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The Incident

A Flash Fire occurred during the separation and transfer of an aqueous phase from a Toluene mixture into a 10-litre High Density Polyethylene (HDPE) container.

The Investigation

The organic/aqueous mixture had previously been agitated at 50 °C in a 50-litre glass vessel and then allowed to separate. The vessel and HDPE container where located inside a laminar flow booth (LFB). Following an initial separation the organic phase was washed once again with water and it was during the transfer of the second aqueous phase that a Flash Fire occurred around the neck on the container.

Conclusions

It is well known that making a mix of non-polar hydrocarbon solvent and water will result in a build up of static. It is concluded that the transfer of the first aqueous phase transferred enough toluene to form a toluene/air mixture in the container. On transferring the second phase, the induced static electricity ignited the mixture.

Lessons Learnt

Even some processes in moderate (large laboratory) scale chemistry can cause unexpected problems that would normally only be assigned to "plant" processes. In this case the use of conducting plastic containers would have been a useful addition to the process.

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