One firefighter is dead and six others hospitalized after battling a massive natural gas explosion in Wisconsin yesterday. One civilian was treated and released.

News reports say the leak the led to the blast was caused by a contractor who punctured a 4-inch natural gas main. Authorities had already begun an evacuation of residents in the area when the explosion occurred – a move that likely saved lives, according to Sun Prairie police Lt. Kevin Konopacki.

In a press conference held Wednesday morning, Konopacki confirmed that the firefighter who died was a 10-year veteran of the department. One of the firefighters who are hospitalized has serious injuries but is expected to recover.

The explosion, which sent smoke and flames into the air, reportedly did significant damage to several buildings.