Abstract: On August 24, 1996, a company was using a 5 ft diameter, 5 ft tall GCA vacuum furnace to heat treat silicon carbide parts. The furnace, manufactured by Vacuum Industries, Inc., was a bottom-loading, cold-walled batch furnace equipped with a closed loop water cooling system. The furnace, vertical and cylindrical in shape, uses electrical resistance heating elements. While the furnace operator was on break, an employee noticed a break in the cooling water line that supplied water to the bottom head of the furnace. He got Employee #1, a mechanic. Employees #2 and #3 arrived at the furnace to evaluate the problem. Employee #2 went over to the furnace and shut off the water valve for the bottom head water line which had ruptured. The furnace was at its maximum operating temperature of 2,150 degrees centigrade. The furnace exploded shortly thereafter, seriously burning Employees #1, #2, and #3. The explosion was caused by failures in the water cooling system and backup safety features. The furnace did not comply with all the safety requirements listed in NFPA 33D.