What is it about?

Nous avons déjà parlé dans ce blog des catastrophes industrielles d’origine chimique qui se sont déroulées dans le monde (1) : un petit rappel par ordre chronologique :

+ Explosion of the powder factory of Grenelle in Paris August 31, 1794, 150 tons of powder, a thousand victims;

+ Blowout in a mine in Courrières (France) on March 10, 1906, 1099 dead;

+ Feyzin (France) January 4, 1966, explosion followed by a fire due to a propane leak, 18 dead;

+ Seveso (Italy), July 10, 1976, dioxin leak. No deaths but a massive dioxin spreading, 15,000 people evacuated, 1,800 hectares of land unoccupied for 10 years and very heavy financial consequences;

+ Bhopal (India), December 3, 1984, leak of 40 tons of methyl isocyanate (MIC), 3,828 deaths and more than 20,000 in the 20 years that followed;

Toulouse (France), September 21, 2001, explosion of 400 tons of ammonium nitrate in the AZF factory, 30 dead;

Tianjin (China), August 12, 2015 explosion at a factory storing several types of hazardous materials: calcium carbide, toluene diisocyanate, ammonium, potassium and sodium nitrates, and 700 t of sodium cyanide. One hundred and seventy-three dead, 70 missing (mainly firemen);

Beirut (Lebanon), August 4, 2020, explosion of 2,750 tons of ammonium nitrate, 215 dead.

Autopsy of an industrial disaster: the explosion of the AZF factory in Toulouse

The factory

The AZF (Azote Fertilisant) plant, owned by the TotalFinaElf group, employed 469 people and manufactured nitrogen fertilizers and industrial nitrates from ammonia synthesized on site and transformed into ammonium nitrate. It also synthesized chlorine derivatives used in water treatment and melamine, a raw material for resins.

Reminder of the facts: the accident

On September 21, 2001, the AZF factory exploded and devastated the southern districts of Toulouse (2). The explosion created a large crater about 40 meters in diameter and 7 meters deep ? The explosion was heard by the inhabitants of Castres, 74 km away, and significant dust fallout occurred.

The human impact

The death toll was very high, with 31 dead, including 21 site employees, and 2,500 injured (2). Some people were killed at a distance from the plant, including a student from a high school located 500 m away, who died under the collapse of a concrete structure. Thousands of people were hospitalized (mutilations, burst eardrums, contusions of organs (spleen and liver), open fractures. More than 8,000 people consulted their general practitioner for acute post-traumatic stress in the weeks following the explosion and 5,000 people started psychotropic treatment (anxiolytic, antidepressant, hypnotic), in order, among other things, to recover sleep.

Social disruptions related to the destruction and degradation of housing, community facilities, technical unemployment, and job loss were added to the medical problems. 

The material assessment

The AZF factory, with a surface area of 70 hectares, was largely ravaged.

Damage was observed in the industrial establishments on the other bank of the Garonne, including SEVESO 2 classified establishments: the 1,100 employees of these establishments were shut down. Fortunately, the much feared “domino effect” on the many chemical product storage facilities nearby (chlorine, ammonia, fertilizers, phosgene, etc.) did not occur!

The material damage was considerable: 25,000 homes destroyed or damaged and 1,200 families had to be rehoused urgently. Public buildings such as schools with 82 schools, 15 high schools and 4 higher education institutions were affected.

The windows were broken up to 7 kms away.

One thousand three hundred companies representing 20,000 jobs were affected to varying degrees.

Finally, telecommunications were disrupted within a 100 km distance, with fixed lines and cell phone networks completely saturated for several hours after the explosion.

According to the insurance companies, the damage was estimated at nearly 2 billion euros.

The environmental balance sheet

Air pollutants consisting of nitric acid (HNO₃), ammonia (NH₃), nitrogen dioxide (NO₂) and nitrous oxide (N₂O), the breakdown products of ammonium nitrate, were released into the atmosphere. Witnesses suffered significant eye and throat irritation.

Discharges of nitric acid and nitrogen solutions, and in particular ammonia, polluted the Garonne. Several tens of kg of fish were poisoned.

Terrorist attack ?

The President of the Republic, Jacques Chirac, and his Prime Minister, Lionel Jospin, went to the site the same day. Occurring ten days after the attack on the World Trade Center in New York, the explosion could have been a terrorist attack. However, this theory was quickly dismissed by the experts who turned to the possibility of a chemical accident. 

What caused the accident?

There is no doubt that the explosion was caused by the presence of 15 to 20 tons of ammonium nitrate that had been unloaded in the shed the day before. We have already seen in this blog why ammonium nitrate is so dangerous (4).

How to explain the explosion? Numerous investigations have been carried out to find out what the cause of the explosion was:

            Unintentional external causes: lightning, meteorite, falling aircraft parts…all these hypotheses proved to be unfounded;

                        Intentional external causes (attack, missile), plausible in the context of the attacks of September 11, 2001. No evidence was found to support this theory;

            Process incident: electric arc or missile effect of a part projected at high speed. These hypotheses were rejected;

           Accidental chemical reaction; the nitrates involved being polluted by iron oxides, sulphur or the bitumen constituting the floor covering of building 221 where they were stored. Perhaps a mixture of nitrates with sodium dichlorocyanurate = DCCNa (swimming pool treatment)?

On 16 May 2006, the final report of the expert investigators confirmed the theory of a chemical accident, attributing the causes of the disaster to an unfortunate mixture of a few dozen kilos of DCCNa with 500 kg of ammonium nitrate spilled on the main nitrate pile 20 minutes before the explosion.

It should be remembered that explosions with ammonium nitrate as their origin have already been described:

+ On July 26, 1921, in Kriewald, the “unhooking” of ammonium nitrate cars with explosives resulted in a detonation that killed 19 people;

+ On September 21 of the same year, in the German factory of Oppau, the exploitation with explosives of a heap of nitrate and coated ammonium sulfate caused a detonation resulting in 561 deaths, and the virtual destruction of the city;

+ Twenty years later, in Belgium, an explosive attack on a pile of ammonitrate resulted in several hundred deaths in Tessenderloo ;

+ Beirut, August 4, 2020, explosion of 2,750 tons of ammonium nitrate, 215 dead and destruction of the port.

Intervention and rescue

The Particular Intervention Plan (PPI) and the red plan were activated: during the first 6 days 1,430 people were mobilized, 460 firefighters from Haute Garonne, 620 from other departments, 350 soldiers from the Civil Security Instruction and Intervention Units (UIISC), 50 doctors, 32 nurses and 80 ambulance drivers also participated.

Site remediation

The site remediation, carried out by the operator, consisted mainly of reducing the concentrations of hydrocarbons, lead, arsenic and mercury in the soil. After two years of work, more than 750,000 m³ of soil were excavated, and the soil and concrete were cleaned up on site by washing and heat treatment at 850°C. The work was completed in 2008.

The site now houses the Toulouse Oncopole (University Cancer Institute).

The penal consequences

The trial took place from February 23 to June 30, 2009. At the end of the debates, the public prosecutor requested a fine of 225,000 euros against Grande Paroisse (the company operating the site), as well as a suspended sentence of three years in prison and a fine of 45,000 euros against the plant manager. At the end of the deliberations, the criminal court of Toulouse acquitted the defendants for the benefit of the doubt.

During the appeal, the court condemned the company Grande Paroisse and its former director for manslaughter and involuntary injury due to “clumsiness, inattention, negligence, imprudence or failure to comply with a safety obligation”. The fines were confirmed for Grande Paroisse and its director, as well as the three years of imprisonment, two of which were suspended and one of which was suspended under the semi-liberty regime. However, the Court once again ruled that the proceedings requested by certain civil parties against the Total group and its former CEO were “inadmissible”. The Court of Cassation later upheld the sentences.

Conclusion

The explosion was considered unlikely in the case of ammonium nitrates that met the standard. The risk assessment method was found to be insufficient. The hazard study must consider the hazard potential of the installations, examine the possible accidents and their consequences, including the most dramatic or improbable. Moreover, the evolution of urbanization was not taken into account, the factory built in the middle of a field in 1930 found itself in the middle of a city a few years later.

For this reason, the public authorities have initiated various discussions and actions in the field of prevention and control. Please refer to the publication 1.

References

1. Les catastrophes chimiques : domaine du NRBCe, François Renaud, Ouvry, 2015
2. La catastrophe de l’usine AZF à Toulouse. Lumni, ministère de l’éducation nationale (2007, 2022).
3. Explosion dans l’usine de fabrication d’engrais AZF. Le 21 septembre 2001, Toulouse (Huate Garonne) France. Ministère chargé du développement durable – DGPR / SRT / BARPI
4. Le nitrate d’ammonium : François Renaud,  Ouvry, 2020