Development of Moisture Tolerant Rock Dust for Improved Mine Safety

August 26, 2015

Dave Anstine - Senior Technical Leader, Building and Chemicals

Development Background

Tragic explosion at the Upper Big Branch Mine in West Virginia in 2010 Extensive investigations were launched by the Mine Safety and Health Administration (MSHA) and found:

Mine was poorly dusted 78.92% were out of compliance with the federal standard

The significance of the analysis and the role that Rock Dust played in the Upper Big Branch Mine explosion prompted MSHA to ask NIOSH to evaluate current Rock Dusts in North America and their compliance to specifications and its use in greater detail 47% of Rock Dust Samples did not meet the particle size requirement All Rock Dust Samples tested, caked when wetted & dried and did not disperse with a light blast of air

30 CFR 75.2 Rock Dust Definition Pulverized limestone, dolomite, gypsum, anhydrite, shale, adobe, or other inert material Particle Size:

‒ 100% minus 20 Mesh‒ Minimum 70% minus 200 Mesh

Particles of which when wetted & dried will not cohere to form a cake which will not be dispersed into particles by a light blast of air

Does not contain more than 5 percent combustible matter Does not contain more than a total of 4 percent free and combined silica(SiO2)

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Current Rock Dust Samples Subjected to “Wet” Conditions

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Rock Dust Simple Caking Test

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NIOSH Dust Dispersion Chamber

A laboratory dust dispersion chamber was developed by NIOSH to provide a reproducible air pulse across the surface of the sample to compare relative dispersibility of Rock Dust samples

All test samples were subjected to the same 0.3-second pulse from a 40psi compressed air source to give a peak dynamic pressure of approximately 4.2 psi.

. Sample trays were weighed before and after each air pulse to determine the amount of dust dispersed..

While this apparatus and test procedure cannot hope to duplicate the dust dispersal mechanism in advance of a propagating mine explosion, it does provide a repeatable dynamic pressure source and quantitative measure of the relative mass loss and dispersibility of dusts under controlled dispersion conditions. pressure.

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NIOSH Dust Dispersion Chamber

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NIOSH Dust Dispersion Trays with Rock Dust: After and Before Dispersion

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NIOSH Dust Dispersion Trays: Dry, Wet & Wet with Filter Paper

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NIOSH Dust Dispersion Chamber “Wet” Test Results:Current Rock Dust Samples

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Sample IdentificationParticle Size d(50) microns

Dry Weight Loss (%)

Wet Weight Loss (%)

Imerys ImerWhite 22.5 11.5 0

Competitive Sample #1 29.5 8.4 0

Competitive Sample #2 25.5 9.6 0

Competitive Sample #3 23.1 12.0 0

Competitive Sample #4 17.6 12.6 0

Competitive Sample #5 14.6 13.9 0

Competitive Sample #6 11.0 15.0 0

Competitive Sample #7 10.6 11.0 0

Humidity Chamber

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NIOSH Dust Dispersion Chamber “Wet” Test Results: Moisture Tolerant Samples

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Imerys Sample # Particle Size d(50) Microns Dry Weight Loss (%) Wet Weight Loss (%)

2A075K-925R 35.2 8.1 2.4

2A125K-875R 29.5 8.9 3.2

2A125S-875R 28.1 9.3 3.3

2A075S-925R 34.9 8.6 3.5

2A075S-9258 25.4 12.2 5.1

2A075S-925M 21.6 11.9 5.3

2A125S-875M 18.9 13.3 5.4

2A125K-8758 22.1 11.3 5.6

2A125S-8758 22.6 11.8 6.0

2A075S-92510 16.0 13.4 6.1

2A125K-875M 18.3 12.5 6.1

2A125S-87510 14.6 13.4 6.1

2A075K-925M 20.9 12.3 6.3

2A075K-9258 25.2 11.9 6.6

NIOSH Dust Dispersion Chamber “Wet & Humid” Test Results: Moisture Tolerant Samples

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Imerys Sample # Particle Size d(50) Microns Weight Loss (%)

0 Days 7 Days 14 Days 21 Days

2C100S-900M 20.5 8.3 2.5 3.7 3.3

2B075K-9258 24.7 6.7 2.8 3.3 3.7

SU125K-875M 19.1 7.1 2.9 3.3 3.1

2C075S-925M 21.5 6.9 3.0 3.2 3.3

3100S-900M 20.1 7.0 3.2 4.0 3.4

2C100K-900M 20.3 7.1 3.2 5.1 4.3

2B125K-875M 17.6 10.8 3.3 5.8 2.8

2B100K-9008 22.5 10.7 3.6 5.0 5.1

2C075K-925M 21.0 6.9 3.9 2.1 3.0

3125K-875M 19.4 7.7 4.0 3.0 3.2

2B100S-90010 14.9 13.0 4.0 6.0 5.4

2B100S-9008 22.8 8.5 4.1 4.8 4.1

2B075S-9258 24.5 6.0 4.7 4.5 4.3

2C075S-92510 13.8 11.6 4.8 4.2 4.1

Imerys Samples Tested in NIOSH 20L Explosibility Chamber

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Coal Concentration(g/cu.m) 200 200 200 200 400 400 400 400 600 600 600

Rockdust Concentration(%) 65 70 75 80 65 70 75 80 65 70 75

Imerys Sample No.

#2B075K-9258 dnt go no-no dnt dnt go no-no dnt dnt go no-no

#2B100S-9008 dnt go-go no-no no-no dnt go no-no dnt dnt go no-no

#2B125S-8758 dnt go no-no dnt dnt go no-no dnt dnt go no-no

#2B125K-875M dnt go no-no dnt dnt go no-no dnt go no-no no

#2B075K-925M dnt go no-no dnt dnt go no-no dnt go no-no no

#2B100S-90010 dnt go no-no dnt go no-go no dnt go no-no no

#2B125S-87510 dnt go no-no dnt go no-no no dnt go no-no no

#3125K-875M go no-go no-no dnt go no-go no-no dnt go no-go no-no

#3100S-90010 dnt go no-no dnt go no-go no-no dnt go no-no no

#3100S-900M dnt go no-no dnt go no-go no-no dnt go no-no no

#SU125K-875M dnt go no-no dnt dnt go no-no dnt dnt go no-no

ImerWhite dnt go-go no-no dnt dnt go no-no dnt dnt go no-no

no-no = two tests conducted and both inerted the coal dust

go = explosion no = no explosion, dnt = did not test

Modified & Current Rock Dusts: After “Wet” and Humid Conditions

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Imerys Rock Dust Samples Comparison to 30 CFR 75.2

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Imerys Sample # Particle Size d(50) um

Sieve Retains: Combustible Material %

% SiO2Free & Combined

20% Mesh 200% Mesh

30CFR-75.2 - 0 (max) 30 (max) 5 (max) 4 (max)

2A075S-925R 34.9 0 27.5 <0.2 <0.7

2A125K-875R 29.5 0 26.0 <0.2 <0.7

2B075S-9258 24.5 0 2.7 <0.2 <0.7

2B100K-9008 22.5 0 2.7 <0.2 <0.7

2B125K-8758 21.9 0 2.6 <0.2 <0.7

2C075S-925M 21.5 0 0.3 <0.2 <0.7

2C100S-900M 20.5 0 0.3 <0.2 <0.7

2C100K-900M 20.3 0 0.3 <0.2 <0.7

3100S-900M 20.1 0 0.3 <0.2 <0.7

3100S-90010 20.1 0 <0.1 <0.2 <0.7

SU125K-875M 19.1 0 0.2 <0.2 <0.7

2B125K-875M 17.6 0 0.3 <0.2 <0.7

2B125K-875M 13.8 0 <0.1 <0.2 <0.7

2B125S-87510 12.8 0 <0.1 <0.2 <0.7

Summary

All samples have shown greatly improved dispersibility over the current Rock Dusts being used in North American coal mines when subjected to moisture and high humidity and then dried.

The samples performed as well as the current Rock Dusts in their ability to inert explosions

All samples meet the current requirements for 30CFR 75.2 Moisture Tolerant Rock Dust has been applied to a section of a Rib at the Bruceton

Experimental Mine on the NIOSH Campus in Pittsburgh, PA Compared to ImerWhite which was on a different section of a Rib The Moisture Tolerant Rock Dust has been applied for over 6 months and is still

dispersing with a light puff of air

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Questions?