Underground » Detection and Prevention of Fires and Explosions
The bag-barrier system, invented by the South African group, CSIR-Miningtek, and now used in Australia, represents a significant change to the management of explosion suppression in underground coal mines. This report summarises the initial testing of the bagged barrier leading to its recent use in Australia, and details the latest results from testing in the multi-heading Lake Lynn Experimental Mine in USA.
Original testing in Germany and South Africa was all undertaken in single-entry style test galleries, up to 22 m2 in section. Based on this, guidelines for their use were developed and adaptations made for Australian use. A Queensland Department of Mines Approval was granted in 1999.
This original testing has now been supplemented by testing in the multi-gallery Lake Lynn mine in the USA. From this testing, it is reasonable to conclude that the bagged barrier configurations considered were successful at preventing the propagation of a coal dust explosion in the heading in which they were installed. The flame extension in the base-line coal dust explosion was about 250m and this was significantly reduced by the presence of the concentrated or the distributed barrier in all the tests conducted.
It was also seen that:
- The bagged barrier functions at dynamic pressures as low as 4kPa which is lower than other barriers previously studied by ACIRL, and validates prior testing in Germany and South Africa
- Total dust dispersal efficiency is lower in a multi-heading environment than a single entry, but the barrier can function effectively
- Bags suspended in areas of pressure equalisation, such as cross-cuts, did not operate as efficiently as in the headings (but nor would other barriers).
There were also indications that under some circumstances it would be possible for explosion to go around a barrier in marginally protected flanking roads. It is almost certain that at some point, reducing the stone dust concentration in flanking roadways would allow explosion propagation around an adjacent barrier. It can, therefore, be concluded, that all roadways need protection against explosion propagation, by explosion barriers and/or adequate stone dusting.
Nothing in the recent tests would suggest that barrier distances from possible sources of ignition, should be changed.
The testing at Lake Lynn was partially funded by ACARP who also engaged staff of ACIRL to partake in the trials and prepare this report.