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6161 Chemical accident in USA with nitric acid fuming
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General accident information
Class/Quality * * * * *
Year 1983
Summary Puncture of tankwagon on
Railyard during switching
Caused release & 34 casualties
Country USA
Chemicals Nitric acid fuming, Sodium carbonate (soda ash)
Cause Technical-failure
Fatalities/Injuries 0 / 34
Occurrences or events Break, Chemical reaction, Chemical reaction, Collision,
Disperse/Spread, Drive, Drive, Evacuation,
Fire, Fire fighting/Emergency response, Fire fighting/Emergency response, Ignition,
Penetrate/Puncture, Release, Switch, Traffic-interruption,
Vaporize, Wrong-action
Full accident information 
download accident report Click here to view a document containing the full accident information

Date : 1983 0403

During a switching operation a coupler broke. This lead to the separation of 4th and further wagons. They stopped 45/meters from the train. The train crew did not notice this because it was dark. The train began to drive and hit the 4th wagon with 5/m/s. The 4th wagon, an empty freightcar, hit the 3rd wagon, a tankwagon filled with nitric acid. The tankwagon was punctured and released 53.7/m3 of nitric acid. This caused some small fires and a big vapour cloud. Firemen used water to remove the acid, as described in the hazardous materials guide. This information was wrong, the cloud became bigger. The nearby area was evacuated, 5/km2 with about 9000 persons. The hazardous materials squad, which had arrived, advised to use soda ash to neutralize the spill. A train with 7 wagons of soda ash was found nearby and was used to neutralize the spill. 34 persons were injured.

The coupler was weakened because of a hidden, pre-existing fracture. The switching caused it to break completely.

Lessons learned (recommendations)
Install head shields to protect DOT specification aluminium tankwagon ends from puncture.
Periodically inspect the hidden components of a tankwagon and incorporate this inspection as a rule in the wagon interchange requirements.

The flat switching of cars was being performed in accordance with normal industry practices.
No Federal regulation or industry practice requires periodic inspection of hidden car components: therefore, the empty box car, which had an undetected fracture in the pin hole area of a coupler continued in service.
The repeated quick in accelerations and stops, required in the switching operation, sufficiently stressed the weakened coupler to the point of complete failure, resulting in a separation in the string of cars.
Because of darkness and their positions the separation of the cars occurred at a location where no crewmembers were in position to see it. All the crewmembers were at the positions assigned by the engine foreman to accomplish the switching of the cars.
There was a heavy impact when the moving cars overtook and struck the separated cars. An override followed in which a tank car was breached and spilled nitric acid. The spilled acid resulted in a vapour cloud and ignited some crossties in the track.
No cooperative emergency plan for the city railyard had been developed between the company and city public safety organizations.
There were delays in notifying the city safety organizations because the company did not have an emergency plan.
Firefighters relied on the Railroad's Computer Generated Emergency Hazardous Material guide waybill instructions furnished them by the company and applied water to the spill.
The water used to knock down the vapours and to fight the fire spread the pool of nitric acid and enlarged the vapour cloud.
The City Hazardous Materials Coordinating Chief correctly decided to use soda ash to neutralize the nitric acid based on his past experience with the material.
The emergency instructions and DOT Emergency Response guidelines were not specific enough to indicate in what environments the various methods of attacking a spill should be used.
The tank car involved in this accident was not equipped with a head shield which may have prevented the accident.

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