Deflagration
Definition
A subsonic combustion front propagating through an explosive by thermal conduction. Characteristic of low explosives such as black powder and smokeless powder; produces a pressure pulse but not the supersonic shock wave of detonation.
- Reaction speed
- Subsonic propagation, typically millimeters to a few meters per second
- Driving mechanism
- Thermal conduction of heat from the reaction front
- Pressure effects
- Produces a pressure pulse without a supersonic shock wave
- Common examples
- Black powder and smokeless propellants in firearms
Common questions
How is deflagration different from detonation?+
Deflagration is a subsonic combustion process where the flame front travels at subsonic speeds (mm/s to a few m/s), without producing a shock wave. Detonation is supersonic and generates a powerful shock wave. This distinction matters in ballistics: smokeless powder deflagrates to push a bullet, while high explosives detonate with far greater destructive force.
What actually happens during deflagration?+
During deflagration, a combustion reaction front spreads through an explosive or propellant by thermal conduction. Heat from the reaction conducts forward through the material, igniting the next layer, producing rapid gas evolution and pressure. The pressure rises and falls over tens of milliseconds, but without the violent shock wave of detonation.
Which explosives deflagrate versus detonate?+
Low explosives like black powder and smokeless propellants deflagrate. High explosives detonate. This is why smokeless powder works safely inside a firearm (controlled deflagration), while TNT or dynamite would detonate explosively if confined the same way.
Related terms
- Detonation
- A supersonic shock wave coupled to a chemical reaction front, propagating through a high explosive at velocities between approximately 4,500 and 9,100...
- Brisance
- The shattering power of a detonating explosive, distinct from heave (bulk displacement). Measured by the Trauzl lead block test. High-brisance explosives (RDX,...
- Oxygen Balance
- A percentage expressing the surplus or deficit of oxygen in an explosive molecule relative to stoichiometric complete oxidation of carbon to CO2...
- Primary Explosive
- A high explosive sensitive enough to detonate from friction, spark, percussion, or flame without confinement or a separate booster. Examples: mercury fulminate,...
- Secondary Explosive
- A high explosive insensitive to normal friction, spark, and percussion; requires a primary explosive shock or blasting cap to initiate detonation. Examples:...
- ANFO
- Ammonium nitrate fuel oil: 94% ammonium nitrate prills + 6% diesel fuel oil. Detonation velocity approximately 4,500-4,800 m/s. The most widely used...
- API 579
- The American Petroleum Institute's Fitness-For-Service standard, which provides assessment methods for determining whether a damaged or corroded pressure vessel or piping component...
- Backdraft
- A deflagration event triggered when air is suddenly admitted to a compartment where a fire has been oxygen-depleted but has continued to...
- Ballistic Coefficient (BC)
- The ratio of a projectile's sectional density to its drag relative to a reference standard (G1 or G7). Higher BC means less...
- BLEVE
- Boiling liquid expanding vapour explosion. Catastrophic failure of a vessel containing a superheated liquid, producing an expanding pressure wave and, if the...
- Chapman-Jouguet Velocity
- The minimum stable detonation velocity for a given explosive at a specific density, a thermodynamic property of the explosive composition. Used to...
- Corrosion Under Insulation (CUI)
- External corrosion of a pipe or vessel surface that occurs beneath thermal insulation, hidden from visual inspection, driven by moisture infiltrating the...
Explained in these topics
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- Explosives Classification: Low vs High, Primary vs SecondarySubsonic propagation of a combustion reaction front through an explosive by thermal conduction, producing rapid gas evolution without a shock wave. Characteris...
- Explosives Classification: Low, High, Primary, Secondary, TertiaryA subsonic combustion front propagating through an explosive by thermal conduction. Characteristic of low explosives such as black powder and smokeless powder;...
- Explosives: Definition, Types and ClassificationSubsonic burning of a propellant or low explosive driven by heat conduction. Reaction front travels at mm/s to a few m/s. Black powder and smokeless powder def...
- Fire Dynamics: Flashover, Backdraft and Ventilation-Controlled BurningSubsonic combustion in which the flame front propagates through the flammable mixture at less than the speed of sound. Distinguished from detonation (supersoni...
- Internal, External and Terminal Ballistics: BasicsSubsonic combustion wave that propagates through a propellant by thermal conduction. Smokeless powder deflagrates; high explosives detonate.