Daytona Beach, Fla. ? An explosion Wednesday at a wastewater treatment plant that was undergoing hurricane repairs killed one worker and burned six others, two critically, authorities said.

Employees of Daytona Beach’s Bethune Point Treatment Plant were on a metal roof with a blow torch near methanol and sodium sulfate tanks, said Lt. John King, a fire department spokesman.

The cause of the explosion was under investigation. King said it likely was related to a cutting torch being used to repair hurricane damage to a roof.