What was the Seveso disaster?

On 10 July 1976 an industrial accident occurred at a small chemical manufacturing plant in Seveso. This resulted in a population of 17,000 people becoming exposed to the chemical ‘trichlorophenol’. Manufacture of the chemical requires high temperatures through the distillation process.

Within days of the chemical’s release more than 3,000 animals allocated to the human food chain were found dead. The government investigated and concluded that trichlorophenol, commonly known as dioxin, was a poisonous and carcinogenic by-product of an uncontrolled exothermic reaction.

There was widespread dispersal of dioxin which was lethal to human health. This resulted in immediate contamination of some 10 square miles of land and vegetation. More than 600 people were evacuated from their homes and more than 2,000 treated for poisoning.

How did the Seveso disaster happen?

Italian law at the time required such manufacturing processes to be closed down while the plant was not occupied over weekends. Across the plant processes were being closed down resulting in a loss of power consumption and load on the plant turbine system.

The adverse effect heighted the exhaust steam temperature to 300°c - a higher process steam than the process was designed for, and above the product’s boiling temperature.

With the process not running but the higher temperatures localised, the product developed a slow decomposition runaway reaction. The reactor relief valve eventually opened, releasing six tonnes of chemicals into the surrounding environment, some 18 km2.

What can the industry learn from the Seveso disaster?

The accident led to defining legislation for process safety, and to the European Union Directive 82/501/EC, which came to be known as the Seveso directive.

The legislation aims to prevent the occurrence of major accidents at sites that store and provide dangerous substances in sufficient quantities to constitute a serious health, safety and/or environmental risk, and to limit the consequences for people and the environment in the event of such an accident.