A densely populated area of the greater Los Angeles region became very familiar this past weekend with the word BLEVE (rhymes with levee). BLEVE is an acronym for boiling liquid expanding vapor explosion. While BLEVEs can involve a vast range of materials, in this case, the BLEVE was due to an unwanted polymerization reaction occurring at the GKN Aerospace factory in Garden Grove, CA. The fire department spent days spraying water on the site, and 50,000 people were ordered to evacuate.
While the full details of this incident are yet to be determined, the well-known chemical characteristics and reactivity of the chemicals involved make it easy to provide the big picture of what occurred and what might have occurred had the diligent fire department not saved the day.
MMA for polymerization
The GKN facility had a ~7,000-gallon tank for storing methyl methacrylate (MMA). The MMA would have been pumped to different equipment and used as part of a polymerization process. Pure MMA can start polymerizing by itself to create poly(methyl methacrylate) (PMMA), more commonly known by the trade name Plexiglas. Unfortunately for GKN, the MMA started polymerizing, and their storage tank unintentionally became a reactor. Why this started isn’t clear and may never be known. MMA will have inhibitors in it to prevent an auto-reaction, but they don’t appear to have worked.
The polymerization produces heat, which raises the pressure in the headspace of the tank. There should have been a pressure-relief valve on the tank, but for unknown reasons, it was not working effectively, and so there was no way for GKN to release the pressure…