Explosions & Deflagrations

Watching Mythbusters today they claimed that the first explosive was... gunpowder.I have to break it to them but it doesn't explode. It burns really quickly sure... but it's not classified as an explosion.It goes through a process called deflagration -- which is a sub-sonic combustion. This is opposed to what happens in a explosion which is a supersonic, and quite violent, oxidation of the substance.I've already shown a while back it that it burns quite slow (at least in ordinary atmospheric pressures) It takes more than a pressure wave to get gunpowder going... it takes pressure and heat.If all it took was pressure or a shock wave... you'd be in some trouble since your magazine, just a tiny bit below the action (quite literally), would go off easily. It doesn't. It's quite safe, relatively speaking.