The reaction of CO decomposition can be judged qualitatively from the soot carbon in the throat dust after wet purification of the gases. The presence of carbon resulting from CO decomposition in fine dust fractions in the form of complex knots, chains and individual whiskers during operation of the blast furnace with a throat gas pressure of 1. 5 atm (abs. ) and oxygen enrichment of the blast is confirmed. Nucleation and growth of individual branches of soot occur on the reactive zone of particles of freshly reduced iron. The occurrence of CO decomposition can introduce significant distortions into the thermal balance of blast furnace smelting, as determined from the total gas composition.