Three persons died on the spot while eight others were injured, of whom two succumbed to burns day before yesterday and one this morning.
The other injured persons are undergoing treatment at the government hospital.
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 on Sunday.
Two foremen at the unit and an accountant were arrested yesterday under various IPC sections and Explosives Act.
The explosion apparently occurred due to friction among the chemicals.
Virudhunagar district collector Hariharan has issued orders to officials to inspect all fireworks units in the area.
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