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Unchecked Process/Plant change cause Incident

Background

A decarboxylation reaction was carried out in a 30cu.m GLMS vessel, the charge was 24 tons at 35% concentartion.  The original basis of safety relied on a heat-up rate of 20-150°C over 4-5 hours

The reaction strength was increased to 45%, at the same time the vessel was changed to Hastelloy due to corrosion of the GLMS.

The Consequences

The change in heat transfer meant that the heat up period was reduced to 2 hours

The change in strength obviously increased the volume of gas to be discharged

These factors worked together to cause a large proportion of the batch to be ejected via the vent system

Follow Up

Further calculation later showed that the increase in strength would probably have been processed safely, however the critial change was the heat up rate which meant that any batch size over 18 tons would give rise to two-phase flow, and loss of contents.

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