As we explore deeper for mineable ore reserves, an increase in heat of the surrounding strata commonly results. This rock surface temperature or virgin rock temperature (VRT) can pose certain problems in a mine environment. In some underground metalliferous operations, the VRT of the rock can reach 80oC, which can raise safety issues with the use of certain explosive compounds such as the traditional ammonium nitrate/diesel ANFO-type compound. This has lead to the development of new explosive compounds using substitutes for diesel in traditional ANFO compounds. One of these groups of new compounds uses paraffin oil as the diesel substitute. Although these compounds have been proven as an effective explosive, the follow-on effects on the mine environment have not been investigated in as much depth. This project aimed to compare the post-blast fumes of paraffin oil ANFO with traditional diesel ANFO compounds using both small-scale tests at The University of Queensland Experimental Mine (UQEM) and large-scale tests at MIM Enterprise.
The small-scale experimental work involved the detonation of a small amount of explosive in the velocity of detonation (VOD) chamber. The air inside the VOD chamber was monitored for NO, NO2, and CO for around 30 minutes after detonation. The results of these experiments suggest that the re-entry time should be extended for paraffin-based ANFO as compared to diesel based ANFO, but some inconclusive results cast some doubt over the validity of these results. Many problems were encountered during the small-scale experimental work, most of which occurred early in the test work and were corrected, however the rather varied results suggest a new testing method may be required in the future.
The experimental work conducted at MIM Enterprise investigated only development heading blasts, the majority of which were ventilated by auxiliary fans and ducting. All blasts were monitored for NO, NO2 and CO concentrations in return air, with some also being monitored for NOX, and O2. For blasts ventilated by auxiliary ventilation, it was found that re-entry should not occur prior to at least 30 minutes after the blasts.
The overall aim of this project was to provide some useful information for underground metalliferous mines to prevent possible harm to their employees due to post-blast gases. A survey of Australian underground metalliferous mines was conducted to provide information about current industry practices and safety incidents that have occurred at some mines in recent years. In was found that even though the monitoring of blast gases in underground metalliferous mines had increased by 13% over the last 6 years, the number of mines that have experienced safety incidents due to blasting gases has increased from 39% to 56%. It is evident also that once a mine has experienced some sort of safety incident, they still refuse to change their procedures regarding re-entry to a blasted heading.
The small-scale research has consistently shown that the production of blasting gases is larger when paraffin oil is used as the fuel oil as opposed to diesel. However a review of the procedure is necessary if similar research is to continue and it is recommended that a new test procedure be developed utilising a well-ventilated area of the UQEM. The large-scale tests proved that all blasts are different and produce different results. Therefore, it is not recommended that re-entry times be established using theoretical calculations but rather practical research similar to the tests done in this project. Also, it is recommended that mine personnel subjected to high gas concentrations on a regular basis be given a gas monitoring device.