In the evening of 2 March 1944 the freight train 8017 started from
Naples heading to
Potenza. It consisted of 47 freight wagons and had a remarkable mass of 520 tonnes; it also carried many illegal passengers.
The first part of the journey took place on flat railway, and the train was pulled by a
E.626 electric engine. At 19:00 the train left
Battipaglia and entered the steeper, non-electrified
Battipaglia–Metaponto railway; the electric engine had been replaced by two steam engines (the
480.016 followed by the
476.058).
In
Eboli some
stowaways were forced off, but more boarded on following stops until they numbered about 600, making the train grossly overloaded. At midnight the train arrived in the
Balvano-Ricigliano station, the last one before the disaster, where it stopped for maintenance on the engines.
At 00:50 the train restarted towards the adjoining
Bella-Muro station, and reached a speed of about 15 kilometres per hour (9.3 mph). After 1.8 kilometres (1.1 mi) of travel, it approached the Armi tunnel, narrow and poorly ventilated, which is 1,968 metres (2,152 yd) long with a 1.3% incline. As the engines entered the tunnel, the wheels started to slide on the rails (which were wet due to humidity), despite the use of
sand boxes, and the train lost speed until it stopped, with almost all the cars inside the tunnel.
The air was already filled with smoke since another train had passed shortly before, and the drivers' effort to restart the train caused the locomotives to produce even more
carbon monoxide–laden smoke. As a result, the crew and stowaways were asphyxiated, so slowly that they failed to realize what was happening to them. Most died in their sleep. Of the few survivors most were in the last few wagons, which were still in the open air.
At some point the driver of the 476 locomotive tried to engage the reverse gear in attempt to exit the tunnel, but he fainted before suceeding. Moreover, he couldn't communicate with the driver of the other engine (which in fact continued to push in the forward direction) because the 476 was an Austrian-built engine with right-hand drive, while the 480 had left-hand drive as usual in Italian railways.
At 05:10 the Balvano station master learned of the disaster from last car's brakeman, who had walked back to the station. At 05:25 a locomotive reached the site but the many corpses on the track prevented it from removing the train from the tunnel; only some forty survivors in the last wagons could be assisted. At 08:40 a second rescue team arrived which hauled the train back to the station. Among the crew, only the one brakeman, and the second locomotive's fireman, survived.
Due to the large number of corpses, the wartime lack of resources, and the poverty of many of the victims, only the train staff received a proper burial; stowaways were buried without a religious service in four common graves at the
Balvano cemetery.