As of 2030 Directive (EU) 2018/850 introduces restrictions concerning landfilling of all waste suitable for recycling or other recovery of materials or energy, and in general, this legal act aims to limit the amount of municipal waste landfilled to 10% by 2035. The dangerous process of storing sewage sludge in the form of landfills requires the identification of flammable properties, among others of dried sewage dust, which has the capacity to ignite and to spontaneously combust during storage in silos. Hence, the aim of the study was to experimentally determine selected flammable properties of the sewage dust selected for testing, and to show the hazards that occur during their mass storage. The study determined the minimum ignition temperatures of layers and clouds of the tested sewage dust at constant temperature setting of the furnace surface in accordance with EN ISO/IEC 80079-20-2:2016 and at a constant increase in the furnace temperature of 3 °C/min in accordance with EN 60079-14:2014. A self-heating and self-ignition analysis of the deposited sludge dust was performed according to EN 15188: 2021 and a thermogravimetric test according to EN ISO 11358-1: 2014, and additionally the burning heat was determined according to EN ISO 1716:2018. In order to determine the possibility of reducing the susceptibility of dried sewage to self-heating, which leads to spontaneous combustion, two selected extinguishing powders for extinguishing class A, B, C and D fires were used in the tests. The minimum ignition temperature of the sewage sludge dust layer at constant temperature of the furnace surface with a layer thickness of 5 mm is 270 °C, and for a layer thickness of 12.5 mm – 250 °C. ABC Favorit was found to be the most effective extinguishing powder, and increased the value of the minimum ignition temperature of the layer (5 mm thick) to 360 °C. The self-ignition temperature value depends on the volume of the stored material. For the biggest studied volume (100 cm3), the lowest self-ignition temperature was recorded which equalled to 144 °C. An analysis of the obtained test results allows the presumption that the dried sewage dust is a combustible material with properties similar to combustible materials of organic origin (biofuels).