Hazards of ammonium nitrate
Stability and explosion hazards
Heat, fire and combustion hazards
Accidents
Physical properties
Chemical properties
Health effects
Stability and explosion hazards
Ammonium nitrate is stable in solid, molten or in solution. However, it can become less resistant to detonation/initiation due to the presence of contaminants or on exposure to high temperatures (e.g. fire or radiant heat).
The following can cause ammonium nitrate to become less stable and at greater risk of detonation:
- Exposure to contaminants including:
- chlorides
- metals such as chromium, copper, cobalt, and nickel
- A decrease in pH (increased acidity)
- If bubbles are permitted to form in molten ammonium nitrate or solutions of ammonium nitrate.
Once ammonium nitrate becomes molten (particularly if confined) the risk of an explosion increases and increases dramatically if pH of molten ammonium nitrate falls or if it comes into contact with oxidisable material e.g. organics eg oil, diesel, paper, rag, or straw.
Ammonium nitrate may explode due to the following factors:
- Exposure to strong shocks (e.g. from shock waves of nearby explosions.
- Exposure to high temperatures under confinement (e.g. in a closed pipe).
- A smaller detonation can trigger an explosion in larger quantities stored nearby.
Heat, fire and combustion hazards
Ammonium nitrate does not burn. However, it will support and increase the rate of combustion in the presence of flammable or combustible materials even in the absence of oxygen.
When heated it will melt, decompose and release toxic gases including nitrogen oxides (NOx) and ammonia gas (NH3). When heated excessively (e.g. as in a fire) it can cause an explosion in an enclosed space and closed containers or vessels may rupture violently.
Accidents
Ammonium nitrate explosion in Toulouse - France
On 21 September 2001 an explosion occurred at the AZF Fertiliser factory in Toulouse, France where approximately 200-300 tonnes of ammonium nitrate exploded.
The explosion was caused by unknown causes related to handling practices. Twenty workers were killed at the site. The blast caused damage 3 km away, causing disruption of telephone lines up to 100 km away. Over 500 homes were left uninhabitable and 85 schools were damaged.
A secondary explosion was also triggered in a neighbouring munitions factory.
Physical properties
- Melting point: 170 °C
- Decomposition temperature: < 210 °C.
Chemical properties
- Strong oxidizer that can react violently with other incompatible materials.
- Acidic: pH of 5.4.
Health effects
- Harmful if swallowed.
- Irritating to eyes, skin and respiratory tract.
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