Crystalline silica exposure in platinum mining : a task based approach

Abstract

Background: Workers will be exposed to silica dust (SiO2) in any working environment where mineral deposits or rock types are being processed contain silica as a component. To prevent the development of silica related disease, the exposure to silica dust should be kept as far below the time weighted average (TWA) occupational exposure level (OEL). Exposure below the TWA OEL is considered to be safe. The silica content of platinum ore is low and exposure below the TWA OEL (Stanton et al., 2006), however studies have shown evidence of silicosis in workers that had no other exposure to silica outside of the platinum industry (Nelson and Murray., 2012). Objectives: To evaluate the silica exposure levels of 4 different high risk tasks at a platinum mine. To evaluate the sufficiency of the current South African OEL. To compare the differences in protocols used by the mine to NIOSH method 7602. Methods: Dust sampling was conducted by means of two cyclone samplers (aspirated at 2.2 L/min) in the breathing zone of each of the 48 workers in 4 different areas. Two cyclone samplers were used to compare two different protocols. The first protocol reflected the method used by the mine and the second was done in accordance with the NIOSH method 7602 (NIOSH, 2003). Sampling was done in the vamping, development cleaning, belt attendant and grout plant areas. A 25 mm MCE filter was used to capture the respirable fraction. The quartz content of the filter was determined by a SANAS accredited laboratory using qualitative infrared spectroscopy in accordance with NIOSH method 7602. Additional bulk samples were taken to be analysed for silica as well. Results: Most of the samples were below the respective OELs of 0.1 mg/m3 (MHS, 1996), 0.05 mg/m3 (NIOSH, 2002) and 0.025 mg/m3 (ACGIH, 2012). A single sample in the development cleaning area in the Merensky reef had a value of 0.032 mg/m3. Nearly no significant differences were found in the exposure levels between the two protocols, the two reefs or the different underground areas. Although the differences in protocol are not statistically significant the protocol implemented by the mine yielded lower exposure values. The grout plant had the lowest silica exposure levels. Conclusions: Upon evaluating the silica exposures of platinum mine workers there does not seem to be a health or safety risk involved at these low levels. The implemented control measures are sufficient in preventing the development of applicable health and safety risks. However if any new cases of severe illness (e.g. silicosis) occur it may be necessary to re-evaluate the risks involved with silica exposure. Recommendations: The goal of silica monitoring should be to obtain accurate data that represents the actual exposure levels experienced by a worker during a working shift. Accurate data gives insight into the safety of the worker. To achieve this, the monitoring should be done as accurately as possible to adhere to the prescribed methods. Employees/workers should be trained in order to assist in identifying and correcting problems that may occur during sampling.