Icmesa chemical company, Seveso, Italy. 10th July 1976
Accident summary
At approximately 12:37 on Saturday 10th July 1976 a bursting disc on a
chemical reactor ruptured. Maintenance staff heard a whistling sound and a
cloud of vapour was seen to issue from a vent on the roof. A dense white
cloud, of considerable altitude drifted offsite. The release lasted for some
twenty minutes. About an hour after the release the operators were able to
admit cooling water to the reactor.
Among the substances of the white cloud released was a small deposit of
TCCD, a highly toxic material. The nearby town of Seveso, located 15 miles
from Milan, had some 17,000 inhabitants.
Over the next few days following the release there was much confusion due
to the lack of communication between the company and the authorities in
dealing with this type of situation.
No human deaths were attributed to TCCD but many individuals fell ill. A
number of pregnant women who had been exposed to the release had abortions.
In the contaminated area many animals died.
Failings in technical measures
- The production cycle was interrupted, without any agitation or
cooling, allowing a prolonged holding of the reaction mass. Also, the
conduct of the final batch involved a series of failures to adhere to
the operating procedures. The original method of distillation patent
specified that the charge was acidified before distillation. However, in
the plant procedures the order of these steps was reversed.
- Operating Procedures: safe
operating procedures
- The bursting disc was set at 3.5 bar, and was to guard against
excessive pressure in the compressed air that was used to transfer the
materials to the reactor. Had a bursting disc with a lower set pressure
been installed, venting would have occurred at a lower and less
hazardous temperature.
- Relief Systems / Vent Systems:
venting of excessive pressures, sizing of vents for exothermic reactions
- The reactor control systems were inadequate both in terms of the
measuring equipment for a number of fundamental parameters and also in
the absence of any automatic control system.
- Control Systems: sensors
- Alarms / Trips / Interlocks: loss of
cooling, agitator failure
- The company was aware of the hazardous characteristics of the
principal exotherm. However, studies showed that weaker exotherms
existed that could lead to a runaway reaction.
- Reaction / Product Testing:
calorimetry methods, thermal stability
- There was no device to collect or destroy the toxic materials as they
vented. The manufacturer of the bursting disc recommended the use of a
second receiver to recover toxic materials. No such vessel was fitted.
- Design Codes - Plant: nature of
hazardous releases
- Secondary Containment: catchpots
- Information on the chemicals released and their associated hazards was
not available from the company. Communication was poor and failed both
between the company and the local authorities and within the regulatory
authorities.
- Emergency Response / Spill Control:
safety management system, site emergency plan
References
Lees, F.P., ‘Loss Prevention in the Process Industries – Hazard
Identification, Assessment and Control’, Volume 3, Appendix 3, Butterworth
Heinemann, ISBN 0 7506 1547 8, 1996.
Public Register of COMAH Establishments
