517 people in a steam-hauled, coal-burning freight train (mostly stowaways) died of carbon monoxide poisoning during a protracted stall in a tunnel.

People in large cities such as Naples began bartering fresh produce for commodities brought by servicemen, and stowed away on freight trains to reach their suppliers' farms.

The burning of low-grade substitutes in locomotives reduced their power output and produced a large volume of carbon monoxide, an odorless and poisonous gas, a particularly severe problem in Italy's railway network, which crosses mostly mountainous land, and hence makes large use of tunnels with steep inclines of up to 3.5%.

[4] After 1.8 kilometres (1.1 mi) of travel, it approached the narrow and poorly ventilated Armi tunnel, which is 1,968 metres (2,152 yd) long with a 1.3% incline.

At some point, the driver of the 476 locomotive tried to engage the reverse gear in an attempt to exit the tunnel, but he fainted before succeeding.

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.

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.

Contributing factors were the low-quality coal, the lack of ventilation in the tunnel, the wet rails, and the fact that the train had a double heading instead of a push–pull configuration.

"The station masters of Balvano and Bella-Muro were blamed because they did not act to determine the location of the train when it appeared late on the roadmap.

The Command itself organized a train to check the condition of the disaster, with staff equipped with oxygen masks, which recognized the actual development of abnormal amounts of toxic gases.