In a workshop at an amino acid plant, ammonia (NH3) fumes were released around 9:20 am during a sterilisation phase on a fermentation tank and its accessory equipment prior to putting the yeast in culture. The shutoff valve on the NH3 circuit automatically closed upon triggering the alarm threshold on a nearby sensor. Afterwards, all shutoff valves on the NH3 network were automatically closed due to pressure loss in one of the branches. The NH3 pipe could thus be entirely isolated within 1 min. Workshop personnel sought shelter in the confinement room (control room), and 2 members of the intervention team verified that no one had fallen victim and moreover that the risk had been contained through use of portable NH3 detectors. Since the situation could be restored to normal in less than 30 min, the internal emergency plan that had been preliminarily activated as a result of implementing a management flowchart for emergency situations was not fully activated.
Two employees sustained severe irritations and had to be hospitalised a few hours and placed under observation. Plant production resumed at normal levels 90 min after the incident. The operator informed the mayors of all neighbouring municipalities of this event.
This specific workshop section, closed for several years, had recently been placed back into service in order to develop a new yeast. After a number of tests, the incident occurred during production start-up on the first batch. Relying on circulating steam in the fermentation tank, the sterilisation step necessitated, whenever relevant, handling several valves on the tank’s NH3 supply pipe. An inappropriate closing / opening sequence on these valves led to a release of NH3 fumes inside the workshop via a drain valve left in the open position on this pipe.
The classified facilities inspectorate, notified at 11 am by the operator, arrived onsite the next day to record observations. Several factors contributed to the NH3 discharge: transmission of inappropriate instructions between the technician responsible for launching the sterilisation step the day before the incident and the technician overseeing finalisation; positioning of the set of valves by the initial technician in a configuration different from that specified in the operating protocol, which called for manual positioning of the valves in a configuration typically prohibited by the process control automaton. During preliminary testing, it was decided to modify the operating procedure on the intended valve configuration, without first updating the risk analysis. Moreover, testing and production continued even though the risk analysis and initial tests had indicated the benefit, from a safety perspective, of physically modifying the pipeline. The inspectorate pointed to flawed oversight of pipeline modifications and requested an incident analysis report; the pipeline would eventually be modified.
