Pollution
Humain
Environnement
Economique

At 6:20 pm, a hose with an air/SO3 mix broke inside a plant making surface active agents (detergents/cosmetics). Damage extended to 2 pipelines running upstream of the sulfonation reactor (R2) with 2 associated valves and flat joints. Pipeline 1 (C1) was feeding R2 with an air + SO3 mix. Pipeline 2 (C2) was a hose connected to an extractor used to suction residual acid emanations before having personnel intervene in the head of the reactor. The valve on Pipeline 2 was closed and backed up by a flat joint while R2 was operating.

Eight days prior to the accident, the maintenance team installed a flat joint on C1 in order to isolate the R2 on Reactor 1, which was responsible for producing an alkylate. The operating protocol was not fully respected: the C2 valve remained open and without a flat joint. Moreover, the R2 status report was mistakenly deleted from the status report table.

When the sulfonation technician launched R2 production, the air/SO3 mix introduced by C1 at 261 mbar escaped via C2. Exposed to the pressure effect, C2 burst and its end was ejected, breaking a bulb on the fire network, causing a deluge that covered the entire workshop.

Once smoke began to appear in the building and the deluge was underway, the technician shut down the sulphur supply line (290 kg/h) and directed the air/SO3 mix to the H2SO4 absorption tower. The head of maintenance stopped the inundation and residual SO3 flow. The on-duty supervisor activated by punching the injection of runoff water (200 m³) to the overflow basin. This water flow would be treated by a subcontractor. The quantity of SO3 discharged into the atmosphere was estimated at 26 kg. A slight wind dissipated the toxic cloud. The local town hall was apprised of the incident. No complaint or any kind of intoxication was recorded.

The plant’s safety manager then restarted the deluge protection network. The nearby ethoxylation unit, which had been shut down as a precaution at 6:25 pm, was reactivated at 7:30 pm. Resumption of sulphur burning was overseen by the workshop supervisor around 1 am, and the sulfonation reaction resumed at 3 am.

This incident was caused by noncompliance with the intervention order from successive human error and deletion of the status report table.

An immediate analysis revealed the lack of respect for operating procedures, as observed by the Classified Facilities Inspectorate during an inspection held on 14th April, 2007. The operator drafted a reactor reporting procedure to be initialled by technicians and displayed on the control room status report table. The operator included on the reactor’s control console a red blinking box to indicate the “safe reactor” mode, to be activated and deactivated by maintenance staff both before and after a report update. Sulfonation and maintenance personnel were given instructions on how to maintain the corresponding status report table up to date prior to their intervention.