Description of Incident
A teaching assistant was preparing a 30L solution 0.04 M KMnO4 in 0.5 M H2SO4 for use in chemistry instructional laboratories. She was working by herself. This is a laboratory where all solutions for use in the general chemistry laboratories are prepared. Her supervisor was working in his office, which is adjacent to the preparation lab and connected by a doorway. A chemistry class was underway in a lab across the hallway. This teaching assistant had a BS and MS in chemistry and working at the university for two years. Her responsibilities included preparing solutions for the chemistry program since the start of her employment.
She indicated she was following a procedure she has followed without incident in previous semesters (estimated 10-12 previous preparations). She indicated the procedure was contained in a notebook containing standard procedures for preparing all of the reagents used in the two classes. On the day of solution preparation, was not referring directly to the written procedure since she had used it sufficiently in the past that she did not need to refer to it. The quantity prepared is typically 10-20 liters ; this was the first instance she could recall in which 30L was to be prepared.
Probable Cause of the Incident
Several pertinent references in the literature regarding the mixtures of potassium permanganate and sulfuric acid indicate caution. Bretherick's Handbook of Reactive Chemical Hazards states:
"Addition of concentrated sulfuric acid to the slightly damp permanganate caused an explosion. This was attributed to formation of permanganic acid, dehydration to dimanganese heptoxide and explosion of the latter, caused by heat liberated from interaction of sulfuric acid and moisture. A similar incident was reported previously, when a solution of potassium permanganate in sulfuric acid, prepared as a cleaning agent, exploded violently.
Manganese heptoxide is formed as a dense green-brown oil by reaction between potassium permanganate and concentrated sulfuric acid. Kleinberg, Argersinger and Griswold, Inorganic Chemistry, p. 534 states that the reaction between potassium permanganate and sulfuric acid is:
2 KMnO4 + H2SO4 = Mn2O7 + K2SO4 + H2O
