Explosion Effects

on Mine Ventilation

Stoppings

RI 9676

REPORT OF INVESTIGATIONS/2008

Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Report of Investigations 9676 

Explosion Effects on Mine Ventilation Stoppings 

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

 Gary J. Shemon, Dennis A. Beiter, and John E. Urosek

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

November 2008
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DHHS (NIOSH) Publication No. 2009–102 

November 2008 

SAFER • HEALTHIER • PEOPLETM
 CONTENTS 

Page

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

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

Experimental mine and test procedures ...........................................................................................3 

Stopping construction ......................................................................................................................6 

 Concrete block stoppings.........................................................................................................6 

 Steel panel stoppings..............................................................................................................14 

Australian woven cloth stoppings..........................................................................................21 

Explosion test results .....................................................................................................................26 

Dry-stacked hollow-core concrete block stoppings in crosscuts ...........................................26 

 Test #427........................................................................................................................27 

 Test #428........................................................................................................................28 

 Test #429........................................................................................................................38 

 Test #430........................................................................................................................38 

 Test #432........................................................................................................................38 

 Test #433........................................................................................................................42 

 Test #434........................................................................................................................46 

Steel panel stoppings in crosscuts..........................................................................................50 

 Test #457........................................................................................................................50 

 Test #458........................................................................................................................50 

Dry-stacked solid-concrete-block stoppings in crosscuts........................................................54 

 Test #457........................................................................................................................54 

 Test #458........................................................................................................................54 

 Test #459........................................................................................................................56 

 Test #460........................................................................................................................57 

 Test #461........................................................................................................................58 

 Test #462........................................................................................................................58 

 Test #463........................................................................................................................62 

Wet-laid solid-concrete-block stoppings in crosscuts..............................................................65 

 Test #510........................................................................................................................65 

 Tests #511–#514 ............................................................................................................65 

 Test #515........................................................................................................................65 

 Tests #516–#518 ............................................................................................................67 

 Test #519........................................................................................................................67 

Dry-stacked hollow-core concrete block stoppings in entry and crosscuts ...........................70 

 Test #491........................................................................................................................72 

 Test #494........................................................................................................................72 

 Test #495........................................................................................................................72 

 Test #496........................................................................................................................72 

 Test #497........................................................................................................................74 

Australian woven cloth stoppings in crosscuts ......................................................................80 

 Test #459........................................................................................................................80 

 Test #460........................................................................................................................80 

 Test #461........................................................................................................................85 

 Test #462........................................................................................................................85 
CONTENTS—Continued 

Page

Discussion and conclusions ...........................................................................................................89 

Acknowledgments..........................................................................................................................91 

References......................................................................................................................................92 

Appendix.—Summary tables of explosion pressure data for the LLEM tests.................................94 

ILLUSTRATIONS 

 

 1. Plan view of the Lake Lynn experimental mine.......................................................................4 

 2. Plan view of the LLEM showing the multiple-entry area and stopping locations during 

 LLEM tests #457 and #458 .................................................................................................5 

 3. Dry-stacked hollow-core concrete block stopping construction, with staggered joints ...........7 

 4. Dry-stacked hollow-core concrete blocks used in construction of the stoppings.....................8 

 5. Installation of wood wedges between the stopping and rib for dry-stacked hollow-core 

concrete block stopping .......................................................................................................8

 6. Installation of wood header boards and wood wedges between the stopping and roof for 

dry-stacked hollow-core concrete block stopping ...............................................................9 

 7. Coating the dry-stacked hollow-core concrete block stopping with sealant.............................9 

 8. Dry-stacked solid-concrete-block stopping construction with staggered joints .....................10 

 9. Wood wedges between the stopping and rib for dry-stacked solid-concrete-block stopping ...11 

10. Wood header boards and wood wedges between the stopping and roof ................................11 

11. Completed dry-stacked solid-concrete-block stopping in X-5 as viewed from C-drift, 

with the total explosion pressure transducer at the upper right .........................................12 

12. Wet-laid solid-concrete-block stopping construction with staggered joints...........................13 

13. Completed 6-in (15-cm) thick, wet-laid solid-concrete-block stopping in X-7, as viewed 

 from A-drift........................................................................................................................13 

14. Horizontal steel angles for attaching the steel stopping panels ..............................................15 

15. Three horizontal steel angles inset into rib .............................................................................15 

16. Horizontal steel angles (with open sides facing panels on left), as viewed from B-drift .......16 

17. Polystyrene foam head seal used to provide enhanced closure between metal panel and 

roof, as viewed from the C-drift side.................................................................................17 

18. Temporary jack used to exert roof-to-floor pressure on the metal panel during installation ....17 

19. Metal twist clamp used to secure open side of panel to the horizontal angle.........................18 

20. Overlap panel used to close gap between rib panel and second panel, as viewed from 

the front or C-drift side ......................................................................................................18 

21. Side extensions used to fill gaps between rib panel and rib, viewed from the back or 

B-drift side .........................................................................................................................19 

22. Polyurethane sealant used on perimeter and vertical panel joints ..........................................20 

23. Nearly completed steel panel stopping in X-6 showing closed, smooth panel sides 

facing C-drift......................................................................................................................20 

24. Nearly completed steel panel stopping in X-6 showing the open panel side attached to 

the horizontal rib-to-rib angles on the B-drift side ............................................................21 

25. Inserting pipe into top sleeve of woven cloth .........................................................................23 

26. Inserting pipe/sleeve into top box section...............................................................................23 
CONTENTS—Continued 

Page

27. Anchoring top box section to the mine roof ...........................................................................24 

28. Wedging woven cloth into mine rib........................................................................................24 

29. Sealant along perimeter of the stopping, viewed from C-drift ...............................................25 

30. Rib bolts installed in the X-6 stopping, viewed from B-drift .................................................25 

31. Completed woven cloth stopping design in X-6, viewed from the explosion or C-drift 

side .....................................................................................................................................26 

32. Plan view of the multiple-entry area of LLEM showing effects of explosion test #428........29 

33. LVDT displacement, pressure-time integrals, and pressures versus time at dry-stacked 

 hollow-core concrete block stopping in X-4 during LLEM test #428...............................30 

34. Debris from dry-stacked hollow-core concrete block stopping in X-4 after LLEM test 

 #428, viewed from C-drift .................................................................................................31 

35. Expanded map of debris from the X-4 dry-stacked hollow-core concrete block stopping 

after LLEM test #428.........................................................................................................31

36. LVDT displacement, pressure-time integrals, and pressures versus time at the drystacked hollow-core concrete block stopping in X-5 during LLEM test #428..................32 

37. Debris from X-5 dry-stacked hollow-core concrete block stopping after LLEM test #428, 

viewed from C-drift ...........................................................................................................33 

38. Expanded map of debris from the X-5 dry-stacked hollow-core concrete block stopping 

after LLEM test #428.........................................................................................................33

39. Remnants of the dry-stacked hollow-core concrete block stopping in X-5 after LLEM 

test #428.............................................................................................................................34 

40. LVDT displacement, pressure-time integrals, and pressures versus time at the drystacked hollow-core concrete block stopping in X-6 during LLEM test #428..................35 

41. Dry-stacked hollow-core concrete block stopping in X-6 remained intact after LLEM 

test #428.............................................................................................................................36 

42. LVDT displacement, pressure-time integrals, and pressures versus time at the drystacked hollow-core concrete block stopping in X-7 during LLEM test #428..................36 

43. Pressures at walls (ribs) and at dry-stacked hollow-core concrete block stopping locations during LLEM test #428.............................................................................................37 

44. Expanded cross-sectional views of the blocks remaining in X-6 after test #430. ..................39 

45. Crosscut 6 dry-stacked hollow-core concrete block stopping viewed from B-drift side 

after LLEM test #430, showing blocks dislodged by explosion........................................40 

46. Closeup of B-drift side of X-6 dry-stacked hollow-core concrete block stopping after 

test #430, showing dislodged and damaged blocks ...........................................................40 

47. Closeup of C-drift side X-6 dry-stacked hollow-core concrete block stopping after test 

#430, showing missing and damaged blocks.....................................................................41 

48. The dry-stacked hollow-core concrete block stopping in X-7 remained intact after 

LLEM test #430 ...............................................................................................................41 

49. Expanded cross-sectional view of the blocks remaining in X-6 after test #433.....................42 

50. Debris from X-6 dry-stacked hollow-core concrete block stopping after LLEM test #433, 

viewed from C-drift ...........................................................................................................43 

51. Part of the inby side of X-6 dry-stacked hollow-core concrete block stopping remaining 

after LLEM test #433, viewed from C-drift.......................................................................43 
CONTENTS—Continued 

Page

52. Expanded map of debris from the X-6 dry-stacked hollow-core concrete block stopping 

after LLEM test #433.........................................................................................................44

53. Expanded cross-sectional view of the blocks remaining in X-7 after explosion test #433, 

viewed from C-drift side....................................................................................................44 

54. Condition of X-7 dry-stacked hollow-core concrete block stopping after explosion test 

#433, viewed from C-drift side..........................................................................................45 

55. Expanded view of top part of X-7 dry-stacked hollow-core concrete block stopping 

after explosion test #433, showing damaged blocks..........................................................45 

56. Expanded view of hollow-core concrete block that is almost dislodged from X-7 drystacked stopping after explosion test #433 ........................................................................46 

57. Effects of explosion test #434 on the dry-stacked hollow-core concrete block stoppings, 

with expanded cross-sectional views of the blocks remaining in X-6 and X-7.................47 

58. Additional blocks partially dislodged from the right side of X-6 dry-stacked hollow-core 

concrete block stopping after test #434, viewed from C-drift ...........................................48 

59. Crosscut 7 dry-stacked hollow-core concrete block stopping viewed from B-drift after 

LLEM test #434 .................................................................................................................48 

60. Crosscut 7 dry-stacked hollow-core concrete block stopping viewed from C-drift after 

LLEM test #434 .................................................................................................................49 

61. Map of debris from the X-7 dry-stacked hollow-core concrete block stopping after 

LLEM test #434 .................................................................................................................49 

62. LVDT displacement, pressure-time integrals, and pressures versus time at the steel 

 panel stopping in X-6 during LLEM test #458 .................................................................51 

63. Debris from steel panel stopping in X-6 after LLEM test #458, viewed from C-drift...........52 

64. Map of debris from the X-6 steel panel stopping after LLEM test #458................................52 

65. LVDT displacement, pressure-time integrals, and pressures versus time at the steel 

 panel stopping in X-7 during LLEM test #458 .................................................................53 

66. Debris from steel panel stopping in X-7 after LLEM test #458, viewed from B-drift...........53 

67. Closeup of steel panel stopping still partially attached to outby rib in X-7 after LLEM 

test #458, viewed from B-drift...........................................................................................54 

68. LVDT displacement, pressure-time integrals, and pressures versus time at the drystacked solid-concrete-block stopping in X-4 during LLEM test #458.............................55 

69. LVDT displacement, pressure-time integrals, and pressures versus time at the drystacked solid-concrete-block stopping in X-4 during LLEM test #459.............................56 

70. Displacement of the second block course on the X-4 dry-stacked solid-concrete-block 

stopping after LLEM test #459, viewed from C-drift........................................................57 

71. LVDT displacement, pressure-time integrals, and pressures versus time at the drystacked solid-concrete-block stopping in X-4 during LLEM test #462.............................59 

72. Debris from the dry-stacked solid-concrete-block stopping and remaining blocks on the 

outby rib line in X-4 after LLEM test #462, viewed from C-drift ....................................59 

73. Debris from the dry-stacked solid-concrete-block stopping and remaining blocks on the 

inby rib line in X-4 after LLEM test #462, viewed from C-drift.......................................60 

74. Map of debris from the X-4 dry-stacked solid-concrete-block stopping after LLEM 

test #462.............................................................................................................................60 
CONTENTS—Continued 

Page

75. LVDT displacement, pressure-time integrals, and pressures versus time at the drystacked solid-concrete-block stopping in X-5 during LLEM test #462.............................61 

76. Pressures at walls (ribs) and at the dry-stacked solid-concrete-block stopping locations 

during LLEM test #462 ....................................................................................................62 

77. LVDT displacement, pressure-time integrals, and pressures versus time at the dry- 

 stacked solid-concrete-block stopping in X-5 during LLEM test #463.............................63 

78. Remaining blocks from the dry-stacked solid-concrete-block stopping at the inby rib in 

X-5 after LLEM test #463, viewed from B-drift ...............................................................64 

79. Debris map for the X-5 dry-stacked solid-concrete-block stopping after LLEM test #463......64 

80. LVDT displacement, pressure-time integrals, and pressures versus time at the 8-in 

 (20-cm) thick, wet-laid solid block stopping in X-6 during LLEM test #515...................66 

81. LVDT displacement, pressure-time integrals, and pressures versus time at the 6-in 

 (15-cm) thick, wet-laid solid block stopping in X-7 during LLEM test #515...................67 

82. LVDT displacement, pressure-time integrals, and pressures versus time at the 8-in 

 (20-cm) thick, wet-laid solid block stopping in X-6 during LLEM test #519...................68 

83. LVDT displacement, pressure-time integrals, and pressures versus time at the 6-in 

 (15-cm) thick, wet-laid solid block stopping in X-7 during LLEM test #519...................69 

84. Debris from 6-in (15-cm) thick, wet-laid solid block stopping in X-7 after LLEM test 

#519, viewed from A-drift .................................................................................................69 

85. Completed dry-stacked hollow-core concrete block stopping with simulated open 

regulator across B-drift ......................................................................................................71 

86. Dry-stacked hollow-core concrete block stopping between B- and C-drifts in X-4 showing individually numbered block, viewed from C-drift.....................................................71 

87. Debris map after LLEM test #491 ..........................................................................................73 

88. Pressure-time integrals and pressures versus time at the dry-stacked hollow-core concrete block stopping across B-drift during LLEM test #497 .............................................74 

89. Debris from the dry-stacked hollow-core concrete block stopping across B-drift after 

LLEM test #497 .................................................................................................................75 

90. Pressure-time integrals and pressures versus time at the X-4 dry-stacked hollow-core 

 concrete block stoppings during LLEM test #497.............................................................75 

91. Damage to the X-4 dry-stacked hollow-core concrete block stopping between B- and 

C-drifts after LLEM test #497 ...........................................................................................76 

92. Debris from the X-4 dry-stacked hollow-core concrete block stopping between A- and 

B-drifts after LLEM test #497 ...........................................................................................76 

93. Pressure-time integrals and pressures versus time at the X-3 dry-stacked hollow-core 

 concrete block stoppings during LLEM test #497.............................................................77 

94. Damage to the X-3 dry-stacked hollow-core concrete block stopping between B- and 

C-drifts after LLEM test #497 ...........................................................................................77 

95. Debris map after LLEM test #497 ..........................................................................................78 

96. Total explosion pressure versus time at the dry-stacked hollow-core concrete block stoppings in X-4 and in B-drift during LLEM test #497..........................................................79 

97. Pressure-time integrals and pressures at the X-6 woven cloth stopping during LLEM 

test #459 ...........................................................................................................................81 
CONTENTS—Continued 

Page

 98. Pressure-time integrals and pressures at the X-7 woven cloth stopping during LLEM 

 test #459 ..........................................................................................................................82 

 99. Pressure-time integrals and pressures at the X-6 woven cloth stopping during LLEM 

 test #460 ..........................................................................................................................82 

 100. Pressure-time integrals and pressures at the X-7 woven cloth stopping during LLEM 

 test #460............................................................................................................................83 

 101. Tears in the woven cloth on the outby rib of X-6 stopping after LLEM test #460, 

 viewed from C-drift ..........................................................................................................84 

 102. Initial tear in the woven cloth at the corner steel roof bolt plate position on the inby rib 

 of the X-7 stopping after LLEM test #460, viewed from C-drift .....................................84 

 103. Pressure-time integrals and pressures at the X-6 woven cloth stopping during LLEM 

 test #462 ..........................................................................................................................86 

 104. Pressure-time integrals and pressures at the X-7 woven cloth stopping during LLEM 

 test #462 ..........................................................................................................................87 

 105. Damage to the woven cloth stopping in X-6 after LLEM test #462....................................88 

 106. Damage to the woven cloth stopping in X-7 after LLEM test #462....................................88 

 107. Results of the LLEM block stopping evaluations compared to the critical design param- 

 eters and the transverse load capacity predictions of the NIOSH empirical correlation 

 by Barczak and Batchler (for dry-stacked block walls) and WAC (for wet-laid block 

 walls) ................................................................................................................................90 

TABLES 

1. Evaluations of mine stoppings during the LLEM explosion tests ........................................27 

2. Peak total explosion pressure data at dry-stacked hollow-core concrete block stoppings 

for test #428 in C-drift .......................................................................................................38 

3. Peak total explosion pressure data at dry-stacked solid-concrete-block stoppings for 

test #462 in C-drift ...........................................................................................................62 

4. Peak total explosion pressure data at wet-laid solid-concrete-block stoppings for test 

#510 in A-drift ...................................................................................................................65 

5. Peak total explosion pressure data at wet-laid solid-concrete-block stoppings for test 

#515 in A-drift ...................................................................................................................66 

6. Peak total explosion pressure data at wet-laid solid-concrete-block stoppings for test 

#519 in A-drift ...................................................................................................................70 

 7. Peak total explosion pressure data at Australian woven cloth stoppings for test #460 in 

C-drift ..............................................................................................................................83 

 8. Peak total explosion pressure data at Australian woven cloth stoppings for test #462 in 

C-drift ..............................................................................................................................85 

 9. Total explosion pressures necessary to destroy typical U.S. stoppings in the LLEM..........89 

A-1. Maximum explosion pressures during LLEM test #427 ......................................................94 

A-2. Maximum explosion pressures during LLEM test #428 ......................................................94 

A-3. Maximum explosion pressures during LLEM test #429 ......................................................95 

A-4. Maximum explosion pressures during LLEM test #430 ......................................................95 
CONTENTS—Continued 

Page

 A-5. Maximum explosion pressures during LLEM test #432 ....................................................96 

 A-6. Maximum explosion pressures during LLEM test #433 ....................................................96 

 A-7. Maximum explosion pressures during LLEM test #434 ....................................................97 

 A-8. Maximum explosion pressures during LLEM test #457 ....................................................97 

 A-9. Maximum explosion pressures during LLEM test #458 ....................................................98 

A-10. Maximum explosion pressures during LLEM test #459 ....................................................98 

A-11. Maximum explosion pressures during LLEM test #460 ....................................................99 

A-12. Maximum explosion pressures during LLEM test #461 ....................................................99 

A-13. Maximum explosion pressures during LLEM test #462 ..................................................100 

A-14. Maximum explosion pressures during LLEM test #463 ..................................................100 

A-15. Maximum explosion pressures during LLEM test #491 ..................................................101 

A-16. Maximum explosion pressures during LLEM test #494 ..................................................101 

A-17. Maximum explosion pressures during LLEM test #495 ..................................................102 

A-18. Maximum explosion pressures during LLEM test #496 ..................................................102 

A-19. Maximum explosion pressures during LLEM test #497 ..................................................103 

A-20. Maximum explosion pressures during LLEM test #510 ..................................................103 

A-21. Maximum explosion pressures during LLEM test #512 ..................................................104 

A-22. Maximum explosion pressures during LLEM test #515 ..................................................104 

A-23. Maximum explosion pressures during LLEM test #519 ..................................................105 
ACRONYMS AND ABBREVIATIONS USED IN THIS REPORT 

CFR Code of Federal Regulations 

 DG data-gathering 

 LLEM Lake Lynn Experimental Mine 

LVDT linear variable displacement transducer 

 MSHA Mine Safety and Health Administration 

 NIOSH National Institute for Occupational Safety and Health 

PRL Pittsburgh Research Laboratory (NIOSH) 

WAC Wall Analysis Code 

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

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

 cm centimeter 

 ft foot 

 ft2

 square foot 

 ft3

 cubic foot 

 g/m3 gram per cubic meter 

 in inch 

 km kilometer 

 kPa kilopascal 

 kPa-s kilopascal second 

 m meter 

 m

2

 square meter 

 m3

 cubic meter 

 mm millimeter 

MPa megapascal 

ms millisecond 

 psi pound-force per square inch 

 psi-s pound-force per square inch - second 

 sec second 
EXPLOSION EFFECTS ON MINE VENTILATION STOPPINGS 

By Eric S. Weiss,1 Kenneth L. Cashdollar,2 Samuel P. Harteis,3

 Gary J. Shemon,4

 Dennis A. Beiter,5 and John E. Urosek6

ABSTRACT

 The National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety 

and Health Administration (MSHA) conducted joint research to evaluate explosion blast effects 

on typical U.S. mine ventilation stoppings in the NIOSH Pittsburgh Research Laboratory’s 

(PRL) Lake Lynn Experimental Mine (LLEM). An innovative Australian-designed brattice stopping was also evaluated. 

 After mine explosion accidents, MSHA conducts investigations to determine the cause(s) 

as a means to prevent future occurrences. As part of these postexplosion investigations, the condition of underground stoppings, including the debris from damaged stoppings, is documented as 

evidence of the approximate strength and the direction of the explosion forces. The LLEM data 

showed that a typical dry-stacked and coated solid-concrete-block stopping survived a total 

explosion pressure of ~6.7 psi (~46 kPa) and was destroyed at a total explosion pressure of 

~7.6 psi (~52 kPa). In comparison, a typical dry-stacked and coated hollow-core concrete block 

stopping survived a total explosion pressure of ~3.4–4.3 psi (~23–30 kPa) and was destroyed at a 

total explosion pressure of ~3.6–5.2 psi (~25–36 kPa), depending on the length of the pressure 

pulse and the value of the pressure-time integral. A typical steel panel stopping design survived 

a total explosion pressure of 0.8 psi (5.5 kPa) and failed at a total explosion pressure of 1.3 psi 

(9 kPa). The LLEM data also showed that an obstacle blocking the path of a pressure wave 

resulted in a higher reflected pressure at the obstacle. An 8-in (20-cm) thick wet-laid solidconcrete-block stopping coated on one side survived a total explosion pressure of ~26 psi 

(~180 kPa); this stopping was not tested to failure. A 6-in (15-cm) thick wet-laid solid-concreteblock stopping coated on one side survived a total explosion pressure of ~14 psi (~97 kPa) and 

was destroyed at a total explosion pressure of ~25 psi (~172 kPa). An innovative Australian 

woven cloth stopping survived an explosion pressure of 4.0 psi (27 kPa) and was destroyed at 

an explosion pressure of ~6.1 psi (~42 kPa). These results will help investigators determine the 

approximate explosion forces that destroy or damage stoppings during actual coal mine 

explosions. 

 

 1Team Leader (Senior Research Mining Engineer), Lake Lynn Laboratory Section, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA. 

 2

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

and Health, Pittsburgh, PA. 

 3

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

Health, Pittsburgh, PA. 

 4

Mining Engineer, Mine Ventilation and Emergency Services Branch, Ventilation Division, Pittsburgh Safety and 

Health Technology Center, Mine Safety and Health Administration, Triadelphia, WV. 

 5

Supervisory Mining Engineer, Mine Ventilation and Emergency Services Branch, Ventilation Division, Pittsburgh Safety and Health Technology Center, Mine Safety and Health Administration, Triadelphia, WV. 

 6

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

Administration, Pittsburgh, PA. 
2

INTRODUCTION

 Permanent stoppings are used to control and direct the ventilation airflow through underground coal mines to dilute and render harmless methane, entrained coal dust, and other contaminants at the working face and other areas of the mine. 30 CFR7

 75.333 requires that permanent 

stoppings be built and maintained between intake and return air courses beginning at the third 

connecting crosscut outby the working face and to separate other air courses and direct air as 

specified. To perform the intended function and meet the requirements of 30 CFR 75.333, 

permanent stoppings are to be constructed in a traditionally accepted method and of materials 

that have been demonstrated to perform adequately or in a method and of materials that have 

been tested and shown to have a minimum strength equal to or greater than the traditionally 

accepted in-mine controls. A few examples of traditionally accepted [61 Fed. Reg.8

 9764 (1996)] 

stopping construction methods are as follows: (1) 8-in (20-cm) and 6-in (15-cm) concrete block 

(both hollow-core and solid) with mortared joints, (2) 8-in (20-cm) and 6-in (15-cm) concrete 

blocks, dry-stacked and coated on one or both sides with a strength-enhancing sealant suitable 

for dry-stacked stoppings, and (3) steel stoppings (minimum 20-gauge) with seams and perimeter 

sealed with a suitable mine sealant. 

 Unlike mine ventilation seal structures [30 CFR 75.335; Greninger et al. 1991; Mitchell 

1971; Weiss et al. 1993, 1996, 1999, 2002] that are commonly used to isolate unused sections of 

the mine, stoppings are not intended to withstand explosion overpressures. Unfortunately, mine 

explosions do occur. Depending on the location and severity, explosions can result in fatalities 

and injuries to underground mining personnel and cause considerable underground damage to 

equipment and structures. In the mine explosions in Alabama in 2001 and West Virginia in 2006, 

ventilation stoppings were destroyed [McKinney et al. 2002; Gates et al. 2007]. Mine Safety and 

Health Administration (MSHA) personnel conduct investigations into these types of explosion 

accidents to determine the root cause(s) as a means to prevent future occurrences. As part of 

postexplosion investigations, the location and condition of underground ventilation structures 

and debris are mapped. This information helps the investigators determine the strength and the 

direction of the forces of the explosion. 

 Previous research by Kawenski et al. [1965] conducted in the Bruceton Experimental 

Mine on the strength of stoppings revealed that a 16-ft (4.9-m) wide by 6-ft (1.8-m) high drystacked, concrete block stopping constructed with hollow-core block, wedged at the roof, and 

coated on the low-pressure side was ruptured when subjected to a 2.5-psi (17-kPa) pressure pulse 

generated from the burning of black powder. A similar concrete block stopping with hollow-core 

block but with fully mortared joints, no wedges, and coated on the low-pressure side ruptured at 

about 5.8 psi (40 kPa). The hollow-core concrete blocks used during these evaluations at 

Bruceton were cinder block (8 in by 8 in by 16 in (20 cm by 20 cm by 40 cm)) for some stopping 

designs and solid gravel block (8 in by 6 in by 16 in (20 cm by 15 cm by 40 cm)) for others. 

As expected, this research also showed that the pressure required for rupture decreased as the 

stopping width increased. 

 The more recent stopping evaluations in the Lake Lynn Experimental Mine (LLEM) 

involved various full-scale designs subjected to known overpressures generated from methane 

and/or coal dust explosions. These stopping designs were typical of those currently used in 

U.S. underground coal mines. In addition to evaluating the effects of the explosion on typical 

 

7

Code of Federal Regulations. See CFR in references. 8

Federal Register. See Fed. Reg. is references. 
3

dry-stacked and coated concrete block stoppings located in crosscuts (perpendicular to the flow 

of the pressure pulse), a similar study was conducted with a stopping installed across the entry 

outby from where the explosion was initiated. This study was designed to simulate actual explosion accidents in coal mines where some crosscut stoppings near the ignition location survived 

the initial explosion pressure pulse, but stoppings farther away were destroyed. Wet-laid solidconcrete-block stoppings coated on one side were also evaluated to determine the enhanced 

explosion overpressure resistance provided by the mortared joints. In addition, in cooperation 

with the Australian mining industry, a new and innovative woven cloth stopping proposed for 

use in Australian mines was evaluated. The construction and testing methods, explosion test data, 

and postexplosion condition of each stopping design are presented in this report. 

 In addition, the results from the numerous stopping evaluations conducted in the LLEM 

were compared to predictions using a NIOSH empirical correlation for dry-stacked concrete 

block walls [Barczak 2005; Barczak and Batchler 2006, 2008] and the Wall Analysis Code 

(WAC) for wet-laid concrete block walls developed by the U.S. Army Corps of Engineers 

[Slawson 1995]. 

EXPERIMENTAL MINE AND TEST PROCEDURES 

 The explosion evaluation tests on the coal mine stopping designs were conducted at the 

NIOSH Lake Lynn Laboratory [Mattes et al. 1983; Triebsch and Sapko 1990]. Lake Lynn 

Laboratory is a multipurpose research laboratory designed to provide a modern, full-scale, 

realistic environment for conducting surface and underground research in mining health and 

safety technology. Lake Lynn Laboratory is located about 50 miles (80 km) southeast of 

Pittsburgh, near Fairchance, Fayette County, PA, and occupies a former limestone mine. It is one 

of the world’s foremost mining laboratories for conducting large-scale surface and underground 

health and safety research. 

 The underground LLEM (Figure 1) is unique in that it can simulate current U.S. coal 

mine geometries for a variety of mining scenarios, including multiple-entry room-and-pillar 

mining and longwall mining. The old limestone mine workings are shown on the left in Figure 1. 

Five new drifts (horizontal passageways in a mine) were developed to simulate the geometries of 

modern U.S. coal mines. LLEM has four parallel drifts: A, B, C, and D. D-drift is a 1,640-ft 

(500-m) long single entry that can be separated from E-drift by an explosion-proof bulkhead 

door. To simulate room-and-pillar workings, drifts A, B, and C can be used. These three drifts 

are each approximately 1,600 ft (490 m) long, with seven crosscuts at the inby end. An 

explosion-proof bulkhead door is used to separate the multiple entries from E-drift. Drifts C and 

D are connected by E-drift, a 500-ft (152-m) long entry that simulates a longwall face. Explosion 

tests can be conducted in the single-entry D-drift; the multiple-entry area of A-, B-, and C-drifts; 

or various other configurations including the longwall E-drift. The entries are about 20 ft (6 m) 

wide by about 6.5 ft (2 m) high, with cross-sectional areas of 130–140 ft2

 (12–13 m2). From 

August 1983 (when the first explosion test was conducted) to July 2008, a total of 

527 consecutively numbered explosion tests were conducted in the LLEM. 
4

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

 Figure 2 shows an expanded view of the stopping test area in the multiple-entry section 

of the LLEM. The faces, or closed ends, of A-, B-, and C-drifts are on the right in the figure. 

Most of the explosion evaluations were conducted in C-drift and the stoppings were built in the 

crosscuts between B- and C-drifts, as shown in Figure 2. Note that, in the LLEM, the first crosscut (“1” in Figure 2) is the one nearest the face. During four of the evaluations, the permanent 

stoppings were constructed in crosscut 4 (X-4)9

 at 355 ft (108 m), X-5 at 451 ft (138 m), X-6 at 

547 ft (167 m), or X-7 at 647 ft (197 m) from the face of C-drift. The crosscuts are 17–19 ft 

(5.2–5.8 m) wide by ~7.2 ft (~2.2 m) high with a cross-sectional area of about 130 ft2

 (12 m2). 

Explosion-resistant seals from a previous study were located in X-1 through X-3. The head-on 

explosion pressure evaluation in B-drift included stoppings in X-3 and X-4 between A- and 

B-drifts and between B- and C-drifts and one stopping across B-drift between X-4 and X-5. The 

evaluation of the wet-laid stoppings was conducted in A-drift as part of another explosion program with the stoppings located in X-6 and X-7 between A- and B-drifts; there were seals 

located in X-1 through X-5 between A- and B-drifts. These last two scenarios are not shown in 

Figure 2. Before each explosion test, a 60-ton pneumatically operated, track-mounted, concrete 

and steel bulkhead was positioned across E-drift to contain the explosion pressures within the 

multiple-entry area. The LLEM bulkhead door and some of the other infrastructure were 

designed to withstand explosion overpressures of up to 100 psi (690 kPa). Higher pressures 

have been recorded at areas away from these structures. 

 

 

9

The abbreviation “X” stands for “crosscut” throughout this report, e.g., “X-1” stands for “crosscut 1.” 
5

 Figure 2.—Plan view of the LLEM showing the multiple-entry area and stopping locations 

during LLEM tests #457 and #458. 

 For the LLEM explosion tests, natural gas was injected into the ignition zone. This 

natural gas is composed of ~97%–98% methane, ~1.5% ethane, and small percentages of other 

higher hydrocarbons. Sample lines within the ignition zone were used to draw gas samples to an 

infrared analyzer on the surface for continuous monitoring of the methane concentration. In addition, samples were collected in evacuated test tubes and sent to verify the analyses using gas 

chromatography. Most of the tests for these stopping failure evaluations used a ~9% methane-air 

concentration within a 10-ft (3-m) deep by 11-ft (3.4-m) wide ignition zone (~760 ft3

 (~21.5 m3)) 

contained in the C-drift face area with a clear plastic diaphragm. A few of the tests used a larger 

gas ignition zone. A fan with an explosion-proof motor housing mixed the natural gas and air 

prior to ignition. Electrically activated matches located either at the face (closed end) or outby 

the face within the gas ignition zone, depending on the explosion overpressure desired, were 

used to ignite the methane-air mixtures. In some of the tests, shelves of pulverized bituminous 

coal dust were located at a distance of 10–40 ft (3–12 m) from the face as a means to increase the 

explosion overpressures. For each of these explosion tests, the gas was ignited and the explosion 

pressure traveled out C-drift. In addition, five of the explosion tests were conducted in B-drift to 

evaluate the effect of an obstruction in the path of an oncoming pressure wave. During these 

B-drift tests, the ~6%–10% methane-air concentration was contained within a 20-ft (6-m) or 

40-ft (12-m) long section of entry located between X-2 and X-3. For the explosion tests conducted in A-drift, the length of the gas ignition zone was varied to obtain higher total explosion 

overpressures at the stopping locations, i.e., the ~10% methane-air concentration was contained 

within a 40-, 50-, or 85-ft (12-, 15-, or 26-m) long gas ignition zone (as measured from the 

closed end of A-drift) for the different tests. 

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

shown in Figures 1 and 2. Each DG station houses a strain gauge transducer to measure the 

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

dynamic in nature and is composed of two components: an omnidirectional pressure component 

(the pressure that is exerted in all directions and is measured perpendicular to the gas flow; also 

referred to by others as a “quasi-static pressure”) and a wind or velocity pressure component 

(pressure due to gas flow). The total explosion pressure is the sum of the omnidirectional 
6

pressure and the wind or velocity pressure. The transducers in the DG stations in the wall measure the omnidirectional pressure. All of the explosion pressures presented in this report are 

overpressures or gauge pressures (pressures above local atmospheric pressure) rather than 

absolute pressures. 

In the past, Nagy [1981, p. 58] referred to the omnidirectional pressure as the “static pressure” to differentiate it from the “dynamic pressure,” or velocity component. However, the omnidirectional pressure is not actually “static” as it does vary with time during the explosion. This 

terminology by Nagy had been used in previous U.S. Bureau of Mines and NIOSH publications, 

but it was confusing to many readers and will no longer be used. 

The pressure transducers of particular interest for these stopping evaluations were along 

the C-drift rib at 304, 403, 501, 598, and 757 ft (92.7, 122.8, 152.7, 182.3, and 230.7 m); along 

the B-drift rib at 257, 329, and 427 ft (78.3, 100.3, and 130.2 m); and along the A-drift rib at 550, 

649, and 807 ft (167.6, 197.8, and 246.0 m) as measured from the respective C-, B-, and A-drift 

faces. There were also pressure transducers mounted on the C-drift side of each of the stoppings 

when the explosion was initiated in C-drift, on the B-drift side of the stoppings when the explosion was initiated in B-drift, and on the A-drift side of the stoppings when the explosion was 

initiated in A-drift. These transducers faced the explosion forces traveling into the crosscuts and 

measured the total explosion pressures at the stoppings. The velocity (or wind) pressure would 

act on objects in an open entry as the explosion travels down the entry. When the velocity 

(or wind) pressure reaches a solid surface, such as a stopping across the entry or crosscut, the 

velocity would go to zero and the omnidirectional pressure at that location becomes approximately the same as the total explosion pressure. In addition, when the pressure pulse reaches an 

obstruction across the entry (such as a stopping in B-drift for one of these evaluations), it is 

reflected and the resulting total reflected pressure can be about twice the incoming pressure 

pulse value. 

Attached at the center (midheight and midwidth) of the nonexplosion side of the concrete 

block and steel panel stoppings was a linear variable differential transducer (LVDT) that measured the movement of the center of the stopping during each explosion. A photograph and 

details of the operation of the LVDT are presented by Weiss et al. [1999, pp. 5–6]. For the 

C-drift tests, the spring-loaded LVDT was mounted around a 90° bend on the B-drift rib line 

outside of the crosscut and connected to the stopping via lightweight, near zero stretch fishing 

line. This mounting system protected the expensive LVDT from flying debris from the stopping. 

For the explosions initiated in B-drift, the LVDTs were not used. For the A-drift tests, the LVDTs 

were mounted within the crosscut behind a heavy steel angle designed to protect the sensor from 

flying debris; the sensor was connected to the stopping via the fishing line. During the explosion 

tests, a high-speed, PC-based National Instruments data acquisition system collected the data 

from the various instruments at a sampling rate of 1,500 per sec. The reported data were averaged over 10 ms using a 15-point smoothing technique to filter the higher frequency data. 

STOPPING CONSTRUCTION 

Concrete Block Stoppings 

 For the first series of tests, four 6-in (15-cm) thick dry-stacked hollow-core concrete 

block stoppings were constructed in X-4 through X-7 between C- and B-drifts in the LLEM 

(Figure 2). Crosscuts 4 and 5 were about 19 ft (5.8 m) wide by 7.2 ft (2.2 m) high, and crosscuts 

6 and 7 were about 17 ft (5.2 m) wide by 7.2 ft (2.2 m) high at the positions of the stoppings. 
7

Each stopping was located approximately 5 ft (1.5 m) toward B-drift from the midpoint of the 

crosscut (approximately 23 ft (7 m) deep into the crosscut, as measured from closest C-drift rib). 

The blocks were three-core concrete blocks, with nominal dimensions of 8 in by 6 in by 16 in 

(20 cm by 15 cm by 40 cm). The nominal uniaxial compressive strength of the block material 

was 1,900 psi (13 MPa). Full block testing by Barczak and Batchler [2008] revealed a hollowcore concrete block compressive strength of less than 1,000 psi (7 MPa). There was an 8-in 

(15-cm) thick reinforced concrete floor in the crosscuts where the stoppings were installed. 

To level the floor, a small concrete foundation that tapered from 0- to 3-in (0- to 8-cm) thick as 

measured from C- to B-drift was installed along the width of each crosscut, and a small amount 

of mortar was used under the first course of block to assist in the leveling of the first course of 

block. The remaining blocks were dry-stacked (no mortar between the block joints) with staggered joints (Figure 3). A closeup view of the dry-stacked hollow-core concrete blocks is shown 

in Figure 4. Wood wedges were used to tighten each block course at the mine ribs (Figure 5). 

Wood header boards and wedges were used between the top block course and the mine roof to 

tighten the structure from both sides of the stopping (Figure 6). An approximately 0.5-in (6-mm) 

thick coating of an approved sealant (Quikrete B-Bond, product No. 1227-50) was applied to 

both sides of the stoppings, as shown in Figure 7. The application of coatings on dry-stacked 

stoppings varies widely in practice. Some mines have coated their stoppings only on the highventilation pressure side, some have fully coated the high-ventilation pressure side with only a 

perimeter coating on the other side, and other mines have fully coated both sides. 

Figure 3.—Dry-stacked hollow-core concrete block stopping construction, with staggered joints. 
8

Figure 4.—Dry-stacked hollow-core concrete blocks used in construction of the stoppings. 

 Figure 5.—Installation of wood wedges between the stopping and rib for dry-stacked 

hollow-core concrete block stopping. 
9

 Figure 6.—Installation of wood header boards and wood wedges between the stopping 

and roof for dry-stacked hollow-core concrete block stopping. 

Figure 7.—Coating the dry-stacked hollow-core concrete block stopping with sealant. 
10

 After completing the explosion test evaluation and removing the first set of dry-stacked 

hollow-core concrete block stoppings, two additional 6-in (15-cm) thick dry-stacked concrete 

block stoppings were constructed in X-4 and X-5 using solid concrete blocks, with nominal 

dimensions of 8 in by 6 in by 16 in (20 cm by 15 cm by 40 cm). Full block testing by Barczak 

and Batchler [2008] revealed a solid-concrete-block compressive strength of 1,330–1,780 psi 

(9–12 MPa). These stoppings were constructed in the same manner as the previously evaluated 

hollow-core concrete block stoppings. The solid concrete blocks were dry-stacked (no mortar 

between the block joints) with staggered joints (Figures 8–9). Wood wedges were used to tighten 

each block course at the mine ribs (Figures 9–10). Header boards were used between the top 

block course and the mine roof, and wedges were used between the header boards and mine roof 

to tighten the structure (Figures 9–10). An approximately 0.25-in (6-mm) thick coating of an 

approved sealant (Quikrete B-Bond, product No. 1227-50) was applied to both sides of the stoppings. The completed dry-stacked solid-concrete-block stopping in X-5, covered with sealant, 

is shown in Figure 11, with a pressure transducer suspended from the roof in the upper-right side 

of the photo. 

Figure 8.—Dry-stacked solid-concrete-block stopping construction with staggered joints. 
11

 Figure 9.—Wood wedges between the stopping and rib for dry-stacked 

solid-concrete-block stopping. 

Figure 10.—Wood header boards and wood wedges between the stopping and roof. 
12

 Figure 11.—Completed dry-stacked solid-concrete-block stopping in X-5 as viewed from C-drift, 

with the total explosion pressure transducer at the upper right.

 Two additional solid-concrete-block stoppings were constructed in X-6 and X-7 between 

A- and B-drifts. These stoppings were constructed in the same manner as the previously evaluated solid-concrete-block stoppings in C-drift, except these stoppings were not dry-stacked. 

As can be seen in Figure 12, a full mortar bed (wet-laid) of Type S mortar was used in all of the 

horizontal and vertical block joints, including the perimeter gaps to the mine roof, ribs, and floor. 

Wood wedges were not used during the construction of these stoppings. An approximately 

0.25-in (6-mm) thick coating of Quikrete’s B-Bond was applied to the A-drift face (highventilation pressure side) of each stopping. The high-ventilation pressure side of a stopping may 

not necessarily be the side subjected to an explosion in an actual coal mine. All of the stoppings 

discussed in this report were coated on both sides or just on the high-ventilation pressure side, 

which was then also the side subsequently subjected to an explosion within the LLEM. Stoppings coated only on the nonexplosion side were not evaluated in the LLEM. The completed 

wet-laid solid-concrete-block stopping in X-7 is shown in Figure 13.
13

Figure 12.—Wet-laid solid-concrete-block stopping construction with staggered joints. 

 Figure 13.—Completed 6-in (15-cm) thick, wet-laid solid-concrete-block stopping in X-7, as viewed 

from A-drift. 
14

Steel Panel Stoppings 

Jack Kennedy Steel Stoppings, manufactured by Jack Kennedy Metal Products & Buildings, Inc., (hereinafter referred to as “steel panel stoppings”), were constructed within the LLEM 

per the manufacturer’s instruction guide.10 Both of the steel panel stoppings were installed, with 

assistance from NIOSH Lake Lynn staff and by personnel from Jack Kennedy Metal Products & 

Buildings, Inc., and its distributor, Ken-Air, Inc. These stoppings consisted of a series of 12-in 

(30-cm) wide by 72-in (183-cm) high by 2-in (5-cm) thick vertical telescoping steel panels 

(formed from 20-gauge galvanized steel sheeting) that could be lengthened or shortened to 

accommodate roof heights between 6 and 10 ft (1.8 and 3 m). 

 The stoppings were constructed on a small concrete foundation that tapered from 0- to 

3-in (0- to 8-cm) thick along the width of X-6 and X-7 for leveling purposes. Each stopping was 

located approximately 5 ft (1.5 m) toward B-drift from the midpoint of the crosscut (or approximately 23 ft (7 m) deep into the crosscut, as measured from closest C-drift rib). Since the LLEM 

installation required the use of panel heights in excess of 5 ft (1.5 m) (MP-61020 kit, which can 

accommodate entry heights from 6 to 10 ft (1.8 to 3 m)), three rows of steel angle bars, extending horizontally from one rib to the other, were required, in accordance with the manufacturer’s 

instruction guide (Figure 14). The angle bars were on the back or B-drift side of the steel panel 

stopping. The 1.5-in (3.8-cm) by 1.5-in (3.8-cm) by 12-ft (3.7-m) long hot-dipped galvanized 

steel angle bars (0.125 in (3 mm) thick) were positioned into small holes (approximately 2-in 

(5-cm) deep) that were cut into each rib (Figure 15). Two 12-ft (3.7-m) long lengths of angle 

were required per row to span the approximately 20-ft (6-m) wide crosscuts; the ~4-ft (~1.2-m) 

length of extra angle was merely overlapped into the other piece and taped in place. The angle 

bars were located at 22, 39, and 68 in (56, 99, and 173 cm) from the mine floor. As shown in 

Figure 16, the open end of the horizontal steel angles faced C-drift so as to rest against the channels of each vertical panel (on the back or open side of the panel). The front or smooth side of 

the panel (the closed side of the panel facing away from the horizontal rib-to-rib angles) was 

designed to face the entry with the highest ventilation pressure, i.e., toward C-drift for the LLEM 

evaluations. 

 

 10Contact the manufacturer for additional information on construction techniques and/or to obtain a detailed 

instruction guide. 
15

 Figure 14.—Horizontal steel angles for attaching the steel stopping panels. 

The photo also shows the installed center panel. 

Figure 15.—Three horizontal steel angles inset into rib. 
16

Figure 16.—Horizontal steel angles (with open sides facing panels on left), as viewed from B-drift. 

 To start the steel panel installation, the first panel was installed near the center of the 

crosscut (Figure 14). As part of the installation, a head seal (polystyrene foam) was manually 

inserted at the top and bottom of each panel to provide a better seal with the roof and floor 

(Figures 17–18). For coal mine applications, the head seal is generally only inserted at the top of 

the panel. However, for the LLEM application, a head seal was also used at the bottom of the 

panel to provide a better seal to the concrete mine floor. Then, a specially designed installation 

jack was positioned within the panel’s top and bottom grooves and used to exert a roof-to-floor 

pressure until the jack started to slightly bow (per the manufacturer’s instruction guide) to 

temporarily hold the stopping panel in place (similar to that shown in Figure 18). A wire twist 

clamp (Figure 19) was fastened around the horizontal rib-to-rib angle, inserted into the inside 

flanges of the panel, and then tightened. Six clamps were used on the panel to attach it to the 

three horizontal angles. The installation jack was then removed from the panel. The steel angles 

and clamps maintain compression and keep the panels aligned. 

 After installing the center panel, a second panel was installed against the outby rib, 

jacked into place, and secured with twist clamps. The panels were alternated such that the intersection of the telescoping panel sections offset each other. This was accomplished by turning 

every other panel upside down. The panel installation process was repeated until enough panels 

were added to reach the center panel, at which point the clamps on the center panel were 

loosened and that panel was slid over to the adjacent panel. Additional panels continued to be 

added to the point of being within 3–4 ft (~1 m) of the opposite rib. At that point, a panel was 

installed against the (opposite) rib and additional panels were then added back toward the other 

previously installed panels until the gap was ≤1 ft (≤30 cm). An overlap panel (indicated by an 

“X” in Figure 20) was used to cover this and other gaps between panels, and side extensions 

were used to cover any large gaps between the panels and the mine rib (Figure 21). 
17

 Figure 17.—Polystyrene foam head seal used to provide enhanced closure between metal panel 

and roof, as viewed from the C-drift side. 

Figure 18.—Temporary jack used to exert roof-to-floor pressure on the metal panel during installation. 
18

Figure 19.—Metal twist clamp used to secure open side of panel to the horizontal angle. 

 Figure 20.—Overlap panel (indicated by an “X”) used to close gap between rib panel and second 

panel, as viewed from the front or C-drift side. 
19

Figure 21.—Side extensions used to fill gaps between rib panel and rib, viewed from the back or B-drift side. 

 The stopping was sealed with a polyurethane VERSI-FOAM system (manufactured by 

RHH Foam Systems, Inc., New Berlin, WI, and distributed by Ken-Air, Inc., as the MP-567 

sealant foam pack). The sealant was applied to the perimeter on both sides of the stopping and 

between all of the vertical panel joints on the smooth, or closed, panel side, which is the highventilation pressure side in an actual coal mine installation (Figure 22). All of the steel panel 

stoppings were constructed such that the high-ventilation pressure side of each stopping was on 

the C-drift side, which was the side that would be directly impacted by the explosion forces. 

Figure 23 shows the nearly completed steel panel stopping in X-6 as shown from the C-drift side 

(explosion or high-pressure side). Figure 24 shows the same stopping from the B-drift side. 
20

Figure 22.—Polyurethane sealant used on perimeter and vertical panel joints. 

Figure 23.—Nearly completed steel panel stopping in X-6 showing closed, smooth panel sides facing C-drift. 
21

 Figure 24.—Nearly completed steel panel stopping in X-6 showing the open panel side attached to the 

horizontal rib-to-rib angles on the B-drift side. 

Australian Woven Cloth Stoppings11

 Two Flexi-Stop stopping designs were constructed in X-6 and X-7 between C- and 

B-drifts in the LLEM after completing the explosion evaluations of the steel panel stoppings. 

(There were already seals in X-1 through X-3 and concrete block stoppings in X-4 and X-5.) 

The stopping in X-6 was located approximately 6 ft (1.8 m) toward C-drift as measured from the 

center of the crosscut or approximately 15 ft (4.6 m) into the crosscut from the closest C-drift rib. 

The X-7 stopping was approximately 8 ft (2.4 m) toward C-drift from the center or approximately 12 ft (3.7 m) into the crosscut. Crosscuts 6 and 7 were about 17 ft (5.2 m) wide and 7.2 ft 

(2.2 m) high. This report will only briefly summarize the basic construction materials and techniques; detailed information on the stopping construction can be obtained from representatives of 

Minova Australia. 

 The stopping designs consisted of a woven high-strength polymeric fiber coated with a 

fire-resistant product. Note that this Flexi-Stop stopping design as constructed and evaluated 

within the LLEM may not meet the fire-resistant qualities required for use in U.S. mines. The 

Flexi-Stop cloth was precut to the appropriate length and width based on the area where it was to 

be installed. A 0.8-in (2-cm) diameter galvanized steel pipe (rigid conduit with a ~0.1-in 

 

11The woven cloth stopping evaluations were funded by Minova Australia. 
22

(~0.25-cm) wall thickness) the length of the crosscut width was then installed through a heavily 

reinforced sewn sleeve along the top and bottom sections of the cloth (Figure 25). The woven 

cloth, with pipes installed, was then attached to each of the two box steel sections by means of a 

slot provided along the entire length of steel on one side of each box section. This resulted in the 

sleeve-pipe curtain assembly being inside the steel box section (Figure 26). The slot on the box 

section was large enough to allow the passage of the woven cloth but much smaller than the 

diameter of the pipe within the woven cloth sleeve, thereby providing a means to anchor the 

woven cloth to the roof and floor. The 2.5-in by 2.5-in (6.4-cm by 6.4-cm) steel box section used 

in X-6 had a wall thickness of 0.25 in (6 mm) and a slot width of approximately 0.5 in (1.3 cm). 

The 2-in by 2-in (5-cm by 5-cm) steel box section used in X-7 had a wall thickness of 0.1875 in 

(5 mm) and a slot width of about 0.3 in (8 mm). The assembly of these components was completed within the LLEM. Six steel ~3-in (~7.5-cm) long rings (~1.5-in (~3.8-cm) I.D. pipe for the 

X-6 frame and ~1.6-in (~4.1-cm) I.D. pipe for the X-7 frame), welded to one side of each steel 

box section, provided a means to anchor the box section to the mine roof and floor through the 

use of roof bolts. The steel rings that are attached to the box frame can be seen in Figure 27. The 

top and bottom box sections, with the woven cloth attached, were then bolted to the mine roof 

and floor using 1-in (2.5-cm) diameter by 26-in (66-cm) long resin bolts embedded 22 in (56 cm) 

into 1.375-in (3.5-cm) diameter drill holes (Figure 27). The woven cloth was intentionally oversized so as not to create a pretensioned surface. The woven cloth was then anchored to each rib 

by wedging the cloth (using wood wedges) into a 0.75-in (1.9-cm) wide by 8-in (20-cm) deep 

slot in each rib that extended from roof to floor (Figure 28). A small quantity of shotcrete was 

applied by trowel to a few of the larger gaps between the top box section in each crosscut and the 

roof. Minova’s Tekflex sealant was then applied to the entire stopping perimeter from the C-drift 

side of each stopping (Figure 29). Following the first explosion test, 1-in (2.5-cm) diameter by 

16-in (40-cm) long resin bolts were installed through the woven cloth from the B-drift side and 

into each rib (embedded 12 in (30 cm)) on the C-drift side of the rib slots. Standard steel 6-in by 

6-in by 0.25-in (15-cm by 15-cm by 0.64-cm) thick roof bolt plates were used in conjunction 

with the bolts. An oversized piece of conveyor belt (R-11) was used under the bolt plate to 

protect the woven cloth from tearing. Five equally spaced bolts were used on each rib for the 

X-6 stopping and four bolts on each rib for the X-7 stopping. Figure 30 shows the installed rib 

bolts as seen from the B-drift side (nonexplosion side) of the X-6 stopping. Figure 31 shows the 

completed X-6 stopping as seen from the C-drift or explosion side, with the pressure transducer 

suspended from the roof in the center of the photo. 
23

Figure 25.—Inserting pipe into top sleeve of woven cloth. 

Figure 26.—Inserting pipe/sleeve into top box section. 
24

Figure 27.—Anchoring top box section to the mine roof.

Figure 28.—Wedging woven cloth into mine rib. 
25

Figure 29.—Sealant along perimeter of the stopping, viewed from C-drift. 

Figure 30.—Rib bolts installed in the X-6 stopping, viewed from B-drift. 
26

Figure 31.—Completed woven cloth stopping design in X-6, viewed from the explosion or C-drift side.

EXPLOSION TEST RESULTS 

Dry-Stacked Hollow-Core Concrete Block Stoppings in Crosscuts 

The four dry-stacked hollow-core concrete block stoppings were evaluated in a series of 

LLEM explosion tests (#427–#430 and #432–#434). A summary of these LLEM explosion tests 

is presented in Table 1. The first two columns in the table list the test number and date. The third 

column describes the ignition zone, where “C0-10 gas” means a methane-air zone in C-drift from 

0 to 10 ft from the face. The peak explosion pressure generally occurs near the face of C-drift; 

the pressures are lower at the positions of the stoppings further from the face. A complete listing 

of the B- and C-drift omnidirectional wall pressures and the stopping pressures for each test is 

given in Tables A-1 through A-7 in the appendix. The stopping pressure is the total explosion 

pressure, which is also the omnidirectional pressure until such time as the stopping would fail. 

Note that the pressure results were averaged over 10 ms (15-point smoothing). Some of these 

tests were conducted for purposes other than the explosion evaluation of the stoppings. This is 

why some tests had lower explosion pressures than a preceding test. 
27

Table 1.—Evaluations of mine stoppings during the LLEM explosion tests 

Peak explosion 

wall pressure4 Test # Date Ignition zone Match 

location psi kPa 

Result 

427 Feb. 12, 2003 C0-10 gas C10 1.2 9 No damage. 

428 Feb. 13, 2003 C0-10 gas Face 5.1 35 X-4 and X-5 hollow block stoppings 

 destroyed. 

429 Feb. 26, 2003 C0-10 gas1 C103 3.7 26 Little damage to X-6 and X-7 hollow 

 block stoppings. 

430 Mar. 6, 2003 C0-10 gas1

 Face3 6.2 43 Some block damage to X-6 hollow 

 block stopping. 

432 Mar. 13, 2003 C0-10 gas1

 C103 3.6 25 Additional block damage to X-6 hollow 

 block stopping. 

433 Mar. 17, 2003 C0-10 gas1

 Face3 8.9 61 X-6 hollow block stopping destroyed. 

434 Mar. 25, 2003 C0-10 gas2

 Face3 7.6 52 X-7 hollow block stopping destroyed. 

457 Oct. 27, 2003 C0-10 gas C10 1.6 11 No damage. 

458 Oct. 28, 2003 C0-10 gas C6 1.9 13 X-6 and X-7 steel panel stoppings 

 failed. 

459 Nov. 13, 2003 C0-10 gas C3 4.3 30 Some cracking on X-4 and X-5 solid 

 block stoppings. 

460 Nov. 18, 2003 C0-10 gas Face3

 6.3 43 Tearing of Australian stoppings; more 

 cracking on solid block stoppings with 

 some block displacement. 

461 Nov. 20, 2003 C0-27 gas Face NA NA No additional damage. 

462 Nov. 20, 2003 C0-27 gas Face3

 NA NA Solid block stoppings destroyed in X-4, 

 X-6, and X-7; additional cracking/ 

 block displacement on X-5 solid block 

 stopping. 

463 Nov. 25, 2003 C0-47 gas Face ~20 ~138 X-5 solid block stopping destroyed. 

491 May 10, 2005 B202-240 gas B221 5.5 38 Hollow block stoppings destroyed. 

494 June 9, 2005 B240-260 gas B250 0.5 3 No damage. 

495 June 10, 2005 B240-260 gas B250 1.2 8 No damage. 

496 June 13, 2005 B240-260 gas B250 3.5 24 Hairline cracks on X-4 and B446 

 hollow block stoppings. 

497 June 15, 2005 B202-240 gas B221 5.1 35 X-4 and B446 hollow block stoppings 

 destroyed; little to no damage to X-3 

 hollow block stoppings. 

510 Dec. 11, 2007 A0-40 gas Face 14.6 101 No damage. 

512 Jan. 9, 2008 A0-40 gas 

A40-340 dust 

Face 13.2 91 No damage. 

515 Jan. 28, 2008 A0-50 gas Face 14.0 96 No damage. 

519 Mar. 3, 2008 A0-85 gas Face 24.9 172 Hairline cracks on X-6 wet-laid solid 

 block stopping; X-7 wet-laid solid 

 block stopping destroyed. 

 NA Not available. 

 1

Pulverized coal dust on shelving from C10-40 to result in a loading of 200 g/m3. 

 2

Pulverized coal dust on shelving from C10-40 (200 g/m3 concentration) and a 200 g/m3 coal loading with 65% added rock dust 

from C40-310. 

 3

Ignition zone fan remained on during test to increase turbulence and peak overpressures. 

 4

Peak omnidirectional pressure near the face; the stoppings were generally subjected to lower pressures. 

Test #427 

 During test #427, there was little or no observable damage to the dry-stacked hollow-core 

concrete block stoppings, as listed in the last column of Table 1. The total explosion pressures at 

the stoppings in X-4 and X-7 were 0.74 psi (5.1 kPa) and 0.73 psi (5.0 kPa), respectively. The 

pressure transducers in front of the X-5 and X-6 stoppings did not work properly for this test, but 

the pressures there would have been similar to those at X-4 and X-7. The pressures in B-drift 

behind the stoppings were approximately zero (see Table A-1). There was no discernable movement on the LVDT sensor at the X-4 through X-6 stoppings, and the X-7 stopping had a permanent displacement of <0.05 in (<1.3 mm). 
28

Test #428 

 During test #428, the dry-stacked hollow-core concrete block stoppings in X-4 and X-5 

were destroyed by the explosion, as shown in Figure 32. The dry-stacked hollow-core concrete 

block stoppings in X-6 and X-7 showed little damage from this explosion. The left side of 

Figure 32 shows a plan view of the LLEM, with debris shown to the left of the original position 

of the stoppings in X-4 and X-5. The right side of the figure shows expanded cross-sectional 

views of the blocks remaining from the stoppings destroyed in X-4 and X-5. The LVDT 

displacement, the pressure-time integrals, and the pressures versus time at the stopping in X-4 

and at nearby wall transducers during LLEM test #428 are shown in Figure 33. Graph A at the 

top of Figure 33 is the trace from an LVDT, which measures the displacement of the block near 

the center of the stopping. It shows that the stopping moved more than 3 in (8 cm) (maximum 

displacement that can be measured by the LVDT) as the stopping was destroyed. Graph B of 

Figure 33 shows the pressure-time integrals of the data from the inby (C-drift, 304 ft (93 m)) and 

outby (C-drift, 403 ft (123 m)) wall transducers, as well as the X-4C (355 ft (108 m)) transducer 

that is mounted from the mine roof at the midwidth of the crosscut just in front of the X-4 stopping location. Graph C of Figure 33 shows the total explosion pressure trace at the X-4 transducer, along with the pressures at the wall inby and outby the stopping location. The pressure 

pulse reaches the 304-ft (93-m) position first, then the stopping location, and finally the 403-ft 

(123-m) position. The maximum total explosion pressure from the X-4C transducer was 5.2 psi 

(36 kPa). The B-drift pressure behind the stopping was near zero until after the stopping was 

destroyed. Note that the total explosion pressure at the stopping was higher than the interpolated 

pressure (3.6 psi (25 kPa)) from the inby and outby wall pressure transducers. The inby and 

outby wall pressure transducers do not measure the total explosion pressures. 

In previous literature [Weiss et al. 1999, 2002, 2006], the interpolated wall pressure 

(listed as the “static” pressure at the seal or stopping) was reported along with the “total pressure” at the seal or stopping. However, recent research has shown that this interpolated “static” 

wall pressure does not show the true explosion pressure exerted on the seal. The “total” pressure 

measured directly at the seal is higher than the interpolated wall pressure. Since the interpolated 

wall pressure is not the same as the actual explosion pressure at the seal or stopping location, 

it will no longer be used to describe the pressure at the seal or stopping. These different pressures 

are also discussed in the earlier “Experimental Mine and Test Procedures” section. 

Figure 34 shows the debris from the destroyed X-4 stopping. Figure 35 shows a plan 

view map of the debris pattern, with black squares representing whole or partial blocks and the 

smaller markings representing smaller pieces of blocks. The original position of the stopping is 

shown by the double horizontal line in the crosscut near the bottom of the figure. The debris 

traveled into and beyond the intersection of X-4 and B-drift.
29

Figure 32.—Plan view of the multiple-entry area of LLEM showing effects of explosion test #428. The explosion destroyed the dry-stacked hollow-core concrete block stoppings in X-4 and X-5 and left the stoppings in 

X-6 and X-7 intact. The right part of the figure shows expanded cross-sectional views of the blocks remaining 

in X-4 and X-5, as seen from C-drift. 
30

 Figure 33.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at dry-stacked hollow-core concrete block stopping in X-4 during LLEM test #428. 
31

 Figure 34.—Debris from dry-stacked hollow-core concrete block stopping in X-4 

after LLEM test #428, viewed from C-drift. 

 Figure 35.—Expanded map of debris from the X-4 dry-stacked hollow-core concrete block 

stopping after LLEM test #428. Black squares represent whole or partial blocks, and smaller 

markings represent pieces of blocks. 
32

 Figure 36 shows similar LVDT displacement, pressure-time integral, and pressure versus 

time data at and near the stopping in X-5, which was also destroyed during explosion test #428. 

There was no total explosion pressure measurement at X-5, because that transducer did not work 

properly during the test. The interpolated omnidirectional pressure from the wall-mounted DG 

panel sensors inby and outby the stopping location was 3.4 psi (23 kPa). The total explosion 

pressure at the X-5 stopping likely would have been higher, based on the data from X-4. The 

LVDT data showed that the X-5 stopping moved more than 3 in (8 cm) as the stopping was 

destroyed. Figure 37 shows the debris from the destroyed stopping in X-5. Figure 38 shows a 

plan view map of the debris from the X-5 stopping, with black squares representing whole or 

partial blocks and the smaller markings representing smaller pieces of blocks. The debris 

traveled into the intersection of X-5 and B-drift. 

 Figure 36.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the dry-stacked hollow-core concrete block stopping in X-5 during LLEM test #428. 
33

 Figure 37.—Debris from X-5 dry-stacked hollow-core concrete block stopping after 

LLEM test #428, viewed from C-drift. 

 Figure 38.—Expanded map of debris from the X-5 dry-stacked hollow-core 

concrete block stopping after LLEM test #428. Black squares represent whole 

or partial blocks, and smaller markings represent pieces of blocks. 
34

Remnants of the X-4 stopping were still attached to much of the floor, and a few blocks 

remained at the roof/rib interfaces. Mortar used at the floor to level the first course of block may 

have increased the overall strength of the stoppings. For the X-5 stopping, large sections of the 

original stopping were still attached along the entire interface of both ribs (Figure 32). There was 

clear evidence of block shearing along the edges of these still intact areas of the stoppings, indicating failure was mainly due to excessive forces acting on the whole wall. Figure 39 shows the 

inby crosscut rib remnants (viewed from B-drift) of the X-5 dry-stacked hollow-core concrete 

block stopping where block shearing occurred. This block shearing is a clear indication of roofto-floor arching action. 

 Figure 39.—Remnants of the dry-stacked hollow-core concrete block stopping in X-5 after LLEM test #428. 

The block shearing indicates roof-to-floor arching action. 

Figure 40 shows the LVDT displacement, pressure-time integral, and pressure versus 

time data at and near the dry-stacked hollow-core concrete block stopping in X-6 that withstood 

the explosion pressures generated during test #428. There was no total explosion pressure 

measurement at X-6 because that transducer did not work properly during the test. There was 

little damage to the X-6 stopping, as shown in Figure 41. The interpolated omnidirectional pressure from the wall-mounted DG panel sensors inby and outby the stopping in X-6 as shown in 

graph C of Figure 40 was 3.2 psi (22 kPa). The total explosion pressure at the X-6 stopping 

likely would have been higher, based on the data from X-4 (Figure 33). The LVDT data 

(Figure 40) showed almost no movement of the stopping. 
35

Similarly, Figure 42 shows the LVDT displacement, pressure-time integral, and pressure 

versus time data at and near the dry-stacked hollow-core concrete block stopping in X-7. This 

stopping survived the test #428 explosion, and the LVDT showed a movement of less than 0.2 in 

(5 mm). The total explosion pressure was 3.4 psi (23 kPa). The interpolated omnidirectional 

pressure from the wall-mounted DG panel sensors inby and outby the stopping was lower 

(2.9 psi (20 kPa)). 

 

 Figure 40.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the dry-stacked hollow-core concrete block stopping in X-6 during LLEM test #428. 
36

 Figure 41.—Dry-stacked hollow-core concrete block stopping in X-6 remained intact 

after LLEM test #428. Chalk highlighted the cracks in the surface coating material.

 Figure 42.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the dry-stacked hollow-core concrete block stopping in X-7 during LLEM test #428. 
37

A summary of the pressure data at the dry-stacked hollow-core concrete block stopping 

positions is shown in Figure 43 and Table 2. The peak omnidirectional wall pressures in C-drift 

at the various DG panel positions are shown in Figure 43 as a function of distance from the face. 

Note that the omnidirectional wall pressures decrease from about 5 psi (35 kPa) near the face to 

slightly less than 3 psi (21 kPa) at 757 ft (231 m) from the face. At the top of Figure 43 is a schematic showing the locations of the four stoppings in X-4, X-5, X-6, and X-7 at distances of 355, 

451, 547, and 647 ft (108, 138, 167, and 197 m) from the face, respectively. The B-drift pressures are the maximum values up until 0.1 sec after peak pressure in C-drift at the same distance 

from the face. (The pressures in B-drift were somewhat higher at later times due to the pressures 

from the destroyed stoppings.) The total explosion pressures were only available at the X-4 and 

X-7 stoppings. The pressure-time integrals in Table 2 are the average values up until the pressure 

first goes negative; these do not include any contributions from later secondary peaks (Figures 33 

and 42). Because the pressure transducers at the stoppings in X-5 and X-6 did not work properly 

during the test, there are no data for these stoppings in Table 2. In summary, this type of drystacked hollow-core concrete block stopping, as constructed in the LLEM, survived a total 

explosion pressure of 3.4 psi (23 kPa) and was destroyed by a total explosion pressure of 5.2 psi 

(36 kPa) during this evaluation. If total explosion pressure data had been available for the X-5 

and X-6 stoppings, the known range of pressures from survival to destruction would probably 

have been better defined. 

0

1

2

3

4

5

6

7

8

9

0 100 200 300 400 500 600 700 800

Distance from face, ft

Explosion pressure, psi

0

1

2

3

4

5

6

7

8

9

 total pressure at stopping

 C-drift omnidirectional wall pressure

 B-drift omnidirectional wall pressure

<-------------------stoppings------------------>

 Figure 43.—Pressures at walls (ribs) and at dry-stacked hollow-core concrete block stopping locations 

during LLEM test #428. 
38

Table 2.—Peak total explosion pressure data at dry-stacked hollow-core 

concrete block stoppings for test #428 in C-drift 

Distance Peak total explosion 

pressure Pressure-time integral Location 

ft m psi kPa psi-s kPa-s 

Crosscut 4 355 108 5.2 36 0.51 3.5 

Crosscut 5 451 138 NA NA NA NA 

Crosscut 6 547 167 NA NA NA NA 

Crosscut 7 647 197 3.4 23 0.48 3.3 

 NA Not available (pressure transducers did not work properly during the test). 

Test #429 

During test #429, the explosion pressures were lower. All of the pressure transducers at 

the stopping locations worked properly for this test. The total explosion pressure was ~1.2 psi 

(~8 kPa) at the X-6 dry-stacked hollow-core concrete block stopping. The total explosion pressure at the X-7 stopping was ~1.0 psi (~7 kPa). The LVDTs showed movements of less than 

0.2 in (4 mm). There was little observable damage to these two remaining stoppings during 

test #429. 

The LVDT data for the X-6 and X-7 stoppings were questionable. The signals may have 

been associated with the explosion pressures coming through the open inby crosscuts (X-4 and 

X-5) and then moving the fishing lines that were strung between the X-6 and X-7 stoppings and 

the sensors in B-drift. 

Test #430 

Although the pressure near the face was higher for test #430 than for test #428 (Table 1), 

the pressures at the stoppings were not any higher because of the venting through the open X-4 

and X-5. The total explosion pressure was 3.8 psi (26 kPa) at the X-6 stopping and 2.2 psi 

(15 kPa) at the X-7 stopping. During this explosion, about three blocks were knocked out from 

the X-6 stopping and other blocks were damaged. Expanded drawings of the damage to the X-6 

stopping, as viewed from both sides, are shown in Figure 44. Figures 45–46 show the damage to 

the X-6 stopping, as viewed from B-drift. Figure 47 shows the damage to the X-6 stopping, as 

viewed from C-drift. The damage to the X-6 stopping was due mainly to the shearing of the 

block on the center sections of the first and second block courses, which resulted from the arching of the stopping wall. As shown in Figure 48, there was little observable damage to the stopping in X-7. 

Test #432 

During test #432, the explosion pressures were lower than those for test #430. The total 

explosion pressure was ~1.7 psi (~12 kPa) at the X-6 stopping and ~1.2 psi (~9 kPa) at the X-7 

stopping. During this explosion, an additional couple of blocks were knocked out from the X-6 

stopping. There was little observable damage to the X-7 stopping. By this time, the two remaining dry-stacked hollow-core concrete block stoppings in X-6 and X-7 had been subjected to 

multiple explosions and, to some extent, had been damaged and/or weakened. 
39

Figure 44.—Expanded cross-sectional views of the blocks remaining in X-6 after test #430. 
40

 Figure 45.—Crosscut 6 dry-stacked hollow-core concrete block stopping viewed from B-drift side after 

LLEM test #430, showing blocks dislodged by explosion. 

 Figure 46.—Closeup of B-drift side of X-6 dry-stacked hollow-core concrete block stopping after test #430, 

showing dislodged and damaged blocks. This is clear evidence of roof-to-floor arching action. 
41

 Figure 47.—Closeup of C-drift side X-6 dry-stacked hollow-core concrete block stopping after test #430, 

showing missing and damaged blocks. 

 Figure 48.—The dry-stacked hollow-core concrete block stopping in X-7 remained intact after LLEM 

test #430. 
42

Test #433 

During test #433, the total explosion pressure was ~3.6 psi (~25 kPa) at the X-6 stopping, 

and this stopping was mostly destroyed (see Figures 49–51). Only about 5–6 ft (1.5–1.8 m) of 

the inby part of the X-6 stopping remained after the explosion, as shown in Figures 49 and 51. 

Also shown in Figures 50–51 is the pressure transducer that was suspended from the roof in front 

of the stopping location. A plan view map of the debris from the X-6 stopping is shown in 

Figure 52. At the X-7 stopping, the total explosion pressure was ~2.8 psi (~19 kPa). There was 

one block that was partially dislodged in the X-7 stopping, and several other blocks had broken 

faces. Figure 53 shows the damage to the C-drift side of the X-7 stopping. Figure 54 shows an 

overview of the C-drift side of the X-7 stopping after test #433. There is some damage to the 

blocks at the top of the stopping just to the right of the pressure transducer. This is shown in 

more detail in Figure 55. Figure 56 shows one block that was almost dislodged from the X-7 

stopping, as noted in the Figure 53 drawing. This block movement is attributed mainly to a failure of the coating. 

Figure 49.—Expanded cross-sectional view of the blocks remaining in X-6 after test #433.
43

 Figure 50.—Debris from X-6 dry-stacked hollow-core concrete block stopping after 

LLEM test #433, viewed from C-drift. 

 Figure 51.—Part of the inby side of X-6 dry-stacked hollow-core concrete block 

stopping remaining after LLEM test #433, viewed from C-drift. 
44

 Figure 52.—Expanded map of debris from the X-6 dry-stacked hollow-core 

concrete block stopping after LLEM test #433. Black squares represent whole 

or partial blocks, and smaller markings represent pieces of blocks. 

 Figure 53.—Expanded cross-sectional view of the blocks remaining in X-7 after 

explosion test #433, as seen from C-drift side. 
45

 Figure 54.—Condition of X-7 dry-stacked hollow-core concrete block stopping after explosion test #433, 

viewed from C-drift side. 

 Figure 55.—Expanded view of top part of X-7 dry-stacked hollow-core concrete block stopping after 

explosion test #433, showing damaged blocks. 
46

 Figure 56.—Expanded view of hollow-core concrete block that is almost dislodged from X-7 dry-stacked 

stopping after explosion test #433. 

Test #434 

All of the previous LLEM explosion tests (#429–#430, #432–#433) had a small methaneair zone, plus a short zone of coal dust. Test #434 had a long zone (40–310 ft (12–94 m)) of 

35% bituminous coal dust and 65% limestone rock dust, and the explosion flame traveled to 

~770 ft (~235 m). Although the total explosion pressure at the one remaining dry-stacked 

hollow-core concrete block stopping in X-7 was only ~2.3 psi (~16 kPa), a large section of the 

X-7 stopping was knocked out during the explosion. Damage from previous explosion tests 

likely weakened the X-7 stopping, resulting in failure at a lower-than-expected total explosion 

pressure. The pressure-time integrals are much larger for the dust explosion test (3.0 psi-s 

(21 kPa-s)) compared to the previous gas explosion tests (0.48-0.66 psi-s (3.3–4.6 kPa-s)) at this 

stopping location. Figure 57 shows the plan view of the LLEM multiple-entry area and crosssectional drawings of the remaining blocks left from the stoppings in X-6 and X-7. Figure 58 

shows additional blocks partially dislodged from the X-6 stopping. Figures 59 and 60 show the 

B- and C-drift sides, respectively, of the X-7 stopping after test #434. There was much less 

debris on the C-drift side of the stopping compared to the B-drift side, and the C-drift debris was 

located very near the stopping. Figure 61 shows a map of the debris from the X-7 stopping. 

Figures 59–61 show there was debris from the X-7 stopping on both the B- and C-drift sides. 
47

Figure 57.—Effects of explosion test #434 on the dry-stacked hollow-core concrete block stoppings, with 

expanded cross-sectional views of the blocks remaining in X-6 and X-7. 
48

 Figure 58.—Additional blocks partially dislodged from the right side of X-6 dry-stacked hollow-core 

concrete block stopping after test #434, viewed from C-drift. 

 Figure 59.—Crosscut 7 dry-stacked hollow-core concrete block stopping viewed from B-drift 

after LLEM test #434. 
49

 Figure 60.—Crosscut 7 dry-stacked hollow-core concrete block stopping viewed from C-drift 

after LLEM test #434. 

 Figure 61.—Map of debris from the X-7 dry-stacked hollow-core concrete block 

stopping after LLEM test #434. Black squares represent whole or partial blocks, 

and smaller markings represent pieces of blocks. 
50

Steel Panel Stoppings in Crosscuts 

The two steel panel stoppings in X-6 and X-7 were evaluated during a series of two 

LLEM explosion tests (#457–#458). A summary of these LLEM explosion tests is presented in 

Table 1. A complete listing of the B- and C-drift omnidirectional wall pressures and the stopping 

pressures for each test is given in Tables A-8 and A-9 in the appendix. 

Test #457 

During test #457, there was little or no observable damage to either of the steel panel 

stoppings. The total explosion pressure was ~0.8 psi (~5.6 kPa) at the X-6 steel panel stopping 

and ~0.8 psi (~5.2 kPa) at the X-7 stopping. The pressures in B-drift behind the stoppings were 

negligible. The LVDT data showed ~0.4-in (~1-cm) maximum displacement for each of the two 

steel panel stoppings, but the stoppings returned close to their original positions after the 

explosion. 

Test #458 

During test #458, the steel panel stoppings in X-6 and X-7 failed during the explosion. 

The LVDT displacement, pressure-time integrals, and pressures versus time associated with the 

steel panel stopping in X-6 during test #458 are shown in Figure 62. The total explosion pressure 

measured with the transducer in front of the steel panel stopping is listed as “X-6C.” The total 

explosion pressure measured at X-6 was 1.3 psi (9 kPa). The B-drift pressure behind the stopping 

in X-6 was near zero until after the stopping failed. At the top of Figure 62 in graph A is the trace 

from an LVDT showing that the stopping moved over 3 in (8 cm) and failed. Graph B of Figure 

62 shows the pressure-time integrals at the position of the X-6 stopping. The reported pressuretime integral data in Table A-9 are the values up until the pressure first goes negative; they do 

not include any contributions from later secondary peaks. The debris from the failed X-6 steel 

panel stopping is shown in Figures 63–64. The three horizontal steel angles that were inset into 

the X-6 ribs on the B-drift side of the stopping deformed and pulled out of the shallow rib insets 

(2 in (5 cm) deep) as the C-drift explosion pressure was exerted on the stopping. This deformation of the steel angles can be seen in Figure 63. The stopping in X-6 was displaced from its 

original position as a unit, with only a few detached panels. 

 Similar pressure data were collected for the steel panel stopping in X-7. Figure 65 shows 

the LVDT displacement, pressure-time integral, and pressure versus time data for this stopping. 

The total explosion pressure at the stopping in X-7 as shown in graph C of Figure 65 was 1.3 psi 

(9 kPa). The LVDT also showed over 3 in (8 cm) of movement as the stopping failed (graph A of 

Figure 65). Figures 66–67 show the postexplosion condition of the X-7 steel panel stopping. 

After the test, one side of the X-7 stopping was still partially attached to the outby rib, but the 

remainder of the stopping was on the floor. The three horizontal steel angles that were inset into 

the X-7 inby rib deformed and pulled out of the rib insets as the explosion pressure was exerted 

on the stopping. 

In summary, this particular type of steel panel stopping as constructed in the LLEM survived a total explosion pressure of ~0.8 psi (~5.5 kPa) and failed at a total explosion pressure of 

1.3 psi (9 kPa). The primary mode of failure for this steel panel stopping may be more related to 

the strength and deformation of the horizontal steel angles behind the stoppings than the failure 
51

of the steel panels. The method of failure indicates that the horizontal steel angles contribute to 

the integrity of the stopping. If the horizontal steel angle had been stronger and/or inset deeper 

into the crosscut ribs, the steel panel stoppings may have resisted higher explosion overpressures. 

 Figure 62.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the steel panel stopping in X-6 during LLEM test #458. 
52

Figure 63.—Debris from steel panel stopping in X-6 after LLEM test #458, viewed from C-drift. 

Figure 64.—Map of debris from the X-6 steel panel stopping after LLEM test #458. 
53

 Figure 65.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the steel panel stopping in X-7 during LLEM test #458. 

Figure 66.—Debris from steel panel stopping in X-7 after LLEM test #458, viewed from B-drift. 
54

 Figure 67.—Closeup of steel panel stopping still partially attached 

to outby rib in X-7 after LLEM test #458, viewed from B-drift.

Dry-Stacked Solid-Concrete-Block Stoppings in Crosscuts 

 The two dry-stacked solid-concrete-block stoppings in X-4 and X-5 were evaluated during a series of seven explosion tests (#457–#463). A summary of these LLEM explosion tests is 

presented in Table 1. A complete listing of the B- and C-drift omnidirectional wall pressures and 

stopping pressures for each test is given in Tables A-8 through A-14 in the appendix. 

Test #457 

During test #457, there was little or no observable damage to the two dry-stacked solidconcrete-block stoppings located in X-4 and X-5. The total explosion pressures were 0.78 psi 

(5.4 kPa) and 0.75 psi (5.2 kPa) at the stoppings in X-4 and X-5, respectively. The pressures in 

B-drift behind the stoppings were negligible (<0.1 psi (<1 kPa)). The LVDT showed no movement on the two stoppings. 

Test #458 

During test #458, the dry-stacked solid-concrete-block stoppings in X-4 and X-5 showed 

no noticeable damage. The LVDT displacement, pressure-time integrals, and pressure versus 

time traces associated with the dry-stacked solid-concrete-block stopping in X-4 are shown in 

Figure 68. The total explosion pressure measured with the transducer in front of the stopping is 
55

labeled as “X-4C” and shown as a solid black line. As shown in graph C of Figure 68, the solidconcrete-block stopping in X-4 was subjected to a total explosion pressure of 1.6 psi (11 kPa). 

As is shown in graph A of Figure 68, no significant movement (only ~0.06 in (~1.5 mm)) was 

observed on the LVDT. Similar displacement and pressure data were measured at the X-5 

stopping during this test. The stoppings returned close to their original positions after the 

explosion. 

 Figure 68.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the dry-stacked solid-concrete-block stopping in X-4 during LLEM test #458. 
56

Test #459 

During test #459 (see Table A-10), the total explosion pressure was 4.6 psi (32 kPa) at 

the X-4 dry-stacked solid-concrete-block stopping (graph C of Figure 69). For the X-5 stopping, 

the total explosion pressure was 3.4 psi (23 kPa). The LVDTs showed movement of nearly 0.7 in 

(18 mm) for the X-4 stopping (graph A of Figure 69) and 0.4 in (10 mm) for the X-5 stopping. 

After the explosion, the X-4 stopping had a permanent displacement of ~0.3 in (~8 mm) at the 

midpoint sensor location, and the X-5 stopping a permanent displacement of ~0.15 in (~4 mm) at 

the midpoint sensor location. However, both stoppings survived, with only limited damage. Both 

stoppings exhibited near rib-to-rib cracking of the sealant coating between the first and second 

block courses from the floor, with an approximately 0.5-in (0.6-cm) displacement of the entire 

second block course toward B-drift for X-4 stopping (Figure 70) and no significant displacement 

of this second block course for the X-5 stopping. A hairline horizontal crack was also observed 

near the roof above the top block course for the X-4 stopping.

 Figure 69.—(A) LVDT displacement, (B) pressure-time integrals, and 

(C) pressures versus time at the dry-stacked solid-concrete-block stopping 

in X-4 during LLEM test #459. 
57

 Figure 70.—Displacement of the second block course at the X-4 dry-stacked solid-concrete-block 

stopping after LLEM test #459, viewed from C-drift. 

For all of the dry-stacked hollow-core and solid-concrete-block stoppings discussed in 

this report, a small amount of mortar was used under the first course of block to assist in the 

leveling of this first course in the sloped entry. Since the first block course was mortared to the 

concrete mine floor, it was expected that any block movement due to the explosion pressure 

would initially occur above the first course. 

Test #460 

 During test #460 (Table A-11), the total explosion pressure was 6.7 psi (46 kPa) at the 

X-4 dry-stacked solid-concrete-block stopping. At the X-5 dry-stacked solid-concrete-block 

stopping, the total explosion pressure was 4.7 psi (33 kPa). The LVDTs showed movements of 

about 1.2 in (30 mm) for the X-4 stopping and about 0.8 in (20 mm) for the X-5 stopping. These 

LVDT displacements were recorded ~0.02 sec after the occurrence of the peak total explosion 

pressure on each stopping. This time delay may be due to the inertia of the stopping. After the 

explosion test, both stoppings were essentially intact. However, pronounced cracking was evident on the X-4 stopping between the first and second block course, with a 0.5- to 1-in (1.3- to 

2.5-cm) total displacement of the entire second block course toward B-drift. Additional horizontal cracking above the entire top block course was noted, and a new hairline crack extended 

nearly rib to rib across the centerline of the stopping. For the X-5 stopping, a pronounced crack 

was observed between the first and second courses, with a 0.25-in (0.6-cm) displacement of the 

entire second course toward B-drift. 
58

Test #461 

During test #461, the total explosion pressures at the stoppings were not higher than those 

during test #460. The total explosion pressure was 4.2 psi (29 kPa) at the X-4 dry-stacked solidconcrete-block stopping, while the total explosion pressure was 4.0 psi (28 kPa) at the X-5 drystacked solid-concrete-block stopping. The LVDTs showed movements of 0.6 in (15 mm) for the 

X-4 stopping and about 0.3 in (8 mm) for the X-7 stopping. No significant additional damage to 

the stoppings was observed following this explosion. 

Test #462 

During test #462, the total explosion pressure was 7.6 psi (52 kPa) at the X-4 dry-stacked 

solid-concrete-block stopping (graph C of Figure 71). This stopping was essentially destroyed. 

Only a few blocks remained in place along the outby rib line and on the floor near the outby rib 

line (Figure 72). Approximately 2 ft (0.6 m) of the stopping block remained in place along the 

inby rib line and the floor near the inby rib line (Figure 73). Many of these remaining blocks 

from the original stopping location showed evidence of shearing failure (Figures 72–73). A map 

of the debris field from the destroyed X-4 stopping is shown in Figure 74. B-drift is at the lower 

part of the figure, and A-drift is at the top of the figure. The original position of the stopping is 

shown by the double horizontal line in X-4 near the bottom of the figure. Most of the stopping 

blocks were scattered to and beyond the B-drift intersection, with a few blocks thrown to the far 

wall of A-drift. 

Figure 75 shows the LVDT displacement, pressure-time integrals, and pressures versus 

time at the X-5 dry-stacked solid-concrete-block stopping during test #462. As is shown in 

graph C of Figure 75 for the X-5 dry-stacked solid-concrete-block stopping, the total explosion 

pressure was 6.7 psi (46 kPa). The stopping withstood the pressure pulse. The stopping exhibited 

a more pronounced horizontal crack between the first and second block course, with an approximately 0.5-in (1.3 cm) displacement of the entire second block course toward B-drift. A new 

hairline crack extending from the right center of the stopping to the outby floor corner was also 

evident. At the center of the X-5 stopping, the LVDT showed movement of slightly over 0.9 in 

(23 mm) during the explosion, but returned close to its original position after the explosion 

(graph A of Figure 75). This displacement data may have been affected by the pressure coming 

through the inby crosscut (X-4 when that stopping was destroyed) and subsequently moving the 

fishing line extended between the X-5 stopping and the sensor in B-drift. 

A summary of the pressure data at the dry-stacked solid-concrete-block stopping positions for test #462 is given in Figure 76 and Table 3. The maximum omnidirectional wall pressures in C-drift at the various DG panel positions are shown in Figure 76 as a function of 

distance from the face. At the top of Figure 76 is a schematic showing the locations of the stoppings. The stoppings in X-4 and X-5 were at distances of 355 and 451 ft (108 and 138 m) from 

the face, respectively. The B-drift pressures are the maximum values up until 0.1 sec after peak 

pressure in C-drift. (The pressures in B-drift were somewhat higher at later times due to the failure of the stoppings.) The total explosion pressures and pressure-time integrals at both of the drystacked solid-concrete-block positions are listed in Table 3. 
59

 Figure 71.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus 

time at the dry-stacked solid-concrete-block stopping in X-4 during LLEM test #462. 

 Figure 72.—Debris from the dry-stacked solid-concrete-block stopping and remaining 

blocks on the outby rib line in X-4 after LLEM test #462, viewed from C-drift. 
60

 Figure 73.—Debris from the dry-stacked solid-concrete-block stopping 

and remaining blocks on the inby rib line in X-4 after LLEM test #462, 

viewed from C-drift.

 Figure 74.—Map of debris from the X-4 dry-stacked solid-concrete-block 

stopping after LLEM test #462. Black squares represent whole or partial 

blocks (smaller block pieces are not shown). 
61

 Figure 75.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus 

time at the dry-stacked solid-concrete-block stopping in X-5 during LLEM test #462. 
62

0

1

2

3

4

5

6

7

8

9

0 100 200 300 400 500 600 700 800

Distance from face, ft

Explosion pressure, psi

0

1

2

3

4

5

6

7

8

9

 total pressure at stopping

 C-drift omnidirectional wall pressure

 B-drift omnidirectional wall pressure

<--------------------stoppings----------------->

 Figure 76.—Pressures at walls (ribs) and at the dry-stacked solid-concrete-block stopping 

locations during LLEM test #462. 

Table 3.—Peak total explosion pressure data at dry-stacked 

solid-concrete-block stoppings for test #462 in C-drift 

Distance Peak total explosion 

pressure Pressure-time integral Location 

ft m psi kPa psi-s kPa-s 

Crosscut 4 355 108 7.6 52 1.04 7.2 

Crosscut 5 451 138 6.7 46 1.06 7.3 

Test #463 

The X-5 dry-stacked solid-concrete-block stopping was destroyed during test #463. 

Figure 77 shows the LVDT displacement, the pressure-time integrals, and the pressures versus 

time at the X-5 dry-stacked solid-concrete-block stopping during test #463. This test generated 

much higher pressures than the previous tests since it was designed to exert a 20-psi (138-kPa) 

explosion pressure pulse on a seal in X-1 that had been remotely installed from the surface 

through a borehole into the mine. During this test, the total explosion pressure was 16.6 psi 

(115 kPa) at the X-5 stopping (graph C of Figure 77). As shown in graph A of Figure 77, the 

LVDT also moved more than 3 in (8 cm) as the stopping was destroyed. Nearly all of the stopping blocks were scattered from the original stopping position except for a few blocks at the inby 

floor corner (Figure 78, which shows block shearing) and one block still intact at the outby floor 

corner. Figure 79 shows the debris map for the X-5 dry-stacked solid-concrete-block stopping 

after test #463. The stopping blocks were thrown into and beyond B-drift, with some blocks all 

the way into A-drift. 
63

 Figure 77.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the dry-stacked solid-concrete-block stopping in X-5 during LLEM test #463. 
64

 Figure 78.—Remaining blocks from the dry-stacked solid-concrete-block 

stopping at the inby rib in X-5 after LLEM test #463, viewed from B-drift.

 Figure 79.—Debris map for the X-5 dry-stacked solid-concrete-block 

stopping after LLEM test #463. Black squares represent whole or 

partial blocks (smaller block pieces are not shown). 
65

Wet-Laid Solid-Concrete-Block Stoppings in Crosscuts

 The two wet-laid solid-concrete-block stoppings in X-6 and X-7 between A- and B-drifts 

were evaluated during a series of 10 explosion tests (#510–#519) with total pressures ranging 

from 9.5 to 26.8 psi (66 to 185 kPa) at the X-6 stopping and 9.4 to 25.3 psi (65 to 174 kPa) at the 

X-7 stopping. A summary of three methane-only LLEM explosion tests (tests #510, #515, and 

#519) and one of the propagating coal dust explosion tests (test #512) is presented in Table 1. 

A complete listing of the A-drift omnidirectional wall pressures and stopping pressures for these 

three methane-only tests and the one test involving a coal dust explosion is also given in 

Tables A-20 through A-23 in the appendix. 

Test #510 

During the methane-only test #510, which consisted of a 40-ft (12-m) long gas ignition 

zone at the face of A-drift, there was little or no observable damage to the two wet-laid solidconcrete-block stoppings. The total explosion pressures were 14.5 psi (100 kPa) and 13.5 psi 

(93 kPa) at the stoppings in X-6 and X-7, respectively. The LVDTs showed movement toward 

B-drift of 0.3 in (7 mm) on the 8-in (20-cm) thick X-6 stopping and 0.5 in (13 mm) on the 6-in 

(15-cm) thick X-7 stopping. The pressures in B-drift behind the stoppings were very low 

(<0.6 psi (<4 kPa)) and were a result of the pressure traveling inby B-drift from the open end 

well past the time of the initial outward traveling pressure pulse in A-drift. The total explosion 

pressures and the pressure-time integrals at both of the wet-laid solid-concrete-block positions 

are listed in Table 4. 

Table 4.—Peak total explosion pressure data at wet-laid 

solid-concrete-block stoppings for test #510 in A-drift 

Distance Peak total explosion 

pressure Pressure-time integral Location 

ft m psi kPa psi-s kPa-s 

Crosscut 6 600 183 14.5 100 3.0 21 

Crosscut 7 699 213 13.5 93 3.0 21 

Tests #511–#514 

Tests #511–#514 were mainly conducted to determine the rock dust inerting requirements 

of various sized coal dusts. The purpose of these tests was to determine whether the flame from a 

40-ft (12.2-m) long gas ignition zone at the closed end of A-drift would continue to propagate 

through a 300-ft (91.4-m) long zone of a coal and rock dust mixture. The results from these dust 

tests will be published in a future report. During these four methane and coal dust explosion 

tests, there was no observable damage to the stoppings. The total explosion pressures ranged 

from 9.5 to 13.6 psi (66 to 94 kPa) at the X-6 stopping and 9.4 to 10.8 psi (65 to 75 kPa) at the 

X-7 stopping. 

Test #515 

 Figures 80–81 show the pressure data at the wet-laid solid-concrete-block stopping positions for test #515, which used a 50-ft (15.2-m) long gas ignition zone and no coal dust. The X-6 

and X-7 stoppings were both subjected to a total explosion pressure of 14.2 psi (98 kPa). The 
66

LVDTs showed movement of 0.3 in (7 mm) on the 8-in (20-cm) thick X-6 stopping and 0.7 in 

(18 mm) on the 6-in (15-cm) thick X-7 stopping. The total explosion pressures and the pressuretime integrals at both of the wet-laid solid-concrete-block positions are listed in Table 5. 

Table 5.—Peak total explosion pressure data at wet-laid solid-concrete-block 

stoppings for test #515 in A-drift 

Distance Peak total explosion 

pressure Pressure-time integral Location 

ft m psi kPa psi-s kPa-s 

Crosscut 6 600 183 14.2 98 3.9 27 

Crosscut 7 699 213 14.2 98 3.9 27 

 Figure 80.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the 8-in (20-cm) thick, wet-laid solid block stopping in X-6 during LLEM test #515. 
67

 Figure 81.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the 6-in-thick, wet-laid solid block stopping in X-7 during LLEM test #515. 

Tests #516–#518 

 Tests #516–#518 again involved coal and rock dust mixtures. During these tests, the 

explosion pressures ranged from 11.0 to 12.5 psi (76 to 86 kPa) at the X-6 stopping and 10.0 to 

10.6 psi (69 to 73 kPa) at the X-7 stopping. The LVDTs showed movement of ~0.3 in (~8 mm) 

on the 8-in (20-cm) thick X-6 stopping and ~0.6 in (~18 mm) on the 6-in (15-cm) thick X-7 

stopping during these tests. Small horizontal center cracks were first observed on the 6-in 

(15-cm) thick X-7 stopping after test #516. The 8-in (20-cm) thick X-6 stopping did not show 

any outward signs of damage during these tests. 

Test #519 

For test #519, there was an 85-ft (26-m) long gas zone at the face of A-drift, with no 

added coal dust. A summary of the pressure data at the wet-laid solid-concrete-block stopping 

positions for test #519 is given in Figures 82–83. The X-6 and X-7 stoppings were subjected to a 
68

total explosion pressure of 26.8 psi (185 kPa) and 25.3 psi (174 kPa), respectively. The LVDT 

showed movement of 1.0 in (26 mm) on the 8-in (20-cm) thick X-6 stopping, and a small 

horizontal center crack was observed on the A-drift side of the stopping after the test. The 6-in 

(15-cm) thick, wet-laid solid-concrete-block stopping in X-7 was destroyed during the test. 

Figure 84 shows the debris from the 6-in (15-cm) thick stopping in X-7 after test #519. The 

debris extended beyond B-drift to the far wall of C-drift. The block showed evidence of shearing. 

The total explosion pressures and the pressure-time integrals at both of the wet-laid solidconcrete-block stopping positions are listed in Table 6. 

 Figure 82.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the 8-in (20-cm) thick, wet-laid solid block stopping in X-6 during LLEM test #519. 
69

 

 Figure 83.—(A) LVDT displacement, (B) pressure-time integrals, and (C) pressures versus time 

at the 6-in (15-cm) thick, wet-laid solid block stopping in X-7 during LLEM test #519. 

 Figure 84.—Debris from 6-in (15-cm) thick, wet-laid solid block stopping in X-7 after 

LLEM test #519, viewed from A-drift.
70

Table 6.—Peak total explosion pressure data at wet-laid 

solid-concrete-block stoppings for test #519 in A-drift 

Distance Peak total explosion 

pressure Pressure-time integral Location 

ft m psi kPa psi-s kPa-s 

Crosscut 6 600 183 26.8 185 4.2 29 

Crosscut 7 699 213 25.3 174 3.2 22 

 NOTE.—These stoppings were subjected to a total of 10 explosion tests, with 

pressures ranging from 9.5 to 26.8 psi at the X-6 stopping and 9.4 to 25.3 psi at 

the X-7 stopping. 

Dry-Stacked Hollow-Core Concrete Block Stoppings in Entry and Crosscuts 

 MSHA investigations following methane and/or coal dust explosions in underground coal 

mines have documented cases where stoppings close to the ignition location have withstood the 

explosion pressure pulse, but stoppings farther away were destroyed. 

 To try to simulate this scenario, four and then later five dry-stacked hollow-core concrete 

block stoppings were constructed in the LLEM. The stoppings were located between A- and 

B-drifts and B- and C-drifts in X-3 and X-4. These stoppings were constructed in the same 

manner as previously described in the “Concrete Block Stoppings” section, except that sealant 

was only applied to one side of the stopping. Since many mines commonly coat stoppings on 

only one side, this series also provided an opportunity to evaluate the performance of these stoppings in comparison with those coated on both sides. The stoppings between A- and B-drifts 

were installed approximately 5 ft from A-drift (as measured from the closest A-drift rib) or about 

35 ft from the closest B-drift rib line. The stoppings between B- and C-drifts were installed 

approximately 10 ft from the C-drift entry (as measured from the closest C-drift rib) or about 

30 ft from the closest B-drift rib line. Later, a fifth stopping was installed across B-drift at 446 ft 

(136 m) from the face. A 2.6-ft (0.8-m) high by 3.8-ft (1.1-m) wide opening in the center of this 

stopping simulated an open regulator (Figure 85). All of the stoppings were coated with sealant 

on the B-drift (explosion) side. All of the blocks from each of the stoppings were sequentially 

numbered on the nonexplosion side of the stopping starting from the top. The blocks of each 

course were also designated with a letter, i.e., the blocks in the top course were labeled A-1, A-2, 

A-3, etc., the blocks in the second course from the top were labeled B-14, B-15, etc., as shown in 

Figure 86. A wire loop was installed on each stopping (nonexplosion side) to establish an electrical circuit or breakwire. This breakwire was designed to separate and thereby break the electrical 

circuit when the stopping was damaged or destroyed. The time of this event would be recorded 

and matched to the corresponding pressure peak. There were no LVDTs on these stoppings. 
71

 Figure 85.—Completed dry-stacked hollow-core concrete block stopping with simulated open regulator 

across B-drift. 

 Figure 86.—Dry-stacked hollow-core concrete block stopping between B- and C-drifts in X-4 showing 

individually numbered block, viewed from C-drift.
72

Test #491 

After installing the crosscut stoppings but before installing the stopping across B-drift, 

a short series of methane ignition experiments were conducted as part of another research program. It was not anticipated that the pressures generated from the ignition of a 38-ft (11.6-m) 

long, 10% methane-air concentration located between B-202 and B-240 would exceed 3 psi 

(21 kPa). This assumption was found to be incorrect. The ignition of this methane zone 

(LLEM test #491) generated total explosion pressures at the stopping locations ranging from 

3.6 to 6.4 psi (25 to 44 kPa), which destroyed all four of the crosscut stoppings. The complete 

explosion pressure data for this test (LLEM test #491) are listed in Table A-15. These data are 

consistent with the results discussed in the “Dry-Stacked Hollow-Core Concrete Block Stoppings 

in Crosscuts” section, where similar dry-stacked hollow-core concrete block stoppings with 

coatings on both sides were destroyed at total explosion pressures between 3.4 psi (23 kPa) and 

5.2 psi (36 kPa). The debris field of each stopping was mapped (Figure 87), and the information 

will assist in future accident investigations. Many of these remaining blocks from the original 

stopping location showed evidence of shearing failure. 

Test #494 

For test #494 (Table A-16), the four crosscut stoppings were rebuilt in addition to the 

stopping with an open regulator across B-drift at 446 ft (136 m) from the face. The methane 

ignition zone was reduced from 38 ft (11.6 m) long to 20 ft (6.1 m) long, located between B-240 

and B-260 (between X-2 and X-3). The goal for this test was a lower-strength pressure pulse. 

Therefore, for test #494, a ~6% methane-air concentration was ignited by electric matches at the 

center of the 20-ft (6.1-m) long gas zone. The total explosion pressure was ~0.4 psi (~3 kPa) at 

the four crosscut stoppings and ~0.5 psi (~3.4 kPa) at the stopping across B-drift. Note that the 

listed pressure at the B-drift stopping was from a pressure transducer that was 18 ft (5.5 m) in 

front of the stopping or 428 ft (130 m) from the face. The pressure directly at this stopping may 

have been somewhat higher. All five of the dry-stacked hollow-core concrete block stoppings 

were still intact after the explosion test. 

Test #495 

During test #495, the gas concentration within the 20-ft zone was increased to 

~7% methane-air. The total explosion pressure near the crosscut stoppings during this test 

(Table A-17) ranged from ~0.9 to ~1.1 psi (~6 to ~7.5 kPa). The total pressure was 1.2 psi 

(8.6 kPa) at the stopping across B-drift. All five of the stoppings were again intact after the 

explosion. 

Test #496 

 During test #496, a ~9.5% methane-air concentration was ignited in the center of the 

20-ft (6.1-m) gas zone, resulting in a total explosion pressure of 3.5 psi (24 kPa) at the stopping 

across B-drift at 446 ft from the face. All four of the crosscut stoppings were subjected to an 

explosion pressure pulse of ~3 psi (~21 kPa). A few hairline cracks in the sealant were observed 

on the stopping across B-drift and the stoppings in X-4. A complete listing of the B- and C-drift 

omnidirectional wall and stopping pressures for LLEM test #496 is given in Table A-18. 
73

Figure 87.—Debris map after LLEM test #491 (overall view of entire area). 
74

Test #497 

 During test #497, the length of the gas ignition zone was almost doubled to 38 ft (11.6 m) 

(located between B-202 and B-240). An ~8% methane-air concentration was ignited at the center 

of this 38-ft (11.6-m) long gas zone. The total explosion pressure on the B-446 stopping located 

across the drift was 5.2 psi (36 kPa) (see graph B of Figure 88 and Table A-19), which destroyed 

the stopping. Figure 89 shows the debris from the dry-stacked hollow-core concrete block stopping across B-drift; shearing of the blocks was also observed. The total explosion pressures near 

the stoppings in X-4 ranged from 3.6 to 3.8 psi (25 to 26 kPa), as shown in graph B of Figure 90. 

The X-4 stopping between B- and C-drifts was mostly destroyed, and the X-4 stopping between 

A- and B-drifts was totally destroyed, as shown in Figures 91 and 92, respectively. The total 

explosion pressure at the stoppings in X-3 was 4.3 psi (30 kPa), as shown in Figure 93. The stopping located between A- and B-drifts in X-3 was not damaged, and the stopping between B- and 

C-drifts in X-3 was only partly damaged (Figure 94). This seemed to be due to the failure of the 

coating since several individual blocks were knocked loose. A complete listing of the B- and 

C-drift omnidirectional wall and stopping pressures for this test is given in Table A-19. Figure 95 

shows the debris map for all of the dry-stacked hollow-core concrete block stoppings after 

LLEM test #497. Three of the four seals that had been in X-1 and X-2 were removed prior to this 

test. A framed check curtain was installed in X-2 between B- and C-drifts, and it was knocked 

down by the explosion. These open crosscuts allowed additional venting of the pressures during 

this test. 

 Figure 88.—(A) Pressure-time integrals and (B) pressures versus time at the dry-stacked 

hollow-core concrete block stopping across B-drift during LLEM test #497. 
75

 Figure 89.—Debris from the dry-stacked hollow-core concrete block stopping across B-drift after 

LLEM test #497. 

 Figure 90.—(A) Pressure-time integrals and (B) pressures versus time 

at the X-4 dry-stacked hollow-core concrete block stoppings during 

LLEM test #497. 
76

 Figure 91.—Damage to the X-4 dry-stacked hollow-core concrete block stopping between B- and C-drifts 

after LLEM test #497. 

 Figure 92.—Debris from the X-4 dry-stacked hollow-core concrete block stopping between A- and B-drifts 

after LLEM test #497. 
77

 Figure 93.—(A) Pressure-time integrals and (B) pressures versus time 

at the X-3 dry-stacked hollow-core concrete block stoppings during 

LLEM test #497. 

 Figure 94.—Damage to the X-3 dry-stacked hollow-core concrete block stopping between B- and C-drifts 

after LLEM test #497. 
78

Figure 95.—Debris map after LLEM test #497 (overall view of entire area). 
79

 The results of test #497 demonstrated that a low-level pressure pulse (~3 psi (~21 kPa)) 

developed at the methane ignition zone (between X-2 and X-3) can move through an entry 

without damaging stoppings located in the nearby X-3. However, when that pressure pulse 

approaches an obstruction within the entry (a dry-stacked hollow-core concrete block stopping 

with an open regulator for this experiment), the pressure increases due to reflection at the B-drift 

stopping and thereby destroys the stopping. This reflected pressure increase is clearly evident on 

the B-257 wall pressure trace in Figure 93 where the initial outward traveling pressure pulse is 

~2.3 psi (~16 kPa) and was subsequently increased to 3.4 psi (23 kPa) by the inward traveling 

reflected pressure pulse. The reflected pressure phenomenon is also shown on the B-drift 428-ft 

(130-m) pressure trace in Figure 96 where the initial outward traveling pressure pulse is ~2.3 psi 

(~16 kPa) at ~0.82 sec followed by a peak reflected pressure of 5.2 psi (36 kPa). The explosion 

pressure pulse also destroyed the inby X-4 stoppings at about the same time (Figure 96). These 

stoppings were recessed into X-4 between A- and B-drifts and between B- and C-drifts about the 

same distance that the stopping across B-drift was located outby of X-4. Only minor damage was 

evident on the X-3 stoppings. In this test, the stoppings in X-4 were destroyed at peak explosion 

pressures of 3.6–3.8 psi (25–26 kPa), while the stoppings in X-3 survived even though they were 

exposed to a peak pressure of 4.3 psi (30 kPa). However, the pressure-time integral was 

0.93–0.94 psi-s (6.4–6.5 kPa-s) at the X-4 stoppings and only 0.70-0.71 psi-s (4.8–4.9 kPa-s) at 

the X-3 stoppings (Table A-19). This shows that the values of the pressure-time integral, as well 

as the peak total explosion pressure, are factors that affect whether a stopping will survive or be 

destroyed. In addition, the rate of pressure loading on a structure is also important in determining 

the response of the structure to an explosion. 

0

1

2

3

4

5

6

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Time, s

Explosion pressure, psi

 X-4 BA, 377 ft

 X-4 BC, 377 ft

 B-drift, 428 ft

 Figure 96.—Total explosion pressures versus time at the dry-stacked hollow-core concrete block 

stoppings in X-4 and in B-drift during LLEM test #497. 
80

Australian Woven Cloth Stoppings in Crosscuts 

 Four full-scale explosion tests (LLEM tests #459–#462) were conducted in C-drift of the 

LLEM to evaluate the Australian-designed Flexi-Stop woven cloth stoppings in X-6 and X-7. 

These gas explosion tests were designed to provide an increasingly higher pressure pulse on the 

stopping designs during each subsequent test. A complete listing of the B- and C-drift omnidirectional wall pressures and the stopping pressures for each test are given in the Tables A-10 

through A-13 in the appendix. The Flexi-Stop stopping designs were located in X-6 at 547 ft 

(167 m) and X-7 at 647 ft (197 m) from the face of C-drift. Both stopping designs were 

eventually destroyed during the fourth explosion test. 

 A summary of these LLEM explosion tests is presented in Table 1. The first two tests had 

a 10-ft (3-m) deep by 12-ft (3.7-m) wide methane-air ignition zone contained in the face area by 

a clear plastic diaphragm. For the last two tests, the methane-air ignition zone was extended out 

to 27 ft (8.2 m) from the face. 

Test #459 

 During test #459, there was very little observable damage to either of the two stopping 

designs. Figure 97 shows the pressure-time integrals and pressures versus time at the X-6 stopping during test #459; Figure 98 shows similar data at the X-7 stopping. The total explosion 

pressures, as measured ~4 ft (~1.2 m) directly in front of the stopping design, were 3.0 psi 

(21 kPa) at the X-6 stopping and 2.8 psi (19 kPa) at the X-7 stopping. For these evaluations, 

a pressure transducer was also mounted ~11 ft (~3.3 m) behind each stopping on the B-drift side. 

These transducers were centered within the crosscut and mounted so the sensor opening was 

perpendicular to any explosion gas flow or air displacement passing by the sensor location. In 

this orientation, the sensor would record the omnidirectional pressure. The pressure in B-drift 

behind each of the stoppings was initially zero but increased to about 0.1–0.2 psi (0.7–1.4 kPa). 

In Figures 97–98, the B-drift pressures recorded behind the X-6 and X-7 stoppings are designated as X-6B and X-7B, respectively. This slight pressure rise behind the stopping was most 

likely due to the compression of the air behind the stopping caused by the initial rapid billowing 

of the woven cloth toward B-drift during the explosion test. The recorded B- and C-drift pressure 

traces are shown in graph B of Figure 97 for the X-6 stopping and graph B of Figure 98 for the 

X-7 stopping. Graph A of Figures 97 and 98 shows the pressure-time integral for the X-6 and 

X-7 stoppings. The calculated pressure-time integral for the X-6 stopping was approximately 

0.54 psi-s (4 kPa-s). For the X-7 stopping, the pressure-time integral was 0.55 psi-s (4 kPa-s).

Test #460 

 Prior to the second test against these Australian stopping designs (test #460), rib bolts 

were installed through the woven cloth and into each rib on each stopping (Figure 30). These rib 

bolts were designed as an additional anchoring technique to allow the stopping to withstand 

higher-level explosion pressures. Test #460 generated a total explosion pressure of 4.0 psi 

(27 kPa) for the X-6 design and 3.9 psi (27 kPa) for the X-7 stopping, with corresponding 

pressure-time integral values of 0.50 psi-s (3.4 kPa-s) for the X-6 stopping and 0.50 psi-s 

(3.5 kPa-s) for the X-7 stopping (Figures 99–100 and Table 7). Postexplosion observations 

revealed that the woven cloth was damaged (torn) along the rib lines at the locations of many of 
81

the rib bolt sites. It seemed that the square steel rib bolt plates provided a point loading contact 

area that ruptured the woven cloth starting at the plate corners. Figure 101 shows the damage to 

the woven cloth at the outby rib of X-6 after test #460 as viewed from C-drift. It can be readily 

seen in Figure 102 that the tears in the woven cloth on the inby rib of the X-7 stopping initiated 

at the bolt plate corners. A clear determination for the cause of the initial and subsequent 

pressure rises as measured from the transducer located behind each stopping was not readily 

discernable for this test or the subsequent tests. The pressure rises measured by these transducers 

could be a combination of two factors—displacement of the air column behind the stopping as 

resulting from the woven cloth billowing toward B-drift as the initial (and subsequent) explosion 

pressure pulse(s) impacted the C-drift side of the stopping and/or the pressure traveling through 

the tears in the woven cloth and/or damaged framework. 

 Figure 97.—(A) Pressure-time integrals and (B) pressures at the X-6 woven cloth stopping 

during LLEM test #459.
82

 Figure 98.—(A) Pressure-time integrals and (B) pressures at the X-7 woven cloth stopping 

during LLEM test #459.

 Figure 99.—(A) Pressure-time integrals and (B) pressures at the X-6 woven cloth stopping 

during LLEM test #460.
83

 Figure 100.—(A) Pressure-time integrals and (B) pressures at the X-7 woven cloth stopping 

during LLEM test #460.

Table 7.—Peak total explosion pressure data at Australian woven 

cloth stoppings for test #460 in C-drift 

Distance Peak total explosion 

pressure 

Pressure-time 

Location integral 

ft m psi kPa psi-s kPa-s 

Crosscut 6 547 167 4.0 27 0.50 3.4 

Crosscut 7 647 197 3.9 27 0.50 3.5 
84

 Figure 101.—Tears in the woven cloth on the outby rib of X-6 stopping after LLEM test #460, 

viewed from C-drift. 

 Figure 102.—Initial tear in the woven cloth at the corner steel roof bolt plate position on the 

inby rib of the X-7 stopping after LLEM test #460, viewed from C-drift. 
85

Test #461 

 Test #461 was designed to provide a 5-psi (35-kPa) total explosion pressure at the stopping locations. However, the pressure levels were lower than expected. This may have been due 

to the improper mixing of the natural gas within the zone (the circulation fan was too small) 

and/or insufficient turbulence within the ignition zone to enhance the burning of the gas. The 

total explosion pressure was 3.7 psi (25.5 kPa) at the X-6 stopping and 3.6 psi (25 kPa) at the 

X-7 stopping. Postexplosion observations revealed very little indications of additional damage to 

the stoppings.

Test #462 

For test #462, a double-point ignition source was used to initiate the methane, a larger 

circulation fan was used in the ignition zone, and the fan was left on during the ignition of the 

gas to provide increased turbulence. These changes were sufficient to provide the desired 

pressure loadings on the stoppings. The total explosion pressure was 6.1 psi (42 kPa) at the X-6 

stopping and 5.4 psi (37 kPa) at the X-7 stopping, with corresponding pressure-time integral 

values of 0.71 psi-s (4.9 kPa-s) for the X-6 stopping and 0.85 psi-s (5.9 kPa-s) for the X-7 

stopping (Table 8 and Figures 103–104). Postexplosion observations following test #462 

revealed that the top steel box section and woven cloth for the X-6 stopping was on the floor 

(Figure 105). The four center bolts sheared at the roof and the steel rings on each end of the box 

section were sheared (roof bolts still anchored to the roof). The pipe/cloth assembly in the X-7 

stopping pulled out from the slot in the top box section frame along a center 12-ft (3.5-m) portion 

of the frame. This resulted in an approximately 3-ft (1-m) opening between the mine roof and the 

now sagging woven cloth along most of the top section of the stopping (Figure 106). Both stoppings were rendered ineffective by the explosion. 

Table 8.—Peak total explosion pressure data at Australian 

woven cloth stoppings for test #462 in C-drift 

Distance Peak total explosion 

pressure 

Pressure-time 

Location integral 

ft m psi kPa psi-s kPa-s 

Crosscut 6 547 167 6.1 42 0.71 4.9 

Crosscut 7 647 197 5.4 37 0.85 5.9 
86

 

 Figure 103.—(A) Pressure-time integrals and (B) pressures at the X-6 woven cloth stopping during 

LLEM test #462. 
87

 Figure 104.—(A) Pressure-time integrals and (B) pressures at the X-7 woven cloth stopping during 

LLEM test #462. 
88

Figure 105.—Damage to the woven cloth stopping in X-6 after LLEM test #462. 

Figure 106.—Damage to the woven cloth stopping in X-7 after LLEM test #462. 
89

DISCUSSION AND CONCLUSIONS 

NIOSH and MSHA conducted full-scale evaluation studies to determine the explosion 

pressures required to destroy typical coal mine ventilation stoppings in the LLEM. A summary 

of the total explosion pressure data for the various stoppings is shown in Table 9. A typical drystacked solid-concrete-block stopping, as installed in the LLEM for these tests, survived a total 

explosion pressure of ~6.7 psi (~46 kPa) and was destroyed at a total explosion pressure of 

~7.6 psi (~52 kPa). In comparison, a typical dry-stacked hollow-core concrete block stopping 

survived a total explosion pressure of ~3.4–4.3 psi (~23–30 kPa), depending on the length of the 

pressure pulse and the value of the pressure-time integral. The dry-stacked hollow-core concrete 

block stopping was destroyed at a total explosion pressure of ~3.6–5.2 psi (~25–36 kPa), depending on the length of the pressure pulse and the value of the pressure-time integral. A typical steel 

panel stopping survived a total explosion pressure of 0.8 psi (5.5 kPa) and failed at a total explosion pressure of 1.3 psi (9 kPa). A 6-in (15-cm) thick wet-laid solid-concrete-block stopping survived a total explosion pressure of ~14 psi (~97 kPa) and was destroyed at a total explosion 

pressure of ~25 psi (~172 kPa). An 8-in (20-cm) thick wet-laid solid-concrete-block stopping 

survived a ~26-psi (~180-kPa) explosion pressure. The peak explosion pressures at which the 

concrete block and steel panel stoppings survived or failed was also dependent on the length of 

the pressure pulse, but there were insufficient data from these series of tests to quantify this. The 

value of the pressure-time integral, as well as the peak total explosion pressure and the pressure 

rise time, are factors affecting whether a stopping will survive or be destroyed. Note that for all 

of these stopping evaluations, the failure pressures are based on the construction conditions and 

explosion tests within the nonyielding limestone strata in the LLEM and the use of mortared 

floor joint to the concrete floor for the first course of blocks. Stopping strengths in mines may 

vary from these LLEM results when the stoppings are constructed in a coal seam and if subjected 

to roof convergence and/or floor heave or have significantly different boundary conditions. 

Table 9.—Total explosion pressures necessary to destroy typical U.S. stoppings in the LLEM 

Total explosion pressure 

at which stopping 

survived 

Total explosion pressure 

Stopping type at which stopping failed 

psi kPa psi kPa 

Steel panel 0.8 5.5 1.3 9 

6-in-thick dry-stacked hollow-core concrete block ~3.4–4.3 ~23–30 ~3.6–5.2 ~25–36 

6-in-thick dry-stacked solid concrete block ~6.7 ~46 ~7.6 ~52 

6-in-thick wet-laid solid concrete block ~14 ~97 ~25 ~172 

8-in-thick wet-laid solid concrete block ~26 ~180 — — 

A NIOSH empirical correlation based on arching was recently developed by Barczak 

[2005] to determine the true transverse load capacity of dry-stacked concrete block walls. The 

load capacity would be the pressure that the stopping could withstand. In a mine, arching is 

achieved by the restraint of the block wall against the roof and floor, whereby compressive 

forces are developed within the wall. A systematic study of the design parameters that affect 

arching capability in dry-stacked concrete block walls was simulated in the NIOSH-PRL Mine 

Roof Simulator [Barczak and Batchler 2006]. The study included a theoretical assessment of 
90

arching and development of design formulations that can accurately define the transverse load 

capacity of dry-stacked concrete block wall constructions under various loading conditions. The 

correlation between three critical parameters (compressive strength (fc), wall thickness (t), and 

wall height (H)) is shown (solid line) in Figure 107 as a function of the transverse load capacity. 

This correlation represents data from more than 70 tests including 8 different block materials, 

4 nominal heights, 4 nominal thicknesses, and 10 concrete block compressive strengths. The 

term, fc(t/H)2, was derived from the moment equilibrium requirements of a half-wall loading 

[Barczak and Batchler 2006]. 

0

5

10

15

20

25

30

0 5 10 15 20 25

fc(t/H)2, psi

Transverse load capacity, psi

Wet-laid, failed

Wet-laid, survived

Dry-stacked, failed

Dry-stacked, survived

WAC arching

Barczak and Batchler

[2008]

 Figure 107.—Results of the LLEM block stopping evaluations compared to the critical design 

parameters (block compressive strength, wall height, and wall thickness) and the transverse load 

capacity predictions of the NIOSH empirical correlation by Barczak and Batchler [2008] (for dry-stacked 

block walls) and WAC (for wet-laid block walls) [Slawson 1995]. 

The strength of a stopping strongly depends on the boundary conditions around the 

perimeter of the stopping. Under rigid arch conditions, the lateral displacement of the wall is 

controlled by the stiffness and elastic response of the block wall. The transverse load capacity 

will decrease as the wall stiffness decreases since more lateral displacement will occur. The 

increase in lateral displacement reduces the force couple provided by the arching thrust, causing 

a decrease in the transverse load capacity of the stopping. If the abutments are not rigid, then the 

lateral displacement will increase further, resulting in a further reduction in the transverse load 

capacity of the stopping. The boundary condition in coal mines can vary significantly from one 

stopping location to another based on the perimeter strata conditions, the original stopping con-
91

struction, and the subsequent degradation of the stopping and/or strata over time. The boundary 

conditions of the LLEM, with its limestone roof and ribs and concrete floor, are considered rigid 

abutment. The various data points for the LLEM stopping tests are shown in Figure 107. The 

LLEM explosion tests against the dry-stacked hollow-core concrete block stoppings and drystacked solid-concrete-block stoppings correlate well with the empirical correlations of Barczak 

and Batchler [2008]. The solid red circles in Figure 107 represent the dry-stacked concrete block 

stoppings that survived the LLEM explosion tests. The open circles represent the dry-stacked 

concrete block stoppings that failed the explosion tests. 

Also shown in Figure 107 is the calculated static-elastic resistance for a wet-laid concrete 

block wall obtained from WAC [Slawson 1995] assuming one-way, roof-to-floor arching action 

and the same heights, thicknesses, and compressive strengths used in the NIOSH empirical 

correlations of Barczak and Batchler [2008]. The WAC-calculated static-elastic resistance for 

wet-laid concrete block walls (blue dashed line in Figure 107) shows a higher load capacity, as 

expected. The LLEM explosion tests against the wet-laid solid-concrete-block stoppings show 

reasonable agreement with the WAC-calculated predictions for wet-laid solid-concrete-block 

walls, although the LLEM data for the wet-laid stoppings are not as narrowly quantified as those 

for the dry-stacked stoppings. The blue solid squares represent the wet-laid solid-concrete-block 

stoppings that survived the LLEM explosion tests; the open square represents the one that failed 

the explosion test. 

Explosion tests were also conducted in the LLEM that support observations from actual 

coal mine explosions where stoppings close to the ignition location can withstand a given explosion pressure impulse while stoppings farther away are destroyed, as discussed in the section 

entitled “Dry-Stacked Hollow-Core Concrete Block Stoppings in Entry and Crosscuts.” 

A program to evaluate the strength characteristics and air leakage resistance of an 

innovative Australian-designed woven cloth stopping showed that the stopping successfully 

withstood an explosion that generated a total explosion pressure of 4.0 psi (28 kPa) at the stopping location. The stopping failed when subjected to a subsequent explosion that generated a 

total explosion pressure of ~6.1 psi (~42 kPa) at the stopping location. Based on the results of 

this evaluation, this woven cloth stopping is now being used in underground coal mines in 

Australia. 

The results from the LLEM stopping evaluations, coupled with the use of predictive wall 

strength models (which are based on the critical parameters including block strength, stopping 

height and thickness, and boundary conditions), can assist investigators in more accurately determining the range of explosion pressures that destroy or damage stoppings during actual coal 

mine explosions. 

ACKNOWLEDGMENTS 

 The authors thank C. W. Moore and James Baca, Mining Engineers with the Ventilation 

Division, Pittsburgh Safety and Health Technology Center, MSHA, Triadelphia, WV, for their 

contributions to the mapping of the block stopping debris following several of the explosion 

evaluations. 

 We also thank the following NIOSH-PRL personnel without whose contributions this 

program could not have been accomplished: Kenneth W. Jackson, Electronics Technician, for 

sensor calibrations and installations, for operation of the data acquisition systems, and for his 

participation in the testing and data analyses; Frank A. Karnack, Donald D. Sellers, and 
92

William A. Slivensky, Physical Science Technicians, for their participation in the installation of 

sensors and mounting equipment, the construction of the stoppings, testing, and cleanup; and 

John J. Glad (now retired), James D. Addis (now a Physical Science Technician with PRL), 

Timothy Glad, James Rabon, Bernie Lambie, and Brandin Lambie, Mechanical Technicians with 

Akima and Ki, for their installation of the concrete block and Australian stopping designs. 

 The authors acknowledge William Kennedy, President of Jack Kennedy Metal Products 

& Buildings, Inc., and Robert Cox, President of Ken-Air, Inc., for constructing the Kennedy steel 

panel stoppings. 

 We also acknowledge I. Verne S. Mutton, Senior Mining Engineer with Minova 

Australia, for his innovative, woven cloth coal mine stopping designs and his direct contributions 

to the installation of these designs in the LLEM. 

 All photographs in this report were taken by Kenneth L. Cashdollar, Eric S. Weiss, or 

Frank A. Karnack of NIOSH-PRL. 

REFERENCES 

 61 Fed. Reg. 9764 [1996]. Mine Safety and Health Administration, 30 CFR part 75: 

safety standards for underground coal mine ventilation; final rule. 

 Barczak TM [2005]. Evaluation of the transverse load capacity of block stoppings for 

mine ventilation control [Dissertation]. Morgantown, WV: West Virginia University, Department of Mining Engineering. 

 Barczak TM, Batchler TJ [2006]. Development of new protocols to evaluate the transverse loading of mine ventilation stoppings. In: Mutmansky JM, Ramani RV, eds. Proceedings 

of the 11th U.S./North American Mine Ventilation Symposium (University Park, PA, June 5–7, 

2006). London: Taylor & Francis Group, pp. 569–577. 

 Barczak TM, Batchler TJ [2008]. Comparison of the transverse load capacities of various 

block ventilation stoppings under arch loading conditions. In: Wallace KG Jr., ed. Proceedings of 

the 12th U.S./North American Mine Ventilation Symposium (Reno, NV, June 9–11, 2008). 

Reno, NV: University of Nevada, pp. 225–231. 

CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office, 

Office of the Federal Register. 

 Gates RA, Phillips RL, Urosek JE, Stephan CR, Stoltz RT, Swentosky DJ, Harris GW, 

O’Donnell JR Jr., Dresch RA [2007]. Report of investigation: fatal underground coal mine 

explosion, January 2, 2006. Sago mine, Wolf Run Mining Company, Tallmansville, Upshur 

County, West Virginia, ID No. 46-08791. Arlington, VA: U.S. Department of Labor, Mine 

Safety and Health Administration. 

 Greninger, NB, Weiss ES, Luzik SJ, Stephan CR [1991]. Evaluation of solid-block and 

cementitious foam seals. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, 

RI 9382. NTIS No. PB 92-152115. 

 Kawenski EM, Mitchell DW, Bercik GR, Frances A [1965]. Stoppings for ventilating 

coal mines. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 6710. 

 Mattes RH, Bacho A, Wade LV [1983]. Lake Lynn Laboratory: construction, physical 

description, and capability. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, 

IC 8911. NTIS No. PB 83-197103. 
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 McKinney R, Crocco W, Stricklin KG, Murray KA, Blankenship ST, Davidson RD, 

Urosek JE, Stephan CR, Beiter DA [2002]. Report of investigation: fatal underground coal mine 

explosions, September 23, 2001. No. 5 Mine, Jim Walter Resources, Inc., Brookwood, 

Tuscaloosa County, Alabama, ID No. 01-01322. Arlington, VA: U.S. Department of Labor, 

Mine Safety and Health Administration. 

 Mitchell DW [1971]. Explosion-proof bulkheads: present practices. Pittsburgh, PA: 

U.S. Department of the Interior, Bureau of Mines, RI 7581. NTIS No. PB 205 507. 

 Nagy J [1981]. The explosion hazard in mining. Pittsburgh, PA: U.S. Department of 

Labor, Mine Safety and Health Administration, IR 1119. 

 Slawson TR [1995]. Wall response to airblast loads: the Wall Analysis Code (WAC). 

Prepared for the U.S. Army Energy Research and Development Center, Vicksburg, MS. 

 Triebsch G, Sapko MJ [1990]. Lake Lynn Laboratory: a state-of-the-art mining research 

laboratory. In: Proceedings of the International Symposium on Unique Underground Structures. 

Vol. 2. Golden, CO: Colorado School of Mines, pp. 75-1 to 75-21. 

 Weiss ES, Greninger NB, Stephan CR, Lipscomb JR [1993]. Strength characteristics and 

air-leakage determinations for alternative mine seal designs. Pittsburgh, PA: U.S. Department of 

the Interior, Bureau of Mines, RI 9477. NTIS No. PB94111275. 

 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, Cashdollar KL, Mutton IVS, Kohli DR, Slivensky WA [1999]. Evaluation of 

reinforced cementitious seals. Pittsburgh, PA: U.S. Department of Health and Human Services, 

Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 99-136, RI 9647. 

 Weiss ES, Cashdollar KL, Sapko MJ [2002]. Evaluation of explosion-resistant seals, 

stoppings, and overcast for ventilation control in underground coal mining. Pittsburgh, PA: 

U.S. Department of Health and Human Services, Public Health Service, Centers for Disease 

Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) 

Publication No. 2003–104, RI 9659. 

 Weiss ES, Cashdollar KL, Harteis SP, Shemon GJ, Beiter DA, Urosek JE [2006]. Explosion evaluation of mine ventilation stoppings. In: Mutmansky JM, Ramani RV, eds. Proceedings 

of the 11th U.S./North American Mine Ventilation Symposium (University Park, PA, June 5–7, 

2006). London: Taylor & Francis Group, pp. 361–366. 
94

APPENDIX.—SUMMARY TABLES OF EXPLOSION PRESSURE DATA 

FOR THE LLEM TESTS 

Table A-1.—Maximum explosion pressures during LLEM test #427 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.04 0.3 13 4 1.24 8.6 

108 33 0.05 0.3 84 26 0.87 6.0 

158 48 0.04 0.3 134 41 — — 

211 64 — — 184 56 0.74 5.1 

257 78 0.03 0.2 234 71 — — 

329 100 0.04 0.3 304 93 0.69 4.8 

427 130 — — 403 123 — — 

526 160 0.05 0.3 501 153 0.73 5.0 

626 191 0.03 0.2 598 182 0.73 5.0 

782 238 0.04 0.3 757 231 ~0.71 ~4.9 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Hollow-core block 0.74 5.1 0.51 3.5 

Crosscut 5 451 138 Hollow-core block — — — — 

Crosscut 6 547 167 Hollow-core block — — — — 

Crosscut 7 647 197 Hollow-core block 0.73 5.0 0.54 3.7 

Table A-2.—Maximum explosion pressures during LLEM test #428 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.6 4 13 4 5.1 35 

108 33 0.4 3 84 26 4.5 31 

158 48 0.3 2 134 41 — — 

211 64 — — 184 56 4.4 30 

257 78 0.3 2 234 71 — — 

329 100 0.4 2 304 93 3.8 26 

427 130 — — 403 123 3.4 24 

526 160 — — 501 153 3.4 24 

626 191 0.4 2 598 182 2.9 20 

782 238 0.5 4 757 231 2.7 19 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Hollow-core block1 5.2 36 0.51 3.5 

Crosscut 5 451 138 Hollow-core block1 — — — — 

Crosscut 6 547 167 Hollow-core block — — — — 

Crosscut 7 647 197 Hollow-core block 3.4 23 0.48 3.3 

1

Destroyed during test. 
95

Table A-3.—Maximum explosion pressures during LLEM test #429 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 1.4 10 13 4 3.7 26 

108 33 1.3 9 84 26 3.0 21 

158 48 1.2 8 134 41 3.1 21 

211 64 ~1.1 ~8 184 56 3.0 21 

257 78 1.0 7 234 71 2.8 19 

329 100 0.7 5 304 93 2.1 14 

427 130 — — 403 123 1.3 9 

526 160 — — 501 153 1.1 7 

626 191 — — 598 182 1.0 7 

782 238 1.1 8 757 231 1.0 7 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 None 1.4 9 — — 

Crosscut 5 451 138 None 1.1 8 — — 

Crosscut 6 547 167 Hollow-core block 1.2 8 0.66 4.6 

Crosscut 7 647 197 Hollow-core block 1.0 7 0.48 3.3 

Table A-4.—Maximum explosion pressures during LLEM test #430 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 2.4 17 13 4 6.2 43 

108 33 1.9 13 84 26 5.7 39 

158 48 1.8 12 134 41 5.4 38 

211 64 ~1.9 ~13 184 56 5.5 38 

257 78 1.7 12 234 71 5.2 36 

329 100 1.7 12 304 93 4.9 34 

427 130 — — 403 123 3.8 26 

526 160 — — 501 153 2.7 19 

626 191 — — 598 182 2.3 16 

782 238 1.7 11 757 231 ~1.7 ~12 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 None 3.3 23 — — 

Crosscut 5 451 138 None 2.5 17 — — 

Crosscut 6 547 167 Hollow-core block1 3.8 26 0.86 5.9 

Crosscut 7 647 197 Hollow-core block 2.2 15 0.66 4.6 

1

Three or four blocks knocked out near bottom of stopping during test. 
96

Table A-5.—Maximum explosion pressures during LLEM test #432 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 1.6 11 13 4 3.6 25 

108 33 1.5 10 84 26 3.3 23 

158 48 1.3 9 134 41 3.2 22 

211 64 ~1.1 ~8 184 56 3.2 22 

257 78 1.0 7 234 71 3.0 21 

329 100 0.9 6 304 93 2.8 19 

427 130 — — 403 123 2.0 14 

526 160 — — 501 153 1.4 9 

626 191 — — 598 182 1.2 8 

782 238 1.1 8 757 231 1.2 8 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 None 1.7 12 — — 

Crosscut 5 451 138 None 1.4 10 — — 

Crosscut 6 547 167 Hollow-core block1

 1.7 12 0.61 4.2 

Crosscut 7 647 197 Hollow-core block 1.2 9 0.51 3.5 

1

Two additional blocks knocked out near bottom of stopping during test. 

Table A-6.—Maximum explosion pressures during LLEM test #433 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

10 3 2.9 20 13 4 8.9 61 

108 33 — — 84 26 6.9 48 

158 48 1.7 12 134 41 8.4 58 

211 64 ~1.8 ~12 184 56 7.3 50 

257 78 1.8 12 234 71 7.3 50 

329 100 2.3 16 304 93 6.6 45 

427 130 2.1 15 403 123 5.0 35 

526 160 — — 501 153 3.5 24 

626 191 — — 598 182 2.8 19 

782 238 2.0 14 757 231 ~1.9 ~13 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 None 4.2 29 — — 

Crosscut 5 451 138 None 3.1 21 — — 

Crosscut 6 547 167 Hollow-core block1 3.6 25 0.91 6.3 

Crosscut 7 647 197 Hollow-core block 2.8 19 0.64 4.4 

1

Destroyed during test. 
97

Table A-7.—Maximum explosion pressures during LLEM test #434 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 2.8 19 13 4 7.6 53 

108 33 — — 84 26 6.7 46 

158 48 2.7 18 134 41 7.4 51 

211 64 3.0 21 184 56 6.4 44 

257 78 2.8 19 234 71 6.7 47 

329 100 2.2 15 304 93 5.1 35 

427 130 2.2 15 403 123 4.1 29 

526 160 — — 501 153 2.9 20 

626 191 — — 598 182 2.4 16 

782 238 2.0 14 757 231 2.3 16 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 None 3.4 23 — — 

Crosscut 5 451 138 None 2.6 18 — — 

Crosscut 6 547 167 None 2.9 20 — — 

Crosscut 7 647 197 Hollow-core block1

 2.3 16 3.0 21 1

Destroyed during test. 

Table A-8.—Maximum explosion pressures during LLEM test #457 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

10 3 <0.1 <1 13 4 1.6 11 

108 33 <0.1 <1 84 26 0.8 6 

158 48 <0.1 <1 134 41 0.6 4 

211 64 <0.2 <1 184 56 0.8 5 

257 78 <0.1 <1 234 71 0.7 5 

329 100 <0.1 <1 304 93 0.7 5 

427 130 <0.1 <1 403 123 0.7 5 

526 160 <0.1 <1 501 153 0.7 5 

626 191 <0.1 <1 598 182 0.8 5 

782 238 <0.1 <1 757 231 0.7 5 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Solid block 0.78 5.4 0.51 3.5 

Crosscut 5 451 138 Solid block 0.75 5.2 0.53 3.7 

Crosscut 6 547 167 Steel panel 0.81 5.6 0.55 3.8 

Crosscut 7 647 197 Steel panel 0.75 5.2 0.55 3.8 
98

Table A-9.—Maximum explosion pressures during LLEM test #458 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.6 4 13 4 1.9 13 

108 33 0.6 4 84 26 1.6 11 

158 48 0.5 3 134 41 1.1 8 

211 64 ~0.4 ~3 184 56 1.5 10 

257 78 ~0.3 ~2 234 71 1.4 9 

329 100 0.4 3 304 93 1.4 9 

427 130 0.4 3 403 123 1.4 10 

526 160 0.4 3 501 153 1.2 8 

626 191 0.2 1 598 182 — — 

782 238 0.2 1 757 231 1.2 8 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Solid block 1.6 11 0.51 3.5 

Crosscut 5 451 138 Solid block 1.5 10 0.38 2.6 

Crosscut 6 547 167 Steel panel1 1.3 9 0.30 2.0 

Crosscut 7 647 197 Steel panel1 1.3 9 0.30 2.0 1

Failed during test. 

Table A-10.—Maximum explosion pressures during LLEM test #459 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.2 1 13 4 4.3 30 

108 33 0.2 1 84 26 3.5 24 

158 48 0.2 1 134 41 2.5 17 

211 64 0.2 1 184 56 3.8 26 

257 78 0.2 1 234 71 3.5 24 

329 100 0.1 1 304 93 3.4 23 

427 130 0.2 1 403 123 2.8 19 

526 160 0.3 2 501 153 2.7 19 

626 191 0.4 2 598 182 2.3 16 

782 238 0.4 2 757 231 2.4 17 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Solid block 4.6 32 0.47 3.3 

Crosscut 5 451 138 Solid block 3.4 23 0.48 3.3 

Crosscut 6 547 167 Australian woven cloth 3.0 21 0.54 3.7 

Crosscut 7 647 197 Australian woven cloth 2.8 19 0.55 3.8 
99

Table A-11.—Maximum explosion pressures during LLEM test #460 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.3 2 13 4 6.3 43 

108 33 0.2 1 84 26 5.8 40 

158 48 0.2 1 134 41 5.6 39 

211 64 0.2 1 184 56 5.5 38 

257 78 0.2 1 234 71 5.2 36 

329 100 0.2 1 304 93 5.0 34 

427 130 0.2 2 403 123 4.0 27 

526 160 0.3 2 501 153 3.7 26 

626 191 0.4 3 598 182 3.4 23 

782 238 0.3 2 757 231 3.1 22 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Solid block 6.7 46 0.57 3.9 

Crosscut 5 451 138 Solid block 4.7 33 0.56 3.8 

Crosscut 6 547 167 Australian woven cloth 4.0 27 0.50 3.4 

Crosscut 7 647 197 Australian woven cloth 3.9 27 0.50 3.5 

Table A-12.—Maximum explosion pressures during LLEM test #461 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.2 1 13 4 NA NA 

108 33 0.1 1 84 26 4.1 28 

158 48 0.1 1 134 41 4.3 30 

211 64 0.2 1 184 56 4.0 28 

257 78 0.2 1 234 71 4.0 28 

329 100 0.1 1 304 93 3.4 23 

427 130 0.1 1 403 123 3.5 24 

526 160 0.2 1 501 153 3.2 22 

626 191 0.2 1 598 182 3.2 22 

782 238 0.1 1 757 231 3.2 22 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Solid block 4.2 29 1.32 9.1 

Crosscut 5 451 138 Solid block 4.0 28 1.18 8.1 

Crosscut 6 547 167 Australian woven cloth 3.7 26 1.18 8.1 

Crosscut 7 647 197 Australian woven cloth 3.6 25 1.19 8.2 

NA Not available. 
100

Table A-13.—Maximum explosion pressures during LLEM test #462 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.9 6 13 4 NA NA 

108 33 0.8 6 84 26 6.5 44 

158 48 0.7 5 134 41 6.8 47 

211 64 0.6 4 184 56 6.1 42 

257 78 0.5 4 234 71 6.4 44 

329 100 0.8 5 304 93 5.5 38 

427 130 0.9 6 403 123 5.8 40 

526 160 1.1 7 501 153 5.2 36 

626 191 0.8 6 598 182 4.9 34 

782 238 0.7 5 757 231 4.8 33 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 Solid block1 7.6 52 1.04 7.2 

Crosscut 5 451 138 Solid block 6.7 46 1.06 7.3 

Crosscut 6 547 167 Australian woven cloth1

 6.1 42 0.71 4.9 

Crosscut 7 647 197 Australian woven cloth1

 5.4 37 0.85 5.9 

NA Not available. 1Destroyed during test. 

Table A-14.—Maximum explosion pressures during LLEM test #463 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 3.9 27 13 4 NA NA 

108 33 3.5 24 84 26 17.7 122 

158 48 3.3 23 134 41 18.1 125 

211 64 3.0 20 184 56 20.0 138 

257 78 2.8 19 234 71 15.1 104 

329 100 4.6 32 304 93 16.6 114 

427 130 4.6 32 403 123 12.4 85 

526 160 4.3 30 501 153 9.6 66 

626 191 3.6 25 598 182 7.2 50 

782 238 2.8 20 757 231 5.4 37 

TOTAL EXPLOSION PRESSURES ON THE C-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 4 355 108 None 11.6 80 NA NA 

Crosscut 5 451 138 Solid block1 16.6 115 1.34 9.2 

Crosscut 6 547 167 None 7.2 50 NA NA 

Crosscut 7 647 197 None 5.9 41 NA NA 

NA Not available. 1Destroyed during test. 
101

Table A-15.—Maximum explosion pressures during LLEM test #491 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 5.5 38 13 4 6.2 43 

108 33 3.2 22 84 26 4.4 30 

158 48 3.8 26 134 41 3.7 26 

211 64 3.4 23 184 56 3.5 24 

257 78 4.2 29 234 71 3.6 25 

329 100 3.7 25 304 93 2.8 19 

427 130 3.1 21 403 123 3.3 23 

526 160 2.3 16 501 153 2.4 17 

626 191 — — 598 182 2.0 14 

782 238 2.2 15 757 231 1.9 13 

TOTAL EXPLOSION PRESSURES ON THE B-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type1

psi kPa psi-s kPa-s 

Crosscut 3AB 281 86 Hollow-core block 6.4 44 1.4 9.4 

Crosscut 3BC 281 86 Hollow-core block — — — — 

Crosscut 4AB 377 115 Hollow-core block 4.0 28 1.2 8.1 

Crosscut 4BC 377 115 Hollow-core block 3.6 25 — — 

 NOTE.—Ignition at ~221 ft (~67 m) from closed end of B-drift. 1

All of the stoppings were destroyed during the test. 

Table A-16.—Maximum explosion pressures during LLEM test #494 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.40 2.8 13 4 0.40 2.8 

108 33 0.40 2.8 84 26 0.38 2.6 

158 48 0.39 2.7 134 41 0.36 2.5 

211 64 0.40 2.8 184 56 0.35 2.4 

257 78 0.35 2.4 234 71 0.35 2.4 

329 100 0.39 2.7 304 93 0.28 1.9 

427 130 0.48 3.3 403 123 0.29 2.0 

526 160 0.27 1.9 501 153 0.29 2.0 

626 191 0.28 1.9 598 182 0.29 2.0 

782 238 — — 757 231 0.25 1.7 

TOTAL EXPLOSION PRESSURES ON THE B-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 3AB 281 86 Hollow-core block 0.37 2.6 0.37 2.6 

Crosscut 3BC 281 86 Hollow-core block 0.40 2.8 0.39 2.7 

Crosscut 4AB 377 115 Hollow-core block 0.44 3.0 0.40 2.8 

Crosscut 4BC 377 115 Hollow-core block 0.44 3.0 0.40 2.8 

B-drift 446 136 Hollow-core block with 

 regulator 

0.49 3.4 0.45 3.1 

 NOTE.—Ignition at ~250 ft (~76 m) from closed end of B-drift. 
102

Table A-17.—Maximum explosion pressures during LLEM test #495 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 0.75 5.2 13 4 0.85 5.9 

108 33 0.67 4.6 84 26 0.74 5.1 

158 48 0.63 4.3 134 41 0.62 4.3 

211 64 0.78 5.4 184 56 0.56 3.9 

257 78 0.82 5.7 234 71 0.56 3.9 

329 100 0.80 5.5 304 93 0.53 3.7 

427 130 1.21 8.3 403 123 0.44 3.0 

526 160 0.45 3.1 501 153 0.47 3.2 

626 191 0.42 2.9 598 182 0.46 3.2 

782 238 — — 757 231 0.43 3.0 

TOTAL EXPLOSION PRESSURES ON THE B-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 3AB 281 86 Hollow-core block 0.89 6.1 0.49 .04 

Crosscut 3BC 281 86 Hollow-core block 0.96 6.6 0.53 3.7 

Crosscut 4AB 377 115 Hollow-core block 1.08 7.5 0.53 3.7 

Crosscut 4BC 377 115 Hollow-core block 1.06 7.3 0.53 3.7 

B-drift 446 136 Hollow-core block with 

 regulator 

1.24 8.6 0.54 3.7 

 NOTE.—Ignition at ~250 ft (~76 m) from closed end of B-drift. 

Table A-18.—Maximum explosion pressures during LLEM test #496 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 2.5 17 13 4 3.1 21 

108 33 1.6 11 84 26 2.1 15 

158 48 1.9 13 134 41 1.9 13 

211 64 2.3 16 184 56 1.7 12 

257 78 2.4 16 234 71 1.7 12 

329 100 2.2 15 304 93 1.6 11 

427 130 3.5 24 403 123 1.5 10 

526 160 1.0 7 501 153 1.2 8 

626 191 0.9 6 598 182 1.1 8 

782 238 — — 757 231 1.0 7 

TOTAL EXPLOSION PRESSURES ON THE B-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 3AB 281 86 Hollow-core block 2.8 19 0.53 3.7 

Crosscut 3BC 281 86 Hollow-core block 2.9 20 0.53 3.7 

Crosscut 4AB 377 115 Hollow-core block 3.1 21 0.84 5.8 

Crosscut 4BC 377 115 Hollow-core block 3.0 21 0.83 5.7 

B-drift 446 136 Hollow-core block with 

 regulator 

3.5 24 0.87 6.0 

 NOTE.—Ignition at ~250 ft (~76 m) from closed end of B-drift. 
103

Table A-19.—Maximum explosion pressures during LLEM test #497 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

B-drift C-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 10 3 4.2 29 13 4 4.0 28 

108 33 2.7 19 84 26 3.2 22 

158 48 2.4 17 134 41 2.7 19 

211 64 2.5 17 184 56 2.6 18 

257 78 3.4 23 234 71 2.6 18 

329 100 3.1 21 304 93 2.4 17 

427 130 5.1 35 403 123 2.1 15 

526 160 1.7 12 501 153 1.8 12 

626 191 1.6 11 598 182 1.6 11 

782 238 1.6 11 757 231 1.4 10 

TOTAL EXPLOSION PRESSURES ON THE B-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 3AB 281 86 Hollow-core block 4.3 30 0.70 4.8 

Crosscut 3BC 281 86 Hollow-core block1 4.2 29 0.71 4.9 

Crosscut 4AB 377 115 Hollow-core block2 3.8 26 ~0.94 ~6.5 

Crosscut 4BC 377 115 Hollow-core block2

 3.6 25 0.93 6.4 

B-drift 446 136 Hollow-core block with 

 regulator2

5.2 36 0.97 6.7 

 NOTE.—Ignition at ~221 ft (~67 m) from closed end of B-drift. 1

Partially damaged during test. 

2

Destroyed during test. 

Table A-20.—Maximum explosion pressures during LLEM test #510 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

A-drift B-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 0 0 14.6 101 10 3 0.7 5 

 22 7 14.2 98 108 33 — 

 81 25 13.5 93 158 48 — 

132 40 14.0 96 211 64 0.3 2 

183 56 12.4 86 257 78 0.3 2 

233 71 13.6 93 329 100 0.3 2 

283 86 12.6 87 427 130 0.3 2 

355 108 12.2 84 526 160 0.4 3 

453 138 11.6 80 626 191 0.6 4 

550 168 10.8 74 782 238 1.0 7 

649 198 10.7 74 

807 246 10.3 71 

TOTAL EXPLOSION PRESSURES ON THE A-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 6 600 183 8-in (20-cm) thick wet- 

 laid solid concrete 

 block 

14.5 100 3.0 21 

Crosscut 7 699 213 6-in (15-cm) thick wet- 

 laid solid concrete 

 block 

13.5 93 3.0 21 
104

Table A-21.—Maximum explosion pressures during LLEM test #512 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

A-drift B-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 0 0 13.2 91 10 3 0.6 4 

 22 7 13.1 90 108 33 — — 

 81 25 12.5 86 158 48 — — 

132 40 11.8 82 211 64 0.3 2 

183 56 10.3 71 257 78 0.3 2 

233 71 10.7 74 329 100 0.3 2 

283 86 10.0 69 427 130 0.3 2 

355 108 8.3 57 526 160 0.4 3 

453 138 8.4 58 626 191 0.5 3 

550 168 8.1 56 782 238 0.8 6 

649 198 8.2 57 

807 246 8.4 58 

TOTAL EXPLOSION PRESSURES ON THE A-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 6 600 183 8-in (20-cm) thick wet- 

 laid solid concrete 

 block 

10.4 72 4.6 32 

Crosscut 7 699 213 6-in (15-cm) thick wet- 

 laid solid concrete 

 block 

10.1 69 4.4 31 

Table A-22.—Maximum explosion pressures during LLEM test #515 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

A-drift B-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 0 0 13.4 93 10 3 0.8 6 

 22 7 13.3 91 108 33 — — 

 81 25 13.0 90 158 48 — — 

132 40 14.0 96 211 64 0.3 2 

183 56 12.7 88 257 78 0.4 2 

233 71 13.9 96 329 100 0.3 2 

283 86 12.7 88 427 130 0.4 3 

355 108 11.9 82 526 160 0.5 4 

453 138 ~12 ~83 626 191 0.6 4 

550 168 11.5 79 782 238 1.1 8 

649 198 11.7 80 

807 246 11.1 76 

TOTAL EXPLOSION PRESSURES ON THE A-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 6 600 183 8-in (20-cm) thick wet- 

 laid solid concrete 

 block 

14.2 98 3.9 27 

Crosscut 7 699 213 6-in (15-cm) thick wet- 

 laid solid concrete 

 block 

14.2 98 3.9 27 
105

Table A-23.—Maximum explosion pressures during LLEM test #519 

OMNIDIRECTIONAL PRESSURES AT THE WALL 

A-drift B-drift 

Distance Pressure Distance Pressure 

ft m psi kPa ft m psi kPa 

 0 0 24.8 171 10 3 4.7 32 

 22 7 23.8 164 108 33 — — 

 81 25 22.1 152 158 48 — — 

132 40 23.7 163 211 64 2.7 18 

183 56 21.7 150 257 78 2.5 17 

233 71 24.9 172 329 100 2.5 17 

283 86 21.5 148 427 130 2.0 14 

355 108 20.9 144 526 160 2.1 14 

453 138 ~20 ~135 626 191 2.6 18 

550 168 19.3 133 782 238 2.6 18 

649 198 19.6 135 

807 246 17.6 122 

TOTAL EXPLOSION PRESSURES ON THE A-DRIFT SIDE STOPPINGS 

Distance Pressure Pressure-time integral, 

Location ∫Pdt 

ft m 

Type 

psi kPa psi-s kPa-s 

Crosscut 6 600 183 8-in (20-cm) thick wet- 

 laid solid concrete 

 block 

26.8 185 4.2 29 

Crosscut 7 699 213 6-in (15-cm) thick wet- 

 laid solid concrete 

 block1 

25.3 174 3.2 22 

1

Destroyed during test.
DHHS (NIOSH) Publication No. 2009–102

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