Dust contamination is a risk factor for the population of the town of Ruse. It is very strongly expressed during the heating period. The paper presents the results from long-lasting investigations of dust content in the free air by residential districts, at different weather conditions and other factors. Results are compared with sociologic research among the townspeople. An attempt is made to assess the influence of Thermo-electric Power Plant and other industrial sources. Criticality is assessed according to the differential risk for dangerous action. It is compared with data about sick rate among population.