<p>Burners are used extensively in the metallurgical industry ranging from melting to heat treatment. The control of burners is complicated by the scarcity of direct information from the flames. In most cases, the available information is limited to offgas analysis, which may be affected by secondary combustion with leakage air. Optical spectroscopy is a method for detecting the presence of elements and molecules in a light source, but high-temperature furnaces pose specific challenges for such measurements. The measurement system captures all radiation reaching the sensor, and the hot furnace walls emit a significant amount of visible and infrared radiation, which can complicate data analysis. This work evaluates the applicability of the optical emission spectroscopy (OES) for in situ flame diagnostics in furnaces and to determine the extent to which wall radiation interferes with flame radiation. Based on the findings of this study, molecular emissions can be measured from furnace flames with relatively straightforward methods when the wavelengths are below 600&#xa0;nm. At longer wavelengths, wall radiation significantly hampers the measurements. To counter this, an approach for subtracting wall radiation from measured spectra was employed. Finally, the performance of a laboratory-grade spectrometer and an industrial spectrometer was compared for this type of measurement. Both were found to be suitable for flame measurements in furnace environments, although the laboratory-grade spectrometer, as expected, provided higher accuracy.</p>