On 12 December 1996, a tank wagon carrying hydrosilicofluoric acid derailed in Jämsä and the contents of the tank began to leak out. The leakage increased when the fire department sought to block the leak, since the tank was in poor condition. The fire department transferred the contents of the tank into another tank wagon brought to the scene of the derailment. Some hydrosilicofluoric acid leaked onto the ground. The soil was subsequented neutralized with lime.
The sequence of events began when another train was unable to climb a hill south of the Jämsä railyard. The train pulling the wagon that subsequently derailed came to assist in pulling this second train. Towards the end of this procedure, when the first train began to brake, the second train which was being pulled behind pushed the carriages together. When this happened, the elastic limits of the buffers of the carriage in front of the wagon carrying the acid ended and a buffer got broken. The tank wagon carrying the acid rose on the buffers of the carriage in front, and as a result the wagon derailed at the next switch. The contents of the tank wagon which had been constructed in 1971 and lined with rubber in 1990, began to leak, although it did not hit anywhere.
The firemen rose to a dangerous height in pulling slings over the leaking tank wagon, even though the electricity had not been cut from the power lines. The delay in cutting off the electricity had been due to the fact that another wagon was being brought next to the leaking wagon for the transfer of the load. The firemen were aware that the electricity had not been cut.
The economic loss from the accident was less than FIM 500,000 (ca. 80,000 euros or USD 100,000).
According to the order documents the leaking tank should have been lined with
neoprene rubber, which was known to be able to enclose the hydrosilicofluoric
acid. However, an analysis carried out by the VTT (State Technical Research
Centre) showed that the lining was polyurethane, and no information is available
on the chemical reaction between this and the hydrosilicofluoric acid