The root cause analysis for a deflagration incident in a large dust collector will be summarized. This includes evidence collection, development of the why tree, additional data collection, and follow-up. Findings from this investigation illustrate the hazards of combustible dust and key preventative measures that can be used to prevent this type of incident. It also illustrates why combustible dust hazards should be considered in process changes made through management of change. (C) 2010 American Institute of Chemical Engineers Process Saf Prog 29: 340-344, 2010