Thermobaric explosives are members of the class of highly energetic materials and the subclass of volumetric explosives, and appear to release additional combustion energy in addition to the detonation energy of conventional explosives. This combustion energy, when used in weapons and specialized demolitions, may provide energy of a different type than the detonation, and thus greater effects. The class of volumetric explosives also contain fuel-air explosives, which have both similarities to and differences from volumetrics.
In a military context, the greatest interest in thermobaric explosives is against confined spaces, such as bunkers and caves. The additional heat produced is also of potential value in destroying, rather than scattering, chemical and biological weapons.
The class is usually considered to have been introduced by Russia, although the Russian military and scientific literature often conflicts on terminology. Where the Russian military refers to thermobarics, their scientific literature speaks of low-density explosives or metallized volumetric explosives. Western terminology includes "enhanced blast" or "fuel-rich". "Fuel-rich" must not be confused with fuel-air explosives, which also draw oxidizer from the environment, but have different pressure and thermal characteristics.
Military volumetric explosives are of two types, fuel-air (FAE) and thermobaric (TBE). One might draw a rough analogy between those types, and the difference between a jet engine and a rocket motor: the FAE and the jet depend on atmospheric oxidizer, where the thermobaric and rocket are atmosphere-independent. Not all thermobaric explosives ignore oxygen in their environment; some ground-penetrating bombs with thermobaric warheads deliberately exhaust the oxygen in the target, to asphyxiate those who are not killed by blast and thermal effects.
TBE and FAE both achieve their effects through multi-step detonation processes in which an HE bursting charge disperses an oxygen-deficient energetic fuel. They have different pressure-vs-time versus high explosive and one another. Both share the property of needing a very thin walled case, so more of the weapon weight can go into explosive payload.
The fluid dynamics of these explosions was much less understood, in the early 2000s, than tjat pf FAEs. In particular, there are at least three phenomena: the initial detonation wave, a continued pressure wave, and coupling of the fireball to the target.
The implementation of thermobarics may offer the first major shift in explosives application since the introduction of the shaped charge....In a TBE detonation... an intermediate anaerobic combustion reaction lasting a few hundred microseconds precedes the aerobic combustion of the fuel. (Common powders used as the fuel for TBE include the highly energetic light metals aluminium, titanium, boron, and magnesium.) In this second step, larger fuel particles burn anaerobically and increase the duration of the initial detonation impulse. In the final process, the expanding shockwave heats and mixes the fuel-rich air, igniting the volatile atmosphere at 3000 meters per second and further extending the pressure impulse duration. The resulting 5400+° F fireball and 29-atmosphere pressure wave lasts longer than a conventional blast-fragmentation warhead, resulting in much higher temperatures and a destructive pressure wave. The primary working mechanisms of TBE weapons is to create high thermal radiation and pressure in an enclosed area followed by a deep vacuum.
One U.S. thermobaric warhead is the BLU-118, which has been mated to various guidance kits, such as the GBU-15/AGM-130 weapons with electro-optical guidance, PAVEWAY laser guidance, and Joint Direct Attack Munition.
- Board on Manufacturing and Engineering Design (2004), 3: Thermobaric Explosives, Advanced Energetic Materials, National Academy of Sciences, pp. 16-18
- "Thermobaric explosive", Globalsecurity
- Gerald Gallegos (May 2008), Weapons of Minute Destruction (WmD): Adapting Conventional & WMD Weapons for Micro Air Vehicles, Air Command and Staff College, U.S. Air Force, pp. 14-16