The RCMP allege the bomb plot suspects ordered and received three tonnes of ammonium nitrate. RCMP officers intercepted the group's order for the powdered fertilizer and, according to the Toronto Star, switched it with a harmless powder before making the delivery by truck.

The compound is used in fertilizers because of its high nitrogen content. On its own, ammonium nitrate is benign, but when mixed with certain hydrocarbons, such as fuel oil, it can become a powerful explosive. Such a mixture of ammonium nitrate and fuel oil is commonly called ANFO.

RCMP Assistant Commissioner Mike McDonell noted that the amount of ammonium nitrate seized in the series of June raids could have caused significant damage. It was three times as much as the amount used in the bombing of a U.S. government building in Oklahoma City, which killed 168 people on April 19, 1995.

ANFO has been widely used for blasting in quarries and mines since the 1930s as a safer alternative to dynamite. As a commercial explosive it is usually a mixture of ammonium nitrate and diesel oil in a 94:6 ratio by weight and is usually coloured with red dye.

ANFO can also be made using ammonium nitrate fertilizer and some other fuel oil, such as kerosene or, as was the case in Oklahoma City, nitromethane, a fuel used in drag racing. ANFO has been used in attacks by such extremists as the Provisional IRA in Ireland and the revolutionary group known as FARC in Colombia.

There have been several other major incidents involving ammonium nitrate. Among them, an accidental explosion at a warehouse in the French city of Toulouse in 2001 killed 31 people and injured 2,400. It also left a crater 10 metres deep. In 2004, a freight train loaded with ammonium nitrate exploded in North Korea. The blast destroyed a small town, killed 161 people and injured more than 3,000.

In 1947, a fire broke out in the hold of a cargo ship in Texas City, Texas. The ship was carrying 2,600 tonnes of ammonium nitrate. An hour later, the ship exploded, killing several hundred people. The blast started a fire in another ship 250 metres away. It was carrying sulfur and ammonium nitrate. The next day it, too, exploded.

Agricultural grade ammonium nitrate is no longer produced in this country, although some is still imported for use in eastern Canada. It is not currently a controlled substance, although federal limitations under the Explosives Act are being considered. It has also been used as an oxidizer in some solid fuel rockets and to help deploy airbags in cars. Other uses include as a heat absorber in instant cold packs. Ammonium nitrate, mixed with zinc and ammonium chloride, can be found in survival kits because it will ignite on contact with water.