A Samsung Electronics chip plant in Hwaseong, Gyeonggi Province sprung another toxic leak on Thursday, the third this year. The first two happened in January and May.
According to local police, four staff of a Samsung subcontractor who were working outside the plant in Hwaseong, complained of an ammonia smell and stinging in their eyes and throat on Thursday afternoon and were taken to hospital.
Samsung immediately checked both inside and outside the plant but found no ammonia, and leakage levels were normal when the local authority conducted its own survey.
Police believe that ammonia gas must have leaked when pipes for the dust-filtering vacuum pump were replaced.
On January 27, highly poisonous hydrofluoric acid leaked in Samsung's main chip plant in Hwaseong, killing one worker and injuring four. On May 2, residual hydrofluoric acid leaked again while the pipes that caused January's leakage were being replaced, injuring further staff.