This pamphlet describes how to safely store and transport ammonium nitrate.
Pure solid ammonium nitrate (AN) is very safe when stored and transported correctly.
Solid AN is a stable chemical and not liable to explode. It is not shock sensitive and requires a very strong initiating event for it to detonate. It does not burn, but when involved in a fire, it will release oxygen and intensify the fire. Because of this, AN is classified as a Division 5.1 oxidising substance. AN is also a precursor for manufacturing explosives and, hence, is a security sensitive ammonium nitrate (SSAN).
AN has a low melting point (169oC) and a low decomposition point (270oC), which is even lower with fuel contaminants. When molten, it becomes shock sensitive and can easily explode with a relatively small stimulus.