1407 cdt alarm received fire at heartland grain and fuels in huron sd as first officer arrived on scene report of explosion on n side of plant in the distillery area 4 workers injured two transported with 2nd and 3rd degree burns one suffered burns to the face fire contained to ground floor room with airport crash rescue truck and foam fire was knocked down and out with 45 mins fire no structure damage reported plant had been shut down for aprox a week for upgrades fire was started by a welder