Three hundred tons of ammonium nitrates were stored (the maximum capacity was 2,000 tons) in the hangar #221. The whole factory was destroyed making a crater of depth 20 to 30 m (65 to 100 ft), with a diameter of 200 m (650 ft); steel girders were found 3 km away from the explosion. The explosion was heard 80 km away (50 miles). Due to the acoustics of the hills and the large sound, the explosion was reported as occurring in multiple places. Police at first believed that at least five bombs had simultaneously gone off. There is still controversy over the exact number of explosions.
The factory was close to the city: one of the most inhabited areas, Le Mirail, is just one kilometer away (0.6 miles). Several schools, one university campus, one hospital and a psychiatric hospital had to be evacuated.
40,000 people — 10 % of the population — were made homeless for a few days.
Specifically it is believed by mandated official experts that "a mislabeled 500kg bin of sodium dichloroisocyanate mistakenly thought to be ammonium nitrate was dumped in the off spec ammonium nitrate warehouse. Here under sufficiently hot and humid conditions it could have reacted with the ammonium nitrate to form nitrogen trichloride which is an exceedingly unstable compound. The decomposition of the nitrogen trichloride could have provided the heat and pressure required to detonate the ammonium nitrate which when used as an industrial explosive typically requires detonators."
On October 4 2001, France's then Environment Minister Yves Cochet announced that the explosion "may have been a terrorist attack" and identified Hassan Jandoubi, a plant sub-contractor killed in the blast, as a person under investigation. French anti terrorist authorities were prohibited by the Toulouse prosecutor from searching Jandoubi's house for five days after the incident. Police declared that Jandoubi had "possible Islamic fundamentalist sympathies", yet by the time the search was finally conducted, Jandoubi's girlfriend had disposed of all traces of his clothes or photos. French authorities described the delay as damaging to the investigation.