In a wood processing plant, the door on an autoclave suddenly opened while its contents (wood + wood treatment product) were still pressurised at 11 bar inside. Given the door’s dimensions and the pressure setting, the product spewed out of the device like a wave, most of which overflowed the retention basin. As a result of this installation’s configuration, the flow of product separated into two streams: one portion of the liquid headed towards the wood storage buildings, whose floor had been concreted; while the other portion flowed towards outdoor storage and handling zones (which had been fitted with manholes connected to the site’s stormwater collection network).

At the time of the accident, the 44-m3 volume autoclave had contained 41 m³ of product. The operator estimated that a 12-m³ quantity of pollutant had entered the stormwater network and then the natural environment at the outfall into the Diouric River, which 2 km further downstream emptied into the Aber Benoit.

Stormwater system cleaning enabled recovering a small percentage of the treatment products. Ultimately, the quantity reaching the Diouric was evaluated at between 4 and 8 m³. Dead fry, fish, tadpoles and worms were detected by gendarmes and fire-fighters during their investigations. Water samples were extracted and sent to a specialised body for analysis. Neighbouring municipalities issued orders prohibiting fishing. Classified Facilities inspectors conducted a site inspection on 23rd April and recorded their findings.

Subsequent to this accident, the plant operator updated the technician’s instruction sheet related to autoclave operations and installed cut-off valves or similar systems on all stormwater outlets.

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