Thermal characterisation of the furnace tap floor environment of a platinum group metals smelter

Abstract

Background: South Africa is the leading global producer of platinum group metals (PGMs), a vital industry that relies on high-temperature smelting processes. The smelting of PGM ore occurs in furnaces operating at extreme temperatures of 1350–1600°C, which generate significant radiant heat. Molten materials, released from the furnace during furnace tapping, pose an additional source of radiant heat. This intense thermal environment creates substantial risks of heat stress for workers performing tasks on the furnace tap floors. Despite the critical role these areas play in smelting operations, the thermal environment of furnace tap floors at PGM smelters remains poorly characterised. Understanding these conditions is essential for improving worker safety and informing the design of effective protective equipment. Objectives: To quantify various environmental variables (heat flux, dry-bulb temperature [DBT], wet-bulb temperature [WBT], globe temperature [GT], relative humidity [RH], wet-bulb globe temperature [WBGT] and air velocity) on the matte and slag tap floors, to assess and compare the spatial variation of the thermal variables within and across the tap floors, and to compare the heat flux and WBGT values to reference values. Method: Environmental variables were measured across a grid on the matte and slag tap floors at a PGM smelter during normal tapping conditions. Environmental monitoring instruments, including heat stress monitors and a thermal comfort measurement system, were used to quantify heat flux, DBT, WBT, GT, RH and indoor wet-bulb globe temperature (WBGTi) on the tap floors. Contour maps of the thermal variables were generated using Surfer® software to assess spatial variations. Observations were made regarding the tappers’ duration of presence in various locations, activity levels and clothing. This information was used to estimate the time-weighted average effective WBGT (TWA-WBGTeff) values according to the ISO 7243 standard for various exposure scenarios. Heat flux exposure at various locations was estimated and compared to the recommended maximum durations for aluminised clothing. Results: The following mean levels of thermal variables were measured on the slag tap floor: 35.6 ± 3.6°C (DBT), 22.1 ± 1.9°C (WBT), 50 ± 10.4°C (GT), 16.2 ± 5.5% (RH), 29 ± 3.7°C (indoor wet-bulb globe temperature [WBGTi]) and 974 ± 537 W/m² (heat flux). The matte tap floor exhibited the following levels of these variables: 35.8 ± 3.1°C (DBT), 20.8 ± 1.8°C (WBT), 48.5 ± 9.2°C (GT), 11.1 ± 2.3% (RH), 27.8 ± 3.2°C (WBGTi) and 554 ± 458 W/m2 (heat flux). Hotspots on the matte tap floor were observed surrounding the active tap-hole and launder, whereas the slag tap floor exhibited a hotspot at the centre front and cooler regions at the sides. A moderate to strong and statistically significant correlation was observed between WBGT and heat flux on both the matte (rs(15) = 0.68, p = 0.006) and slag tap floors (rs(19) = 0.67, p = 0.002). The TWA-WBGTeff exceeded their respective limits in all scenarios except when only 20 minutes per hour was spent on the tap floors. The heat flux levels at various locations (< 4600 W/m2) did not exceed the exposure durations since no maximum exposure duration is recommended at this heat flux level. Conclusion: The matte and slag tap floors present distinct and non-uniform thermal environments with spatially varying conditions. On the matte tap floor, heat is concentrated around the active launder while the slag tap floor presents a more balanced thermal environment, reflecting the difference in tapping practices between the floors. The correlation between heat flux and WBGT suggests future research regarding its potential as a proxy for conventional heat stress metrics. Elevated thermal conditions are present on the tap floors that pose a risk of heat stress to furnace tappers depending on location and exposure duration. More than 20 minutes per hour on the tap floor when wearing an aluminised suit poses a risk of heat stress to furnace tappers. These findings could inform future workplace interventions by identifying high-risk areas and understanding the factors contributing to heat stress, enabling more targeted and effective strategies to protect furnace tappers.