To test dispersed stone-dust barriers for effectiveness in bord and pillar

The project was successfully completed at the National Institute for Occupational Safety and Health (NIOSH), Pittsburgh Research Laboratory’s (PRL), Lake Lynn Experimental Mine (LLEM) during the period from January 1999 through May 2000.  The tests were conducted in a three-entry section of LLEM.
The prime objective of Phase I (January 1999 through April 1999) of the work was to evaluate single bag performance at various positions in the gallery when exposed to different explosions.  These methane explosions varied in strength and position to generate varied explosion pulses and explosion generation directions.
The evaluation of the functional performance of the bags included visual inspections of the bags and an estimation of the stone dust distribution on the mine floor after the explosions.
The major conclusions of the work can be summarised as follows:
  • That a bag can operate at dynamic pressure as low as 4 kPa.
  • The static pressure is reduced and almost reaches equilibrium in the three entries at distances far (>100 m) from the ignition position in B-drift.
  • Stone dust bags suspended in these areas of pressure equalization (in the crosscuts between the entries) did not operate effectively.
It can be concluded that the pressure pulse created in a single methane explosion can result in effective bag operation in a low seam (~2 m high), multiple entry mine when suspended close to the roof. The effective distribution of stone dust is dependent on the distance from the explosion source as well as the position or placement of the bag, i.e., if it is suspended in a drift or a crosscut.  It was further noted that the total dust dispersal efficiency is less for multiple entry tests when compared to previous test work in single entry tests.
The prime objective of the tests against coal dust explosions (Phase II of the project conducted from October 1999 through March 2000) was to evaluate the distributed and concentrated bagged barrier performance in a multi-entry mine section. To this end two evaluation explosions were used.  The fuel zone of the first explosion type was only in the center B-drift, and the barrier was also installed in B-drift.  The distributed barrier extended from about 74 to 170 m and the concentrated barrier extended from about 74 to 104 m in B- drift.  In the second explosion type, coal-rock dust fuel mixtures were placed in all three drifts. A total of six explosions, two baseline and four barrier evaluation explosions, were conducted. Two explosions each were used to evaluate the distributed and concentrated barriers.
The distributed barrier was successful in both types of explosion tests in inhibiting flame propagation.  The flame extended further for the explosion tests where the dust was loaded in all three entries compared with dust loaded only in the center entry, but in both cases the flame was stopped within the barrier zone.  The concentrated barrier was also successful in stopping flame propagation within the barrier zone in both explosion tests.
From the full-scale experimental mine test results, it can be concluded that both bagged barrier designs were effective in stopping coal dust explosions in the multiple entries of the LLEM.