Thermobaric weapon


A thermobaric weapon, also called an aerosol bomb, or erroneously a vacuum bomb, is a type of explosive munition that works by dispersing an aerosol cloud of gas, liquid or powdered explosive. This allows the chemical combustion to proceed using atmospheric oxygen, so that the weapon does not need to include an oxidizer.
The fuel is usually a single compound, rather than a mixture of multiple substances. Many types of thermobaric weapons can be fitted to hand-held launchers, and can also be launched from airplanes.

Terminology

The term thermobaric is derived from the Greek words for 'heat' and 'pressure': thermobarikos, from thermos 'hot' + baros 'weight, pressure' + suffix -ikos '-ic'.
Other terms used for the family of weapons are high-impulse thermobaric weapons, heat and pressure weapons, vacuum bombs, and fuel-air explosives.

Mechanism

Most conventional explosives consist of a fuel–oxidiser premix, but thermobaric weapons consist only of fuel and as a result are significantly more energetic than conventional explosives of equal weight. Their reliance on atmospheric oxygen makes them unsuitable for use under water, at high altitude, and in adverse weather. They are, however, considerably more effective when used in enclosed spaces such as tunnels, buildings, and non-hermetically sealed field fortifications.
The initial explosive charge detonates as it hits its target, opening the container and dispersing the fuel mixture as a cloud. The typical blast wave of a thermobaric weapon lasts significantly longer than that of a conventional explosive.
In contrast to an explosive that uses oxidation in a confined region to produce a blast front emanating from a single source, a thermobaric flame front accelerates to a large volume, which produces pressure fronts within the mixture of fuel and oxidant and then also in the surrounding air.
Thermobaric explosives apply the principles underlying accidental unconfined vapor cloud explosions, which include those from dispersions of flammable dusts and droplets. Such dust explosions happened most often in flour mills and their storage containers, grain bins, and earlier in coal mines, prior to the 20th century. Accidental unconfined vapor cloud explosions now happen most often in partially or completely empty oil tankers, refinery tanks, and vessels, such as the Buncefield fire in the United Kingdom in 2005, where the blast wave woke people from its centre.
A typical weapon consists of a container packed with a fuel substance, the centre of which has a small conventional-explosive "scatter charge". Fuels are chosen on the basis of the exothermicity of their oxidation, ranging from powdered metals, such as aluminium or magnesium, to organic materials, possibly with a self-contained partial oxidant. The most recent development involves the use of nanofuels.
A thermobaric bomb's effective yield depends on a combination of a number of factors such as how well the fuel is dispersed, how rapidly it mixes with the surrounding atmosphere and the initiation of the igniter and its position relative to the container of fuel. In some designs, strong munitions cases allow the blast pressure to be contained long enough for the fuel to be heated well above its autoignition temperature so that once the container bursts, the superheated fuel autoignites progressively as it comes into contact with atmospheric oxygen.
Conventional upper and lower limits of flammability apply to such weapons. Close in, blast from the dispersal charge, compressing and heating the surrounding atmosphere, has some influence on the lower limit. The upper limit has been demonstrated to influence the ignition of fogs above pools of oil strongly. That weakness may be eliminated by designs in which the fuel is preheated well above its ignition temperature so that its cooling during its dispersion still results in a minimal ignition delay on mixing. The continual combustion of the outer layer of fuel molecules, as they come into contact with the air, generates added heat which maintains the temperature of the interior of the fireball, and thus sustains the detonation.
In confinement, a series of reflective shock waves is generated, which maintain the fireball and can extend its duration to between 10 and 50 ms as exothermic recombination reactions occur. Further damage can result as the gases cool and pressure drops sharply, leading to a partial vacuum. This rarefaction effect has given rise to the misnomer "vacuum bomb". Piston-type afterburning is also believed to occur in such structures, as flame-fronts accelerate through it.

Fuel–air explosive

A fuel–air explosive device consists of a container of fuel and two separate explosive charges. After the munition is dropped or fired, the first explosive charge bursts open the container at a predetermined height and disperses the fuel in a cloud that mixes with atmospheric oxygen. The cloud of fuel flows around objects and into structures. The second charge then detonates the cloud and creates a massive blast wave. The blast wave can destroy reinforced buildings, equipment, and kill or injure people. The blast wave's antipersonnel effect is magnified in confined spaces, such as foxholes, tunnels, bunkers and caves.

Effects

Conventional countermeasures such as barriers and personnel armour are not effective against thermobaric weapons. A Human Rights Watch report of 1 February 2000 quotes a study made by the US Defense Intelligence Agency:
According to a US Central Intelligence Agency study,
Another Defense Intelligence Agency document speculates that, because the "shock and pressure waves cause minimal damage to brain tissue... it is possible that victims of FAEs are not rendered unconscious by the blast, but instead suffer for several seconds or minutes while they suffocate".

Development

German

The first attempts occurred during the First World War when incendiary shells used a slow but intense burning material, such as tar impregnated tissue and gunpowder dust. These shells burned for approximately 2 minutes after the shell exploded and spread the burning elements in every direction.
In World War II, the German Wehrmacht attempted to develop a thermobaric weapon, under the direction of the Austrian physicist Mario Zippermayr.
The weapon was claimed by a weapons specialist to have been tested on the Eastern front under the code-name "Taifun B" and was ready for deployment during the Normandy invasion in June, 1944. Apparently, canisters of a charcoal, aluminium and aviation fuel would have been launched, followed with a secondary launch of incendiary rockets. It was destroyed by a Western artillery barrage minutes before being fired just before Operation Cobra.

United States

FAEs were developed by the United States for use in the Vietnam War. The CBU-55 FAE fuel-air cluster bomb was mostly developed by the US Naval Weapons Center at China Lake, California.
Current American FAE munitions include the following:
The XM1060 40-mm grenade is a small-arms thermobaric device, which was fielded by US forces in Afghanistan in 2002, and proved to be popular against targets in enclosed spaces, such as caves. Since the 2003 invasion of Iraq, the US Marine Corps has introduced a thermobaric "Novel Explosive" round for the Mk 153 SMAW rocket launcher. One team of Marines reported that they had destroyed a large one-story masonry type building with one round from. The AGM-114N Hellfire II, uses a Metal Augmented Charge warhead, which contains a thermobaric explosive fill that uses aluminium powder coated or mixed with PTFE layered between the charge casing and a PBXN-112 explosive mixture. When the PBXN-112 detonates, the aluminium mixture is dispersed and rapidly burns. The result is a sustained high pressure that is extremely effective against people and structures.

Soviet, later Russian

Following FAEs developed by the United States for use in the Vietnam War, Soviet Union scientists quickly developed their own FAE weapons. Since Afghanistan, research and development has continued, and Russian forces now field a wide array of third-generation FAE warheads, such as the RPO-A. The Russian armed forces have developed thermobaric ammunition variants for several of their weapons, such as the TBG-7V thermobaric grenade with a lethality radius of, which can be launched from a rocket propelled grenade RPG-7. The GM-94 is a pump-action grenade launcher designed mainly to fire thermobaric grenades for close combat. The grenade weighed and contained of explosive, its lethality radius is, but due to the deliberate "fragmentation-free" design of the grenade, a distance of is considered safe.
The RPO-A and upgraded RPO-M are infantry-portable rocket propelled grenades designed to fire thermobaric rockets. The RPO-M, for instance, has a thermobaric warhead with a TNT equivalence of and destructive capabilities similar to a high-explosive fragmentation artillery shell. The RShG-1 and the RShG-2 are thermobaric variants of the RPG-27 and RPG-26 respectively. The RShG-1 is the more powerful variant, with its warhead having a lethality radius and producing about the same effect as of TNT. The RMG is a further derivative of the RPG-26 that uses a tandem-charge warhead, with the precursor high-explosive anti-tank warhead blasting an opening for the main thermobaric charge to enter and detonate inside. The RMG's precursor HEAT warhead can penetrate 300 mm of reinforced concrete or over 100 mm of rolled homogeneous armour, thus allowing the -diameter thermobaric warhead to detonate inside.
Other examples include the semi-automatic command to line of sight or millimeter-wave active radar homing guided thermobaric variants of the 9M123 Khrizantema, the 9M133F-1 thermobaric warhead variant of the 9M133 Kornet, and the 9M131F thermobaric warhead variant of the 9K115-2 Metis-M, all of which are anti-tank missiles. The Kornet has since been upgraded to the Kornet-EM, and its thermobaric variant has a maximum range of and has a TNT equivalence of. The 9M55S thermobaric cluster warhead rocket was built to be fired from the BM-30 Smerch MLRS. A dedicated carrier of thermobaric weapons is the purpose-built TOS-1, a 24-tube MLRS designed to fire thermobaric rockets. A full salvo from the TOS-1 will cover a rectangle. The Iskander-M theatre ballistic missile can also carry a thermobaric warhead.
Many Russian Air Force munitions have thermobaric variants. The S-8 rocket has the S-8DM and S-8DF thermobaric variants. The S-8's brother, the S-13, has the S-13D and S-13DF thermobaric variants. The S-13DF's warhead weighs only, but its power is equivalent to of TNT. The KAB-500-OD variant of the KAB-500KR has a thermobaric warhead. The ODAB-500PM and ODAB-500PMV unguided bombs carry a fuel–air explosive each. ODAB-1500 is a larger version of the bomb. The KAB-1500S GLONASS/GPS guided bomb also has a thermobaric variant. Its fireball will cover a radius and its lethal zone is a radius. The 9M120 Ataka-V and the 9K114 Shturm ATGMs both have thermobaric variants.
In September 2007, Russia exploded the largest thermobaric weapon ever made, and claimed that its yield was equivalent to that of a nuclear weapon. Russia named this particular ordnance the "Father of All Bombs" in response to the American-developed Massive Ordnance Air Blast bomb, which has the backronym "Mother of All Bombs" and once held the title of the most powerful non-nuclear weapon in history.