Toxic gas release caused by the thermal decomposition of a bulk powder blend containing sodium dichloroisocyanurate



A thermal runaway reaction occurred during the mixing of a batch of a bulk powder that resulted in the production and release of toxic gases. The mixture consisted of an oxidizer (sodium dichloroisocyanurate), some organic compounds, and inert compounds. This toxic release led to the evacuation of the building and resulted in extensive damage to the facility. This was only the fourth time an 1,100-pound batch of this material had been mixed in this equipment. Prior to this production run, the material had been prepared in small batches of 2 to 50 kilograms. Accelerated Rate Calorimetry (ARC) testing had been performed prior to the scale-up to production batches.

This paper looks into the root causes of this particular accident and demonstrates how proper analysis of the testing data and other warning signs observed during the bench testing could have revealed the likelihood of this accident. Further, this paper will consider how simple design changes to the manufacturing process resulted in an inherently safer design.