Explosives in the 21st Century: Stage 1 - An Investigation into the Rationale of Explosive Used in Underground Coal Mines

This project was funded in two stages - both published reports are sold together and summarised below:

-  C13025 Permitted Explosives for 21st Century

-  C14039 Permitted Explosives for 21st Century: Stage 2

C13025  Explosives in the 21st Century: Stage 1 - An Investigation into the Rationale of Explosive Used in Underground Coal Mines

This investigation examines the tests conducted on explosives for permitted use in underground coal mines to decipher the scientific basis behind each testing regime. The testing methods used within Australia are the United Kingdom's Buxton Tests. These have been compared with methods around the world, including the United States of America, France, South Africa and Japan. Once examined, the importance of various criteria and the level of restrictions required to create a safe and effective permitted explosive is evaluated.

There are a number of issues relating to the testing methods currently used around the world and in particular the Buxton Tests used in Australia as these are the current set of tests that provide guidance for the acceptance of permitted explosives. These issues mostly relate to the decreasing availability of permitted explosives due to a reduction of manufacturers making nitro-glycerine, a lack of testing facilities, the age of the testing methods, and the lack of new research to validate the appropriateness of explosive testing methods with non nitro-glycerine based explosives.

From the information gathered and research presented in this report, it is clear that testing around the world has developed by devising empirical tests that have been considered by most overseas testing facilities to be more severe than any condition that could occur in reality. The ability to measure the actual behaviour of an explosive and the determination of any factor of safety provided by these tests does not exist. Having examined these tests there are sufficient similarities to enable some comparisons. However, it would be difficult to answer any question that required a definitive answer in relation to these comparisons.

This raises a number of issues associated with the current explosive testing methods. These methods require further quantitative analysis and the adoption of additional guidelines in order to adapt them to the explosives currently available and the mining conditions present today.

Although the current testing methods have produced safe explosives in the past, they may not be the most appropriate tests to determine the suitability of modern explosives and a variance from these testing methods or the adoption of alternate tests could still provide safe and suitable explosives without compromising safety.

C14039 Explosives for the 21st Century: Stage 2

In an effort to provide the underground coal mining industry with an understanding of what governs if an explosive is classed as permitted, a research project was undertaken to investigate the scientific basis of the British Health and Safety Executives Testing Memorandum#2 (TM2). Previous literature indicates that the TM2 standard is empirical and based on comparative testing of the explosive in use at the time, nitro-glycerine. Eighty Type I tests were carried out and it was found that the mechanism to ignitions were a reflected shockwave compressing and reheating detonation products. The origin of the reflected pressure wave changed as the primer position alters within the cannon. With a pressure transducer and pyrometer mounted on the side of the gallery the measurements aided in identifying those maximum pressures and temperatures prior to ignition that are collectively a set of parameters that could be used to identify if an explosive would cause an ignition in the gallery. One hundred and eight deflagration tests were conducted in the Type II cannon. The main finding was that the longer a receptor is subjected to elevated pressures due to confinement the higher the probability of deflagration. Additionally emulsion explosives were found to detonate in the cannon rather than deflagrate raising the question if the explosive is consumed instantaneously then the risk of deflagration is not present?