CONTRACTOR EE (THYSSEN MINING CONSTR. OF CANADA) WAS CUTTING OUT DAMAGED BOLTS AND WIRE WITH A CUTTING TORCH. THE OXYGEN AND ACETYLENE BOTTLES WERE 15-20 FEET AWAY. A SPARK FROM THE MATERIAL BEING CUT IGNITED ACETYLENE THAT WAS LEAKING FROM OR AROUND THE HIGH PRESSURE SIDE OF THE ACETYLENE REGULATOR, STARTING A FIRE THAT LASTED 45 MINS. NO INJURIES OCCURRED.