Three workers are being treated for burns after corn dust exploded at a silo south of Phoenix.

Maricopa police Sgt. Stephen Judd says employees were offloading corn dust into a pit Monday morning when the blast occurred.

The three injured workers have been taken by helicopter to a hospital burn unit with first- and second-degree burns, mostly to their faces, arms, and hands.

Judd says one worker was in critical condition Monday afternoon and the others were in good condition.

Judd says a welder had been doing routine maintenance work on the elevator a few minutes before the explosion. He says it's unclear whether that had anything to do with the explosion, which was so powerful it tore steel anchoring rods out of concrete.