A violent explosion occurred at 1:28 pm on a rubber components manufacturing line at a 1.4-ha medical instruments plant. The explosion, accompanied by a large fireball, could be heard 20 km away and was followed by fire at the plant’s storage zone. Fed by the mineral oil spilling from two damaged 28-m3 plastic tanks, this blaze raged for 2 days, and a whole week would be necessary for its complete extinction. Broken window panes were reported within a 3-km radius. The splatter of ignited debris caused fire to break out in woody areas near the heavily damaged plant. Property loss was estimated at USD 150 million.

The human toll was especially high: 6 employees were killed and 38 injured, including 2 fire-fighters in the line of duty and 1 student in a school 1 km away due to broken glass.

The investigation conducted by the U.S. Chemical Safety Board (CSB) revealed that an explosion of fine dust of polyethylene (PE) powder used as an anti-adhesive lining on rubber bands caused this accident, despite regular cleaning of the production chain. This chain was composed of 2 floors, namely: a mixer on the upper floor (where rubber was introduced), followed on the lower floor by a crusher and a rolling mill for manufacturing the bands, which were then covered by PE from a tank of powder suspended in water. PE dust formed during drying and was suctioned by the ventilation system before landing on the production line.

Installation of a suspended ceiling between the 2 floors a few years earlier created the space in which this dust accumulated, thus creating a zone prone to explosion. While the initial explosion was confirmed by suspended ceiling slabs found to be burned exclusively on their upper face, the cause of dust suspension and ignition could not be determined due to the building’s destruction.

The plant operator had not identified the risks of either PE dust ignition or explosion, despite an incident (not archived by the company) several months prior: a weld during maintenance work had caused PE dust to ignite nearby, with the fire self-extinguishing.

Dust accumulation had not been visible and regular cleaning of the production line (excluding suspended ceilings) was being performed. The employees, who most likely had been poorly trained in risk management given that maintenance personnel had observed a significant dust layer in the suspended ceiling a few weeks before the explosion, failed to provide any signal after failing to draw a correlation with an explosion risk.

Experts underscored the importance of analysing such risks, as evidenced by a series of accidents in the U.S. (in 2003, see ARIA 24130). They also recommended compliance with fire protection safety standards. 14 months after the explosion, the plant was rebuilt on another site, although without the rubber manufacturing part (which was subcontracted).