Inside a plant specialised in pharmaceutical and agrochemical products, the connections of liquid and gas hoses on a disulphur dichloride container (S2Cl2) were reversed, causing 75 kg of this substance to flow back. One of the workshops manufactured disulphur, an intermediate product when manufacturing FIPRONIL (an insecticide) derived from S2Cl2. Since a spherical S2Cl2 tank was empty, a technician thought to replace it by a full one and proceeded to hook up the hoses for the first time to such a rented vessel. The identification engravings were difficult to read, and the connection outlets on these rented tanks were not appropriately colour-coded. The technician, wearing a chemical protection suit and self-breathing apparatus, connected the gas outlet where the flange had been painted red (which according to the colour code practiced by the firm should have been a liquid tap). Nitrogen supply was thus connected to the ‘liquid’ tap. Given that the nitrogen seal test conducted at 1.8 bar of pressure proved conclusive, the tank was degassed into the venting line. Under the pressure of liquid S2Cl2, which was rising inside the vent, the sampling plug popped out. The 75 kg of released S2Cl2 spewed onto a valve and over the insulated steam pipe before decomposing into sulphur and HCl. The sulphur self-ignited in the hot steam pipe insulation. Both the (HCl) gas and explosive atmosphere detectors were tripped. Employees on duty equipped with self-breathing apparatuses noted the formation of acid fog engulfing the ground floor and removed the burning insulation. The use of extinguishers made it possible to control the outbreak. The air conditioning shutoff in the confinement room was not servo-controlled by gas detectors. The site’s first response office activated the internal emergency plan and requested assistance from external fire-fighters, who showed up but did not need to intervene.
The extinction water was recovered in the workshop retention pit and treated, after analysis, at the on-site facility. Property damage was limited to the steam pipe insulation.
This accident was due to both human and organisational flaws. The plant operator was required to implement protective actions (threaded plugs on measurement devices) and preventive actions (operating protocol enhancements, appropriate valve markings on containers), as well as improve facility management (acceptance procedure for new spherical tanks).