Ammonium Nitrate Disasters

  Most chemical reactions involve the transfer of electrons from one element or compound to another. In most of these reactions (combustion for example) we can ignore the transfer of electrons as a primary cause and still understand what happened.

However, there are some reactions that can ONLY be understood in terms of electron transfer, and one of these in particular has made headlines a disturbing number of times.

Let’s take a look at the compound ammonium nitrate (\(NH_4NO_3\)). If we carelessly assign oxidation numbers to this compound, we might do the following:

H = +1 (Rule 3), and O = -2 (Rule 4), N = x

\(0 = 4(1) + 2(x) + 3(-2)\), which when rearranged would give \(N=+1\). However, that is really WRONG.

The reason it is wrong is that this compound is ionic and each ion has a separate “identity”. If we re-assign oxidation numbers to the two separate ions, we get something very different.

\(NH_4^{+1}\) : H = +1, N = x

\(N = -3\)

\(NO_3^{-1}\): O = -2, N = x

\(N=+5\)

That means that in this compound, there are some nitrogen ions that have 3 extra electrons and some which are missing 5 electrons. To appreciate this, imagine two toddlers. You take 5 toys away from the first and give three extra toys to the other. Then lock the toddlers in a room together. It is, as you can imagine, a recipe for disaster.

With a little kick of activation energy, the nitrogen atoms will exchange electrons with a HUGE release of energy.

Why is this (dangerous) compound around?

Nitrogen is a key element in plant growth (in both the +5 and -3 forms), however nitrogen in the atmosphere is “locked” up as \(N_2\). This molecule is held together by a triple bond which most plants cannot break. As a result, most plants cannot get the nitrogen they need from the atmosphere. Thus, there is a problem that farmers need to solve.

A few plants can obtain the nitrogen they need from the atmosphere - a process called “fixing” nitrogen. Beans, and other legumes, can do this, as can some soil fungi. As a result, one solution is to mix crops (say beans and corn). These can be mixed in the same field or mixed over time (beans one year and corn the next). However, beans are not nearly as lucrative as corn and other “cash” crops, so farmers, who make barely enough money as it is to survive cannot afford to give fields over to beans on a regular basis. Planting beans in among another crop makes harvesting difficult and expensive.

The other choice is to fertilize fields with nitrogen compounds in the forms that the plants need. The simplest (and therefore least expensive) way to add both forms of nitrogen to a field is the compound ammonium nitrate. As a result, ammonium nitrate is produced, stored, transported and applied in vast quantities.

Disasters involving ammonium nitrate

Texas City Disaster (Wikipedia link)

Galveston County Daily News

On April 16, 1947, a fire started on a ship filled with about 2300 tons of ammonium nitrate in Galveston Harbor. The resulting explosion started a chain reaction of other fires and explosions including oil storage facilities and another ammonium nitrate-containing ship.

The explosion leveled nearly 1,000 buildings on land, blew two small planes out of the sky and shattered windows in Galveston, nearly 16 miles away.

The disaster killed 567 people and is considered the worst industrial accident in US history.

Oklahoma City Bombing - Murrah Federal Office Building (Wikipedia link)

ABC News

On the morning of April 19, 1995, Timothy McVeigh parked a Ryder Rental Truck filled with ammonium nitrate and other explosives in front of the Murrah Federal Office building in Oklahoma City. The bomb was detonated shortly after 9 in the morning, destroying more than a third of the building and killing 168 people and injuring 680 others.

McVeigh and his partner Terry Nichols were anti-government extremists, and chose the date to coincide with the anniversary of the fire that ended the federal siege of the Branch Davidian Complex in Waco. Texas, an event that many in their movement considered the ultimate example of the danger posed by the federal government.

West Fertilizer Company Explosion (Wikipedia link)

NBC News

On April 17, 2013, a fire at the West Fertilizer Company Factory led to an explosion that left a 93 foot wide crater where the factory had been. The explosion destroyed or damaged 150 buildings including a 50 unit apartment building and a nearby nursing home. 15 people were killed and more than 160 were injured. 

Beirut, Lebanon (Wikipedia link)

CNN

On August 4, 2020, a warehouse in the harbor of Beirut, where more than 2750 metric tons was stored without proper safety measures exploded. The United States Geological Survey measured the blast as a 3.3 on the Richter scale while the Jordan Seismological Survey measured it at 4.5. The explosion was heard more than 150 miles away.

The explosion killed at least 207 people, injured more than 7500 and did at least $15 billion in property damage.

The blast left a crater 407 feet wide and 141 feet deep. Homes, as far as 6 miles away, were destroyed or made uninhabitable and an estimated 300,000 people were left homeless. More than half of Beirut city was damaged by the explosion and the city’s largest medical center (Saint George Hospital) was so damaged that the injured had to be treated outside.