This case study describes the investigation of an explosion that occurred during the startup of a vinyl chloride monomer (VCM) distillation column. The column had been idle for a few days while work was performed elsewhere in the process. However, the contents of the column, consisting primarily of VCM and ethylene dichloride, had not been removed prior to shutdown. A series of exothermic reactions occurred inside the column, beginning during the idle period. These reactions initially went unnoticed. However, they became more rapid and energetic as the column was started up and steam was applied. The final exotherm resulted in a failure of the column wall, releasing its contents. The contents ignited upon release, generating a large fireball and then a sustained jet fire, until the inventory was consumed. Fortunately, no one was injured as a direct result of the incident, but the column and nearby equipment were destroyed.
Following the scientific method, data from a variety of sources were reviewed and chemical and physical tests were performed to evaluate hypotheses. It was ultimately concluded that chlorine gas had leaked past a block valve intended to isolate the column from a downstream reactor vessel. Lessons learned will also be discussed.