The Dutch Safety Board has published a report detailing what caused the explosions in a reactor at the SMPO (styrene monomer – propylene oxide) plant at Moerdijk in June 2014. Sections of the reactor were blasted 250 meters away, while other debris was found at distances as far away as 800 meters.
The accident happened during start-up after catalyst replacement. The reactor was being flushed with warm ethylbenzene. This had been done many times before and was assumed to be safe, bases on a 1977 reactivity test at 130°C with the catalyst then in use. Several plant changes and an improved catalyst, however, made this assumption invalid, as the ethylbenzene reacted with the improved catalyst. The heat developed in this reaction caused a run-away.
Start-up procedures have now been changed and flushing the reactor is now done with nitrogen.
A video with a detailed explanation of what happened and a PDF file with a summary of the report can be found here.