ENVIRONMENTAL STRESSES AND STRAINS IN AN EXTREME SITUATION - THE REPAIR OF ELECTROMETALLURGY FURNACES

Whenever a continuous casting furnace breaks down, the emergency inter vention necessary to repair it has to be carried out under exceptional environmental conditions caused mainly by heat, as the furnace must b e stopped for the shortest possible time. In this study, we aimed to e valuate the stresses and strains to which boilermakers are subjected d uring the replacement of an electrode element of a 20 MW furnace. The thermal stress was evaluated by the wet bulb globe temperature (WBGT) index. CO2 was measured continuously at the furnace periphery and spor adically in the center of the furnace using an electrochemical method, while CO was also measured in both areas, using Drager tubes. Dusts w ere sampled by a CPM3 (Andersen particle fractionating sampler) and a CIP10 (personal sampler). The strain was evaluated by continuous ECG r ecording with an Aclan IFC 85, breathing performance was assessed with an HI 298 microspirometer, and blood oxygen saturation was evaluated using a Biox oximeter. Thermal stresses are extreme: WBGT was 55-degre es-C in the furnace center and 34-degrees-C in the furnace periphery. In spite of the ventilation, the reduction in heat during the 6 h of t he intervention was negligible and did not provide sufficient cooling. The analysis of gases and dusts were of minor interest, although the mean CO level at the furnace periphery was 40 ppm, with a peak level o f 140 ppm in furnace center. CO2 and SO2 levels did not exceed TLV-TWA and TLV-Stel values. The damage to the human body was significant wit h average heart rates of 150/min during the working period and a ''rel ative cardiac cost'' of 37%-69%, leading to major fatigue. The thermal strain was the most stressful (''thermally induced additional heart b eats'' represented 86.8%-100% of the global cardiac cost). Spirometers did not revealed a reduction in dynamic lung volumes after 4 hours' w ork. The SaO2 and HbCO were not significantly modified. The overall di fficulty of this time-consuming repair and the risks inherent in the p hysical and thermal stresses placed on the human body show that urgent technical improvements are badly needed; this is especially true of t he tools used for manutention, the organization and duration of the re pair, the planning of rest periods, and medical supervision.