Today's graphic outlines the biggest ammonium nitrate explosions over the last 20 years.

Before getting into the details, first thing's first—what is ammonium nitrate?

Ammonium nitrate is formed when ammonia gas is combined with liquid nitric acid. The chemical compound is widely used in agriculture as a fertilizer, but it's also used in mining explosives. It's highly combustible when combined with oils and other fuels, but not flammable on its own unless exposed to extremely high temperatures.

It's actually relatively tough for a fire to cause an ammonium nitrate explosion—but that hasn't stopped it from happening numerous times in the last few decades.

The Death Toll

Some explosions involving ammonium nitrate have been deadlier than others. Here's a breakdown of the death toll from each blast: