Ammonium Nitrate Storage

Loss prevention: Ammonium Nitrate Storage

Many hazardous chemicals are indispensable raw materials and additives necessary for the production of goods that benefit society. Their production, storage, transportation and use are unavoidable. Correctly identifying and understanding hazardous chemicals, while managing them scientifically in a targeted manner, has become the highest priority in risk management and control. Ammonium Nitrate is one such chemical, having caused dozens of severe explosions worldwide - including the recent Beirut and the Tianjin port explosions.

What is ammonium nitrate?

Ammonium nitrate is a white, crystalline solid that looks like salt. It can occur naturally but is also manufactured in large quantities by the reaction of ammonia with nitric acid. Mainly used as a fertilizer, Ammonium Nitrate is also used in pyrotechnics, herbicides, insecticides, an oxidizer for rocket propellants and explosives. There have also been instances of the materials being used as part of criminal activities.

Why does ammonium nitrate frequently cause large-scale accidents?

While in its pure form, ammonium nitrate is stable, heat and confinement or a severe shock can lead to detonation – which history has shown, can be disastrous. For example, in a fire, molten ammonium nitrate may become confined (e.g. in drains or machinery) and it could explode if it becomes contaminated. Typically, an initiating explosion is required with ammonium nitrate already sensitized by heat and/or contaminants.

Long term storage of ammonium nitrate poses a major risk due to contamination. Ammonium nitrate will react violently with various materials, particularly organics such as fuel oil. While the thermal decomposition temperature of ammonium nitrate is 200°C, the presence of contaminants can significantly reduce this.

Solid ammonium nitrate-based fertilizers can pose a similar threat. Specifically blends containing 60% or more, or 40% or more ammonium nitrate mixed with ammonium sulphate. Percentages are by weight. We recommend applying the same guidance to such fertilizers as you do to pure ammonium nitrate.

The hazards of ammonium nitrate are well known by the people that manufacture it, but less so by the multiple organizations that transport and store it around the world.

Proper Ammonia Nitrate Storage Guidance for loss prevention

The hazards of ammonium nitrate are well known by the people that manufacture it, but less so by the multiple organizations that transport and store it around the world. Because of its widespread use, it can be found in ports, warehouses and other logistical facilities in all corners of the world. A lack of knowledge and understanding of the hazards involved with storing ammonium nitrate can result in poor outcome.

We have identified the main threats for ammonium nitrate storage as contamination, confinement and construction. The following needs to be taken into consideration by any facility storing ammonium nitrate:

  • Contamination – ammonium nitrate needs to be stored away from combustible materials or any other sensitizers, which include acids, chlorides, chromates and metals; in general contamination with any substance, even litter or lube oil leaking from machinery, should be avoided. Ideally, ammonium nitrate should be stored in bags rather than bulk piles, as this poses less of a risk from contamination. It also makes the material less likely to absorb water over time. However, as seen during the explosion in Beirut, bag storage alone is not an adequate control measure.
  • Confinement – ammonium nitrate should be stored outside where possible or in a well segregated and well-ventilated structure
  • Construction – ammonium nitrate should NEVER be stored in a combustible building and ideally should be stored well away from any sources of heat, combustion or hot work (e.g. welding)
  • Ammonium nitrate should be stored well away from areas where people live and work.
  • Anyone storing ammonium nitrate should be aware of its origins. Ammonium nitrate originating in the EU and UK should be subject to a Detonation Resistance Test (DRT). A DRT confirms a sufficient degree of resistance to detonation. The Ammonium Nitrate Materials (High Nitrogen Content) Safety Regulations 2003 (developed by DEFRA) prohibit the import, manufacture, supply or storing of ammonium nitrate-based materials where the nitrogen content is greater than 28% by weight unless the material has a certificate attesting that it has passed a DRT.
  • If the material does not satisfy the quality requirements set forth by contract or regulation, it cannot be stored in any significant quantities. Typically, such material should be retained by manufacturers for re-processing.

The best risk mitigation measure is elimination, but it is recognized that ammonium nitrate is a very valuable chemical with a myriad of uses.  It is also noted that there has been no explosion involving ammonium nitrate where it has been stored without contamination, without combustible materials or in a non-combustible building. Regardless, limiting quantities and opting for bags rather than bulk are both significant mitigation strategies.