UNITED STATES BUREAU OF MINES

UNITED STATES DEPARTMENT OF THE INTERIOR

RI 9632 REPORT OF INVESTIGATIONS/1995

Secondary Explosion Hazards During Blasting

in Oil Shale and Sulfide Ore Mines
U.S. Department of the Interior

Mission Statement

As the Nation’s principal conservation agency, the Department of the

Interior has responsibility for most of our nationally-owned public

lands and natural resources. This includes fostering sound use of our

land and water resources; protecting our fish, wildlife, and biological

diversity; preserving the environmental and cultural values of our

national parks and historical places; and providing for the enjoyment

of life through outdoor recreation. The Department assesses our

energy and mineral resources and works to ensure that their

development is in the best interests of all our people by encouraging

stewardship and citizen participation in their care. The Department

also has a major responsibility for American Indian reservation

communities and for people who live in island territories under U.S.

administration.
Report of Investigations 9632

Secondary Explosion Hazards During Blasting 

in Oil Shale and Sulfide Ore Mines

By Eric S. Weiss, Kenneth L. Cashdollar, Michael J. Sapko,

and Eugene M. Bazala 

UNITED STATES DEPARTMENT OF ENERGY

PITTSBURGH RESEARCH CENTER
International Standard Serial Number

ISSN 1066-5552
CONTENTS

Page

Abstract ...................................................................................... 1

Introduction .................................................................................... 2

Oil shale mining ............................................................................... 2

Historical development of oil shale ............................................................... 2

Properties of oil shale ........................................................................ 4

Sulfide ore mining ............................................................................. 4

Explosion hazards of oil shale dusts ................................................................... 5

Large-scale experimental mine data ................................................................. 6

Laboratory data ............................................................................... 7

Dust, pressure, and flame during blasting in oil shale mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Gas generation during oil shale mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Horse Draw oil shale mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

White River oil shale project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Gas monitoring system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Methane emissions during mining operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Methane emissions from core analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Development of safer explosives for gassy oil shale mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Initial explosives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Bruceton Experimental Mine tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Minimum charge weight for ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Stemming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Full-scale field studies with ANFO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Low-incendive explosives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Lake Lynn cannon gallery tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Full-scale field tests with a low-incendive blend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Unocal's Long Ridge Mine tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Occidental's Logan Wash Mine tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Explosion hazards of sulfide ore dusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Laboratory data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Large-scale experimental mine data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Full-scale validation tests in sulfide ore mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Appendix.—Abbreviations used in this report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

ILLUSTRATIONS

1. Map showing four basins of the Green River Oil Shale Formation and locations of oil shale mines .................. 3

2. Optical microscope photograph of oil shale particles and the corresponding SEM x-ray maps for the elements

calcium, silicon, and aluminum ................................................................. 5

3. Plan view of the Bruceton Experimental Mine ........................................................ 6

4. Side view of the face area in the main entry of the Bruceton Experimental Mine showing instrumentation

 positions ................................................................................. 7

5. Vertical cross section of the Pittsburgh Research Center's 20-L dust explosibility test chamber ..................... 7

6. Explosibility data from 20-L chamber for three oil shales ................................................ 9

7. Summary explosibility data from 20-L chamber for four oil shales compared with high- and low-volatile

 bituminous coals and anthracite ................................................................ 9

8. Minimum explosible concentrations for hybrid mixtures of coal or oil shale dusts with methane gas from

20-L chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

9. Map of part of the Colony Oil Shale Mine showing entry and blasting area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

ILLUSTRATIONS—Continued
ii

Page

10. Map of blasting area showing instrumentation and sampling pan positions for blast 3 at Colony Mine . . . . . . . . . . . . . . . . 12

11. Map of blasting area showing instrumentation positions and faces for blasts 4 and 5 at Long Ridge Mine . . . . . . . . . . . . . 13

12. Map of blasting area showing instrumentation positions for blast 6 at Colony Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

13. Diagram of Long Ridge Mine face showing blasting pattern for blasts 4 and 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

14. Diagram of Colony Mine face showing blasting pattern for blast 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

15. Mine face before blast 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

16. Mine face after blast 6, showing rubblization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

17. Pittsburgh Research Center researchers with large boulders in the rubble pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

18. Summary of floor dust loadings (minus 20-mesh fraction) after five blasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

19. Pressure generated by blast 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

20. Frames from high-speed movie during blast 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

21. Isometric view of White River Shale Project mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

22. Gas monitoring trailer near air shaft at White River Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

23. Flow diagram of gas sampling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

24. Typical methane released during blasting at White River Mine as measured underground in the east heading . . . . . . . . . . . 23

25. Methane released from core sections taken near the White River shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

26. Plan view of the face area in the main entry of the Bruceton Experimental Mine used for gas and predispersed

dust tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

27. Static pressure traces for typical mine dust explosions in the Bruceton Experimental Mine using oil shale . . . . . . . . . . . . . 26

28. Floor dust loadings (minus 20-mesh fraction) of unstemmed and stemmed ANFO face blasts compared with

pre-1988 unstemmed ANFO blast data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

29. Flame exiting from cannon after detonation of blasting agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

30. Coal dust ignited by unstemmed ANFO at the Lake Lynn cannon gallery showing flame exiting from both ends . . . . . . . . 33

31. Map of Long Ridge Mine showing instrumentation locations for full-face blast in heading 6 . . . . . . . . . . . . . . . . . . . . . . . 37

32. Diagram of Long Ridge Mine face showing blasting pattern in heading 5 for 1990 tests . . . . . . . . . . . . . . . . . . . . . . . . . . 37

33. Explosives being loaded into borehole at Long Ridge Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

34. Map of Logan Wash Mine showing instrumentation locations for 1990 tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

35. Diagram showing drill pattern used during Logan Wash face blasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

36. Explosibility data for 1983 pyritic and sulfide ore dusts from the 20-L chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

37. Explosibility data for 1985 and 1987 sulfide ore dusts from the 20-L chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

38. Explosibility data for 1989 pyritic and sulfide ore dusts from the 20-L chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

39. Explosibility data from the 20-L chamber for a mixture of 80-pct sulfide ore and 20-pct rock dust compared

 with data for sulfide ore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

TABLES

1. Properties of the oil shale and comparison dusts ...................................................... 8

2. Laboratory explosibility data for oil shales and comparison dusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3. Full-face blasts during oil shale mine field tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4. Methane liberated during blasting at White River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5. Minimum charge weights required for ignition in the Bruceton Experimental Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6. Effectiveness of various stemming materials in suppressing ignitions when detonating explosives into a

flammable gas zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7. Ideal detonation properties of emulsion and other explosives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8. Ideal detonation properties of various ANFO formulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

9. Crawshaw-Jones data for various explosive products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

10. Gelled water inert stemming weights to prevent methane-air ignitions in the Lake Lynn cannon gallery . . . . . . . . . . . . . . . 34

11. Relative incendivity of unstemmed explosives in a flammable coal dust cloud at the Lake Lynn cannon gallery . . . . . . . . . 35

12. Chemical and size data for sulfide ores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

13. Laboratory explosibility data for sulfide ores and comparison dusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

14. Predispersed sulfide ore dust tests in the Bruceton Experimental Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
iii

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

bar/s bar per second L/t liter per ton (metric)

cal/g calorie per gram m meter

cm centimeter m/s meter per second

fr/s frame per second m square meter 2

ft foot m cubic meter 3

g gram m /min cubic meter per minute 3

g/cm gram per cubic centimeter m /t cubic meter per ton (metric) 3 3

g/m gram per cubic meter mbar millibar 3

gal/st gallon per short ton min minute

gr/ft grain per foot mm millimeter

h hour mol/kg mole per kilogram

J joule ms millisecond

K kelvin pct percent

kbar kilobar s second

kg kilogram t ton (metric)

kg/m kilogram per cubic meter t/d ton (metric) per day 3

kJ kilojoule vol pct volume percent

km kilometer wt pct weight percent

km square kilometer μm micrometer 2

L liter EC degree Celsius

Mention of any company name or product does not constitute endorsement by the U.S. Department of Energy Pittsburgh Research

Center.

Visit our Mining Health and Safety Research site on the Internet, accessible via http://www.usbm.gov.
SECONDARY EXPLOSION HAZARDS DURING BLASTING

IN OIL SHALE AND SULFIDE ORE MINES

By Eric S. Weiss, Kenneth L. Cashdollar, Michael J. Sapko, and Eugene M. Bazala 1 2 3 4

 ABSTRACT

The data presented in this report are the results, to date, of an ongoing Pittsburgh Research Center Disaster 5

Prevention research program on the explosion hazards associated with blasting operations in noncoal mines.

Laboratory and experimental mine tests have shown that oil shale and sulfide ore dusts can be ignited given the

proper predispersed dust concentrations, particle size, and kerogen or sulfur content. Methane (CH ) gas may 4 also

be present in deep oil shale formations and can pose a significant added hazard to underground blasting operations.

The most common explosive used for blasting in oil shale had been ANFO, a combination of ammonium nitrate

and fuel oil; blasting in sulfide ore had used ANFO and/or dynamites.

Tests conducted at the cannon gallery at Lake Lynn Laboratory near Fairchance, Fayette County, PA, provided

a means of evaluating the relative incendivity characteristics of new and existing explosive products. Three

explosives—a pumpable emulsion-ANFO blend, a packaged water gel, and an emulsion blasting agent—exhibited

low-incendive qualities compared with other more highly incendive products such as ANFO and some dynamites.

Based on the data collected during numerous full-scale blasts in oil shale and sulfide ore mines, the low-incendive

products significantly reduced or eliminated the ignition hazards while at the same time providing effective

fragmentation of the rock.

Based on the positive results from the gallery and field testing, low-incendive explosives, coupled with good

blasting procedures, show promise in reducing dust and/or gas ignitions associated with blasting operations in oil

shale and sulfide ore mining applications.

Mining engineer. 1

Supervisory research physicist. 2

Research supervisor. 3

Physical science technician. 4

Pittsburgh Research Center, U.S. Department of Energy, Pittsburgh, PA.

This work originated under the U.S. Bureau of Mines prior to transferring to the U.S. Department of Energy on April 4, 1996. 5
2

INTRODUCTION

OIL SHALE MINING Historical Development of Oil Shale

Alternative fuel sources have been viewed over the past several Worldwide, oil shale formations are found on nearly every

decades as possible replacements for, or additions to, the crude continent. The U.S. Geological Survey (6, pp. 85-98) estimated

U.S. petroleum supply. The development of alternative fuels that over 4×10 t of oil shale exists in worldwide deposits having

could also benefit our national security by reducing the reliance on a potential shale oil yield of approximately 3×10 L. Among the

foreign oil. This lack of energy self-reliance was demonstrated fossil fuels, oil shale reserves are second only to coal reserves in

quite effectively during the 1973 oil embargo by the oil exporting terms of heating value or energy. The larger deposits are located

nations. During this period, a resurgence in the U.S. oil shale in Asia, Africa, North America, South America, Europe, Australia,

industry occurred. The embargo catalyzed the United States to and New Zealand. The Green River formation in Colorado,

seriously consider developing an industry to derive oil from shale Wyoming, and Utah is the largest concentration of high-grade oil

rock. shale in the world.

Oil shale must be heated to convert the solid hydrocarbon The shale oil industry has experienced many high (boom) and

(kerogen) in the rock to crude shale oil. The retorting technology low (bust) cycles over the years. As early as the 14th century, oil

can be accomplished either in situ or at a surface facility. The in shales of Austria and Switzerland were heated to produce a rock

situ retorting process (1-2) is conducted within the shale oil, which was then refined to an ointment (6, p. 108). In the 6

formation. For aboveground retorting (3) operations, the shale United States, Native Americans and early pioneers used pieces of

rock is removed from the ground and transported to the surface oil shale in their campfires (7). Many oil shale processing plants

facility. Both methods require extensive underground facilities (6, p. 108) existed in the Atlantic States before Drake's first oil

which are generally developed through blasting operations. Many well in Pennsylvania in 1859. These plants converted eastern

potential hazards are encountered when conducting large-scale U.S. oil shale into fuel oils. In 1874, transcontinental rail workers

underground mining and blasting activities, not the least of which also discovered and used the western U.S. oil shale from the Green

are the explosives used for these blasting operations. Due to the River formation in Wyoming in their campfires (6, p. 108). The

high volume of material that is required to be extracted in these discovery by Drake and others of crude petroleum in the United

large mine entries, blasting agents are generally utilized instead of States in the late 1800's and subsequent discoveries of abundant

the more expensive cap-sensitive explosive products. A blasting quantities of inexpensive oil in the Texas and Arabian oilfields

agent is defined as any material or mixture consisting of fuel and were the primary reasons for the bust in the oil shale industry in

oxidizer intended for blasting, which as mixed for use or shipment the United States and why it had not developed commercially, as

cannot be detonated by means of a No. 8 test blasting detonator was the case in many foreign countries. The People's Republic of

(0.40 to 0.45 g pentaerythritol tetranitrate (PETN) base charge) China, for example, has large deposits of oil shale and has been

when unconfined. An explosive material is considered to be cap- producing shale oil for over 60 years (8). Much of China's oil

sensitive if it detonates with a No. 8 test detonator. Much of the shale overlies thick seams of coal. Because the coal and oil shale

knowledge gained in studying the explosion hazards in oil shale are mined together, production costs for shale oil in China are low

mining can be directly applied to other noncoal mining (8-9). Pulverized oil shale is also mixed with coal and burned

operations, such as sulfide ore mining. directly for power generation in China. In Estonia, most of the oil

The Pittsburgh Research Center, as part of its Disaster shale is burned under boilers and contributes significantly to

Prevention research program to improve safety for underground Estonia's electrical power needs (6, p. 108).

mine workers, initiated numerous research programs (4-5) from In the United States during World War II, when concerns were

the 1970's through the early 1990's under the former U.S. Bureau raised regarding the reliability of imported fuel supplies, the U.S.

of Mines (USBM) to define the fire and explosion hazards Congress enacted the Synthetic Liquid Fuels Act of 1944, which

inherent in the mining of oil shale. In addition, the Mine Safety authorized the USBM to develop domestic oil shale. The USBM

and Health Administration (MSHA) had reservations about the established a facility at the Anvil Points Mine located in the Roan

applicability of existing metal/nonmetal mine safety regulations to Cliffs west of Rifle, CO (10-11). Many technological advances in

oil shale mining. MSHA, therefore, requested that the USBM the mining and processing of oil shale were developed at this site

conduct additional research to evaluate the adequacy of these (10-14). To further promote private development of oil shale, the

regulations. This report focuses only on the hazards associated Federal Prototype Oil Shale Leasing Program was enacted by the

with the extraction of the oil shale through underground mining U . S .

operations and summarizes oil shale research conducted by the

Pittsburgh Research Center

Italic numbers in parentheses refer to items in the list of references preceding the 6

appendix.

since the previous reports (4-5). Some of the data presented here

have been published previously in various forums and are cited in

the text.

15

17
3

Figure 1.—Map showing four basins of the Green River Oil Shale Formation and locations of oil shale mines.

Congress in 1974. The program enabled large tracts of federally Much of the world's oil shale deposits can be extracted through

owned lands to be leased by industry to conduct exploration and surface mining techniques (9). However, to extract the rich oil

research aimed toward commercial-scale operations. This, coupled shales of the Western United States, underground mining

with the 1973 oil embargo, created a boom for oil shale, and techniques must be employed (12). Due to low worldwide oil

many experimental- and commercial-scale facilities were prices, as well as the high initial capital expenditures required to

constructed and placed into operation for various periods of time develop an oil shale mine, retort facilities, and refineries, the

in the 1970's and 1980's. These included Occidental Oil Shale western U.S. oil shale mines are currently uneconomical, and all

Corp.'s Cathedral Bluffs and Logan Wash oil shale projects (15), had been closed by 1991. However, in the event of another enUnocal Corp.'s Long Ridge project (3), Exxon Co. U.S.A.'s ergy crisis that would escalate the price of crude petroleum, many

Colony Shale Oil Project (16), and the White River Shale Project of these facilities could be made operational for only a fraction of

(17) jointly owned by Phillips, Sohio, and Sunoco. Figure 1 is the original development costs because the transportation, power,

a map (adapted from figure 3 of reference 10 and from reference mine, and other infrastructure are already in place. At such time,

18) showing the location of these western U.S. oil shale mines. research by the Pittsburgh Research Center into the explosion

hazards of oil shale would again become needed.
4

Properties of Oil Shale the x rays from a particular element to form an image showing the

To better understand the fire and explosion hazards of oil shale, figure 2A. A comparison of the three x-ray images corresponding

the physical and chemical nature of oil shale must first be to the 600-μm transparent particle shows that the particle contains

examined. Note that the research was conducted with oil shales a large amount of Ca and only trace amounts of Si and Al.

from the Green River formation (19-21), and discussions in the Therefore, that particle is most likely calcitic in composition. In the

remainder of this report are limited to only that formation. The upper right quadrant of figure 2A is an opaque dark particle. This

Green River formation covers about 88,000 km in Colorado, particle is clearly much more heterogeneous in structure than the 2

Utah, and Wyoming (figure 1). This formation is divided into four calcitic particle. Some areas of the particle appear quite dark and

major basins: the Piceance Creek Basin in Colorado, the Uinta are probably high in kerogen content; lighter areas are probably

Basin in Utah, and the Green River and Washakie Basins in mineral matter. The corresponding x-ray maps show a large

Wyoming. These oil shale formations were deposited in the amount of Si and lesser amounts of Ca and Al for this particle.

Tertiary period on the bottom of the ancient Lake Uinta. Contrary Therefore, the mineral matter in this particle is probably mainly

to its name, oil shale is not a shale rock and does not directly quartz. The dark particle in the lower left quadrant of figure 2A is

contain oil. Oil shale actually is a lake-deposited sediment that even higher in kerogen content, with only a small amount of Si

contains organic matter (6, pp. 85-98). As the mineral silts and mineral matter as shown by the x-ray maps. The lower right

organic matter were deposited simultaneously, heat and pressure quadrant of figure 2A contains a large number of very small

formed the deposits into a stable mix of minerals and solid organic particles from the minus 400-mesh sieved fraction. Probably each

matter. These oil shales are a marlstone consisting mainly of of these small, individual mineral particles is fairly homogeneous

dolomite, quartz, and calcite. The solid organic material is known in structure, with most of them high in mineral content as shown

as kerogen. by the x-ray maps.

The kerogen is comprised of hydrogen and carbon molecules

that are tied to oxygen and sulfur atoms. The kerogen is bound SULFIDE ORE MINING

within the mineral matrix of the oil shale rock. When the oil shale

is heated (pyrolyzed) above 200 EC, vaporized shale oil and other Sulfide mines provide several metallic ores, particularly of the

gaseous products are formed from the kerogen. These oil vapors nonferrous metals such as lead (Pb), zinc (Zn), and copper (Cu).

are condensed and further processed to obtain the final fuel That is why the sulfide ore mines are also called base metal mines.

product. The amounts of oil and gas that can be derived from the Some of the minerals that compose sulfide ores are pyrite (FeS ),

oil shale can be estimated by the standard Fischer assay (22-23). pyrrhotite (~FeS), galena (PbS), sphalerite (ZnS), and chalcopyrite

The standard notation for oil yield or assay by this method is (CuFeS ). Although there is iron in the sulfide ores, it is usually

gallons of oil per short ton of shale. not recovered. In addition to the base metals, some sulfide ore 7

The kerogen and minerals within the oil shale rock are shown mines produce small amounts of precious metals, such as silver

in figure 2A, which is an optical microscope photograph of (Ag) and gold (Au). As in the oil shale mines, developmental

particles from pulverized oil shale. Three large individual particles headings and production stopes are mined by blasting.

and a group of minus 400-mesh fine particles are shown in figure This report summarizes research conducted by the Pittsburgh

2A. The structural heterogeneity of oil shale is clearly illustrated by Research Center during the 1980's and early 1990's on sulfide ore

the optical photomicrograph and the three accompanying scanning explosibility and the investigation of less incendive blasting agents

electron microscope (SEM) x-ray maps (24) for the elements for mining.

calcium (Ca), silicon (Si), and aluminum (Al). In the upper left

portion of figure 2A is a 600-μm particle that is optically

transparent. The three corresponding SEM x-ray maps (figures 2B,

C, and D) were made by collecting only 

To convert from gallons per short ton to liters per metric ton, multiply by 4.17. 7

distribution of that element over the same field of view as in

2

2

8

Some of the data were presented in an unpublished report entitled “Hazards of 8

Secondary Dust Explosions in Sulfide Ore Mining” by E. S. Weiss, K. L. Cashdollar, and M.

J. Sapko (Pittsburgh Research Center Internal Report No. 4646, Jan. 1987).
5

Figure 2.—Optical microscope photograph of oil shale particles (A), and the corresponding SEM x-ray maps for the elements calcium

(B), silicon (C), and aluminum (D).

EXPLOSION HAZARDS OF OIL SHALE DUSTS

The rich oil shale deposits in the Western United States are shale dust.

generally extracted by drilling and blasting techniques (12) and When fine particles of a combustible dust (oil shale, sulfide ore,

transported to a surface retort facility. The underground headings coal, etc.) are suspended in an atmosphere that contains sufficient

are developed by regular room-and-pillar mining methods. Even oxygen to support combustion, a dust explosion can occur. In

for in situ retorting techniques (1-2), headings are blasted at various underground mining, the energy required to ignite this dust cloud

levels within the mine to develop the underground retort chamber is supplied by the explosives used in development and production

and raw oil collection facilities. The mining operations in oil shale blasting. Along with the useful work energy derived from the

are regulated under the standards developed for metal and nonmetal detonation of the explosives, large quantities of high-temperature

mines (25). Permissible explosives for use in hazardous areas of gases and particles are released. Blasting operations also generate

metal and nonmetal mines are tested and approved in accordance large quantities of dust due to the fracturing of the rock. When an

with 30 CFR 15 (25). Concern raised by the USBM and MSHA ignition of this dust cloud occurs, a local aerodynamic disturbance

in the 1970's regarding the adequacy of these regulations for oil (wind) is created that stirs up the fine dust particles that had been

shale mining led to USBM research into the explosibility of oil previously deposited along the back, ribs, and sill of the mine
6

Figure 3.—Plan view of the Bruceton Experimental Mine.

workings. The flame front from the initial localized dust explosion minus 20-mesh (<850 μm) and 57 to 85 pct minus 200-mesh

then develops into a secondary explosion, consuming this new dust (<75 μm). For the coarse dusts, 90 pct of the dust was minus

cloud and propagating through the mine heading. 20-mesh and 27 pct minus 200-mesh. Data from the BEM tests

LARGE-SCALE EXPERIMENTAL MINE DATA shale dusts that assayed less than ~85 L/t (~20 gal/st). This is to

Very early USBM tests (26) in a 20-cm-diam by 5.2-m-long than 88 pct did not produce explosions. For oil shales with assays

pipe showed that some oil shales were explosible. The initial from 92 to 208 L/t (22 to 50 gal/st), the minimum nominal

USBM large-scale studies in the 1970's determined the ignitability explosible concentration ranged from 600 to 200 g/m ,

characteristics of oil shale dust in terms of its particle size and respectively. Data from the BEM tests also showed that the finer,

kerogen content. These data were collected from both pulverized oil shale required less dust for an explosion than coarse

experimental mine and laboratory tests. Scores of explosion tests oil shale of the same kerogen content. The explanation is that the

with oil shale dusts were conducted in the 1970's through the early finer particles can pyrolyze and produce volatiles more rapidly in

1980's by Richmond and colleagues (4, 27-29) at the Bruceton the flame front.

Experimental Mine (BEM) located at the Pittsburgh Research

Center. These explosion tests with oil shale dust were conducted

in the main entry of the BEM shown in figure 3. The main entry

is 400 m long and has a cross section 1.8 m high by 2.8 m wide.

Several types of instrumentation acquire data on the explosions, as

shown in figure 4. Pressure transducers that measure the static

pressures generated by the explosion were mounted into the face

and outby into the rib. At these same stations, 16 optical flame

sensors were mounted outby to 200 m. These sensors transmitted

signals from which the flame velocity and duration were

determined. Optical dust probes (30-31) and three-color

pyrometers (32-33) were also positioned outby the ignition zone,

as shown in figure 4. The dust probes measured the relative

airborne dust concentrations entrained by the explosion. Flame

temperatures could be calculated from the pyrometer data. The raw

data signals from the various instruments were recorded by a highspeed computer data acquisition system, as well as on high-speed

photographic chart paper oscillographs.

The dust test zone for the oil shale mine tests was usually

92 m long. The oil shale dust was distributed on cross shelves

located near the roof of the mine on 3-m intervals. At the face, a

30-m volume of 8.5-pct methane (CH ) in air was used as the 3

4

ignition zone, as had been used previously for coal dust tests. An

electric match located at the face served as the point source for

ignition of the gas. The initial gas explosion would both disperse

and ignite the dust.

Based on the BEM tests (4, 27-29), it was determined that the

explosibility of oil shale dust was a function of its kerogen content

and particle size. The data showed that the oil shales that contained

higher kerogen content required lower dust concentrations to

produce an explosion. The reason is that the dusts with the higher

kerogen content emit more combustible volatiles per mass of dust.

The particle size distribution of the dusts tested in the BEM were

classified as either pulverized or coarse dust. For the pulverized

dusts, 100 pct of the dust was

(4, 27-29) showed that explosions did not occur in pulverized oil

say that the pure oil shale dusts with incombustible contents greater

3
7

Figure 4.—Side view of the face area in the main entry of the Bruceton Experimental Mine showing instrumentation positions.

Figure 5.—Vertical cross section of the Pittsburgh Research

Center’s 20-L dust explosibility test chamber.

LABORATORY DATA 

The standard laboratory test chamber used by the Pittsburgh Research Center for studying the explosibility and inerting of

combustible dusts is the 20-L chamber (34-36) shown in figure 5.

The test procedure included the partial evacuation of the chamber

and the dispersion of the dust by a blast of air from the bottom.

The ignition source was energized after the pressure had returned

to about 1 bar absolute and the dust had been uniformly dispersed.

At ignition, there was a moderate turbulence level. Details of the

operating procedures and dust dispersion uniformity measurements

are in reference 34. Instrumentation with the 20-L chamber includes a pressure transducer, optical dust probes (30-31) for

measuring dust dispersion uniformity, and multichannel infrared

pyrometers (32-33) for measuring explosion temperatures. The

data from the various instruments are collected by a high-speed PCbased data acquisition system. The ignition sources used for the

20-L tests were electrically activated, pyrotechnic ignitors

manufactured by Fr. Sobbe GmbH of Germany. For the data

reported here, 2,500- or 5,000-J ignitors were used. The 5,000-J

ignitor energy was used previously for hard-to-ignite dusts, such as

coal and rock dust mixtures (35-36). The oil shales are also hard

to ignite because they also contain a large amount of inert material.

The chemical and physical properties of the pulverized oil shale

and comparison dusts are listed in table 1. The oil shales are

identified by a four-digit number used in previous USBM
8

Table 1.—Properties of the oil shale and comparison dusts

Properties Oil shale dusts Coal dusts1

5082 6114 6238 0000 5084 hvb lvb anthra

Assay, gal/st . . . . . . . . . 19 23 34 42 49 NAp NAp NAp

Assay, L/t . . . . . . . . . . . . . 82 95 140 174 205 NAp NAp NAp

Volatility, pct . . . . . . . . . . . 9 10 15 19 22 37 17 5

Heating value, cal/g . . . . 1,010 1,190 1,790 2,280 2,610 7,700 8,150 7,140

Minus 200-mesh, pct . . . 85 57 74 84 78 80 75 77

D , med Fm .............. 21 35 19 29 30 48 52 18

ö W, Fm ............... 37 115 53 43 51 51 58 37

ö , Fm ............... S 14 16 12 17 17 32 39 13

ö (%T), Fm ........... S 16-34 12-27 12-29 17-35 16-37 27-58 24-50 24-34

NAp Not applicable.

"hvb" refers to high-volatile bituminous, "lvb" refers to low-volatile bituminous, and "anthra" refers to anthracite. 1

publications (4-5). These were the same pulverized oil shale dusts the 20-L chamber at the time of ignition (36). Summary data for

used for the mine tests. The comparison coals include high-volatile the three oil shales from figure 6 plus a fourth oil shale are shown

bituminous (Pittsburgh Seam), low-volatile bituminous in figure 7, where they are compared with the data for the two

(Pocahontas Seam), and anthracite. The Fischer oil shale assay is bituminous coals and the anthracite. For these data, 5,000-J

listed in terms of both gallons per short ton and liters per metric ton ignitors were used for the oil shales and the anthracite; 2,500-J

in the table. The uncertainty in the Fischer assays is 1 to 2 gal/st. ignitors, for the bituminous coals. For the dusts shown in the

Based on additional data, the Fischer assays have been revised figure, the high-volatile bituminous (hvb) coal dust has the lowest

slightly from the values in earlier reports. The volatility is the sum minimum explosible concentration (MEC) or lean flammable limit

of the oil and gas amounts from the Fischer assays (22-23). Based (LFL). It also had the highest explosion pressure and dP/dt. In

on the relationship in references 4 and 37, the sum of the oil and terms of MEC and explosion pressure, the next most hazardous

gas in percent is about 0.45 times the oil shale assay in gallons per dust was the low-volatile bituminous (lvb) coal. The 205-L/t

short ton. The total organic content is 0.58 times the oil shale (49-gal/st) oil shale had a higher MEC and lower explosion

assay. The heating value was measured in an adiabatic bomb pressure than those of the two bituminous coals. The dP/dt of the

calorimeter. The percent passing through a 200-mesh sieve is listed 205-L/t oil shale was significantly lower than that of the hvb coal,

next. The size data are from a combination of sonic sieving and but was slightly higher than that of the lvb coal. The lower assay

Coulter (electrolytic conductivity through a small orifice) counter oil shales had progressively higher MEC's and lower explosion

size analyses. For the Coulter data, the dusts were dispersed in pressures. For the 82-L/t (19-gal/st) oil shale dust at very high

isopropyl alcohol. D is the mass median diameter, ö is the concentrations (800 to 1,400 g/m ), only about one-half of the tests med W

volume or mass mean diameter, and ö is the surface mean produced explosions in the 20-L chamber. These laboratory results S

diameter. Lastly, table 1 lists ö as calculated from the optical dust are comparable with the full-scale mine data (4) that showed that S

probe transmission (%T) data measured while the dust was fine-sized oil shales with Fischer assays greater than ~85 L/t

dispersed in the 20-L chamber. As described in reference 30, the (~20 gal/st) could propagate explosions. For the anthracite coal,

dust probe transmission T is related to ö by Bouguer's law: the slight pressure rise observed was only due to a small amount of S

 T ' exp(-3QC R/2Dö ), (1) propagation. Therefore, this 5-pct volatile anthracite is considered m S

where Q = a dimensionless extinction coefficient, have also shown that anthracites do not propagate explosions.

C = the mass concentration, bility limit for the dusts. At the higher dust concentrations, the m

R = the path length, oxygen in the chamber is consumed. At even higher dust

and D = the density of a particle. pressure nevertheless remains constant. The normal rich

The 20-L detailed explosibility data (5, 38) for three oil shale not observed for the dusts. An explanation of this effect, at least

dusts of varying kerogen content are shown in figure 6. The for many dusts, is that the solid phase fuel must first devolatilize

5,000-J ignitors were used for these data. The explosion pressure before it can mix with the air. As soon as sufficient volatiles are

(gauge) and the pressure rise rate (dP/dt) are plotted versus the generated to form a stoichiometric concentration of volatiles in air,

dispersed dust concentration. It should be noted that the dP/dt data the flame front propagates rapidly through the mixture before

depend greatly on the particular turbulence level in excess fuel volatiles can be generated.

3

burning around the ignition source and does not signify flame

nonexplosible in air in the 20-L tests. Full-scale mine tests (27)

The data in figures 6 and 7 show no evidence for a rich explosimaximum pressures and rates of pressure rise level off as all of the

concentrations, although the mixtures are nominally fuel-rich, the

flammability limit observed for hydrocarbon gases such as CH is 4
9

Figure 6.—Explosibility data from 20-L chamber for three oil shales.
10

 Figure 7.—Summary explosibility data from 20-L chamber for four oil shales compared

 with high- and low-volatile bituminous coals and anthracite. hvb = high-volatile bituminous;

lvb = low-volatile bituminous.
11

 Figure 8.—Minimum explosible concentrations for hybrid mixtures of coal or oil shale dusts with methane gas from 20-L chamber.

A summary of the laboratory explosibility and ignitability data

for the oil shales and comparison coals is presented in ta-ble 2. The

MEC data were measured at 2,500 and 5,000 J. The variation in

the measured MEC values with ignition energy indicates the ease

or difficulty in igniting the various dusts. The lower grade oil

shales could not be ignited with the 2,500-J ignitors. The

maximum explosion pressures (P ) and the maximum pressure max

rise rates (dP/dt) were taken from the data curves in figure 7. As max

shown in figure 6 and table 2, the 82-L/t (19-gal/st) oil shale only

produced explosions at very high concentrations in the 20-L

chamber, even with the 5,000-J ignitor.

The minimum autoignition temperature (MAIT) data shown in

table 2 were measured in a 1.2-L furnace (5, 39). The MAIT

values listed in table 2 were modified slightly from earlier reported

MAIT values (5, 38-40) based on a revised ignition criterion (41).

The new criterion for ignition in the 1.2-L furnace is flame

observed out of the furnace within 3 s, as opposed to the previous

criterion of flame within 1.5 s.

The presence of even a small amount of CH gas can lower the Therefore, the curvature is more likely an effect of ignitability 4

minimum explosible concentrations of the oil shale dusts. Hybrid rather than of flammability.

mixtures of oil shale dusts with CH gas were also studied in the 4 There were also some 20-L tests to determine whether CH

20-L chamber using 2,500-J ignitors. Data for hybrid mixtures of added to a high concentration of oil shale dust would produce a

the 205-L/t (49-gal/st) oil shale and CH are shown as the triangle rich mixture that would be incapable of propagating an explosion. 4

data points in figure 8; the 140-L/t (34-gal/st) oil shale mixtures are The data in figures 6 and 7 showed there was no rich explosibility

shown as the circles. For comparison, data are also shown for limit for the oil shales out to high dust concentrations. In the

mixtures of Pittsburgh hvb coal and CH . The area above and to additional tests, 2.5 pct CH added to 1,000 g/m of the 205 L/t oil 4

the right of each curve is explosible, or flammable, for that dust; shale in the 20-L chamber still produced an explosion.

the area below and to the left of each curve is nonexplosible, or In summary, laboratory and experimental mine research at the

nonflammable. The data for mixtures of Pittsburgh coal and CH Pittsburgh Research Center has shown that oil shale dust clouds can 4

in figure 8 show a linear or near-linear mixing relationship similar be ignited and therefore could present a hazard during underground

to Le Chatelier's law for hydrocarbon gases (42-43). The measured blasting operations. This research has also shown that small

LFL for the pure CH with the 2,500-J ignitor is 4.4 pct, but this amounts of CH can significantly reduce the lower limits of 4

is an overdriven system as shown by tests in a larger 120-L explosibility for oil shale dusts. If one combines the above results

chamber (44). The more appropriate LFL for CH is the 4.9-pct with the highly incendive (or flame-generating) blasting agents 4

value measured with a 1,000-J ignitor in the 20-L chamber. The typically used in oil shale mining, then a potentially hazardous

data for the two oil shale dusts show some curvature. This is condition exists in the oil shale mining industry. For these reasons,

probably due to the great difference in ignitability between the oil field investigations at several oil shale operations were initiated to

shale and the CH , i.e., the dust becomes more easily ignited as measure dust generation, gas emissions, flames, and pressures 4

small amounts of CH are added. during commercial-scale mining operations. 4

4

4

3

4

Table 2.—Laboratory explosibility data for oil shales and comparison dusts

Explosibility data Oil shale dusts Coal dusts

5082 6114 6238 0000 5084 hvb lvb anthra

Assay, L/t . . . . . . . . . . . . 82 95 140 174 205 NAp NAp NAp

MEC, kg/m3

 @ 2.5 kJ ............

 @ 5 kJ . . . . . . . . . . . . .

NA NI 0.40 0.20 0.20 0.08 0.12 NA

~0.8 0.6 .25 .16 .13 .06 .09 NI

P , bar . . . . . . . . . . . . . max 2.7 3.0 3.7 4.5 4.5 5.6 5.0 0.4

(dP/dt) , bar/s max ....... 13 22 45 ~88 88 145 77 <1

MAIT, EC . . . . . . . . . . . . 490 ~490 490 470 450 530 ~610 ~670

NAp Not applicable. NA No data available. NI Nonignitable.
12

DUST, PRESSURE, AND FLAME DURING BLASTING IN OIL SHALE MINES

The Pittsburgh Research Center was invited to participate in dust collection plates, and other equipment utilized in the third

studies of blasting practices at several western U.S. oil shale mines blast are detailed in this diagram.

during the 1980's and early 1990's. A summary of these field tests In August 1985, one additional face blast (46) was monitored

is listed in table 3. The individual blasts are discussed in detail at Colony Mine, and two blasts were monitored at Unocal's Long

below and in the sections of this report entitled "Full-Scale Field Ridge Mine. The emphasis on these tests was to acquire more

Studies With ANFO" and "Full-Scale Field Tests With a Low- accurate and detailed data in several areas of uncertainty from the

Incendive Blend." In addition to the full-face blasts listed in the earlier blasts. These areas included more accurate sampling of the

table, there were additional single-hole blasts at some field sites. dust loadings on the rubble pile, measurements of airborne dust

In March 1983, April 1984, and August 1985, Exxon invited concentrations and static pressure generated during the blasts, and

the Pittsburgh Research Center to participate in monitoring several the collection and analysis of postblast gas samples.

of its full-scale oil shale blasts (45-46). This provided an excellent Unocal's Long Ridge oil shale mine (3) is located north of

opportunity to compare data from laboratory and small-scale tests Parachute, CO (figure 1). The mine enters the Green River oil

with data obtained from a commercial-scale operation. shale formation from an outcrop 300 m above the valley floor at an

Exxon's Colony Shale Oil Project (16) is located north of elevation close to that of Colony Mine. The mining level includes

Parachute, Garfield County, in western Colorado (figure 1). The the rich Mahogany zone. Unocal used a room-and-pillar mining

mine site was developed from an outcrop of the Green River oil method that extracted about 13,500 t/d for its on-site retorting

shale formation that occurs at an elevation of approximately operations. The shale realized an average crude oil yield of 158 L/t

2,150 m in this part of the Rocky Mountain Range. Figure 9 is a (38 gal/st). The locations of the two face blasts at Long Ridge

partial mine map showing the entrance and the blasting zone. This Mine are shown in figure 11; blast 6 at Colony Mine is shown in

underground test site was designed to accommodate commercial- figure 12.

scale mining. Ceilings 9.1 m high and headings 16.8 m wide were One area of concern that was evaluated during these 1984-85

typical dimensions in this type of mining operation. blasts was the amount of combustible oil shale dust generated

The first and third blast conducted at Colony Mine originated during the blasting operation. As shown in figure 10, more than

at the face as shown in figures 9 and 10. The second blast started 40 sample pans were distributed from 30 m to over 150 m outby

the development of crosscut 9. Figure 10 is an enlarged diagram the face in room 1 during the third blast at Colony Mine. The pans

of the blasting zone. The positions of the instruments, were 0.36-m galvanized steel plates that were bolted to the mine 2

floor. These plates served as collection surfaces that permitted a

representative measurement of the dust fallout

Table 3.—Full-face blasts during oil shale mine field tests

Date Blast No. Blasting agent Company Mine 1

Mar. 1983 ........... 1 ANFO (u,n) .............. Exxon ........ Colony.

2 ANFO (u,n) .............. Exxon ........ Colony.

Apr. 1984 ........... 3 ANFO (u,n) .............. Exxon ........ Colony.

Aug. 1985 ........... 4 ANFO (u,n) .............. Unocal ....... Long Ridge.

5 ANFO (u,n) .............. Unocal ....... Long Ridge.

6 ANFO (u,n) .............. Exxon ........ Colony.

Sept. 1988 .......... 7 ANFO (u,n) .............. Unocal ....... Long Ridge.

8 ANFO (u,n) .............. Unocal ....... Long Ridge.

9 ANFO (s,e) .............. Unocal ....... Long Ridge.

10 ANFO (s,e) .............. Unocal ....... Long Ridge.

Aug. 1989 . . . . . . . . . . . 11 Emulsion (s,e) ............ Unocal ....... Long Ridge.

12 Emulsion (s,e) ............ Unocal ....... Long Ridge.

13 Emulsion (s,e) ............ Unocal ....... Long Ridge.

14 Emulsion (s,e) ............ Unocal ....... Long Ridge.

June 1990 . . . . . . . . . . 15 Emulsion (s,e) ............ Unocal ....... Long Ridge.

16 Emulsion (s,e) ............ Unocal ....... Long Ridge.

17 Emulsion (s,e) ............ Unocal ....... Long Ridge.

 18 Emulsion (s,e) ............ 2 Occidental .... Logan Wash.

"u" refers to unstemmed, "s" refers to stemmed, "n" refers to nonelectric initiation, and "e" refers to electric initiation. 1

Methane-air zone added at face. 2
13

Figure 9.—Map of part of the Colony Oil Shale Mine showing entry and blasting area.

Figure 10.—Map of blasting area showing instrumentation and sampling pan positions for blast 3 at Colony Mine.
14

 Figure 11.—Map of blasting area showing instrumentation positions and faces for blasts 4 and 5 at

Long Ridge Mine.

Figure 12.—Map of blasting area showing instrumentation positions for blast 6 at Colony Mine.

associated with the oil shale blast. Based on dust sample size from determine if the concentration nearer the face may have been of

the first two blasts, the surface area of the pans had been increased sufficient quantity to represent an ignition hazard. The entry floor,

for the third blast to allow for larger dust samples, which were roof, and ribs were washed with water before each of the six blasts

needed for more accurate laboratory analyses. As will be described to eliminate contamination of the sample plates by preexisting dust.

later in this report, sampling of the floor dust loadings deposited Postblast dust samples were then collected from the plates and the

during the first three blasts at Colony Mine in 1983 and 1984 rubble pile. The dust samples collected after each blast were

provided a reliable estimate of the airborne or float dust weighed and sized in the laboratory. Only the minus 20-mesh dust

concentrations up to 165 m downstream of the original face. was analyzed, eliminating small flyrock and other debris that may

However, the postblast rubblization generally covered the have accumulated on the plates.

collection plates within 40 m of the original face. Therefore, for For blasts 3 through 6 in table 3, respirable dust samplers were

blast 5 at Long Ridge Mine and blast 6 at Colony Mine, careful also positioned throughout the area to measure the airborne fine

attention was directed toward sampling dust from the rubble pile to dust particles generated from the blast. These units were not meant
15

to represent the respirable dust to which miners would be exposed blast heading at the rear of crosscut 9 to observe the turbulent dust

because miners were not present during the blasting. The total dust clouds resulting from the explosion and also to observe the blast

samples collected from the filter cassettes and cyclone cups were effect on a roof-mounted ventilation bag. A multiple flash bulb

weighed, and the filters were also analyzed for quartz content. The system was used for each camera to provide the necessary lighting.

sampler units were turned on approximately 0.5 h before the event The flash sequence was designed to start 1 s before detonation and

and continued sampling for 1.5 h. to illuminate each camera's field of view for approximately 8 s.

The instrument stand for blast 3 was positioned approxi- mately This was accomplished by using long-duration flash bulbs and

75 m outby the face near the rib as shown in figure 10. This firing sequential series of these flash bulbs through the use of time

location permitted relative safety from flyrock and other debris that delay relays. During blasts 4 and 5, two cameras were mounted to

would be generated by the blast. The risk of damage to the the mine roof (see figure 11) about 40 m outby the face to

instruments from flyrock was the reason for positioning the stands document any flame occurrence. One camera was filming at a rate

in the crosscuts in blasts 4 and 5 (see figure 11). For blast 6 at of 32 fr/s; the other, at a rate of 64 fr/s. A multiple flash bulb

Colony Mine, one stand was located approximately 85 m outby the system was also used during these tests to illuminate the blast face.

face at midentry; the other stand was 15 m further down the entry During blast 6, a camera was mounted on the mine roof 38 m

(see figure 12). For this blast, the instrument stands were in direct outby the face (see figure 12).

line of sight to the face. Instrumentation on or near the stand A prototype high-speed, evacuated-vial gas sampling system

locations consisted of drag probes, optical dust probes, pressure was field tested for the first time during blasts 4, 5, and 6. This

transducers, and cameras. Data from the various instruments were system was capable of obtaining 18 test tube samples in the entry

recorded on a high-speed chart recorder. Two drag probes of at preset time intervals. The sample time and the interval between

different sensitivities were used in the measurement of the dynamic samples could be adjusted in advance. The unit was activated by

pressure during blast 3. One drag probe utilized a 9-cm-diam the initial blast wave and programmed to draw gas samples every

target disk; the other, a 20-cm-diam disk. 2 min immediately following the preshear detonation.

Optical dust probes (30-31) were installed to monitor the Several variations in the blast hole pattern had been tested by

airborne oil shale dust produced during the blasting process. The Exxon and Unocal to determine the most effective system for

dust probes measure the transmission through the dispersed dust rubblization with minimal damage to the entry roof and ribs. The

cloud. Air jets directed over the light source and sensor windows blast hole pattern, powder factor, and depth of round are the

eliminate obscuration due to dust coating the windows. The primary factors that can affect the fineness of dust associated with

optical path length for the dust probe was 5 cm. The dust probe mining of oil shale. The blast hole pattern used for blasts 4 and 5

data, in conjunction with the floor dust data, allowed for a more at Long Ridge Mine is shown in figure 13; that for blast 6 at

comprehensive understanding of the dust generation problem as it Colony Mine is shown in figure 14. (The patterns for blasts 1 to

related to various blasting techniques. For blast 3, the probe was 3 were very similar to these patterns.) For blasts 4 and 5, the faces

mounted approximately 1 m from the mine floor on the instrument at Long Ridge were 15 m wide by 8 m high and were drilled to a

stand, 73 m from the face. Three optical dust probes were utilized depth of 7.3 m. The preshear and production holes for each blast

in each of blasts 4 through 6 to provide a better estimation of the were 11 cm in diameter. Seven preshear holes were drilled into the

dust concentration and to attempt to calculate, from the dust cloud face along each rib. Preshear blasting is a technique designed to

arrival times at the probes, the wind velocities of the dust clouds. prevent the shock pressures from the detonating production holes

In blasts 4 and 5 at Long Ridge Mine, the dust probes were from severely damaging the riblines. The preshear holes were

positioned within the first open crosscut about 40 m from the face drilled in a vertical pattern parallel and close to each rib. Typically,

(see figure 11). Two probes were mounted on one stand: the first these holes were then loaded with explosives of smaller diameter

1.5 m and the second 3 m above the mine floor. Across the entry, than that of the drill hole. The decoupled charges were detonated

the other probe was about 1 m off of the floor. before the production holes, thereby creating a vertical fracture or

Pressure transducers were installed during each blast to measure crack extending from the roof along the entire length of the holes.

the static overpressures developed from the shock waves of the This crack reduced the effects of the shock waves produced from

detonating explosives during the blasting operation. A pressure the detonating production holes from traveling into and damaging

transducer was flush mounted to the right inby rib near the the new pillars. The blast face at Colony Mine was 17 m wide by

instrument stand for blast 3. A static pressure transducer was flush 9 m high and was drilled to a depth of 9.5 m.

mounted to the left inby rib approximately 1 m in from the crosscut

for blasts 4 and 5. For blast 6, a transducer was located on the

right inby rib about 85 m from the face; several other transducers

were about 350 m further downstream. A pressure transducer was

also installed at the control base for each blast.

Cameras were used to obtain a visual record of the blasts to

determine if any flame was evident, to study the dust generation,

and, if possible, to witness the actual face destruction. Two 16-mm

movie cameras (filming at 32 fr/s) were installed in explosionresistant steel boxes 40 m from the face during blast 3 (see

figure 10). One camera was mounted on the mine roof and viewed

the face. The other camera was positioned perpendicular to the
16

 Figure 13.—Diagram of Long Ridge Mine face showing blasting

pattern for blasts 4 and 5. Open circles are the preshear charge with

no delay; solid circles are the main charge.

 Figure 14.—Diagram of Colony Mine face showing blasting

pattern for blast 6. Open circles are the preshear holes with no

delay; solid circles are the production holes.

This pattern (figure 14) used one additional preshear hole along the face were high enough to promote secondary dust ignitions.

each rib and contained four fewer production holes. The preshear The nominal concentrations on the rubble piles (from blasts 5 and

and production holes for the blast were 11 cm in diameter. The 6) ranged from 6 to 28 g/m as the distance to the face decreased.

detonation of the preshear holes 25 ms before the initial detonation These average concentrations were an order of magnitude below

of the production holes provided the necessary expansion space, the experimentally determined lean limit concentrations (4-5, 38)

similar to that of undercutting a coal face, and minimized rib for explosions of fine-sized oil shale dusts of similar grade. The

damage. The dashed lines in both figures 13 and 14 show the 32E nominal concentrations outward from the pile steadily declined to

V-cut at the center of the faces. These angled holes are detonated a low of about 0.1 g/m or less at 150 m downstream.

in pairs to provide a relief area for the holes detonating later in the Some of the floor dust samples collected during the 1983-85

round. Each of the 16 preshear holes in both patterns were loaded blasts were also analyzed for size distribution and oil assay. The

to within 1 m of the collar with 2.5-cm-diam explosive charges. surface mean diameters, ö , and the volume or weight mean

The other production holes were loaded from the back to within diameters, ö , were calculated from the measured size distributions

5 m of the collar at Colony Mine (50 kg ANFO per hole) and to of the minus 20-mesh fractions. Within 45 m of the face, ö

within 3 to 5 m of the collar at Long Ridge Mine (20 to 36 kg ranged from 15 to 137 μm, ö ranged from 50 to

ANFO per hole). Nonelectric detonators with time delays of 0

through 600 ms were used to initiate the holes.

The chart recorders, power supplies, and timer-delay initiation

system were located in a mobile control base that was positioned in

a relatively safe area nearby the blast face. A timer and relay

system was used to sequence the start and stop of the recorder,

cameras, flash system, and compressed air for the dust probes; it

also initiated the blast round. The timer system activated the

monitoring equipment 1 s before detonation. This allowed the

equipment to achieve full power and establish stable baselines.

Detonating cord was used to initiate the detonators in the blast

holes.

Figures 15 and 16 illustrate the face area before and after blast

6 at Colony Mine as seen from the instrument stand. The square

markings on the face (figure 15) outline the preshear holes,

adjacent to each rib, and the angled center holes. Note the

horizontal flash assembly mounted on the roof (about 15 m from

the original face) in the upper center of both figures. The

detonation of this round generated approximately 3,000 t of oil

shale rubble. The shale rubble extended out nearly 70 m from the

face. The fragmentation and distribution of the shale (figure 16)

were also more uniform than those of earlier tests without preshear

holes.

The larger boulders shown in figure 17 were typical for blasts

4 and 5 at Long Ridge and resulted from the design of the blast

hole pattern. The larger material was preferred at this mine because

of its retorting process and problems with processing fines. The

rubble pile extended outby the original face about 50 m for these

blasts.

Dust samples were collected from the collection plates and/or

measured rock surfaces at various locations on the rubble piles for

all face blasts, except blast 4. The samples were weighed, sized,

and assayed. Only the minus 20-mesh fraction of the dust from

each sample was analyzed, eliminating the small flyrock and very

coarse particles, which would not contribute to an explosion flame.

Figure 18 shows the floor dust loadings generated during each

of the 1983-85 blasts. Note that the distances in this figure are

specified relative to the new face after the blast. The volumetric

concentrations on the right ordinate are calculated assuming a

uniform dispersion of the dust throughout the cross section. The

dust collected during blasts 1, 2, and 3 provided a reasonable

estimate of the dust loadings from 40 to 165 m outby the new face.

The samples in blasts 5 and 6 were taken exclusively from the

rubble piles to determine if the nominal dust concentrations nearer

3

3

s

w

s

w
17

Figure 15.—Mine face before blast 6. (Photo by Kenneth L. Cashdollar, Pittsburgh Research Center.)

 Figure 16.—Mine face after blast 6, showing rubblization. (Photo by Kenneth L. Cashdollar, Pittsburgh Research

Center.)
18

 Figure 17.—Pittsburgh Research Center researchers with large

boulders in the rubble pile.

Figure 18.—Summary of floor dust loadings (minus 20-mesh fraction) after five blasts.

320 μm, and the minus 200-mesh fraction ranged from 10 to The floor dust samples from blast 3 at the Colony Mine were

81 pct. No systematic variation with distance was found within generally too small to obtain Fischer assay data; therefore, the

this area. However, the powder factor and the blast hole pattern assays were calculated from the measured heating values based on

can affect the size distribution of the dust. For the floor samples the previously determined linear relationship (4). Through- out the

farther from the face (70 to 140 m), ö ranged from 22 to 28 μm; rubble pile, the calculated assays of the Colony Mine floor dust s

ö ranged from 70 to 140 μm. These finer sized dust samples at samples from blast 3 ranged from 125 to 142 L/t (30 to 34 gal/st). w

greater distances from the face, beyond the rubble pile, are Farther from the original face, the assay dropped to about 108 L/t

consistent with the expected results of airborne transport of dust (26 gal/st) at 100 m and to 92 L/t (22 gal/st) at 135 m outby.

particles. These results are consistent with previous data (4-5, 38) that

showed a lower assay for the finer sized particles if oil shale dust is

size separated. In the face blasts, the dust was apparently size

separated by the natural dynamics of the air flows, whereas the

previous laboratory data came from dust that was separated by

mechanical sieving. For the mine dust samples from the rubble

pile for blast 6 at Colony Mine in 1985, the assay of the floor dust

samples was approximately 100 L/t (24 gal/st), somewhat lower

than that from the earlier blast 3 at Colony Mine. For the mine

dust samples from the rubble pile for blast 5 at Long Ridge Mine

in 1985, the assay of the floor dust samples ranged from 63 to 103

L/t (15 to 25 gal/st).

The analyses of the dust samples collected from the respirable

dust sampler devices showed that the quartz content of the samples

ranged from 2 to 5 wt pct. The measured total mass concentration

collected by the samplers would be consistent with the measured

floor dust loadings at the same locations if the majority of the dust

was deposited on a time scale of the order of a few minutes.
19

Figure 19.—Pressure generated by blast 3.

For blasts 4, 5, and 6, very low dust concentrations were rebounding pressure waves gradually faded. In blasts 4, 5, and 6,

calculated from the high transmission data (95 to 99 pct) recorded

by the optical dust probes. However, even these transmissions over

a 5-cm optical path length of the probe would correspond to a very

low visibility over a distance of a few meters. The measured

transmission values of 95 to 99 pct are consistent with the

measured floor dust loadings at the positions of the dust probes.

Close to the face, there were probably higher airborne dust

concentrations, as shown by the billowing clouds in the high-speed

movies and the higher floor dust loadings on the rubble pile near

the face.

Figure 19 is a plot of the signal from the pressure transducer

during blast 3. Approximately 0.25 s after the blast initiation, the

static wall pressure rose to a peak of 100 mbar. This pressure pulse

is believed to be associated with the preshear holes and the initial

center angled holes, since it would take about 0.25 s for the

pressure pulse at the face to travel at the speed of sound in air to the

instrument stand 73 m from the face. The small signals earlier than

0.25 s were probably associated with vibrations of the solid mine

rock itself, inasmuch as the speed of sound in rock is about 20

times the speed of air. The dynamic pressure measured by the drag

probes was approximately 26 mbar, corresponding to a wind

velocity of about 60 m/s.

The static pressure was approximately 0.3 bar at about 25 m

from the face for blasts 4 and 5 at Long Ridge Mine. The pressure

65 m from the face was 40 mbar; the pressure 115 m from the face

was approximately 20 mbar. At Colony Mine, the measured

pressure was about 100 mbar at a distance of 85 m from the face

during blast 6. This pressure was nearly the same as the pressures

measured during blasts 1 and 3 that occurred in the same blasting

zone. The peak pressure recorded at the control base located

145 m from the face in blast 6 at Colony Mine was about 50 mbar.

Additional transducers were mounted on several test stoppings

located over 430 m from the blast face during blast 6. The

maximum recorded pressure exerted against these ventilation

stoppings was about 11 mbar. A cyclic pressure wave was

developed from blast 6 that was clearly evident after viewing the

movie film taken of a ventilation curtain located about 155 m from

the face. The curtain was being alternatively pulsed outward, then

inward as it encountered the successive shock waves generated

from the face detonations and rebounding pressure waves. The

pulses decreased in intensity and the interval between pulses

became l onger as the

the pressure decayed approximately linearly with distance, except

when it reached an area with multiple rooms and passageways,

where it decayed more rapidly. A computer model could be

developed to predict the pressures that would be generated for a

particular blasting pattern and powder factor; these predictions

could be applied in the construction of durable ventilation

stoppings for these large headings.

The use of the prototype high-speed, evacuated vial sam- pling

system resulted in very limited samples. During two of the three

blasts, flyrock damaged the unit and/or severed the pneumatic lines

and supports. In one blast, however, the unit was able to obtain 18

gas samples over a 34-min period. Analyses of these samples

showed trace amounts of hydrogen (H ) and CH , perhaps 2 4

generated from the cracking of the shale kerogen as it was heated

by the explosives. Another source of these gases would be the

detonation byproducts from the explosives. These measurements

were in the absence of any net ventilation flow and would be

reduced greatly after the main fans were turned on. The CH4

amounts were negligible compared with those in gassy mines, such

as the Horse Draw and White River Mines (4, 29). This was

expected since both the Colony and Long Ridge Mines were near

outcrops and had not detected any CH .4

The two 16-mm movie cameras were successful in observing

the face during each blast. Frames from the movies of blast 6 are

shown in figure 20. The start of the blasting sequence was clearly

evident by the brilliant flash (figure 20A) of the detonating cord as

it initiated the time delay detonators in the preshear and production

holes. Figure 20B shows flame from an unstemmed blast hole

during the detonation of the angled holes in the center

approximately 45 ms into the blasting sequence. Figure 20C

shows the blasting face about 110 ms after ignition. The lighting

on the upper right of these photographs (figure 20B and C) is due

to the multiple flash system; that on the left is due to the flame

exiting from the borehole. Flame was evident for at least 220 ms

after ignition, at which time the dust and rock totally obscured the

view of the cameras. Similar results were observed during blast 3

in this mine and during blasts 4 and 5 at Long Ridge Mine. The

flame luminosity lasted too long to result solely from the

explosives themselves; it is uncertain from the film whether the

flame was the result of afterburning of the detonating cord or

burning oil shale dust clouds. It is possible that there were

localized areas where the dust concentrations were above the lower

limit requirements for an oil shale dust ignition. However, any

ignitions that may have resulted from these dust clouds would have

been small localized occurrences that would not be able to

propagate very far based on the measured average floor dust

loadings. There was no evidence of flame luminosity after the end

of the blasting sequence.
20

Figure 20.—Frames from high-speed movie during blast 6.

A, initial face detonation; B, luminosity at face at 45 ms; C, luminosity at face at 110 ms, with horizontal flash system in upper

right of frame. 
21

Exxon's Colony Mine and Unocal's Long Ridge Mine were (4). The combination of CH liberated from the fragmentation of

known to be nongassy due to their proximity to the outcrops. the blasted shale, the background CH emissions con- tinuously

However, CH posed an explosion hazard in other oil shale mines, released from the developed headings, and the fine-sized dust 4

which will be discussed in the next section of this report. generated in localized high concentration clouds at the face would

Experimental results have shown that the presence of CH , even in pose a potential localized ignition hazard during some underground 4

small quantities, will significantly decrease the lean limit oil shale mining operations.

concentration of oil shale dust required to initiate an explosion 

4

4

GAS GENERATION DURING OIL SHALE MINING

HORSE DRAW OIL SHALE MINE and background, were calculated and compared with the mass of

Generally, CH was not associated with the early oil shale mines As the mining progressed in the various levels of Horse Draw 4

in the Green River formation. All of the mines were developed Mine, the tube bundles were extended to provide data on the CH

from oil shale outcrops, and CH was never detected. In 1977, a levels in the vicinity of the blast face. A CH emission rate of 1.6 4

732-m-deep shaft was driven into the Piceance Creek oil shale m /t of oil shale was determined to be a reasonable value for the

basin at Horse Draw, in Rio Blanco County, Colorado (47-48). ventilation design based on the data gathered by the gas monitoring

CH was encountered at this location, confirming earlier core data trailer ( 4 52). This value was in the same range as that reported from

(49-50). Because this area was at least 24 km from an outcrop and outgassing of cores taken nearby in the formation (49-50).

located below two aquifers, the CH did not have the opportunity Continuous background CH emissions ranged between 4 0.37 and

to migrate out of the formation. Matta and others (50) indicated 0.51 m /min both during the mining operations and shortly after

that the amount of CH present in any particular formation is the cessation of mining in late 1981 (53). 4

proportional to its kerogen content, distance from an outcrop, and In 1988 and 1992, further gas samples were collected and

depth. An increase in any one or more factors increased the analyzed as part of a continuing study of background CH

potential for CH to be encountered in the formation. emissions (54). At the Horse Draw oil shale mine site in Colorado, 4

From April 1979 to October 1981, Multi-Mineral Corp. had several gas samples and air velocity measurements were taken from

operated Horse Draw Mine under a cooperative agreement with the a vent pipe protruding through a concrete shaft seal (part of the

USBM and the Bureau of Land Management. Part of Weichman's 1986 site reclamation). All mining at Horse Draw had ended in

research (51) was directed toward analyses of cores for CH late 1981. Natural ventilation occurred in the mine due to the 4

content. Unlike the study of Matta and others (50), no conclusive temperature gradient between the outside ambient air and the

data could be obtained to link CH content to the kerogen content atmosphere inside the mine. This natural draft could vary between 4

or depth of formation. However, the differences in the CH 50 and 100 m /min. Analyses of the 1988 samples showed that the 4

content from the two studies may be due to geological conditions, mine continued to liberate CH at a rate of approximately 0.74

such as fractures and/or the numerous occurrences of leached m /min. Samples collected in 1992 showed that the mine was still

nacholite zones. These zones of porous nacholite may store CH liberating CH at a rate of 0.63 m /min. Although these rates were 4

in quantities above those predicted from the original study. Oil somewhat higher than the previous data (53), they are believed to

shale, unlike coal, has a low permeability, and the CH would not be more accurate since all venting was through a single small 4

easily be liberated in advance of mining. opening instead of several conduit openings as in the earlier

It is important to detect CH in a mining operation for safety sampling studies. 4

reasons. Once CH is detected, it should be quantitatively 4

monitored during the mining operations and, if possible, correlated WHITE RIVER OIL SHALE PROJECT

with the CH content found in cores. If this approach is successful, 4

the quantity of CH to be expected in future mining operations can In 1984, the Pittsburgh Research Center monitored gas 4

be better predicted. emissions during development blasting operations at the White

In 1980, the Pittsburgh Research Center installed a gas River Shale Oil Project. An isometric view of the White River

monitoring system (52) at Horse Draw Mine to quantify the Shale Project (17) mine is shown in figure 21. The project is

amounts of CH generated during blasting operations. A gas located on Federal leases Ua and Ub in Uinta County, UT. The air 4

monitoring trailer was set up on the surface. Carbon monoxide shaft shown on the left of figure 21 is about 335 m deep. The

(CO) and CH were monitored continuously by means of tube mine was designed to extract over 180,000 t of oil shale per day 4

bundles into the mine. Gas concentration data were recorded in from the rich Mahogany zone of the Green River formation.

analog fashion on strip charts. Pitot probes were installed in Room-and-pillar mining was to be used, leaving rooms about 18 m

exhaust fan ducts at various levels to measure the air flows in order high by 16 m wide after benching. The development headings

to compute the gas emissions at those levels. During underground were 4 m high by 6 m wide and drilled to a depth of 3 m for

blasting, the personnel were evacuated to the surface, but the gas blasting rounds.

emission and air flow data continued to be collected through the

tube bundles to the surface trailer. By continuous monitoring, the Gas Monitoring System

total gas emissions, including emissions from blasting, mucking,

oil shale realized from the blast round and from core samples.

4

4 3

4 3

4

3

4 3

4

3
22

Figure 21.—Isometric view of White River Shale Project mine showing decline on right and vertical air shaft on left.

The gas monitoring system trailer had been returned to the Any water in the tubes and/or dust in air was removed by filters

Pittsburgh Research Center after cessation of mining at Horse Draw and desiccant. Scanning valves connected the analyzers to a

in 1981. The system was redesigned for improved performance programmed series of gas and pressure port positions selected by

and monitoring capabilities. In March 1984, the gas monitoring the operator for analysis. The system had a capacity of 24 separate

trailer was positioned near the headframe of the White River oil sample positions throughout the mine.

shale mine (figure 22). It was operated by White River Mine Gas analyzers determined the concentrations of CH and CO by

personnel. The trailer was environmentally controlled to extend measuring the infrared radiation absorbed by these gases. When

the operating range of the gas monitoring system to any type of any of the sampling positions were 10 pct greater than the previous

environment. In the event of a power outage, the trailer was sample, the computer held on that position for three consecutive

furnished with a backup battery system to ensure an uninterrupted samples; if there was no further increase by more 

power source for an additional 4 h. A local alarm sounded to alert than 5 pct, it would resume its programmed sequence. This feature

the mine personnel of power outages and dips. was particularly important because it alerted the mine personnel to

The gas monitoring trailer was connected to a 10-tube bundle unexpected rises in gases during off-hours. The system could also

of fire-resistant tubes, each of 1-cm-diam polyethylene. The tubes be programmed with limits on gas concentrations and could be

were extended down the shaft; as mining progressed, some of the interfaced with local alarms to alert mine personnel when gas limits

tubes were used to follow the face and some were used to provide had been exceeded.

local information regarding CH and CO levels in case of fire. By measuring the pressure differentials and flows within 4

Figure 23 shows a flow diagram (53) of the gas monitoring system. individual tubes in the bundle, the system had a built-in method of

Pumps installed beneath the trailer draw gas samples through the self-checking for leaks and/or plugs. The air flows and pressures

tube bundles into the gas analyzer. within the underground mine vent pipes could also be monitored,

4

along with air velocity measurements accurate to

1 m/s in the entries or shafts.

The gas analyzer and its associated functions were all controlled

by a microprocessor. The microprocessor had a large storage

capacity able to hold the data until such time as it was removed

from the memory remotely or to the local terminal. Strip charts

were also available as an additional record in case of a computer

failure. A main computer located at the Pittsburgh Research Center

automatically retrieved the microprocessor data at regular intervals.

The raw data were then processed and plotted using the latest

calibration values.
23

Figure 22.—Gas monitoring trailer near air shaft at White River Mine.

Figure 23.—Flow diagram of gas sampling system. (Drawing shows sampling through AN valve.)

Methane Emissions During Mining Operations A typical plot of CH emissions following a blast at the White 4
24

 Figure 24.—Typical methane released during blasting at White

River Mine as measured underground in the east heading.

River oil shale mine is shown in figure 24. Zero time on the plot

corresponds to the time the CH first arrived at the gas analyzer. 4

The average background level of CH (0.02 to 0.03 vol pct) was 4

subtracted from these emission data. As seen in figure 24, the CH4

level associated with the rubblization of the rock rose to 0.39 vol

pct of the total ventilation flow. It eventually declined back to the

background emission level.

The CH emissions generated from the east heading de- 4

velopment at White River in 1984 were divided into two time

periods. The initial emission was defined as the CH measured at 4

the shaft collar during the first 50 min following the blast. These

CH emission data ranged from a low of 0.05 m /t to a high of 4

3

0.4 m /t. The average initial CH emission was 0.2 m /t. 3 3

4

Following the initial blast data, the CH concentration continued 4

to be measured until the background level for the mine was reached

at approximately 3 h after the blast. The average total CH4

emission was 0.4 m /t over the 3-h period following the blast. 3

Table 4 summarizes a portion of the CH emission data collected 4

at the White River Shale Oil Project. The average oil shale grade

in the east heading was 125 L/t

(30 gal/st).

Table 4.—Methane liberated during blasting at the

White River Shale Oil Project

Blast No. Initial emission, m /t Total emission, 3

(first 50 min) m /t 3

2 .................. 0.37 0.64

4 . . . . . . . . . . . . . . . . . . .22 .60

5 . . . . . . . . . . . . . . . . . . .23 .34

6 . . . . . . . . . . . . . . . . . . .17 .27

9 . . . . . . . . . . . . . . . . . . .21 .23

11 . . . . . . . . . . . . . . . . . .31 .40

13 . . . . . . . . . . . . . . . . . .18 .30

15 . . . . . . . . . . . . . . . . . .16 .17

18 . . . . . . . . . . . . . . . . . .05 .07

20 . . . . . . . . . . . . . . . . . .06 .08

33 . . . . . . . . . . . . . . . . . .19 .27

36 . . . . . . . . . . . . . . . . . .37 .70

37 . . . . . . . . . . . . . . . . . .40 .67

40 . . . . . . . . . . . . . . . . . .27 .54

42 . . . . . . . . . . . . . . . . . .25 .40

44 . . . . . . . . . . . . . . . . . .29 .43

46 . . . . . . . . . . . . . . . . . .34 .48

49 . . . . . . . . . . . . . . . . . .17 .30

56 . . . . . . . . . . . . . . . . . .24 .73

59 . . . . . . . . . . . . . . . . . .35 .53

61 . . . . . . . . . . . . . . . . . .34 .58

Average . . . . . . . . . . . . .25 .42

Standard deviation . . . . .10 .20

Methane Emissions From Core Analyses

The amounts of CH released during blasting operations were 4

compared with the CH measured in core samples. The analyses of 4

the oil shale core samples were conducted by Matta and others (50)

in 1976. Sections of core were sealed off, and escaping CH was 4

measured as a function of time and extrapolated back to a zero

time, thereby obtaining an estimation of the total volume of gas

contained in the original core. The total included gas released by

the solid core and that released after crushing. This volume

divided by the weight of the core gave the specific concentration

of CH in m /t. Oil assays were also performed on the cores. 4

3

Figure 25 (from figure 7 of reference 50) shows a plot of gas

concentration versus oil assay yield of a core near the White River

shaft. The figure summarizes direct-method field CH sampling 4

results for four sections of core taken from the same drill hole in the

Uinta Basin. Matta and others (50) indicated that the kerogen

contained in the oil shale could absorb 10 times more CH than 4

could be accounted for through its containment in the pore spaces

alone. The four core samples in figure 25 were within 6 m of the

Mahogany Marker where a drill stem equilibrium pressure of

approximately 21 bar was measured at a depth of 330 m. The

dashed line in figure 25 represents the maximum quantity of CH4

that can be contained in shale at 21 bar and varying oil yields; the

lower curve represents the measured CH emitted from the core 4

sections under atmospheric conditions. The lower curve would
25

 Figure 25.—Methane released from core sections taken near the

White River shaft (lower curve). Dashed line shows maximum methane that could be absorbed by the cores.

more nearly represent the CH released during blasting operations. This research into CH emissions has shown that mining activity 4

The field CH emissions averaged about 60 pct of the maximum in deep oil shale formations will undoubtedly encounter potential 4

CH that could be absorbed in the core samples. Based on this gas hazards during the operations. Combining this hazard with the 4

1976 core analysis (50), the CH emissions from oil shale blasting large quantities of dust generated near the face during blasting 4

operations should not have exceeded a release of 0.4 to 0.6 m /t for operations and the hot combustion products exiting from the 3

oil shale yielding 83 to 125 L/t (20 to unstemmed blast holes, a potentially dangerous condition existed

30 gal/st). for localized CH and/or oil shale dust ignitions.

The 1984-85 studies at White River (53) measured an average

CH release of 0.4 m /t over a 3-h period following the 4

3

blasting operation. The core analysis work (50) predicted a CH4

release of 0.6 m /t for 125 L/t (30 gal/st) oil shale. This variation 3

in amount of CH release may be due to the fact that the core 4

samples were crushed to release all of the CH , whereas the blasting 4

process often left large rocks and boulders. To date, very little is

known about the initial CH release versus powder factor used in 4

the blast design. Conceptually, the larger the powder factor, the

smaller the rubblization and the greater the initial CH release 4

followed by a more rapid dilution to background levels. However,

no study has been undertaken in this area.

The CH content of oil shales is one-twentieth or less than that 4

for hvb coals at comparable depths (53, 55). However, the CH is 4

usually released continuously in coal mines, whereas it is suddenly

released as a pulse during blasting in oil shale mines.

Additional samples were also taken in 1988 from the main

exhaust at the idle workings of the White River Shale Oil Project.

Based on the measured natural ventilation rate, the background

CH emissions ranged from 4 0.04 to 0.08 m /min (54). These 3

values were substantially lower than the 0.3 m /min background 3

emissions recorded following the mine's closure in 1986 (53).

Samples collected and analyzed in 1992 revealed that the mine was

liberating CH at a rate ranging from 0.02 to 0.05 m /min. This 4

3

continued reduction in the CH yield was encouraging because as 4

future mining operations increase in volume, the ventilation

requirements to dilute and remove the CH from the mine workings 4

may not be as formidable.

4

4

9

DEVELOPMENT OF SAFER EXPLOSIVES FOR GASSY OIL SHALE MINES

As part of the research into the hazards associated with the methods, and innovation in underground blasting procedures. The

mining and processing of oil shale, hundreds of experimental mine data directly impact regulatory standards for blasting under gassy

and gallery tests have been conducted to evaluate preferred mine conditions. MSHA awaited the results of this research

combinations of explosives and inerting materials to prevent the program to promulgate blasting regulations at

ignition of oil shale dust and mixtures of oil shale dust and CH . 30 CFR 57.22601 (25) for subcategory I -A mines, which include 4

This research was jointly sponsored by the USBM, the U.S. oil shale mines. These regulations, which state that all personnel

Department of Energy (DOE), and the Colorado Mining must be removed to the surface before blasting underground in

Association, along with MSHA support. Considerable technical such mines, were stayed in 1988 and may remain stayed until

contributions have also been provided by the following explosives commercial oil shale mining is resumed.

manufacturers: Explosives Technologies International, Atlas

Powder Co., ICI Explosives Canada, and IRECO, Inc.; and by the

following mining companies: Unocal Corp., Exxon Co. U.S.A.,

and Occidental Oil Shale Corp.

This Disaster Prevention research focused on developing

procedures and recommendations for acceptable underground

oil shale blasting that maintain a high level of safety for

underground workers when operating under gassy mine conditions

while fulfilling operational requirements for efficiency. The

research was aimed at providing new information, alternative

 On December 7, 1995, a CH ignition occurred in the 9.1-m-diam ventilation shaft of the 9

4

White River Shale Project during mine sealing operations. One worker was killed and two

others were injured as a result of this welding-induced CH ignition. 4
26

INITIAL EXPLOSIVES entitled "Low-Incendive Explosives" later in this report.

Four explosives were initially tested: (1) ANFO, (2) an ex- BRUCETON EXPERIMENTAL MINE TESTS

perimental emulsion, (3) a 50:50 emulsion-ANFO blend, and (4)

a granular explosive. The ANFO was the formulation commonly The purpose of our blasting research program was to deterused in mining: 94 pct ammonium nitrate and 6 pct fuel oil. The mine the relative incendivity of various blasting agents in igniting

Institute of Makers of Explosives defines an emulsion as an fine-sized oil shale dust clouds, CH , and oil shale and CH

explosive material containing substantial amounts of oxidizers mixtures. These incendivity tests (58) on the oil shale dusts and

dissolved in water droplets surrounded by an immiscible fuel. The CH were conducted in the main entry of the BEM (figure 3). The

granular explosive—Atlas 8W—is a permissible explosive (25, 56) tests were conducted near the closed end of the main entry, as

designed for use in underground coal mines where the presence of shown in figure 26. The oil shale dust was predispersed

flammable gases or combustible dusts presents an abnormal throughout the test zone before detonation of the explosive. This

blasting hazard. The key specifications of a permissible explosive was accomplished by loading the dust into the seven steel

are: V-troughs. Pressurized air, exiting from holes in the bottom of the

charge. The dust cloud was confined within the 9.1-m-long test • The explosive composition must be within tolerance as

determined by MSHA.

• It must pass a series of propagation tests and have an airgap

sensitivity of at least 7.6 cm for a 3.2-cm-diam charge.

• The explosive must pass nonignition tests when fired

unstemmed into a mixture of CH , air, and coal dust. 4

• It cannot produce over 70.8 L of toxic gases per 0.45 kg of

explosive.

• It must exhibit insensitivity in the pendulum friction test.

• It must be used in a permissible manner, i.e., with proper

and adequate stemming.

Details on these standard permissibility test methods can be found

in reference 56. The permissible explosive was chosen as a

reference to compare its relative incendivity with the

nonpermissibles in preventing the ignition of predispersed

explosible concentrations of oil shale and coal dust.

Tests were conducted to determine the detonation velocities (56)

of each explosive. The permissible explosive was initiated with a

No. 6 strength electric detonator; the ANFO, emulsion, and the

50:50 emulsion-ANFO blend were initiated with the No. 6

detonator and a PETN booster. These small, rubberlike boosters

are a mixture of high explosive and an elastomeric binder that are

highly resistent to detonation by mechanical impact. They

detonate at approximately 7,315 m/s, generating almost equal

priming energy in all directions.

The velocity measurements were made within a 3.7-m-diam

sphere (56-57). Each 50-cm-diam charge configuration was 80-cm

long with the detonator and booster inserted at one end. An

enamel-coated twisted pair of copper wires was wrapped around

the charge at 25 cm from the detonator; a second pair was wrapped

around the charge at 75 cm from the detonator. Each twisted pair

was attached to a counter to record the time required for the

detonation wave to travel from the first pair to the second pair. As

the detonation wave passed the first twisted pair, the wires were

shorted and the counter started. The counter stopped when the

detonation wave passed the second set. The detonation rate was

then calculated from the length of the explosive column between

the wire sets (50 cm) divided by the time measured by the counter.

The detonation velocities for the explosives used in the BEM tests

were as follows: 5,155 m/s for the emulsion, 3,240 m/s for the

emulsion-ANFO blend, 1,000 to 2,000 m/s for the ANFO

(confined in a steel cannon), and 2,700 m/s for the permissible

explosive. These detonation velocities are considerably lower than

the calculated ideal detonation velocities listed in the section

4 4

4

troughs, dispersed the dust before detonation of the explosive

zone by the plastic diaphragm. The mine entry was 1.8 m high by

2.7 m wide, giving a test zone of 44 m .3

The explosive charges and stemming, when used, were loaded

to the back of the steel cannon (57-mm-diam bore). The various

charges were rear-primed with an electric detonator and booster

(10 g). The cannon was located near the closed end of the entry

(figure 26). If the detonated charge produced suf- ficient flame to

ignite the predispersed cloud of oil shale dust and the flame

traveled beyond the plastic diaphragm, the result was considered

ignition and propagation. However, if the flame was quenched

within the dusted zone (inby the diaphragm), the test was

considered a nonignition. Typical ignition and nonignition static

pressure traces are shown in figure 27. The initial pressure peaks

were due to the detonating explosives and varied with the blasting

agent. However, if the charge weight was sufficient to ignite the

dust, a second pressure rise resulted from the propagating oil shale

dust explosion, as shown in the bottom trace of figure 27. The

magnitude of this second pressure rise depended on the type and

amount of dust and explosive being tested. Instrumentation for

these tests included flame sensors, pressure transducers, an infrared

pyrometer, optical dust probes, and a high-speed camera.

Minimum Charge Weight for Ignition

The first series of tests (58) focused on determining the

minimum amount of explosive (unstemmed) that would ignite

Pittsburgh pulverized coal (PPC) dust and various grades of oil

shale dust. The PPC, a reference dust, was tested strictly for

comparison purposes. In these tests, an explosible concentration of

each dust was predispersed from the air dispersion troughs before

the detonation of the explosive charge. The blasting agents

(charges) were detonated within the 57-mm-diam bore steel

cannon, and the combustion products dis- charged from the cannon

into the dust cloud. Three blasting agents (ANFO, the

experimental emulsion, and the 50:50
27

 Figure 26.—Plan view of the face area in the main entry of the Bruceton Experimental Mine used for gas and

predispersed dust tests.

 Figure 27.—Static pressure traces for typical mine dust explosions in the Bruceton Experimental Mine using oil shale.

emulsion-ANFO blend) were tested. The Atlas 8W permissible

explosive was also tested for comparison data. The results of these

tests are summarized in table 5. Note that all of the dusts (oil shale,

PPC, and sulfide ore) for these tests were of finer particle size than

that collected during production-scale blasting in the oil shale

mines, as discussed in the earlier section entitled "Dust, Pressure,

and Flame During Blasting in Oil Shale Mines."

In table 5, the ignition test results for various explosive charge

weights are listed for the four dusts that were dispersed. For the

140-L/t (34-gal/st) oil shale dust, a 550-g charge of ANFO did not

ignite the dust; however, a 600-g charge of ANFO ignited the dust.

Neither a 1,050-g charge of the emulsion-ANFO blend nor a

1,000-g charge of the emulsion ignited the same concentration of

oil shale dust. When 205-L/t (49-gal/st) oil shale dust was tested,

only 400 g of the ANFO was necessary to ignite the dust cloud.

However, 1,800-g of the emulsion-ANFO blend failed to

ignite the dust, as did a 1,300-g charge of the permissible

explosive. A 1,000-g charge weight of the emulsion-ANFO blend

also failed to initiate an explosion, even with 2.5- to 4.0-pct CH4

dispersed with the 205-L/t oil shale dust. All attempts to ignite

predispersed clouds of 205-L/t fine-sized oil shale with the

emulsion blend were unsuccessful, even with the added CH . The 4

tests were limited to a maximum charge weight of 2,000 g so as

not to damage the steel cannon.

Additional tests (58) were conducted to determine the minimum

amount of explosive required to ignite a predispersed cloud of PPC

dust (table 5). A minimum charge weight of 250 g of ANFO was

sufficient to initiate a coal dust explosion. This confirms that the

coal dust is easier to ignite than even the rich 205-L/t (49-gal/st) oil

shale. A 600-g charge of the permissible explosive ignited the

PPC cloud, whereas a 1,200-g charge of the emulsion blend was

required to ignite the coal dust. A maximum charge weight of

2,000 g (limit for cannon) of the emulsion did not ignite the PPC.

These tests show that the emulsion-ANFO blend is significantly

less incendive than ANFO or even the permissible explosive.

Relatively small amounts of ANFO readily ignited the oil shale

dust. However, all attempts to ignite the fine-sized, rich oil shale

dust clouds failed when using the emulsion-ANFO blend, even in

the presence of up to 4.0 pct added CH .4

Stemming

Another series of tests (58) was conducted in the BEM

(figure 26) to determine the effectiveness of stemming materials in

preventing a mixture of 8.5 pct CH in air from being ignited by 4

detonating explosives. The 4.6-m section of the main entry was

sealed with the plastic diaphragm and injected with 1.7 m3

of CH . When this gas was uniformly mixed within this zone, 4
28

as measured by infrared analysis, the explosive was detonated in CH -air. Ammonium phosphate powder (80 pct minus 200-

the steel cannon located near the face (figure 26). Water, mesh) was also tested because laboratory and large-scale minetests

limestone rock dust, and ammonium phosphate powder were (59-61) have shown this material to be very effective against CH

used as stemming agents. They were evaluated in terms of their explosions. The data in table 6 show that a stemming length of

ability to suppress the flame of the detonating charge and to 20.3 cm (455 g) of ammonium phosphate powder was required

prevent ignition of the CH . The water and limestone are thermal to s 4 uppress the flame associated with the detonation of a 500-g

inhibitors; the ammonium phosphate may be a chemical inhibitor. charge of the ANFO-emulsion blend. A 30.5-cm length of

The explosive charge weights were fixed at 500 g; the stemming ammonium phosphate powder was required to prevent ignition

lengths were varied to achieve suppression. The results of the when using ANFO. The ammonium phosphate powder required

stemming effectiveness tests are shown in table 6. Two significantly less material than the rock dust to prevent ignition;

explosives were tested: ANFO and the emulsion-ANFO blend. however, it was still not as effective as water.

Table 6 lists each stemming agent, length and weight, and test Based on these limited results from the BEM, water was the

result. most effective and economical stemming inhibitor for preventing

Water was evaluated in the form of a plastic tube of water and the ignition of a flammable CH -air mixture. The BEM tests

as a gelled water. A 10.2-cm-long water pack (a self-sealing showed that over 30 pct less water stemming (pack) was needed

4.5-cm-diam plastic tube) was enough to prevent the ignition of to prevent ignitions by the emulsion-ANFO blend compared with

the 8.5-pct CH -air mixture when detonating the 500-g emulsion- ANFO. Due to its ease of handling (including its potential for 4

ANFO explosive charge. However, a 15.3- cm-long water pack pneumatic loading) and its superior performance on a borehole

was required to prevent ignition of the CH by the ANFO. This length basis (due to its increased density over plain water), gelled 4

confirms the results of the previous minimum explosive charge water was determined in the BEM tests to be the preferred

tests, which showed that the ANFO was more incendive. stemming material.

Additional BEM tests with the gelled water units showed that this Another type of water stemming device was then tested: a

stemming material was comparable, on a mass basis, with lightweight, yet durable, cylindrical polyethylene plug that was

ordinary water packs. These gelled water units primarily consist designed to be inserted into a borehole and then filled with water.

of a guar gum and salt blended with water to form a gelatin inert The water plug was designed to provide an effective coupling to

material. the bore. During each test, the plug was positioned in the

Two dry stemming agents were also evaluated. The lime- 57-mm-diam cannon bore against the 500-g charge of ANFO,

stone rock dust was the standard material used for rock dusting in then inflated with water until the plug had reached an internal

mines. Compared with the water, about eight times (by weight) pressure of 1.4 bar. Initial testing of a 15-cm-long water

more rock dust was required to prevent ignition of the

4

4

4

Table 5.—Minimum charge weights required for ignition in the Bruceton Experimental Mine

Predispersed dust cloud

Explosive charge weight, g, and test result

Emulsion ANFO Emulsion- Atlas 8W 

ANFO blend permissible

Oil shale, 140 L/t 600 I 

 @ 350 g/m .............. 3 1,000 NI 1,050 NI 550 NI NA 

Oil shale, 205 L/t 400 I 

 @ 250 g/m .............. 3 NA 1,800 NI 350 NI 1,300 NI 

PPC 1,200 I 250 I 600 I 

 @ 200 g/m .............. 3 2,000 NI 1,000 NI 200 NI 500 NI 

Sulfide ore 

 @ 800 g/m .............. 3 NA 1,000 I 1,000 I NA 

I ignition. NI Nonignition. NA No data available.

Table 6.—Effectiveness of various stemming materials in suppressing ignitions

when detonating explosives (500-g charge) into a flammable gas zone

Stemming material

Emulsion-ANFO blend ANFO

Length, cm Weight, g Result Length, cm Weight, g Resul

t

Water pack . . . . . . . . . . . . 7.6 120 I 10.2 160 I 

10.2 160 NI 15.3 240 NI 

Gelled water . . . . . . . . . . . 2.5 60 I 10.2 260 I 

5.1 140 NI 12.7 350 NI 

Ammonium phosphate . . . 15.3 350 I 25.4 570 I 

20.3 455 NI 30.5 740 NI 

Limestone rock dust .... 25.4 920 I 61.0 2,200 I 

30.5 1,105 NI 66.0 2,400 NI 

I Ignition. NI Nonignition.

plug (filled with 350 g of water) showed it to be effective in preventing the ignition of a flammable concentration of CH -air. 4
29

To determine the extent to which borehole coupling improves direct line of sight 120 m from the face. The cameras filmed at

stemming efficiency, several shorter length plugs were tested in rates of 32, 64, and 100 fr/s. A video camera was also installed

the same manner. A plug 11 cm long containing 165 g of water adjacent to the other cameras to provide an immediate visual

prevented the hot products from the detonating ANFO charge record of each test within minutes after blasting. In contrast to the

from igniting the flammable CH -air atmosphere. Therefore, the earlier field tests, no additional illumination of the blast zone was 4

water plugs provided a greater degree of protection against the required since the only concern was to determine the incendivity

CH ignitions than even the inert gelled water stemming material. l 4 evels (flames) associated with each of the 1988 tests. The flash

The enhanced coupling to the bore effectively contained, for a of the detonating cord and/or any exiting hot gas combustion

longer period of time, the hot combustion products within the products from the boreholes would provide the relative

bore. The result was that these detonation products exited the incendivity indication for each test.

bore at lower temperatures, thereby requiring less stemming to The mine's routine 36-hole blast pattern for a 8.2-m-high by

prevent the CH ignition. Based on the effectiveness of the gelled 12.2-m-wide heading was similar to that (figure 13) used in the 4

water stemming materials in preventing the ignition of the CH previous blasts. The preshear and production holes were each 4

atmosphere during the experimental tests, several production-scale 89 mm in diameter and were drilled to a depth of 7.3 m. Nonblasts were monitored at an oil shale mine to evaluate the electric time-delayed detonators were typically used at this mine.

performance of the gelled water stemming when used during a The preshear and center angled holes were detonated intypical blast loaded with ANFO. stantaneously to provide the expansion space necessary for the

FULL-SCALE FIELD STUDIES WITH ANFO fairly sound rib lines for long-term stability. Four production

In September 1988, four full-scale tests (54) were conducted acted as lifters to produce a fairly uniform floor. The detonators

at Unocal's Long Ridge oil shale mine in Colorado to compare used during these tests were noted for precise delay periods. The

the relative incendivity levels of different blasting procedures. total time of 700 ms was required to complete the initiation of all

These tests are listed as blasts 7 through 10 in table 3. The tests of the blast holes in the face. Precision delay detonators provided

were conducted in an area of the mine similar to that shown in improved fragmentation along with better vibration control by

figure 11. In two of the tests, nonelectric initiation of unstemmed significantly reducing the occurrence of mistimed borehole detANFO was used; in the other two blasts, gelled water was used onations. The production holes were loaded with ANFO from

to stem the ANFO, which was initiated with electric delay the back of each hole to within 1.2 to 3 m of the collar. The

detonators. The tests were monitored for air blast overpressures, preshear holes were loaded to within 1 m of the collar with a

flame duration, and dust generation. These data were also 45-mm-diam water-gel charge. When stemming was used for

compared with data collected from the previous unstemmed blasts 9 and 10, each preshear and production hole was stemmed

development rounds (45-46). with five inert water units. These prepackaged units, each 65 mm

Instrumentation for these tests served mainly to measure and in diameter and 400 mm long, were slit and tamped into the

observe the flame associated with the ANFO face blasts. During holes, resulting in an effective cross-sectional stemming plug

the three previous full-face blasts in 1985 (46), large amounts of approximately 1.1 m long.

flame were ejected from the boreholes during round detonation. The relative incendivities associated with nonelectric versus

Also evident were large billowing clouds of oil shale dust electric initiation and with stemmed versus unstemmed oil shale

generated from the face blasts. Previous dust sampling after the face blasts using ANFO were compared in these four blasts. The

blasts (figure 18) had shown that concentrations were an order of flame sensors and high-speed movie cameras measured the

magnitude below the experimentally determined lean limit relative flame intensity as a function of the time. For the unconcentrations (5, 38) for explosions of fine-sized oil shale dusts stemmed blasts 7 and 8 with nonelectric initiation, approximately

of similar grade. However, a small amount of CH (well below 70 ms of flame radiation was detected with the photosensor 4

the 5-pct lower flammability limit) has been shown to sig- before its field of view was obscured by the dust generated during

nificantly reduce the lean limit dust concentration necessary to the blast. This correlated with the detonation of the preshear and

produce a localized ignition, which could cause extensive damage the initial angled holes. Flame existed over the entire blasting

to equipment, ventilation ducts, and stoppings in the blast zone sequence, as documented by the cameras, but due to the limited

area. field of view and the dust-blinding factor, only the first 70 ms of

During each of the 1988 tests, a flame sensor (silicon photo- flame was recorded by the photosensor. From the 16-mm movie

detector) was positioned approximately 30 m outby the face to film, visible flame was evident along the lengths of the detonating

measure the relative flame intensity and duration of the hot cord trunklines and was particularly concentrated across the face

combustion products exiting from the blast holes. Pressure wherever the cord and nonelectric shock tube connections were

transducers were used to measure the air blast overpressures. One knotted. Large amounts of flame and dust were also observed

static pressure transducer was flush mounted to the rib about ejecting from the preshear, centered angled, and initial production

10 m inby the last open crosscut (or about 50 m from the face). holes early in the blasting cycle. Over 160 ms of flame was reThe second pressure transducer was located 100 to 120 m outby corded by the cameras compared with 70 ms for the flame sensors

the blast face to measure the decay rate of the pressure pulse as a due to the camera's larger field of view, which enabled longer obfunction of distance. The power supplies, recorder, and timer- servation times before the dust obscured the blast face.

delay initiation system were located in the second open crosscut Experiments in the BEM have shown that detonating small

from the face. Three 16-mm movie cameras were located in a amounts of unstemmed ANFO or detonating cord (25 gr/ft) will

larger production holes. In this mine, preshearing resulted in

holes near the floor were the last in the blasting sequence and
30

readily ignite a flammable CH -air mixture. In these mine tests, 4

however, no CH was present, and the oil shale dust generated 4

during blasting was insufficient to develop into an explosion that

would propagate down the heading. However, a localized dust

ignition near the blast face area could occur because of the large

volumes of dust generated during the blast. Although the dust

sampling has shown that these dust ignitions would probably be

limited to the blast zone, significant damage can still result to the

mine's ventilation stoppings and other mining equipment.

For blasts 9 and 10 in table 3, no flame or illumination of any

kind was detected by either the flame sensors or cameras during

the ANFO tests that were stemmed with gelled water and initiated

with an all-electric system. This showed much lower incendivity

for these blasting procedures compared with blasts 7 and 8.

For the unstemmed blasts 7 and 8, the pressure transducers

recorded peak air blast overpressures of approximately 0.3 bar at

50 m from the face (inby the first open crosscut). A transducer

120 m down the heading measured peak overpressures of about

0.15 bar. These values correspond to the instantaneous detonation of the charges in the preshear and initial center production holes and were similar to those measured during previous

unstemmed ANFO face blasts (45-46). For the tests in which

stemming was present, the peak air blast overpressures ranged

from 0.15 to 0.21 bar at 50 m from the face (also inby the first

open crosscut). At 110 m from the face, the maximum

overpressure recorded was about 0.07 bar. The air blast pressure

generated during the stemmed ANFO blast was about one-half

that of a typical unstemmed ANFO test. A postblast qualitative

inspection of the rubble pile showed no significant difference in

fragmentation with or without stemming.

Dust samples were collected from measured rock surfaces at

several locations within the rubble zone to determine the concentration of fine dust generated during blasting. The minus

20-mesh dust from each sample was weighed, and the data are

plotted with data from previous blasts in figure 28. Laboratory

and experimental mine tests (38) have shown that only the minus

20-mesh dust presents a potential explosion hazard. In figure 28,

the floor dust loadings (left ordinate) in grams per square meter

are plotted as a function of distance from the face. The nominal

volumetric concentrations (right ordinate) in grams per cubic

meter were calculated assuming a complete and uniform

distribution of the dust throughout the entire cross section of the

heading. The concentrations of dust from blasts 7 and 8 showed

no significant differences from the earlier tests and were an order

of magnitude below the concentrations required for a large-scale

explosion. However, a small amount of CH released during 4

blasting in gassy mining conditions could significantly increase

the hazard if nonelectric initiation and unstemmed ANFO are

used.

Stemming may also serve as a means of further reducing the

concentration of the dust clouds generated during the blasting

sequence. Based on limited dust surveys after blasts 9 and 10, the

dust generated during the blast was less for the stemmed tests

(represented by open circles in figure 28) compared with the

unstemmed tests (solid circles). Stemming appears to reduce dust

generation compared with that normally ejected from the

unstemmed boreholes.

LOW-INCENDIVE EXPLOSIVES

The Pittsburgh Research Center worked together with several

explosive manufacturers in formulating new, low-incendive,

high-energetic blasting agents for use in gassy mining conditions.

Three types of prototype emulsion formulations containing

different oxidizers were blended with ANFO and evaluated for

incendivity (62). The oxidizers were ammonium nitrate

(NH NO ), calcium nitrate (Ca(NO ) ), 4 3 3 2

and sodium nitrate (NaNO ). For this discussion, they are 3

represented as AN, CN, and SN, respectively. One type of

emulsion contained an AN and SN oxidizer mixture in the base

emulsion; the second type contained a mixture of AN and CN;

and the third type consisted only of AN. All of the emulsion

types were mixed with conventional ANFO. Within each type,

the amount of fuel was varied to adjust the oxygen balance of

each individual explosive blend in table 7. Properties of the

various emulsion-ANFO blends, ICI Breakrite

2 water-gel explosive, and the Atlas 8W permissible are in table

7; properties of the various ANFO formulations are listed in

table 8. The ideal hydrodynamic-thermodynamic equilibrium

calculations of various detonation properties for each explosive

tested are listed in tables 7 and 8. These calculated data were

provided by the explosive manufacturers. All of the emulsionANFO blends in table 7 were 80 pct emulsion and 20 pct ANFO,

except for B, which was a 50:50 blend. The B formulation is the

same 50:50 explosive blend discussed earlier in this report in the

"Initial Explosives" section. The 80:20 blends were more

practical in that they could be conveniently pumped into the

borehole; the 50:50 blend was too viscous. The ICI Breakrite 2

is a water-gel explosive that was being used as a low-incendive

booster for detonating the emulsion blends. A water gel is

defined as an explosive material containing substantial portions

of water, oxidizers, and fuel, plus a cross-linking agent. The

permissible explosive, Atlas 8W, was chosen as a reference

material for comparison with the emulsion-ANFO blasting agents

in preventing the ignition of predispersed flammable

concentrations of oil shale and coal dust. Detailed explanations

of the ideal detonation properties can be found in reference 63.

In tables 7 and 8, the oxygen balance denotes whether the

formulation is oxygen-deficient (negative values) or oxygen-rich

(positive values). The expansion work is one of the most realistic

measures of explosive power because it approximates the amount

of work that the gaseous products of the explosion can

accomplish as
31

Figure 28.—Floor dust loadings (minus 20-mesh fraction) of unstemmed (solid circles) and stemmed (open circles)

ANFO face blasts compared with pre-1988 unstemmed ANFO blast data.

Table 7.—Ideal detonation properties of various emulsion and other explosives

Ideal detonation property

Explosive product

A: AN B: AN-SN C: AN-SN D: AN-SN E: Breakrite 2

Emul- Emul-ANFO Emul-ANFO Emul-ANFO water gel 

ANFO

Oxygen balance, pct ............... &9.5 &2.3 &6.0 &2.0 &0.2 

Density, g/m .................... 3 1.34 1.28 1.34 1.34 1.13 

Expansion work, cal/g .............. 740 799 747 763 785 

Reaction temperature, K ........... 2,638 2,830 2,650 2,680 2,720 

VOD, m/s ....................... 6,310 6,270 6,100 6,100 5,060 

Chapman-Jouguet pressure, kbar .... 110 106 102 100 63 

Gas, mol/kg ..................... 43.5 44.4 40.5 39.6 38.6 

H , mol/kg ....................... 2 1.32 1.83 1.17 0.66 0.24 

CO, mol/kg ....................... 0.64 0.87 0.54 0.29 0.10 

Ideal detonation property

Explosive product 

F: AN G: AN-CN H: AN-CN I: Atlas 8W

Emul- Emul-ANFO Emul-ANFO permissible

ANFO

Oxygen balance, pct ............... &1.8 &2.5 &5.9 %7.8 

Density, g/m .................... 3 1.26 1.26 1.26 1.19 

Expansion work, cal/g .............. 874 612 581 658 

Reaction temperature, K ........... 2,080 2,041 2,000 2,043 

VOD, m/s . . . . . . . . . . . . . . . . . . . . . . . NA NA NA NA 

Chapman-Jouguet pressure, kbar .... 38.7 32.5 32.3 31.7 

Gas, mol/kg ..................... 44.5 38.9 38.9 37.3 

H , mol/kg ....................... 2 0.53 0.62 0.87 NA 

CO, mol/kg ....................... 0.22 0.42 0.64 NA 

NA No data available.

they expand from the initial detonation conditions to atmos- the explosive. The calculated velocity of detonation (VOD) is the

pheric conditions. The reaction temperature is the calculated speed at which a detonation wave travels through a column of

maximum adiabatic temperature generated by the detonation of explosive. Note that the calculated values of VOD in table 7 are
32

considerably higher than the experimental values listed earlier in To help understand this potential source of excess fuel (from

the "Initial Explosives" section. The Chapman-Jouguet (C-J) the explosive) burning outside the cannon, experimental tests

pressure is the calculated pressure behind the rear boundary, or were conducted in the Crawshaw-Jones apparatus (56), which is

C-J plane, of the detonation front. Finally, tables 7 and 8 list the used for determining explosive gas production. The test was

total gas produced per kilogram of explosive, the amount of performed by detonating 300 g of a given explosive in a steel

hydrogen (H ) produced, and the amount of carbon monoxide cannon and collecting the expansion products in a 90-L evacu- 2

(CO) produced. ated chamber. The gases were analyzed by standard gas chromaTable 8.—Ideal detonation properties

 of various ANFO formulations

ANFO ANFO ANFO ANFO

96:4 95:5 94:6 92:8 

Oxygen balance,

 pct . . . . . . . . . . . . . . . +5.4 +1.8 -1.8 -9.1

Density, g/m ........ 3 0.85 0.85 0.85 0.85

Expansion work,

 cal/g . . . . . . . . . . . . . . 785 875 906 850

Reaction temper-

 ature, K . . . . . . . . . . . 2,820 3,060 3,140 2,990

VOD, m/s . . . . . . . . . . . 4,420 4,620 4,760 4,770

Chapman-Jouguet

 pressure, kbar . . . . . 42 46 48 49

Gas, mol/kg ......... 43.4 43.3 43.8 45.7

H , mol/kg ........... 2 <0.01 <0.01 0.75 3.63

CO, mol/kg .......... <0.01 <0.01 0.33 1.75

Two important factors to consider when formulating lowincendive explosives are the oxygen balance and the detonation

reaction temperature. As might be expected, a correlation between the explosive's detonation reaction temperature and its

incendivity was evident from these limited number of explosive

products and will be discussed in the subsequent section entitled

"Lake Lynn Cannon Gallery Tests." Some effects of the oxygen

balance of the explosive formulation will be discussed here.

Table 7 indicates that in the negative oxygen balance cases

(excess fuel), there was not enough oxygen to oxidize all of the

fuel and to convert all of the CO to carbon dioxide (CO ); there- 2

fore, H and CO were formed. The higher the negative oxygen 2

balance, the more excess hot H and CO would be discharged 2

from the borehole. It is believed that this excess hot fuel, particularly the H with its very high diffusivity, expands from the 2

borehole, mixes with the air, and then burns. Experimentally, the

lean flammability limit for H at 25 EC is 4 pct for upward, 6 pct 2

for horizontal, and 8 pct for downward propagation (64-65).

Using the Burgess-Wheeler law (42, 64) to extrapolate to higher

temperatures, the limits for upward propagation would be 1.9 pct

at 500 EC and 0.6 pct at 800 EC. In addition, H -air self-ignites 2

at temperatures above 500 EC (43).

The detonation of a stoichiometric ANFO mixture (94.4 pct

AN and 5.6 pct FO) can be approximated by the following

reaction by using CH to approximate the fuel oil: 2

3NH NO % CH 6 3N % 7H O % CO . (A) 4 3 2 2 2 2

The amount and type of products will change as a function of the

FO content. The ideal detonation properties calculated for AN:FO

ratios of 96:4, 95:5, 94:6, and 92:8 are listed in table 8. When the amount of FO falls below 5.6 pct, the reaction

is oxygen-positive and nitric oxides are produced. By contrast,

a negative oxygen balance (excess fuel) tends to generate H and 2

CO (66).

tography. Table 9 lists the gas analyses from the CrawshawJones tests for the ANFO formulations, the emulsion-ANFO

blends, and the other explosives. There is relative agreement between the experimental data for ANFO in table 9 and the calculations in table 8 in that the predicted H and CO concen- 2

trations increase with increasing FO in both tables, even though

the experimental data show higher gas values for each formulation. For all except one of the emulsion blends tested, the data

in table 9 show that the blends produced less H and CO than 2

standard ANFO (94:6). The blend that produced more H and 2

CO than standard ANFO was the emulsion blend A, which had

a high negative oxygen balance (&9.5). Generally, the more

oxygen-balanced blends produced less H and CO than the 2

negative oxygen blends when comparing similar formulations.

Likewise, the blends that contained only AN in the base emulsion

generally produced more H and CO than those containing SN or 2

CN in the base emulsion when all other factors remained

relatively constant. In general, relatively good agreement between the experimental Crawshaw-Jones data (table 9) and the

equilibrium calculations (table 7) was shown for the emulsion

blends.

Table 9.—Crawshaw-Jones data for various

 explosive products

Explosive Gases produced, mol/kg

 H CO NO 2 x 

ANFO 96:4 .... 0.13 0.23 0.47

ANFO 95:5 . . . . .81 .62 .31

ANFO 94:6 .... 1.45 1.09 .14

Blend A ....... 1.81 1.05 .02

Blend B . . . . . . . .15 .44 1.64

Blend D . . . . . .09 .20 .72

Water gel E . . .78 .41 .04

Blend F . . . . . . . .67 .54 .07

Blend G . . . . . . .36 .38 .60

Blend H . . . . . .80 .70 .26

Permissible I . 1.53 1.54 .04

To study the possible ignition of the excess fuel from the

explosives, high-speed photographs were taken of the hot detonation products exiting from a steel cannon (57-mm-diam bore).

Results indicated that the time duration of the flame outside the

cannon increased with increasing fuel content. Flame durations

ranged from 5 to 10 ms for the near oxygen-balanced emulsions

to 30 to 40 ms for the fuel-rich formulations. It was believed that

this longer lasting envelope of flame was contributing to the

incendivity of these formulations. This flame envelope was

believed to be associated with the hot combustible fuels,

particularly due to the high diffusivity of H , which mixed with 2

atmospheric oxygen and burned outside the borehole.

Because of the possibility that prilled ANFO (prill diameter

range from 1,100 to 1,600 μm) was less able to sustain a steady

detonation in the 57-mm-diam borehole compared with larger

diameter holes and thus might be contributing to the incendivity
33

Figure 29.—Flame exiting from cannon after detonation of

blasting agent. (Photo by Kenneth L. Cashdollar, Pittsburgh Research Center.)

through incomplete detonation, tests were conducted with a

ground ANFO (<840 μm) to obtain a higher bulk density in an

attempt to approach more ideal detonation conditions. Incendivity tests (similar to those described earlier in the section

entitled "Bruceton Experimental Mine Tests") showed about the

same level of incendivity with either prill or ground AN for both

5 and 6 pct FO formulations of ANFO.

LAKE LYNN CANNON GALLERY TESTS

To facilitate the continuing research into the development of

the low-incendivity explosives, the testing program was relocated

from the BEM to a surface gallery at Lake Lynn Laboratory near

Fairchance, Fayette County, PA. The use of the surface gallery

eliminated the mandatory delays that were encountered during the

mine tests for the removal of the detonation and combustion

gases.

The Lake Lynn cannon gallery (LLCG) is a 6.7-m-long by

2.4-m-diam horizontal steel cylinder open at both ends. Mounted

inside the LLCG near one end is a 1.5-m long by 0.6-m-diam

steel cannon with a 57-mm-diam by 1.2-m-long bore. Figure 29

shows an example of flame exiting from the cannon after

detonation of a blasting agent. In the standard LLCG tests, the

flame and combustion products from a detonating explosive

charge exit the cannon toward the geometric center of the gallery,

where combustible dust has been predispersed or an atmosphere

of flammable CH -air is present. An example of coal dust ignited 4

by unstemmed ANFO in the LLCG is shown in figure 30.

Various explosives have been tested in the LLCG as possible

replacements for ANFO, which is an inexpensive blasting agent

that is used effectively in many noncoal mining operations.

However, ANFO is also a highly incendive product when detonated and has resulted in numerous dust ignitions following

blasting operations, particularly in sulfide ore mines in Alaska

and Canada. Also, CH is present in some deep oil shale forma- 4

tions (4, 52-53), and blasting with ANFO in these mines has

resulted in CH ignitions. For these reasons, research has been 4

conducted to develop various replacement explosives and safer

blasting procedures for use in these high-risk dust and gas areas.

The research has focused on prototype emulsion and water-gel

formulations as potential replacements for the ANFO that was

typically used in oil shale blasting operations and the dynamite

product that was commonly used in sulfide ore mines. The prototype explosive products generally exhibit good fragmentation

characteristics and have relatively low incendivity levels compared with those of ANFO and dynamite. The results from these

preliminary tests determine which explosives warrant further

evaluation in actual full-scale mining operations.

One of the LLCG tests determined the amount of stemming

required to prevent the hot combustion products (from the explosive) from igniting a flammable atmosphere of CH -air. For 4

this incendivity test with CH , a fixed-weight 500-g explosive 4

charge was loaded to the back of the steel cannon. Various

amounts of inert gelled water stemming (in 50-g increments) were

tamped against the charge. The CH was then injected into 4

the gallery and was contained between plastic diaphragms secured

at both ends of the gallery. A small fan (with explosion-proof

motor housing) located inside the gallery mixed the CH with the 4

air to provide a uniform flammable concentration. The CH4

concentration was continuously monitored by sampling through

a small tube extending from the gallery to an infrared CH4

analyzer. The tests were made at a concentration of about 9.4 pct

CH -in-air. 4

For the dust incendivity tests in the LLCG, a 5.0-m-long steel

V-trough was positioned on the gallery floor in front of the

cannon. Detonating cord was attached to the bottom of the

 V-trough, and PPC dust was loaded on top of the cord. The initiation of the detonating cord resulted in the dispersal of the dust.

The unstemmed charge in the cannon was subsequently initiated

after a 500-ms delay to allow sufficient time for the dust to

disperse throughout the gallery. The objective of this test was to

determine the minimum amount of unstemmed charge that would

ignite the dust cloud (figure 30). The standard PPC dust was

used during these tests due to its low flammability limit, the ease

in which it dispersed, and its availability. This PPC dust has been

used for many years as a comparison standard for flammability

(44). The unstemmed explosive charge weight that would ignite

the dust was only a relative indicator of the explosive's

incendivity characteristics compared with actual blasting

operations. The LLCG incendivity results were conservative

because coal dust ignites more readily than oil shale or sulfide ore

dusts and there was no borehole expansion work done in the

cannon as would occur in rock. However, previous data

(described earlier in the section entitled "Bruceton Experimental

Mine Tests") had shown that the relative incendivity ranking of

various explosive products that were tested against predispersed

coal dust maintained their ranking compared with similar tests

using predispersed oil shale dust clouds of varying grade or assay.

The explosives were received from the manufacturer in a prepackaged or bulk form. All of the explosives were tested in 
34

Figure 30—Coal dust ignited by unstemmed ANFO at the Lake Lynn cannon gallery showing flame exiting from both ends. (Photo

by Kenneth L. Cashdollar, Pittsburgh Research Center.)

approximately 50-mm-diam packages and were loaded and (for both the stemmed explosives detonating into CH and the

tamped firmly to the back of the steel cannon. With the unstemmed explosives detonating into predispersed PPC dust)

prepackaged explosives, the manufacturer delivered the product was verified by at least three LLCG tests.

already packaged in the 50-mm diameter. The bulk repumpable Incendivity tests were conducted in the LLCG to determine

products were generally delivered in 11-kg units, which, before preferred explosives that would reduce the probability of igloading into the cannon, were repackaged in nitions during blasting operations under gassy mine conditions.

50-mm-diam polyethylene lay-flat tubing. All of the cap- Experiments in the LLCG have shown that the detonation of

sensitive charges were initiated with a No. 8 strength copper unstemmed 500-g charges of standard ANFO (94:6) readily

detonator. In addition to the detonator, a PETN-based booster ignited flammable concentrations of CH and/or fine oil shale

unit was used with the blasting agents. An incision was made dust. To study this incendivity level, tests were conducted with

along the length of the stemming package containing the inert various ANFO formulations. A 500-g charge of standard ANFO

gelled water material. The stemming unit was then loaded into required 350 g of a tamped, gelled water stemming material to

the cannon bore and tamped firmly against the explosive charge, prevent the hot combustion products from igniting the

which resulted in an effective coupling of the stemming and surrounding CH mixture in the LLCG. When the FO content of

explosive to the cannon bore. The ANFO was prepared on-site the ANFO was increased to 8 pct, an increased amount of gelled

with an approximate loading density of water stemming (400 g total) was required to prevent the CH

0.88 g/cm . The other explosives were supplied by the manu- ignition (table 10). Conversely, when the FO content was 3

facturers with densities ranging from 1.25 to 1.34 g/cm for the decreased to 4 pct, only 250 g of tamped gelled water was 3

emulsion-ANFO blends, 1.12 to 1.20 g/cm for the emulsions, necessary to prevent the CH ignition. However, as the 3

1.3 g/cm for the water gels, and 0.95 g/cm for the semigelatin incendivity characteristics of the ANFO were reduced by 3 3

dynamite product. decreasing the FO content, the production of toxic nitric oxides

The LLCG tests were to be used as one of many relative in- was increased (table 9).

dicators of an explosive's incendivity characteristics and were not Incendivity tests were also conducted in the LLCG with new

part of any standardized testing schedule for evaluating and reformulated emulsion-ANFO blasting agents as received

explosives used during blasting operations in noncoal mines. from various explosive manufacturers. The pumpable blends

However, a degree of uniformity and reproducibility was strived consisted of 80 pct emulsion and 20 pct ANFO. Also tested was

for during this testing program. Incendivity tests in the LLCG blend B, which was a 50:50 mix and too viscous for pumping.

were conducted only when outside temperatures were above One technique designed to significant7 EC. Likewise, reasonable attempts were made to maintain the ly reduce an explosive's incendivity is through oxygen balancing

temperature of the candidate explosive in the range of 7 to 15 EC.

This was accomplished by storing the product in an underground

explosive magazine. To maintain reliability of the data with

limited testing, each data point corresponding to a nonignition

4

4

4

4

4

of the formulation. Comparing the oxygen balance percentages

found in table 7 for the emulsion-ANFO blend A (&9.5 pct) with

the emulsion blend F (&1.8 pct), an increased amount of gelled

water inert stemming was required with the emulsion blend A to
35

prevent the CH -air ignition in the LLCG, as listed in table 10. minimum of hot particles after detonation. These products 4

Substitution of materials in the formulation is another technique contained very little aluminum, which not only is a source of hot

that can reduce an explosive's incendivity. The blends that

contained AN (blends A and F) in the base emulsion were more

incendive (table 10) than those that contained CN (blends G and

H) or SN (blends B, C, and D), thus requiring more inert

stemming to prevent ignition of the CH zone under the LLCG 4

test conditions. A 500-g charge of these lower incendive blends

required only 100 to 150 g of tamped gelled water stemming to

prevent the ignition of a 9.4 pct CH -in-air zone, compared with 4

350 g for the standard ANFO. The lower incendive blends, as

determined from the LLCG tests, were essentially oxygenbalanced and substituted AN with either SN or CN in the

emulsion portion of the blend. In the LLCG tests, the emulsionANFO blends were generally the least incendive blasting agents

tested because they required the least amount of stemming to

prevent ignition of the CH . Emulsion blend D exhibited the 4

lowest incendivity characteristics of any of the blends and was

subsequently field tested in several oil shale mines, as described

later in this report.

Table 10.—Gelled water inert stemming weights to prevent

methane-air ignitions in the Lake Lynn cannon gallery

Maximum stemming, Minimum stemming,

 g, for ignition g, for nonignition 

ANFO 96:4 . . . . 200 250

ANFO 95:5 . . . . 300 350

ANFO 94:6 . . . . 300 350

ANFO 92:8 . . . . 350 400

Blend A . . . . . . . 400 450

Blend B . . . . . . . 60 140

Blend C . . . . . 100 150

Blend D . . . . . 50 100

Blend F . . . . . . . 250 300

Blend G . . . . . . 100 150

Blend H . . . . . 100 150

Water-gel A . . 1 250 300

Water-gel B . . 2 250 300

Emulsion A . . 3 250 300

Emulsion B . . 4 200 250

Dynamite .... 5 100 150

Cap-sensitive water gel. 1

Water gel blasting agent. 2

Emulsion blasting agent. 3

Cap-sensitive emulsion. 4

Cap-sensitive semigelatin dynamite. 5

NOTE.—Explosive charge for each test was 500 g.

Also listed in table 10 are two prototype water-gel-based

explosives that were tested in the LLCG. These were formulated

to have a low-detonation temperature and to produce a

particles, but can also produce H as a detonation product. 2

Atmospheric air and H can form a flammable mixture, which 2

could extend the duration of flame from the detonating explosives. Table 10 lists the amount of inert gelled water stemming material required to be tamped in front of the explosive

charge in the cannon bore to prevent ignition of the CH in the 4

LLCG. Water-gel explosives A and B required 300 g of the inert

stemming to prevent the CH ignition, compared with 100 to 4

150 g for the emulsion-ANFO blends C, D, G, and H. Standard

ANFO (94:6) required 350 g of the gelled water material to

prevent the CH ignition. The reaction temperatures, as 4

determined from hydrodynamic-thermodynamic equilibrium

calculations provided by the explosive manufacturers, were 2,000

to 2,680 K for the emulsion blends (C, D, G, and H) and

2,675 K for the water-gel explosives; these temperatures were

significantly lower than the 3,140 K for ANFO. However, the

water-gel explosives showed only marginal improvement relative

to standard ANFO in preventing the CH ignitions, whereas the 4

stemming requirements to prevent the CH ignition with the 4

emulsion blends were much lower than those for ANFO. The

water-gel explosives contained dissolved AN, whereas the

emulsion blends replaced the AN in the 80-pct base emulsion

with CN or SN. LLCG incendivity data have shown that the

explosive products that contained AN ignited the CH more 4

readily than those that consisted of other less incendive materials.

The emulsions A and B and the dynamite listed in table 10 will

be discussed below.

Table 11 lists the maximum unstemmed charge weight for

nonignition and the minimum unstemmed charge weight

for ignition of an explosible, predispersed concentration

(200 g/m ) of PPC dust in the LLCG. Coal dust was used during 3

these tests due to its availability. The PPC dust is even more

hazardous than oil shale or sulfide dust; it is more easily ignited

and requires less dust to form an explosible concentration.

Therefore, the LLCG data in table 11 are conservative and are

only a relative indicator of an explosive product's incendivity.

When detonating unstemmed charges from the steel cannon in the

LLCG, all of the hot combustion products were ejected out of the

bore and into the CH or dust atmosphere. When detonating in 4

ore, much of the hot combustion products are rapidly cooled

during the fragmentation process by the rock, which is a natural

thermal sink. Standard ANFO detonated unstemmed from the

57-mm-diam bore readily ignited the coal dust cloud in charge

weights as low as 100 g. It required 2,000 g of the unstemmed

emulsion blend D to ignite the PPC dust; a 1,750-g charge did

not ignite the dust. With the water-gel explosives A and B, a

maximum cannon charge weight of 2,000 g did not ignite the

PPC dust cloud with either explosive. Unstemmed 800-g charges

of the emulsion A ignited the dust; 750-g charges did not.
36

Table 11.—Relative incendivity of unstemmed explosives in a

 flammable coal dust cloud at the Lake Lynn cannon gallery

Explosive Minimum charge, g, Maximum charge, g,

for ignition for nonignition 

ANFO 96:4 . . . . 100 NA

Blend D . . . . . . 2,000 1,750

Water gel A . . . 1 >2,000 2,000

Water gel B . . . 2 >2,000 2,000

Emulsion A . . . 3 850 750

Emulsion B . . . 4 500 400

Dynamite ...... 5 300 250

NA No data available.

Cap-sensitive water gel. 1

Water-gel blasting agent. 2

Emulsion blasting agent. 3

Cap-sensitive emulsion. 4

Cap-sensitive semigelatin dynamite. 5

NOTE.—Maximum cannon charge weight was 2,000 g.

The two water-gel explosives, the ANFO-emulsion blend D

and the emulsion A, showed desirable low-incendive characteristics compared with those of ANFO when detonated

unstemmed into an explosible concentration of PPC dust in the

LLCG. The water gel A and the emulsion A explosives have

also, to date, eliminated the dust ignition hazards associated with

blasting operations in sulfide ore mines (as discussed later in the

section entitled "Full-Scale Validation Tests in Sulfide Ore

Mines"). It is presently unclear why the water-gel explosives

exhibited lower incendivity characteristics relative to the coal dust

than to the CH . It is also uncertain why the dynamite showed 4

low incendivity against CH in table 10, but high incendivity 4

against coal dust in table 11.

In the LLCG tests, a correlation appeared to exist between an

explosive's detonation reaction temperature and its incendivity.

ANFO (94:6) was chosen as a reference explosive because it was

used extensively for blasting operations in oil shale mines and

was also used at times for blasting in sulfide ore mines. The

ANFO (94:6) required 350 g of inert gelled water stemming to

prevent the CH ignition in the LLCG tests. Comparing the 4

minimum stemming requirement (table 10) for each explosive

with its ideal detonation reaction temperature (listed in tables 7

and 8), the following correlation can be drawn. Explosives (95:5

ANFO, 94:6 ANFO, 92:8 ANFO, and blend A) that required

stemming of 350 g or more to prevent the CH ignition had 4

detonation reaction temperatures ranging from 2,638 to 3,140 K

(average of 2,957 K). Explosives (blends B, C, D, F, G, and H;

96:4 ANFO; and water-gel A) that required 300 g or less of inert

stemming to prevent the CH ignition had detonation reaction 4

temperatures ranging from 2,000 to 2,830 K (average of

2,478 K). Based on these limited data, an explosive's incendivity

can be correlated generally with its reaction temperature.

However, many factors, including the water content of the

explosive product and the type of oxidizer used, influence this

detonation reaction temperature. Of the four most incendive explosives in table 10, the one (blend A) with the lowest reaction

temperature had a

large negative oxygen balance, which would make it more

incendive than other explosives with similar reaction temperatures. Therefore, the final comparison with incendivity must

include both reaction temperature and oxygen balance.

Tests were also conducted in the LLCG to evaluate the

explosives' luminosity because the extent of flame outside the

cannon was presumably related to the incendivity. In these tests,

500-g charges of various stemmed and unstemmed explosives

were loaded into the cannon and detonated, thereby allowing the

combustion products to discharge into the gallery. An optical

flame sensor was mounted inside the gallery to measure, in terms

of duration and intensity, the flame exiting from the cannon bore.

With standard ANFO, the detonation of an unstemmed charge

produced highly luminous byproducts that were observed for

over 15 ms. The unstemmed water gel and ANFO-emulsion

blend explosives each produced a 12-ms flame with a 50 pct

lower relative luminosity than the ANFO. The explosives were

then stemmed with 150 g of a tamped inert gelled water material

to evaluate the effect of the stemming on the detonation byproduct luminosity. The gelled water stemming contained the

detonation products within the bore for a longer period, resulting

in a lowering of the temperatures of these products before exiting

from the bore. The detonation of the stemmed ANFO charge still

resulted in 15 ms of luminosity; however, the intensity was at a

reduced level. The stemmed water gel and ANFO-emulsion

blend explosive charges showed no evidence of any luminosity

from the detonation byproducts exiting from the cannon bore.

In summary, the LLCG tests evidenced that an explosive's

formulation can be altered to result in a product that exhibits lowincendive characteristics relative to its tendency to ignite

combustible dusts and/or CH . The incendivity of an explosive 4

product depends on many of the factors previously discussed,

including oxygen balance, detonation reaction temperature, and

type of oxidizer used. Field evaluations with the explosive

products that exhibited lower incendivity characteristics were then

conducted during production-scale oil shale and base metal

mining operations.

FULL-SCALE FIELD TESTS WITH

A LOW-INCENDIVE BLEND

During the next phase of the program, full-scale validation

tests (single-hole, multiple-hole, and full-face blasts) were

conducted using the emulsion blend D with the inert gelled water

stemming in two Colorado oil shale mines in the presence of

shale dust and/or CH (67). 4

Unocal's Long Ridge Mine Tests

Field tests (67) were conducted at Unocal's Long Ridge oil

shale mine in August 1989 (blasts 11 through 14 in table 3) to

compare the experimental, low-incendive emulsion blend with
37

the previous ANFO field data from 1988. Instrumentation was plastic chamber that contained a flammable CH -air atmosphere.

similar to that used during the 1988 tests as described in the These tests were conducted underground at Exxon's Colony Mine

previous section on "Full-Scale Field Studies With ANFO." and are not listed in table 3. They were designed to evaluate the

These tests were designed to reduce the probability of hot incendivity of two blasting agents (ANFO and the emulsiondetonation products exiting from the blast holes while still ANFO blend) through the detonating of these charges in the

maintaining effective rubblization. The blasting agent used was presence of a flammable 10 pct CH -air environment. Video and

the ANFO-emulsion blend D, which was 80 pct emulsion and 20 16-mm high-speed movie cameras were used to document the

pct ANFO, as listed in tables 7, 10, and 11. Each 76-mm-diam detonation of the various explosive products within these holes.

by 7.3-m-deep production hole was loaded with the emulsion No flame was observed with the detonation of the emulsionblend, stemmed with a 1-m plug of gelled water inert material ANFO blend D into the CH -air zone, even with a full,

(approximately 2.7-kg inert per hole), and initiated with an unstemmed column (worst-case scenario) loading in horizontal

electric millisecond delay detonator. The holes were each primed holes 76 mm in diameter and 7.3 m deep. However, ignition of

with a 1.4-kg, 6.4-cm-diam, cap-sensitive water-gel product ("E" the CH zone was evident after the initiation of the unstemmed

in table 7). This product provided for a high-energy, low- ANFO charge in the

incendive booster while offering a much greater degree of 76-mm-diam holes.

protection against CH and/or dust ignitions, particularly when 4 Even though the indications were that a properly stemmed

driving crosscuts, than the commonly used, highly incendive ANFO round produced no flame generation outside the borePETN boosters. holes (based on the 1988 full-face blasts conducted in the absence

Unocal's standard preshearing procedure was to use a high- of CH ), the potential for a CH and/or dust ignition is greater

velocity presplit powder loaded almost to the collar, as discussed when using ANFO instead of the emulsion blend (or similar lowin the previous section on "Full-Scale Field Studies With incendive blasting agent). If one or more boreholes in the pattern

ANFO." This was replaced during the 1989 tests with the are inadvertently left unstemmed during the loading operations in

experimental emulsion-ANFO blend D using an air-cushioning a gassy mine condition, both the experimental (BEM and LLCG)

technique. For these tests, each 76-mm-diam by 7.3-m-long test results (57-58, 62) and the oil shale mine single-hole results

preshear hole was primed with the water-gel E booster, and about (67) showed that the unstemmed hole loaded with the emulsion

4.5 kg of the emulsion-ANFO blend D was then pumped in on blend should provide a much reduced probability for an ignition

top, followed up with a half a cartridge of the water-gel E than an unstemmed hole loaded with ANFO.

product. The hole then was stemmed at the collar with three units In addition to the hazards related to using standard ANFO

of tamped, inert gelled water material (1-m plug), which provided charges, a permissible system will be required to initiate the

a column (approximately 5.5 m long) of air between the charge rounds when blasting in gassy mine conditions. BEM tests have

and the stemming. shown that the detonating cord typically used to initiate the

As with the stemmed ANFO shots in 1988, no flame was rounds in the current nongassy oil shale mines will readily ignite

evident outside the boreholes in 1989 after the detonation of the flammable concentrations of CH . Therefore, a permissible

stemmed emulsion blend-loaded rounds (also in the absence of initiation system, such as the all-electric system used in coal

CH ). Results showed that the rock fragmentation of the mines, will be required when blasting in a gassy oil shale mine. 4

emulsion-ANFO blend D in 76-mm-diam holes was at least In June 1990, another test series (69) at Unocal's Long Ridge

equivalent to or better than that of the mine's standard ANFO Mine was conducted in headings 5, 6, and 7 of production panel

round in 89-mm-diam holes. The air-cushioning technique also B, as shown in figure 31. These tests are listed as blasts 15

showed very encouraging results during these tests in that core through 17 in table 3. The average cross-sectional area in these

borings of the rib line showed only minor fractures 0.3 to 0.5 m headings was about 110 m . The drill hole pattern used in each

deep compared with cracks 3 to 4 m deep into the pillars during test was similar to Unocal's standard drill hole pattern. All of the

this mine's typical blasting operations. The stemming reduced the holes in each of the three drill patterns were 89 mm in diameter

air blast overpressures in half and also reduced the quantity of by 7.3 m deep. As part of the drill pattern in headings 6 and 7,

dust generated during the blasting sequence. six equally spaced preshear holes were drilled along each rib; in

For both the 1988 and 1989 full-face tests (62, 67), the drill heading 5, seven preshear holes were used (figure 32). Each

patterns, column loadings, and sequencing of detonators were pattern utilized 23 production holes, including three pairs of

similar to that mine's typical blasting operation described by angled holes that were designed to provide a relief area for the

Baloo in reference 68 and shown in figure 13. The primary dif- rock during the blasting sequence. Each hole was initiated with

ferences between the experimental face blasts in 1989 and the a precision delay electric detonator and a cap-sensitive booster

mine's typical face blasts were smaller borehole diameters, electric ( w a t e r - g e l E p r o d u c t ,

initiation, and the use of the low-incendive blasting agent and 89 mm in diameter by 200 mm long). The emulsion blend D

stemming in both the preshear and production holes. was loaded into the holes using a pneumatic pumping unit

In addition to the full-scale performance tests, single-hole

charges were detonated and allowed to discharge into a 7-m3

4

4

4

4

4 4

4

2
38

Figure 31.—Map of Long Ridge Mine showing instrumentation

locations for full-face blast in heading 6.

Figure 32.—Diagram of Long Ridge Mine face showing

blasting pattern in heading 5 for 1990 tests.

Figure 33.—Explosives being loaded into borehole at Long

Ridge Mine.

(figure 33). Loading times were initially longer using the emul- not be documented by the outby cameras due to dust

sion blend compared with those for ANFO; however, as the obscuration. The rounds were again initiated by a relay system

loading crew gained experience, the loading times improved that was designed to allow the instruments to establish stable

significantly (2-h loading time for the third test compared with baselines and the cameras to achieve full operating speeds before

1.5 h for ANFO loading). The powder factor for each round was initiation of the round. A portable PC was interfaced with this

adjusted slightly for each test to obtain optimal rubblization based system for easier and more accurate data gathering and

on the geologic structures encountered in the headings. The subsequent analyses.

average powder factor for the three tests was 1.1 kg/m of realized For each of the three tests, the video and 16-mm movie film 3

shale. After loading the emulsion blasting agent, each hole was showed only short duration (<5 ms) detonation flashes

then stemmed with two gelled water units that were each 76 mm associated with several holes. The optical flame sensor supported

in diameter by 400 mm long. This stemming was tamped against the camera data in that it recorded very little luminosity

the charge column. Typical nonelectric initiation was not utilized

during these tests because the detonating cord used in this type of

system can ignite a flammable CH -air atmosphere, and these tests 4

are designed to evaluate potential blasting agents and procedures

for blasting in gassy mine conditions. Therefore, an all-electric

initiation system was used.

Instrumentation used to monitor these tests included pressure

transducers and optical flame sensors. Both video and highspeed 16-mm cameras (64 and 250 fr/s) were used to document

any evidence of flame outside of the boreholes. The cameras

were positioned approximately 120 m outby the 

face. The static pressure transducers were located 45 and

120 m from the face. The optical flame sensor was positioned 25

m from the face. This sensor was located relatively close to the

face in an attempt to record any occurrence of flame that may

have been generated during the later stages of the round but could during each test, and that which it did show was very short-lived.
39

Figure 34—Map of Logan Wash Mine showing

instrumentation locations for 1990 tests.

Figure 35.—Diagram showing drill pattern used during

Logan Wash face blasts. (Numbers represent detonator delay

periods.)

The performance of the emulsion blend in terms of fragmentation accomplish this, a wooden framework was mounted around the

and incendivity characteristics during these test blasts was perimeter of the drift approximately 2.4 m outby the face. A

encouraging since there was uncertainty over the size-scaling portable foaming unit was then used to seal the gaps between the

effect in going to larger diameter holes. In similar full-face tests framework and the mine surfaces to prevent leakage during the

in 1989 using the emulsion blend D at Unocal, each hole was CH injection period. Clear plastic sheeting was then attached as

76 mm in diameter and stemmed with three gelled water units. a diaphragm to the framework, resulting in a relatively airtight

In these tests, no flame was observed during blasting. Therefore, 77-m containment zone. The CH was remotely injected into the

in the 1990 tests, only two inert stemming units were used zone through two 12-mm-diam tubes from cylinders located

because the 1989 single-hole test data at Exxon's mine showed no about 150 m outby the face near the control base shown in

evidence of flame even when detonating the emulsion blend D figure 34. A remotely operated fan with a sealed motor housing

unstemmed into small containment zones of flammable CH -air. was used to mix the incoming CH with the air. During the gas 4

However, the 1990 tests at Long Ridge Mine and subsequent injection, the CH concentration was monitored by sampling

tests conducted the following week at Logan Wash Mine showed through a 6-mm-diam tube located inside the containment zone.

that two gelled water units were insufficient to totally eliminate The sample was drawn through the tube by a vacuum pump to

flame outside the borehole. a gas analyzer located at the control base. When the required

The maximum static pressures recorded during the 1990 Long concentration was reached, the gas injection was stopped.

Ridge tests using the stemmed emulsion blend D were consistent Instrumentation was similar to that used during the Unocal

with those from the 1989 tests and were only one-half the value tests (pressure transducers, cameras, and flame sensors). A

measured during the earlier rounds (62) using unstemmed pressure transducer and flame sensor were located just inby the

ANFO. One pressure transducer was located inby the last open main heading and about 22 m from the CH zone at the

crosscut approximately 45 m from the face. The pressures ranged

from 0.1 to 0.2 bar at this location with the stemmed emulsion

blend D compared with 0.3 bar for a typical unstemmed ANFO

round. At about 120 m from the face (at the second outby

crosscut), the pressure values for the three tests averaged about

0.02 bar. The use of stemming not only cooled the byproducts

of detonation, but also allowed for more work on the rock by

containing the gas pressures within the borehole for a longer

period of time. Another contributing factor to these lower

pressure values was the use of the air-cushioning technique on the

preshear holes. The advantage of this method was that less

explosive was used per hole and the explosive was loaded only

at the back of the hole with stemming at the collar.

A postblast analysis was conducted following each round to

evaluate the effectiveness of the emulsion blend D compared with

the standard ANFO round. The three 1990 tests at Long Ridge

Mine using the stemmed emulsion blend D resulted in

fragmentation approximately equivalent to that of a typical

unstemmed ANFO round loaded in a similar drill pattern. The

dust generated during these tests appeared to be less than that of

the standard unstemmed ANFO rounds and still at least an order

of magnitude lower than that required for a large-scale dust

explosion.

Occidental’s Logan Wash Mine Test

A full-face test and a multiple-hole spacing test were conducted at Occidental's Logan Wash oil shale mine (15) located

northeast of De Beque, Mesa County, CO. This mine consisted

of three interconnecting levels and had been primarily used to

develop and test an in situ retorting method (1-2). The 1990 tests

(69) were conducted in a 25-m-long stub drift located off the

main heading approximately 300 m inby the mine portal, as face. A video camera and two 16-mm cameras were positioned

shown in figure 34. This stub drift had a cross-sectional area of 28 m from the face. A second pressure transducer was located

about 32 m . 150 m outby the face near the control base shown in figure 34. 2

One purpose of the tests at Logan Wash was to evaluate the The same computer and shotfire initiation system used at Unocal

effect of a full-face blast into a flammable CH -air zone. To was used during these tests. 4

4

3

4

4

4

4
40

In preparation for the detonation of a full-face round into a reduce the overpressure values by one-half. This, coupled with

flammable CH -air zone, a baseline test was conducted with the the higher powder factor at Logan Wash, would account for the 4

ignition of the CH -air only. Following the CH injection and higher overpressures recorded during these tests. The high 4 4

gas analysis period, the shotfire system was armed and activated. powder factor resulted in relatively uniform fragmentation of the

For the baseline test, a small chemical ignitor was used to ignite shale in much reduced sizes than that obtained during the Long

the flammable CH -air mixture near the face. The static pressure Ridge tests. 4

transducer located near the face recorded a slow pressure rise that Data from the flame sensor and cameras indicated with

peaked at 0.04 bar overpressure. The transducer located 150 m reasonable certainty that an ignition of the CH -air mixture

outby the face recorded a maximum overpressure less than 0.01 occurred as a result of the detonation of the full-face pattern

bar. The video and 16-mm cameras observed a fireball that stemmed with two inert gelled water units; at least, a bright flash

began from the lower center ignition point, expanded throughout of light occurred at the start of the round. However, because of

the containment zone, then traveled outby the drift. The optical the short distance from the face to the T-intersection at the main

flame sensor located nearer to the face recorded about 1.25 s of heading where the cameras and flame sensor were located, the

flame associated with the CH burning. overpressures and debris generated during the detonation of the 4

After the baseline test, a full-face round was detonated into a round damaged the instruments and cameras shortly after

CH -air zone using the emulsion blend D in the boreholes. The initiation of the round. Several contributing factors may have 4

drill pattern for the full-face test, shown in figure 35, consisted of enhanced the probability of an ignition. One factor would be the

twenty-six 89-mm-diam holes drilled to an average depth of high powder factor, which was over twice that normally used in

3.7 m. The face along each rib line had five equally spaced typical operations. Another change from past tests was the use of

preshear holes. Two pairs of angled holes were drilled in the larger diameter holes. It would appear that the 89-mm-diam holes

middle of the face to provide an expansion relief zone to facilitate require at least as much or more stemming compared with the 76-

the detonation of the later holes. Each hole was primed with the mm-diam holes to prevent the hot detonation gases from exiting

water-gel E booster and a precision delay electric detonator. The from the hole and igniting the CH . The spacings of the drill

16 production holes were then loaded with the emulsion blend D, holes in the face pattern may also have been a major contributor

and two stemming units were tamped into each hole against the to the CH ignition. An explosive loaded in a hole can be desencharge column. The powder factor for the face test was 2.4 kg/m sitized by the detonation of an adjacent hole should that hole be 3

of realized shale. The powder factor was substantially greater too close. The result is that the desensitized charge will not

than the 1.1 kg/m powder factor used for the Unocal headings. detonate properly as evidenced by its lower velocities and may 3

This high powder factor would present a higher CH ignition deflagrate rather than detonate. Separate tests to evaluate the 4

risk. The air-cushioning technique was used for the 10 preshear spacing of blast holes are discussed below.

holes, which were loaded at the back of each hole with 22 kg of A multiple-hole test (69) was conducted at Logan Wash Mine

the emulsion blend D. These holes were then stemmed at the after the full-face test to measure the detonation velocities of

collar with two units of the inert gelled water material. loaded holes spaced at various increments from one another. As

After loading the explosives, another plastic sheet was attached part of the field evaluation with the experimental, low-incendive

to the wooden framework of the 77-m gas containment zone. emulsion blend D, this test was designed to evaluate the 3

The CH 4 was then injected into the containment zone and mixed performance of the explosive and determine the minimum

with the fan until the gas analyzer showed the concentration to be spacings required between blast holes. The minimum spacing

10 pct CH -air, a worst-case scenario. Gas samples were also requirement is critical in preventing potential misfires because the 4

taken for subsequent laboratory analyses; the results were detonation of the adjacent short delay rounds can desensitize the

consistent with the on-line analyzer readings. The round was explosive in the longer delay holes. Desensitization can occur

initiated with a permissible system consisting of electric when the sensitizing agent in the explosive, typically glass

detonators. microbubbles, is crushed from the shock waves produced from

A maximum static overpressure of about 0.9 bar was recorded the detonation of adjacent holes. The concentration of microon the transducer located 22 m from the face and inby the main bubbles in a formulation determines the explosive's sensitivity

heading. The second transducer located 150 m outby the face and the strength of the initiator required to detonate the explosive.

recorded maximum overpressures less than 0.01 bar. Typical The spacing test entailed eight holes drilled horizontalblasting overpressures with ANFO in this size drift from previous ly into two opposite oil shale ribs (four holes per rib). There was

operations within the Logan Wash Mine were not available. a distance of 2.1, 1.5, and 1.0 m between the holes in each set;

However, the overpressures obtained during this test did not each hole was 6 m deep and 89 mm in diameter. The

appear to be unreasonable considering the high powder factor and

the small cross-sectional area of the drift. Previous tests (45-46,

54) at the Long Ridge and Colony Mines have generated

overpressures ranging from 0.1 to 0.3 bar when the pressure

transducers were located at similar distances from the face.

However, the Long Ridge and Colony Mine headings had nearly

four times the cross-sectional area of the Logan Wash Mine drift.

Experimental results (70) have shown that doubling the area will

4

4

4
41

emulsion blend D was bulk loaded in the back 4.6 m of each hole

and stemmed with a gelled water inert material to maximize the

shock pressures to the surrounding strata. A velocity-ofdetonation recorder (VODR) was used to measure the detonation

velocities in each hole. This method of recording the detonation

velocity within an explosive column can also be referred to as the

resistance wire method (71). Constant current is supplied to two

insulated conductors, such as the center wire and shield of the

coaxial cable used during these experiments. A continuous

length of coaxial cable was looped into each of the eight holes

and then connected to the VODR. At the far end of the coaxial

cable, which was located at the back of the first hole to be

detonated, the two conductors were shorted. As the detonation

progressed through the explosive column, the coaxial cable

conductors were forced into contact as the cable was crushed.

This shorting reduced the circuit voltage since this action reduced

the length of the electrical path and therefore the resistance of the

probe. Recording the change in voltage over time provided the

detonation rate. A sequential blaster machine initiated the holes

at 10-ms intervals. Results from this first test indicated that a

spacing of 2.1 m between holes had no detrimental effect on the

performance of the emulsion blend in the oil shale formation.

However, the holes on 1.5-m or closer spacings did not detonate

properly, as evidenced by the lower velocities. Many of the holes

in the Logan Wash full-face drill pattern (figure 35) were spaced

less than 2 m apart. It was quite possible that the CH ignition 4

during the full-face test may have been the result of the improper

performance of the explosive in some of the holes. Additional

spacing tests need to be conducted in oil shale to verify these

preliminary findings. Future full-face tests using the emulsion

blend D should be conducted with hole spacings of at least 2 m.

EXPLOSION HAZARDS OF SULFIDE ORE DUSTS

The Pittsburgh Research Center, at the request of the MSHA, However, a significant number of dust ignitions have been asexpanded its research program on developing safer explosives sociated with development headings and the secondary blasting

and blasting procedures for gassy oil shale mine conditions to of ore at draw points. There are numerous documented accidents

include sulfide ore mines. Working in cooperation with several relating to the various hazards associated with the mining and

explosives manufacturers, the Pittsburgh Research Center processing of these ores (79-82). Fortunately, the number of

continued to test various explosive formulations, including water- fatalities associated with these ignitions has been minimal due to

gel and emulsion products, in the LLCG to evaluate their relative the practice of evacuating mines before stope blasts. However,

incendivity compared with standard ANFO and other explosives. many operators report extensive damage during many of the dust

There were some very early reports of sulfide mine dust ignitions. Even with minor dust ignitions, there was appreciable

explosions in the 1920's, as described in references 72 and 73. In lost production while a mine was checked for toxic levels of

recent decades, there has been a significant increase in the number sulfur dioxide and hydrogen sulfide and the damage to the

and severity of blast-induced sulfide dust ignitions in the ventilation system was repaired to safely purge the mine of these

underground workings of massive sulfide deposits in Europe, the toxic gases. However, dust ignitions have caused extensive

Republic of South Africa, Australia, Canada, and, more recently, damage to ventilation ducts and stoppings and also to the mining

the United States. These recent sulfide dust explosions have been equipment, thereby creating potentially hazardous situations for

summarized in a literature survey by Job (74) and in several the miners (81). The intense heat and flame associated with these

papers by Enright (75-77). Another literature survey on explosions can ignite timber sets and other combustible materials

spontaneous combustion and sulfide mine fires was presented by in the area. The destructive pressures generated from a sulfide

Ninteman (78). The explosives normally used in sulfide ore dust ignition are generally limited to the blast face area and, in

mining were dynamites and/or ANFO. Most of these dust most cases, do not extend significant distances into other areas of

ignitions have occurred in open stopes where large-diameter drill the mine. This is due primarily to the significant decrease in the

holes were used with bench blasting or vertical retreat mining. concentration of entrained sulfide ore dust outby the immediate
42

blast area. Reddish dust or reddish stains of iron oxide (Fe O ) 2 3 LABORATORY DATA

on rock or equipment can be used to track the extent of flame

propagation. Magnetite (Fe O ), although black, is also The laboratory explosibility data for the sulfide ore dusts were 3 4

sometimes produced during sulfide dust ignitions and is also measured in the 20-L chamber (34-36) shown in figure 5. The

useful in detecting the extent of the explosion. test procedures were identical to those used for the oil shale dust

In 1986, Wheeland and McKinnon summarized the sulfide explosibility measurements described in the "Explosion Hazards

dust explosion problem and current mining practices at the time of Oil Shale Dusts" section earlier in this report.

(83). One critical factor affecting sulfide dust ignitions is the The chemical assays and size analyses of the sulfide ores are

sulfur content of the ore; the ore with the higher content is more listed in table 12. The sulfide ores are identified by date

explosible in that it requires less mass suspended in the air to (month/year) received. One sulfide ore was identified by the

propagate an explosion (76-77, 83-86). In sulfide ores, higher mine as being high in pyrite (FeS ) content and is so noted. The

sulfur content is often associated with higher pyrite (FeS ) content table then lists the location of the sulfide ore mine from which 2

because pyrite is the most common host sulfide and has the each sample was obtained. The first four samples were from

highest sulfur content (53 pct) of the common sulfide ores (84). Brunswick Mining and Smelting Corp. (a division of Noranda)

Pyrrhotite (~FeS) is also a reactive host sulfide even though it has in Bathurst, New Brunswick, Canada. The 1983 samples were

a lower sulfur content than pyrite. received as rocks and were crushed and pulverized at the

2

Pittsburgh Research Center. The 1985 and 1987 samples were

from a dust collector at the processing plant in New Brunswick,

Canada. In the table, the two 1989 samples from Greens Creek

Mine in Alaska are differentiated by an "s" for the standard

sulfide ore and a "p" for the sample that was higher in pyrite

content. The sulfur content and metals analyses are then listed in

the table. These sulfide ores were mined mainly for zinc and lead

content. The heating value was measured in a bomb calorimeter.

Note that the ores that have the higher sulfur contents have the

higher heating values. The particle size analyses shown in table

12 are in a form similar to those used in table 1. The 1983 dusts

are significantly larger in size than those from 1985, 1987, and

1989. The dusts were stored under nitrogen.

Table 12.—Chemical and size data for sulfide ores

Data Sulfide ore dusts

12/83-py 12/83 7/85 4/87 8/89-p 8/89-s 1 

Location ............. New Brunswick, New Brunswick, New Brunswick, New Brunswick, Alaska Alaska

Canada Canada Canada Canada 

S, pct . . . . . . . . . . . . . . . ~40.0 33.5 27.0 28.0 ~34.5 24.5

Si, pct . . . . . . . . . . . . . . . 2.6 4.9 7.4 7.6 0.6 1.0

Ca, pct . . . . . . . . . . . . . . . 0.5 2.3 3.8 3.4 1.8 2.6

Fe, pct . . . . . . . . . . . . . . . 39.0 24.0 23.1 23.5 25.5 4.8

Cu, pct . . . . . . . . . . . . . . . 0.5 0.3 0.3 0.5 0.3 0.3

Zn, pct . . . . . . . . . . . . . . . 1.3 13.8 10.8 11.0 18.6 32.5

Pb, pct . . . . . . . . . . . . . . . 0.4 4.7 3.8 3.6 3.8 24.4

Heating value, cal/g . . . . 1,300 1,000 790 840 1,100 770

Minus 200-mesh, pct . . . 79 82 96 99 99 98

D , med Fm.............. 34 23 13 13 12 12

öW, Fm ............... 44 36 23 17 19 20

ö , Fm ............... S 20 16 10 10 9 10

ö (%T), Fm ........... S 16-50 15-35 8-18 8-20 6-11 8-12

Identified by mine as mainly pyrite. 1
43

Figure 36.—Explosibility data for 1983 pyritic and sulfide ore dusts from the 20-L chamber.

Figure 37.—Explosibility data for 1985 and 1987 sulfide ore dusts from the 20-L chamber.

The laboratory data for the explosibility of the sulfide ore because they both came from a dust collector at the processing

dusts are shown in figures 36-38 in forms similar to those of the plant. The 7/85 sample was tested twice. The first time was

oil shales depicted in figures 6-7. The data were obtained in the shortly after it was received, and the data points are denoted by

20-L chamber using the 5,000-J chemical ignitors. The data the filled circles. The second time was 2 years later (open circle

show that some sulfide ore dusts can propagate an explosion if data points), and the tests produced only a slight pressure rise that

the particle size is fine enough and the ignition source is strong would not be considered a propagation. This lower explosibility

enough. The data in figure 36 show that the pyritic sample of the sulfide ore may be due to some possible oxidation of the

ignites at lower dust concentrations and produces higher pressures sample over time. Although there was an attempt to keep the

and rates of pressure rise than the regular sulfide ore sample from sample under nitrogen, there may have been an air leak into the

1983. The two samples in figure 37 show somewhat similar storage jar.

c h a r a c t e r i s t i c s , a s e x p e c t e d ,
44

Figure 38.—Explosibility data for 1989 pyritic and sulfide ore dusts from the 20-L chamber.

The pyritic sample from 1989 (figure 38) showed the highest was not listed. Mintz and Dainty (84) measured pressures of 2.2

pressures and rates of pressure rise of all of the sulfide ore to 2.6 bar for pyrite and pyrrhotite in a 20-L chamber using a

samples. It was significantly finer in size than the other two ores 5,000-J ignitor, similar to the values for the higher sulfur content

that were high in sulfur content (12/83 and 12/83-py). It also had ores in table 13. Liu (85) and Liu and Katsabanis (86) conducted

a higher sulfur content than the other fine-sized dusts from 1985, experiments in a 1-m (1,000-L) chamber using an explosive

1987, and 1989. This combination of finer size and higher sulfur charge as the ignitor. One of the samples (listed as type I from

content probably caused its higher explosibility. The standard Brunswick Mining and Smelting Corp.) that they tested was a

sulfide ore (8/89-s) from Alaska shown in figure 38 could not be sulfide ore similar in size to the 7/85 and 4/87 ores shown in

ignited, even with the 5,000-J ignitors. This sulfide ore had the tables 12 and 13, but with slightly higher sulfur content. Their

lowest sulfur content of all of the ores tested. type I sample had P ' 3.0 bar. This is higher than the P

The sulfide ore explosibility and ignitability data are compared value for the 7/85 and 4/87 ores, but they used a much stronger

with the coal dusts in table 13 in a form similar to that for the oil ignition source (15 g of Detasheet explosive, or 72 kJ). The

shales in table 2. Even the five sulfide ore samples that ignited in other sample (type II) that they tested was pyrite ore with

the 20-L tests had much higher MEC values and lower P and P ' 3.7 bar. Soundararajan (87) and Soundararajan, Amyotte, max

(dP/dt) values than those of the two bituminous coals. The max and Pegg (88) measured the explosibility of sulfides in a 20-L

explosibility data are closest to the 82- and 95-L/t (19- and chamber using a 5-kJ ignitor. They measured P ' 3.1 bar for

23-gal/st) oil shale data in table 2. The 8/89-s sulfide ore could a pyrite dust with 46 pct sulfur. The dP/dt values from the

not be ignited by the 5,000-J ignitor, similar to the anthracite various researchers cannot be compared directly with the data in

coal. The 8/89-s sulfide ore produced an explosion in a single table 13 because of possibly different turbulence levels in the

test at 4,500 g/m using a 10,000-J ignitor, although it is various chambers. 3

uncertain whether that ignitor would overdrive the 20-L chamber. Enright (76-77) and Liu and Katsabanis (86) concluded that

Based on the data in the table, one can conclude that the sulfide ~20 pct was the minimum sulfur content for sulfide ore

ore is a weak explosion hazard, but that it can be ignited if the explosibility. In the Pittsburgh Research Center 20-L laboratory

particle size is fine enough, the sulfur content is high enough, and tests, >26 pct sulfur content was required for an explosion using

the ignition energy is strong enough. 5,000-J ignitors. The difference is probably related to the

The maximum pressure data for the sulfide ores in table 13 are stronger ignition sources used by Enright and by Liu and

consistent with those of other researchers. Enright (76-77) Katsabanis. For sulfur contents between 20 and 40 pct, Liu and

measured somewhat higher pressures, but he used a much Katsabanis reported that explosion violence increased

stronger ignition source (1.5 g of nitrocellulose or 15 kJ) in a significantly with sulfur content. There is a general correlation in

36-L chamber. The particle size of his sulfide dust samples the Pittsburgh Research Center data (table 13), but it is

3

max max

max

max

complicated by the variation in particle size of the dusts tested

(table 12).

Table 13.—Laboratory explosibility data for sulfide ores and comparison dusts
45

Explosibility data Sulfide ore dusts Coal dusts

12/83-py 12/83 7/85 4/87 8/89-p 8/89-s hvb lvb anthra

MEC, kg/m3

 @5 kJ . . . . . . . . . . ~0.4 ~0.6 ~0.7 ~0.8 ~0.4 NI 0.06 0.09 NI

P , bar . . . . . . . . . max ~2.3 ~2 2.0 ~1.4 2.8 0.3 5.6 5.0 0.4

(dP/dt) , bar/s . . . max ~13 ~7 10 ~7 36 <1 145 77 <1

MAIT, EC ........ ~490 ~520 — ~530 — — 530 ~610 ~670

NI Nonignitable.

NOTE.—A dash means not analyzed.

The MAIT values (490 to 530 EC) for three of the sulfide ores followed by the nominal dispersed dust concentration, the

are listed in table 13. These values are comparable with those of loading distribution of the dust between the V-troughs and the

the hvb coal and the oil shales (table 2), but are lower than those shelves, the flame travel distance (measured from the cannon),

of the lvb coal and the anthracite. Mintz and Dainty (84) and maximum pressure rise. The pressure was measured after the

measured a similar MAIT of 510 EC for pyrite. Soundararajan decay (>100 ms) of the pressure peak from the detonating

(87) measured a MAIT of 480 EC for his finest sized pyrite dust ANFO. Therefore, this listed pressure would be that due to any

and higher MAIT values for larger sizes. propagating sulfide dust explosion.

In the bituminous coal mining industry, limestone rock dust In a baseline experiment where only the cannon ignitor charge

is added to the deposited float coal dust to make it nonexplosible. was detonated, the maximum static pressure was approximately

Bags of rock dust suspended near the face have also been 800 mbar with a flame extension of about 3 m from the cannon

considered as a means to prevent sulfide ore dust ignitions during bore or 4 m from the face. In the initial test (No. 4202) with the

a blast. Figure 39 shows data from the 20-L chamber for a sulfide dust, a nominal concentration of 800 g/m was uniformly

mixture of 20 pct limestone rock dust and 80 pct of the 7/85 loaded into the seven V-troughs. The dust was then dispersed

sulfide ore. The slight pressure rises shown in the lower part of with the compressed air system, and the ANFO was detonated

the figure were only due to a small amount of burning in and about 1 s later. Flame was observed out to 7 m from the cannon,

around the ignitor flame. The rate of pressure rise data show that but it did not go beyond the dusted zone. Upon inspection of the

there was no sustained propagation beyond the ignitor, and zone after the test, significant amounts of sulfide dust were

therefore these mixtures would be considered nonignitable. For beneath the troughs, indicating inadequate dispersion. However,

Pittsburgh coal dust of similar size, about 75 pct rock dust in the an iron oxide residue covered the entire test zone, which

coal-rock mixture was required to inert for the same test evidenced considerable burning of the sulfide dust. In the second

conditions (35-36). In similar tests, Enright (76) found that more test (No. 4204) with an 800 g/m concentration, 38 pct of the

than 40 pct limestone was required to inert pyrite ore. dust was suspended above the troughs on three roof shelves. The

LARGE-SCALE EXPERIMENTAL MINE DATA In this test, the flame traveled 14 m from the cannon (6 m beyond

The large-scale flammability tests on the sulfide ore dust were considered to be a propagating sulfide ore dust explosion, even

conducted in the main entry of the BEM (figure 3). The though the pressure was rather low. A more uniform entrainment

predispersed tests were conducted near the face (figures 4 and 26) of the dust occurred when the roof shelves were used and the dust

in a manner similar to the predispersed oil shale tests. The test loading in the air troughs did not exceed 500 g/m . This was

zone was 9.1 m long and had a volume of 44 m . For each test determined by the concentration measurements of the three 3

in this limited series, the sulfide ore dust (7/85 and 4/87 from optical dust probes in the test zone and from a visual inspection

table 12) was loaded into seven V-troughs and/or on three of the zone after the test. In test No. 4203, all of the dust was

suspended roof shelves. Pressurized air, exiting from holes in the loaded in the V-troughs, but the flame only went 3 m beyond the

bottom of the V-troughs, dispersed the dust within the 44-m test cannon; this test showed evidence of poor dispersion. 3

zone. The dust on the shelves would be dispersed by the pressure Additional tests were conducted with dust both on the shelves

pulse from the detonating ANFO in the cannon. The ignition and in the troughs to determine the lowest concentration that

source for the sulfide ore tests consisted of a 644-g charge of 2.5 would propagate an explosion. In two tests

pct aluminized ANFO. This charge was detonated from the

cannon using an electric blasting cap and two tetryl boosters (3 g

each). The criterion for ignition and propagation of the sulfide

dust was that flame be observed beyond the test zone, i.e., 9 m

from the face or 8 m from the cannon.

A series of six tests was performed in the BEM to determine

the minimum concentration for propagating explosions of the

sulfide ore dust. The test series was ended when the limited

quantity of sulfide dust was exhausted. The results of these tests

are listed in table 14. The table indicates the BEM test number,

3

3

remainder of the dust was loaded into the air dispersion troughs.

the diaphragm) with a pressure rise of 90 mbar. This test was

3
46

Figure 39.—Explosibility data from the 20-L chamber for a mixture of 80-pct sulfide ore and 20-pct rock dust

compared with data (solid curves) for sulfide ore.

Table 14.—Predispersed sulfide ore dust tests in the Bruceton Experimental Mine

Test No. Concentration, Dust loading, Flame Pressure rise,

 g/m pct travel, m mbar 3

1

4211 ............ 0 0 3 0

4207 . . . . . . . . . . . . 630 100 (S) 10 21

4205 . . . . . . . . . . . . 650 54 (T), 46 (S) 3 0

4206 . . . . . . . . . . . . 725 59 (T), 41 (S) 3 0

4202 . . . . . . . . . . . . 800 100 (T) 7 NA

4204 . . . . . . . . . . . . 800 62 (T), 38 (S) 14 90

4203 . . . . . . . . . . . . 1,000 100 (T) 3 0

NA No data available.

T refers to V-troughs; S refers to shelves. 1

with 650 and 725 g/m loadings, the flame extended only 3 m and a strong ignition source are necessary to generate a propa- 3

from the cannon, which was attributed solely to the ignitor flame gating sulfide dust explosion.

travel. Very little iron oxide residue was evident after these tests. The Pittsburgh Research Center large-scale tests of the exIn a final test with the remainder of the sulfide ore dust, a 630- plosibility of sulfide ores are consistent with other tests conducted

g/m nominal loading was deposited entirely on the three roof at Russian sulfide ore mines (89). For these experimental blasts, 3

shelves. The dust was dispersed by the shock wave of the the normal precautions of stemming and wetting the face were not

detonating ANFO charge. The flame extended slightly outby the taken. The Russian tests showed that sulfide ore with high pyrite

plastic diaphragm. Both the laboratory and experimental mine content (40 to 50 pct sulfur content) could propagate slow

tests show that a high concentration of dust explosions to distances up to 76 m.

FULL-SCALE VALIDATION TESTS IN SULFIDE ORE MINES

Until recently, control of sulfide dust ignitions in mines was detonation sequence. Water sprays or mists were also used to

based primarily on limestone inerting of the dust generated quench the flame and reduce the dispersibility of the previously

during blasting and/or quenching the ignition process with water deposited dust.

sprays. The most common method was to disperse crushed Several low-incendive explosive product formulations

limestone dust into the face area at the beginning of the for sulfide mines were evaluated in the LLCG, as discussed earlier
47

in section entitled "Lake Lynn Cannon Gallery Tests." Several 3. The remainder of the drift within 30 m of the face was

of these explosives have undergone field testing and have been thoroughly washed down 45 min before blasting. Any ventiextremely successful in preventing dust ignitions in sulfide ore lation tube or bag in the drift was also thoroughly washed down.

mines in areas most susceptible to these ignitions (69). 4. A water-mist spray system was hung from the rib no more

In July 1990, Kennecott Minerals Co., working together with than 23 m from the face and directed toward the face. This was

the Pittsburgh Research Center and two explosives manufacturers, turned on at least 15 min before blasting.

began an extensive testing program with a low-incendive watergel explosive at its Greens Creek Mine, located on Admiralty These procedures were labor-intensive and, although reducing

Island 29 km southwest of Juneau, AK. The ore types that the number of incidents, did not eliminate them. In fact, the use

comprise the mineralized horizon at the Greens Creek Mine are of water caused other problems. The mine strata are composed of

basically divided into two types (table 12): a massive sulfide ore a complex package of strongly altered volcanic rock that

that is composed of 80 to 90 pct pyrite, and a massive sulfide ore degraded quickly when exposed to water. The preventive

with a high base metal content and a low pyrite (10 to 15 pct) measures designed to limit the sulfide dust ignitions seriously

content. Historically, the fine-grained, high-sulfur content areas degraded haulage roads, thereby affecting production.

have created the greatest difficulty in controlling sulfide dust Production-scale evaluations of the low-incendive water-gel A

ignitions. The dust generated during the mining cycle consisted explosive product (tables 10 and 11) at the Greens Creek Mine

primarily of pyritic and lead-zinc sulfide. The mining zones began in July 1990. This water-gel explosive comes in

containing the various bodies of ore varied greatly in all respects; prepackaged cartridges rather than in bulk form. Approximately

dips ranged from flat to vertical, and thicknesses ranged from 125 kg of the 38-mm-diam by 400-mm-long water-gel explosive

0.6 to 9.1 m. The dip of the ore body dictated the type of mining cartridges was used during each face blast. The water-gel

method used. The three most frequently employed mining explosive A is cap-sensitive and does not require a booster.

methods were drift and fill with back stoping (used in steeply Initially, the testing was limited to high-sulfur-bearing areas in the

dipping sections), drift and fill (used in structures dipping mine that were prone to dust ignitions. The standard precautions

between 20E and 50E from horizontal), and room-and-pillar with already in use (outlined above) were employed with the initial

backfill (used in areas of flat-lying ore). In general, drifting testing. Nearly 4,750 kg (approximately 38 average rounds) of

rounds with burn cuts comprised 50 to 60 pct of mine the low-incendive water-gel explosive was consumed using the

production. A typical production drift had dimensions of 3.7 by full precautions. No sulfide dust ignitions occurred. As testing

3.7 m. Blasting was conducted using nonelectric detonators, progressed, the preventive control procedures were gradually

high-velocity detonation cord, and a fuse-detonator initiation sys- decreased. The water spray was first eliminated while

tem. The cross-sectional area of the drifts ranged from 9 to maintaining the washing down of the drift and the use of water

28 m . The holes in the pattern were 41 mm in diameter and stemming. After successfully using an additional 8,430 kg (ap- 2

were drilled 2.4 to 3 m deep. proximately 68 rounds) of the low-incendive water-gel A exThe first sulfide dust ignition at the Greens Creek Mine oc- plosive with no dust ignitions, the use of water stemming was

curred in 1989 while using the mine's standard explosive: then dropped; wetting down of the area before blasting was consemigelatin dynamite. Others occurred later, with minor injuries tinued. To date, Greens Creek Mine has consumed well over

to employees primarily associated with the inhalation of 136,000 kg (approximately 1,100 rounds) of the low-incendive

combustion products. No major damage was sustained, but water-gel product and has experienced no sulfide dust ignitions.

production delays resulted in losses averaging about $40,000 per The blasting efficiency of the water-gel product at Greens

incident. When the Greens Creek Mine first began to experience Creek was very high. The water-gel explosive cartridges tamped

problems with sulfide dust ignitions, strong preventive measures well, and compaction ratios of 90 pct or greater were the norm.

were instituted. Management designated areas of the mine that This high degree of coupling improved the brisance (shattering

presented a potential hazard for a sulfide dust ignition. Once an power) and effective work characteristics of the explosive. This

area had been so designated, the procedures below were followed. kept undetonated particles to a minimum and enhanced the

1. The face, ribs, and back within 3 m of the face were powder factor ranged from 3 to 3.8 kg/m and averaged 3.6

thoroughly washed down before loading. kg/m . The holes were initiated with long-period nonelectric

2. All loaded holes were stemmed with one filled water bag. detonators.

product's ability to control ignition of the sulfide dust. The 3

3

In February 1991, a temporary gap in the supply of the watergel explosive caused the Greens Creek Mine to return to the use

of the mine's usual semigelatin dynamite explosive.
48

As a result, the mine experienced three sulfide dust ignitions in a washing down the drift to remove fine sulfide dust deposits.

2-week period, even while the mine returned to the full list of Another benefit attributed to these low-incendive explosives was

preventive measures. Past experience had shown that extreme improved haulage roads because the use of water to control the

caution was warranted when blasting in the stope where these sulfide dust ignitions was greatly reduced.

ignitions occurred. Two days following the last ignition, the Initial incendivity studies at the Greens Creek Mine with the

supply of the water-gel product was reestablished. The first new water-gel cartridges and bulk emulsion product were conducted

round detonated in this stope using the water-gel product used the in 41-mm-diam holes and resulted in no sulfide dust ignitions.

full precautions. No sulfide dust ignition occurred, and the However, to optimize explosive performance and rock

precautions were reduced to wetting down of the blast area and fragmentation, the blast holes were increased slightly to 44 mm

beyond, which also resulted in no dust ignitions. The Greens in diameter. Both the prepackaged and the bulk products

Creek personnel by then had developed confidence in the water- continued to provided excellent results in terms of low

gel product and undertook a project to test the product under incendivity and good fragmentation characteristics. Again, no

extreme conditions. A stope had been mined to a point where a sulfide dust ignitions occurred when using the lower incendive

slash-while-retreating method was being employed. During the products in the 44-mm-diam holes.

occurrence of the dust ignitions while using the gelatin dynamite, The lower incendive water-gel explosives have also been used

only one slash, no greater than 3.7 m high by 3.1 m long by with success in two Canadian base metal mines to reduce the

3.1 m deep, was taken. This procedure was in effect to minimize probability of sulfide dust ignitions following blasting operations.

dust generation and, hopefully, to eliminate dust ignitions. These mines are the Westmin Resources Ltd.

During the experiment to evaluate the ability of the low-incendive H-W Mine on Vancouver Island, British Columbia, and the Hudwater-gel product to eliminate ignitions, slashes on each side of son Bay Mining and Smelting Co. Ltd. Ruttan Operation near

the initial drive were detonated at the same time with substantial Leaf Rapids, Manitoba. The Ruttan Operation had been avdelay. Four such experimental blasts were conducted with this eraging 2.7 sulfide dust ignitions per month over a 16-month

configuration, and no sulfide dust ignitions occurred. Again, the period. During that time, the sulfide dust ignitions accounted for

only precaution taken was wetting down of the blast area and be- 14 pct of their blast delays, which averaged 2.6 h per occurrence.

yond. All slash sizes were approximately 3.7 m by 3.1 m by Any blast that had produced sulfur dioxide (SO ) was considered

1.8 m. After over 2 years of testing and full production use, no to be a sulfide dust ignition. Mine reentry following blasting

sulfide dust ignitions have occurred at the Greens Creek Mine operations was restricted until the ventilation system had removed

when using the water-gel product. and/or diluted the toxic gases to a safe level. The mine's policy

Greens Creek then began full-scale blasting evaluations with was to send mining personnel home if these toxic gases were not

a bulk product (emulsion A in tables 10 and 11) that had been cleared within 4 h, which then resulted in lost production time.

tested in the LLCG and shown to be another preferred lower This occurred one to two times monthly. Preliminary data show

incendive product. No sulfide dust ignitions have occurred since no sulfide dust ignitions have occurred when using the lowthe mine began using the bulk product. Greens Creek has since incendive water-gel product at these two Canadian mines.

installed a 455-kg hopper and two more pumping systems for Because of the encouraging results in both base metal and oil

face loading of the bulk product in the development rounds. shale mines, the Colorado Mining Association, DOE, the

Overall blasting costs were significantly reduced when using the Canadian Institute of Mining and Metallurgy, the Canadian base

bulk product compared with the water-gel cartridges. Pumping metal industry, MSHA, and various explosive manufacturers

reduced the labor involved in the loading process by at least one- continue to support Pittsburgh Research Center research on

half compared with the loading times with the prepackaged explosive incendivity, stemming, and initiation systems as a

cartridges. Preblast precautions have been even further reduced means of reducing the dust and/or gas ignition probability during

t o only occasionally normal development blasting.

2

RECOMMENDATIONS

In 1984, an ad hoc committee representing oil shale producers, standard test method could be developed to evaluate the

MSHA, the Pittsburgh Research Center, and explosive incendivity characteristics of new and/or existing explosive

manufacturers produced a report (90) outlining the need for formulations that may be used during blasting operations under

research into the development of safe, effective blasting hazardous mining conditions, such as in the oil shale and sulfide

procedures for the oil shale industry. Many of the committee's ore mines. More experimental data on the temperatures and

recommended research directives have been accomplished by the extent of afterburning may lead to a more complete

Pittsburgh Research Center, as summarized in this document. In understanding of how best to prevent the ignition of flammable

addition to this research, the authors believe that research should gas or dust atmospheres.

continue on the development of safer explosives and procedures Should the oil shale industry again become active, additional

for blasting in the presence of combustible dusts and CH gas in full-scale validation field tests in operating mines need to be 4

noncoal mines. Intermediate-scale research in the LLCG has been conducted to further evaluate the incendivity and performance of

effective in determining the incendivity of blasting agents. A the low-incendive explosive products and alternative blasting
49

procedures before formal recommendations are made. Most systems to stray electricity. This use of nonelectric initiation

importantly for oil shale mines, these tests need to be conducted eliminates one of the major causes of unwanted detonations in

in the presence of CH to determine and confirm the amount of blasting, thus improving safety. However, nonelectric initiation 4

stemming material required in each hole to prevent the gas systems, as they exist now, cannot be used in flammable

ignition. Additional studies also need to be conducted within the atmospheres due to the inherent potential for igniting that attarget strata to determine the minimum spacing requirement mosphere. A nonelectric initiation system that would not present

between blast holes with the various explosive products to avoid a hazard in gassy mines would greatly improve the safety of

shock-induced desensitization of the explosives in the adjacent blasting operations. Any proposed, new nonelectric initiation

blast holes. This may then require modifying drill patterns and systems would have to be evaluated for safe use in gassy mines.

powder factors to optimize the effectiveness of the explosive There is also a need to develop a toxic fumes standard for

product while reducing the probability of combustible dust approval of various low-incendive blasting agents. Reduction in

and/or CH ignitions. the amounts of toxic fumes generated in noncoal blasting 4

The mine tests described in this report used an all-electric operations would improve safety, as well as increase efficiency by

initiation system because the current nonelectric systems will allowing work to commence sooner in the shot area. Several

ignite flammable gas. However, it would be more beneficial to areas affecting toxic fumes should be examined. First, a standard

develop a nonelectric initiation system for use in gassy method needs to be developed to determine the toxic fumes

atmospheres. The majority of noncoal mine blasting operations generated by blasting agents. Tests exist for cap-sensitive

today rely on nonelectric methods for initiation of the explosives explosives, but not for blasting agents. Second, the toxicity of

mainly because of the immunity of nonelectric blasting fumes should be better defined. Currently, guidelines

exist that only limit the total quantity for as many as seven types

of fumes. Because the toxicity of some of these types of fumes

is greater than that of others, the guidelines should follow some

type of weighted-average technique. Finally, the fume

characteristics of the explosives need to be determined. This

would entail determining which types of explosives generate less,

or more, toxic fumes than others and which parameters affect the

detonation of the explosives.

CONCLUSIONS

Our research has contributed to a better understanding of the headings of typical oil shale operations. However, cameras

fire and explosion hazards of blasting in commercial-scale monitoring these same full-scale tests have recorded highunderground oil shale and sulfide ore mining operations. The concentration dust clouds generated by the detonation of the blast

data were obtained through laboratory, gallery, and experimental holes. The ignition of these dust clouds by the hot detonation

mine tests and through full-scale blasts in operating oil shale and products could result in an unwanted explosion near the blast

sulfide ore mines. face. Inert gelled water stemming has been shown in full-scale oil

The experimental mine and laboratory tests have shown that shale field tests to reduce the dust generated from blasting and to

oil shale and sulfide ore dust can be ignited given the proper also reduce the air blast overpressures in half. Sulfide ore dusts

predispersed concentrations, particle size, and kerogen or sulfur also exhibit a higher degree of explosibility as the particle size becontent. In the Pittsburgh Research Center evaluations, comes finer and the sulfur content increases. Numerous docuexplosions did not occur in oil shale dusts with oil assays less mented sulfide dust ignitions have occurred following blasting

than ~85 L/t (~20 gal/st). For the sulfide ores, explosions did not operations and have resulted in personnel injuries and production

occur with sulfur contents less than about 20 to 25 pct, and equipment losses.

depending on the particle size and ignitor strength. The oil shale The presence of CH in many of the deep oil shale formations

dusts with the higher kerogen content (higher assays) released poses a significant hazard to underground blasting operations. A

more volatiles when heated and thus required a lower entrained gas sampling system installed at the White River Shale Project in

dust concentration to ignite and propagate down the heading. Utah sampled the CH emission rates following blasting

These tests have also shown that the oil shale dusts with finer operations. The average total CH emission rate was 0.4 m /t as

particle sizes required less entrained dust to ignite because the sampled over a 3-h period following the blast. Long-term

smaller particles were pyrolyzed at a faster rate by the ignition background emission rates have been monitored at two deep oil

zone flame front, thereby emitting the volatile gases at a faster shale mines. At Horse Draw Mine, CH was continuing to be

rate. Even though oil shale dust has been shown to be explosible liberated at a rate of 0.74 m /min over

in the experimental mine tests, sampling of dust depositions 10 years after mine closure. At the White River Shale Project, on

following blasting in oil shale mines has shown that the dust the other hand, background CH emissions decreased from 0.3

generated during blasting was an order of magnitude below the m /min following mine closure in 1986 to about

concentrations required to propagate an explosion in the large 0.06 m /min 2 years later. Both mines have experienced a CH

4

4

4

3

4 3

4 3

3

4
50

ignition following blasting. Experimental mine tests have shown shale blasts utilizing drill patterns with hole diameters up to

that even a small amount of CH can significantly reduce the 89 mm, the emulsion-ANFO blend appeared to be considerably 4

lower explosible concentration for predispersed oil shale dusts. less incendive than the conventional blasting agent ANFO while

Our research also focused on developing safer explosives for still providing effective fragmentation.

blasting in gassy oil shale mines. Tests conducted at the LLCG As a direct result of this research, the Canadian base metal

provided a means of evaluating the relative incendivity industry and MSHA requested that the research on development

characteristics of an explosive product. Two explosives, a pump- of safer explosives and blasting procedures for oil shale mines be

able emulsion-ANFO blend and a prepackaged water gel, were applied to base metal mines in an attempt to reduce the frequency

determined, through these tests, to exhibit low-incendive qualities of dust ignitions when blasting in high-sulfur-bearing ore. Many

compared with other more highly incendive products, such as of these mines had been experiencing several ignitions monthly,

ANFO. These products were then evaluated in operating mines. resulting in significant production delays. Working in

Full-scale field testing of experimental low-incendive conjunction with explosive manufacturers, the Pittsburgh

explosives was conducted at three oil shale mines in Colorado. Research Center has been involved in the recent development and

Based on data and observations collected during numerous oil testing of a prototype water-gel explosive and an emulsion

blasting agent that have been shown through LLCG testing to

exhibit low-incendive characteristics. Full-scale validation tests

were conducted at a base metal mine in Alaska and several mines

in Canada. After several years of testing and full-production use,

no sulfide dust ignitions have occurred when using these lowincendive explosive products.

Based on positive experimental and field testing results, lowincendive explosives show promise as a means of greatly

reducing the occurrences of dust and/or gas ignitions following

blasting operations in oil shale and sulfide ore mines.

ACKNOWLEDGMENTS

The authors thank the management and operations personnel Technologies International; D. Cranney, Manager of Research,

of Exxon Co. U.S.A., Unocal Corp., Occidental Oil Shale Corp., and R. Hopler, Manager of Technical Services, IRECO Corp.;

and Kennecott Minerals Co. for their valuable contributions of C. Wade, Technical Manager, Atlas Powder Co.; and

their mines, materials, and time to this Disaster Prevention P. Rodriquez, Technical Manager, ICI Explosives Canada. We

research program. We especially wish to thank the following also thank Blasting Analysis International, Inc., for its conspecific individuals who contributed to the success of this tributions in measuring the detonation velocities at the Logan

program: L. A. Weakly, Exxon Senior Staff Engineer; Wash site.

A. Randle, Vice President, A. Salter, Superintendent, and We acknowledge T. Bartke, Director, and L. Dockter, ChemG. Baloo, Mining Engineer, Unocal Energy Mining Div.; ical Engineer, Laramie Project Office of DOE; D. Cole, President,

D. Starbuck, Senior Project Engineer, and L. Page, Mine Colorado Mining Association; and R. Fischer, Physical Scientist,

Manager, White River Shale Oil Corp.; R. Zahradnic, President, and W. Bruce, Chief of Ventilation Div., MSHA's Denver Safety

Occidental Oil Shale Corp.; C. Graham, Vice President, and and Health Technology Center, for their continued support of this

D. VanHouten, Site Manager, Logan Wash, of the EMRx Corp.; project.

J. Earnshaw, Superintendent, and J. Morrison and J. Vickery, We also acknowledge the Brunswick Mining and Smelting

Project Engineers, Greens Creek Mining Co. Corp. and Kennecott's Greens Creek Mine for the samples

Additionally, we thank the following for their consider- of sulfide ore. In addition, we thank the following Pittsburgh Reable contributions to the development of the low-incendive search Center personnel: Ronald S. Conti, Fire Prevention Enexplosive formulations and the full-scale testing program: gineer, for the autoignition temperature measurements, and

B. Fox, Technical Manager, J. Heinlen, Technical Consult- Gregory M. Green, Physical Science Technician, for assistance in

ant, J. Dalton, Senior Programs Development Manager, the laboratory explosibility measurements.

and G. Weimer, Marketing Representative, Explosive
51

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52

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APPENDIX.—ABBREVIATIONS USED IN THIS REPORT

ANFO ammonium nitrate-fuel oil MEC minimum explosible concentration

BEM Bruceton Experimental Mine MSHA Mine Safety and Health Administration

CFR Code of Federal Regulations PETN pentaerythritol tetranitrate

DOE U.S. Department of Energy PPC Pittsburgh pulverized coal

hvb high-volatile bituminous SEM scanning electron microscope

LFL lean flammable limit USBM U.S. Bureau of Mines

LLCG Lake Lynn cannon gallery VOD velocity of detonation

lvb low-volatile bituminous VODR velocity-of-detonation recorder

MAIT minimum autoignition temperature
55

Cover photo: Logan Wash oil shale mine at outcrop near De

Beque, Mesa County, CO. (Photo by Kenneth L. Cashdollar,

Pittsburgh Research Center.)