While three persons died on the spot, eight others were injured, two of whom succumbed to their burn injuries last night at the government hospital, they said.
The victims were workers of the unit at Narayanapuram village, four km from Sivakasi, the country's fireworks hub, and they were engaged in making crackers when the explosion occurred yesterday.
Police said two foremen at the unit and an accountant were arrested this morning under various IPC sections and Explosives Act.
The explosion apparently occurred due to friction between the chemicals.