To reveal the flame-propagation behavior and the thermal-radiation effects during coal-dust explosions, two coal-dust clouds were tested in a semi-enclosed vertical combustion tube. A high-speed video camera and a thermal infrared imaging device were used to record the flame-propagation process and the thermal-radiation effects of the fireball at the combustion-tube outlet. The flame propagated more quickly and with a higher temperature in the more volatile coal-dust cloud. The coal-dust concentration also significantly affected the propagation behavior of the combustion zone. When the coal-dust concentration was increased, the flame-propagation velocity and the fireball temperature increased before decreasing overall. Based on the experimental results, a dynamic model of the thermal radiation was employed to describe the changes in the fireballs quantitatively and to estimate the thermal-radiation effects during coal-dust explosions. (c) 2014 Elsevier Ltd. All rights reserved.