A deflagration occurred in a pilot scale vessel containing an oxygen atmosphere and an organic solvent well below the flash point. This was unexpected since the experiment had been carried out on a smaller scale over 50 times. Further investigation of the incident showed that the loading of the vessel and agitation system produced a flammable mist which was capable of explosion at temperatures below the flash point. Simulation studies of the mist conditions in a controlled flammability system were also conducted. Ignition sources were also investigated and at least two were shown to be feasible.