nominal TIC Average Impulse 

at 100 m (Ip/Ip ig)

60% TRD 7.7 (# 1, 3, 11)

60% NTRD 11.8 (# 2, 10)

50% TRD 15.6 (# 4, 6, 8)

50% NTRD 16.7 (# 5, 7, 9)
Polish Testing Conclusions

• Inerting properties of the treated rock dust (TRD) are at least as good as those of the 

non-treated rock dust (NTRD)

• Experimental results suggest better performance of the treated rock dust at TIC values 

larger than 50%
Limitations

Tests conducted using homogenous coal 

dust/rock dust mixtures

• No layering of dusts

Due to location, shipment of US dusts is cost 

prohibitive

Tests conducted in higher relative humidity

• (75% – 92%)
Review of Stockton Mine Testing

Measured respirable dust downwind of application

• Treated rock dust

• Untreated rock dust

Moisture infiltrated untreated rock dust before application

Applied the mine’s supply of rock dust to cover

Administrative controls necessary when applying rock dust
Experience with Treated Rock Dust

Untreated Rock Dust Application in Mine
Experience with Treated Rock Dust

Treated Rock Dust Application in Mine
Experience with Treated Rock Dust

Untreated Rock Dust

Initial Application 1 Year Later 2 Years Later
Experience with Treated Rock Dust

Treated Rock Dust

Initial Application 1 Year Later 2 Years Later
Comments from Others with Experience Using Treated Rock Dust
Engineered Rock Dust
Why Engineered Rock Dust? 

• Reduce or eliminate respirable component of the rock dust

• Hence,

• Should not contribute to CPDM readings

• Should not contain respirable silica particles

Ideal Engineered Rock Dust

• It should be as effective as the dry rock dust used to support 80% TIC rule

• Should remain dispersible when applied to wet surfaces
Particle Size Analysis and Distribution

Reference rock dust

• ~30% of the mass

• ~3% of the surface area

Classified RD using

• Ro-Tap

• Air Jet Sieve
Performance Assessment Methods

• Beckman-Coulter Particle Size Analyzer

• 20-L Explosibility Test Chamber [ASTM E1515]

• Dust Dispersion Chamber

• Simple Caking Test

Beckman Coulter Optical Particle Size Analyzer

Simple Caking Test

“Overview of dust explosibility characteristics”. Journal of Loss Prevention in the 

Process Industries [2000], 13, pp.183-199, Cashdollar, K.L.
20-L Explosibility Chamber Results for the Rock Dust as 

received – Treated and Untreated

Criteria for an explosion:

• The maximum explosion 

pressure ≥ 2 bar

• The volume normalized rate of 

pressure rise

(dP/dt) V1/3 ≥ 1.5 bar-m-s

-1
Inerting Relationship of Engineered Reference Rock Dust
20-L Explosibility Chamber Results for the Engineered Rock 

Dust

Treated RD Untreated RD

Size Fraction, μm Inert at 75% Inert at 75% 

20-38 Inert Inert

20-75 Explosion Explosion

38-75 Explosion Explosion

minus 38 Inert Inert

minus 75 Inert Inert

As-received rock dust Inert Inert
Dust Dispersion Chamber

• Based on LLEM coal dust explosion data

• Generates a reproducible air pulse

• 4.2 psi for 0.3 sec

“Design and development of a dust dispersion chamber to quantify the dispersibility of rock dust”, Journal of Loss Prevention in the Process Industries [2016] Vol. 

39, pp 7-16, Perera et al.
Dispersion of Treated and Untreated Dusts After Moisture 

Exposure
Will the Engineered Rock Dust disperse as 

well as the Reference dust?
Dispersion of Engineered Reference Rock Dust
Will the Engineered Rock Dust (Treated and 

Untreated) inert as well as the Reference dust?
Engineered Rock Dust 20-38 m

Rock Dust

20-L chamber Results at 

75% RD

Untreated A Inert

Treated A Inert

Untreated B Explosion

Treated B Explosion

Untreated C Inert

Treated C Inert
Will the Engineered Rock Dust (Treated) disperse 

when wetted and dried?
Simple Caking Test with 20-38 micron size fraction 

of Treated Rock Dust
Simple Caking Test with 20-38 micron size fraction 

of Treated Rock Dust
Pilot Scale Engineered Rock Dust Particle Size

5.9% < 10 μm

35.7% < 10 μm
Preliminary Full-scale Dispersion Results

200 lb of RD dispersed

• Pilot Scale Classified Rock Dust

• Reference Rock Dust

CPDM positioned 100 ft and 500 ft

downwind

Average PDM Dust Concentrations

Air Velocity < 10 μm Intake 100 ft 500 ft

ft/min % mg/m3 mg/m3 mg/m3

Pilot Scale Classified Rock Dust 95 5.9 0.03 43.24 28.84

Pilot Scale Classified Rock Dust 232 5.9 0.04 20.84 17.33

Reference Rock Dust 221 32.5 NA 131.61 94.80
Ideal Engineered Rock Dust

If we can eliminate only the < 15 micron size fraction instead of < 20 micron, 

that would provide more surface area

Which means...

• Will have better inerting effectiveness

• Able to maintain 20-L chamber inerting limits

• May lift better with the smaller coal dust particles

Technical success (inerts in the 20-L) but practical failure (cost, time).

Concerns regarding the preferential dispersion of coal dusts.
Foamed Rock Dust
Ideal Foamed Applied Rock Dust

• Applied wet

• Adheres to ribs/roof

• Stable in high humidity conditions

• When dry, is as dispersible as the rock dust supporting the 80% TIC rule

• Inerts as well as the rock dust supporting the 80% TIC rule

• Generates very little respirable dust 
Dust Dispersion Chamber

• Based on LLEM coal dust explosion data

• Generates a reproducible air pulse

• Nozzle orientation is parallel to the tray 

sample 

“Design and development of a dust dispersion chamber to quantify the dispersibility of rock dust”, Journal of Loss Prevention in the Process Industries [2016] Vol. 

39, pp 7-16, Perera et al.
Nozzle orientation of the dispersion chamber limited the perpendicular force 

otherwise observed during an explosion 
Modifications of the dispersion chamber allow for vertical loading of the 

samples

• does not simulate the 

passing of a shockwave 

• induces additional vertical 

pressure via the rapid 

release of the air jet.
3 foamed rock dust samples were tested

Company A Company B Company C

Pre-dispersion Post-dispersion
1 sample resulted in the same dispersion characteristics as the reference rock dust
BEM Pilot scale testing of foamed rock dust
Foam preparation Flow chart

Foam

generation

Component A 

Water

Compressed air

Foam 

stabilization

Component B 

Water 

Blending

Slurry

addition

Rock dust 

Water 

Mixing

What was done

• A total of eleven tests were conducted. 

• Two sections were used for shakedown tests.

• Three sections were sprayed with the best performing formulation from lab study and 

applied with a “shower” nozzle.

• One test section was run with the same formulation without the nozzle attachment

• One test section was run with the same formulation with a “Putzmeister” nozzle 

• Two test sections were run with ± 15% rock dust

• Two test sections were run with ± 15% of the additional water used to pre-wet the rock 

dust
Measurements to be made

Assessment of foam dispersibility via the “canned air” as well as samples collected in 

trays for testing in the dispersion chamber.

Measurement of foam drying times by periodically recording the weights of foam samples 

and taking rib samples for moisture analysis.

Foamed Rock Dust

Current formulation shows the most promise in laboratory testing

Additional engineering required to optimize the application process

Need to know how the foam will react to a shockwave

• Large-scale testing

Future partnership assistance to locate underground application site
Moving Forward – Next Steps

Larger-scale testing at Polish CMI

• Layers of coal/rock dust - treated vs 

untreated 

• Foamed rock dust

Engineered rock dust

• Technical success vs practical failure

• Questions regarding preferential 

dispersion of the coal dust

• No further action planned

Foamed rock dusts

• Pursue continued optimization of the 

foam mix

• Pursue application optimization

• Request partnership support for 

underground testing – test site

Toxicity – back burner

Cost/Benefit analyses
Thank You

Fires and Explosions Branch

Marcia L. Harris – ztv5@cdc.gov

Dr. Eranda Perera – iju9@cdc.gov

Connor Brown – kqr4@cdc.gov

Dr. Gerrit V.R. Goodman – gcg8@cdc.gov

Disclaimer: The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of any company or product does not constitute endorsement by NIOSH.

NIOSH Mining Program

www.cdc.gov/niosh/mining

Disclaimer: The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of any 

company or product does not constitute endorsement by NIOSH.