A railcar containing toluene diisocyanate (TDI) waste exploded during the unloading process at a hazardous waste-treatment and disposal facility. The TDI waste material was to be used as a fuel at the RCRA-permitted facility. Because of the viscous, almost solidlike consistency of the waste, the railcar was steam-heated to facilitate unloading. The attempted unloading took place over a 5-day period. The railcar was heated on two separate occasions and unloading was unsuccessfully attempted three times. The decision was made to reject the railcar shipment, but it remained at the unloading station. Approximately 2 days after the last heating cycle, the railcar exploded.

This paper summarizes the accident investigation, with particular emphasis on the assessment of the reactivity hazards and self-heating potential of the railcar contents. Under the circumstances of this accident, TDI should not undergo significant thermal decomposition. The evidence suggested the explosion was caused by the thermal decomposition of a contaminant that was not normally present in the TDI waste. © 2004 American Institute of Chemical Engineers Process Saf Prog, 2004