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Ignition of Solvent vapours in Reactor

The Incident

Examination of a batch crystallizer showed the presence of a thin layer of black carbon like material covering all the surfaces of the reactor, agitator, etc., above the batch surface.  This was some two layer than the last inspection where the batch was sampled.

The Investigation

The batch was composed of a hydrocarbon solvent and a crystallized product.  It is known that such a system (stirred solid suspension in non-conducting liquid), can generate hazardous levels of electrostatic charge, even though appropriate measures to earth have been taken.  It is concluded that the reactor was not sufficiently inerted following the sampling operation, and that there was a subsequent electrostatic discharge which ignited the vapour mixture in the ullage space.

Lessons

When sampling such mixtures it is essential to prevent the ingress of air into the reactor, often it is necessary to rapidly increase the nitrogen flow to achieve this goal.

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