I’m still confused about rapid oxidation in a non-confined space being capable of this magnitude explosion?
Ammonium nitrate has a formula of NH4NO3, i.e. containing hydrogens and oxygens, as well as nitrogen. When the material explodes, the hydrogens and oxygens get together, making water (H2O), which is where the energy comes from, and there is nitrogen and oxygen left over. Some of those combine under the heat of the explosion to make nitrogen dioxide, in addition to nitrous oxide, nitrogen, and oxygen. When sufficient fuel oil is added, the extra oxygen is used up to make carbon dioxide and more water, from the C’s and H’s in the oil, and little to no nitrogen oxides or free oxygen is produced. But without it, there is oxygen remaining, because each molecule of AN has 4 H’s, which requires 2 O’s to turn to water - but a molecule of AN has 3 atoms, not 2, of oxygen. So there’s one atom of oxygen extra - and this for every single molecule of AN.