The document summarizes the Seveso disaster that occurred on July 10, 1976 in Seveso, Italy when a chemical plant had an uncontrolled reaction during the production of trichlorophenol, releasing a large cloud of toxic gases and chemicals including dioxins. No one died immediately, but many animals died and thousands more were slaughtered. Residents developed health issues and the area had to be evacuated. The incident led to increased safety regulations and directives for chemical plants in Europe called the Seveso Directives.

1. Pankaj Kumar
3rd Year B.Tech
Dyestuffs Technology & Intermediate
Institute of Chemical Technology , Mumbai

2. INTRODUCTION
• 10 July 1976
• Seveso, Lombardy, Italy
• ICMESA (Industrie Chimiche Meda Società Azionaria)
• Run-away reaction
• Desired product :2,4,5 trichlorophenol sodium salt (TCP)
• side product :2,3,7,8 tetrachloro dibenzo dioxin (TCDD)
• Death toll : no people died as an immediate result ,Around 3,300
domestic animals (including poultry) perished within days and
another 80,000 were slaughtered

3. Company Overview
• ICMESA (Industrie Chimiche Meda Società Azionaria)
• subsidiary of Givaudan, which in turn was a subsidiary of
Hoffmann-La Roche (Roche Group) : A swiss company
• ICMESA had manufactured 2,4,5-trichlorophenol (TCP) since
1971
• TCP a toxic substance used in herbicides and for the
preparation of cosmetics .

4. TCP
• 2,4,5 tri chloro phenol sodium salt
• used in medicated soaps , shampoos and cosmetics
• manufactured by alkaline hydrolysis of 1,2,4,5 tertachloro benzene
• reaction is carried out temp about 135- 160 0C

5. TCDD
• 2,3,7,7 tetrachlorodibenzo
paradioxin
• dioxin have no common uses
• highly toxic
• formed as a by product in the
manufacturing of TCP
(herbisides)
• Absorbed by plants and soil

6. TCDD formation Reaction

7. Manufacturing method of TCP
• Tetrachlorobenzenes is heated to 135 to 1600 C
• Reaction with NaOH
• Solvent is ethylene gycol
• xylene addition and azeotropic distillation at 1600C
• Removal of remaining xylene by distillation
• 50% ethylene glycol recovery under reduced pressure conditions
• Termination of manufacturing by cooling the product to 50 0C by
addition of water

8. Reactor Design

9. What actually went wrong ?
• Stopping of the uncompleted process
• Addition of water was not carried out hence temp remained
158 0C
• Steam present in the jacket continued to heat the reactor
• Stopping of agitation process and cooling process .
• Operator left the site

10. UNDESIRED REACTION
• Steam valve was closed so superheated steam present in the jacket
continued to heat the reactor
• Stopping of agitation caused the local temp rise
• Triggering of an Exothermic reaction
• Rupture disc operation
• Release of the gas containing TCP , TCDD to the atmosphere

11. Chemical Events
Operation course leading to leakage
• At 8:00 PM Friday july 9, 1976 batch reaction which caused the
incident is started
• At 4:37 AM Saturday july 10 ,1976 reaction and distillation process of
the batch finished (only 15% recovery of glycol)
• steam valve was closed and agitation was stopped and plant was
shut down during the weekend according to Italion law and the
Operator went home
• At 12:37 PM rupture disc suddenly operated and reactor contents
began to leak

12. Cause of Operation of Rupture Disc and Leackage of Contents
• At that time it was thought runaway reaction would not occur temp
less than 230 0C so operator stopped the operation at 158 0C .
• Further it was found in research exothermic reaction can occur at 180
0C
• Superheated steam remained in the jacket continued to heat the
liquor and cause the temp increase over 180 0C locally .
• An exothermic reaction began in the liquid and expanded throughout
the reactor

13. Continued.....
• Rupture Disc was directy open to the atmosphere .
• Company did not refer to other accidents that had occured before this
accident so it is thought that the contravention of instructions might not
happen either and study had not been conducted seriously .
• There were at least 14 other similar accidents at other TCP manufacturing
plants at minor scale .
• 1949 Monsanto (USA);
• 1953 BASF (Germany);
• 1960 Dow Chemicals (USA);
• 1963 Phillips Duphar (Netherlands);
• 1968 Coalite Chemical Productions (UK)

14. Course after the Leakage
• July 10 , 1976 technical manager of the company advised the locals
not to touch or eat locally grown fruits and vegetables .
• On Monday july 12 ,1976 first signs of health hazard appeared
• By july 14th Locals hospitals were filled with patients .
• On july 15th the parent company found a high concentration of TCDD
in the leacked material but did not announce this outside the
company including the local government untill they reconfirmed the
existence of TCDD on 20th july .
• on 24th july local government ordered the evacuation from the A
area and further it was expanded

15. • Zone A had a TCDD soil concentration
of > 50 micrograms per square metre
(µg/m²) , it had 736 residents.
• Zone B had a TCDD soil concentration
of between 5 and 50 µg/m², it had
about 4700 residents.
• Zone R had negligible or a TCDD soil
concentration of < 5 µg/m², it had
31,800 residents.

16. Immediate Effects
• Within days a total of 3,300 animals, mostly poultry and rabbits, were
found dead. Emergency slaughtering commenced to prevent TCDD from
entering the food chain, and by 1978 over 80,000 animals had been
slaughtered. 15 children were quickly hospitalised with skin inflammation
• By the end of August, Zone A had been completely evacuated and
fenced, 1,600 people of all ages had been examined and 447 were found
to suffer from skin lesions or chloracne and blurred vision .
• Italian government allotted 40 billion lire (US $47.8 million) for
quarantining and decontaminating the area. This amount would be
tripled two years later.

17. Long Term Effects
• A study published in 1998 concluded that chloracne was the only effect established with
certainty. Early health investigations including liver function, immune function, neurologic
impairment, and reproductive effects yielded inconclusive results.
• An excess mortality from cardiovascular and respiratory diseases was uncovered, and
• excess of diabetes cases was also found. Results of cancer incidence and mortality follow-
up showed an increased occurrence of cancer of the gastrointestinal sites and of the
lymphatic and hematopoietic tissue.
• A 2001 study confirmed in victims of the disaster, that dioxin is carcinogenic to humans
and corroborate its association with cardiovascular- and endocrine-related effects.
• In 2009, an update including 5 more years (up to 1996) found an increase breast cancer.
• Seveso and its residents continue to function as a kind of "living laboratory" into the
effects of dioxin exposure on people and animals

18. Compensation and Criminal Court Case
• On 17 december 1980 Italian Republic and Givaudan/ICMESA signed a
compensation agreement in the presence of the prime minister of Italy, Arnaldo
Forlani. The total amount would reach 20 billion lire (approx 24 million USD)
• On September 1983, the Criminal Court of Monza sentenced five employees of
ICMESA or its parent company, Givaudan, to prison sentences ranging from 2.5
years to 5 years. They all appealed.
• In May 1985, the Court of Appeal in Milan found three of the five accused not
guilty; the two was still facing prosecution appealed to the Supreme Court in
Rome.
• On May 23, 1986, the Supreme Court in Rome confirmed the judgment against
the two remaining defendants .

19. Aftermath
• ICMESA was completely shut down .
• Industrial safety regulations were passed in the European
Community in 1982 called the Seveso Directives
• Purpose of the “Seveso” Directive is to set up a procedure to
ensure that major hazards are prevented and that their
consequences are mitigated.

20. Seveso Directives
• Operators should have a general obligation to take all necessary
measures to prevent major accidents, to mitigate their consequences
and to take recovery measures.
• The operator should provide competent authourity a safety report .
• The Safety Report should contain details of …. possible major accident
scenarios and risk analysis, prevention and intervention measures and
the management systems available in order to prevent and reduce the
risk

21. Safety Report Contents ?
The Safety Report shall provide
• Information on the management system and the organisation;
• Information on the Plant and the Site;
• Information on the technological and process aspects;
• Identification and accidental risk analysis and prevention methods;
• Information on measures for protection and mitigation.

23. References
1) Explosion of chemical plant in seveso , Italy , Mitsuo kobayashi ,
failur knowledge database
2) http://www.legislation.gov.uk/uksi/2015/483/contents/made
3) Sharing Experience in Process Safety and SEVESO Directive ,Giovanni
Uguccioni , 2014
4)B. De Marchi; S. Funtowicz; J. Ravetz. "4 Seveso: A paradoxical classic
disaster". United Nations University
5)https://www.siznursing.be/index.php?preaction=joint&id_joint=7179
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