Abstract At present the emission measuring is used for mapping the injurants in order to minimize that. This article describes principle of utilization the emission measuring and speed of changes monitoring for metallurgical technologies control, steel production mainly. The principle of identification the components concentrations changes in steel bath is described. It is based on measuring the component concentrations changes in outlet gas. Elementary relationships in the field of chemical kinetic are deduced. It shows necessity to measure much more other technological parameters, not only emissions. The theory described in this contribution is also applicable for other metallurgical technologies.