The Seveso incident.
On 10 July 1976, at, there was an accident in Givaudan's chemical plant belonging to the ICMESA firm near Seveso, Northern Italy.
A reactor vessel safety plate ruptured, resulting in the release of a toxic vapour cloud. The reactor was used for the production of 2,4,5-trichlorophenol (TCP) and the cloud contained various components and byproducts of the process, including TCP, ethylene glycol and chlorinated phenols. Most notably, it also contained 2,3,7,8-tetrachloro-dibenzo-para-dioxin (TCDD).
The cloud spread over a large area, contaminating humans, animals, crops and land in the vicinity of the plant. The failure of the safety plate occurred while the plant was shut down for the weekend. The plant had closed midway through the production of a batch of TCP, leaving the reactor full of material at an elevated temperature. Among these were ethylene glycol and sodium hydroxide, which eventually underwent an uncontrolled exothermic reaction that released sufficient gas to exceed the pressure limit of the safety plate. The reaction also raised the reactor temperature to 450-500 Celsius, conditions that greatly increased the formation of TCDD. The reactor had no automatic cooling system; since only maintenance and repair personnel were in the plant over the weekend, no one was present to initiate cooling manually and suppress the reaction. Fortunately, the cloud vented for only 20 minutes before a worker noticed and stopped the release. It is estimated that 2kg of the dioxin were in the cloud, and the area was immediately sealed off and the population was evacuated.
Locally grown food was banned for several months, and several inches of topsoil were removed and incinerated, as were the livestock from the local farms. However, despite all these worries, only one person, to date, appears to have died from liver cancer, although there were a number of cases of skin disease (chloracne). No employees of the company suffered damage to their organs, a number of women had abortions due to the potential danger to their unborn children. The incidence of malformed children was comparable to that found elsewhere, so it appears as though the inhabitants of Seveso escaped relatively lightly.