UPDATE: An explosion at Mitsubishi Materials Yokkaichi polysilicon plant has resulted in the death of five workers with a further 12 injured, according to reports.

A spokesman for the company confirmed to PV Tech by telephone that the accident had taken place at 2:05pm local time. The plant is located in Mie Prefecture, on the main Japanese island of Honshu.

Japanese news outlets reported that of the deaths, three were directly employed by Mitsubishi Materials and the other two were subcontracted workers.

Broadcaster NHK reported that one of the injured, a 39 year old critically injured man was rushed to hospital by helicopter.

The incident was said to have happened during scheduled maintenance with the plant's heat exchangers when an explosion occurred and a fire started, later extinguished by fire services. It is suspected that the explosion was caused by a reaction involving Trichlorosilane as heat exchangers were removed for cleaning.

The company spokesman told PV Tech that following the small, quickly extinguished fire caused by the explosion, it was thought the complex would not have to be closed for any extended period of time and suspension of other work at the plant was not likely to be necessary. The materials that caused the blast had been removed from the main equipment housing them and taken outside the facility for cleaning and therefore there was little damage to equipment inside the factory.

However, beyond stating that work at the facility prior to the explosion had been carried out safely to the knowledge of the company, the spokesman declined to comment further before the results of investigations into the incident begin to emerge. The spokesman said that although it was not the first explosion to have been experienced at a Mitsubishi Materials polysilicon plant, it was the first to have caused serious injury or death.

The spokesman said Mitsubishi Materials was preparing a statement to post on the company website.

Mitsubishi Materials restarted polysilicon production at the Yokkaichi plant in the middle of 2010, after technical and safety upgrades. The initial plant was established in 1968 and had primarily served polysilicon requirements for the semiconductor industry and had a capacity of around 1,800MT per annum and therefore not a major producer.

Additional reporting by Andy Colthorpe.

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