Ammonium nitrate is not flammable under normal applications and is not considered a fire risk, but will support combustion in an existing fire by liberating oxygen – even if smothered.
It is for this reason that fires involving ammonium nitrate cannot be extinguished by the prevention or air ingress (for example,
smoldering with steam) because of the in situ provision of oxygen from the ammonium nitrate itself.
Thermal decomposition may result in toxic gases, such as oxides of nitrogen and ammonia, being produced.
After combustion ammonium nitrate can be severely dangerous because of the white, orange, or brown fumes of toxic oxides of nitrogen.
A fire anywhere is a cause of concern, but a fire at a fertilizer plant is a potential catastrophe. Ammonium nitrate is a highly explosive compound, as shown by the massive fireball at a fertilizer plant in the town of West, Texas (April 17).
Nitrogen, phosphorous, and potassium are essential plant nutrients, and fertilizers are graded by the amounts of these elements fertilizers contain.
Ammonium nitrate, or NH4-NO3, is frequently added to improve a fertilizer’s nitrogen content. It’s relatively stable under most condition and is inexpensive to manufacture making it a popular alternative to other, more expensive, nitrogen sources.
The lethal downside of ammonium nitrate is if it comes in contact with an open flame or other ignition source, which causes a violent explosion. The explosive force occurs when solid ammonium nitrate decomposes very rapidly into two gases, nitrous oxide and water vapor.
The deadliest industrial accident in U.S. history occurred in the port of Texas City, Texas, in 1947. A carelessly tossed cigarette started a fire aboard a ship carrying about 2,300 tons (2,086,000 kilograms) of ammonium nitrate packed in paper sacks.
When the chemical exploded, it caused a blast powerful enough to knock people to the ground in Galveston, Texas, 10 miles (16 kilometres) away.