TABLE OF CONTENTS Detonations and deflagrations are forms of explosions. An explosion can be defined in very simple terms as a very rapid combustion reaction resulting in a very high overpressure. To have such a rapid combustion reaction, a mixture of flammable gas/vapor or combustible dust and air must be ignited. The ignition precipitates a flame front and a pressure front. The pressure front moves through the unburned fuel/air medium at the velocity of sound through that medium. The velocity at which the flame front travels through the unburned medium varies considerably depending on the fuel involved. In a detonation the flame front moves through the medium at a velocity greater than the speed of sound in that medium. In a deflagration the flame front moves through the medium at a velocity less than the speed of sound in that medium.
The rapid combustion reaction in a detonation or deflagration results in heating, expansion and overpressure.
In a deflagration the pressure front is moving through the unburned medium faster than the flame front so that it can push off the exterior wall panels used to vent the explosion. This considerably reduces the overpressure that would have developed in an unvented enclosure since it allows some of the unburned fuel/air mixture to burn outside the enclosure and allows a path for the expanded products of combustion.
In a detonation the pressure front does not arrive at the wall panels before the flame front. All...
