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10257 Chemical accident in Italy with nitric acid
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General accident information
Class/Quality * * * *
Year 1988
Summary Explosion during unloading of nitric acid from
Road tanker to storage tank caused toxic cloud
And at least 8 casualties
Country I
Activity TRANSSHIPMENT
Location STORAGE/DEPOT
Chemicals Acid n.o.s., Ammonia, Formic acid, Nitric acid,
Nitric oxide (no)
Cause Unknown-cause
Fatalities/Injuries 1 / 7-11
Occurrences or events Clean, Dilute, Explosion, Fire fighting/Emergency response,
Mount/Connect, Operators error, Pollution/Contamination, Release,
Run-away-reaction, Safety-measures, Traffic-interruption, Unload
 
 
Full accident information 
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Country: ITALY (I)
Date : 1988 0516


At about 0755 hours, a strong explosion inside a tank occurred during the unloading of nitric acid from a road tanker, followed by the release of a cloud with a yellow/red colour. This produced a rapid exothermic reaction that led to the explosion. The cloud had a strong smell and caused irritation of the eyes and skin. The main pollutants were nitrogen oxides. It seems that, by mistake, the operator connected the road tanker to the wrong tank, i.e. he emptied the nitric acid into a tank containing formic acid. The mixing of the two acids produced a rapid exothermic reaction that led to the explosion. Another possibility is that he connected the right tank, but that tank was filled with ammonia residues. The man attending the operation was killed by the explosion. Few minutes later the fire brigade intervened (using personal breathing apparatuses and protective clothing), diluted the liquid acid on the ground with water and created a containment to prevent the acid spreading over on the ground. Nebulized water was also used to dilute the nitrogen oxides vapours. In the meantime the evolution of the cloud (directed towards the sea) was continuously observed from a helicopter. Personnel on the helicopter relieved that the cloud was rapidly dispersing in about 100/meters from the source of release. At about 1200 hours the concentration of the cloud, diluted by the action of wind, was no more dangerous.
The explosion seriously damaged some tanks.

The exploded tank was cut along the inferior weld; some parts have been found at about 50/meters away while the top flange in which the relief valves were installed was found at about 100/meters away. Two other empty tanks, nearby to the exploded one, were found at 25 meters from the point where the accident occurred. The road tanker struck a wall. Some buildings inside the establishment suffered extensive damages. Some walls and roofs inside the establishment were put down. Broken windows were found up to 300/meters away. Road traffic around the establishment was prohibited for some hours. The water to the water treatment plant, connected with the chemical factory, reached a low pH (about 3.5) and returned to pH=7 after the intervention of fire brigade in diluting the liquid acid on the ground with water.

On the basis of some stoichiometric calculations it has been estimated that, following the explosion, a cloud of about 12000 Nm3 was released. The cloud was composed by oxygen, nitrogen, water and nitrogen oxides.

No data are available about the amounts of nitric acid and formic acid involved in the explosion. Also, no data are available about the amount of nitrogen oxides released into the environment as a consequence of the reaction between nitric acid and formic acid. On the basis of some stoichiometric calculations it had been estimated that, following the explosion, a cloud of about 12E+3/m3 was released. The cloud was composed by oxygen, nitrogen, water and nitrogen oxides.

Consequences
1 person killed, 7-10 persons injured, material damage both inside (destruction of tanks, damage to buildings) and outside (windows broken within 300/m) of the establishment, closure of roads to traffic.

Causes
Immediate:
operator error (operation-related), unexpected chemical reaction.
Underlying: managerial/organizational omissions (insufficient operating procedures) and/or appropriate (operation) procedures not followed.
Under these hypotheses the tank explosion could be explained because the reaction between the formic acid (a reducing substance) and the nitric acid (a strong oxidizing substance) is very rapid and highly exothermic and leads to the formation of water, carbon dioxide and nitrogen oxides. The operator's error in the unloading operation was caused by an inadequate training/instruction together with an insufficient operating procedures.


Une citerne routi??re d'acide nitrique explose lors de son d??potage dans un r??servoir contenant encore de l'ammoniac. L'incendie qui en r??sulte est ??teint en 5 h. Un mort est ?? d??plorer ainsi que 11 intoxiqu??s qui sont hospitalis??s. Les employ??s des usines voisines sont ??vacu??s. Des vitres sont d??truites et un nuage orange de vapeurs nitr??es se disperse sur une zone habit??e en provoquant de vives r??actions de la population.



 
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