INJURED AND OTHER EE WERE ASSIGNED TO REPLACE 2 BREAKERS IN LCK1 UNIT SUBSTATION. BREAKERS WERE K1A AND CH. THE BREAKERS WERE OPENED AND DISCHARGED, THEN RACKED OOT TO THE DISCONNECT POSITION. BREAKER DOORS WERE OPENED AND THE TRIP UNIT SETTINGS WERE TRANSFERRED TO REPLACEMENT BREAKERS. FIRE AND FLASH FROM THE EXPLOSION ESCAPING THE STARTER CUBICLE BURNED BOTH EMPLOYEES.