Abstract: ON APRIL 26, 1985, A MOLTEN SOLUTION OF 50% SODIUM NITRATE AND 50% POTASSIUM NITRATE, USED IN HEAT TREATING ALUMINUM RODS, EXPLODED. EMPLOYEES #1, 2 AND 3 WERE KILLED. EMPLOYEES #13,14 AND 18 WERE SEVERELY BURNED AND REQUIRED HOSPITALIZATION. EMPLOYEES #4,5,6,7,8,9,10,11,12,15,16,17,19 AND 20 WERE TREATED FOR BRUISES, CONTUSIONS, AND ABRASIONS AND WERE RELEASED. THE AREAS AFFECTED BY THE EXPLOSION INCLUDED THE ENTIRE HEAT TREAT DEPARTMENT, THE SCREW MACHINE DEPARTMENT, SIX ELECTRIC FURNACES, THE ENGINE ROOM, THE SHIPPING DEPARTMENT, AND PART OF THE MAINTENANCE AREA. AN INVESTIGATION REVEALED THAT THE AUTOMATIC TEMPERATURE CONTROL EQUIPMENT DID NOT FUNCTION TO SHUT DOWN THE HEATING SOURCE AS IT SHOULD WHEN A TEMPERATURE OF MORE THAN 970 DEGREES FAHRENHEIT IS REACHED. INSTEAD, THE CONTROLS FUNCTIONED IN REVERSE, CALLING FOR MORE HEAT UNTIL A VOLATILE TEMPERATURE WAS REACHED, CAUSING THE MOLTEN SALTS TO EXPLODE. THESE PARTICULAR CONTROLS HAD BEEN IDLE SINCE FEBRUARY OF 1985. THIS ACCIDENT COULD HAVE BEEN AVOIDED IF THE EMPLOYER HAD ESTABLISHED A SAFE STANDARD OPERATING PROCEDURE. ONE THAT, FOR EXAMPLE, REQUIRED THE TANK OPERATOR TO MEASURE THE TEMPERATURE OF THE MOLTEN SALTS WITH A PYROMETER TO COMPARE WITH THE TEMPERATURE RECORDED BY THE AUTOMATIC EQUIPMENT. THEN, IF THE TEMPERATURE REACHED 970 DEGREES FAHRENHEIT AND THE AUTOMATIC EQUIPMENT FAILED TO SHUT OFF THE BURNERS, THE OPERATOR COULD HAVE SHUT THEM OFF HIMSELF.