The blast happened about 10 a.m. at the Nebraska Public Power District's coal-burning Sheldon power station.
Three employees were welding inside a mechanical room near the top of the 100-foot-tall silo at the time of the explosion, according to Lancaster County Sheriff Terry Wagner.
Welder Terry Egger, 50, and engineering manager Duane Swoboda, 49, were thrown through an outside door by the blast and were killed by the fall.
Another welder, whose name was not released, suffered minor cuts and apparently survived because he was not standing near the outside door during the blast.
"It looks like they had been doing some welding work all morning and shortly after they stopped, the explosion happened," Wagner said.
The explosion ignited a small fire that burned for about an hour inside the silo before being extinguished by the plant's fire and rescue squad.
The silo, which is used to store flying ash captured from the plant's burning area was relatively new and the crew was making some modifications in its operations room, said NPPD spokeswoman Sharon Soltero.
The plant has been temporarily shut down. NPPD officials said they don't know when the plant will return to operation but added that no customers would experience power outages because of the move.
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