A deflagration explosion requires four elements:

1. Fuel
2. Oxygen
3. An Ignition Source
4. A Confined Space

Fuel can come from a bulk material that produces dust clouds, a flammable gas or a volatile chemical that creates vapors. Oxygen is readily available in most plant processes. The required source of ignition may be generated by a fire, a flame, a welding arc, spontaneous combustion, frictional sparks or electrostatic hazards. Finally, the majority of plant processes are enclosed volumes .

Once all four elements are together, the potential for an explosion exists.

How Does it Develop?

Technically speaking, an explosion is a freely propagating combustion wave, or deflagration, moving at less than the speed of sound.
Unconfined, this flame front travels initially at slow speeds, but increases velocity shortly after ignition to form a high pressure wave.
Since industrial processes usually are not designed to withstand the pressures developed in an explosion, a rupture occurs releasing a destructive pressure shock wave and flame.