Seveso Accident: A Case Study Of Polivaudan

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CHEM3001 – Case Study Nicola Broun 21151388

Seveso Accident

Background
In the town of Seveso 25 km from Milan, the ICMESA factory (based on Swiss company Givaudan) was responsible for the manufacture of 2,4,5-trichlorophenol (TCP), a herbicide (Lees and Mannan, 2005). The reaction process normally required a time frame of approximately 14 hours (Sambeth, 1983). This process involves the alkaline hydrolysis of 1,2,4,5 – Tetrachlorobenzene in Ethyleneglycol solvent. Xylene is also added to the reaction mixture to remove any water that is produced. The sodium 2,4,5-trichlorophenate product is distilled to remove the solvents, acidified and purified by fractional distillation to produce TCP (Lees and Mannan, 2005).
The Accident
Production commenced on the 9th July as per normal, with 1,2,4,5,-Tetrachlorobenzene (2 000kg), sodium hydroxide (1 050 kg), Ethyleneglyol (3 300kg) and Xylene (600kg) (Sambeth, 1983). It was a requirement for the chemical plant to shut down for the weekend, with the final shift concluding at 6am on Saturday morning (Sambeth, 1983). Due to this, the reaction was interrupted but not terminated on Saturday morning. If 50% of the Ethyleneglyol had been distilled by 5am (as it normally was), the reaction would have been cooled to 50-60⁰C by quenching it with 3000 litres of water, instead heating and stirring was turned off completely and the reaction mixture was left at 158⁰C (Sambeth, 1983). This decision was made because the distillation procedure was only 15% complete at the time and there was no known dangers for TCP at 158⁰C (Sambeth, 1983). At 12:37 pm, six and a half hours after the reaction had been stopped, the safety disk that was responsible for withstanding high pressures gave way, releasing...

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...ds, and an emergency evacuation plan for surrounding areas.

References
Sambeth, J, 1983. The Seveso Accident. Chemosphere, Volume 12, Issue 4-5, pp. 681-686. Available at: http://www.sciencedirect.com.ezproxy.library.uwa.edu.au/science/article/pii/0045653583902278#[Accessed 14 March 2014].

Fortunati, U, 1985. The Seveso Accident. Chemosphere, Volume 14, Issue 6-7, pp. 729-737. Available at: http://www.sciencedirect.com.ezproxy.library.uwa.edu.au/science/article/pii/004565358590181X# [Accessed: 14 Mar 2014].

Lees, F. P. and Mannan, S. 2005. Lee's loss prevention in the process industries. Third Edition. Burlington, MA: Elsevier Butterworth-Heinemann.

Ec.europa.eu. 2014. Chemical Accidents (Seveso II) - Prevention, Preparedness and Response - Environment - European Commission. [online] Available at: http://ec.europa.eu/environment/seveso/ [Accessed: 14 Mar 2014].

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