Lead exposure of workers employed as tappers in a platinum smelting environment / Morné de Beer
The study was undertaken after initial surveys indicated that lead (Pb) was present at concentrations in excess of the occupational exposure limit (OEL) on the matte tapping floor (MTF). A follow up study was designed in accordance with the Occupational Exposure Sampling Strategy Manual (OESSM), to determine personal exposure levels of the tappers to Pb whom are employed on the MTF. Following the initial static samples taken during the identification phase, follow up static samples were taken during the follow up personal exposure survey. This enabled us to determine if there were any significant changes in conditions between the initial and static samples. Simultaneously personal samples were taken on a representative group of the 30 tappers employed in the furnace building on the two tapping floors. Samples were taken over a 12 hour period due to the shift duration worked by the tappers. A decision was taken to compare the MTF and the slag tapping floor (STF) due to the similarities in the processes used on both floors. In order to evaluate the possible effect of lead on the workers employed as "tappers", a group of 30 workers employed in the furnace on the tapping floors of the Polokwane Smelter building were evaluated. The group consists of 30 men from multicultural urban environments. This group was further divided into smokers and non-smokers. Personal samples were conducted on 16 of the workers in the aforementioned group of “tappers", who were randomly selected to ensure a top 10% exposure, with a 90% confidence level as prescribed by OESSM. A short calculation gave an indication that the exposure to Pb according to the Lead Regulations of the Occupational Health and Safety Act (OHS Act), Act 85 of 1993, the OEL for Pb other than tetraethyl Pb is 0.15 mg/m3 for an 8-hour shift would decrease to 0.10 mg/m3 for a 12-hour shift. This value was then used to compare exposure levels to the adapted statutory limits. Lead serves no useful purpose in the human body, and it's presence in the body can lead to toxic effects, regardless of the exposure pathway. The blood lead level (BLL) could be expected to be between 1 and 5 µg/dL in rural people and around 13 µg/dL in urban The results of the BLL tests performed during the study however indicated that all BLL were under 10 µg/dL, which indicated that the current control measures that are in place are keeping the exposure of the tappers to Pb down. The amount of time per individual spent on the MTF is being kept to a minimum by rotating the 30 tappers on a shift basis, which means that a particular employee will only work for one shift on the MTF before being rotated to another area within the plant. The results obtained showed that there is no significant difference between the initial and static samples taken on the MTF and STF. The BLL tests performed on the group of tappers were cross-referenced against the risk factors that were identified, as being possible sources of non-occupational sources of exposure to Pb. No significant results were obtained for this comparison showing no effect on the BLL's due to non-occupational exposures to Pb. Lastly there was a significant difference between the personal exposures measured at the MTF and the STF, indicating that there is a higher level of Pb in the ambient atmosphere of the MTF. This was expected, due to the fact that Pb is a heavy metal and would tend to group and sort with the rest of the valuable metals, which are found on the MTF. The electric arc furnace is designed to incorporate a slant downward from the STF to the MTF. Bone dry concentrate is fed pneumatically into the furnace. The concentrate which is in powder form is then smelted and reaches a temperature of approximately 1500°C. In the time it takes for this concentrate to be smelted and reach a fluid state, the valuable heavy metals, including lead, move down the slope toward the MTF and to accumulate where it can then be "tapped" out by opening the tap hole on the MTF. However a small amount of Pb and other heavy metals like: platinum, gold, rhodium, rubidium, silver, etc., remain caught up in the mixture and are passed out along with the waste product slag, on the STF. This explains why small amounts of Pb were also found in the ambient atmosphere of the STF. Recommendations were made to improve on the current extraction ventilation system, to increase the effective uptake of Pb from the ambient atmosphere on the MTF whilst the molten metal is being allowed to run along the launder to the ladle. By optimising the shift rotation roster it could be ensured that the minimum amount of time is spent on the MTF by each individual. An increased awareness of personal hygiene, and standard operating procedures could further decrease personal exposure to Pb. The problem however lies in decreasing the amount of airborne Pb on the MTF to below the OEL, and as an interim this area has been declared a respirator zone. Personal Protective Equipment (F'PE) was the only effective form of control at the time of the survey. Half mask respirators with chemical cartridges, which along with dust filters present a barrier between the lungs and the ambient atmosphere of the MTF.
- ETD@PUK