Ammonium Nitrate

CAS RN: 6484-52-2


Decomposes @ 210 deg C, with evolution of nitrous oxide.
Decomposition creates toxic gases containing ammonia and nitrogen oxides. The resulting nitrogen oxides will support combustion, even in the absence of other oxygen. The resulting heat and pressure from the decomposition of ammonium nitrate may build up if the reaction takes place in a confined space and the heat and gases created are not able to dissipate. As the temperature rises, the rate of decomposition increases. In a confined space, the pressure can reach dangerous levels and cause an explosion that will include the detonation of the ammonium nitrate. When dealing with a large quantity of ammonium nitrate, localized areas of high temperature may be sufficiently confined by the mass of material to initiate an explosion. The explosion of a small quantity of ammonium nitrate in a confined space (e.g., a pipe) may act as a booster charge and initiate the explosion of larger quantities (e.g., in an associated vessel).
Decomposition of sodium hypochlorite takes place within a few seconds with the following salts: ammonium acetate, ammonium carbonate, ammonium nitrate, ammonium oxalate, and ammonium phosphate.
The decomposition of ammonium nitrate in the presence of ammonium chloride (0.1%) becomes violent around 175 deg C. The gases liberated contain chlorine.
The nitrate containing 0.1% of ammonium chloride decomposes vigorously below 175 deg. Presence of 0.1% of calcium chloride or iron(III) chloride in the nitrate lowers its initiation temperature sufficiently to give violent or explosive decomposition.
Ammonium nitrate melts at 337 deg F (170 deg C) and begins to undergo decomposition when molten. Hazardous scenarios with ammonium nitrate can involve simple thermal decomposition initiated by external fire or other heating, self-sustained decomposition also known as "cigar burning," and detonation.
Most types of ammonium nitrate do not continue to decompose once a fire has been extinguished. However, some types of ammonium nitraet fertilizers containing a small percentage of chlorides (e.g., potassium chloride) undergo a smoldering (self-sustaining) decomposition that can spread throughout the mass to produce substantial toxic fumes, even when the initial heat source is removed. These fertilizers that can self-sustain decomposition, known as "cigar burners" are normally compound fertilizers that contain between 5% to 25% nitrogen from ammonium nitrate, up to 20% phosphate (as P2O5) and chloride (which may only be present as a small percentage).
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