Following an unsuccessful hydrolysis operation (hydrolysis flooded with water) inside a chemical plant, the foreman requested, around 2 am, that the technician assigned to oversee the hydrolysers discharge 11.7 tonnes of hydrolysate contained in a reactor to a reservoir typically intended to receive the aqueous phase (water + isopropyl alcohol + HCl) of the hydrolysates.

To do so, the technician transitioned from a mode of automated supervision to a semi-automatic mode, making it possible to route the contents of the reservoir in order to neutralise the limestone flux pit. This operation, which had basically not been performed since the process started up, enabled draining the washing water from the reactor to a limestone flux pit.

This action caused a mix of toluene resin and acid water to be accidentally channelled first to the limestone pit then to a settlement pit outside the site boundary. The resin, which contained toluene and with a density < 1, was retained in the supernatant phase on the settlement pit, while the acid water containing isopropyl alcohol was discharged into the natural environment. Upon realising his error in judgment, the technician stopped after 5 minutes the drainage operation to the limestone pit, overriding the automated mechanism. The loss of isopropyl alcohol was estimated at 350 kg.

Given the rapid increase in pollution at the plant outlet, the foreman initiated pumping of both the basin and limestone pit, then called the fire department as well as the on-call supervisor.

The operator had scheduled to eliminate the automated mechanism, in addition to: locking shut the valve that allowed for dispatching into the limestone pit as part of an “automated” sequence, issuing a temporary guideline to explain the prohibition of drainage into the limestone pit and the cessation of all automated processes on the valve prior to issuing a definitive guideline, reminding technicians and foremen of the various automated drainage mechanisms as well as a review of all execution and instrumentation protocols, and lastly modifying the procedures and supervisory screen synoptic in order to produce more comprehensible descriptions of the various drainage phases.