One Thangapandi died this afternoon without responding medical treatment at hospital following injuries, they said.
Three persons were undergoing treatment at the hospital and their condition was out of danger, they said.
Three persons were killed and eight injured in the incident on April 28. Four more persons succumbed to injuries in subsequent days.
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.
The explosion apparently occurred due to friction among the chemicals.
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