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Smoke was seen coming from the locality of a charge pot used to mix catalyst with the feed to a batch hydrogenator.  This occurred shortly after a charging operation had been completed.  Lab tests showed an absence of reactivity at room temperature.   About 3 days before the incident some of the reactor batch had been dropped back to the charge pot for extra catalyst to be added.  This 'top-up' operation was occasionally needed with this process.  The catalyst charge is normally adequate for 3 hydrogenation batches but occasionally the activity of the catalyst would drop to the point where extra new catalyst would be needed to complete the third batch.  It was concluded that the partially spent catalyst (a partially oxidised poisoned base metal catalyst) had exothermed on contact with air.  Although the catalyst is sold as a non-pyrophoric grade, the reduced form, containing finely divided base metal, can be pyrophoric.  This was not widely known within the company, probably influenced by tests done several years ago (by a contract house) which indicated little or no pyrophoric activity.

Actions to prevent recurrence included a cessation of the 'top-up' operation.  The line allowing recycle of reactor contents was removed.  Warnings were inserted in the operating instructions.

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