The deceased was identified as K Arun Kumar who was undergoing treatment at a private hospital, said sub-inspector of Atchuthapuram police station, S Sanyasi Rao.
The first casualty of the explosion was B Biswas (40) who hailed from West Bengal.
The condition of another worker, Lakshmana Rao (30), hailing from Bhogapuram, continues to be critical.
The plant manufactures ferro manganese.