Fuel-air Explosive

A thermobaric weapon, also called an aerosol bomb, a vacuum bomb or a fuel air explosive (FAE), is a type of explosive that uses oxygen from the surrounding air to generate a high-temperature explosion. The fuel–air explosive is one of the best-known types of thermobaric weapons.

Thermobaric weapons are almost 100% fuel and as a result are significantly more energetic than conventional explosives of equal weight. Many types of thermobaric weapons can be fitted to hand-held launchers, and can also be launched from airplanes. The largest Russian bomb contains a charge of approximately 7 tons of a liquid fuel that when detonated creates an explosion of 39.9 tons TNT equivalent.

Terminology

The term ''thermobaric'' is derived from the Greek words for 'heat' and 'pressure': ''thermobarikos'' (θερμοβαρικός), from ''thermos'' (θερμός) 'hot' + ''baros'' (βάρος) 'weight, pressure' + suffix ''-ikos'' (-ικός) '-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

File:Dust explosion 00.jpg, Experimental setup
File:Dust explosion 01.jpg, Finely-ground flour is dispersed
File:Dust explosion 02.jpg, Cloud of flour is ignited
File:Dust explosion 03.jpg, Fireball spreads rapidly
File:Dust explosion 04.jpg, Intense radiant heat has nothing to ignite here
File:Dust explosion 05.jpg, Fireball and superheated gases rise
File:Dust explosion 06.jpg, Aftermath of explosion, with unburned flour on the ground

Most conventional explosives consist of a fuel–oxidizer 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 (foxholes, covered slit trenches, bunkers).

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 which 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, and later 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 center.

A typical weapon consists of a container packed with a fuel substance, the center 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 aluminum 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 (FAE) 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 (and possibly ionizes it, depending on whether a fused quartz dispersal charge container was employed) in a cloud that mixes with atmospheric oxygen (the size of the cloud varies with the size of the munition). 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 antipersonnel effect of the blast wave is more severe in foxholes and tunnels and in enclosed spaces, such as bunkers and caves.

Effects

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, "the effect of an FAE explosion within confined spaces is immense. Those near the ignition point are obliterated. Those at the fringe are likely to suffer many internal, invisible injuries, including burst eardrums and crushed inner ear organs, severe concussions, ruptured lungs and internal organs, and possibly blindness." 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".Defense Intelligence Agency, "Future Threat to the Soldier System, Volume I; Dismounted Soldier – Middle East Threat", September 1993, p. 73.

Development

German

The first attempts occurred during the First World War when incendiary shells (in German 'Brand Granate') 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 vacuum bomb under the direction of the Austrian physicist Mario Zippermayr.

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 (NWC) at China Lake, California.

Current American FAE munitions include the following:
* BLU-73 FAE I
* BLU-95 (FAE-II)
* BLU-96 (FAE-II)
* CBU-72 FAE I
* AGM-114 Hellfire missile
* XM1060 grenade
* SMAW-NE round for rocket launcher

The XM1060 40-mm grenade is a small-arms thermobaric device, which was delivered to US forces in April 2003. Since the 2003 Invasion of Iraq, the US Marine Corps has introduced a thermobaric "Novel Explosive" (SMAW-NE) 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 (MAC) warhead, which contains a thermobaric explosive fill that uses aluminum powder coated or mixed with PTFE layered between the charge casing and a PBXN-112 explosive mixture. When the PBXN-112 detonates, the aluminum 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.Lester W. Grau and Timothy L. Thomas (2000)
Russian Lessons Learned From the Battles For Grozny
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) 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 (RPGs), 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 (HEAT) 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 (SACLOS) 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 also 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. 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 (MOAB) bomb, which has the backronym "Mother of All Bombs" and once held the title of the most powerful non-nuclear weapon in history. The Russian bomb contains a charge of approximately 7 tons of a liquid fuel, such as pressurized ethylene oxide, mixed with energy-rich nanoparticles, such as aluminum, surrounding a high explosive burster that when detonated created an explosion equivalent to 39.9 tons of TNT.

Spanish

In 1983, a program of military research was launched with collaboration between the Spanish Ministry of Defence (Directorate General of Armament and Material, DGAM), Explosives Alaveses (EXPAL) and Explosives Rio Tinto (ERT) with the goal of developing a Spanish version of a thermobaric bomb, the BEAC (''Bomba Explosiva de Aire-Combustible''). A prototype was tested successfully in a foreign location out of safety and confidentiality concerns. The Spanish Air and Space Force has an undetermined number of BEACs in its inventory.

Chinese

In 1996, the People's Liberation Army (PLA) began development of the PF-97, a portable thermobaric rocket launcher, based on the Soviet RPO-A Shmel. Introduced in 2000 it is reported to weigh 3.5 kg and contains 2.1 kg of thermobaric filler. An improved version called the PF-97A was introduced in 2008.

China is reported to have other thermobaric weapons, including bombs, grenades and rockets. Research continues on thermobaric weapons capable of reaching 2,500 degrees.

Indian

Based on the high-explosive squash head (HESH) round, a 120 mm thermobaric round was developed by the Indian Ministry of Defence, which packed thermobaric explosives into the tank shells to increase the effectiveness against enemy bunkers and light armoured vehicles.

The design and the development of the round was taken up by Armament Research and Development Establishment (ARDE). The rounds were designed for the Arjun MBT. The TB rounds contains fuel rich explosive composition called thermobaric explosive. As the name implies, the shells, when they hit a target, produce blast overpressure and heat energy for hundreds of milliseconds. The overpressure and heat causes damage to enemy fortified structures like bunkers and buildings and for soft targets like enemy personnel and light armoured vehicles.

British

In 2009, the British Ministry of Defence (MoD) acknowledged that Army Air Corps (AAC) AgustaWestland Apaches had used AGM-114 Hellfire missiles purchased from the United States against Taliban forces in Afghanistan. The MoD stated that 20 missiles, described as "blast fragmentation warheads", were used in 2008 and a further 20 in 2009. MoD officials told ''Guardian'' journalist Richard Norton-Taylor that the missiles were "particularly designed to take down structures and kill everyone in the buildings", as AAC AgustaWestland Apaches were previously equipped with weapon systems deemed ineffective to combat the Taliban. The MoD also stated that "British pilots' rules of engagement were strict and everything a pilot sees from the cockpit is recorded."

In 2018, the MoD accidentally divulged the details of General Atomics MQ-9 Reapers utilised by the Royal Air Force (RAF) during the Syrian civil war, which revealed that the drones were equipped with AGM-114 Hellfire missiles. The MoD had sent a report to a British publication, ''Drone Wars'', in response to a freedom of information request. In the report, it was stated that AGM-114N Hellfire missiles which contained a thermobaric warhead were used by RAF attack drones in Syria.

History

Military use

United States

FAEs such as first-generation CBU-55 fuel-air weapons saw extensive use in the Vietnam War. A second generation of FAE weapons were based on those, and were used by the United States in Iraq during Operation Desert Storm. A total of 254 CBU-72s were dropped by the United States Marine Corps, mostly from A-6Es. They were targeted against mine fields and personnel in trenches, but were more useful as a psychological weapon.

The US military also used thermobaric weapons in Afghanistan. On 3 March 2002, a single laser guided thermobaric bomb was used by the United States Air Force against cave complexes in which Al-Qaeda and Taliban fighters had taken refuge in the Gardez region of Afghanistan. The SMAW-NE was used by the US Marines during the First Battle of Fallujah and the Second Battle of Fallujah.

The AGM-114N Hellfire II was first used by US forces in 2003 in Iraq.

Soviet Union and Russia

FAEs were reportedly used against China in the Sino-Soviet border conflict. Russia used the RPO-A in Chechnya.

The TOS-1 system was test fired in Panjshir Valley during the Soviet–Afghan War in the late 1980s. MiG-27 attack aircraft of the 134th APIB also used ODAB-500S/P fuel-air bombs against Mujahideen forces in Afghanistan, but they were found to be unreliable and dangerous to ground crew.

Unconfirmed reports suggest that Russian military forces used ground-delivered thermobaric weapons in the storming of the Russian parliament during the 1993 Russian constitutional crisis and during the Battle for Grozny (first and second Chechen Wars) to attack dug-in Chechen fighters. The use of TOS-1 heavy MLRS and "RPO-A Shmel" shoulder-fired rocket system during the Chechen Wars is reported to have occurred.

It is thought that a multitude of handheld thermobaric weapons were used by the Russian Armed Forces in their efforts to retake the school during the 2004 Beslan school hostage crisis. The RPO-A and either the TGB-7V thermobaric rocket from the RPG-7 or rockets from either the RShG-1 or the RShG-2 is claimed to have been used by the Spetsnaz during the initial storming of the school.Beslan still a raw nerve for Russia
, BBC News, 1 September 2006 At least three and as many as nine RPO-A casings were later found at the positions of the Spetsnaz. The Russian government later admitted to the use of the RPO-A during the crisis.A Reversal Over Beslan Only Fuels Speculation
, ''The Moscow Times'', 21 July 2005

During the 2022 Russian invasion of Ukraine, CNN reported that Russian forces were moving thermobaric weapons into Ukraine. On 28 February 2022, Ukraine's ambassador to the United States accused Russia of deploying a thermobaric bomb.

United Kingdom

During the War in Afghanistan, British forces, including the Army Air Corps and Royal Air Force, used thermobaric AGM-114N Hellfire missiles against the Taliban. In the Syrian civil war, British military drones also used AGM-114N Hellfire missiles; in the first three months of 2018, British drones fired 92 Hellfire missiles in Syria.

Syria

Reports by the rebel fighters of the Free Syrian Army claim the Syrian Air Force used such weapons against residential area targets occupied by the rebel fighters, such as during the Battle of Aleppo and in Kafar Batna. A United Nations panel of human rights investigators reported that the Syrian government had used thermobaric bombs against the rebellious town of Al-Qusayr in March 2013.

The Russia and Syrian governments have used thermobaric bombs and other thermobaric munitions during the Syrian civil war against insurgents and insurgent-held civilian areas.

Non-state actor use

Thermobaric and fuel–air explosives have been used in guerrilla warfare since the 1983 Beirut barracks bombing in Lebanon, which used a gas-enhanced explosive mechanism that was probably propane, butane, or acetylene. The explosive used by the bombers in the US 1993 World Trade Center bombing incorporated the FAE principle by using three tanks of bottled hydrogen gas to enhance the blast. Jemaah Islamiyah bombers used a shock-dispersed solid fuel charge, based on the thermobaric principle, to attack the Sari nightclub during the 2002 Bali bombings.

International law

International law does not prohibit the use of thermobaric munitions, fuel-air explosive devices, or vacuum bombs against military targets. Their use against civilian populations or infrastructure may be banned by the United Nations (UN) Convention on Certain Conventional Weapons (CCW). , all past attempts to regulate or restrict thermobaric weapons have failed.

See also

* Bunker buster
* Flame fougasse

References

External links

*

{{DEFAULTSORT:Thermobaric Weapon
Explosive weapons
Ammunition

Anti-personnel weapons