Seveso

The use of an unnecessarily hot utility or heating medium should be avoided. This may have been a major factor that led to the runaway reaction at Seveso in Italy in 1976, which released toxic material over a wide area. The reactor was liquid phase and operated in a stirred tank (Fig. 9.3). It was left containing an uncompleted batch at around 160 C, well below the temperature at which a runaway reaction could start. The temperature required for a runaway reaction was around 230 C. ... 

There have been suggestions of alterations in sex ratios following accidental environmental exposure to dioxin in Seveso, Italy, in 1976. Between 1977 and 1984, 74 births occurred in the most heavily contaminated zone which showed an excess of females (26 males and 48 females born). Preliminary evidence suggests that the excess was associated with high dioxin exposure in both parents. Over a later period, between 1985 and 1994, the ratio declined (60 males and 64 females) and was no longer statistically significant. 

EEC Directive on major accident hazards (Seveso Directive)... 

Thermal runaway is a partieular problem in unsteady state bateh reaetions, where the rate of reaetion and, therefore, the rate of heat produetion varies with time. The eonsequenees of thermal runaway are sometimes severe as in the ineidents at Seveso [3]. In this ease, a bursting disk ruptured on a reaetor. The reaetor was used to manu-faeture triehlorophenol at a temperature of 170-185°C and was heated... 

Adapted from the Seveso website http //www.roche.com/roche/about/esevesg i htm and Growl (1990). 

Are toxic materials being processed This was the cause of the Bhopal accident, and the less disastrous Seveso accident. 

Seveso, Italy, caused wide-spread pollution of the industrial site as well as its surroundings. Serious effects of dioxin were detected both in dontestic animals, such as cows and sheep, and in humans, the most serious early effects being a serious skin disease, chloracne, and alterations in the function of the immune system. Follow-up studies have demonstrated that this accident also increased the cancer risk in exposed individuals. ... 

TCDD is the most potent inducer of chloracne. This has been well known since the accident in Seveso, Italy, in 1976 in which large amounts of TCDD were distributed in the environment subsequent to an explosion in a factory that produced a chlorophenoxy herbicide, 2,4,5-T. TCDD is an impurity produced during the production of 2,4,5-T. The most common long-term effect of TCDD exposure was chloracne. Exposed individuals also suffered increased excretion of porphyrins, hyper-pigmentation, central nervous system effects, and liver damage and increased risk of cancer was a long-term consequence of the exposure. In addition to TCDD, polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans, and polychloronaphthalens cause chloracne as well as other effects typical of TCDD. 7i... 

The use of an unnecessarily hot heating medium led to the runaway reaction at Seveso, Italy, in 1976, which caused a fallout of dioxin over the sun ounding countryside, making it unfit for habitation. Although no one was killed, it became one of the best-known chemical accidents, exceeded only by Bhopal, and had far-reaching effects on the laws of many countries. 

A number of environmental issues have received widespread publicity (Table 7.1), from major accidents at plants (e.g., Seveso and Bhopal) to the global and regional impacts associated with energy utilization (e.g., carbon dioxide, acid rain, and photochemical oxidants), the improper disposal of chemical waste (e.g., Love Canal and Times Beach), and chemicals that have dispersed and bioaccumulated affecting wildlife (e.g., PCBs and DDT) and human health (e.g., cadmium, mercury, and asbestos). 

Site-specific Dioxins (Seveso, Love Canal, and Times Beach)... 

Many accidents resulting from dangerous reactions have a history of repeating themselves over the years, without the lessons of history being properly drawn. For example, the accident at Seveso, arising from difficulties in controlling the reaction temperature of sodium hydroxide with 1,2,4,5-tetrachlorobenzene, had already happened three times a few years before. The symptoms due to acute intoxication caused by dioxin were already known. 

The nucleophilic substitution reaction was involved in the SEVESO (1976) disaster . Another accident of the same nature might be mentioned before going into further details. 

In the United Kingdom this is covered by the Control of Major Accident Hazards Regulations 1999 (COMAH), set up by the HSE (Health and Safety Executive) to implement the Seveso II directive of the EC (European Union) see www.hse.gov.uk. The COMAH regulations supersede the previous CIMAH (1984) regulations, set up under Seveso I. 

The comprehensive and detailed assessment of the risks required for a safety-case can only be satisfactorily carried out for major installations with the aid of computer software. Suites of programmes for quantitative risk analysis have been developed over the past decade by consulting firms specializing in safety and environmental protection. Typical of the software available is the SAFETI (Suite for Assessment of Flammability Explosion and Toxic Impact) suite of programs developed by DNV Technica Ltd. These programs were initially developed for the authorities in the Netherlands, as a response to the Seveso Directives of the EU (which requires the development of safety cases and hazard reviews). The programs have subsequently been developed further and extended, and are widely used in the preparation of safety cases see Pitblado el al. (1990). 

Cardillo P and Girelli A (1981) The Seveso Runaway Reaction A Thermoanalytical Study, IChemE Symp Ser, 68, 3/N 1. 

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