Combustion of biomass is becoming an increasingly important energy source. This is especially true for wood pellets, as several power companies have decided to use this fuel instead of coal. In this process, the wood pellets are ground in big mills and, from there, pneumatically transported to the burners in the boiler where they are consumed. The grinding of biomass and coal represents an explosion hazard, which can potentially result in considerable damage to the power plant upon propagation of the explosion from the mill into other parts of the installation. An experimental investigation was performed aiming at understanding explosion loads that can occur due to an accidental dust explosion in a mill under realistic operating conditions. The tests were performed in a roller mill (capacity 36 metric tons coal/h; internal volume 23.2 m(3)) connected to a coal feeder located on top of the mill. Test conditions were predefined using the computational fluid dynamic-based dust explosion simulation tool DESC. DESC was used to estimate the flow conditions inside the roller mill during normal operating conditions. In the full-scale tests, these flow conditions have been simulated injecting the dust pneumatically. In total, 25 tests were performed, and a number of parameters were varied, including dust type (wood dust and coal dust.), dust concentration, and dust cloud location. (C) 2010 American Institute of Chemical Engineers Process Saf Prog 30: 87-96, 2011