Underground » Detection and Prevention of Fires and Explosions
In recent times, the effectiveness of traditional methods of coal dust explosion suppression in underground mines has come under increasing scrutiny. Current methods are based upon the widespread distribution of stone dust in mine roadways, and the construction of various types of explosion barriers utilizing stone dust or water. It has long been known that passive explosion barriers of this type are limited in the range of explosion conditions that can be successfully handled. Further, they are considered expensive, and difficult to install and maintain, particularly in a high production longwall panel.
Active explosion barriers differ significantly to traditional passive barriers by detecting the approach of an explosion and triggering the assisted dispersal of a suppression agent. Modern light detectors can be used to detect the approach of the explosion flame eliminating the reliance on pressure rise as a means of triggering, which has limited the application of active barrier technology to explosion suppression in the past. Trials of an active barrier system were recently successful in preventing the flame propagation in a coal dust explosion travelling at 120m/s.
ACARP Project C8010 began the demonstration of the technology proposed for use in an active explosion barrier. That project which has been reported earlier was intended to demonstrate the capabilities of certain technologies for the development of a low cost effective active roadway explosion barrier that could be considered as an alternative to traditional passive barriers. The test work was carried out in conjunction with the South African company, Fire and Explosion Suppression Systems (FESS) at CSIR's Kloppersbos Explosion Testing Station. The barrier utilises components developed by FESS for military and civilian explosion and fire suppression. Unfortunately, considerable difficulties were experienced and it was not until very late in the project that a successful trial was achieved.
This project was intended to expand upon the successful result obtained at the close of Project C8010 by repeating the successful trial and commencing and programme of varied test conditions for the barrier trials. Despite optimism that most of the problems had been overcome, additional testing of the barrier configuration used in Project C8010 failed repeatedly. It was concluded, however, that sufficient testing had been done to demonstrate the physical ability to detect the approach of a flame in a coal dust cloud with sufficient reliability to trigger a dispersal system. The problems identified were the reliability of some components of the dispersal system which limited the volume of extinguishant release and the suitability of the NAF extinguishant for suppressing a coal dust explosion.
As the project was of such importance to the coal industry, testing of different extinguishing agents was scheduled as part of a revised work programme. It has not been possible to commence this work due to protracted legal conflicts in South Africa.
This report will present the results of the test conducted and the conclusions to be drawn from these tests to date. It should be read in conjunction with ACARP report C8010 which provides additional background to the project and the results of earlier testing.