An external contractor was cleaning the floor with a motorized floor scrubber when he smelled propane. The contractor got off the scrubber and opened up the compartment with the propane tank and took it halfway out to check connections. When he tried starting the scrubber back up, the scrubber erupted in flames and he sustained burns. The contractor summoned additional employees. While trying to extinguish the fire with a fire extinguisher, the scrubber exploded again and caused burns to another employee's head, face, neck, and left hand.