An investigation into the ignition and deflagration mechanisms relating to the testing of permitted explosives with reference to British health and safety executive#146;s TM2

摘要

In an effort to provide the underground coal mining industry with an understanding of what governs if an explosive is classed as permitted, a preliminary 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, nitroglycerine.Eighty Type I tests were carried out and preliminary findings were that the mechanism that causes ignition is a reflected shockwave which compresses and reheats detonation products. The origin of the reflected pressure wave changed when the primer position was altered 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.Additionally numerical modelling was employed to characterise pressure, temperature and velocity profiles within the gallery for blown out and cut off shots. Whilst the pressure and temperature results predicted by the CFD model were 1.5 to 3 times the magnitude of those measured in the field, the modelling results exhibited the behaviour of the shockwaves reflecting off the gallery walls, rebounding, gaining intensity and travelling back towards the centre axis of the gallery. This predicted behaviour reinforced the belief that re-heating of detonation gases by reflected shockwaves is the prime ignition mechanism of the Type I TM2 tests.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 isn't the risk of deflagration occurring eliminated’?In reading this thesis it must be noted that all findings are preliminary and many more tests are required to confirm trends and behaviours observed in the testing to date.