One worker was killed and six others were burned after an explosion Wednesday at a wastewater treatment plant that was undergoing hurricane repairs.

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The explosion happened around 11:30 a.m. at the city's Bethune Point Treatment Plant when employees who were working to repair a metal roof damaged by last year's hurricanes, used a cutting torch near methanol and sodium sulfate tanks, said Lt. John King, spokesman for Daytona Beach Fire Department.

Firefighters had to fight the fire from a distance with unmanned hoses because of concerns about chemical vapors, King said. The Volusia County bomb squad was using a robot to assess the situation, he said.

The injured men were taken to Halifax Medical Center - one had third-degree burns over 100 percent of his body, said Mark O'Keefe EVAC ambulance spokesman.

O'Keefe said the other had second-degree burns over 80-90 percent of his body. Four other victims are in stable condition. Their names were not immediately released.

King said authorities will launch an investigation to determine the exact cause of the explosion, but said it likely was related to the cutting torch.

Methanol, a form of alcohol, is highly flammable and used to remove nitrates from waste water. Sodium sulfate is a nonflammable powder normally used in treatment plants to neutralize chlorine.

The explosion did not effect the city's water treatment, O'Keefe said.