At 7:50 am, the trailer of a lorry containing 20 tonnes of synthetic resin in solution placed in styrene (flashpoint: 32°C) became unhitched from the tractor just after the rig exited the lower-tier Seveso-rated basic plastics manufacturing plant, where it had been loaded. The trailer tilted by approx. 20 degrees but did not show any leaking. The lorry driver, wearing a safety vest, turned on his emergency flashers and the vehicle’s emergency lights; in seeing smoke rising from electrical cables ripped apart after losing the trailer, he cut the lorry’s electrical supply by means of a battery isolation switch. Alerted by the noise, the resin manufacturer’s employees contacted the emergency services and police offices, closed the road to traffic and delivered to the scene the equipment necessary to contain an eventual leak. The emergency crew deployed considerable resources given the proximity to a Seveso site, then set up a safety perimeter and secured the zone using fire nozzles. Police officers took control of traffic, preventing many personnel from accessing neighbouring companies. A specialised firm lifted the cistern and re-hitched the tractor. Next, the lorry was parked and secured on the lot inside the plant’s premises; it was then routed to the transport company’s site, where the container was positioned on another chassis in order to continue the delivery.

The driver had conducted 2 traction tests before leaving the plant to verify the trailer’s proper attachment and did not detect any anomaly. The hitching protocol however was not fully respected: when backing up to attach the trailer, the saddle was too low and the centre pin became interlocked with the saddle’s locking hook while remaining positioned above. With the container’s weight, the centre pin stayed attached to the saddle though only retained by a thin metal net. The trailer detached when the driver accelerated on an at-grade crossing, causing a top-to-bottom movement leading to lifting of the pin, spacing of the centre pin saddle, and a major swinging effect in the cistern.

The transport firm that was subcontracting this mission issued a reminder for its drivers and subcontractors regarding the internal hitching-unhitching and trailer-locking procedure using the blocking systems, in addition to: organising onsite audits of the resin manufacturer for its drivers and subcontractors, drawing the attention of drivers to an information document detailing the experience feedback derived from this incident, presenting an internal intervention response plan to the plant director, and scheduling an accident simulation (internal emergency plan). A similar incident, recognised as a common occurrence, had already occurred in this same plant during 2007. At the request of the Classified Facilities Inspectorate, the plant updated its safety report.