The explosion took place in OFK's Section F-2 building number 140, when explosive powder was being filled in the 84 mm bomb at around 9.55 am, Khamaria police station in-charge R P Tiwari told reporters.
Four employees were injured in the mishap and the condition of one of them, identified as Santosh Raidas (40), was stated to be serious. He has been admitted in the Marble City Hospital, he said.
The other three injured, Pankaj Gotia, Rupesh Pal and Prabhat, were admitted in OFK hospital for treatment, Tiwari said.