EE was repairing a crack 4.5' above ground level on the bucket of a CAT 5230 front shovel when right pant leg caught on fire from sparks or welding slag. He was sitting on a 5 gal. bucket as he welded. He was treated for a 2nd degree burn and released to work his next scheduled shift. (On May 6 a low grade infection set in and he was prescribed antibiotics and bed rest).