An investigation conducted by the United States Environmental Protection Agency (EPA) concluded in 1996 that the explosion was initiated by an accelerated thermal decomposition reaction as "a direct result of unsafe operating procedures and conditions" at the plant. The investigation team concluded that the explosion resulted from a lack of written, safe operation procedures at the Terra Port Neal ammonium nitrate plant. The lack of safe operating procedures resulted in conditions in the plant that were necessary for the explosion to occur. The significant conditions that caused the explosion were:
