A reaction between cyanuric chloride and sulphanilic acid ran away inside a fine chemistry unit. Water, sulphanilic acid and cyanuric chloride were loaded into an 8,000-litre reactor. According to the new operating protocol, 1 tonne of ice was supposed to be introduced just before the soda (the previous protocol called for ice to be loaded prior to introducing cyanuric chloride). The pneumatic ice supply valve however was blocked, and the reactor was kept in a stirred state without cooling while waiting for repairs. Depending on the knowledge acquired to run this process, such a state is typically free of danger. At 9:23 am, while repairs were ongoing, the removable lid on the reactor manhole was lifted. A gas cloud containing 107 kg of hydrochloric acid and foam was released through the manhole lid and reactor ventilation system. The 4 individuals present in the unit quickly exited the premises and sounded the alarm. Vapours spread inside the workshop and were escaping during 40 min via the building’s aeration chimney. Internal fire-fighters arrived at the scene. At 9:35, a first response team recorded a temperature of 103°C in the reactor and observed that the stirrer on the device was inoperable. Brine circulation (at -24° to -27°C) was manually activated inside the double shell in order to cool the reaction medium. The reactor stirrer however remained blocked, thus slowing the cooling process underway. The manholes on the other reactors were closed and since no other reaction was ongoing, the installations were placed in safe operating mode (shutdown of heating, bleeding and stirring). At 9:45 am, a second team flooded the reactor with 1,900 litres of water and then closed the plant’s residual water discharge valve emptying into the Seine River. Both the products spread over the ground and acid vapours were neutralised using an ammonia solution diluted at 12%.

The facility notified neighbours to remain indoors. No victims were reported and no noteworthy environmental impacts detected. Authorities issued an order suspending site operations. Property damage was appraised at 18,000 francs; operating losses reached 200,000 francs.

This accident was primarily caused by: malfunction of the pneumatic ice supply valve; no knowledge of possible reactions without additional soda; a newly adopted operating protocol (one month into testing when the reaction occurred); an inadequate risk analysis; and the lack of a high-temperature alarm on the reactor.

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