Memories of Switzerland's worst environmental disaster haunted the town of Schweizerhalle on Thursday, after an explosion ripped through a factory, owned by the specialty chemicals company, Ciba.
The explosion took place in the early hours of Thursday morning. No one was injured, although 21 firefighters suffered from the effects of inhaling poisonous chemicals and acid burns.
The company said the blast had released some chemicals but that they were not acutely toxic, and posed no danger. Nevertheless, residents were told to keep their windows closed for some hours after the blast as a precaution.
The explosion evoked memories of a fire which broke out at a factory owned by Sandoz - which later merged with Ciba-Geigy to become Novartis - in Schweizerhalle in 1986. That incident caused some 1,351 tonnes of chemicals to go up in flames, releasing a toxic cloud over Basel and polluting the Rhine.
The cause of the disaster - the worst environmental catastrophe in Switzerland's history - was never established.
Ciba said Thursday's explosion occurred when a chemical reactor overheated, causing a fire. The factory concerned produces chemicals for the manufacture of plastics. Ciba said the cause of the overheating was not known, but that the reactor had not been in use for eight weeks.
Some 20 people were working in the building at the time, but all managed to escape unharmed.
In February a similar incident occurred at a factory in Schweizerhalle owned by the pharmaceutical giant, Novartis. Nobody was injured in that blast, which took place in a medicine factory.
swissinfo with agencies