EMPLOYEE HAD OPENED INSPECTION PLATE AT ALKALI BY-PASS FLAPPER VALVE TO CHECK FOR BLOCKAGE. HOT MATERIAL FELL INTO THE SCROW WHICH FEEDS THIS VALVE AND FLUSHED THROUGH CAUSING EMPLOYEE TO BE H IT WITH DUST. EMPLOYEE RECEIVED MINOR BURNS TO FACE AND NECK, HOWEVER BOTH FOREARMS HAD RECEIVED 1ST & SOME 2ND DEGREE BURNS. EE WAS TREATED & DID RETURN TO WORK RESTRICTED AWAY FROM HOT AREA