Over the years ammonium nitrate fertilizers have been involved in several accidents that have influenced the legislation of transport, storage and handling. Decompositions during transport and in storage have caused release of toxic gases and hazardous situations.
United Nation has issued the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). The GHS is harmonized with the UN Recommendation on the Transport of Dangerous Goods – Model Regulation, regarding test methods and identifying hazards.
The international UN ‘Recommendations on the Transport of Dangerous Goods’ (www.unece.org/trans/danger/danger.html) is adopted in international fertilizer transport legislation by IMO (shipping). National and local regulations apply for storage of fertilizers.
To ensure correct information about a product or raw materials used in the production or processing of fertilizers, the best thing to do is to request the new updated version of the safety data sheets (SDS) compiled according to legislations for the country where the products are used. A correct safety data sheet will have information about possible hazards and recommendation regarding handling and storage, unwanted situations and disposal. A correct safety data sheet will also contain transport classification information.
AN 33.5 is classified as an oxidizer (Class 5.1) by UN due to its high ammonium nitrate content. Special regulation for storage is given by national authorities. Yara ammonium nitrate based fertilizers pass the resistance to detonation test, and have very high resistance to detonation. When bagged fertilizers are involved in a fire, the bags may melt and break, but they will have insignificant effect on the fire.
Spillage from conveyor belts or from bags should be collected quickly, handled and sold as normal product if free from contamination and meeting the requirement of the fertilizer regulations.
If not, the material shall be dissolved or be made inert. If seriously contaminated, product should be treated as a waste material, and hazardous material should be handled according to local legislation.
Ammonium nitrate in NPK fertilizers can decompose at high temperatures. Exothermic reactions cause evolution of heat and gases from the fertilizer after an initial period with decreasing pH. The rate of decomposition accelerates in the presence of chloride, organic substances and some metal ions – particularly copper (Cu2+). The decomposition is retarded in the presence of phosphate, carbonaceous material and high pH.
Some ammonium nitrate-based NPK fertilizers exhibit characteristics of self-sustaining decomposition (SSD). SSD can be initiated by accidental heating (> 120°C) over time for some fertilizers. Such decomposition will continue after the heat source has been eliminated, and can be very difficult to extinguish. The decomposition is normally not dangerous in itself, but the released gas contains toxic components (e.g. Cl2, HCl, NO
CN fertilizer contains approximately 15 % crystal water that minimizes the oxidizing properties of the material. fertilizers based on nitric acid ammonium calcium are classified in GHS/CLP as “Acute Tox, 4 H302., Eye Damage/Irritation, H318”. The product bags are labeled according to the appropriate chemical regulations. No severe accident has ever occurred with CN fertilizer.
Urea products are not classified as hazardous material according to the UN transport regulations, but are potentially dangerous because they can release ammonia if exposed to strong heat. Urea should not be mixed with other chemicals, mixing with Nitric acid may be particularly hazardous.