ATHENS, Ala.?Four electricians were badly burned after a high-voltage breaker at the Browns Ferry nuclear power plant malfunctioned, officials said.

No radioactivity was released in Tuesday’s incident, which left four men with burns and other unspecified injuries. Their conditions were upgraded from critical to satisfactory condition Wednesday at University Hospital in Birmingham.

Officials said an electrical arc jumped out of a 4,160-volt breaker in the Unit 3 turbine room, burning the four.

The Tennessee Valley Authority-run plant had been shut down for routine maintenance earlier Tuesday.

Investigators were trying to determine the cause of the incident.

The plant, about 95 miles north of Birmingham, suffered a major electrical fire in 1975 after workers using a candle to search for air leaks ignited insulation on cables in a reactor control room.