Page 12 - CCPS Golden Rules - Ammonium Nitrate

Golden Rules for Ammonium Nitrate (AN)

Golden Rule #4: NEVER store ammonium nitrate for extended periods

❖ Why:

1) Similar to other reactive chemicals (for example, peroxides), excessive storage periods of AN can permit
slowly developing decomposition reactions to proceed. These reactions can generate toxic gases and
other reactive byproducts which can accelerate decomposition and initiate an explosion if permitted to
accumulate. The material involved in the Beirut event in 2020 discussed below had been stored there
for more than 6 years. All types of facilities handling or storing AN need to define the maximum time
for AN storage in their facility. For extended plant outages, all AN-containing materials remaining in
the vessels should be removed to prevent inadvertent decomposition. Excessive storage time is
particularly an issue in customs warehouses, where shipments may be detained or seized for a variety
of reasons. Storage periods of more than 1 year should be avoided. [8]
2) “Sugaring” of AN is a good example of the issues that can occur with extended, unmanaged storage.
Sugaring is a solid-solid phase transition that occurs at temperatures of 30-33 C (86-92 F), temperatures
that can routinely occur in warehouses. The density of material changes as the product transitions back
and forth between the two solid states, resulting in particles breaking at the grain boundaries. Over
time, AN prills disintegrate into a granular product. Depending upon other components or
contaminants present, this size degradation may result in inadvertently creating a low-grade explosive.

3) Liquid AN products should never be stored in a concentrated form. AN solutions often must be heated
to be stored to prevent solids precipitation. Long periods of heating may cause the solution to become
acidic, resulting in catalyzing AN decomposition. Operations must continually monitor the solution pH
and keep it basic. Diluting the AN tp 60% (wt) with water would allow the material to be safely stored
indefinitely at room temperature.

Incident History – Beirut, Lebanon (2020)

On August 4, 2020, a major fire broke out in a Port of Beirut warehouse and spread to 2,750 tons of
ammonium nitrate which had been impounded and stored for six years after it was seized from an
abandoned ship in 2014 [11]. The resulting explosion caused immense damage throughout the entire
city. The shock wave was reportedly so intense it was felt in Cyprus, 250 km (150 miles) from Lebanon.
A giant orange cloud was seen following the detonation. There were at least 6,500 confirmed injuries
and over 200 confirmed fatalities. According to Beirut's city governor, up to 300,000 people lost their
homes. The yield of the explosion in terms of TNT equivalent mass was estimated to be 0.5 kilotons as
a "best estimate" and 1.12 kilotons as a "reasonable upper bound estimate.” [11] These figures point
out the fact that some AN incidents are equivalent to the effects associated with the use of AN as a
weapon.

Key Incident Learnings
a. The port management at Beirut had no plan for managing AN in storage, which most likely
allowed for decomposition, greatly increasing the hazard. Additionally, combustible materials as
well as several other incompatible materials, including fireworks, were stored in the same area
as bulk AN.
b. There was no management plan to dispose of AN after a certain time period, allowing the seized
AN to remain in the warehouse for over 6 years.

Issued April 2025 Page 9 of 20