Abstract: This invention relates to an improvement in control apparatus which prevents formation of smoke in a combustion process. The conventional control includes apparatus for first providing the proper flow of either air or fuel to the process to satisfy the required demand for heat. A ratio device is then used to determine the flow of the remaining component necessary for obtaining proper combustion conditions. Where the BTU content of the fuel is likely to vary, a device for analyzing stack gases, typically an oxygen probe is then used to provide a signal to adjust the ratio device based on conditions indicated by the stack gases. The improvement of this invention includes a device for determining when the proportion of the exhaust gas component is outside limitations indicating smoking may occur and an emergency control device actuated when such conditions exist for rapidly adjusting the proportions of fuel and air supplied to the process in order to prevent smoking.