A detonation is a particular type of
destabilization event. In a true detonation, a
shock wave passing through a detonating
substance or
mass destabilizes the substance at the
wavefront, causing it to explosively
decompose, thus fueling the shockwave further. It should be noted that the 'wavefront' travels inside the substance, whether from the inside out or the outside in, but wherever it reaches the surface it expands outward as explosive
gases and/or
electromagnetic energy.
High explosives are those which detonate; at least, they detonate at
standard temperature and pressure. This is not to be confused with
deflagration, which while similar is not the same phenomenon.
Low explosives tend to
deflagrate rather than
detonate.
Therefore, if the reaction front arrives before or simultaneous with the shock wave from the explosion, it was a detonation rather than a deflagration. Both reactions can be exhibited in the same explosion; this can be caused either by multiple reactants and/or reactions taking place (some detonating, some deflagrating) or by a deflagration 'morphing' into a detonation via a Deflagration to Detonation Transition.