Although there is a plenty of experimental data on explosibility of coal dust, new coal mining technologies, e.g. top coal caving in thick beds, to be introduced require additional investigation of dust formation processes and fire/explosion hazard characteristics of coal dust. The fire/explosion hazard of coal dust was tested on an experimental setup in the form of a vertically set thick-wall glass tube with a round spray meant to ensure uniform distribution of coal dust in the working space of the tube. The transparent walls allowed viewing the process of filling the tube with dust, ignition of the dust and flame propagation up/down the tube. The observations over flame front travel showed that burning of coal dust up to certain concentrations was characterized by a weak increase in the excess pressure in the reaction chamber. By an analogy with combustion of air and hydrocarbon mixtures, it can be expected that cold flame mode is also valid for coal dust. Transition of the burning front to the hot flame mode (which means essential pressure buildup) took place in the test when the coal dust concentration was increased by 100–150 g/m3 and more depending on the temperature of the ignition source. The proposed experimental procedure makes it possible to determine critical conditions of flame propagation during uniform distribution of dust cloud under varied temperature of the ignition source. It enables more exact rating of coal dust and, thus, whole mining practice by the fire/explosion hazard criterion with the appropriate preventive control.The study has been supported by the Ministry of Education and Science of the Russian Federation in theframework of the Federal Targeted Program on R&D in Priority Areas of Advancement in the Science and Technology of Russia for 2014–2020, Project: Efficient Robotic Top-Coal Caving Technology, Agreement No. 14.604.21.0173 dated September 26, 2017.