RI 9678 

Report of Investigations/2009 

Results of In-Mine Research 

in Support of the Investigation 

of the Sago Mine Explosion 

Department of Health and Human Services 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 
 

Report of Investigations 9678 

Results of In-Mine Research in Support of the Investigation 

of the Sago Mine Explosion 

By Kenneth L. Cashdollar, Eric S. Weiss, Samuel P. Harteis, P.E., 

Michael J. Sapko, and John E. Urosek, P.E. 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

September 2009 
This document is in the public domain and may be freely copied 

or reprinted. 

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DHHS (NIOSH) Publication No. 2009–168 

September 2009 

SAFER • HEALTHIER • PEOPLETM 
 CONTENTS
 

Page

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

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

Experimental facilities and instrumentation ....................................................................................2 

Summary of explosion tests.............................................................................................................8 

Test 1 (LLEM test #501), April 15, 2006 ................................................................................8 

Test 2 (LLEM test #502), June 15, 2006 ...............................................................................17 

Test 3 (LLEM test #503), August 4, 2006.............................................................................29 

Test 4 (LLEM test #504), August 16, 2006...........................................................................32 

Test 5 (LLEM test #505), August 23, 2006...........................................................................36 

Test 6 (LLEM test #506), October 19, 2006..........................................................................55 

Summary and conclusions .............................................................................................................74 

Acknowledgments..........................................................................................................................76 

References......................................................................................................................................76 

Appendix A.—MSHA-WVOMHS&T-NIOSH protocols for the LLEM explosion tests ............78 

NIOSH-MSHA-WVOMHS&T seal testing – test No. 1 protocol – LLEM test #501 ..........79 

NIOSH-MSHA-WVOMHS&T seal testing – test No. 2 protocol – LLEM test #502 ..........85 

NIOSH-MSHA-WVOMHS&T seal testing – test No. 3 protocol – LLEM test #503 ..........89 

NIOSH-MSHA-WVOMHS&T seal testing – test No. 4 protocol – LLEM test #504 ..........94 

NIOSH-MSHA-WVOMHS&T seal testing – test No. 5 protocol – LLEM test #505 ..........97 

NIOSH-MSHA-WVOMHS&T seal testing – test No. 6 protocol – LLEM test #506 ..........99 

Appendix B.—Seal construction descriptions ............................................................................104 

1. Standard 40-in Omega block seal, 2001 design, in crosscut 2, March 23, 2006 ............104 

2. Hybrid 40-in Omega block seal design in crosscut 3, March 24, 2006..........................111 

3. 40-in Omega block seal, 2001 design, at 320 ft outby C-drift face, May 18, 2006........115 

4. Sago 40-in Omega block seal design in crosscut 3, July 5, 2006 ...................................119 

5. Sago 40-in Omega block seal design at 320 ft outby C-drift face, July 7, 2006 ............123 

6. Mitchell-Barrett solid-concrete-block seal in crosscut 3, September 11–15, 2006 ........128 

7. Sago 40-in Omega block seal design using the blocks from Sago mine at 320 ft 

 outby C-drift face, September 21, 2006.......................................................................132 

Appendix C.—Air leakage data for seals ...................................................................................134 

ILLUSTRATIONS 

1. Plan view of the Lake Lynn experimental mine .........................................................................3 

2. Seal test area in the LLEM..........................................................................................................4 

3. Front and side views of pressure transducers in front of seals ...................................................5 

4. LVDT mounted behind seal to measure movement ...................................................................5 

5. Roof plates and belt hanger at 134 ft from the face....................................................................6 

6. Roof plates and belt hanger at 234 ft from the face....................................................................7 

7. Setup for test 1 (LLEM #501).....................................................................................................9 

8. Pressures and LVDT displacement at the Omega block seal in X-2 during test 1 

 (LLEM #501)........................................................................................................................10 

9. Pressures and LVDT displacement at the Omega block seal in X-3 during test 1 

 (LLEM #501)........................................................................................................................11 
CONTENTS—Continued 

Page

10. Wood cribs at 312 ft looking inby in C-drift before test 1 (LLEM #501)..............................14 

11. Battery charger located at ~602 ft in C-drift...........................................................................14
 

12. Battery charger and debris from the wood cribs near X-7 after test 1 (LLEM #501) ............15 

13. Roof plates at various distances from the face after test 1 (LLEM #501) ..............................16 

14. Setup for test 2 (LLEM #502) ................................................................................................17 

15. Pressures and LVDT displacement at the Omega block seal in X-2 during test 2 

(LLEM #502).....................................................................................................................18 

16. Pressures and LVDT displacement at the Omega block seal in X-3 during test 2 

(LLEM #502).....................................................................................................................19 

17. Pressures and LVDT displacement at C-drift Omega block seal during test 2 

(LLEM #502).....................................................................................................................20 

18. Remains of X-3 seal viewed from C-drift after test 2 (LLEM #502) .....................................23 

19. Postexplosion view looking outby from original seal position in C-drift...............................24 

20. Postexplosion view looking outby from 403 ft after test 2 (LLEM #502) .............................24 

21. Debris after test 2 (LLEM #502) looking outby from X-6 location .......................................25 

22. Debris after test 2 (LLEM #502) looking outby from X-7 location .......................................25 

23. Debris after test 2 (LLEM #502) looking outby from 850 ft..................................................26 

24. Final location of battery charger at ~770 ft ............................................................................27
 

25. Roof plates at various distances from the face after test 2 (LLEM #502) ..............................28 

26. Setup for test 3 (LLEM #503).................................................................................................29 

27. Pressures and LVDT displacement at the X-2 seal during test 3 (LLEM #503) ....................30 

28. Pressures and LVDT displacement at the X-3 seal during test 3 (LLEM #503) ....................30 

29. Pressures and LVDT displacement at the C-drift seal during test 3 (LLEM #503) ...............31 

30. Setup for test 4 (LLEM #504).................................................................................................32 

31. Pressures and LVDT displacement at the X-2 seal during test 4 (LLEM #504) ....................33 

32. Pressures and LVDT displacement at the X-3 seal during test 4 (LLEM #504). ...................33 

33. Pressures and LVDT displacement at the C-drift seal during test 4 (LLEM #504) ...............34 

34. Setup for test 5 (LLEM #505).................................................................................................36 

35. Pressures and LVDT displacement at the X-2 seal during test 5 (LLEM #505) ....................37 

36. Pressures and LVDT displacement at the X-3 seal during test 5 (LLEM #505) ....................38 

37. Pressures and LVDT displacement on an expanded time scale for the X-3 seal during 

 test 5 (LLEM #505) ...........................................................................................................38 

38. Pressures and LVDT displacement at the C-drift seal during test 5 (LLEM #505) ...............39 

39. Pressures and LVDT displacement on an expanded time scale at the C-drift seal during 

test 5 (LLEM #505) ...........................................................................................................40 

40. Seal in X-2 that survived test 5 (LLEM #505) .......................................................................43 

41. Debris from X-3 seal after test 5 (LLEM #505) viewed from C-drift....................................43 

42. Debris from X-3 seal after test 5 (LLEM #505) looking into X-3 toward B-drift..................44 

43. Debris from the X-3 seal at the X-3 stopping location after test 5 (LLEM #505)..................44 

44. Debris from the X-3 seal and stopping piled against the far wall of A-drift after test 5 

(LLEM #505).....................................................................................................................45 

45. Postexplosion view in C-drift looking outby toward original seal location at 320 ft.............46 

46. Debris in C-drift after test 5 (LLEM #505) looking outby toward X-4 (right side of 

photo) at 355 ft...................................................................................................................46 
CONTENTS—Continued 

Page

 47. Debris from C-drift seal, stopping, and wood cribs looking outby from 403 ft ...................47 

48. Debris in C-drift after test 5 (LLEM #505) looking outby from X-6 at 547 ft ....................47 

49. Debris in C-drift after test 5 (LLEM #505) looking outby from ~600 ft..............................48 

50. Debris in C-drift after test 5 (LLEM #505) looking outby from 757 ft................................49 

51. Debris in C-drift after test 5 (LLEM #505) at ~850 ft..........................................................49 

52. Debris in C-drift after test 5 (LLEM #505) at ~880 ft..........................................................50 

53. Final location of battery charger near 720 ft after test 5 (LLEM #505) ...............................51 

54. Roof plates at 84, 134, and 184 ft from the face after test 5 (LLEM #505) .........................52 

55. Roof plates at 234, 304, and 403 ft from the face after test 5 (LLEM #505) .......................53 

56. Belt hanger near DG panel at 403 ft .....................................................................................54 

57. Belt hanger at 403 ft after test 5 (LLEM #505) ....................................................................54 

58. Setup for test 6 (LLEM #506)...............................................................................................55 

59. Pressures and LVDT displacement at the X-2 seal during test 6 (LLEM #506) ..................56 

60. Pressures and LVDT displacement at the X-3 seal during test 6 (LLEM #506) ..................57 

61. Pressures and LVDT displacement at the C-drift seal during test 6 (LLEM #506) .............58 

 62. Pressures and LVDT displacement on an expanded time scale at the C-drift seal during

 test 6 (LLEM #506) .........................................................................................................58 

 63. Raw and smoothed pressure data for the horizontal transducer during test 6 (LLEM #506) ....59 

 64. Raw and smoothed pressure data for the embedded transducer during test 6 (LLEM #506) ....59 

65. Postexplosion view in C-drift looking outby toward original seal location at 320 ft 

after test 6 (LLEM #506) .................................................................................................62 

66. Postexplosion view in C-drift looking outby from X-4 at 355 ft..........................................63 

67. Debris in C-drift after test 6 (LLEM #506) looking outby from 403 ft................................63 

68. Debris in C-drift after test 6 (LLEM #506) looking outby from ~500 ft..............................64 

69. Debris in C-drift after test 6 (LLEM #506) looking outby from ~600 ft..............................64 

70. Debris in C-drift after test 6 (LLEM #506) looking outby from 757 ft................................65 

71. Debris in C-drift after test 6 (LLEM #506) looking outby from ~850 ft..............................65 

72. Debris after test 6 (LLEM #506) looking outby from ~950 ft .............................................66 

73. Debris after test 6 (LLEM #506) looking outby from ~1,050 ft...........................................67 

74. Debris after test 6 (LLEM #506) looking outby from ~1,150 ft...........................................67 

75. Debris in C-drift after test 6 (LLEM #506) looking outby from ~1,240 ft ..........................68 

76. Debris in C-drift after test 6 (LLEM #506) looking outby from ~1,440 ft ..........................68 

77. Final position of battery charger after test 6 (LLEM #506)..................................................69 

78. Roof plates at 84 and 134 ft from the face after test 6 (LLEM #506) ..................................70 

79. Roof plates at 184 and 234 ft from the face after test 6 (LLEM #506) ................................71 

80. Roof plates at 304 and 403 ft from the face after test 6 (LLEM #506) ................................72 

81. Belt hanger near DG panel at 403 ft ....................................................................................73 

82. Belt hanger at 403 ft after explosion test 6 (LLEM #506)....................................................73 

Standard 40-in Omega block seal, 2001 design, in crosscut 2, March 23, 2006: 

B-1. BlocBond applied to concrete mine floor ...........................................................................106 

B-2. BlocBond being applied to gaps between the Omega blocks.............................................106 

B-3. As each Omega block course was completed, BlocBond was also coated on the 

 exposed B- and C-drift sides of the blocks ....................................................................107 
CONTENTS—Continued 

Page

 B-4. Schematic illustrating alternating courses and staggered block joints..............................107 

B-5. Cut blocks on top course to provide 2-in gap to roof .......................................................108 

 B-6. View of top portion of seal from C-drift side after B-drift side was completed...............108 

 B-7. One row of wood placed flush with the edge of the blocks on the B-drift side................109 

B-8. View from the C-drift side showing the rough-cut lumber wedged between the 

 mine roof and blocks across the center of the seal.......................................................109 

B-9. Closeup of the wood wedges, installed between the mine roof and the rough-cut 

 board, used to tighten the Omega block seal ...............................................................110 

Hybrid 40-in Omega block seal design in crosscut 3, March 24, 2006: 

B-10. Dry BlocBond being spread to a 0.5-in-thick layer on the dampened concrete floor 

in X-3 ...........................................................................................................................113 

B-11. Wetting the dry layer of BlocBond before positioning the Omega blocks.......................113 

B-12. Positioning the first course of Omega blocks ...................................................................114 

B-13. Applying BlocBond to the top of the first course.............................................................114 

40-in Omega block seal, 2001 design, at 320 ft outby C-drift face, May 18, 2006: 

B-14. A 0.25- to 0.5-in-thick layer of properly mixed BlocBond on the floor...........................117 

B-15. Omega blocks laid wet with fully mortared (BlocBond) horizontal and vertical joints......117 

B-16. Completing the 11th and final full block course on the outby side ..................................118 

B-17. Hand slinging the BlocBond to fill the gaps between the previously installed center 

board and the outby board............................................................................................118 

Sago 40-in Omega block seal design in crosscut 3, July 5, 2006: 

B-18. Applying the 1.5-in-thick layer of dry BlocBond to the dampened concrete floor 

in X-3 ...........................................................................................................................121 

B-19. Applying a fine water spray to the dry BlocBond layer ...................................................121 

B-20. Applying the properly mixed BlocBond to the first course of Omega blocks..................122 

B-21. Driving the wedges (skin to skin) between the crossboard and mine roof .......................122 

Sago 40-in Omega block seal design at 320 ft outby C-drift face, July 7, 2006: 

B-22. Applying a 1.5-in-thick layer of dry BlocBond on the dampened concrete floor 

across C-drift................................................................................................................125 

B-23. Wetting the dry layer of BlocBond with a fine spray of water.........................................125 

B-24. Positioning the Omega blocks in a staggered pattern for the first course.........................126 

B-25. Applying BlocBond by shovel and gloved hands to the first course................................126 

B-26. Positioning the second course of Omega blocks in a transverse pattern ..........................127 

B-27. Installing the crossboard on the outby side of C-drift seal ...............................................127 
CONTENTS—Continued 

Page

Mitchell-Barrett solid-concrete-block seal in crosscut 3, September 11–15, 2006: 

B-28. Full wet-bed construction on all horizontal and vertical block joints...............................129 

B-29. Installing cut blocks on top course....................................................................................130 

B-30. Completely filling the gap between the top course of blocks and the mine roof with 

 mortar...........................................................................................................................130 

B-31. Mortar filling the gaps between the steel angle hitching and the blocks along the 

floor and ribs................................................................................................................131 

TABLES 

1. Explosion tests of seals for MSHA during LLEM explosion research.................................8 

2. Pressures and LVDT displacement at the seals during test 1 (LLEM #501)......................12 

3. Wall pressures and flame travel during test 1 (LLEM #501) ............................................12 

4. MSHA guidelines for acceptable air leakage through a seal ..............................................13 

5. Pressures and LVDT displacement at the seals during test 2 (LLEM #502)......................22 

6. Wall pressures and flame travel during test 2 (LLEM #502) .............................................22 

7. Pressures and LVDT displacement at the seals during test 4 (LLEM #504) ....................35 

8. Wall pressures and flame travel during test 4 (LLEM #504) ............................................35 

9. Pressures and LVDT displacement at the seals during test 5 (LLEM #505)......................41 

10. Wall pressures and flame travel during test 5 (LLEM #505) .............................................42 

11. Pressures and LVDT displacement at the seals during test 6 (LLEM #506)......................60 

12. Wall pressures and flame travel during test 6 (LLEM #506) .............................................61 

13. Summary of explosion pressures on various seals..............................................................74 

C-1. Air leakage measurements before test 1 (LLEM #501)....................................................134 

C-2. Air leakage measurements after test 1 (LLEM #501).......................................................134 

C-3. Air leakage measurements before test 2 (LLEM #502)....................................................134 

C-4. Air leakage measurements after test 2 (LLEM #502).......................................................134 

C-5. Air leakage measurements before test 3 (LLEM #503)....................................................135 

C-6. Air leakage measurements after test 3 (LLEM #503).......................................................135 

C-7. Air leakage measurements after test 4 (LLEM #504).......................................................135 

C-8. Air leakage measurements after test 5 (LLEM #505).......................................................135 

C-9. Air leakage measurements before test 6 (LLEM #506)....................................................136 

C-10. Air leakage measurements after test 6 (LLEM #506).......................................................136 
 

 

 

 

 

ACRONYMS AND ABBREVIATIONS USED IN THIS REPORT 

ASTM American Society for testing and Materials 

BDP bidirectional probe 

CFR Code of Federal Regulations 

CH4 methane 

DG data-gathering 

KS Kinetic Systems 

LVDT linear variable displacement transducer 

MSHA Mine Safety and Health Administration 

NI National Instruments 

NIOSH National Institute for Occupational Safety and Health 

LLEM Lake Lynn Experimental Mine 

PRL Pittsburgh Research Laboratory (NIOSH) 

WVOMHS&T West Virginia Office of Miners’ Health, Safety, and Training 

X crosscut (e.g., “X-1” stands for “crosscut 1”) 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

cfm cubic foot per minute 

ft foot 

ft2 square foot 

ft3 cubic foot 

gal gallon 

hr hour 

Hz hertz 

in inch 

in2 square inch 

in H2O inch of water 

lb pound 

min minute 

ms millisecond 

psi pound-force per square inch 

sec second 
DEDICATION 

This report was initially prepared by Kenneth L. Cashdollar and is 

dedicated to his memory. Ken passed away on March 4, 2009. Ken never 

wavered from his continuing commitment to conduct the highest-quality, 

solution-oriented, scientific research focused on reducing the risk of fatalities 

from explosions in the mining and chemical industries. 

 

RESULTS OF IN-MINE RESEARCH IN SUPPORT OF THE 

INVESTIGATION OF THE SAGO MINE EXPLOSION 

By Kenneth L. Cashdollar,1

 1Principal Research Physical Scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and 

Health, Pittsburgh, PA (deceased). 

 Eric S. Weiss,2

 2

Team Leader (Senior Research Mining Engineer), Lake Lynn Laboratory Section, Pittsburgh Research Laboratory, 

National Institute for Occupational Safety and Health, Pittsburgh, PA. 

Samuel P. Harteis, P.E.,3
 

 3

Research Mining Engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

Michael J. Sapko,4

 4

Principal Research Physical Scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety 

and Health, Pittsburgh, PA (retired).

and John E. Urosek, P.E.5
 

 5

Chief, Mine Emergency Operations, Pittsburgh Safety and Health Technology Center, Mine Safety and Health 

Administration, Pittsburgh, PA. 

ABSTRACT 

The Mine Safety and Health Administration (MSHA) and the West Virginia Office of 

Miners’ Health, Safety, and Training (WVOMHS&T) investigated the explosion at the Sago Mine 

in West Virginia, which occurred on January 2, 2006, and resulted in 12 fatalities. As part of the 

investigation, the agencies requested that the National Institute for Occupational Safety and 

Health’s (NIOSH) Pittsburgh Research Laboratory evaluate the effects of explosions on specific 

mine ventilation seals and other structures and objects at its Lake Lynn Experimental Mine 

(LLEM). The results of the LLEM study would assist MSHA and WVOMHS&T in a more 

thorough understanding of the various questions that arose during their investigations of the 

explosion. Six large-scale explosion tests were conducted in the LLEM from April to October 2006. 

The protocols for these tests, and in particular the procedures for constructing various Omega block 

seals, were developed mainly by MSHA and WVOMHS&T. NIOSH developed the experimental 

procedures at the LLEM that would provide the required range of explosion pressures against the 

seals. Three 40-in-thick seal designs using Omega 384 low-density block were constructed in the 

LLEM and exposed to various explosion pressures. These seal designs are referred to in this report 

as the “2001 design,” the “hybrid design,” and the “Sago design.” 

The 2001-design Omega block seal (80 in high) located in crosscut 2 of the LLEM survived 

all six explosions, with pressure loadings up to 51 psi. The 2001-design Omega block seal (88 in 

high) in C-drift was destroyed during Test 2, which subjected the seal to a head-on explosion that 

resulted in a pressure loading of 51 psi. The height difference between the two seals and the 

orientation of each seal to the explosion were contributing factors. The higher seal would be weaker 

for the same seal thickness. The hybrid Omega block seal in crosscut 3 survived an explosion at a 

pressure loading of 25 psi and failed during another explosion at a pressure loading of 39 psi at the 

seal. Based on these tests, it seems that the hybrid seal design is weaker than the 2001 seal design. 

The Sago Omega block seals were constructed in crosscut 3 and C-drift before Test 3. The crosscut 

3 seal survived a pressure loading of 18 psi and was destroyed during an explosion at a pressure 

loading of 35 psi at the seal. The C-drift seal survived a head-on explosion that resulted in a 

pressure loading of 21 psi and was destroyed during an explosion with a pressure loading of 57 psi 
2
 

at the seal. Based on these LLEM tests, it seems that the Sago seal design is weaker than the 2001 

seal design, yet it still complied with the requirements of 30 CFR 75.335(a)(2) that were in effect at 

the time of the mine disaster. 

During these LLEM explosion tests, the distance of seal debris travel was also measured. 

In Test 5, the C-drift seal was destroyed during a head-on explosion that resulted in a pressure 

loading of 57 psi, and the seal debris was thrown over 500 ft. In Test 6, the C-drift seal was 

destroyed during a head-on explosion that resulted in a pressure loading of 93 psi, and the Omega 

block debris was thrown over 900 ft. During these tests, the explosion pressure effects on other 

structures and objects were also documented. Unless otherwise specified, all of the pressure data 

listed in this report represent the highest recorded smoothed (averaged over 10 ms) explosion 

pressure loadings. 

The information in this report was used by MSHA and WVOMHS&T as supporting data in 

their analyses and investigative reports of the Sago Mine explosion. 

INTRODUCTION 

At the request of the Mine Safety and Health Administration (MSHA) and the West Virginia 

Office of Miners’ Health, Safety, and Training (WVOMHS&T), the National Institute for 

Occupational Safety and Health’s (NIOSH) Pittsburgh Research Laboratory (PRL) evaluated the 

effects of explosions on specific mine ventilation seals at its Lake Lynn Experimental Mine 

(LLEM) to assist the agencies in their investigations of the explosion at the Sago Mine in West 

Virginia, which occurred on January 2, 2006, and resulted in 12 fatalities. Six full-scale explosion 

tests were conducted in the LLEM from April to October 2006 to help answer questions regarding 

possible scenarios for the Sago explosion. The protocols for these tests, and in particular the 

procedures for constructing various Omega block seals, were developed mainly by MSHA and 

WVOMHS&T. NIOSH developed the experimental procedures at the LLEM that would provide the 

required range of explosion pressures against the seals. NIOSH also documented the seal 

construction, determined and installed the appropriate instrumentation, conducted the explosion 

tests, analyzed the data, and photographically documented the postexplosion observations. By 

comparing the results of known explosion loading pressures on the various ventilation structures 

and objects in the LLEM with their observations at the Sago Mine, MSHA and WVOMHS&T 

could better analyze the explosion pressures that may have occurred at the Sago Mine. 

EXPERIMENTAL FACILITIES AND INSTRUMENTATION 

The full-scale explosion tests were conducted in the LLEM [Mattes et al. 1983; Triebsch and 

Sapko 1990] (Figure 1). The LLEM is a former limestone mine, and five new drifts (horizontal 

passageways in a mine) were developed in 1979–1980 to simulate the geometries of modern 

U.S. coal mines. The mine has four parallel drifts: A, B, C, and D. D-drift is a 1,640-ft-long single 

entry that can be separated from E-drift by an explosion-proof bulkhead door. To simulate roomand-pillar workings, drifts A, B, and C can be used. These three drifts are each approximately 

1,600 ft long, with seven crosscuts at the inby end. An explosion-resistant bulkhead door is used to 

separate the multiple entries from E-drift (Figure 1). Drifts C and D are connected by E-drift, a 500­

ft-long entry that simulates a longwall face. An 8-in-thick reinforced concrete floor runs the entire 

length of each of these drifts and crosscuts. The explosion tests were conducted in the multipleentry area of A-, B-, and C-drifts. The entries are about 20 ft wide by about 6.5 ft high, with crosssectional areas of 130–140 ft2

. The LLEM bulkhead door and some of the other infrastructure were 
 

designed to withstand explosion overpressures of up to 100 psi. Higher pressures have been 

recorded at areas away from these structures. 

Each LLEM drift has 10 data-gathering (DG) stations inset in the rib wall at the locations 

shown in Figures 1 and 2.

Figure 1.—Plan view of the Lake Lynn Experimental Mine. 

 Each DG station houses a strain gauge transducer to measure the pressure 

and an optical sensor to detect the flame arrival. The explosion pressure is dynamic in nature and is 

composed of two components: a quasi-static pressure component (the pressure that is exerted in all 

directions and measured perpendicular to the gas flow) and a wind or velocity pressure component 

(pressure due to gas flow). The total explosion pressure is the sum of the quasi-static pressure and 

the wind or velocity pressure. The transducers in the DG stations in the wall, which is perpendicular 

to the gas flow, measure the quasi-static pressures. All of the explosion pressures presented in this 

report are an averaged overpressure or gauge pressure (pressures above local atmospheric pressure) 

rather than absolute pressures. In the past, Nagy [1981, p. 58] referred to the quasi-static pressure as 

the “static pressure” to differentiate it from the “dynamic pressure,” or velocity component. 

However, the quasi-static pressure is not actually static as it does vary with time during the 

explosion. Zipf et al. [2007] provide a more detailed discussion on explosion pressures. Other 

instruments may also be installed at various locations in the LLEM during an explosion test. 

During the normal course of underground coal mining, it sometimes becomes necessary to 

install seals to isolate abandoned or worked-out areas of a mine. Since 1992, 30 CFR6

6

Code of Federal Regulations. See CFR in references. 

3
 

 75.335 

required a seal to “withstand a static horizontal pressure of 20 pounds per square inch.” This 

regulation formed the basis for previous PRL evaluations of explosion-resistant seals at the LLEM 

[Stephan 1990a,b; Greninger et al. 1991; Weiss et al. 1993a,b,c; 1996; 1997; 1999]. During the 

1990s, PRL and MSHA jointly evaluated the capability of various seal construction materials and 

designs to meet or exceed the requirements of the CFR. 
 

Figure 2 is a closeup plan view of the seal test area in the multiple-entry area of the LLEM. 

4
 

Figure 2.—Seal test area in the LLEM. 

In this example, there are seals in the first four crosscuts from the face or closed end of C-drift. Note 

that, in the LLEM, the first crosscut (“1” in Figure 2) is the one nearest the face. The crosscuts are 

17–19 ft wide by ~7.2 ft high with a cross-sectional area of about 130 ft2. Explosion-resistant seals 

from a previous study were located in X-17

7

The abbreviation “X” stands for “crosscut” throughout this report, e.g., “X-1” stands for “crosscut 1.” 

and X-2. The flammable CH4-air gas zone is at the face 

(closed end) of C-drift. The gas zone is confined on the outby end by a plastic diaphragm. The 

bulkhead door is closed between C- and E-drifts before the test. For an explosion test, the gas is 

ignited and the explosion pressure travels out C-drift. 

Examples of pressure transducers in front of a seal are shown in Figure 3. For the first two 

tests (LLEM #501–502) of the series, there was at least one pressure transducer in front of each 

seal. For the later tests (LLEM #503–506), there were generally at least two pressure transducers in 

front of each seal—one mounted horizontally to face the incoming head-on pressure wave 

(to measure the total explosion pressure at that location) and one mounted vertically to be 

perpendicular to the incoming pressure wave (to measure the quasi-static explosion pressure at that 

location). Behind each seal was a linear variable differential transducer (LVDT), as shown in 

Figure 4. The LVDT measures the movement of the seal [Weiss et al. 1999, pp. 5–6]. Also shown in 

Figure 4 are the horizontal and vertical yellow breakwires used to measure the time of seal failure. 

During the explosion tests, a high-speed, PC-based National Instruments (NI) data acquisition 

system collected the data from the various instruments at a sampling rate of 1,500 samples per 

second. The reported data were normally averaged over 10 ms (15-point smoothing). For some of 

the tests, a second Kinetic Systems (KS) data acquisition system collected the data at 5,000 samples 

per second. 
 

Figure 3.—Front and side views of pressure transducers in front of seals. 

Figure 4.—LVDT mounted behind seal to measure movement. 

Typical examples of the round and square roof plates and belt hangers that were attached to 

the LLEM roof at various distances from the face are shown in Figures 5–6. The large round plates 

are ~19 inches in diameter and the metal is 0.033 in thick. The large square plates (also known as 

spider plates) are ~17 in by 17 in and the metal is 0.038 in thick. A small square bearing plate is 

below each large round or square plate in the photos. The small square bearing plates are ~8 in by 

8 in by 0.146 in thick. Unless specified otherwise, all subsequent discussion in this report will refer 

to the large square plates and not the small square plates. The belt hangers at the bottom of Figures 

5–6 are ~4 in by 4 in on each side by 0.25 in thick. 

For this series of LLEM explosion tests, MSHA hired a certified surveyor (Allegheny 

Surveys, Inc., Birch River, WV) to survey the positions of the various objects in the mine before the 

explosions and to survey the debris from seals and stoppings, wood cribs, and various other objects 

after the explosions. 

5
 
 

 

 

 

Viewed from inby Viewed across entry from DG panel 

Figure 5.—Roof plates and belt hanger at 134 ft from the face. 

6
 
 

 

 

 

Viewed from inby

Figure 6.—Roof plates and belt hange

 Viewed across entry from DG panel 

r at 234 ft from the face. 

7
 
SUMMARY OF EXPLOSION TESTS 

A summary of the LLEM explosion tests conducted in 2006 is presented in Table 1. 

Table 1.—Explosion tests of seals for MSHA during LLEM explosion research 

Test Date LLEM 

test # 

Seal Averaged 

peak 

pressure, 

psi 

Result 

Location Type 

1 Apr. 15, 2006 501 X-2 

X-3 

2001-design 40-in Omega 

Hybrid 40-in Omega 

23 

25 

Survived 

Survived 

X-2 2001-design 40-in Omega 22 Survived 

2 Jun. 15, 2006 502 X-3 

C-320ft1 Hybrid 40-in Omega 

2001-design 40-in Omega 

39 

51 

Failed 

Failed 

X-2 2001-design 40-in Omega 13 Survived 

3 Aug. 4, 2006 503 X-3 

C-320ft1 Sago-like 40-in Omega 

Sago-like 40-in Omega 

16 

17 

Survived 

Survived 

X-2 2001-design 40-in Omega 15 Survived 

4 Aug. 16, 2006 504 X-3 

C-320ft1 Sago-like 40-in Omega 

Sago-like 40-in Omega 

18 

21 

Survived 

Survived 

X-2 2001-design 40-in Omega 26 Survived 

5 Aug. 23, 2006 505 X-3 

C-320ft1 Sago-like 40-in Omega 

Sago-like 40-in Omega 

35 

57 

Failed 

Failed 

X-2 2001-design 40-in Omega 51 Survived 

6 Oct. 19, 2006 506 X-3 

C-320ft1 Solid concrete block 

Sago-like 40-in Omega2 

49 

93 

Survived 

Failed 

1 C-drift, 320 ft from the closed end. 

2 This seal was constructed with actual unused Omega blocks from the Sago Mine. 

NOTE: A solid-concrete-block seal was installed in X-1 for all tests. 

Each 

test was given a number (1 through 6) corresponding to the test series and a number (LLEM tests 

#501–506) corresponding to the sequential LLEM test numbering system in place since 1982. The 

first three columns of the table list the current test series number, the date, and the LLEM test 

number. The next two columns list the location and type of mine ventilation seal. The construction 

details for the seals are contained in Appendix B and will be referred to when the seals are 

discussed in subsequent sections of this report. The next column lists the peak total explosion 

pressure loading (averaged or smoothed over 10 ms) from the horizontal transducer located at the 

middle front of each seal. The last column lists whether the seal survived or failed during the 

explosion. The averaged peak total explosion pressure loading is the highest smoothed value from 

either the NI or KS data acquisition system. The pressure values are rounded to the nearest integer. 

Test 1 (LLEM Test #501), April 15, 2006 

For the first test, a solid-concrete-block seal was constructed in X-1, the crosscut closest to 

the face; an Omega block seal based on the 2001 design [Sapko et al. 2004] was constructed in X-2; 

and a hybrid Omega block seal was constructed in X-3 (Figure 7). The solid-concrete-block seal in 

X-1 had a 16-in-thick main wall with an interlocked 32-in pilaster in the center. The 6-in by 8-in by 

16-in solid concrete blocks were laid in a transverse pattern (staggered joints), and high-strength 

mortar was applied to all of the block-to-block interfaces as well as the block-to-strata interfaces. 

The mortar used was BlocBond (product No. 1225-51), a fiber-reinforced surface-bonding cement 

made by Quikrete Co., Atlanta, GA (50-lb average weight per bag). The gap between the top block 

course and the mine roof was completely packed with the BlocBond mortar; no wedges were used 

8
 
during construction of this seal. Keying of the seal was simulated by bolting steel angle to the ribs 

and floor on both sides of the seal. 

 

 

 

 

CB OB HB 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

BD 

X-1 X-2 X-3 X-4 X-5 X-6 X-7 

C-drift 

B-drift 

A-drift 

CB – Concrete block Seal OB – 40-in Omega block seal 

HB – 40-in hybrid Omega block seal – Cribs 

 Roof bolt plates with pie pans and belt hangers arranged alternatively 

- Bulkhead door 

+++ -

BD 

Figure 7.—Setup for Test 1 (LLEM #501). 

The X-2 nominal 40-in-thick Omega block seal was based on the 2001 design. The X-2 seal 

was built using Omega 384 blocks (manufactured by Burrell Mining Products in Bluefield, WV), 

with nominal block dimensions of 8 in by 16 in by 24 in. No pilaster or keying was required with 

this seal design. The block course was alternated to stagger the block joints from front to back and 

left to right. The properly mixed BlocBond mortar was applied at all of the block-to-block 

interfaces and the block-to-strata interfaces, including the floor. Three rows of 1-in-thick by 8-inwide hardwood rough-cut boards were run lengthwise (rib to rib) on the top course of blocks. One 

row of board was placed across the middle of the seal, and one row of board was placed flush with 

each edge of the seal. Wood wedges were driven perpendicular to these boards to tighten between 

the mine roof and the boards, then all gaps between the top course and mine roof were completely 

packed with BlocBond. Both faces of the seal were then coated with BlocBond. 

The nominal 40-in-thick hybrid Omega block seal in X-3 was constructed in a manner 

similar to the X-2 seal except that dry BlocBond was applied to a 0.25-in depth on the floor across 

the width of the crosscut before any blocks were laid. This dry BlocBond layer was then dampened 

with water sprays. The entire first course of Omega blocks was spray-dampened with water on the 

bottom of each block and then positioned on the dampened bed of dry BlocBond before any 

additional BlocBond mortar was applied. The properly mixed BlocBond mortar was then applied by 

gloved hand across the top of this first course and forced as much as possible with gloved hands 

into the vertical block joints. The remaining courses were installed in a similar manner, except the 

bottoms of the blocks were not dampened, the BlocBond was applied by gloved hand to the block 

joints before placement of each block, and the blocks in each subsequent course were alternated to 

stagger the block joints. All of the block work was completed before installing the 1-in-thick by 

6-in-wide hardwood boards. Wood wedges were used between the boards and the mine roof. 

Additional details of the seal construction procedures can be found in Appendix A under “Test 

No. 1 Protocol” and in Appendix B, sections 1 and 2. Details of the test procedures can also be 

found in Appendix A under “Test No. 1 Protocol.” 

9
 
For Test 1 (LLEM #501), a gas ignition zone was confined by a plastic diaphragm across 

C-drift at 47 ft from the face (Figures 2 and 7). About 661 ft3 of natural gas was injected into the 

ignition zone to produce a mixture of ~10% CH4 in air. The flammable gas was ignited at the face 

and the pressure pulse propagated out C-drift past the seals in X-1, X-2, and X-3, as shown in 

Figure 7. Note that the depth of the seals in the crosscuts is not to scale in Figure 7 or subsequent 

test schematics in this report. The seals in the crosscuts experienced the sweeping explosion 

pressure loading, i.e., the seals in the crosscuts were subjected to a nonuniform pressure loading as 

the explosion pressure wave traveled down C-drift past each crosscut seal location. This sweeping 

explosion pressure loading test method is the same method used during the LLEM seal tests during 

the 1990s [Stephan 1990a,b; Greninger et al. 1991; Weiss et al. 1993a,b,c; 1996; 1997; 1999]. The 

pressure loading on a crosscut seal will vary across the face of the seal, but the measurements in this 

report were taken only from the geometric center of the seal, i.e., the pressures can be significantly 

higher or lower near the crosscut ribs depending on the direction of the explosion travel and the 

various pressure wave interactions at these areas. 

In this test, all of the seals survived the explosion. Figure 8 shows the pressure loading at the 

seal in X-2 along with the quasi-static pressures at the wall of C-drift inby (134 ft) and outby 

(184 ft) the seal.

35

40

-0.30

-0.20

-0.10

0 

5 

10 

15 

20 

25 

30 

Pressure, psi 

0.00 

0.10 

LVDT, in 

C-134 ft static

 X-2, 156 ft, front 

C-184 ft static

 X-2 LVDT

 X-2 breakwire 

0.35 0.40 0.45 0.50 0.55 0.60 

Time, sec 

Figure 8.—Pressures and LVDT displacement at the Omega block seal in X-2 during Test 1 (LLEM #501). 

 The pressure transducer at the seal was located approximately in the middle front 

of the seal at 156 ft from the face of C-drift. All of the data were averaged over 10 ms. The pressure 

loading at the seal was 23 psi. The curve at the top of the figure shows the seal displacement as 

measured by the LVDT on the back or B-drift side of the seal. The maximum recorded movement 

during the explosion was 0.03 in. Since the seal did not fail, there was no change in the breakwire 

signal. 

Figure 9 shows the pressure loading at the seal in X-3 along with the quasi-static pressure at 

the wall of C-drift inby (234 ft) and outby (304 ft) the seal. The pressure transducer at the seal was 

located approximately in the middle front of the seal at 256 ft from the face of C-drift. All of the 

data were averaged over 10 ms. The pressure loading at the seal was 25 psi. The curve at the top of 

10
 
the figure shows the seal displacement as measured by the LVDT on the back of the seal. The 

maximum recorded movement during the explosion was 0.12 in. Since the seal did not fail, there 

was no change in the breakwire signal. 

35

40

-0.60

-0.50

-0.40

-0.30

-0.20

-0.10

0 

5 

10 

15 

20 

25 

30 

Pressure, psi 

0.00 

0.10 

0.20 

LVDT, in

 C-234 ft static

 X-3, 256 ft, front

 C-304 ft static

 X-3 LVDT

 X-3 breakwire 

0.40 0.45 0.50 0.55 0.60 0.65 

Time, sec 

Figure 9.—Pressures and LVDT displacement at the Omega block seal in X-3 during Test 1 (LLEM #501). 

Pressures, LVDT displacement, and breakwire summary data for the seals in X-2 and X-3 

during Test 1 (LLEM #501) are shown in Table 2. The first column of the table lists the seal 

location and distance from the face of C-drift. The next two columns list the peak pressure loading 

at the front middle of the seals as measured by the NI and KS data acquisition systems. The data 

were averaged over 10 ms for all of the listed values. The next two columns list the deflection or 

displacement of the middle of the seal, measured in inches. The next column would list the time 

when the wires attached to the seals would break. However, during this test, both seals survived and 

the wires did not break. 

Table 3 lists quasi-static pressure and flame sensor data at the various DG panels on the 

walls of B- and C-drifts during LLEM #501. The data were averaged over 10 ms for all of the listed 

values. The first three columns of the table list the position and quasi-static pressures at the 

DG panels in B-drift. Note that the listed distances were measured from the face of each drift. The 

next column lists the DG panel numbers and depicts the seal and crosscut locations. The two Omega 

block seals in X-2 and X-3 are depicted by blue shading. The next three columns list the position 

and quasi-static pressures at the DG panels in C-drift. The pressures remained relatively constant in 

the region of the seals in the first three crosscuts. The pressure increased somewhat at ~304 ft 

because of the restriction due to two wood cribs at that location. The pressures then decreased as the 

pressure pulse passed the open crosscuts. The last two columns in the table list the flame signal and 

arrival time at each of the DG panels. For this test, the flame went past the 184-ft panel but did not 

reach the 234-ft panel. Therefore, the interpolated flame travel distance was about 210–220 ft. The 

uncertainty of the flame travel distance is about ±20 ft. Note that the interpolation takes into account 

both the strength and duration of the flame signal at the 184-ft DG panel. Based on the initial gas 

zone length of 47 ft, the expansion ratio would be about 4.6 (215 ft/47 ft). 

11
 
Table 2.—Pressures and LVDT displacement at the seals during Test 1 (LLEM #501) 

Seal Seal pressures LVDT Break Seal pressures LVDT 

deflection, time, Seal deflection, 

psi (NI) psi (KS) in sec psi (NI) psi (KS) in 

Break 

time, 

sec 

 

X-2 BC 

156 ft 

22.8 22.1 0.03 — 

 

 

Seal survived 

 

X-3 BC 

256 ft 

25.0 25.2 0.12 — 

 

 

Seal survived 

 C-drift No seal in C-drift for this test 

 

Table 3.—Wall pressures and flame travel during Test 1 (LLEM #501) 

B-drift quasi-static pressures 

Distance, ft psi (NI) psi (KS) 

C-drift quasi-static pressures 

Distance, ft psi (NI) psi (KS) 

Flame signal
 

Volts sec (NI)
 

1 

X-1 

2 

3 

X-2 

4 

5 

X-3 

6 

X-4 

7 

X-5 

8 

X-6 

9 

X-7 

10 

11 

13 

 

84 

134 

 

184 

234 

 

304 

 

403 

 

501 

 

598 

 

757 

1,506 

— 

 

20.1 

20.5 

 

20.5 

18.0 

 

22.5 

 

14.4 

 

9.1 

 

6.1 

 

3.9 

3.1 

 

20.6 

20.4 

 

21.8 

17.5 

 

22.0 

 

12.9 

 

8.2 

 

5.8 

 

3.9 

3.2 

>5 

 

>5 

>5 

 

>5 

~0 

 

~0 

 

~0 

 

~0 

 

~0 

 

~0 

 

0.218 

 

0.396 

0.432 

 

0.523 

 

 

 

 

 

 

 

 

 

 

 

 

10 5.0 5.2 

 

108 4.0 3.9 

158 ~3 ~3 

 

211 3.4 3.4 

257 3.1 3.0 

 

329 5.1 5.0 

 

427 5.2 5.1 

 

526 6.5 6.7 

 

626 5.9 6.3 

 

782 

 

4.4 

 

4.5 

 

12
 
An important factor to consider for any seal design is its ability to minimize air leakage 

through the seal. Measurements of the air leakages across the various seals were conducted before 

and after each of the explosion tests. For these air leakage tests, the D-drift bulkhead door (Figure 1) 

was closed. This directed all of the ventilation flow (from a vertical air shaft in E-drift) toward 

C-drift. A wooden framework with brattice cloth or curtain was erected across C-drift outby the last 

seal position. This curtain effectively blocked the ventilation flow, which resulted in a pressurized 

area on the C-drift side of the seals. By increasing the speed of the four-level LLEM main 

ventilation fan while in the blowing mode, we increased the pressure exerted on the structures from 

approximately 1 in H2O pressure for the lowest fan speed setting to nearly 5.0 in H2O for the 

highest setting. On the B-drift side of each seal, a diaphragm of brattice cloth was installed across 

each crosscut. A vane anemometer was used to monitor the airflow through an opening on each 

brattice to determine the leakage rates through each seal while the differential pressure across the 

seal was measured. 

Based on data previously collected during the early LLEM seal testing program [Stephan 

1990a; Greninger et al. 1991], MSHA developed guidelines for acceptable air leakage rates through 

seals for use during the LLEM seal evaluation programs. Table 4 lists these maximum acceptable 

air leakage rates as a function of pressure differential. 

Table 4.—MSHA guidelines for acceptable air leakage 

through a seal 

Pressure differential, Air leakage rate, 

in H2O cfm 

<1.0 <100 

1.0 < 2.0 <150 

2.0 < 3.0 <200 

>3.0 <250 

For pressure differentials up to 1 in H2O, air 

leakage through the seal must not exceed 100 cfm. For pressure differentials over 3 in H2O, air 

leakage must not exceed 250 cfm. The flow rate was calculated from the linear air speed measured 

by the vane anemometer and the area of the opening through the brattice cloth behind each seal. 

The air leakages of the two seals in X-2 and X-3 were measured after LLEM #501. Both 

seals passed the air leakage test, as shown in Table C-2 in Appendix C of this report. 

In addition to the seals evaluated during the first explosion test, two wood cribs were 

installed at 312 ft from the face in C-drift before the first test (Figure 10). These were standard cribs 

made from 6-in by 5-in by 30-in hardwood timbers. The individual blocks were labeled by letter 

and number, with crib A on the right and crib B on the left, looking inby. Between the two cribs is a 

bidirectional probe (BDP) at ~306 ft (as measured from the closed end of C-drift) that measured 

both total and dynamic explosion pressures at that location. In the background is the yellow brattice 

used during the preexplosion air leakage test of the seals. This brattice was removed for the 

explosion test and later reinstalled for the postexplosion leakage test. 

During the explosion, the pressure at the crib location was 29 psi and the dynamic pressure 

was 9 psi. Both cribs were destroyed during the explosion, and wood debris traveled up to 880 ft 

from the original crib location. 

13
 
Figure 10.—Wood cribs at 312 ft looking inby in C-drift before Test 1 (LLEM #501). 

A battery charger from the Sago Mine had been obtained by WVOMHS&T and was placed 

at ~602 ft from the face in C-drift, as shown on the right looking outby in Figure 11.

Figure 11.—Battery charger located at ~602 ft in C-drift. 

 To the left of 

the battery charger is another BDP mounted vertically from the roof at 604 ft to record the total and 

dynamic pressures at that location during the explosion. The battery charger weighed 1,560 lb and 

was 40 in wide by 22.5 in high by 90.5 in long. 

14
 
The recorded explosion pressure at the battery charger location was 6–7 psi, and the 

dynamic pressure was 0.8 psi. The length of the charger was 7.5 ft. The explosion pressure would 

equalize from the inby to the outby end of the charger at the speed of sound. Therefore, the pressure 

would equalize in about 7 ms. If the pressure pulse rose from about 0 psi to its maximum value in 

less than 7 ms, then the inby end of the charger would have been subjected to a differential pressure 

that was equal to the maximum explosion pressure at that location. For Test 1, the explosion 

pressure loading at this location rose to its maximum value in less than 7 ms. Therefore, the inby 

end of the charger was subjected to a pressure loading of 6–7 psi while the outby end was still at 

~0 psi. The dimensions of the end of the charger were 40 in wide by 22.5 in high, giving a crosssectional area of 900 in2

. The ~6.5-psi pressure loading on that area would result in a total force of 

~5,900 lb on the charger for a few milliseconds. The 0.8-psi dynamic pressure would continue to act 

on the charger for a longer time period. The battery charger moved 22 ft during Test 1. The final 

charger position and some of the wood debris from the cribs are shown in Figure 12. 

Figure 12.—Battery charger and debris from the wood cribs near X-7 after Test 1 (LLEM #501). 

Some of the roof plates were damaged during the explosion, as shown in Figure 13. On the 

left side of the figure, the plates are shown from inby of the plates, looking outby. On the right side 

of the figure, the plates are viewed looking across the entry from the DG-panel side. Four of the 

round plates were severely bent during the explosion. The only square plate that was bent during the 

explosion was the one at 304 ft. There was no obvious damage to the other round plates, square 

plates, or belt hangers. 

15
 
 

 

 

 

 

Viewed from inby Viewed across entry from DG panel 

134 ft from face 

184 ft from face 

234 ft from face 

304 ft from face 

Figure 13.—Roof plates at various distances from the face after Test 1 (LLEM #501). 

16
 
Test 2 (LLEM Test #502), June 15, 2006 

The solid-concrete-block seal in X-1, the 2001-design Omega block seal in X-2, and the 

hybrid Omega block seal in X-3 had survived the previous LLEM explosion test and were left in 

place for the second test. A new 2001-design Omega block seal was installed across C-drift at about 

320 ft from the face. The details of the test procedure and seal description can be found in 

Appendix A under “Test No. 2 Protocol.” Additional details of the C-drift seal construction can be 

found in Appendix B, section 3. A schematic of the test setup is shown in Figure 14. 

 

 

 

 

CB OB HB 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

OB

 BD 

X-1 X-4 X-2 X-3 X-5 X-6 X-7

C-drift 

B-drift 

A-drift 

CB – Concrete block seal OB – 40-in Omega block seal 

HB – 40-in hybrid Omega block seal - Cribs 

+++ Roof bolt plates with pie pans and belt hangers arranged alternatively 

BD - Bulkhead door 

Figure 14.—Setup for Test 2 (LLEM #502). 

-

For Test 2 (LLEM #502), a 47-ft-long, ~10% CH4-air zone was ignited at the face of C-drift. 

The explosion pressure pulse propagated out C-drift past the seals in X-1, X-2, and X-3. However, 

in this test the explosion was confined by the seal at 320 ft in C-drift, and the pressures built up 

higher than in the first test. The seals in the crosscuts experienced the sweeping total explosion 

pressure loading, whereas the seal in C-drift experienced the head-on explosion, i.e., when the 

explosion pressure wave impacted the seal constructed across C-drift head on, it resulted in a 

uniform pressure loading across the entire seal and generated a near instantaneous and much higher 

reflected pressure loading on that seal. 

In this test, the Omega block seal in X-2 survived, but the seals in X-3 and C-drift were 

destroyed by the higher pressures. Figure 15 shows the pressure loading at the seal in X-2 along 

with the quasi-static pressure at the wall of C-drift inby (134 ft) and outby (184 ft) the seal. The 

pressure transducer at the seal was located approximately in the middle front of the seal at 156 ft 

from the face of C-drift. All of the data were averaged over 10 ms. The pressure loading at the seal 

was 22 psi, similar to the value during the first test. The curve at the top of the figure shows the seal 

displacement as measured by the LVDT on the back of the seal. The maximum recorded movement 

during the explosion was 0.03 in. Since the seal did not fail, there was no change in the breakwire 

signal. 

17
 
35

40

-0.30

-0.20

-0.10

 

 

 

 

 

0 

5 

10 

15 

20 

25 

30 

Pressure, psi 

0.00 

0.10 

LVDT, in 

C-134 ft static 

X-2, 156 ft, front 

C-184 ft static 

X-2 LVDT 

X-2 breakwire 

15-pnt smoothed NI data 

0.50 0.55 0.60 0.65 0.70 0.75 0.80 

Time, sec 

Figure 15.—Pressures and LVDT displacement at the Omega block seal in X-2 during Test 2 (LLEM #502). 

The pressure loading at the seal in X-3 (with 10-ms smoothing) is shown in the top graph of 

Figure 16. The bottom graph of Figure 16 shows both the raw data at 1,500 samples per second and 

the smoothed data (10-ms average). The average pressure loading at the seal was 38.5 psi. (Note 

that the pressure values in the text are rounded to the nearest 0.5 psi.) The peak pressure loading 

from the raw data was 51 psi, but it lasted less than 1 ms. (See the section entitled “Test 6, LLEM 

Test #506, October 19, 2006” for further discussion of the relevance of the higher-frequency 

oscillations in the pressure readings.) The curve at the top of the figure shows the seal displacement 

as measured by the LVDT on the back of the seal. The maximum recorded movement during the 

explosion was >6 in as the seal was destroyed. This 6-in displacement was the maximum that the 

LVDT could measure. The breakwire data at the top of the figure are shown as the dot-dashed curve 

that drops below the baseline; the units are arbitrary. The breakwire signal showed that the wire 

broke, but it did not respond as quickly as it was supposed to. This was probably due to the lack of a 

resistor in the circuit. The LVDT and breakwire data show that the seal survived the initial outgoing 

pressure loading of ~25 psi at ~0.71 sec. The seal was destroyed by the subsequent higher pressure 

loading (~38.5 psi) that was reflected back from the C-drift seal at ~0.80 sec. 

The top graph of Figure 17 shows the pressure loading at the middle front of the seal at 

320 ft in C-drift and the quasi-static pressure loading as measured perpendicular to the entry near 

the rib at the edge of the seal. Also shown are the quasi-static pressure at the wall of C-drift at 304 ft 

and the total explosion pressure measured by the BDP at 306 ft. All of the data were averaged over 

10 ms. The bottom graph of Figure 17 only shows the data from the two pressure transducers at the 

seal. The smoothed pressure loading at the seal was 49.5 psi at the front center and 51 psi at the rib. 

The peak pressure loadings from the 1,500-Hz raw data (not shown in Figure 17) were 61 psi at the 

front center and 53 psi at the rib. The recorded seal movement during the explosion was >6 in as the 

seal was destroyed. The two breakwire signals showed that the wires broke as the seal was 

destroyed near the time of peak pressure loading at ~0.73–0.75 sec. 

18
 
60 6 

55 4 

Pressure, psi Pressure, psi 

LVDT, in LVDT, in

50 

seal destroyed 

2 

45 0 

30 

35 

40 X-3, 256 ft, front, 15-pnt snoothed

 X-3 LVDT, 15-pnt smoothed

 X-3 breakwire, 15-pnt smoothed 

-6 

-4 

-2 

25 -8 

20 -10 

15 -12 

10 -14 

5 -16 

0 

0.60 0.65 0.70 0.75 0.80 

Time, sec 

0.85 0.90 0.95 1.00 

-18 

65 6 

50 

55 

60 

 X-3, 256 ft, front, 15-pnt snoothed

seal destroyed 

0 

2 

4 

45 X-3, 256 ft, front, raw data -2 

30 

35 

40 X-3 LVDT, 15-pnt smoothed

 X-3 breakwire, 15-pnt smoothed 

breakwire does not appear to 

have resistor at input to DGpanel card 

-8 

-6 

-4 

25 -10 

20 -12 

15 -14 

10 -16 

5 -18 

0 

0.65 0.70 0.75 0.80 

Time, sec 

0.85 0.90 

-20 

Figure 16.—Pressures and LVDT displacement at Omega block seal in X-3 during Test 2 (LLEM #502). 

19
 
 

 

 

 

 

 

 

70 

80 

Pressure, psi Pressure, psi 

LVDT, in LVDT, in 

60 

50 

40 

30 

20 

10 

0 

0.60 

80 

70 

60 

50 

40 

30 

20 

10 

0 

0.60 

8 

6 

4 

seal destroyed 2 

0 

C-drift-seal, 320-ft, front 

-2 

C-drift seal, 320-ft, rib -4 

C-drift PRL-BDP total, 306-ft -6 

C-drift static, 304-ft -8 

C-drift LVDT -10 

C-drift regular breakwire -12 

C-drift thin-wire breakwire -14 

-16 

15-pnt smoothed NI data 

-18 

-20 

-22 

-24 

0.65 0.70 0.75 0.80 0.85 0.90 

Time, sec 

8 

6 

4 

seal destroyed 2 

0 

-2 

-4 

 C-drift-seal, 320-ft, front -6 

 C-drift seal, 320-ft, rib -8 

 C-drift LVDT -10 

 C-drift regular breakwire -12 

 C-drift thin-wire breakwire -14 

-16 

15-pnt smoothed NI data 

-18 

-20 

-22 

-24 

0.65 0.70 0.75 0.80 0.85 0.90 

Time, sec 

Figure 17.—Pressures and LVDT displacement at C-drift Omega block seal during Test 2 (LLEM #502). 

20
 
Pressures, LVDT displacement, and breakwire summary data for the seals in X-2, X-3, and 

C-drift during Test 2 (LLEM #502) are shown in Table 5, similar to the data for Test 1 in Table 2. 

The pressures at the seals are listed for the NI and KS data acquisition systems. The data were 

averaged over 10 ms for all of the listed values. The smoothed pressure loading at the middle of the 

X-2 seal was ~22 psi, and the seal survived the explosion. The smoothed pressure loading at the 

middle of the X-3 seal was 38.5 psi, and the seal was destroyed. The time that the breakwire on the 

seal broke was somewhat uncertain due to the slow response time of the breakwire circuit. This was 

probably caused by a missing resistor. The C-drift seal experienced a smoothed pressure loading of 

49.5 psi at the center and 51 psi at the rib. The breakwire data show that the C-drift seal was 

destroyed at ~0.74 sec. 

Table 6 lists quasi-static pressure and flame sensor data at the various DG panels on the 

walls of B- and C-drifts during LLEM #502. The positions of the Omega block seals in X-2, X-3, 

and C-drift are depicted by blue shading. On the left of the table are the B-drift wall quasi-static 

pressures; toward the right are the quasi-static wall pressures in C-drift. The C-drift quasi-static wall 

pressures remained relatively constant out to ~184 ft, similar to the values for Test 1. The listed 

pressures increased significantly out to ~320 ft as the pressure pulse was confined by the C-drift 

seal. The pressure pulse that reflected back toward the face from the seal caused the higher 

subsequent pressures at 304 ft, at the X-3 seal at 256 ft, and at 234 ft. After the C-drift seal broke, 

the quasi-static wall pressures beyond the seal were much lower—4.8 psi at 403 ft and 3.9 psi at 

501 ft. The pressures decreased even more as the pressure pulse then passed other open crosscuts. 

The last two columns of Table 6 list the flame signal and arrival time at each of the DG panels. For 

this test, the flame went past the 184-ft panel but did not reach the 234-ft panel. Therefore, the 

interpolated flame travel distance was about 210–220 ft. This was the same as for Test 1. Based on 

the initial gas zone length of 47 ft, the expansion ratio would be about 4.6. 

The air leakage data after Test 2 (LLEM #502) are in Table C-4 of Appendix C. The seal in 

X-2 passed the leakage test. The seals in X-3 and C-drift were destroyed during the test and 

therefore not measured for air leakage. 

21
 
Table 5.—Pressures and LVDT displacement at the seals during Test 2 (LLEM #502) 

Seal Seal pressures 

psi (NI) psi (KS) 

LVDT 

deflection,

in 

Break 

time, 

sec 

Seal Seal pressures 

 psi (NI) psi (KS) 

LVDT 

deflection, 

in 

Break 

time, 

sec 

 

X-2 BC 

156 ft 

 21.9 22.1 0.025 

 —  

 

 

 

 

Seal survived 

 

X-3 BC 

256 ft 

 38.5 38.4 >6 

 

 

~0.83 

 

 

 

 

 

 

 

Seal destroyed, debris traveled ~23 ft

 

C-drift 

321 ft 

Rib 50.9 50.9 

>6 

Center 49.6 49.4 

0.74 

 Seal destroyed, debris traveled ~824 ft 

 

Table 6.—Wall pressures and flame travel during Test 2 (LLEM #502) 

B-drift quasi-static pressures C-drift quasi-static pressures Flame signal
 

Distance, ft psi (NI) psi (KS) Distance, ft psi (NI) psi (KS) Volts sec (NI)
 

10 4.5 4.5 1 13 — — >5 0.340 

 X-1 

108 3.3 3.3 2 84 24.5 24.2 >5 0.560 

158 ~3 3 134 21.7 21.6 >5 0.603 

 X-2 

211 2.5 2.5 4 184 23.5 23.1 >5 0.700 

257 2.1 2.1 5 234 30.7 31.1 ~0.1 

 X-3 

329 2.8 2.9 6 304 47.1 46.5 ~0 

 

 X-4 

427 3.0 3.0 7 403 4.8 4.8 ~0 

 X-5 

526 2.9 2.8 8 501 3.9 3.9 ~0 

 X-6 

626 2.9 2.8 9 598 3.4 3.4 ~0 

 X-7 

782 3.0 2.9 10 757 2.8 2.8 ~0 

 11 1,506 1.9 1.9 

22
 
Figure 18 shows the remains of the X-3 seal that was destroyed during Test 2 (LLEM #502). 

Figure 18.—Remains of X-3 seal viewed from C-drift after Test 2 (LLEM #502). 

There were two very large blocks plus some smaller debris. The debris only traveled ~23 ft toward 

B-drift from the original seal position in X-3. The long boards in the figure were the header boards 

for the seal. 

The debris from the C-drift seal was thrown much farther than the debris from the X-3 seal. 

Figure 19 shows the view looking outby from the original seal position in C-drift. On the left is the 

pressure transducer at the rib. Near the center is the transducer mounted vertically from the roof at 

the middle of the seal. Just to the right of it is the BDP mounted horizontally on a platform 

suspended from the roof. At the far right, only a small amount of seal material remains attached to 

the right rib. Only a few small pieces of seal debris are seen on the floor outby the original seal 

position. 

Figure 20 shows the view looking outby from the DG panel at 403 ft. Even at this distance, 

the seal debris consists only of small pieces. Larger pieces of debris from the C-drift seal are seen in 

Figures 21–22, which show the views looking outby from X-6 at 547 ft and X-7 at 647 ft, 

respectively. 

23
 
Figure 19.—Postexplosion view looking outby from original seal position in C-drift. 

Figure 20.—Postexplosion view looking outby from 403 ft after Test 2 (LLEM #502). 

24
 
Figure 21.—Debris after Test 2 (LLEM #502) looking outby from X-6 location. 

Figure 22.—Debris after Test 2 (LLEM #502) looking outby from X-7 location. 

25
 
Figure 23 shows the seal debris at a position looking outby at a distance of ~850 ft from the 

face or ~530 ft from the original C-drift seal position.

Figure 23.—Debris after Test 2 (LLEM #502) looking outby from 850 ft. 

 The farthest the debris traveled during Test 2 

was ~824 ft from the original C-drift seal location, as noted in Table 5. There were no wood cribs 

for this test. 

For Test 2 (LLEM #502), the 1,560-lb battery charger was placed at 688 ft from the face of 

C-drift or 365 ft from the outby face of the C-drift seal. The charger moved ~79 ft during this 

explosion. Figure 24 shows the final location of the battery charger near 770 ft surrounded by debris 

from the seal. The total explosion pressure at the 604-ft BDP was 3.8 psi and the dynamic pressure 

was 0.3 psi. The quasi-static wall pressure at 757 ft was 2.8 psi. The pressure loading at the charger 

location would have been ~3.5 psi. As for Test 1, the pressure pulse rose to its peak recorded value 

in less than 7 ms. Therefore, the inby end of the charger would have been subjected to the 

maximum explosion pressure loading while the outby end was still at ~0 psi. Based on the crosssectional area of 900 in2

 for the end of the charger and the pressure loading of ~3.5 psi, the total 

force would have been ~3,100 lb for a few milliseconds. The ~0.3-psi dynamic pressure would have 

continued to act on the charger for a longer time period. In addition to the air pressure, the battery 

charger was also hit by debris from the seal, as evidenced in Figure 24. 

26
 
Figure 24.—Final location of battery charger at ~770 ft. 

Some of the roof plates were damaged during the Test 2 explosion, as shown in Figure 25. 

On the left side of the figure, the plates are shown from inby of the plates, looking outby. On the 

right side of the figure, the plates are viewed looking across the entry from the DG-panel side. The 

round plate at 184 ft was slightly bent during the explosion. The round plate at 234 ft from the face 

was the only one that was severely bent during the explosion. There was little or no obvious damage 

to the other round plates, square plates, and belt hangers. 

27
 
 

 

 

 

Viewed from inby Viewed across entry from DG panel 

184 ft from face 

234 ft from face 

304 ft from face 

Figure 25.—Roof plates at various distances from the face after Test 2 (LLEM #502). 

28
 
Test 3 (LLEM Test #503), August 4, 2006 

The solid-concrete-block seal in X-1 and the 2001-design Omega block seal in X-2 had 

survived the previous LLEM explosion tests and were left in place for the third test. New 

Sago nominal 40-in Omega block seals were installed in X-3 and in C-drift at about 320 ft from the 

face. The intent of Test 3 was to determine if an improperly constructed 40-in-thick Omega block 

seal (as constructed at the Sago Mine) could meet the regulatory requirement of 20 psi. The new 

Sago Omega block seals were installed in a manner similar to the previous hybrid Omega block seal 

in X-3 during Test 1, except the dry layer of BlocBond on the floor was 1.5 in thick (instead of 

0.25 in thick) and each course of blocks was positioned completely across the crosscut before 

applying the properly mixed BlocBond to the top of that course and forcing the BlocBond into the 

vertical joints using only gloved hands. Each block course was alternated to stagger the block joints. 

Additional details of the seal construction procedures can be found in Appendix A under “Test 

No. 3 Protocol” and in Appendix B, sections 4 and 5. Figure 26 shows a schematic of the test setup; 

the new seals are shown in blue. Wood cribs were also constructed both inby and outby the seal in 

C-drift, as shown in Figure 26.

HB 

 

 

 

 

C-drift 

B-drift 

# 

# 

# 

# 

CB OB SB 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

SB D

BD 

X-1 X-2 X-3 X-4 X-5 X-6 X-7 

E 

A-drift 

CB – Concrete block seal 

OB – 40-in Omega block seal 

SB – 40-in Sago Omega block seal 

+++ - Roof bolt plates with pie pans and belt hangers arranged alternatively 

D & E - Hollow concrete block stopping

 - Cribs 

BD - Bulkhead door 

Figure 26.—Setup for Test 3 (LLEM #503). 

 A hollow-block stopping was constructed outby the C-drift seal at 

~384 ft (point D in Figure 26). Another hollow-block stopping was constructed in X-3 between 

A- and B-drifts (point E in Figure 26). Roof plates that had been damaged in the previous explosion 

were replaced for this test. 

For Test 3 (LLEM #503), the same 47-ft-long zone of ~10% CH4 in air was used, but it was 

ignited at 35 ft from the face of C-drift. This change in the ignition location resulted in a lower 

pressure explosion propagating out C-drift, as previously observed in the Bruceton Experimental 

Mine by Nagy [1981, p. 52] and Nagy and Mitchell [1963, p. 20]. 

In this test, the Omega block seals in X-2, X-3, and C-drift all survived the explosion. 

Figure 27 shows the smoothed pressure loading at the seal in X-2; Figure 28 shows similar data for 

the X-3 seal. All of the data were averaged over 10 ms. For this test, because the seals survived, the 

29
 
pressure pulse reflected back and forth between the face and the C-drift seal at 320 ft.

25 0.10 

Pressure, psi 

20 0.00 

15 

15-pnt smoothed NI data X-2, 156 ft, front

 X-2 LVDT

 X-2 breakwire 

-0.10 

10 -0.20 

5 -0.30 

0 

0.0 0.5 1.0 1.5 2.0 2.5 

Time, sec 

3.0 3.5 4.0 

-0.40 

Figure 27.—Pressures and LVDT displacement at the X-2 seal during Test 3 (LLEM #503). 

LVDT, in

 This is more 

obvious in Figure 28 for X-3. Pressure, psi 

25 0.1 

20 0.0 

 X-3, 256 ft, front X-3, 256ft, front, vertical

 X-3 breakwire X-3 LVDT 

15 -0.1 

15-pnt smoothed NI data

LVDT, in

10 -0.2 

5 -0.3 

0 -0.4 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

Time, sec 

Figure 28.—Pressures and LVDT displacement at the X-3 seal during Test 3 (LLEM #503). 

The smoothed pressure loading at the X-2 seal was 13.5 psi. At the 

X-3 seal, there were two pressure transducers—one mounted horizontally and one vertically, as 

shown in Figure 3. The pressure loading at the X-3 seal was slightly less than 16 psi for both 

transducers. The maximum recorded LVDT movement during the explosion was 0.01 in for the X-2 

seal and 0.04 in for the X-3 seal. Since the seals did not fail, there were no changes in the breakwire 

signals. 

30 
Figure 29 shows data from three pressure transducers at the C-drift seal at 320 ft from the 

face. 

25 0.1 

20 0.0 

LVDT, in

15-pnt smoothed NI data

15 -0.1 

Pressure, psi 10 -0.2 

5 -0.3 

 C-drift, front, horizontal C-drift, rib

 C-drift, front, vertical C-drift LVDT

 breakwire 

0 -0.4 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

Time, sec 

Figure 29.—Pressures and LVDT displacement at the C-drift seal during Test 3 (LLEM #503). 

Two transducers were near the middle of the seal—one mounted horizontally and one 

vertically, as shown in Figure 3. The third transducer was at the rib, the same as for the previous 

test. The pressure at all three transducers was essentially the same as shown in the figure. The 

smoothed pressure loadings at the horizontal and vertical pressure transducers were 17.2 psi and 

17.0 psi, respectively. Since there was little difference in the two values, this shows that the wind or 

dynamic pressure was approximately zero at the seal. This would be expected since the wind 

velocity has to go to zero as the pressure wave reaches the seal. The smoothed pressure loading at 

the rib was 17.2 psi. The LVDT data in the upper part of the figure show that the seal moved about 

0.04 in during the explosion. 

The air leakage data after Test 3 (LLEM #503) are in Table C-6 of Appendix C. All three 

seals passed the leakage test. In addition to the three seals that survived the explosion, the wood 

cribs and stoppings also survived. There was no obvious damage to the roof plates and belt hangers. 

For this test, the flame went past the 134-ft DG panel, but did not reach the 184-ft DG panel. 

Therefore, the interpolated flame travel distance was about 160 ft. This was a shorter distance than 

for the first two tests even though the initial gas zone length was 47 ft for all three tests. The reason 

was the change in ignition location, which led to slower burning of the gas and more heat losses. 

31 
Test 4 (LLEM Test #504), August 16, 2006 

All three seals, the wood cribs, and the hollow-block stoppings had survived the previous 

LLEM explosion test and were left in place for the fourth test. Since the peak explosion pressures in 

Test 3 were under 20 psi, the intent of Test 4 was to increase the pressure slightly above Test 3 to 

determine if an improperly constructed 40-in-thick Omega block seal (as constructed at the Sago 

Mine) could meet the regulatory requirement of 20 psi. Figure 30 shows a schematic of the test 

setup, which was almost the same as for the previous test.

HB 

 

 

 

C-drift 

B-drift 

A-drift 

# 

# 

# 

# 

CB OB SB 

CB – Concrete block seal 

OB – 40-in Omega block seal 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

E 

SB D

BD 

X-1 X-2 X-3 X-4 X-5 X-6 X-7 

SB – 40-in Sago Omega block seal 

+++ - Roof bolt plates with pie pans and belt hangers arranged alternatively 

D & E - Hollow concrete block stopping 

- Cribs 

BD - Bulkhead door 

Figure 30.—Setup for Test 4 (LLEM #504). 

For Test 4, the same 47-ft-long zone of 

~10% CH4 in air was used, but the ignition point was moved from 35 to 28.5 ft from the face of 

C-drift to achieve slightly higher pressures than for Test 3. Additional details of the test procedure 

can be found in Appendix A under “Test No. 4 Protocol.” 

In Test 4 (LLEM #504), the Omega block seals in X-2, X-3, and C-drift all survived the 

explosion. Figure 31 shows the smoothed pressure loading at the seal in X-2; Figure 32 shows 

similar data for the X-3 seal. Because the seals survived, the pressure pulse reflected back and forth 

between the face and the C-drift seal at 320 ft. This is more obvious in Figure 32 for X-3. The 

smoothed pressure loading at the X-2 seal was 15 psi. At the X-3 seal, there were two pressure 

transducers—one mounted horizontally and one vertically, as shown in Figure 3. The pressure 

loading at the X-3 seal was slightly greater than 18 psi for both transducers. The maximum recorded 

LVDT movement during the explosion was 0.01 in for the X-2 seal and 0.09 in for the X-3 seal. 

Since the seals did not fail, there were no changes in the breakwire signals. 

Figure 33 shows data from three pressure transducers at the C-drift seal at 320 ft from the 

face. As for the previous test, two transducers were near the middle of the seal—one mounted 

horizontally and one vertically, as shown in Figure 3. The third transducer was at the rib. The 

pressure loading at all three transducers was essentially the same as shown in Figure 33. The 

smoothed pressure loadings at the horizontal and vertical pressure transducers were 20.6 psi and 

20.4 psi, respectively. This shows that the dynamic pressure loading was approximately zero at the 

seal. This would be expected since the wind velocity has to go to zero as the pressure wave reaches 

the seal. The smoothed pressure loading at the rib was 20.5 psi. Figure 33 also shows the pressure 

32
 
pulse reflecting back and forth between the face and the C-drift seal, similar to Figure 32. The 

LVDT data in the upper part of the figure show that the seal moved about 0.07 in during the 

explosion. 

33 

25 0.10 

15 

20 

15-pnt smoothed NI data X-2, 156 ft, front

 X-2 LVDT

 X-2 breakwire 

-0.10 

0.00 

10 -0.20 

5 -0.30 

0 

0.0 0.5 1.0 1.5 2.0 

Time, sec 

2.5 3.0 3.5 4.0 

-0.40 

LVDT, in

Pressure, psi 

Figure 31.—Pressures and LVDT displacement at the X-2 seal during Test 4 (LLEM #504). 

LVDT, in

Pressure, psi 

30 0.1 

20 

25 

 X-3, 256 ft, front

 X-3 breakwire

 X-3, 256ft, front, vertical

 X-3 LVDT 

15-pnt smoothed NI data

-0.1 

0.0 

15 -0.2 

10 -0.3 

5 -0.4 

0 -0.5 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

Time, sec 

Figure 32.—Pressures and LVDT displacement at the X-3 seal during Test 4 (LLEM #504). 
5 

30 0.1 

LVDT, in

25 0.0 

 C-drift, front, horizontal C-drift, rib

 C-drift, front, vertical C-drift LVDT

20 breakwire -0.1 

15-pnt smoothed NI data

15 -0.2 

Pressure, psi 10 -0.3 

-0.4 

0 -0.5 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 

Time, sec 

Figure 33.—Pressures and LVDT displacement at the C-drift seal during Test 4 (LLEM #504). 

Pressures, LVDT displacement, and breakwire summary data for the seals in X-2, X-3, and 

C-drift during Test 4 (LLEM #504) are shown in Table 7. The pressures at the seals are listed for 

the NI and KS data acquisition systems. The data were averaged over 10 ms for all of the listed 

pressures. The smoothed pressure loadings at the middle of the X-2 and X-3 seals were ~15 psi and 

~18 psi, respectively. The C-drift seal experienced a pressure loading of ~20.5 psi. All three seals 

survived the explosion. 

Table 8 lists quasi-static wall pressure and flame sensor data at the various DG panels on the 

walls of B- and C-drifts during LLEM #504. The positions of the Omega block seals in X-2, X-3, 

and C-drift are depicted by blue shading. On the left of the table are the B-drift quasi-static wall 

pressures; toward the right are the quasi-static wall pressures in C-drift. All of the B-drift pressures 

were ~0 because the explosion was confined to C-drift by the seals. The C-drift quasi-static wall 

pressures remained relatively constant out to ~184 ft and increased slightly out to ~320 ft as the 

pressure pulse was confined by the C-drift seal. The pressures beyond the seal in C-drift were ~0 

since the seals survived the explosion. The last two columns of Table 8 list the flame signal and 

arrival time at each of the DG panels. For this test, the flame went past the 134-ft DG panel but did 

not reach the 184-ft DG panel. Therefore, the interpolated flame travel distance was about 160 ft. 

This was a distance similar to that in Test 3, which also had the ignition point outby the face. 

The air leakage data after Test 4 (LLEM #504) are in Table C-7 of Appendix C. All three 

seals passed the leakage test. In addition to the three seals that survived the explosion, the wood 

cribs and stoppings also survived. There was no obvious damage to the roof plates and belt hangers. 

34 
Table 7.—Pressures and LVDT displacement at the seals during Test 4 (LLEM #504) 

Seal Seal pressures 

psi (NI) psi (KS) 

LVDT 

deflection, 

in 

Break 

time, 

sec 

Seal Seal pressures 

psi (NI) psi (KS) 

LVDT 

deflection, 

in 

Break 

time, 

sec 

 

X-2 BC 

156 ft 

 

X-3 BC 

256 ft 

 

 

 

H 

 

H 

V 

 

 

 

14.9 14.9 

 

Seal survived 

 

18.2 18.2 

18.2 18.2 

Seal survived 

 

 

 

 

 

0.01 

 

0.09 

 

 

 

 

— 

 

— 

 

 

 

 

 

 

 

 

 

 

C-drift 

321 ft 

 

 

 

 

 

Rib 

H 

V 

 

 

 

 

 

 

 

 

 

20.5 20.5 

20.6 20.6 

20.4 20.4 

Seal survived 

 

 

 

 

 

 

0.07 

 

 

 

 

 

 

 

 

 

— 

H Horizontal. V Vertical. 

Table 8.—Wall pressures and flame travel during Test 4 (LLEM #504) 

B-drift quasi-static pressures C-drift quasi-static pressures Flame signal 

Distance, ft psi (NI) psi (KS) Distance, ft psi (NI) psi (KS) Volts sec (NI) 

10 0.0 0.0 1 13 — — >5 0.807 

 X-1 

108 0.0 0.0 2 84 16.6 16.6 >5 0.448 

158 ~0 ~0 3 134 15.3 15.3 >5 0.621 

 X-2 

211 ~0 ~0 4 184 15.3 15.3 ~0 

257 0.0 0.0 5 234 17.2 17.1 ~0 

 X-3 

329 0.0 0.0 6 304 19.9 19.8 ~0 

 

 X-4 

427 0.0 0.0 7 403 0.0 0.0 ~0 

 X-5 

526 0.0 0.0 8 501 0.0 0.0 ~0 

 X-6 

626 0.0 0.0 9 598 0.0 0.0 ~0 

 X-7 

782 0.0 0.0 10 757 0.0 0.0 ~0 

 11 1,506 0.0 0.0 

35
 
Test 5 (LLEM Test #505), August 23, 2006 

All three seals, the wood cribs, and the hollow-block stoppings had survived the previous 

two LLEM explosion tests and were left in place for the fifth test. Figure 34 shows a schematic of 

the test setup, which was almost the same as for the previous test.

HB 

 

 

 

 

C-drift 

B-drift 

# 

# 

# 

# 

CB OB SB 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

SB D

BD 

X-1 X-2 X-3 X-4 X-5 X-6 X-7 

E 

A-drift 

CB – Concrete block seal 

OB – 40-in Omega block seal 

SB – 40-in Sago Omega block seal 

+++ - Roof bolt plates with pie pans and belt hangers arranged alternatively 

D & E - Hollow concrete block stopping

 - Cribs 

BD - Bulkhead door 

Figure 34.—Setup for Test 5 (LLEM #505). 

 In addition to the seals, there 

were hollow-block stoppings at 384 ft in C-drift and in X-3 between A- and B-drifts. There were 

also wood cribs both inby and outby the C-drift seal, as shown in Figure 34. For Test 5, the same 

47-ft-long zone of ~10% CH4 in air was used, but the ignition point was moved back to the face of 

C-drift to achieve pressures similar to those in Test 2. Additional details of the test procedure can be 

found in Appendix A under “Test No. 5 Protocol.” 

For Test 5 (LLEM #505), the 47-ft-long ignition zone at the face was filled with 661 ft3

 of 

natural gas to give a mixture of ~10% CH4 in air, the same as for Tests 1 through 4. This CH4-air 

zone was ignited at the face of C-drift, and the pressure pulse propagated out C-drift past the seals 

in X-2 and X-3 to the seal in C-drift. Because the gas was ignited at the face, the resulting explosion 

pressures were much higher than those in Tests 3 and 4. 

In this test, the Omega block seal in X-2 survived, but the Omega block seals in X-3 and 

C-drift were destroyed by the higher pressures during Test 5. Figure 35 shows the pressure loading 

at the seal in X-2 along with the quasi-static pressure at the wall of C-drift inby the seal at 134 ft 

and outby the seal at 184 ft. The pressure transducer at the seal was located approximately in the 

middle front of the seal at 156 ft from the face of C-drift. Most of the data are from the NI data 

acquisition system. The pressure data at the X-2 seal are from the KS data acquisition system 

because there was a problem with that channel on the NI system during this test. All of the data 

were averaged over 10 ms. The pressure loading at the X-2 seal was 26 psi. The maximum recorded 

LVDT movement during the explosion was 0.03 in. Since the seal did not fail, there was no change 

in the breakwire signal. 

36
 
45 0.10 

LVDT, in

Pressure, psi 

15-pnt smoothed NI data &
 

51-pnt smoothed KS data
 40 0.05 

35 0.00 

 C-134 ft static, NI X-2, 156 ft, front, KS

30 -0.05 C-184 ft static, NI Series1

 X-2 LVDT X-2 breakwire 

25 -0.10 

20 -0.15 

15 -0.20 

10 -0.25 

5 -0.30 

0 -0.35 

0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 

Time, sec 

Figure 35.—Pressures and LVDT displacement at the X-2 seal during Test 5 (LLEM #505). 

Figure 36 shows the pressure loading and LVDT displacement data at the X-3 seal, along 

with the quasi-static pressure at the wall of C-drift inby the seal at 234 ft. The pressure transducers 

at the seal were located near the middle front of the seal at 256 ft from the face of C-drift. There 

were two pressure transducers at the seal—one mounted horizontally and one vertically, as shown 

in Figure 3. The LVDT and breakwire data at the top of the figure show that the X-3 seal survived 

the initial outgoing pressure loading of ~29 psi at ~0.65 sec. The seal was destroyed by the 

subsequent higher pressure loading (~33–35 psi) that was reflected back from the C-drift seal at 

~0.74 sec. 

Figure 37 shows the pressures from the NI data acquisition system at the X-3 seal on 

an expanded time scale. Both the raw data at 1,500 samples per second and the smoothed data 

(15-point smoothing or 10-ms average) are shown. The averaged pressure loading for the horizontal 

transducer was 34.7 psi. The peak pressure loading from the raw data for the horizontal transducer 

at the X-3 seal was ~42 psi, but it lasted only about 1 ms. The averaged pressure loading for the 

vertical transducer at the X-3 seal was 32.8 psi. The peak pressure loading from the raw data for this 

vertical transducer at the X-3 seal was ~38 psi, but it lasted only about 1 ms. The curve at the top of 

the figure shows the seal displacement as measured by the LVDT on the back of the seal. The maximum recorded movement during the explosion was >6 in as the seal was destroyed. The breakwire 

raw data at the top of Figure 37 are shown as the dotted curves that almost instantaneously drop 

below the baseline; the units are arbitrary. The breakwire signals showed that the wires broke at 

0.743–0.753 sec after ignition. 

37
 
Pressure, psi 

LVDT, in

55 

50 

45 

35 

40 

15-pnt smoothed NI data 

30 

25 

20 

15 

10 

5 

0 

0.4 0.5 0.6 0.7 

6 

3 

 C-234 ft static

 X-3, 256 ft, front, horizontal

 X-3, 256ft, front, vertical

 X-3 breakwire, horizontal -9 

-6 

-3 

0 

 X-3 breakwire, vertical -12 

 X-3 LVDT -15 

-18 

-21 

-24 

0.8 0.9 1.0 1.1 1.2 

-27 

Time, sec 

Figure 36.—Pressures and LVDT displacement at the X-3 seal during Test 5 (LLEM #505). 

 

 

 

 

Pressure, psi 

LVDT, in

60 6 

55 

raw & 15-pnt smoothed NI data 

3 

50 0 

 X-3, 256 ft, horizontal, smoothed X-3, horizontal, raw data

45 X-3, 256ft, front, vertical, smoothed X-3 vertical, raw data -3 

40 X-3 breakwire, horizontal, raw X-3 breakwire, vertical, raw -6 

 X-3 LVDT, smoothed 

35 -9 

30 -12 

25 -15 

20 -18 

15 -21 

10 -24 

5 -27 

0 -30 

0.60 0.65 0.70 0.75 0.80 

Time, sec 

Figure 37.—Pressures and LVDT displacement on an expanded time scale for the X-3 seal 

during Test 5 (LLEM #505). 

38
 
Figure 38 shows NI data from three pressure transducers at the C-drift seal at 320 ft from 

the face.

80

90

-30

-27

-24

-21

-18

-15

-12

-9

-6

-3

0 

10 

20 

30 

40 

50 

60 

70 

Pressure, psi 

0 

3 

6 

LVDT, in

 C-drift, front, horizontal

 C-drift, front, vertical

 C-drift, rib

 C-drift LVDT

 horizontal breakwire

 vertical breakwire 

15-pnt smoothed NI data 

0.4 0.5 0.6 0.7 0.8 0.9 1.0 

Time, sec 

Figure 38.—Pressures and LVDT displacement at the C-drift seal during Test 5 (LLEM #505). 

 Two transducers were near the middle of the seal—one mounted horizontally and one 

vertically, as shown in Figure 3. A third transducer was mounted on the rib perpendicular to the 

entry. The total measured explosion pressure loadings at all three transducers were similar, 

as shown in the figure. The LVDT and breakwire data show that the seal broke near the time of 

peak pressure loading. 

Figure 39 shows the pressures from the NI data acquisition system at the seal on an 

expanded time scale. Both the raw data at 1,500 samples per second and the smoothed data 

(15-point smoothing or 10-ms average) are shown. The smoothed pressure loading for the 

horizontal transducer was 56.6 psi. The peak pressure loading from the raw data for the horizontal 

transducer was ~63 psi, but it lasted only about 1 ms. The smoothed pressure for the vertical 

transducer was 54.1 psi. The peak pressure loading from the raw data for the vertical transducer was 

~57 psi, but it lasted only about 1 ms. The smoothed pressure loading at the rib was 59.1 psi, and 

the peak value from the raw data was ~63 psi. The LVDT data in the upper part of the figure show 

that the seal moved >6 in as the seal was destroyed. The two breakwire signals (from the NI raw 

data) both show a sharp discontinuity as the wires broke at 0.677–0.685 sec. 

39
 
80

90

-32

-30

-28

-26

-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

 

LVDT, in

 C-drift, horizontal, smoothed

 C-drift, horizontal, raw

 C-drift, vertical, smoothed

 C-drift, vertical, raw data

 C-drift, rib, horizontal, smoothed

 C-drift LVDT, smoothed

 horizontal breakwire, raw

 vertical breakwire, raw 

6 

4 

2 

0 

70 

Pressure, psi 

60 

50 

40 

30 

20 

10 

0 

0.60 0.62 0.64 0.66 0.68 0.70 0.72 0.74 

Time, sec 

Figure 39.—Pressures and LVDT displacement on an expanded time scale at the C-drift seal 

during Test 5 (LLEM #505). 

Pressure, LVDT displacement, and breakwire summary data for the seals in X-2, X-3, and 

C-drift during Test 5 (LLEM #505) are shown in Table 9. The explosion pressure loadings at the 

seals are listed for the NI and KS data acquisition systems. The data were averaged over 10 ms for 

the listed pressure values. The breakwire time is from the NI raw data and is the time after ignition. 

The smoothed pressure loading at the middle of the X-2 seal was 25.8 psi (from the KS data 

acquisition system), and the seal survived the explosion. The smoothed pressure loading from the 

horizontal transducer at the middle of the X-3 seal was 34.7 psi and 33.1 psi from the NI and KS 

data acquisition systems, respectively. The smoothed pressure loading from the vertical transducer 

at the middle of the X-3 seal was 32.8 psi from both systems. The X-3 seal breakwire raw data show 

that the vertical wire broke at 0.743 sec and the horizontal wire broke at 0.753 sec as the seal was 

destroyed. The pressure loading in front of the stopping at point E (Figure 34) was 4.0 psi, and the 

stopping was partially destroyed. The stopping breakwire did not break until 2.17 sec. 

The C-drift seal experienced a smoothed pressure loading from the horizontal transducer 

(middle front of seal) of 56.6 psi and 55.7 psi from the NI and KS data acquisition systems, 

respectively. The smoothed pressure loading from the vertical transducer (middle front of seal) was 

54.1 psi from both systems. The smoothed pressure loading at the rib was 59.1 psi and 58.9 psi from 

the NI and KS systems, respectively. The breakwire raw data show that the vertical wire broke at 

0.677 sec and the horizontal wire broke at 0.685 sec as the seal was destroyed. The breakwire data 

show that the C-drift seal was destroyed before the X-3 seal. The smoothed pressure loading in front 

of the stopping in C-drift at 384 ft was 12.4 psi, and the stopping was totally destroyed. The 

breakwire raw data show that the stopping at point D (Figure 34) was destroyed at 1.092 sec. 

40
 
Table 9.—Pressures and LVDT displacement at the seals during Test 5 (LLEM #505) 

Seal or 

stopping 

Seal pressures 

psi (NI) psi (KS) 

LVDT 

deflection, 

in 

Break 

time, 

sec 

Seal or 

stopping 

Seal pressures 

psi (NI) psi (KS) 

LVDT 

deflection, 

in 

Break 

time,

sec 

 

H X-2 BC 

156 ft 

Seal 

 

H X-3 BC 

256 ft V 

Seal 

 

 

X-3 AB H 

Stopping 

 

 

H Horizontal. 

 

— 25.8 0.03 — 

Seal survived 

 

34.7 33.1 0.753 

>6 

32.8 32.8 0.743 

 

Seal destroyed, 

debris traveled >108 ft to far wall of A-drift 

4.0 4.0 2.17 

Stopping partially destroyed, 

debris traveled to far wall of A-drift 

 

 

 

 

 

 

 

 

Wood 

cribs 

 

C-drift 

320 ft 

Seal 

 

 

C-drift 

384 ft 

Stopping 

 

 

A 

B 

 

Rib 

H 

V 

 

 

H 

 

 

 

 

 

 

 

 

 0.671 

 ~0.665 

 

59.1 58.9 

56.6 55.7 >6 0.685 

54.1 54.1 0.677 

Seal destroyed, debris traveled ~556 ft 

 

 12.4 12.4 1.092 

 

Stopping destroyed, 

debris traveled ~460 ft 

V Vertical. 

Table 10 lists quasi-static pressure and flame sensor data at the various DG panels on the 

walls of B- and C-drifts during LLEM #505. The positions of the Omega block seals in X-2, X-3, 

and C-drift are depicted by blue shading. On the left of the table are the B-drift quasi-static wall 

pressures; toward the right are the quasi-static wall pressures in C-drift. The C-drift pressures 

remained relatively constant out to ~184 ft, similar to the values in Test 2. The quasi-static wall 

pressure increased significantly out to ~320 ft as the pressure pulse was confined by the C-drift seal. 

The pressure pulse that reflected back toward the face from the seal caused higher pressures at 

304 ft, the X-3 seal at 256 ft, and at 234 ft. After the seal broke, the explosion pressures beyond the 

seal were much lower: 12.4 psi at the stopping at 384 ft, ~3.6 psi at 403 ft, and ~3 psi at 501 ft, etc. 

The last two columns of Table 10 list the flame signal and arrival time at each of the DG panels. For 

this test, the flame went past the 184-ft panel, but did not reach the 234-ft panel. Therefore, the 

interpolated flame travel distance was about 210 ft, similar to the travel distances for Tests 1 and 2. 

Based on the initial gas zone length of 47 ft, the expansion ratio would be about 4.5. 

41
 
Table 10.—Wall pressures and flame travel during Test 5 (LLEM #505) 

B-drift quasi-static pressures 

Distance, ft psi (NI) psi (KS) 

C-drift quasi-static pressures 

 Distance, ft psi (NI) psi (KS) 

Flame signal 

Volts sec (NI) 

 

1 

X-1 

2 

3 

X-2 

4 

5 

X-3 

6 

 

X-4 

7 

X-5 

8 

X-6 

9 

X-7 

10 

11 

3 

13 

 

84 

134 

 

184 

234 

 

304 

 

 

403 

 

501 

 

598 

 

757 

1,506 

27.0 

— 

 

25.4 

22.3 

 

23.8 

33.9 

 

55.1 

 

 

3.7 

 

3.1 

 

2.6 

 

2.6 

1.6 

27.1 

— 

 

24.7 

22.3 

 

23.1 

33.2 

 

54.0 

 

 

3.5 

 

2.8 

 

2.5 

 

2.7 

1.6

 

>5 

 

>5 

>5 

 

>5 

~0 

 

~0 

 

 

~0 

 

~0 

 

~0 

 

~0 

 

 

0.298 

 

0.513 

0.543 

 

0.643 

 

 

 

 

 

 

 

 

 

 

 

 

 

10 4.6 — 

 

108 3.4 — 

158 4.2 — 

 

211 3.7 — 

257 2.4 — 

 

329 4.0 — 

 

 

 

 

 

 

427 3.1 — 

 

526 2.6 — 

 

626 2.9 — 

 

782 

 

2.8 

 

— 

 

Figure 40 shows the seal in X-2 that survived Test 5 (LLEM #505). The air leakage data are 

in Table C-8 in Appendix C. The X-2 seal passed the leakage test. The seals in X-3 and C-drift were 

destroyed during the test and therefore not measured for air leakage. 

Figures 41–42 show the remains of the X-3 seal that was destroyed during Test 5 

(LLEM #505). Figure 41 shows the view looking toward the original X-3 seal position from slightly 

outby in C-drift. Very little debris can be seen in C-drift. The vertical post holding the pressure 

transducers is still intact. The original seal position was just behind the pressure transducer post. 

The long board hanging from the roof in the figure was one of the header boards for the seal. Figure 

42 shows the view looking directly into X-3 from C-drift. A large amount of debris can be seen 

beyond the original seal location and extending into the B-drift intersection. Figure 43 shows 

additional debris from the X-3 seal piled against the stopping between A- and B-drifts. There is also 

debris beyond the stopping into A-drift. The left side of the stopping was mostly destroyed, but the 

right side remained intact. The pressure transducer post in front of the stopping also survived. 

Figure 44 shows the debris from the X-3 seal and stopping piled against the far wall of A-drift. 

42
 
43
 

Figure 40.—Seal in X-2 that survived Test 5 (LLEM #505). 

Figure 41.—Debris from X-3 seal after Test 5 (LLEM #505) viewed from C-drift. 
44
 

Figure 42.—Debris from X-3 seal after Test 5 (LLEM #505) looking into X-3 toward B-drift. 

Figure 43.—Debris from the X-3 seal at the X-3 stopping location after Test 5 (LLEM #505). 
Figure 44.—Debris from the X-3 seal and stopping piled against the far wall of A-drift after Test 5 (LLEM #505). 

The debris from the C-drift seal was thrown much farther than the debris from the X-3 seal, 

which was stopped by the A-drift wall. Figure 45 shows the postexplosion view looking outby near 

the original seal position in C-drift. Near the center is the pressure transducer post. The original seal 

location was just behind this post. Only a few wood blocks and small pieces of seal debris are seen 

on the floor outby the original seal position. 

Figure 46 shows the view looking outby toward X-4 at 355 ft. Wood blocks and small pieces 

of seal debris are seen in the photo. Some debris was carried into X-4 by the explosion. Figure 47 

shows the view looking outby from the DG panel at 403 ft. At this distance, large amounts of wood 

and seal debris were found. Figure 48, looking outby from X-6 at 547 ft, also shows large amounts 

of debris from the wood cribs, C-drift seal, and C-drift stopping. 

45
 
Figure 45.—Postexplosion view in C-drift looking outby toward original seal location at 320 ft. 

Figure 46.—Debris in C-drift after Test 5 (LLEM #505) looking outby toward X-4 (right side of photo) at 355 ft. 

46
 
Figure 47.—Debris from C-drift seal, stopping, and wood cribs looking outby from 403 ft. 

Figure 48.—Debris in C-drift after Test 5 (LLEM #505) looking outby from X-6 at 547 ft. 

47
 
Figure 49 shows the seal debris at a position looking outby from a distance of ~600 ft from 

the face or ~280 ft from the original seal location. In the distance is X-7 at 647 ft. Pieces of Omega 

blocks from the seal and pieces of hollow concrete blocks from the stopping can be seen in the 

photo. 

48
 

Figure 49.—Debris in C-drift after Test 5 (LLEM #505) looking outby from ~600 ft. 

Figure 50 shows the seal debris looking outby in C-drift from the DG panel at 757 ft from 

the face or ~435 ft from the original seal location. There are numerous large pieces of seal debris in 

the photo. Figure 51 shows the debris at ~850 ft after Test 5. There are still some large pieces of 

seal debris at this location. In the upper right of the photo is a carbon monoxide sensor box hanging 

from the roof. There was no apparent damage to the sensor box during the explosion. 
Figure 50.—Debris in C-drift after Test 5 (LLEM #505) looking outby from 757 ft. 

Figure 51.—Debris in C-drift after Test 5 (LLEM #505) at ~850 ft. 

49
 
Figure 52 shows the last piece of seal debris at ~880 ft. During Test 5 (LLEM #505), pieces 

of Omega blocks traveled as far as 556 ft from the original C-drift seal location, as noted in Table 9 

and shown in Figure 52.

Figure 52.—Debris in C-drift after Test 5 (LLEM #505) at ~880 ft. 

 Debris from the C-drift stopping traveled ~460 ft from the original 

stopping location. Debris from the wood cribs traveled ~437 ft. These values were measured from 

the postexplosion surveys. 

For Test 5 (LLEM #505), the 1,560-lb battery charger was placed at 688 ft from the face of 

C-drift or 365 ft from the outby face of the C-drift seal. Figure 53 shows the final location of the 

battery charger after the test, with large amounts of seal debris. The charger moved 30 ft during this 

explosion. The total explosion pressure at the 604-ft BDP was 2.7 psi, and the dynamic pressure 

was 0.2 psi. The quasi-static wall pressure at 757 ft was 2.6 psi. The pressure loading at the charger 

would have been ~2.5 psi. However, for Test 5 the pressure pulse took much longer than 7 ms to 

reach its maximum value. Therefore, for this test, the maximum differential pressure loading from 

the inby to outby end of the charger was only ~0.33 psi. The cross-sectional area of 900 in2

 and 

differential explosion pressure loading of ~0.33 psi would result in a total force of ~300 lb for a few 

milliseconds. The 0.2-psi dynamic pressure (~180-lb force) would have continued to act on the 

charger for a longer period of time. In addition to the air pressure, the battery charger was also hit 

by debris from the seal, stopping, and wood cribs, as evidenced in Figure 53. 

50
 
Figure 53.—Final location of battery charger near 720 ft after Test 5 (LLEM #505). 

Some of the roof plates were damaged during the Test 5 explosion, as shown in Figures 54– 

55. On the left side of the figures, the plates are shown from inby of the plates, looking outby. On 

the right side of the figure, the plates are viewed looking across the entry from the DG-panel side. 

There was only a slight bending of the round plate at 84 ft. The round plates at 134, 184, and 234 ft 

from the face were severely bent during the explosion. At 304 ft, the round plate was slightly bent, 

but there was no obvious damage to the square plate. There was only some minor impact damage to 

the round plate at 403 ft, but no obvious damage to the square plate. However, the belt hanger at 

403 ft was significantly bent, as shown in Figures 56–57. These views are looking across the entry 

toward the DG panel; therefore, outby is to the right in these photos. This belt hanger was probably 

damaged by flying debris because the inby belt hangers were not damaged even though they were 

exposed to greater explosion pressures. There was little or no obvious damage to the other round 

plates, square plates, and belt hangers throughout C-drift. 

51
 
 

 

 

 

Viewed from inby Viewed across entry from DG panel 

84 ft from face 

134 ft from face 

184 ft from face 

Figure 54.—Roof plates at 84, 134, and 184 ft from the face after Test 5 (LLEM #505). 

52
 
 

 

 

 

 

 

Viewed from inby Viewed across entry from DG panel 

234 ft from face 

304 ft from face 

403 ft from face 

Figure 55.—Roof plates at 234, 304, and 403 ft from the face after Test 5 (LLEM #505). 

53
 
Figure 56.—Belt hanger (circled in red) 

Figure 57.—Belt hanger at 403 ft after

54
 

near DG panel at 403 ft. 

 Test 5 (LLEM #505). 
Test 6 (LLEM Test #506), October 19, 2006 

The 2001-design Omega block seal in X-2 had survived the previous LLEM explosion tests 

and was left in place for the sixth and final test. A new solid-concrete-block seal was installed in 

X-3. This new 16-in-thick solid-concrete-block seal with a 32-in-thick center pilaster was 

constructed in a manner similar to the solid-concrete-block seal in X-1 for Test 1, except the X-3 

seal used Type S mortar (not BlocBond) and was coated on both sides with Quikrete B-Bond 

sealant. Additional details on the construction of this seal can be found in Appendix B, section 6. 

A new Sago nominal 40-in Omega block seal was installed in C-drift about 320 ft from the face. 

This seal was built in a manner similar to the seals built for Test 3, except that it was built with 

Omega blocks from the Sago Mine. Additional details can be found in Appendix A under “Test 

No. 6 Protocol” and in Appendix B, section 7. Figure 58 shows a schematic of the test setup with 

the new Omega seal shown in blue. 

HB 

 

 

 

 

C-drift 

B-drift 

A-drift 

# 

# 

# 

# 

CB OB CB 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

SB D

BD 

X-1 X-2 X-3 X-4 X-5 X-6 X-7 

CB – Concrete block seal 

OB – 40-in Omega block seal 

SB – 40-in Sago Omega block seal 

+++ - Roof bolt plates with pie pans and belt hangers arranged alternatively 

- Hollow concrete block stopping

 - Cribs 

D 

BD - Bulkhead door 

Figure 58.—Setup for Test 6 (LLEM #506). 

Wood cribs were also constructed both inby and outby the seal 

in C-drift, as shown in Figure 58. A hollow-block stopping was constructed outby the C-drift seal at 

~384 ft. Any of the roof plates or belt hangers that had been damaged in the previous explosion 

were replaced for this test. Additional details of the test procedure can be found in Appendix A 

under “Test No. 6 Protocol.” 

For Test 6 (LLEM #506), a longer 71-ft gas ignition zone was used at the face of C-drift in 

order to generate higher pressures than those for Test 5. Test 6 was designed to exert an explosion 

pressure of approximately 90 psi on the Sago seal in C-drift to enable the investigators to better 

evaluate the explosion and seal failure that occurred at the Sago Mine. In this test, the plastic 

diaphragm used to confine the gas mixture was located just outby X-1. The 71-ft-long ignition zone 

was filled with 1,265 ft3

 of natural gas to give a mixture of ~10% CH4 in air. Although this zone 

was only ~50% longer than the ignition zone for Test 5, the flammable gas volume was ~90% 

greater. This was due to the additional volume in X-1 between the seal and bulkhead door leading to 

E-drift, as shown in Figures 2 and 58. The CH4-air zone was ignited at the face of C-drift, and the 

pressure pulse propagated out C-drift past the seals in X-2 and X-3 to the seal in C-drift. Because 

55
 
the flammable gas zone was much larger, the resulting pressures were much higher than those in 

Test 5. 

In Test 6, the Omega block seal in X-2 and the solid-concrete-block seal in X-3 survived, 

but the Omega block seal in C-drift was destroyed. Figure 59 shows the pressure loading at the seal 

in X-2 along with the quasi-static pressure at the wall of C-drift inby the seal at 134 ft and outby the 

seal at 184 ft.

70

80

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

 

 

0 

10 

20 

30 

40 

50 

60 

Pressure, psi 

0.00 

0.05 

0.10 

LVDT, in 

C-184 ft static, NI

 C-156ft X-2, center 

C-134 ft static, NI

 X-2 LVDT

 X-2 breakwire 

15-pnt smoothed NI data 

0.4 0.5 0.6 0.7 0.8 0.9 

Time, sec 

Figure 59.—Pressures and LVDT displacement at the X-2 seal during Test 6 (LLEM #506). 

 The pressure transducer at the seal was located approximately in the middle front of 

the seal at 156 ft from the face of C-drift. All of the graph data were averaged over 10 ms. The 

smoothed pressure loading at the X-2 seal was ~51 psi. The peak pressure loading from the NI raw 

data at 1,500 Hz was ~68 psi at the X-2 seal, but it lasted only about 1 ms. The maximum recorded 

LVDT movement during the explosion was 0.06 in. Since the seal did not fail, there was essentially 

no change in the breakwire signal. 

Figure 60 shows the pressure loadings and LVDT displacement data at the X-3 solidconcrete-block seal, along with the quasi-static pressure at the wall of C-drift inby the seal at 234 ft. 

The pressure transducers at the seal were located near the middle front of the seal at 256 ft from the 

face of C-drift. There were two pressure transducers at the seal—one mounted horizontally and one 

vertically, as shown in Figure 3. However, the vertical transducer did not operate properly during 

this test, and its data are not shown. All of the graph data were averaged over 10 ms. The seal 

survived both the outgoing explosion pressure loading of ~44 psi and the subsequent reflected 

pressure loading of ~49 psi shown in Figure 60. The peak pressure loading from the NI raw data at 

1,500 Hz was ~82 psi at the X-3 seal, but it lasted less than 1 ms. The maximum recorded LVDT 

movement during the explosion was 0.14 in. Since the solid-concrete-block seal in X-3 did not fail, 

there was no change in the breakwire signals. 

56
 
60

70

-1.2

-1.1

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

, 

0 

10 

20 

30 

40 

50 

Pressure, psi 

0.0 

0.1 

0.2 

LVDT, in

 X-3, 256 ft, front, horizontal

 C-234 ft static

 X-3 LVDT

 X-3 breakwire, horizontal

 X-3 breakwire, vertical 

15-pnt smoothed NI data 

0.4 0.5 0.6 0.7 0.8 0.9 

Time, sec 

Figure 60.—Pressures and LVDT displacement at the X-3 seal during Test 6 (LLEM #506). 

Figure 61 shows NI data from the pressure transducers at the C-drift seal at 320 ft from the 

face. Two transducers were near the middle of the seal—one mounted horizontally and one 

vertically, as shown in Figure 3. The third transducer was at the rib, the same as for the previous 

tests. For Test 6, a fourth pressure transducer was embedded into the seal near the center. This 

transducer was horizontal and faced the incoming pressure pulse; it therefore would read the total 

explosion pressure loading. The pressure traces of the three transducers near the middle of the seal 

were all similar, as shown in Figures 61–62. The pressure at the rib was somewhat higher. The 

LVDT and breakwire data in Figure 61 show that the seal broke near the time of peak pressure. 

Figure 62 shows the explosion pressure loadings from the NI data acquisition system at the 

seal on an expanded time scale. Data for all four pressure transducers are shown. The peak 

smoothed (10-ms average) pressure loading for the vertical transducer was 90.1 psi. The peak 

smoothed pressure loading for the horizontal transducer was 91.1 psi. The peak smoothed pressure 

loading for the horizontal transducer that was embedded in the seal was 92.3 psi. The peak 

smoothed pressure loading at the rib was 99.2 psi. The LVDT data in the upper part of the figure 

show that the seal moved >6 in as the seal was destroyed. The two breakwire signals (from the 

NI raw data) both show a sharp discontinuity as the wires broke at 0.575–0.578 sec. 

57
 
120

140

-36

-33

-30

-27

-24

-21

-18

-15

-12

-9

-6

0 

20 

40 

60 

80 

100 

Pressure, psi 

-3 

0 

3 

6 

LVDT, in

 C-drift, rib

 C-drift, center, vertical

 C-drift, center, horizontal

 horizontal breakwire, raw

 vertical breakwire, raw

 C-drift LVDT 

15-pnt smoothed NI data 

0.50 0.55 0.60 0.65 0.70 0.75 0.80 

Time, sec
 

Figure 61.—Pressures and LVDT displacement at the C-drift seal during Test 6 (LLEM #506). 

110

120

130

-33

-30

-27

-24

-21

-18

-15

-12

-9

-6

-3 

 Pressure, psi 

100
 

90
 

80
 

70
 

60
 

50
 

40
 

30
 

20
 

10
 

0
 

 C-drift, rib

 C-drift, center, vertical

 C-drift, center, horizontal

 C-drift, center, embedded

 C-drift LVDT, smoothed

 horizontal breakwire, raw

 vertical breakwire, raw 

transducer embedded in seal was 

destroyed when seal was destroyed 

6
 

3
 

0
 

LVDT, in

0.53 0.54 0.55 0.56 0.57 0.58 0.59 0.60 0.61 

Time, sec 

Figure 62.—Pressures and LVDT displacement on an expanded time scale at the C-drift seal 

during Test 6 (LLEM #506). 

58
 
Figures 63–64 show the smoothed and raw data for the horizontal (on post ~1 ft in front of 

seal) and embedded transducers on the C-drift seal during Test 6 on an expanded time scale. Pressure, psi

120 

100 

80 

60 

40 

20 

 C-drift, center, horizontal, NI smoothed

 C-drift, horizontal, NI raw

 C-drift, horizontal, KS raw
 

0 

0.558 0.560 0.562 0.564 0.566 0.568 0.570 0.572 0.574 0.576 0.578 0.580 

Time, sec 

Figure 63.—Raw and smoothed pressure data for the horizontal transducer during Test 6 (LLEM #506). 

Pressure, psi

 C-drift, center, embedded, NI smoothed

 C-drift, embedded, NI raw

 C-drift, center, embedded, KS raw 

0 

0.558 0.560 0.562 0.564 0.566 0.568 0.570 0.572 0.574 0.576 0.578 0.580 

Time, sec 

Figure 64.—Raw and smoothed pressure data for the embedded transducer during Test 6 (LLEM #506). 

120 

100 

80 

60 

40 

20 

 The 

peak pressure loading from the 1,500-Hz NI raw data for the horizontal transducer was ~104 psi, 

and the peak from the 5,000-Hz KS raw data was ~105 psi. The peak pressure loading from the 

NI raw data for the embedded horizontal transducer was ~117 psi, and the peak from the KS raw 

data was ~120 psi. However, the horizontal transducer on the post (see Figure 3) shows higherfrequency oscillations than the embedded transducer. These oscillations may be due to mechanical 

vibrations. The raw data for the vertical transducer on the post show high-frequency oscillations 

similar to those for the horizontal transducer. The smoothed data for both transducers are almost 

identical. 

59 
 

Pressure, LVDT displacement, and breakwire summary data for the seals in X-2, X-3, and 

C-drift during Test 6 are shown in Table 11.

Table 11.—Pressures and LVDT displacement at the seals during Test 6 (LLEM #506) 

Seal pressures LVDT Break Seal pressures LVDT Break Seal or Seal or 

deflection, time, deflection, time, stopping stopping 

psi (NI) psi (KS) in sec psi (NI) psi (KS) in sec

 

X-2 BC H 50.7 49.2 seal 0.06 156 ft 

Seal survived 

 

X-3 BC H 48.8 48.4 — seal 0.14

V — — — 256 ft 

 Wood A 0.561 

Seal survived cribs B 0.562 

 Cribs destroyed 

 

 Rib 99.2 99.3 C-drift 

 seal H,e 92.3 92.6 >6 320 ft H 91.1 89.0 0.578 

 V 90.1 89.2 0.575 

Seal destroyed, 

 Omega block debris traveled ~917 ft, 

piece of BlocBond traveled ~1,168 ft 

 C-drift H 7.5 7.6 0.790 

stopping Stopping destroyed, 384 ft debris traveled ~748 ft 

H Horizontal. V Vertical. e Embedded. 

 The peak smoothed pressure loadings at the seals are 

listed for the NI and KS data acquisition systems. The data were averaged over 10 ms for the listed 

pressure values. The breakwire time is from the NI raw data. The peak smoothed pressure loading at 

the middle of the X-2 Omega block seal was 50.7 psi and 49.2 psi from the NI and KS data 

acquisition systems, respectively, and the seal survived the explosion. The peak smoothed pressure 

loading from the horizontal transducer at the middle of the solid-concrete-block X-3 seal was 

48.8 psi and 48.4 psi from the NI and KS systems, respectively, and the seal survived. 

The peak smoothed pressure loading from the horizontal and vertical transducers on the post 

at the middle of the C-drift seal was 89–91 psi from the NI and KS data acquisition systems. The 

transducer embedded in the seal saw a slightly higher pressure loading of ~92.5 psi from both data 

acquisition systems. The pressure loading at the rib was ~99 psi from both data acquisition systems. 

The breakwire raw data show that the vertical wire broke at 0.575 sec and the horizontal wire broke 

at 0.578 sec as the seal was destroyed. The pressure loading at the stopping in C-drift (point D in 

Figure 58), as measured from the 384-ft transducer located in front of the stopping, was ~7.5 psi, 

and the stopping was totally destroyed. The breakwire raw data show that the stopping was 

destroyed at 0.79 sec. 

60
 
Table 12 lists quasi-static pressure and flame sensor data at the various DG panels on the 

walls of B- and C-drifts during LLEM #506. 

Table 12.—Wall pressures and flame travel during Test 6 (LLEM #506) 

B-drift quasi-static C-drift quasi-static Flame signal pressures pressures 

Distance, ft psi (NI) psi (KS) Distance, ft psi (NI) psi (KS) Volts sec (NI) 

 3 42.4 42.5 

10 5.6 — 1 13 — — >5 0.227 

 X-1 

108 4.4 — 2 84 36.6 36.7 >5 0.415 

158 ~4 — 3 134 34.7 35.0 >5 0.454 

 X-2 

211 — — 4 184 37.6 37.6 >5 0.510 

257 2.4 — 5 234 38.9 38.9 >5 0.572 

 X-3 

329 2.7 — 6 304 89.5 88.1 ~0 

 

 X-4 

427 3.2 — 7 403 4.6 4.7 ~0 

 X-5 

526 3.3 — 8 501 3.2 2.7 ~0 

 X-6 

626 3.1 — 9 598 3.0 3.1 ~0 

 X-7 

782 3.0 — 10 757 3.0 3.0 ~0 

 11 1,506 2.3 2.2 

The positions of the Omega block seals in X-2 and 

C-drift are depicted by blue shading. On the left of the table are the peak smoothed B-drift quasistatic wall pressures; toward the right are the peak smoothed quasi-static wall pressures in C-drift. 

The C-drift pressures were relatively constant from 84 ft out to 234 ft. The pressure increased 

significantly out to ~320 ft as the pressure pulse was confined by the C-drift seal. After the seal 

broke, the pressures beyond the seal were much lower: 7.5 psi at the stopping at point D (384 ft 

from closed end of C-drift as shown in Figure 58), ~4.6 psi at 403 ft, and ~3 psi at 501 ft, etc. The 

last two columns of Table 12 list the flame signal and arrival time at each of the DG panels. For this 

test, the flame went past the 234-ft panel but did not reach the 304-ft panel. Therefore, the 

interpolated flame travel distance was about 240 ft. Based on the initial gas zone length of 71 ft, 

the expansion ratio would be about 3.4 (240 ft/71 ft). 

The Omega block seal in X-2 and the solid-concrete-block seal in X-3 survived the explosion during Test 6 (LLEM #506). The air leakage data are in Table C-10 in Appendix C. Both seals 

passed the leakage test. The seal in C-drift was destroyed during the test and therefore not measured 

for air leakage. 

61 
The debris from the C-drift seal was thrown a long distance down the drift. Figure 65 shows 

the postexplosion view looking outby near the original seal position in C-drift.

 Figure 65.—Postexplosion view in C-drift looking outby toward original seal location at 320 ft 

after Test 6 (LLEM #506). 

 Near the center is the 

pressure transducer post. The original seal location was just behind this post. The vertical transducer 

is still attached to the back of the post, but the horizontal transducer was broken from the post 

during the explosion. The BDP at 306 ft is in the left center of the photo. Only a few wood blocks 

and small pieces of seal debris are seen on the floor outby the original seal position. 

Figure 66 shows the view looking outby from X-4 at 355 ft. Only a few pieces of wood and 

seal debris are seen in the photo. Figure 67 shows the view looking outby from the DG panel at 

403 ft toward X-5 at 451 ft. At this distance, there are still only a few pieces of wood and seal 

debris. Figure 68 shows the view looking outby from ~500 ft toward X-6 at 547 ft, while Figure 69 

shows the view looking outby from ~600 ft. Both figures show only small amounts of debris from 

the wood cribs, C-drift seal, and C-drift stopping. 

62
 
Figure 66.—Postexplosion view in C-drift looking outby from X-4 at 355 ft. 

Figure 67.—Debris in C-drift after Test 6 (LLEM #506) looking outby from 403 ft. 

63
 
Figure 68.—Debris in C-drift after Test 6 (LLEM #506) looking outby from ~500 ft. 

Figure 69.—Debris in C-drift after Test 6 (LLEM #506) looking outby from ~600 ft. 

64
 
Figure 70 shows the debris looking outby in C-drift from the DG panel at 757 ft from the 

face or ~435 ft from the original seal location. 

Figure 70.—Debris in C-drift after Test 6 (LLEM #506) looking outby from 757 ft. 

The DG panel is on the left edge of the photo. There 

are numerous wood blocks and pieces of seal debris in the photo. Figure 71 shows the view looking 

outby from ~850 ft. Pieces of wood and seal debris are more numerous at this distance. 

65
 

Figure 71.—Debris in C-drift after Test 6 (LLEM #506) looking outby from ~850 ft. 
Figure 72 shows a photo of the postexplosion debris looking outby in C-drift from ~950 ft 

from the face or ~630 ft from the original seal location. At this distance, large amounts of wood and 

seal debris were found. 

Figure 72.—Debris after Test 6 (LLEM #506) looking outby from ~950 ft. 

Figure 73 shows the view looking outby in C-drift from ~1,050 ft after Test 6 (LLEM #506). 

There were large amounts of wood and seal debris at this location also. Figure 74 shows the view 

looking outby from ~1,150 ft from the face or ~825 ft from the original seal location. There was less 

debris at this location. 

Figure 75 shows the view looking outby in C-drift from ~1,240 ft after Test 6. There were a 

few wood blocks and some pieces of seal debris at this location. Figure 76 shows the view looking 

outby from ~1,440 ft from the face or ~1,120 ft from the original seal location. The wood block was 

debris from the wood cribs that were outby the C-drift seal at the start of the test. The piece of seal 

debris (to the left and beyond the wood block) was a piece of BlocBond mortar. These were the 

debris pieces that traveled the farthest in C-drift during explosion Test 6 (LLEM #506). 

66
 
Figure 73.—Debris after Test 6 (LLEM #506) looking outby from ~1,050 ft. 

Figure 74.—Debris after Test 6 (LLEM #506) looking outby from ~1,150 ft. 

67
 
Figure 75.—Debris in C-drift after Test 6 (LLEM #506) looking outby from ~1,240 ft. 

Figure 76.—Debris in C-drift after Test 6 (LLEM #506) looking outby from ~1,440 ft. 

68
 
During Test 6 (LLEM #506), pieces of Omega blocks traveled as far as ~917 ft from the 

original C-drift seal location, as noted in Table 11. A piece of BlocBond mortar traveled ~1,168 ft 

from the original seal location (see Figure 76). Debris from the C-drift stopping traveled ~748 ft 

from the original stopping location. Debris from the wood cribs that were originally inby the C-drift 

seal traveled ~606 ft. Debris from the wood cribs that were originally outby the seal traveled 

~1,139 ft (see Figure 76). These distances were measured from the postexplosion surveys. 

For Test 6, the 1,560-lb battery charger was placed at 688 ft from the face of C-drift or 

365 ft from the outby face of the C-drift seal. The charger moved 356 ft during Test 6 to a location 

~1,044 ft from the face (see Figure 77). The total explosion pressure during Test 6 at the 604-ft 

BDP was 3.0 psi and the dynamic pressure was 0.3 psi. The peak smoothed quasi-static wall 

pressure at 757 ft was 3.0 psi. The peak smoothed pressure loading at the charger would have been 

~3 psi. However, for Test 6, the pressure pulse took longer than 7 ms to reach its maximum value. 

Therefore, for this test, the maximum differential pressure loading from the inby to outby end of the 

charger was only ~1 psi. The cross-sectional area of 900 in2 and differential explosion pressure 

loading of ~1 psi would result in a total force of ~900 lb for a few milliseconds. The 0.3-psi 

dynamic pressure (~270-lb force) would have continued to act on the charger for a longer period of 

time. In addition to the air pressure, the battery charger was also hit by debris from the seal, 

stopping, and wood cribs (see Figure 77). 

Figure 77.—Final position of battery charger after Test 6 (LLEM #506). 

Some of the roof plates were damaged during the Test 6 explosion, as shown in Figures 78– 

80. On the left side of the figures, the plates are shown from inby of the plates, looking outby. On 

the right side of the figure, the plates are viewed looking across the entry from the DG-panel side. 

There was only a slight bending of the round plate at 84 ft. The round plate at 134 ft from the face 

was severely bent during the explosion, but the square plate had no obvious damage. 

69
 
 

 

 

Viewed from inby Viewed across entry from DG panel 

84 ft from face 

134 ft from face 

Figure 78.—Roof plates at 84 and 134 ft from the face after Test 6 (LLEM #506). 

At 184 and 234 ft, both the round and square roof plates were severely bent by the 

explosion, as shown in Figure 79. Two square roof plates instead of just one were inadvertently 

installed at the 184-ft location. The round plate at 234 ft was rotated approximately 180° during the 

explosion. The quasi-static wall pressures as measured by the sensors in the DG panels were ~38 psi 

at the 184-ft panel and ~39 psi at the 234-ft panel. In Figure 80, both the round and square plates at 

304 ft were severely bent by the explosion; the quasi-static wall pressure at this location was 

~89.5 psi. At 403 ft, both the round and square plates were bent at the edges, possibly from being 

hit by flying debris. The round plate at 403 ft rotated about one-quarter turn during the explosion. 

The quasi-static wall pressure at this location was ~4.6 psi. There was little or no obvious damage 

to the other round or square plates throughout C-drift. 

70
 
 

 

 

 

 

 

Viewed from inby Viewed across entry from DG panel 

184 ft from face 

 234 ft from face 

Figure 79.—Roof plates at 184 and 234 ft from the face after Test 6 (LLEM #506). 

71
 
 

 

 

 

Viewed from inby Viewed across entry from DG panel 

304 ft from face 

403 ft from face 

Figure 80.—Roof plates at 304 and 403 ft from the face after Test 6 (LLEM #506). 

The belt hanger at 403 ft was significantly bent, as shown in Figures 81–82. This was 

similar to the damage to this belt hanger during Test 5. These views are looking across the entry 

toward the DG panel. Therefore, outby is to the right in these photos. This belt hanger was probably 

damaged by flying debris because the inby belt hangers were not damaged even though they were 

exposed to greater explosion pressures. The belt hanger seemed to have a small amount of residue 

from the impact of an Omega block. For this test, the carbon monoxide sensor box was hung from 

the roof at ~800 ft from the face or ~475 ft from the seal. There was no apparent damage to the 

sensor box during the explosion. 

72
 
73
 

Figure 81.—Belt hanger (circled in red) near DG panel at 403 ft. 

Figure 82.—Belt hanger at 403 ft after explosion Test 6 (LLEM #506). 
 

SUMMARY AND CONCLUSIONS 

Several seal designs using Omega 384 blocks were constructed at the LLEM during 2006 

and exposed to various explosion pressures. All of the seals were constructed of Omega low-density 

blocks with nominal dimensions of 8 in by 16 in by 24 in. The blocks were alternated to stagger the 

joints. In the 2001 design, properly mixed BlocBond mortar was applied to all of the block-to-block 

and block-to-strata interfaces, including the floor. There were some differences between the 2001 

design and the hybrid and Sago designs. The main differences between the hybrid design and the 

2001 design were that the hybrid design was installed on a 0.25-in-thick layer of dry BlocBond and 

the entire first course of blocks was put into position before applying any mortar to the blocks. For 

all subsequent courses with the hybrid design, the mortar was applied by gloved hand to the block 

joints before placement of each block. The main differences between the Sago design and the 2001 

design were that the Sago design was installed on a 1.5-in-thick layer of dry BlocBond and the 

mortar was forced into the vertical joints after the blocks were positioned for all courses of blocks. 

Comprehensive details of the three seal construction procedures can be found in Appendix B. 

 A summary of the results of the explosions against the three seal designs is presented in 

Table 13. 

Table 13.—Summary of explosion pressures on various seals 

Pressure loading Pressure loading 

Seal Height, Width, at which seal at which seal Location design in in survived, was destroyed, 

psi psi 

2001 X-2 80 226 51 NA 

2001 C-drift 88 224 NA 51 

Hybrid X-3 81 226 25 39 

Sago X-3 80 226 18 35 

Sago C-drift 88 224 21 57 

 NA No data were available for this scenario. 

The first two columns of the table list the type of seal design and location in the LLEM. 

The next two columns list the seal height and width. All of the seals were nominally 40 in thick. 

When the coating thickness on the faces of the seal and the mortar thickness are included, the total 

seal thickness was about 41 in. The next column lists the smoothed explosion pressure loading at 

which a particular seal survived. The final column lists the smoothed explosion pressure loading at 

which a particular seal was destroyed. This value is the peak pressure measured during a particular 

explosion at the middle front of the seal. If a particular design of seal was destroyed during more 

than one explosion, the lower pressure loading is listed. For example, a Sago seal in C-drift was 

destroyed at 57 psi during Test 5 and at 93 psi during Test 6, so only the lower pressure loading of 

57 psi is listed in Table 13. The strength of a particular seal would be somewhere between the 

values in columns 5 and 6 of the table. For example, the 81-in-high hybrid seal survived a pressure 

loading of 25 psi and was destroyed during a later pressure loading of 39 psi. Therefore, its strength 

is greater than 25 psi but less than 39 psi, when comparing the 10-ms peak pressure averages. 

74
 
The 2001-design Omega block seal (see Appendix B, section 1 for construction details) 

located in X-2 survived all six LLEM explosions, with peak pressure loadings of 13, 15, 22, 23, and 

51 psi. Note that all of the pressure loading values were smoothed data that were averaged over 

10 ms. The pressure data here are all from transducers near the geometric center in front of the 

seals. The 2001-design Omega block seal (Appendix B, section 3) in C-drift was destroyed during 

an explosion (Test 2) with a pressure loading of 51 psi. The differences in heights between these 

two seals and the orientation of each seal to the explosion were contributing factors to the fact that 

the X-2 seal survived Test 6 at 51 psi and the C-drift seal was destroyed during Test 2 at 51 psi. The 

C-drift seal was ~88 in high and the X-2 seal was ~80 in high. The higher seal would be weaker for 

the same seal thickness [Anderson 1984]. In addition, the X-2 seal was subjected to a nonuniform, 

sweeping pressure loading while the C-drift seal was subjected to a more uniform, head-on 

explosion pressure loading. The hybrid Omega block seal (Appendix B, section 2) in X-3 survived 

Test 1 at a pressure loading of 25 psi and failed during Test 2 at a pressure loading of 39 psi. Based 

on these LLEM tests, the hybrid seal design is weaker than the 2001 seal design. 

The Sago Omega block seals were constructed in X-3 and C-drift before Test 3, as described 

in Appendix B, sections 4 and 5. The X-3 seal survived Tests 3 and 4 at pressure loadings of 16 psi 

and 18 psi, respectively. It was destroyed during Test 5 at a pressure loading of 35 psi. The C-drift 

seal survived head-on explosions (Tests 3 and 4), which resulted in pressure loadings of 17 psi and 

21 psi, respectively. It was destroyed during Test 5 at a pressure loading of 57 psi. The X-3 and 

C-drift Sago Omega block seals both survived Test 4, which generated a pressure loading of 18 psi 

at the X-3 seal and a pressure loading of 21 psi at the C-drift seal. The X-3 and C-drift seals both 

were destroyed during Test 5 at higher pressure loadings of 35 psi and 57 psi, respectively. Another 

Sago Omega block seal was constructed across C-drift for Test 6; it was destroyed by a pressure 

loading of 93 psi, as expected. Based on these LLEM tests, the Sago seal design is weaker than the 

2001 seal design. 

During these LLEM explosion tests, the distance of seal debris travel was also measured. 

The C-drift seal was exposed to a pressure loading of 51 psi in Test 2, and the seal debris was 

thrown over 800 ft. In Test 2, there was no significant obstacle beyond the C-drift seal that would 

restrict the debris travel. In Tests 5 and 6, there were two wood cribs and a hollow-concrete-block 

stopping beyond the C-drift seal. Even though the cribs and stopping were destroyed in both tests, 

they would absorb blast energy and therefore limit the debris travel distance. In Test 5, the C-drift 

seal was exposed to a pressure loading of 57 psi, and the seal debris was thrown over 500 ft. In 

Test 6, the C-drift seal was exposed to a pressure loading of 93 psi, and the Omega block debris was 

thrown over 900 ft. During these LLEM tests, the explosion pressure effects on other structures and 

objects were also documented, as described earlier in this report. 

The purpose of these LLEM explosion tests conducted in 2006 was to assist MSHA and 

WVOMHS&T in determining the explosion pressure loadings at which various 40-in-thick Omega 

block seal designs would fail relative to LLEM conditions and in studying the explosion effects on 

various mine items, including the debris fields resulting from the destroyed seals. The information 

in this report was used as supporting data in the WVOMHS&T and MSHA analyses of the Sago 

Mine explosion and their subsequent investigative reports [WVOMHS&T 2006; Gates et al. 2007]. 

75
 
ACKNOWLEDGMENTS 

The authors acknowledge the following individuals for the invaluable technical support they 

provided during the development of the test protocols and in the postexplosion observations and 

analyses: Richard A. Gates, MSHA District 11 Manager and the lead Sago Mine accident 

investigator; Clete R. Stephan, Principal Mining Engineer, MSHA Ventilation Division; Monte 

Hieb, P.E., Chief Engineer, WVOMHS&T; J. Brian Mills, District 1 Inspector, WVOMHS&T; 

and Jürgen F. Brune, Ph.D., former Chief, Disaster Prevention and Response Branch, NIOSH-PRL. 

We also acknowledge John Cruse, Technical Analyst, WVOMSH&T, for his contributions to the 

postexplosion observations and documentation. We recognize Benjamin Singleton, Michael Keener, 

Stacy Brown, and Damon Wilkewitz of Allegheny Surveys, Inc., Birch River, WV, for their timely 

and accurate surveys of the debris and objects after each LLEM explosion test and the maps they 

provided of the seal locations and debris fields. In addition, we acknowledge Charles Lash, 

Technical Services Representative, and Michael Shook, Mining Engineer, of Burrell Mining 

Products, Inc., New Kensington, PA, for providing the Omega 384 blocks and for their efforts in the 

construction of the 2001-design Omega block seal in crosscut 2. 

We thank the following NIOSH-PRL personnel without whose contributions the LLEM seal 

evaluation program could not have been accomplished: William A. Slivensky, Frank A. Karnack, 

and Donald D. Sellers, Physical Science Technicians at Lake Lynn Laboratory, for their participation in the installation of sensors for each seal and stopping design, construction of the methane 

ignition zones and installation of the gas sampling lines, systems checks and shotfire during each 

test, postexplosion observations, and documentation of other measurements; Kenneth W. Jackson, 

Electronics Technician at Lake Lynn, for sensor calibrations, operation of the data acquisition 

systems, and initial data analyses; and Cynthia A. Hollerich, Physical Science Technician at PRL, 

for her detailed documentation of the seal installations and postexplosion observations. 

We acknowledge the following mechanical technicians with Ki Corp. (a NIOSH contractor) 

for their extensive efforts in the installation of the Omega block seal designs, solid-concrete-block 

seal, and hollow-core block stoppings; the thorough and timely cleanup of debris after each test; and 

the washdown of the entry: James D. Addis (now a Physical Science Technician with PRL), 

Timothy Glad, James Rabon, and Bernard Lambie. 

All photographs in this report were taken by Cynthia A. Hollerich, Kenneth L. Cashdollar, 

and Eric S. Weiss of NIOSH-PRL. 

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Weiss ES, Slivensky WA, Schultz MJ, Stephan CR, Jackson KW [1996]. Evaluation of 

polymer construction material and water trap designs for underground coal mine seals. Pittsburgh, 

PA: U.S. Department of Energy, RI 9634. NTIS No. PB96-123392. 

Weiss ES, Slivensky WA, Schultz MJ, Stephan CR [1997]. Evaluation of water trap designs 

and alternative mine seal construction materials. In: Dhar BB, Bhowmick BC, eds. Proceedings of 

the 27th International Conference of Safety in Mines Research Institutes (New Delhi, India, 

February 20–22, 1997). Vol. II. New Delhi, India: Oxford & IBH Publishing Co. Pvt. Ltd., pp. 973– 

981. 

Weiss ES, Cashdollar KL, Mutton IVS, Kohli DR, Slivensky WA [1999]. Evaluation of 

reinforced cementitious seals. Pittsburgh, PA: U.S. Department of Health and Human Services, 

Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 

DHHS (NIOSH) Publication No. 99–136, RI 9647. 

WVOMHS&T (West Virginia Office of Miners’ Health, Safety, and Training) [2006]. 

Report of investigation into the Sago mine explosion which occurred January 2, 2006, Upshur Co., 

West Virginia. Charleston, WV: West Virginia Office of Miners’ Health, Safety, and Training. 

Zipf RK Jr., Sapko MJ, Brune JF [2007]. Explosion pressure design criteria for new seals in 

U.S. coal mines. Pittsburgh, PA: U.S. Department of Health and Human Services, Centers for 

Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS 

(NIOSH) Publication No. 2007–144, IC 9500. 

77
 
APPENDIX A.––MSHA–WVOMHS&T–NIOSH PROTOCOLS 

FOR THE LLEM EXPLOSION TESTS 

This appendix contains the protocols from the LLEM explosion tests conducted in 2006 as 

developed by MSHA, WVOMHS&T, and NIOSH. These protocols are reproduced on the following 

pages in their original format. 

78
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 1 Protocol -- LLEM test #501 

MSHA and WVOMHS&T are planning a series of tests at NIOSH’s Lake Lynn Laboratory, 

Experimental Mine, to evaluate 40-inch thick Omega Block Seals. These tests are being 

performed as a direct result of the fatal explosion that occurred at the Sago Mine on 

January 2, 2006, where ten 40-inch thick Omega Block Seals were destroyed. Individual 

tests, within this series, will be designed to address the results of preceding tests, requiring 

a separate protocol for each test. This series of tests will assist investigators in determining 

why 40-inch thick Omega Block Seals failed at the Sago Mine. 

Based on preliminary information, the following may have occurred at the Sago Mine: 

1) Explosion pressures may have exceeded 20 psi; 

2) The seals may not have been properly constructed; 

3) Construction materials may have been substandard; 

4) Cribs inby the seals may have contributed to the failure of the seals; and 

5) A combination of any or all of the four items listed above. 

Test No. 1: 

A 40-inch thick Omega Block Seal was constructed as tested and approved in 2001. A 

second 40-inch Omega Block Seal was constructed with certain modifications, as identified 

below. This hybrid 40-inch thick Omega Block Seal was not intended to be a duplicate of 

the seals at the Sago Mine. However, it includes some similarities. Additional 40-inch 

thick Omega Block Seals will be constructed and tested in the future based on additional 

information including that obtained from this initial explosion test and from other 

engineering tests and evaluations. 

Purpose: 

This first explosion test will attempt to evaluate the results of a 20 psi static pressure pulse 

from an explosion on a 40-inch thick Omega Block Seal, which was constructed in the 

same manner as the seals tested in 2001, and on the hybrid 40-inch thick Omega Block 

Seal. This test will be conducted 22 days after completion of the seals. 

This test is not intended to duplicate the explosion and seal failure that occurred at the 

Sago Mine, and the results should not be interpreted as a replication of those events. This 

test is intended to provide a basis for future seal tests that may offer insight about the Sago 

Mine seal failures. 

Method and Protocol: 

The 40-inch thick Omega Block Seal was constructed as tested and approved in 2001. This 

seal was built by Burrell Mining Products personnel. NIOSH personnel documented the 

construction techniques. 

The hybrid 40-inch thick Omega Block Seal was constructed by NIOSH contractors under 

the direction of MSHA and WVOMHS&T personnel using construction techniques as the 

approved seal, with three exceptions. These exceptions include; applying unmixed mortar 

79
 
 

NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 1 Protocol -- LLEM test #501 

on the mine floor, not applying mortar directly to the vertical joints of the first course of 

blocks, and modifying the installation of wood planks and wedges between the last course 

of the Omega Blocks and the mine roof. 

After a 22-day curing period, the seals will be subjected to an approximately 20 psi static 

pressure pulse from an explosion. 

The openings in the two final seals at the Sago Mine were completed on December 11, 

2005, which was 22 days before the explosion occurred. Test No. 1 will be conducted 22 

days after completion of the seals to replicate the shortest curing period on any portion of 

the 40-inch thick Omega Block Seals at the Sago Mine. 

80
 
 

 

 

NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 1 Protocol -- LLEM test #501 

Test No. 1 

1) Install a Solid Concrete Block Seal in the 1st Crosscut. 

2) Have Burrell Mining Products install a 40-inch thick Omega Block Seal in the 2nd 

Crosscut between the Nos. 2 and 3 Entries according to the approved 2001 methods. 

(See Attachment 1) 

3) Install a hybrid 40-inch thick Omega Block Seal in the 3rd Crosscut between the Nos. 

2 and 3 Entries. (See Attachment 2) 

4) Install 2 cribs in the No. 3 Entry outby the No. 3 Crosscut. 

5) Install belt hangers along the roof in the No. 3 Entry and roof bolt bearing plates 

with pie pans along the roof in the No. 3 Entry. Locate hangers and plates 

alternatively along the entry. 

6) Record all pre-explosion parameters, including volume and percentage of methane. 

7) Test with an approximately 20 psi static pressure pulse from an explosion 22 days 

after completion. 

8) Determine overpressures throughout the test area. 

9) Record and map all post explosion results, including overpressures and flame 

length. 

CB OB HB 

CB – Concrete Block Seal OB – 40-inch Omega Block Seal 

HB – 40-inch Hybrid Omega block seal - Cribs 

+++ - Roof Bolt Plates with Pie Pans and Belt Hangers Arranged Alternatively 

Test No.1 - Sketch of NIOSH’s Lake Lynn Laboratory 

20 psi 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

81
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 1 Protocol -- LLEM test #501 

ATTACHMENT 1 

40-inch thick Omega Block Seal - 2001 

The 40-inch thick Omega Block Seal was constructed at the Lake Lynn Laboratory, 

Experimental Mine, crosscut No. 3 in 2001 by Burrell Mining Products. NIOSH personnel 

assisted with construction, spotting material, mixing BlocBond and documentation. 

•	 Average crosscut dimensions at seal location - 19-ft wide x 6-ft 9-in high. 

•	 No hitching used on this seal. 

•	 BlocBond applied approximately 1⁄4-in thick to floor before starting first row. 

•	 Approximately 264, 8-in x 16-in x 24-in Omega Blocks were used. Average weight of 

block was 45.7 lbs. 

•	 Construction of the front course consisted of nine 8-in x 24-in x 16-in Omega Block plus 

one 8-in x 12-in x 16-in Omega Block. Construction of the back course consisted of 

twelve 8-in x 16-in x 24-in Omega Blocks plus one 8-in x 8-in x 24-in Omega Block. 

Eight courses thereafter were alternated to stagger joints. 

•	 Final seal thickness was 40-inches plus coatings. 

•	 Quikcrete BlocBond high strength, fiber-reinforced Surface Bonding Cement (average 

weight of 50 lb per bag) was applied as joint mortar and sealant on both sides. The 

mix of BlocBond consisted of 2 bags per approximately 4 gallons of water. 

•	 BlocBond was applied approximately 1⁄4-in thick on top and on all four sides of each 

block. 

•	 The gap between the last course and the top of the seal was approximately 2.5 inches. 

•	 Three rows of 1-in x 8-in x 10-foot hardwood boards were run lengthwise from rib to 

rib. One row of wood was placed in the middle of the seal and two rows of wood 

placed symmetrically on each side of the center piece with their respective edges flush 

with the inby and outby side of the seal. Each row of wood was wedged on about 1 

foot centers. The gap between the wedges and the wood rows was filled with 

BlocBond. 

•	 Both faces of the seal were coated with approximately 1⁄4-in thick BlocBond. 

•	 Construction of seal took approximately 9-1/2 hours. 

82
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 1 Protocol -- LLEM test #501 

ATTACHMENT 2 

Method of Construction for Hybrid 40-inch thick Omega Block Seal 

•	 Clear loose material from the ribs, roof, and floor in the location of the seal and for a 

distance of at least 3 feet on each side of the seal’s intended location. No hitching of the 

seal is required. 

•	 Dampen entire crosscut (roof, ribs, and floor) with a fine water spray. If needed, redampen area where seal is to be constructed. Apply approximately a 1⁄4-inch thick 

layer of dry BlocBond on the floor where the seal is to be constructed. Dampen top 

surface of BlocBond with a fine water spray to a wet but not “runny” condition. 

•	 Lay the first course of Omega Block on the floor from rib to rib with approximately a 

1⁄4-inch gap in all vertical joints. Dampen the bottom of each Omega Block with a fine 

water spray prior to installation. The Omega Block should be laid without mortared 

joints and in a normal 40-inch thick pattern. If needed, cut block to fit. 

•	 Mix BlocBond and water to a cement-like consistency according to manufacturer’s 

recommendations. Vary consistency as needed. 

•	 Pour mixture on top of the Omega Blocks and spread by gloved hand. Force BlocBond 

into vertical joints by gloved hand. 

•	 An application of BlocBond is to be applied to the outby face of each row of blocks as 

they are constructed. 

•	 For each subsequent row of blocks, repeat the previous 3 steps, but reverse the pattern 

of laying the Omega Blocks with mortar applied to the vertical joints with gloved hand 

on adjacent courses in order to stagger the vertical joints. If needed, cut block to fit 

from rib to rib. Continue additional courses of Omega Blocks until seal is within 

approximately 2.5 inches of the roof. 

•	 One 1-in x 6-in x 16-ft board of rough cut lumber is to be placed on top of the seal and 

flush with the outby side of the seal. This board may be cut as needed so that there is 

approximately a 1-ft gap to each rib. Wedges are to be driven parallel to the board and 

skin-to-skin between the board and the roof. 

•	 BlocBond is to be thrown along the top of seal to attempt to fill the gap between the top 

of the seal and the roof, from the outby board to near the center of the seal. 

•	 A 1-in x 6-in x 16-ft board of rough cut lumber is to be placed on top of the seal near the 

center. This board may be cut as needed so that there is approximately a 1-ft gap to 

each rib. BlocBond is to be thrown along the top of seal to fill the gap between the top 

of the second board and the roof. 

•	 A 1-in x 6-in x 16-ft board of rough cut lumber is to be placed on top of the seal and 

flush with the inby side of the seal. This board may be cut as needed so that there is 

approximately a 1-ft gap to each rib. Wedges are to be driven lengthwise and skin-toskin between the board and the roof. 

83
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 1 Protocol -- LLEM test #501 

•	 An application of an additional coat of BlocBond is to be applied to both faces of the 

seal from floor to roof and rib to rib with a thickness of 1⁄4-inch. 

•	 Dampen entire crosscut (roof, rib, and floor), including the base of the seal but 

excluding the faces of the seal, with a fine water spray once every 24 hours thereafter. 

No puddles or running water should be created. 

84
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 2 Protocol -- LLEM test #502 

MSHA and WVOMHS&T are planning a series of tests at NIOSH’s Lake Lynn Laboratory, 

Experimental Mine, to evaluate 40-inch thick Omega Block Seals. These tests are being 

performed as a direct result of the fatal explosion that occurred at the Sago Mine on 

January 2, 2006, where ten 40-inch thick Omega Block Seals were destroyed. Individual 

tests, within this series, will be designed to address the results of preceding tests, requiring 

a separate protocol for each test. This series of tests will assist investigators in determining 

why 40-inch thick Omega Block Seals failed at the Sago Mine. 

Based on preliminary information, the following may have occurred at the Sago Mine: 

1) Explosion pressures may have exceeded 20 psi; 

2) The seals may not have been properly constructed; 

3) Construction materials may have been substandard; 

4) Cribs inby the seals may have contributed to the failure of the seals; and 

5) A combination of any or all of the four items listed above. 

Test No. 1 was completed on Saturday April 15. The pre-explosion inspection was 

conducted on Wednesday April 5. The post-explosion inspection was conducted on 

Wednesday April 19. In this test, a 40-inch thick Omega Block Seal was constructed on 

Thursday March 23 in the No. 2 crosscut as tested and approved in 2001. A second 40-inch 

Omega Block Seal was constructed on March 24 in the No. 3 crosscut with certain 

modifications. These seals were both subjected to a static explosion pressure in excess of 

20 psi. Both seals passed the explosion and subsequent leakage test with only slight 

deformation. 

Test No. 2 is a continuing baseline evaluation of the standard seals with an additional 

Omega Block seal constructed across the No. 3 entry. This is the entry in which the 

explosion was propagated. 

Test No. 2: 

As both of the seals passed Test No. 1, they will be used without any changes in Test No. 

2. All of the damaged pie pans and belt hangers from Test No. 1 will be replaced. A 40­

inch thick Omega Block Seal will be constructed in the No. 3 entry outby the No. 3 crosscut 

on May 18. It will be allowed to cure for 28 days. The same quantity of methane and coal 

dust used in Test No. 1 will be used in Test No. 2. The Test No. 2 explosion will be 

conducted on Thursday June 15. The pre-explosion inspection will be conducted on 

Tuesday June 13. The post-explosion inspection was conducted on Wednesday June 21. 

Purpose: 

This second explosion test will attempt to evaluate the results of both a static and dynamic 

pressure pulse from an explosion on the seals. The explosion pressure within the test area 

may result in pressure piling of an unknown magnitude. The amount of pressure is 

expected to be higher than in Test No. 1. This test method will allow NIOSH to evaluate 

85
 
 

NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 2 Protocol -- LLEM test #502 

the explosion pressure for the dynamic pressure pulse situation and to calibrate the system 

for future tests. 

This test is not intended to duplicate the explosion and seal failure that occurred at the 

Sago Mine, and the results should not be interpreted as a replication of those events. This 

test is intended to provide a basis for future seal tests that may offer insight about the Sago 

Mine seal failures. 

Method and Protocol: 

The 40-inch thick Omega Block Seal in the No. 2 Crosscut was constructed on Thursday 

March 23 as tested and approved in 2001. This seal was built by Burrell Mining Products 

personnel. NIOSH personnel documented the construction techniques. The seal passed 

Test No. 1. 

The hybrid 40-inch thick Omega Block Seal was constructed on Friday March 24 in the No. 

3 Crosscut by NIOSH contractors under the direction of MSHA and WVOMHS&T 

personnel using construction techniques as the approved seal, with three exceptions. 

These exceptions include; applying unmixed mortar on the mine floor, not applying 

mortar directly to the vertical joints of the first course of blocks, and modifying the 

installation of wood planks and wedges between the last course of the Omega Blocks and 

the mine roof. The seal passed Test No. 1. 

A 40-inch thick Omega Block Seal will be constructed on May 18 by NIOSH contractors 

under the direction of MSHA and WVOMHS&T in the No. 3 Entry outby the No. 3 

Crosscut as tested and approved in 2001. 

After a 28-day curing period, the seals will be subjected to an explosion using the same 

volume of methane and coal dust used in Test No. 1. The overpressure is expected to be 

larger than in Test No. 1 

86
 
 

 

 

NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 2 Protocol -- LLEM test #502 

Test No. 2 

1) A Solid Concrete Block Seal has been installed in the 1st Crosscut. 

2) Burrell Mining Products has installed a 40-inch thick Omega Block Seal in the 2nd 

Crosscut between the Nos. 2 and 3 Entries according to the approved 2001 methods. 

3) A hybrid 40-inch thick Omega Block Seal has been installed in the 3rd Crosscut 

between the Nos. 2 and 3 Entries. 

4) NIOSH contractors will install a 40-inch thick Omega Block Seal in the No. 3 entry 

outby the No. 3 Crosscut. (See Attachment 1) 

5) Install belt hangers along the roof in the No. 3 Entry and roof bolt bearing plates 

with pie pans along the roof in the No. 3 Entry. Locate hangers and plates 

alternatively along the entry. 

6) Record all pre-explosion parameters, including volume and percentage of methane. 

7) Test with a pressure pulse 1 from an explosion using the same volume of methane 

and coal dust used in Test No. 1 28 days after completion. 

8) Determine overpressures throughout the test area. 

9) Record and map all post explosion results, including overpressures and flame 

length. 

CB OB HB 

CB – Concrete Block Seal OB – 40-inch Omega Block Seal 

HB – 40-inch Hybrid Omega block seal - Cribs 

+++ - Roof Bolt Plates with Pie Pans and Belt Hangers Arranged Alternatively 

Test No.2 - Sketch of NIOSH’s Lake Lynn Laboratory 

>20 psi 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

OB 

87
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 2 Protocol -- LLEM test #502 

ATTACHMENT 1 

40-inch thick Omega Block Seal - 2001 

The 40-inch thick Omega Block Seal was constructed at the Lake Lynn Laboratory, 

Experimental Mine, Crosscut No. 3 in 2001 by Burrell Mining Products. NIOSH personnel 

assisted with construction, spotting material, mixing BlocBond and documentation. 

•	 Average entry dimensions at seal location - 19-ft wide x 6-ft 9-in high. 

•	 No hitching used on this seal. 

•	 BlocBond applied approximately 1⁄4-in thick to floor before starting first row. 

•	 Approximately 264, 8-in x 16-in x 24-in Omega Blocks were used. Average weight of 

block was 45.7 lbs. 

•	 Construction of the front course consisted of nine 8-in x 24-in x 16-in Omega Block plus 

one 8-in x 12-in x 16-in Omega Block. Construction of the back course consisted of 

twelve 8-in x 16-in x 24-in Omega Blocks plus one 8-in x 8-in x 24-in Omega Block. 

Eight courses thereafter were alternated to stagger joints. 

•	 Final seal thickness was 40-inches plus coatings. 

•	 Quikcrete BlocBond high strength, fiber-reinforced Surface Bonding Cement (average 

weight of 50 lb per bag) was applied as joint mortar and sealant on both sides. The 

mix of BlocBond consisted of 2 bags per approximately 4 gallons of water. 

•	 BlocBond was applied approximately 1⁄4-in thick on top and on all four sides of each 

block. 

•	 The gap between the last course and the top of the seal was approximately 2.5 inches. 

•	 Three rows of 1-in x 8-in x 10-foot hardwood boards were run lengthwise from rib to 

rib. One row of wood was placed in the middle of the seal and two rows of wood 

placed symmetrically on each side of the center piece with their respective edges flush 

with the inby and outby side of the seal. Each row of wood was wedged on about 1 

foot centers. The gap between the wedges and the wood rows was filled with 

BlocBond. 

•	 Both faces of the seal were coated with approximately 1⁄4-in thick BlocBond. 

•	 Construction of seal took approximately 9-1/2 hours. 

88
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 3 Protocol -- LLEM test #503 

MSHA and WVOMHS&T are involved in a series of tests at NIOSH’s Lake Lynn 

Laboratory, Experimental Mine, to evaluate the effects of explosion pressures on the 

various seals, including the 40-inch thick Omega Block Seals. These tests are being 

performed as a direct result of the fatal explosion that occurred at the Sago Mine on 

January 2, 2006, where ten 40-inch thick Omega Block Seals were destroyed. Individual 

tests, within this series, will be designed to address the results of preceding tests, requiring 

a separate protocol for each test. Test No. 1 and Test No. 2 were completed on April 15 

and June 15, 2006, respectively. Test No. 3 will be the next test in this series. This series of 

tests will assist investigators in determining why 40-inch thick Omega Block Seals failed at 

the Sago Mine. 

Based on preliminary information, the following may have occurred at the Sago Mine: 

1) Explosion pressures may have exceeded 20 psi; 

2) The seals may not have been properly constructed; 

3) Construction materials may have been substandard; 

4) Cribs inby the seals may have contributed to the failure of the seals; and 

5) A combination of any or all of the four items listed above. 

Test No. 3: 

Since the Solid Concrete Block Seal in Crosscut No. 1 and the Omega block seal in Crosscut 

No. 2 passed Test No. 1 and No. 2, they will be used without changes in Test No. 3. All of 

the damaged pie pans and belt hangers will be replaced. Two Sago 40-inch thick Omega 

Block Seals will be constructed as described in Attachment 1 in the No. 3 crosscut and in 

Drift C outby the No. 3 crosscut. This test is designed to evaluate the conditions and 

construction techniques of the seals at the Sago Mine. They will be allowed to cure for at 

least 28 days. The quantity of methane and coal dust used will subject the seals to an 

approximately 20 psi pressure pulse from an explosion. 

Purpose: 

This third explosion test will attempt to evaluate the results of both a static and a dynamic 

pressure pulse from an explosion on the seals. The explosion pressure within the test area 

is expected to be approximately 20 psi. This test is intended to help investigators evaluate 

the explosion and seal failure that occurred at the Sago Mine. Further tests are anticipated 

to complete this evaluation. 

89
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 3 Protocol -- LLEM test #503 

Method and Protocol: 

The Sago 40-inch thick Omega Block Seal will be constructed in the No. 3 Crosscut and in 

Drift C outby the No. 3 crosscut by NIOSH contractors under the direction of MSHA and 

WVOMHS&T personnel using the same construction techniques as used in the approved 

seal, with three exceptions. These exceptions include; applying unmixed mortar on the 

mine floor, not applying mortar directly to the vertical joints, and modifying the 

installation of wood planks and wedges between the last course of the Omega Blocks and 

the mine roof. 

After at least a 28-day curing period, the seals will be subjected to an approximately 20 psi 

pressure pulse from an explosion. 

 

Procedure: 

1) A Solid Concrete Block Seal has been installed in the 1st Crosscut between Drift B 

and Drift C. This seal has been in place for each of the two preceding tests. 

2) Burrell Mining Products has installed a 40-inch thick Omega Block Seal in the 2nd 

Crosscut between Drift B and Drift C according to the approved 2001 methods. 

This seal has been in place for each of the two preceding tests. 

3) A new Sago 40-inch thick Omega Block Seal will be installed in the 3rd Crosscut 

between Drift B and Drift C and also in Drift C outby the No. 3 Crosscut by NIOSH 

contractors. 

4) Two hollow-core 6-inch x 8-inch x 16-inch concrete block stoppings will be 

constructed as a part of Test No. 3. The stoppings will be dry stacked and coated on 

both sides with B-Bond sealant. The first stopping will be located across Drift C in 

the next pillar outby the Sago seal in Drift C, which is between crosscut Nos. 4 and 

5. The second stopping will be located in Crosscut No. 3, between Drift A and Drift 

B. 

 

5) Two wood cribs will be built approximately 5 feet inby the seal in Drift C and two 

wood cribs will be built approximately 5 feet outby the seal in Drift C. 

6) Where necessary, install new belt hangers along the roof in Drift C and new roof 

bolt bearing plates with pie pans along the roof in Drift C. Locate hangers and 

plates alternatively along the entry. 

7) Record all pre-explosion parameters, including volume and percentage of methane. 

90
 
HB 

 

 

 

 

NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 3 Protocol -- LLEM test #503 

8) Test with a pressure pulse of approximately 20 psi, at least 28 days after completion 

of the final seal. 

9) Determine overpressures throughout the test area. 

10) Record and map all post explosion results, including overpressures and flame 

length. 

Drift C 

Drift B 

Drift A 

# 

# 

# 

# 

CB OB SB 

CB – Concrete Block Seal 

OB – 40-inch Omega Block Seal 

SB – 40-inch Sago Omega Block Seal 

+++ - Roof Bolt Plates with Pie Pans and Belt Hangers Arranged Alternatively 

B - Hollow Concrete Block Stopping

 - Cribs 

Test No.3 - Sketch of NIOSH’s Lake Lynn Laboratory 

20 psi 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

B 

SB B

91
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 3 Protocol -- LLEM test #503 

ATTACHMENT 1 

Method of Construction for the Sago 40-inch thick Omega Block Seal
 

Test No. 3
 

•	 Clear loose material from the ribs, roof, and floor in the location of the seal and for a 

distance of at least 3 feet on each side of the seal’s intended location. No hitching of the 

seal is required. 

•	 Dampen entire crosscut (roof, ribs, and floor) with a fine water spray. If needed, redampen area where seal is to be constructed. Apply approximately a 1.5-inch thick 

layer of dry BlocBond on the floor where the seal is to be constructed. Dampen top 

surface of BlocBond with a fine water spray to a wet but not “runny” condition. 

•	 Lay the first course of Omega Block on the floor from rib to rib, with approximately a 

1⁄4-inch gap in all vertical joints. Dampen the bottom of each of the Omega Blocks on 

the first row with a fine water spray prior to installation. The Omega Block should be 

laid without mortared vertical joints and in a normal 40-inch thick pattern. If needed, 

cut block to fit. 

•	 Mix BlocBond and water to a cement-like consistency according to manufacturer’s 

recommendations. Vary consistency as needed. 

•	 Apply mixture on top of each course of Omega Blocks and spread by gloved hand. 

Vary the consistency of the BlocBond as needed to allow the BlocBond to be forced into 

the vertical joints of each course by gloved hand. 

•	 An application of BlocBond is to be applied to the inby and outby face of each row of 

blocks as they are constructed. 

•	 For each subsequent row of blocks, repeat the previous 3 steps, but reverse the pattern 

of laying the Omega Blocks on adjacent courses in order to stagger the vertical joints. 

The Omega Blocks should be laid with a 1⁄4-inch vertical joint gap and those joints 

should not be mortared. If needed, cut block to fit from rib to rib. Continue additional 

courses of Omega Blocks until seal is within approximately 2.5 inches of the roof. 

•	 One-inch x six-inch boards of rough cut lumber are to be placed on top of the seal near 

the center. These boards may be cut as needed so that they span the distance from rib 

to rib to the extent practicable. An attempt will be made to drive wedges parallel to the 

board and skin-to-skin between the board and the roof to the extent practicable. 

• BlocBond is to be thrown along the top of seal to fill any remaining gap between the 

top of the center board and the roof and the area between the center board and the 

location of the inby and outby board. 

•	 One-inch x six-inch boards of rough cut lumber are to be placed on top of the seal and 

flush with the outby side of the seal. These boards may be cut as needed so that they 

92
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 3 Protocol -- LLEM test #503 

span the distance from rib to rib. Wedges are to be driven parallel to the board and 

skin-to-skin between the board and the roof. 

•	 One-inch x six-inch boards of rough cut lumber are to be placed on top of the seal and 

flush with the inby side of the seal. These boards may be cut as needed so that they 

span the distance from rib to rib. Wedges are to be driven parallel to the board and 

skin-to-skin between the board and the roof. 

•	 BlocBond is to be thrown along the top of seal to fill any remaining gap between the 

top of the boards and the roof 

•	 An application of an additional coat of BlocBond is to be applied to both faces of the 

seal from floor to roof and rib to rib with a thickness of 1⁄4-inch. 

•	 Dampen entire crosscut (roof, rib, and floor), including the base of the seal but 

excluding the faces of the seal, with a fine water spray once every 24 hours thereafter. 

No puddles or running water should be created. 

93
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 4 Protocol -- LLEM test #504 

MSHA and WVOMHS&T are involved in a series of tests at NIOSH’s Lake Lynn 

Laboratory, Experimental Mine, to evaluate the effects of explosion pressures on the 

various seals, including the 40-inch thick Omega Block Seals. These tests are being 

performed as a direct result of the fatal explosion that occurred at the Sago Mine on 

January 2, 2006, where ten 40-inch thick Omega Block Seals were destroyed. Individual 

tests, within this series, will be designed to address the results of preceding tests, requiring 

a separate protocol for each test. Tests No. 1, No. 2 and 3 were completed on April 15, 

June 15, and August 4, 2006, respectively. However, Test No. 3 did not expose the seals to 

the expected 20 psi explosion pressure. Test No. 4 will be the next test in this series. This 

series of tests will assist investigators in determining why 40-inch thick Omega Block Seals 

failed at the Sago Mine. 

Based on preliminary information, the following may have occurred at the Sago Mine: 

1) Explosion pressures may have exceeded 20 psi; 

2) The seals may not have been properly constructed; 

3) Construction materials may have been substandard; 

4) Cribs inby the seals may have contributed to the failure of the seals; and 

5) A combination of any or all of the four items listed above. 

Test No. 4: 

Since the Solid Concrete Block Seal in Crosscut No. 1 and the Omega block seal in Crosscut 

No. 2 passed Tests No. 1, 2 and 3, they will be used without changes in Test No. 4. Also, 

since the two Sago 40-inch thick Omega Block Seals passed Test 3, they will be used 

without change in Test No. 4. This test is designed to evaluate the conditions and 

construction techniques of the seals at the Sago Mine. The quantity of methane and coal 

dust used will subject the seals to an approximate 20 psi pressure pulse from an explosion. 

Purpose: 

This fourth explosion test will attempt to evaluate the results of both a static and a 

dynamic pressure pulse from an explosion on the seals. The explosion pressure within the 

test area is expected to be approximately 20 psi. This test is intended to help investigators 

evaluate the explosion and seal failure that occurred at the Sago Mine. Further tests are 

anticipated to complete this evaluation. 

94
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 4 Protocol -- LLEM test #504 

Method and Protocol: 

Existing constructed seals will be used and no seals will need to be built. 

The seals will be subjected to an approximate 20 psi pressure pulse from an explosion. 

 

Procedure:
 

1) A Solid Concrete Block Seal has been installed in the 1st Crosscut between Drift B 

and Drift C. This seal has been in place for each of the three preceding tests. 

2) Burrell Mining Products has installed a 40-inch thick Omega Block Seal in the 2nd 

Crosscut between Drift B and Drift C according to the approved 2001 methods. 

This seal has been in place for each of the three preceding tests. 

3) A Sago 40-inch thick Omega Block Seal has been installed in the 3rd Crosscut 

between Drift B and Drift C and also in Drift C outby the No. 3 Crosscut. These 

seals were in place for Test No. 3. 

4) Two hollow-core 6-inch x 8-inch x 16-inch concrete block stoppings were 

constructed as a part of Test No. 3. The stoppings were dry stacked and coated on 

both sides with B-Bond sealant. The first stopping is located across Drift C in the 

next pillar outby the Sago seal in Drift C, which is between crosscut Nos. 4 and 5. 

The second stopping is located in Crosscut No. 3, between Drift A and Drift B. 

 

5) Wood cribs built as part of Test No. 3 will remain in place. Two cribs are 

approximately 5 feet inby the seal in Drift C and two cribs are approximately 5 feet 

outby the seal in Drift C. 

6) Record all pre-explosion parameters, including volume and percentage of methane. 

7) Test with a pressure pulse of approximately 20 psi. 

8) Determine overpressures throughout the test area. 

9) Record and map all post explosion results, including overpressures and flame 

length. 

95
 
96
 

NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 4 Protocol -- LLEM test #504 

HB 

 

 

 

Drift C 

Drift B 

Drift A 

# 

# 

# 

# 

CB OB SB 

CB – Concrete Block Seal 

OB – 40-inch Omega Block Seal 

SB – 40-inch Sago Omega Block Seal 

+++ - Roof Bolt Plates with Pie Pans and Belt Hangers Arranged Alternatively 

B - Hollow Concrete Block Stopping 

 - Cribs 

Test No.4 - Sketch of NIOSH’s Lake Lynn Laboratory 

20 psi 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

B 

SB B
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 5 Protocol -- LLEM test #505 

MSHA and WVOMHS&T are involved in a series of tests at NIOSH’s Lake Lynn 

Laboratory, Experimental Mine, to evaluate the effects of explosion pressures on the 

various seals, including the 40-inch thick Omega Block Seals. These tests are being 

performed as a direct result of the fatal explosion that occurred at the Sago Mine on 

January 2, 2006, where ten 40-inch thick Omega Block Seals were destroyed. Individual 

tests, within this series, will be designed to address the results of preceding tests, requiring 

a separate protocol for each test. Tests Nos. 1, 2, 3 and 4 were completed on April 15, June 

15, August 4, and August 16, 2006, respectively. Test No. 5 will be the next test in this 

series. This series of tests will assist investigators in determining why 40-inch thick 

Omega Block Seals failed at the Sago Mine. 

Test No. 5: 

Since the Solid Concrete Block Seal in Crosscut No. 1 and the Omega block seal in Crosscut 

No. 2 passed Tests Nos. 1, 2, 3 and 4, they will be used without changes in Test No. 5. 

Also, since the two Sago 40-inch thick Omega Block Seals passed Tests 3 and 4, they will 

be used without change in Test No. 5. This test is designed to evaluate the conditions and 

construction techniques of the seals at the Sago Mine. The quantity of methane and coal 

dust used will subject the seals to an approximate 50 psi pressure pulse from an explosion. 

Purpose: 

This fifth explosion test will attempt to evaluate the results of both a static and a dynamic 

pressure pulse from an explosion on the seals. The explosion pressure within the test area 

is expected to be approximately 50 psi. This test is intended to help investigators evaluate 

the explosion and seal failure that occurred at the Sago Mine. Further tests are anticipated 

to complete this evaluation. 

Method and Protocol: 

Existing constructed seals will be used and no seals will need to be built. 

The seals will be subjected to an approximate 50 psi pressure pulse from an explosion. 

 

Procedure:
 

1) A Solid Concrete Block Seal has been installed in the 1st Crosscut between Drift B 

and Drift C. This seal has been in place for each of the four preceding tests. 

2) Burrell Mining Products has installed a 40-inch thick Omega Block Seal in the 2nd 

Crosscut between Drift B and Drift C according to the approved 2001 methods. 

This seal has been in place for each of the four preceding tests. 

97
 
HB 

 

 

 

NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 5 Protocol -- LLEM test #505 

3) A Sago 40-inch thick Omega Block Seal has been installed in the 3rd Crosscut 

between Drift B and Drift C and also in Drift C outby the No. 3 Crosscut. These 

seals were in place for Test Nos. 3 and 4. 

4) Two hollow-core 6-inch x 8-inch x 16-inch concrete block stoppings were 

constructed as a part of Test Nos. 3 and 4. The stoppings were dry stacked and 

coated on both sides with B-Bond sealant. The first stopping is located across Drift 

C in the next pillar outby the Sago seal in Drift C, which is between crosscut Nos. 4 

and 5. The second stopping is located in Crosscut No. 3, between Drift A and Drift 

B. 

 

5) Wood cribs built as part of Test Nos. 3 and 4 will remain in place. Two cribs are 

approximately 5 feet inby the seal in Drift C and two cribs are approximately 5 feet 

outby the seal in Drift C. 

6) Record all pre-explosion parameters, including volume and percentage of methane. 

7) Test with a pressure pulse of approximately 50 psi. 

8) Determine overpressures throughout the test area. 

9) Record and map all post explosion results, including overpressures and flame 

length. 

Drift C 

Drift B 

Drift A 

# 

# 

# 

# 

CB OB SB 

CB – Concrete Block Seal 

OB – 40-inch Omega Block Seal 

SB – 40-inch Sago Omega Block Seal 

+++ - Roof Bolt Plates with Pie Pans and Belt Hangers Arranged Alternatively 

B - Hollow Concrete Block Stopping 

 - Cribs 

Test No. 5 - Sketch of NIOSH’s Lake Lynn Laboratory 

50 psi 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

B 

SB B

98
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 6 Protocol -- LLEM test #506 

MSHA and WVOMHS&T are involved in a series of tests at NIOSH’s Lake Lynn 

Laboratory, Experimental Mine, to evaluate the effects of explosion pressures on the 

various seals, including the 40-inch thick Omega Block Seals. These tests are being 

performed as a direct result of the fatal explosion that occurred at the Sago Mine on 

January 2, 2006, where ten 40-inch thick Omega Block Seals were destroyed. Individual 

tests, within this series, have been designed to address the results of preceding tests, 

requiring a separate protocol for each test. Tests Nos. 1, 2, 3, 4 and 5 were completed on 

April 15, June 15, August 4, August 16 and August 23, respectively. Test No. 6 will be the 

next test in this series. This series of tests will assist investigators in determining why 40­

inch thick Omega Block Seals failed at the Sago Mine. 

Test No. 6: 

Since the Solid Concrete Block Seal in Crosscut No. 1 and the Omega Block Seal in 

Crosscut No. 2 passed Tests Nos. 1, 2, 3, 4 and 5, they will be used without changes in Test 

No. 6. The two Sago 40-inch thick Omega Block Seals in Drift C and in Crosscut No. 3 

were destroyed in Test 5. Therefore, a Solid Concrete Block Seal will be build in Crosscut 

No. 3 and a Sago 40-inch thick Omega Block Seal using the blocks supplied from the Sago 

Mine supplemented with additional Omega Blocks obtained from Burrell Mining 

Products, if needed, will be built in Drift C. This test is designed to evaluate the 

conditions and construction techniques of the seals at the Sago Mine. After at least a 28­

day curing period, the seals will be subjected to an approximately 90 psi pressure pulse 

from an explosion. 

Purpose: 

This sixth explosion test will attempt to evaluate the results of a pressure pulse from an 

explosion on the seals. The explosion pressure on the Sago Seal is expected to be 

approximately 90 psi. This test is intended to help investigators evaluate the explosion 

and seal failure that occurred at the Sago Mine. 

Method and Protocol: 

A Solid Concrete Block Seal will be build in Crosscut No. 3 and a Sago 40-inch thick 

Omega Block Seal using the blocks supplied from the Sago Mine will be built in Drift C 

supplemented with additional Omega Blocks obtained from Burrell Mining Products, if 

needed. The seals will be subjected to an approximate 90 psi pressure pulse from an 

explosion. 

99
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 6 Protocol -- LLEM test #506 

 

Procedure: 

1) A Solid Concrete Block Seal has been installed in the 1st Crosscut between Drift B 

and Drift C. This seal has been in place for each of the five preceding tests. 

2) Burrell Mining Products has installed a 40-inch thick Omega Block Seal in the 2nd 

Crosscut between Drift B and Drift C according to the approved 2001 methods. 

This seal has been in place for each of the five preceding tests. 

3) A Solid Concrete Block Seal will be built in the 3rd Crosscut between Drift B and 

Drift C. 

4) A Sago 40-inch thick Omega Block Seal will be installed in Drift C outby the No. 3 

Crosscut. The protocol is outlined in Appendix 1. 

5) A hollow-core 6-inch x 8-inch x 16-inch concrete block stopping will be constructed 

as a part of Test 6. The stopping will be dry stacked and coated on both sides with 

B-Bond sealant. The stopping will be located across Drift C in the next pillar outby 

the Sago seal in Drift C, which is between crosscut Nos. 4 and 5. 

 

6) Two wood cribs will be built approximately 5 feet inby the seal in Drift C and two 

cribs are approximately 5 feet outby the seal in Drift C. 

7) Record all pre-explosion parameters, including volume and percentage of methane. 

9) Test with a pressure pulse of approximately 90 psi. 

9) Determine overpressures throughout the test area. 

10) Record and map all post explosion results, including overpressures and flame 

length. 

100
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 6 Protocol -- LLEM test #506 

101
 

C

HB 

 

 

 

Drift C 

Drift B 

Drift A 

# 

# 

# 

# 

B OB CB 

CB – Concrete Block Seal 

OB – 40-inch Omega Block Seal 

SB – 40-inch Sago Omega Block Seal 

+++ - Roof Bolt Plates with Pie Pans and Belt Hangers Arranged Alternatively 

B - Hollow Concrete Block Stopping 

 - Cribs 

Test No. 6 - Sketch of NIOSH’s Lake Lynn Laboratory 

90 psi 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

SB B
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 6 Protocol -- LLEM test #506 

ATTACHMENT 1 

Method of Construction for the Sago 40-inch thick Omega Block Seal
 

Test No. 6
 

•	 Clear loose material from the ribs, roof, and floor in the location of the seal and for a 

distance of at least 3 feet on each side of the seal’s intended location. No hitching of the 

seal is required. 

•	 Dampen entire crosscut (roof, ribs, and floor) with a fine water spray. If needed, redampen area where seal is to be constructed. Apply approximately a 1.5-inch thick 

layer of dry BlocBond on the floor where the seal is to be constructed. Dampen top 

surface of BlocBond with a fine water spray to a wet but not “runny” condition. 

•	 Use the Omega Blocks supplied from the Sago Mine supplemented with additional 

Omega Blocks obtained from Burrell Mining Products, if needed. 

•	 Lay the first course of Omega Block on the floor from rib to rib, with approximately a 

1⁄4-inch gap in all vertical joints. Dampen the bottom of each of the Omega Blocks on 

the first row with a fine water spray prior to installation. The Omega Block should be 

laid without mortared vertical joints and in a normal 40-inch thick pattern. If needed, 

cut block to fit. 

•	 Mix BlocBond and water to a cement-like consistency according to manufacturer’s 

recommendations. Vary consistency as needed. 

•	 Apply mixture on top of each course of Omega Blocks and spread by gloved hand. 

Vary the consistency of the Blocbond as needed to allow the BlocBond to be forced into 

the vertical joints of each course by gloved hand. 

•	 An application of BlocBond is to be applied to the inby and outby face of each row of 

blocks as they are constructed. 

•	 For each subsequent row of blocks, repeat the previous 3 steps, but reverse the pattern 

of laying the Omega Blocks on adjacent courses in order to stagger the vertical joints. 

The Omega Blocks should be laid with a 1⁄4-inch vertical joint gap and those joints 

should not be mortared. If needed, cut block to fit from rib to rib. Continue additional 

courses of Omega Blocks until seal is within approximately 2.5 inches of the roof. 

•	 One-inch x six-inch boards of rough cut lumber are to be placed on top of the seal near 

the center. These boards may be cut as needed so that they span the distance from rib 

to rib to the extent practicable. An attempt will be made to drive wedges parallel to the 

board and skin-to-skin between the board and the roof to the extent practicable. 

• BlocBond is to be thrown along the top of seal to fill any remaining gap between the 

top of the center board and the roof and the area between the center board and the 

location of the inby and outby board. 

102
 
NIOSH - MSHA- WVOMHS&T Seal Testing 

Test No. 6 Protocol -- LLEM test #506 

•	 One-inch x six-inch boards of rough cut lumber are to be placed on top of the seal and 

flush with the outby side of the seal. These boards may be cut as needed so that they 

span the distance from rib to rib. Wedges are to be driven parallel to the board and 

skin-to-skin between the board and the roof. 

•	 One-inch x six-inch boards of rough cut lumber are to be placed on top of the seal and 

flush with the inby side of the seal. These boards may be cut as needed so that they 

span the distance from rib to rib. Wedges are to be driven parallel to the board and 

skin-to-skin between the board and the roof. 

•	 BlocBond is to be thrown along the top of seal to fill any remaining gap between the 

top of the boards and the roof 

•	 An application of an additional coat of BlocBond is to be applied to both faces of the 

seal from floor to roof and rib to rib with a thickness of 1⁄4-inch. 

•	 Dampen entire crosscut (roof, rib, and floor), including the base of the seal but 

excluding the faces of the seal, with a fine water spray once every 24 hours thereafter. 

No puddles or running water should be created. 

103
 
APPENDIX B.—SEAL CONSTRUCTION DESCRIPTIONS 

–––––––––––––––––––––––– 

104
 

After the Omega block seal evaluations in the LLEM during 2006, the following seal 

construction descriptions were completed in February 2007.1 

 1The seal construction descriptions in this appendix were written by Cynthia A. Hollerich, Eric S. Weiss, and 

Michael J. Sapko (retired) of the NIOSH Pittsburgh Research Laboratory. 

1. Standard 40-in Omega Block Seal, 2001 Design, in Crosscut 2 

Construction Date: March 23, 2006 

NIOSH–MSHA–WVOMHS&T Seal Testing – Test No. 1 Protocol 

On March 23, 2006, a nominal 40-in-thick Omega block seal was constructed by personnel 

from Burrell Mining Products International in crosscut 2 between B- and C-drifts in the LLEM. 

It was constructed of Omega 384 low-density blocks manufactured by Burrell Mining Products. 

This seal was based on the 2001 design. When the coating thickness on the faces of the seal and the 

mortar thickness are included, the total seal thickness was about 41 in. 

• Average crosscut dimensions at seal location: 18.8 ft wide by 6.7 ft high. 

• No hitching was used on this seal. 

•	 The seal was constructed approximately 4 ft into the crosscut (as measured from the 

C-drift side) on a small concrete foundation that tapered from 0 to 3 in thick on top of an 

8-in-thick reinforced concrete floor designed to assist in the leveling of the first course 

of blocks. 

• Quikrete BlocBond (1225-51) was mixed with water and applied approximately 0.25– 

0.5 in thick to the floor (concrete foundation) as the first course was being laid 

(Figure B-1). 

• Construction of the first row (front course, C-drift side) consisted of nine 8-in by 24-in 

by 16-in Omega blocks (24-in block dimension parallel with C-drift) and one Omega 

block cut to fit. The gap between blocks was approximately 0.25–0.5 in. Construction of 

the first row (back course, B-drift side) consisted of fourteen 8-in by 16-in by 24-in 

Omega blocks (16-in block dimension parallel with B-drift) and one Omega block cut to 

fit. The gap between blocks was 0.25–0.5 in, and the gap between the front and back 

course varied approximately 0.25–0.5 in. The blocks were oriented so that the course 

height was about 8 in. Full Omega blocks were laid against each rib, and the cut blocks 

were fitted inside the row. 

• Using shovels and gloved hands, BlocBond was applied to all contact surfaces of the 

Omega blocks. BlocBond was used to fill the gaps (Figure B-2) between the Omega 

blocks and gaps between the Omega blocks and ribs. As each Omega block course was 

completed, BlocBond was also coated on the exposed B- and C-drift sides of the blocks 

(Figure B-3). 

• The remaining eight full-block courses were installed in a manner similar to the first 

course, except the blocks in each subsequent course were alternated to stagger the block 

joints. Figure B-4 is a schematic to illustrate alternating courses and stagger block joints. 
• On the 10th and final block course, each of the blocks was cut and mortared into place to 

leave an approximately 2-in gap between the blocks and the mine roof (Figures B-5 and 

B-6). 

• Approximately 233 new Omega blocks were used in the construction of this seal. These 

blocks were manufactured in the Garards Fort, PA, plant. 

• Three rows of 1-in-thick, 8-in-wide, 10-ft-long hardwood rough-cut boards were run 

lengthwise (rib to rib) on the top course of Omega blocks. One row of wood was placed 

across the middle of the seal, one row of wood was placed flush with the edge of the 

block on the C-drift side, and another flush with the edge of the block on the B-drift side 

(Figure B-7). The rows of wood extended the entire length of the seal (rib to rib). 

• To complete the seal closure to the mine roof, the cut Omega blocks on the B-drift side 

of the seal were first installed (24-in block dimension parallel with C-drift). A 10-ft-long 

rough-cut board was then coated on top with BlocBond, placed on the Omega block 

course tightly against the one rib and flush with the seal face, and then tightly wedged in 

place. A second board was installed in an identical manner across the remainder of the 

seal width on the B-drift side. All gaps between the wedges were filled with BlocBond, 

and all of the wood surfaces were coated with BlocBond. Work then resumed on the 

C-drift side of the seal where the last full Omega block front course (ninth course) was 

intentionally not installed to provide additional working space for installing the middle 

board across the center of the seal. Before installing this middle board, small Omega 

block pieces were first cut (approximately 8 in by 24 in by 6.5 in) and mortared in place 

to within about 2 in of the mine roof to complete the partial block course across the 

middle section of the seal. The rough-cut board for the middle section of the seal was 

then installed in a manner similar to the board on the B-drift side. Finally, the last full 

Omega block course (9th course) and the partial block top course (10th course) on the 

C-drift side were mortared into place. The rough-cut boards were then installed in an 

identical manner as on the B-drift side and coated with BlocBond (Figures B-8 and B-9). 

• Using gloved hands, an approximately 0.25-in-thick coating of BlocBond was then 

applied to both faces of the seal. 

• Construction of the seal took approximately 8.25 hr (41.25 worker-hr). This did not 

include the time required to spot the construction materials to the site. 

• Ninety-three bags of BlocBond (1225-51) high-strength, fiber-reinforced surface 

bonding cement (50-lb average bag weight) were required to complete this seal, 

including that used as joint mortar and face sealant (approximately two bags of 

BlocBond were required to coat each face of the seal). Not including water weight, the 

total weight of BlocBond was approximately 4,650 lb. In general, each batch of mortar 

and sealant used for this seal consisted of two bags of BlocBond mixed with 

approximately 4.5–5.0 gal of water. This calculates to approximately 209–233 gal of 

water used with the 93 bags of BlocBond required for constructing the seal. 

105
 
Figure B-1.—BlocBond applied to concrete mine floor. 

Figure B-2.—BlocBond being applied to gaps between the Omega blocks. 

106
 
 Figure B-3.—As each Omega block course was completed, BlocBond was also coated 

on the exposed B- and C-drift sides of the blocks. 

Figure B-4.—Schematic illustrating alternating courses and staggered block joints. 

107
 
Figure B-5.—Cut blocks on top course to provide 2-in gap to roof. 

 Figure B-6.—View of top portion of seal from C-drift side after B-drift side was completed. 

The last two block courses and middle and inby crossboards were installed from the C-drift 

side to complete the seal. 

108
 
Figure B-7.—One row of wood placed flush with the edge of the blocks on the B-drift side. 

 Figure B-8.—View from the C-drift side showing the rough-cut lumber wedged between 

the mine roof and blocks across the center of the seal. 

109
 
 Figure B-9.—Closeup of the wood wedges, instal

rough-cut board, used to tighten the Omega block 

led between the mine roof and the 

seal. 

110
 
2. Hybrid 40-in Omega Block Seal Design in Crosscut 3 

Construction Date: March 24, 2006 

NIOSH–MSHA–WVOMHS&T Seal Testing – Test No. 1 Protocol 

On March 24, 2006, a nominal 40-in-thick hybrid Omega block seal was constructed by 

personnel from Ki Corp. (a NIOSH contractor) in crosscut 3 between B- and C-drifts in the LLEM. 

It was constructed of Omega 384 low-density blocks manufactured by Burrell Mining Products. 

When the coating thickness on the faces of the seal and the mortar thickness are included, the total 

seal thickness was about 41 in. 

• Average crosscut dimensions at seal location: 18.8 ft wide by 6.75 ft high. 

• No hitching was used on this seal. 

• The seal was constructed approximately 6–7 ft into the crosscut (as measured from the 

C-drift side) on a small concrete foundation that tapered from 0 to 3 in thick on top of an 

8-in-thick reinforced concrete floor designed to assist in the leveling of the first course 

of blocks. 

• The entire crosscut (roof, ribs, and floor) was dampened with a fine water spray just 

before starting the construction. An approximately 0.25-in-thick dry layer of Quikrete 

BlocBond (1225-51) was applied by hand on the floor (concrete foundation) where the 

seal was to be constructed (Figure B-10). This dry layer of BlocBond was then 

dampened with a fine water spray to a wet, but not runny condition (Figure B-11). 

•	 Construction of the first row (front course, C-drift side) consisted of thirteen 8-in by 

16-in by 24-in Omega blocks (16-in block dimension parallel with C-drift) and one 

Omega block cut to fit. Construction of the first row (back course, B-drift side) consisted 

of nine 8-in by 16-in by 24-in Omega blocks (24-in block dimension parallel with 

B-drift) and one Omega block cut to fit. There were irregular gaps (from 0.25 to 0.5 in 

depending on cut of block) left between all blocks. Using a fine spray from a water hose, 

the Omega blocks were dampened on the underside before positioning them onto the 

dampened layer of BlocBond on the floor. No BlocBond was applied to the block joints 

before positioning the blocks onto the floor (Figure B-12). The entire first course was 

laid in the same manner. 

• Using shovels and gloved hands, BlocBond mixed with water was then applied to all 

accessible surfaces of this first course of Omega blocks (Figure B-13). BlocBond was 

used to fill the (vertical) gaps between the Omega blocks as completely as possible by 

gloved hand and also the gaps between the Omega blocks and ribs. As each Omega 

block course was completed, BlocBond was also coated on the exposed B- and C-drift 

sides of the blocks and forced into the outside vertical joints and gaps as completely as 

possible. 

• The remaining eight Omega full-block courses were installed in a manner similar to the 

first course except BlocBond was applied by gloved hand to the block joints before 

placement and the blocks in each subsequent course were alternated to stagger the block 

joints. 

• On the 10th and final course, each block was cut and mortared into place to leave an 

approximately 2.5-in gap between these blocks and the mine roof. The top course of 

blocks for the entire seal was mortared into place before installing any of the boards and 

wedges. 

111
 
• Approximately 215 Omega blocks were used to construct this seal. These blocks were 

manufactured at the Garards Fort, PA, plant. 

• Three rows of 1-in-thick, 6-in-wide, 16-ft-long hardwood rough-cut boards were run 

lengthwise and centered (between ribs) on the top course of Omega blocks. One row of 

wood was placed across the middle section of the seal, and one row of wood was placed 

on the flush end on each side of the seal. These rows of wood extended across the center 

of the seal, leaving an approximately 18-in gap toward each rib. 

• One 1-in-thick by 6-in-wide by 16-ft rough-cut board was placed on top of the seal and 

flush with the outby (B-drift) side of the seal. There was an approximately 18-in gap 

between the centered board and each rib. Wedges were driven parallel to the board 

between the board and the roof. BlocBond was then thrown along the top of the seal and 

spread by gloved hand to fill any gaps (between wedges and the 18-in-long by 2.5-inhigh gap between the end of the board and each rib) and to cover all exposed wood. 

Using gloved hands, an approximately 0.25-in-thick coating of BlocBond was then 

applied to the B-drift side of the seal. Working from the C-drift side, BlocBond was 

thrown by gloved hand along the top of the seal (between the top block course and mine 

roof) to fill the gap between the board on the B-drift side and the center of the seal. Then 

one 1-in-thick by 6-in-wide by 16-ft-long rough-cut board was pushed into place across 

the top of the seal near the center. An approximately 18-in gap remained between the 

ends of the centered board and each rib. BlocBond was again thrown with gloved hands 

along the top of the seal to fill any gaps between the wedges and middle board and the 

mine roof. Additional BlocBond was then thrown by gloved hand to fill the 2.5-in gap 

between the top block course and the mine roof from the middle board to where the 

adjacent board, which was flush-mounted on the C-drift side, will be positioned. Once 

this gap was filled as completely as possible with BlocBond, a final 1-in-thick by 6-inwide by 16-ft-long rough-cut board was placed across the top of the seal and flush with 

the inby (C-drift) side of the seal. (No attempts were made to pack the BlocBond across 

the top of the seal using any tools or implements other than throwing the material by 

gloved hand.) As with the two other boards, an 18-in gap remained between the ends of 

this centered board and each rib. Wedges were driven parallel to the board and skin to 

skin between the board and the roof. BlocBond was again thrown along top of the seal to 

fill any gaps (between the wedges and the 18-in-long by 2.5-in-high gap between the end 

of the board and each rib) and to cover all exposed wood. Using gloved hands, an 

approximately 0.25-in-thick coating of BlocBond was then applied to the C-drift side of 

the seal. 

• Ninety-two bags of BlocBond high-strength fiber-reinforced surface bonding cement 

(50-lb average bag weight) were required to complete this seal, including that used as 

joint mortar and face sealant (approximately two bags of BlocBond were required to coat 

each face of the seal). Not including water weight, the total weight of BlocBond was 

approximately 4,600 lb. In general, each batch of mortar and sealant used for this seal 

consisted of two bags of BlocBond mixed with approximately 4.25–4.50 gal of water. 

This calculates to approximately 195–207 gal of water used with the 92 bags of 

BlocBond required for constructing this seal. 

• Construction of the seal took approximately 8 hr (32 worker-hr). This does not include 

the time required to spot the construction materials to the site. 

112
 
Figure B-10.—Dry BlocBond being spread to a 0.5-in-thick layer on the dampened concrete floor in X-3. 

Figure B-11.—Wetting the dry layer of BlocBond before positioning the Omega blocks. 

113
 
Figure B-12.—Positioning the first course of Omega blocks. 

 Figure B-13.—Applying BlocBond to the top of the first course. The BlocBond is forced 

into the vertical joints using only gloved hands. 

114
 
3. 40-in Omega Block Seal, 2001 Design, at 320 ft Outby C-Drift Face 

Construction Date: May 18, 2006 

NIOSH–MSHA–WVOMHS&T Seal Testing – Test No. 2 Protocol 

On May 18, 2006, a nominal 40-in-thick Omega block seal (based on the design that was 

tested and approved in 2001) was constructed by personnel from Ki Corp. (a NIOSH contractor) in 

C-drift between crosscuts 3 and 4 (~C-320) in the LLEM. This seal was based on the 2001 design. 

It was constructed of Omega 384 low-density blocks manufactured by Burrell Mining Products. 

When the coating thickness on the faces of the seal and the mortar thickness are included, the total 

seal thickness was about 41 in. 

• Average C-drift entry dimensions at seal location: 18.7 ft wide by 7.3 ft high. 

• No hitching was used on this seal. 

• This seal was constructed in nearly the same manner as the 40-in Omega block seal 

constructed by Burrell personnel on March 23, 2006, in crosscut 2 as part of the 

Test No. 1 Protocol. 

• The seal was constructed on the 8-in-thick reinforced concrete floor in C-drift 

(no foundation). 

• Before placement of each Omega block, an approximately 0.25- to 0.5-in-thick layer of 

properly mixed Quikrete BlocBond (1225-51) was applied to the concrete floor where 

the seal was to be constructed (Figure B-14). 

• Construction of the first row (front course, outby) consisted of eleven 8-in by 16-in by 

24-in Omega blocks (16-in block dimension parallel with ribs) and two Omega blocks 

cut to fit. Construction of the first row (back course, inby side) consisted of eight 8-in by 

16-in by 24-in Omega blocks (24-in block dimension laid rib to rib) and one Omega 

block cut to fit. Each block joint consisted of a full wet-bed construction of at least 

0.25-in thickness of BlocBond (Figure B-15). Full Omega blocks were laid against each 

rib; the cut blocks were fitted inside the row. 

• BlocBond was used to fill any remaining vertical gaps between the Omega blocks as 

completely as possible and also the gaps between the Omega blocks and ribs. As each 

Omega block course was completed, BlocBond was also coated on the exposed inby and 

outby sides of the blocks and forced into the outside vertical joints and gaps as 

completely as possible. 

• The remaining 10 Omega full-block courses were installed in a manner similar to the 

first course, except BlocBond was applied to the block joints and all surfaces of the 

block before placement and the blocks in each subsequent course were alternated to 

stagger the block joints. The last full course of blocks on the outby side of the seal was 

not positioned until the inby side was completed to the mine roof (which included 

wedging the boards). 

• On the 12th and final course, each block was cut and mortared into place on the inby 

side of the seal to leave an approximately 2.5-in gap between these blocks and the mine 

roof. A row of 1-in-thick by 8-in-wide by 10-ft-long hardwood rough-cut boards with a 

thin top coating of BlocBond was then set in BlocBond across the flush end of the inby 

side of the seal. Wedges on 6- to 12-in centers were then driven perpendicular between 

the boards and roof and flush with the inby side of the seal. BlocBond was used to fill 

any gaps between the wedges and to cover all exposed wood. Working from the outby 

side, BlocBond was thrown by gloved hand along the top of the seal (between the top 

115
 
block course and the mine roof) to fill the gap between the board on the inby side and 

the center of the seal. A row of rough-cut hardwood boards (1 in thick by 8 in wide by 

10 ft long) was placed (rib to rib) on top of the center section of the seal and wedged 

tightly into place. BlocBond was placed on top of the middle row of boards before 

installation across the top of the seal. BlocBond was again thrown with gloved hands 

along the top of the seal to fill any gaps between the wedges of this middle row of 

boards and the mine roof. 

• The last course of full block (11th course) and the cut block of the 12th course on the 

outby side were then mortared into place (Figure B-16). Additional BlocBond was then 

thrown by gloved hand to fill the 2.5-in gap between the top block course and the mine 

roof from the middle row of boards to where the board flush-mounted on the outby side 

was positioned. Once this gap was filled as completely as possible with BlocBond, 

a final row of 1-in-thick by 8-in-wide by 10-ft-long rough-cut boards was placed across 

the top of the seal and flush with the outby side of the seal. (No attempts were made to 

pack the BlocBond across the top of the seal using any tools or implements other than 

throwing the material by gloved hand, as shown in Figure B-17.) BlocBond was placed 

on top of these boards before installation across the top of the seal. Wedges were driven 

perpendicular to the board on 6- to 12-in centers with the wedge ends flush with the 

outby side of the seal. BlocBond was used to fill any gaps (between the wedges) and to 

cover all exposed wood. Using gloved hands and trowels, an approximately 0.25-inthick coating of BlocBond was then applied to the outby and inby sides of the seal. 

• Approximately 237 Omega blocks from the Bluefield, WV, plant were used to construct 

this seal. 

• Ninety-seven bags of Quikrete BlocBond high-strength fiber reinforced surface bonding 

cement (1225-51; 50-lb average bag weight) were required to complete this seal, 

including that used as joint mortar and face sealant (approximately two bags of 

BlocBond were required to coat each face of the seal). Not including water weight, the 

total weight of BlocBond was approximately 4,850 lb. In general, each batch of mortar 

and sealant used for this seal consisted of two bags of BlocBond mixed with 

approximately 4.25–4.50 gal of water. This calculates to approximately 206–218 gal 

of water used with the 97 bags of BlocBond required for constructing this seal. 

• Construction of the seal took approximately 9 hr (36 worker-hr). This does not include 

the time required to spot the construction materials to the site. 

116
 
Figure B-14.—A 0.25- to 0.5-in-thick layer of properly mixed BlocBond on the floor. 

117
 

Figure B-15.—Omega blocks laid wet with fully mortared (BlocBond) horizontal and vertical joints. 
Figure B-16.—Completing the 11th and final full block course on the outby side. 

 Figure B-17.—Hand slinging the BlocBond to fill the gaps between the previously installed 

center board and the outby board. 

118
 
4. Sago 40-in Omega Block Seal Design in Crosscut 3 

Construction Date: July 5, 2006 

NIOSH–MSHA–WVOMHS&T Seal Testing - Test No. 3 Protocol 

On July 5, 2006, a Sago nominal 40-in-thick Omega block seal was constructed by 

personnel from Ki Corp. (a NIOSH contractor) in crosscut 3 between B- and C-drifts in the LLEM. 

It was constructed of Omega 384 low-density blocks manufactured by Burrell Mining Products. 

When the coating thickness on the faces of the seal and the mortar thickness are included, the total 

seal thickness was about 41 in. 

• Average crosscut dimensions at seal location: 18.8 ft wide by 6.75 ft high. 

• No hitching was used on this seal. 

• The seal was constructed approximately 6–7 ft into the crosscut (as measured from the 

C-drift side) on a small concrete foundation that tapered from 0 to 3 in thick on top of an 

8-in-thick reinforced concrete floor designed to assist in the leveling of the first course 

of blocks. 

• The entire crosscut (roof, ribs, and floor) was dampened with a fine water spray just 

before starting the construction. An approximately 1.5-in-thick dry layer of Quikrete 

BlocBond (1225-51) was applied by hand on the floor (concrete foundation) where the 

seal was to be constructed (Figure B-18). This dry layer of BlocBond (10 bags) was then 

dampened with a fine water spray to a wet, but not runny condition (Figure B-19). The 

water spray was applied as uniformly as possible across the entire layer of dry BlocBond 

for 4 min (~11.6 gal of water). 

• The Omega 384 blocks were manufactured at the Bluefield, WV, plant. 

•	 Construction of the first row (front course, C-drift side) consisted of thirteen 8-in by 

16-in by 24-in Omega blocks (16-in block dimension parallel with C-drift) and one 

Omega block cut to approximately 8 in to fit. Construction of the first row (back course, 

B-drift side) consisted of nine 8-in by 16-in by 24-in Omega blocks (24-in block 

dimension parallel with B-drift) and one Omega block cut to approximately 3.5 in to fit. 

A 0.25-in gap was desired between each block; however, these gaps varied from 0.25 in 

up to as much as 0.5 in between the blocks in this course and subsequent courses 

because of the nonuniform size of the blocks. The undersides of the Omega blocks were 

dampened with a light spray of water before positioning the blocks onto the dampened 

layer of BlocBond that was previously laid on the floor. No BlocBond was applied to 

any of the block joints before positioning the blocks onto the floor. The entire first 

course was laid in the same manner. 

• Using gloved hands, BlocBond mixed with water (according to the manufacturer’s 

recommendations) was then applied to all accessible surfaces of this first course of 

Omega blocks. BlocBond was used to fill the (vertical) gaps between the Omega blocks 

as completely as possible by gloved hand and also the gaps between the Omega blocks 

and ribs. As each Omega block course was completed, BlocBond was also coated on the 

exposed B- and C-drift sides of the blocks and forced into the outside vertical joints and 

gaps as completely as possible using only gloved hands. 

• The remaining eight full courses of Omega blocks were installed in a manner similar to 

the first course except the Omega blocks were not dampened on the underside. All of the 

Omega blocks were first laid in each course, then the BlocBond was applied in the same 

119
 
manner as the first full course (Figure B-20). The remaining rows were alternated to 

stagger the joints. 

• On the 10th and final course, each block was cut as necessary to result in a 2.5-in gap 

between this course and the mine roof. For the blocks on the B-drift side, the Omega 

blocks were cut to approximately 1.5 in by 4 in by 16 in and pushed through from the 

C-drift side. Mortar was then applied by gloved hand from both the B- and C-drift sides. 

From the C-drift side, the Omega blocks were cut to approximately 2.75 in by 5.25 in by 

24 in. Mortar was then applied by gloved hand from C-drift. The gap between the 10th 

course and the mine roof was approximately 2.5 in. 

• Approximately 200 full Omega blocks and 16 cut blocks were used to construct this seal. 

• Three rows of 1-in-thick by 6-in-wide hardwood rough-cut boards were run lengthwise 

(between ribs) on the top course of Omega blocks. One row of wood was placed across 

the middle section of the seal, and one row of wood was placed on the flush end on each 

side of the seal. 

• One 1-in-thick by 6-in-wide by 16-ft-long and one 1-in-thick by 6-in-wide by 3-ft-long 

rough-cut board were placed rib to rib on top of the center of the seal, working from the 

C-drift side. Wedges were driven parallel to the board between the board and the roof. 

BlocBond was then thrown along the top of seal and spread by gloved hand to fill any 

gaps (between wedges) and to cover all exposed wood. At times, one installer used a 

wedge to push the BlocBond to the centered board. Then one 1-in-thick by 6-in-wide by 

16-ft-long and one 1-in-thick by 6-in-wide by 3-ft-long rough-cut board were placed rib 

to rib on top of the of the seal on the inby side (C-drift). Wedges were driven parallel to 

the board and between the board and the roof (Figure B-21). BlocBond was then thrown 

along the top of seal and spread by gloved hand to fill any gaps (between wedges) and to 

cover all exposed wood. Once this gap was filled as completely as possible with 

BlocBond, a final 1-in-thick by 6-in-wide by 16-ft-long and one 1-in-thick by 6-in-wide 

by 3-ft-long rough-cut board were placed rib to rib across the top of the seal and flush 

with the outby side (B-drift) of the seal. (Other than an occasional use of a wedge by one 

installer to assist him in getting the BlocBond to the roof gap and pushing some material 

away from the edge, no other attempts were made to pack the BlocBond across the top 

of the seal using any tools or implements other than throwing the material by gloved 

hand.) Wedges were driven parallel to the board between the board and the roof. 

BlocBond was again thrown along the top of the seal to fill any gaps between the 

wedges and to cover all exposed wood. Using gloved hands, an approximately 0.25-inthick coating of BlocBond was applied to the C-drift and then the B-drift sides of 

the seal. 

•	 Ten bags of dry BlocBond (50-lb average bag weight) were required to provide the 

1.5-in-thick rib-to-rib layer (~44 in wide) before laying the first block course. Sixtyseven additional bags of BlocBond were required to complete this seal, including that 

used as joint mortar and face sealant (approximately two bags of BlocBond were 

required to coat each face of the seal). Not including water weight, the total weight of 

BlocBond was approximately 3,850 lb. In general, each batch of mortar and sealant used 

for this seal consisted of two bags of BlocBond mixed with approximately 4.25–4.50 gal 

of water. This calculates to approximately 142–150 gal of water used with the 67 bags of 

BlocBond required for constructing this seal. 

• Construction of the seal took approximately 8 hr (32 worker-hr). This does not include 

the time required to spot the construction materials to the site. 

120
 
Figure B-18.—Applying the 1.5-in-thick layer of dry BlocBond to the dampened concrete floor in X-3. 

Figure B-19.—Applying a fine water spray to the dry BlocBond layer. 

121
 
Figure B-20.—Applying the properly mixed BlocBond to the first course of Omega blocks. 

Figure B-21.—Driving the wedges (skin to skin) between the crossboard and mine roof. 

122
 
5. Sago 40-in Omega Block Seal Design at 320 ft Outby C-Drift Face 

Construction Date: July 7, 2006 

NIOSH–MSHA–WVOMHS&T Seal Testing – Test No. 3 Protocol 

On July 7, 2006, a Sago nominal 40-in-thick Omega block seal was constructed by 

personnel from Ki Corp. (a NIOSH contractor) in C-drift of the LLEM. It was constructed of 

Omega 384 low-density blocks manufactured by Burrell Mining Products. When the coating 

thickness on the faces of the seal and the mortar thickness are included, the total seal thickness 

was about 41 in. 

• Average entry dimensions at seal location: 18.7 ft wide by 7.3 ft high. 

• No hitching was used on this seal. 

• This seal was constructed in nearly the same manner as the Sago 40-in Omega block seal 

that was installed in crosscut 3 on July 5, 2006. 

• The seal was constructed on the 8-in-thick reinforced concrete floor in C-drift 

(no foundation) at approximately C-320. 

• The entire section of entry (roof, ribs, and floor) was dampened with a fine water spray 

just before starting the construction. An approximately 1.5-in-thick dry layer of Quikrete 

BlocBond (1225-51) was applied by hand on the floor where the seal was to be 

constructed; this dry powder foundation was approximately 48 in wide (Figure B-22). 

This dry layer of BlocBond (12 bags) was then dampened with a fine water spray to a 

wet, but not runny condition (Figure B-23). The water spray was applied as uniformly as 

possible across the entire layer of dry BlocBond for 5 min (~14.5 gal of water). 

• The Omega 384 blocks were manufactured at the Bluefield, WV, plant. 

• Construction of the first row (front course, outby side) consisted of eight 8-in by 16-in 

by 24-in Omega blocks (16-in block dimension parallel with outby side) and one Omega 

block cut to approximately 21 in to fit. Construction of the first row (back course, inby 

side) consisted of thirteen 8-in by 16-in by 24-in Omega blocks (24-in block dimension 

parallel with inby side) and one Omega block cut to approximately 4 in to fit. A 0.25-in 

gap was desired between each block; however, these gaps varied from 0.25 in up to as 

much as 0.5 in between the blocks in this course and subsequent courses because of the 

nonuniform size of the blocks. The undersides of the Omega blocks were dampened with 

a light spray of water before positioning the blocks onto the dampened layer of 

BlocBond that was previously laid on the floor. No BlocBond was applied to any of the 

block joints before positioning the blocks onto the floor. The entire first course was laid 

in the same manner (Figure B-24). 

• Using gloved hands, BlocBond mixed with water (according to the manufacturer’s 

recommendations) was then applied to all accessible surfaces of this first course of 

Omega blocks (Figure B-25). BlocBond was used to fill the (vertical) gaps between the 

Omega blocks as completely as possible by gloved hand and also the gaps between the 

Omega blocks and ribs. As each Omega block course was completed, BlocBond was 

also coated on the exposed outby and inby sides of the block and forced into the outside 

vertical joints and gaps as completely as possible using only gloved hands. 

• The remaining nine full courses of Omega blocks were installed in a manner similar to 

the first course except the Omega blocks were not dampened on the underside. All of the 

Omega blocks were first laid in each course (Figure B-26), then the BlocBond was 

123
 
applied in the same manner as the first full course. The remaining rows were alternated 

to stagger the joints. 

• On the 11th and final course, each block was cut as necessary to result in a 2.5-in gap 

between this course and the mine roof. For the blocks on the outby and inby sides, the 

Omega blocks were cut to approximately 5.5 in by 24 in by 16 in. Mortar was then 

applied by gloved hand from both the inby and outby sides. 

• Approximately 216 full Omega blocks and 41 cut blocks were used to construct this seal. 

NOTE: At times, multiple pieces were used from the same cut blocks. 

• Three rows of 1-in-thick by 6-in-wide hardwood rough-cut boards were run lengthwise 

(between ribs) on the top course of Omega blocks. One row of wood was placed across 

the middle section of the seal, and one row of wood was placed on the flush end on each 

side of the seal. 

• One 1-in-thick by 6-in-wide by 16-ft-long and one 1-in-thick by 6-in-wide by 2-ft-long 

rough-cut board were placed rib to rib on top of the center of the seal, working from the 

outby side. Wedges were driven parallel to the board between the board and the roof. 

BlocBond was then thrown along the top of seal and spread by gloved hand to fill any 

gaps (between wedges) and to cover all exposed wood. At times, one installer used a 

wedge to push the BlocBond to the centered board. Then one 1-in-thick by 6-in-wide by 

16-ft-long and one 1-in-thick by 6-in-wide by 4-ft-long rough-cut board were placed rib 

to rib on top of the of the seal on the inby side. Wedges were driven parallel to the board 

between the board and the roof. BlocBond was then thrown along the top of seal and 

spread by gloved hand to fill any gaps between the wedges and to cover all exposed 

wood. Once this gap was filled as completely as possible with BlocBond, a final 1-inthick by 6-in-wide by 14-ft-long and one 1-in-thick by 6-in-wide by 4-ft-long rough-cut 

board were placed rib to rib across the top of the seal and flush with the outby side of the 

seal (Figure B-27). (Other than an occasional use of a wedge by one installer to assist 

him in getting the BlocBond to the roof gap and pushing some material away from the 

edge, no other attempts were made to pack the BlocBond across the top of the seal using 

any tools or implements other than throwing the material by gloved hand.) Wedges were 

driven parallel to the board between the board and the roof. BlocBond was again thrown 

along the top of the seal to fill any gaps (between the wedges) and to cover all exposed 

wood. Using gloved hands, an approximately 0.25-in-thick coating of BlocBond was 

applied to the inby side and then the outby side of the seal. 

• Twelve bags of dry BlocBond (50-lb average bag weight) were required to provide the 

1.5-in-thick rib-to-rib layer (~48 in wide) before laying the first course of blocks. 

Seventy-eight additional bags of BlocBond were required to complete this seal, 

including that used as joint mortar and face sealant (approximately two bags of 

BlocBond were required to coat each face of the seal). Not including water weight, the 

total weight of BlocBond was approximately 4,500 lb. In general, each batch of mortar 

and sealant used for this seal consisted of two bags of BlocBond mixed with 

approximately 4.25–4.50 gal of water. This calculates to approximately 165.5–175.5 gal 

of water used with the 78 bags of BlocBond required for constructing this seal. 

• Construction of the seal took approximately 9.5 hr (38 worker-hr). This does not include 

the time required to spot the construction materials to the site. 

124
 
 Figure B-22.—Applying a 1.5-in-thick layer of dry BlocBond on the dampened concrete floor 

across C-drift. 

Figure B-23.—Wetting the dry layer of BlocBond with a fine spray of water. 

125
 
Figure B-24.—Positioning the Omega blocks in a staggered pattern for the first course. 

126
 

Figure B-25.—Applying BlocBond by shovel and gloved hands to the first course. 
Figure B-26.—Positioning the second course of Omega blocks in a transverse pattern. 

Figure B-27.—Installing the crossboard on the outby side of C-drift seal. 

127
 
6. Mitchell-Barrett Solid-Concrete-Block Seal in Crosscut 3 

Construction Date: September 11–15, 2006 

NIOSH–MSHA–WVOMHS&T Seal Testing – Test No. 6 Protocol 

On September 11–15, 2006, a 16-in-thick Mitchell-Barrett solid-concrete-block seal with an 

interlocked center pilaster was constructed by personnel from Ki Corp. (a NIOSH contractor) in 

crosscut 3 between B- and C-drifts in the LLEM. 

• Average crosscut dimensions at seal location: 18.6 ft wide by 6.8 ft high. 

• The seal was constructed approximately 6–7 ft into the crosscut (as measured from the 

C-drift side) on a small concrete foundation that tapered from 0 to 3 in thick on top of an 

8-in-thick reinforced concrete floor designed to assist in the leveling of the first course 

of blocks. 

• The crosscut (roof, ribs, and floor) at the seal location was washed using a garden hose 

just before starting the construction. 

• The 6-in by 8-in by 16-in solid concrete blocks used for constructing this seal were 

purchased in April 2002 from Klondike Block & Masonry Supplies, Inc., Uniontown, 

PA. These blocks were stored in the LLEM. 

• The Type S mortar was packaged in 70-lb bags manufactured by Brixment (purchased in 

August 2006 from Stone & Company Concrete & Builders Supplies, Connellsville, PA). 

Each batch of mortar consisted of two parts masonry sand and one part Type S mortar. 

This Type S mortar and sand mixture was then mixed with water according to the 

manufacturer’s recommendations to obtain the proper consistency. 

• The Type S mortar mix (~0.375-in-thick bed) was applied to the concrete floor as each 

block was laid. 

• The dry solid concrete blocks were laid in the wet Type S mortar mix to begin seal 

construction. Using full wet-bed construction, the Type S mortar mix was applied to all 

vertical and horizontal dry block joints (Figure B-28). The vertical and horizontal joints 

were nominally 0.375 in. The blocks were laid in a transverse pattern. 

• Construction of the first row (front course, C-drift side) consisted of thirteen 6-in by 8-in 

by 16-in blocks (16-in block dimension parallel with C-drift) and two partial blocks cut 

to fit within 0.5 in of each rib. Construction of the first row (back course, B-drift side) 

was similar except the blocks were offset to result in a staggered joint pattern (to the 

previously laid block). A total of 26 full blocks and 4 partial blocks were required to 

complete this first bottom course. The blocks were laid in a similar manner for courses 3, 

5, 7, 9, 11, and 13 (although some courses required fewer partial blocks to complete the 

closure to the rib). 

• For the second course, 27 full blocks and 2 partial blocks were installed with the length 

of the block parallel to the crosscut ribs. Courses 4, 6, 8, 10, and 12 were laid in a similar 

manner (although some courses required only one partial block to complete the closure 

to the rib). 

• The blocks used to construct the 16-in by 32-in pilaster were interlocked to the 16-inthick main wall at the center of the seal. The 32-in pilaster dimension was oriented in the 

C-drift to B-drift direction. 

• On the 13th and final course, each block was cut and laid to result in a gap of 

approximately 1–2 in between this top course and the mine roof (Figure B-29). 

128
 
• The gap between the top course of blocks and the mine roof was completely filled with 

mortar throughout the entire width and length of the seal (Figure B-30). No wedges were 

used in the construction of this seal. 

• Approximately 364 full blocks (6 in by 8 in by 16 in) and 23 partial blocks were used to 

construct the seal. Six half-blocks (4 in by 8 in by 16 in) were used at the mine roof. 

• Simulated rib and floor hitching was used on this seal. The hitching was simulated by 

bolting 6-in by 6-in by 0.5-in thick steel angle (ASTM A-36) to both ribs on each side of 

the seal and on the floor on each side. This angle was secured by 1-in-diam by 9-in and 

12-in-long Hilti Kwik bolts III spaced at approximately 18-in centers. A total of 22 bolts 

were installed on each side—four 12-in-long bolts on each rib and fourteen 9-in-long 

bolts on the floor. The steel angle on the floor was installed in three sections on each 

side of the seal. A 16-in section was anchored to the floor against the pilaster (one bolt 

on each end of this angle section), and two ~103-in sections were anchored against the 

seal on the floor to either side of the pilaster (six bolts on each section). Type S mortar 

mix was used to fill any gaps between the steel angles and seal and the steel angles and 

ribs (Figure B-31). 

• 14.5 bags (1,015 lb) of the Type S mortar (subsequently mixed with sand and water) 

were required for construction of this seal, and an additional two bags (140 lb) of Type S 

mortar (mixed with sand and water) were used to fill in the gaps between the steel angles 

and the seal and between the steel angles and the strata interface. 

• Both faces of the seal were subsequently coated with an approximately 0.25-in coating 

of Quikrete B-Bond, four bags of B-Bond on each side. 

• Construction of the seal took approximately 22 hr (79 worker-hr). This included 

approximately 23 worker-hr to install the steel angle on the ribs and floor on both sides 

of the seal. This does not include the time required to spot the construction materials to 

the site. 

129
 

Figure B-28.—Full wet-bed construction on all horizontal and vertical block joints. 
Figure B-29.—Installing cut blocks on top course. 

 

 

Figure B-30.—Completely filling the gap between the top course of blocks and the mine roof 

with mortar. The blocks were not wedged. 

130
 
 Figure B-31.—Mortar filling the gaps between th

blocks along the floor and ribs. 

e steel angle hitching and the 

131
 
7. Sago 40-in Omega Block Seal Design Using the Blocks From Sago Mine 

at 320 ft Outby C-Drift Face 

Construction Date: September 21, 2006 

NIOSH–MSHA–WVOMHS&T Seal Testing – Test No. 6 Protocol 

On September 21, 2006, a Sago nominal 40-in-thick Omega block seal using the Omega 

blocks from the Sago Mine was constructed by personnel from Ki Corp. (a NIOSH contractor) in 

C-drift of the LLEM. It was constructed of Omega 384 low-density blocks manufactured by Burrell 

Mining Products. When the coating thickness on the faces of the seal and the mortar thickness are 

included, the total seal thickness was about 41 in. 

• Average entry dimensions at seal location: 18.7 ft wide by 7.3 ft high. 

• No hitching was used on this seal. 

• The seal was constructed on the 8-in-thick reinforced concrete floor in C-drift 

(no foundation) at approximately C-320. 

• This seal was constructed in the same manner as described in the Test No. 3 protocol for 

the Sago 40-in-thick Omega block seal that was installed across C-drift (C-320) on 

July 7, 2006. 

• The entire section of entry (roof, ribs, and floor) was dampened with a fine water spray 

just before starting the construction. An approximately 1.5-in-thick dry layer of Quikrete 

BlocBond (1225-51) was applied by hand on the floor where the seal was to be 

constructed. This dry powder foundation was approximately 48 in wide. This dry layer 

of BlocBond (12 bags) was then dampened with a fine water spray to a wet, but not 

runny condition. The water spray was applied as uniformly as possible across the entire 

layer of dry BlocBond for 5 min (~14.5 gal of water). 

• The Omega 384 blocks were delivered from the Sago Mine. The blocks were manufactured at the Bluefield, WV, plant. 

• Construction of the first row (front course, outby side) consisted of thirteen 8-in by 16-in 

by 24-in Omega blocks (16-in block dimension parallel with outby side) and one Omega 

block cut to approximately 21 in to fit. Construction of the first row (back course, inby 

side) consisted of eight 8-in by 16-in by 24-in Omega blocks (24-in block dimension 

parallel with inby side) and one Omega block cut to approximately 4 in to fit. A 0.25-in 

gap was desired between each block; however, these gaps varied from 0.25 in up to as 

much as 0.5 in between the blocks in this course and subsequent courses because of the 

nonuniform size of the blocks. The undersides of the Omega blocks were dampened with 

a light spray of water before positioning the blocks onto the dampened layer of 

BlocBond that was previously laid on the floor. No BlocBond was applied to the any of 

the block joints before positioning the blocks onto the floor. The entire first course was 

laid in the same manner. 

• Using gloved hands, BlocBond mixed with water (according to the manufacturer’s 

recommendations) was then applied to all accessible surfaces of this first course of 

Omega blocks. BlocBond was used to fill the (vertical) gaps between the Omega blocks 

as completely as possible by gloved hand and also the gaps between the Omega blocks 

and ribs. As each Omega block course was completed, BlocBond was also coated on the 

exposed outby and inby sides of the blocks and forced into the outside vertical joints and 

gaps as completely as possible using only gloved hands. 

• The remaining nine full courses of Omega blocks were installed in a manner similar to 

the first course, except the Omega blocks were not dampened on the underside. All of 

132
 
the Omega blocks were first laid in each course, then the BlocBond was applied in the 

same manner as the first full course. The remaining rows were alternated to stagger the 

joints. 

• All of the undamaged Omega blocks delivered from the Sago Mine were used. Part of 

the installation of the 10th course required the use of newly purchased Omega blocks 

from the Bluefield, WV, plant on the inby side of the 10th course. These new blocks 

were also used to install the 11th course. 

• On the 11th and final course, each block was cut as necessary to result in a 2.5-in gap 

between this course and the mine roof. For the blocks on the outby and inby sides, the 

Omega blocks were cut to approximately 5.5 in by 24 in by 16 in. Mortar was then 

applied by gloved hand from both the inby and outby sides. 

• Approximately 221 full Omega blocks and 33 cut blocks were used to construct this seal. 

NOTE: At times, multiple pieces were used from the same cut blocks. 

• Three rows of 1-in-thick by 6-in-wide hardwood rough-cut boards were run lengthwise 

(between ribs) on the top course of Omega blocks. One row of wood was placed across 

the middle section of the seal, and one row of wood was placed on the flush end on each 

side of the seal. 

• One 1-in-thick by 6-in-wide by 16-ft-long rough-cut board was placed rib to rib on top 

of the center of the seal, working from the outby side. Wedges were driven parallel to 

the board between the board and the roof. BlocBond was then thrown along the top of 

seal and spread by gloved hand to fill any gaps between the wedges and to cover all 

exposed wood. At times, one installer used a wedge to push the BlocBond to the 

centered board. Then one 1-in-thick by 6-in-wide by 16-ft-long rough-cut board was 

placed rib to rib on top of the seal on the inby side. Wedges were driven parallel to the 

board between the board and the roof. BlocBond was then thrown along the top of seal 

and spread by gloved hand to fill any gaps between the wedges and to cover all exposed 

wood. Once this gap was filled as completely as possible with BlocBond, a final 1-inthick by 6-in-wide by 16-ft-long rough-cut board was placed rib to rib across the top of 

the seal and flush with the outby side of the seal. (Other than the occasional use of a 

wedge by one installer to assist him in getting the BlocBond to the roof gap and pushing 

some material away from the edge, no other attempts were made to pack the BlocBond 

across the top of the seal using any tools or implements other than throwing the material 

by gloved hand.) Wedges were driven parallel to the board between the board and the 

roof. BlocBond was again thrown along the top of the seal to fill any gaps between the 

wedges and to cover all exposed wood. Using gloved hands, an approximately 0.25-inthick coating of BlocBond was applied to the inby side and then the outby side of 

the seal. 

• Twelve bags of dry BlocBond (50-lb average bag weight) were required to provide the 

1.5-in-thick rib-to-rib layer (~48 in wide) before laying the first course of blocks. One 

hundred additional bags of BlocBond were required to complete this seal, including that 

used as joint mortar and face sealant (approximately two bags of BlocBond were 

required to coat each face of the seal). Not including water weight, the total weight of 

BlocBond was approximately 5,600 lb. In general, each batch of mortar and sealant used 

for this seal consisted of two bags of BlocBond mixed with approximately 4.25–4.50 gal 

of water. This calculates to approximately 212.5–225 gal of water used with the 

100 bags of BlocBond required for constructing this seal. 

• Construction of the seal took approximately 9.5 hr (38 worker-hr). This does not include 

the time required to spot the construction materials to the site. 

133
 
APPENDIX C.—AIR LEAKAGE DATA FOR SEALS 

134
 

Table C-1.—Air leakage measurements before Test 1 (LLEM #501) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.8 1.5 2.6 4.85 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 0 0 0 4.4 

Seal in crosscut 3 0 0 4.8 7.4 

Table C-2.—Air leakage measurements after Test 1 (LLEM #501) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.8 1.5 2.5 4.9 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 0 0 0 0 

Seal in crosscut 3 4.4 7.8 12.2 19.1 

Table C-3.—Air leakage measurements before Test 2 (LLEM #502) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.9 1.5 2.5 4.6 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 Use Table C-2 results 

Seal in crosscut 3 Use Table C-2 results 

Seal across C-drift (C-320) 0 0 0 4.8 

Table C-4.—Air leakage measurements after Test 2 (LLEM #502) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.85 1.55 2.55 4.55 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 0 0 0 4.4 

Seal in crosscut 3 Seal destroyed 

Seal across C-drift (C-320) Seal destroyed 
 

Table C-5.—Air leakage measurements before Test 3 (LLEM #503) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.8 1.6 2.4 4.4 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 Use Table C-4 results 

Seal in crosscut 3 0 0 0 4.4 

Seal across C-drift (C-320) 4.8 6.1 8.3 11.7

Table C-6.—Air leakage measurements after Test 3 (LLEM #503) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.85 1.5 2.05 3.5 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 0 0 0 0 

Seal in crosscut 3 0 0 <4.4 5.2 

Seal across C-drift (C-320) 4.4 6.5 7.8 12.2 

Table C-7.—Air leakage measurements after Test 4 (LLEM #504) 

Air leakage rates, cfm, 

Location at pressure differential of— 

1 1.5 2.3 4 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 0 0 0 0 

Seal in crosscut 3 7 10 13.5 17.4 

Seal across C-drift (C-320) 9.6 12.6 15.2 17.8 

 

Table C-8.—Air leakage measurements after Test 5 (LLEM #505) 

Location 

0.8 

Air leakage rates, cfm, 

at pressure differential of— 

1.5 2.3 4.2 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 Not evaluated 

Seal in crosscut 2 0 0 4.8 7.4 

Seal in crosscut 3 

Seal across C-drift (C-320) 

Seal destroyed 

Seal destroyed 

135
 
 

Table C-9.—Air leakage measurements before Test 6 (LLEM #506) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.8 1.5 2.3 4.2 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 104.4 130.5 182.7 243.6 

Seal in crosscut 2 0 0 4.8 7.4 

Seal in crosscut 3 17.4 24.4 33.1 43.5 

Seal across C-drift (C-320) 0 5.2 8.3 11.3 

Table C-10.—Air leakage measurements after Test 6 (LLEM #506) 

Air leakage rates, cfm, 

Location at pressure differential of— 

0.6 1.3 2.2 3.9 

in H2O in H2O in H2O in H2O 

Seal in crosscut 1 87 130.5 174 226.2 

Seal in crosscut 2 0 <4.4 5.2 8.7 

Seal in crosscut 3 17 20 29.1 45.7 

Seal across C-drift (C-320) Seal destroyed 

136
 
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