| Summary: | Ammonium Nitrate-Fuel Oil (ANFO) is the explosive generally used in the mining industry to blast ore from the rock face. The use and detonation of ANFO explosives in an underground mine is an intrinsically hazardous process. The by-products formed during blasting have been well studied over the years and modern mining techniques and methods have evolved to mitigate the inherent blasting and gas emission risks. However, there is insufficient research and quantitative data on mine workers’ respiratory exposure to blasting gasses under realistic underground conditions. Aim: The objective of this study was to determine whether blasting gasses such as nitric oxide (NO), nitrogen dioxide (NO2) and ammonia (NH3) pose an inhalation health risk to underground mine workers cleaning at the blasting panels approximately three hours after the detonation of ANFO explosives. Scraper Winch Operators’ (SWOs) respiratory exposure to selected blasting gasses was simultaneously sampled by means of active and passive sampling methodologies.
Method: Personal exposures to NO, NO2 and NH3 were measured and analysed in accordance with NIOSH methods 6014 and 6015. Along with the active air samplers, respiratory exposure to NO2 and NH3 were measured by means of radial symmetry diffusive samplers (Aquaria® RING). Measurements were taken over an 8-hour period, where this was not applicable; results were time weighed to an average 8-hour exposure concentration in order to compare the Scraper Winch Operators’ (SWOs) respiratory exposure to the Occupational Exposure Limits (OELs) contained in the Regulations of the Mine Health and Safety Act (No. 29 of 1996).
Results: The active air sampling results indicated that the SWOs’ respiratory exposure to NO, NO2 and NH3 complied with their respective OELs contained in the Regulations of the Mine Health and Safety Act (No. 29 of 1996). However, one of the SWOs had an exposure which exceeded the action level (50% of OEL) at which level the implementation of control measures are recommended to reduce the SWO’s exposure. Based on the results of the Wilcoxon matched pairs test, statistical significant differences were observed between the exposure results of the two sampling methodologies for NO2 (p = 0.00078) and NH3 (p = 0.044), with the passive diffusive sampling technique under sampling when compared to the active sampling method. This was also confirmed by a Spearman rank order correlation which indicated a poor relationship between the two sampling methods for NO2 (r = -0.323) and NH3 (r = 0.090). Environmental conditions (i.e. temperature and humidity), as presented in an underground mine, may have been a major factor for the variation between the two sampling methods, mostly affecting the passive samplers.
Conclusion: It was established that engineering and administrative control measures implemented at the underground mine were effective to control SWOs’ respiratory exposure to NO, NO2 and NH3 below their respective OELs. An acute health risk pertaining the inhalation of blasting gasses was, therefore, not presented to mine workers cleaning at the blasting panels approximately three hours after the detonation of ANFO explosives. However, long-term exposure to blasting gasses at low concentrations may present SWOs with a health risk if such exposures are not adequately controlled or mitigated. The dilution and production of blasting gasses also varied from one blasting level to another. Geological formation, explosive charge-up and loading practices, the amount of water vapour inside the stopes and ventilation parameters are among the factors that may have affected the amount of blasting gasses produced underground. In addition, a drop in the carbon monoxide levels as indicated by the mine’s central gas monitoring system would not necessarily mean a lowering in other blasting gas concentrations (i.e. elevated ammonia gas concentrations as identified in the present study). The personal exposure levels between the active and passive sampling measurements also differed considerably. This may be ascribed to the impact underground mining conditions and processes had on the sampling media as well the complexities involved when sampling blasting gasses in general. === MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014
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