An explosion at a Colorado steel mill left at least seven workers with minor injuries and sent smoke and steam billowing into the air Saturday evening, according to reports. 

The blast was caused by an unexpected "release of water" into an electric arc furnace at the plant, causing a buildup of pressure, FOX 31 in Denver reported. The furnaces are used to heat material in the steel-making process. 

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Most of those injured suffered bruises and smoke inhalation, KKTV-TV of Colorado Springs reported. 

The injured were taken to a hospital as a precaution; 28 people were working at the plant at the time. 

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The Pueblo Fire Department responded to the scene to make sure it was safe for workers to return. No fire was reported, according to FOX 31