Eight nearby workers were exposed to a chemical gas plume, and their health is being monitored. So far, DOE investigators believe the explosion was caused by a diluted solution of nitric acid and hydroxylamine nitrate sitting in the tank for four years. From 1993 to late 1996, the water in that solution evaporated through a vent, causing it to shrink from 180 gallons to 36 gallons. Recent tests show evaporation would have increased the concentrations of the two chemicals, taking them from safe concentrations to volatile levels to cause the explosion, said Ron Gerton, head of DOE's investigation. Also, the investigation shows the stainless steel of Tank 109 could have acted as a catalyst for the chemical reaction leading to the explosion, Gerton said.
Stainless steel contains iron, nickel and chromium.
And diluted nitric acid would dissolve those substances. The resulting chemical reaction likely increased the tank's temperature, helping trigger the explosion, Gerton said. The investigation shows past paperwork at PFP warned about the possibility of a explosion with these two chemicals, but the plant's current paperwork does not, Gerton said. A check of other DOE sites showed two documented chemical explosions at the Savannah River site in the 1980s, with one explosion closely resembling May's accident, Gerton said. After those explosions, the Savannah River site installed stricter chemical disposal procedures, including getting rid of waste chemicals within five days.