Xcel Energy, Inc.'s Black Dog facility in Burnsville has been closed after an explosion occurred at the plant on Tuesday morning, resulting in a small fire.

Company spokesman Tom Hoen said that smoldering was observed in a coal bunker- where coal is stored before it is burned-at about 7:15 a.m. and a call was placed to the Burnsville Fire Department around 7:25 a.m.

Hoen said that the fire department arrived at about 8 a.m. and that the explosion occurred shortly after their arrival.

The fire in the coal bunker area resulted in a secondary fire on the roof, which was put out by fire fighters around 2 p.m., Hoen said.

The plant's damage has not yet been assessed, but the company hopes to have the assessment done by the end of the week. Xcel will then put together a restoration plan.

Hoen said that the U.S. Occupational Safety and Health Administration was on the scene yesterday working to determine the cause of the explosion.

No Xcel Energy employees were injured in the blast, but one firefighter was hospitalized with knee injury and three others sustained minor injuries from blast debris that got into their eyes.

When operating at capacity, Xcel's Black Dog facility produces about 540 megawatts of electricity-enough to power about 400,000 homes. The plant, which has about 75 employees, has not had any other fires or explosions since it opened in 1955.

Xcel is Minnesota's 10th-largest company based on its 2008 revenue, which totaled $11.2 billion. The company reported revenue of $9.6 billion in 2009.

-Melissa Loth