An explosion at a fertilizer manufacturing plant in the Western part of Texas that occurred in early 2013 killed 15 people and injured 180 more. The explosion leveled buildings within a five block radius and the instruments at the Geological Survey of the United States recorded a 2.1 magnitude earthquake. The explosion was caused by the reagents used as raw materials for fertilizer manufacturing. Inorganic fertilizer is manufactured from chemical substances such as ammonium nitrate and anhydrous ammonia, which had been stocked at the West plant during the explosion. This paper explores the cause of the explosion, the chemical reactions involved, and how the resulting fire would have been stopped.
On the other hand, ammonium nitrate is very explosive, especially when mixed with a fuel. In fact, ammonium nitrate has been used in the past to make improvised explosive devices. For example, in 1995, two criminals, Terry Nichols and Timothy McVeigh, purchased a bunch of 40 50-pound packs of ammonium nitrate fertilizer to make a bomb. The bombing killed 168 people, and destroyed 324 buildings in Boston city. The damages caused by the bomb were estimated to be in the range of $652 million (Scharr, 2013).
Combustion is a chemical reaction which involves four components, otherwise referred to as a fire tetrahedron. The tetrahedron includes the fuel, heat, oxidizing agent, and a chemical reaction chain. Ammonium nitrate (NH4NO3) though combustible, cannot explode by itself and requires an ignition by an external agent. The fertilizer must be ignited and acted on by a fuel, such as gasoline. When the fuel warms up the ammonium nitrate, the fertilizer breaks down, releasing large amounts of oxygen and other gases such as ammonium and nitrogen. Therefore, ammonium nitrate is the oxidizing agent in this situation as the oxygen it released drives the combustion process (Loyd & Richardson, 2014).
The mixture of a fuel and oxygen accelerates the combustion to explosive levels. The heat from the combustion decays even more ammonium nitrate thereby setting up a chemical reaction chain. To break the chain chemical reaction and contain the fire, the extinguisher should eliminate one of the components in the fire tetrahedron. In this case, the most suitable option was cool down the ammonium nitrate using a cooling agent. Cooling the fertilizer would prevent its decomposition and hence no surplus oxygen would be available for combustion and the fire would eventually go out (Loyd & Richardson, 2014).
Such a fire is speculated to be what happened at the West fertilizer plant. The fire was classified as a class B type of fire. Class B fires are caused by flammable gases, liquids, gasoline, oil, tars, lacquers and other synthetic products. Also, this class of fires spread rapidly and the flames can re-flash even after the flames have been doused. Dry Chemical extinguishers are used to put out class B fires (Loyd & Richardson, 2014).
Ammonium nitrate is a form of inorganic fertilizer that replenishes nutrients in the soil. Also, the fertilizer is rich in oxygen, which is essential for combustion. The fire tetrahedron defines all the necessary components required for combustion, which include heat, fuel, an oxidizing agent, and a chemical reaction. Ammonium nitrate was the oxidizing agent in the West fertilizer plant in Texas. When ammonium nitrate is acted upon by heat, it decomposes thereby releasing oxygen, nitrogen, and ammonium gas. The resulting high concentration of oxygen encourages rapid combustion and sometimes causes explosions. To break the chain reaction in an ammonium nitrate driven fire, one of the components of the tetrahedron must be removed. Cooling the fertilizer stops the decomposition of ammonium nitrate and hence the fire goes out.
References
Loyd, J.B. & Richardson, J.D. (2014). Fundamentals of fire and emergency services (2nd ed.) Upper Saddle River, NJ: Pearson.
Scharr, J. (2013). Why Was the Texas Fertilizer Plant Explosion So Deadly? Scientific America. Retrieved from http://www.scientificamerican.com/article/why-texas-fertilizer-plant- explosion-deadly/
