The interior of a small high-temperature furnace, approximately 24 inches high by 18 inches wide, became contaminated with an unknown material later identified as magnesium. The furnace was disassembled to clean the unknown material from the interior surfaces, and while attempting to clean the bottom of the furnace, the technician tapped the upper lip of the furnace with a spatula and the magnesium flashed. The technician was stepping back from the furnace when the magnesium flashed. He received minor eye irritation and his eyebrows were singed.
Later that week the same technician was attempting to clean the interior surfaces of the top of the furnace and sprayed, as directed, the interior of the top with a water-based cleaning liquid which consisted of 91% water. He stepped around to the back of the unit to get a vacuum cleaner. While he was there, a small explosion occurred. No one was injured by the explosion. Although the furnace is located in a radiological control area, no radioactive contamination was involved.
The unknown material on the inside surfaces of the furnace top was found to be magnesium. A magnesium oxide support/spacer plate was inadvertently used during the process, and was subjected to a temperature of 1830 degrees centigrade in the presence of carbon. The magnesium oxide reacted with the carbon and generated magnesium metal. When the water-based cleaning liquid was sprayed on the magnesium, hydrogen gas was generated. The hydrogen gas subsequently was ignited by either a spark or by heat from the reaction. If the magnesium oxide support/spacer plate had not been used, then the generation of magnesium metal could not have occurred.
A sample taken the following morning was analyzed a couple of days later, and the analysis showed a definite presence of magnesium. Had this fact been determined immediately after the sample was taken, this occurrence could have been prevented. In the future, the lab is going to develop, implement, and enforce interim guidance covering "Stop Work and Restart" for work which has produced a hazardous condition. The procedure will specify when appropriate personnel should be called to respond. The guidance will also contain a requirement that the results of analytical samples be reviewed before work is allowed to restart.
Implementing and enforcing the laboratory's stop work and restart policy and procedures in conjunction with peer reviews for new processes and experiments should help prevent future accidents due to a lack of recognition of potential reactions and hazards. This abnormal event points out the need to call appropriate personnel when an abnormal event occurs. Safety personnel recommended all cleaning products be treated as potentially reactive mixtures.
There is no such thing as an "always safe" cleaning solvent, including water. The reactivity and safety hazards of all materials must be considered, and only materials properly evaluated for the particular process involved must be selected.
In the future, proposed processes and experiments need to be reviewed for potential hazards. Both a chemical engineer and chemist interviewed recognized the potential reactions and hazards when carbon and magnesium oxide or carbon and aluminum oxide are heated to above 1400° C. However, other staff members did not have the same degree of understanding of the potential reactions and hazards involved. The technician was instructed to clean the interior surface of the furnace top before the results of samples taken were analyzed because it was assumed that the support/spacer plate used during the process was an aluminum oxide plate. A peer review of proposed processes and experiments would have provided a needed potential reactions and hazards review.