The Seveso tragedy occurred on July 10, 1976, in Milan, Italy, due to a runaway chemical reaction involving 2,4,5-trichlorophenol and the formation of highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin. Key failures included operator negligence and ineffective hazard management, leading to a large-scale release of toxic gas that contaminated 1800 hectares. The incident resulted in severe health repercussions including chronic dermatitis, cancer, and ecological damage, highlighting the catastrophic consequences of operational violations.

1. SEVESO TRAGEDY
PRESENTED BY,
BASIL C ELDHO
CHEMICAL ENGINEERING
T K M COLLEGE OF ENGINEERING
QUILON-KERALA

2. OVERVIEW
• July 10,1976
• Milan,Italy
• Runaway reaction
• Rupture disk
• 2,4,5 Trichlorophenol sodium salt (TCP)
• 2,3,7,8 tetrahlorodibenzo para dioxin (TCDD)
• 1800 hectares of land

3. AFFECTED AREA

4. TCP
• 2,4,5 Trichlorophenol sodium salt
• Medicated soaps, Cosmetics and Shampoos
• Manufactued by the alkaline hydrolysis of
tetrachloro benzene
• Carried out at temperatures less than 200
degree celsius

5. REACTION

6. TCDD
• 2,3,7,8 tetrahlorodibenzo para dioxin (TCDD)
• Dioxin
• 100000 toxic than sodium cyanide
• Occurs at temperatures above 230 degree
celsius

7. TCDD FORMATION

8. CAUSE OF THE TRAGEDY
• Instructional violation by the operator
• Unawareness of the fact that runaway
reaction can occur at lower temperatures

9. MANUFACURING METHOD
• Tetrachloro benzene is heated to 135 to 160
• Reaction with NaOH
• Xylene addition and azeotropic distillation at 160
• Removal of remaining Xylene by distillation
• 50% ethylene glycol recovery under reduced
pressure distillation
• Termination of manufacturing by cooling the product
to 50 by the addition of water

11. INSTRUCTIONAL FAILURE
• Stopping of the recovery at 15%
• Addition of water was not carried out hence
the final temperature was 158 degree Celsius
• Stopping of agitation
• Operator left the site

12. UNDESIRED REACTION
• Steam valve was closed so the Superheated
steam continued to heat the reactor
• Use of Turbine exhaust
• Stopping of agitation caused development of
local temperature rise
• Triggering of an exothermic reaction
• Rupture disk operation
• Release of gas to the atmosphere
• Formation of mushroom cloud with 30 to 40Kg of
TCDD
• Spread of the gas by wind

13. HAZARD MANAGEMENT FAILURE
• Failure to take counter measures
• Delayed detection of TCDD
• Delayed evacuation

14. SOLVING THE CRISIS
• The contaminants were buried in two large
dug holes of 1,50,000 m3
• Holes enclosed by polyethylene sheet
• Covering of sheet with uncontaminated soil
• Covering the soil with 1m thick layer of
concrete

15. AFTEREFFECTS
• Chronic dermatitis
• Cancer
• Neuropathy
• Deformed babies
• Death of animals

16. CONCLUSION
• Seveso tragedy showed the after-effects of
violation of operational instructions and
failure in hazard management and serves as a
remainder for what will happen if the required
conditions and management are not
maintained

17. REFERENCE
• Mitsuo Kobayashi,Explosion of chemical plant
in italy 1976
• Laura Centemery,The Servo disaster legacy