Evaluation of exposure to airborne soluble platinum in a precious metal refinery during non–routine operations
Background: Platinum refinery workers are exposed to various elements during the refining process, with soluble platinum salts posing a potential health risk. Platinum salts are extremely potent sensitisers that can result in the clinical syndrome of platinum salt sensitivity (PSS) that leads to skin and respiratory hypersensitivity in refinery workers. Several published research articles document refinery workers’ exposure levels to soluble platinum salts during production. However, the exposure levels to soluble platinum salts during non–routine stock take activities are unknown although cases of sensitisation have been diagnosed following these nonoperational periods. Stock take for the platinum refinery under study commenced on 18 January 2010 and ended 22 February 2010. Increased emphasis was placed on flushing plant equipment rather than dismantling it. The aim was to dismantle 10% of what previously was dismantled to reduce the risk of exposing employees to soluble platinum salts, to reduce the chance of damaging plant equipment and for cost and time saving purposes. Aim: The objectives of this study are to: (i) quantify work area and personal exposure levels; (ii) identify work areas and work practices with exposure levels exceeding the occupational exposure limit (OEL) (>2 ug/m3); (iii) determine whether exposure levels differ significantly between: a) personal sampling groups (engineering versus production), b) area sampling groups (open versus closed–face sampling), c) work areas, d) total area and total personal sampling groups and to (iv) evaluate the efficiency of the current control measures utilised. Design and Method: A total of 58 platinum samples were collected, consisting of 38 personal and 20 area samples. Personal sampling consisted of Institute of Occupational Medicine (IOM) samplers housing reusable 25 mm filter cassettes with mixed cellulose ester (MCE) membrane filters for the collection of inhalable airborne particles. Because both the cassette and the filter were pre- and post–weighed as a single unit, all particles collected (even those against the walls of the cassette) were included in the analysis. Sampling was conducted in accordance with the stock take schedule and scope and included a roster for the systematic dismantling and cleaning of the refinery, following the process flow. A target population of maximum five fitters and five operators per area were identified, responsible for dismantling and cleaning plant equipment respectively. The sampling strategy was based on the identification and sampling of employees presumed to have the highest exposure risk. The Occupational Exposure Sampling Strategy Manual (OESSM) refers to this as the “maximum risk employees” (Liedel et al., 1977). The selection of the maximum risk employees was done with reasonable certainty since the employees sampled were working closest to the source of exposure. Sampling was conducted for the total duration of the task consisting of single sample measurements. Area sampling was conducted by means of BUCK Air high volume samplers fitted with preweighed 47 mm MCE filter cassettes to show the spread of the contaminant in the work area. The high volume samplers were calibrated to operate at a sampling volume of 20 L/min. The sampling heads were positioned 1.5 m from the ground surface and as near as possible to the work location or failing this as near as is possible to major sources of exposure. Samples were collected and analysed according to the method for the determination of hazardous substances 46/2 (MDHS 46/2). This is an advanced sampling and analysis standard which enables detection of low levels of soluble platinum (0.01 µg/m3). Results: Thirty eight personal platinum samples were collected, consisting of a sampled engineering (n=15) and production (n=23) subgroup. Out of the thirty eight personal samples taken in total, 21% of the samples’ concentrations exceeded the OEL of 2 µg/m3 and ranged between 0.004–20.479 µg/m3. Twenty area platinum samples were collected, consisting of open (n=10) and closed face (n=10) sampling. Out of the twenty area samples taken in total, 10% of the samples’ concentrations exceeded the OEL of 2 µg/m3 and ranged between 0.0004–5.752 µg/m3. The mean personal exposure levels for the production subgroup (2.739 µg/m3) were significantly higher compared to the engineering subgroup’s mean personal exposure levels (0.393 µg/m3). This significant difference (p=0.033) was expected since the production subgroup was more exposed and involved in the digging out of residues and the cleaning of plant equipment compared to the engineering subgroup with limited exposure and involved in the opening of plant equipment. Although the mean exposure levels for open face sampling (0.725 µg/m3) were higher compared to the mean exposure levels for closed face sampling (0.441 µg/m3) no significant difference (p=0.579) were noted. The mean area exposure levels (0.583 µg/m3) were significantly lower (p=0.004) compared to the mean personal exposure levels (1.813 µg/m3) for similar areas and tasks performed and, therefore, not an effective indicator of personal exposure levels. Higher personal exposure levels were expected since the workers were closer to the source of exposure and since the platinum salts could have diluted in the workplace’s air resulting in lower area exposure levels. Conclusion: The research study addressed the problem statement, met the objectives set out in Chapter 1, hypotheses were accepted and rejected and future studies were recommended. It was hypothesised that: a) refinery workers are exposed to airborne soluble platinum during non–operational periods; b) exposure levels do not differ significantly between the personal sampling groups (engineering vs production); c) exposure levels do not differ significantly between the area sampling groups (open versus closed–face sampling); d) exposure levels do not differ significantly between work areas; e) exposure levels differ significantly between total personal and total area sampling groups. The results confirmed that refinery workers are exposed to airborne soluble platinum during non–operational periods and hypothesis a was accepted. The personal exposure levels of the engineering versus production sampling groups differed statistically (p=0.033) and hypothesis b was rejected. The exposure levels of the open and closed face sampling groups did not differ significantly (p=0.579) and hypothesis c was accepted. In addition no statistical difference (p>0.05) was indicated between the work areas and hypothesis d was accepted. Total personal versus total area exposure levels (p=0.004) differed statistically and hypothesis e was accepted.
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