An exothermic chemical reaction occurred around 9 am in a subcontractor’s tanker lorry during the pumping of a 3-m³ used sodium hydroxide bath, in a surface treatment workshop of a company specialised in the production of aluminium and titanium parts; the increase in pressure caused safety valves on the tanker lorry to open. The decision was taken to transfer sodium hydroxide into the original tank; the hose was unsuitable for a hot product, and 300 litres of sodium hydroxide spilled into the workshop and outside the building. Emergency services were alerted. The tank was isolated and cooled by fire-fighters until the reaction had stopped; absorbent pellets were spread over the pool of sodium hydroxide and then eliminated. The employees and two subcontractors, present during the product transfer step, were equipped with gloves, goggles and suitable protective overalls; they were not injured. The chemical pickling line was stopped for 48 hours. The investigation carried out by the Classified Facilities Inspectorate found that the tanker lorry had been used two days prior, by the same company, to collect the soluble oil used in a machine-tool for aluminium parts. In all likelihood, the presence of fine aluminium particles in the tank were insufficiently cleaned and caused the chemical reaction and release of an estimated 5 kg of hydrogen from the valves on the lorry.
The operator established a cleanliness control of its tanker lorries used in onsite pumping of chemicals (procedure under review) and planned on building a new and original decantation-infiltration basin, in addition to carrying out an internal review of experience feedback of this accident, with an update of procedures for managing such incidents and accidents. The subcontractor planned on increasing controls on the internal cleanliness of tanker lorries and reminding its employees of the cleaning instructions.