Ammonium nitrate
The status of the current official investigation is unknown. However, this kind of incident is a well-known hazard with some types of NPK fertilizers, and is responsible for the loss of several cargo ships and chemical plants, (see examples in Ammonium nitrate disasters). Large stockpiles of the material can be a major fire risk due to their supporting oxidation, it may also detonate. Ammonium nitrate (AN), a common element in inorganic fertilizers like NPKs, exothermically decomposes into gases when heated to temperatures above 210 °C. The reaction can become self-sustaining (known as self-sustaining decomposition, or SSD), which is a thermal runaway (i.e. a fire event with a chemistry not based on oxygen consumption).