Science, Tech, Math › Science The Difference Between Deflagration and Detonation Share Flipboard Email Print Ken Hermann/Getty Images Science Chemistry Physical Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated December 08, 2019 Combustion (burning) is a process by which energy is released. Deflagration and detonation are two ways energy may be released. If the combustion process propagates outward at subsonic speeds (slower than the speed of sound), it's a deflagration. If the explosion moves outward at supersonic speeds (faster than the speed of sound), it's a detonation. While the action of deflagration is to push the air in front it, objects do not explode because the rate of combustion is relatively slow. Because the action of detonation is so rapid, however, detonations result in shattering or pulverizing objects in their path. Deflagration The definition of deflagration, according to the "Collins English Dictionary" is "a fire in which a flame travels rapidly, but at subsonic speed, through a gas. Deflagration is an explosion in which the speed of burning is lower than the speed of sound in the surroundings." Everyday fire and most controlled explosions are examples of deflagration. The flame propagation velocity is less than 100 meters per second (usually much lower), and the overpressure is less than 0.5 bar. Because it is controllable, deflagration can be harnessed to do work. Examples of deflagrations include: internal combustion engine (used in any vehicle that uses fossil fuels such as gasoline, oil, or diesel fuel)gas stove (fueled with natural gas)fireworks and other pyrotechnicsgunpowder in a firearm Deflagration burns outward radially and requires fuel to spread. Thus, for example, a wildfire starts with a single spark and then expands in a circular pattern if there is fuel available. If there is no fuel, the fire simply burns out. The speed at which deflagration moves depends upon the quality of the available fuel. Detonation The word "detonation" means "to thunder down," or explode. When a decomposition reaction or combination reaction releases a lot of energy in a very short span of time, an explosion may occur. A detonation is a dramatic, often destructive, form of an explosion. It is characterized by a supersonic exothermic front (in excess of 100 m/s up to 2000 m/s) and significant overpressure (up to 20 bars). The front drives a shockwave ahead of it. Although technically a form of oxidation reaction, a detonation doesn't require combination with oxygen. Unstable molecules release considerable energy when they split and recombine into new forms. Examples of chemicals that produce detonations include any high explosives, such as: TNT (trinitrotoluene)nitroglycerinedynamitepicric acidC4 Detonations, of course, can be used in explosive weapons such as nuclear bombs. They are also (in a much more controlled manner) used in mining, road construction, and the destruction of buildings or structures. Deflagration to Detonation Transition In some situations, a subsonic flame may accelerate into a supersonic flame. This deflagration to detonation is difficult to predict but occurs most often when eddy currents or other turbulence are present in the flames. This can happen if the fire is partially confined or obstructed. Such events have occurred in industrial sites where extremely combustible gasses have escaped, and when ordinary deflagration fires encounter explosive materials.