A WELDER WAS WELDING IN THE HOUSE OF THE SHOVEL. PROTECTIVE FIRE BLANKETS HAD BEEN PLACED BUT A SPARK FELL THROUGH A SMALL HOLE AND STARTED A FIRE IN THE HIGH VOLTAGE RING SECTION BELOW THE DE CK. IT IS A DIFFICULT LOCATION TO FIGHT FIRE AND IT TOOK ABOUT TWO AND A HALF HOURS TO COMPLETELY EXTINGUISH. FIRE DAMAGE WAS LIMITED ELECTRICAL WIRING.