Thermobaric weapon

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A thermobaric weapon is an explosive weapon that produces a blast wave of a significantly longer duration than most high-explosives. This is useful in military applications where a longer pulse duration makes the pressure wave more difficult to survive—both for people and for structures.

A thermobaric weapon is often dependent on oxygen drawn from the surrounding air to oxidize the underlying combustion reaction, whereas ordinary explosives contain a large percentage of oxidizer in their mixture (e.g., gunpowder is about 15% fuel and about 75% oxidizer). Because thermobaric weapons consist largely of fuel, they are on a pound-for-pound basis much more powerful than ordinary explosives.

Thermobaric weapons generally cannot be used underwater or at very high altitudes, and their effect is unpredictable in extreme weather conditions. Some types of thermobaric weapons therefore incorporate an oxidizer into the mixture to allow for use underwater., etc, although this reduces the effective yield per pound.

They are especially useful when deployed in confined spaces, such as tunnels, caves, and bunkers.

Contents 1 Terminology 2 Mechanism 3 History 3.1 USA developments 3.2 Russian developments 3.3 British developments 3.4 Use by terrorists 4 See also 5 Footnotes 6 External links

[edit] 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), suffix -ic.

Other terms used for this family of weapons are high-impulse thermobaric weapons (HITs), heat and pressure weapons, vacuum bombs, or fuel-air explosives (FAE or FAX).

[edit] Mechanism

Like all explosives, a chemical reaction is utilized to produce a huge amount of superheated gas, which almost instantaneously superheats the surrounding air and thus produces a rapidly-expanding high-temperature pressure wave (called a "blast wave") which does damage.

Thermobaric explosives represent the deliberate application of the principle underlying the vapor cloud explosions and dust explosions that occasionally occur by accident in a variety of industries. Such explosions are the consequence of the rapid burning of a finely dispersed fuel suspended in air in a confined space. An accidental fuel-air explosion may occur as a result of a boiling liquid expanding vapor explosion (BLEVE), for example when a tank containing liquefied petroleum gas bursts. Silo explosions and the ignition of flour in flour mills, phenomenons known since medieval times, are also examples of thermobaric explosions.^[1]

A typical thermobaric weapon consists of a container packed with a fuel substance, in the center of which is a small conventional-explosive "scatter charge". The fuel could be a finely powdered explosive metal such as aluminium or magnesium, or a reactive organic substance such as coal or baking flour.^[2][3][4] It could also be a liquid such as gasoline, in which case it is usually called a "fuel-air bomb".

When a typical thermobaric weapon is detonated, the explosive charge (or some other dispersal mechanism) bursts the container and disperses the fuel in a cloud, the fuel mixes with the air, and the resultant mixture is ignited. Some weapons use separate charges to disperse the fuel and to ignite the fuel. Other designs use a stronger casing, which contains the dispersal explosion long enough to heat the fuel above its auto-ignition temperature. The dispersing fuel particles ignite spontaneously when they thereafter come into contact with oxygen in the air. In either case, the more thoroughly dispersed the fuel is, the faster the fuel can burn and the more rapid (and thus powerful) the explosion will be.^{[5][6][7][8][9][10][11][12][13][14][15]}

For vapor cloud explosion there is a minimum ratio and a maximum ratio of fuel vapor to air outside of which ignition will not occur. This weakness is eliminated in designs where the fuel is pre-heated above ignition temperature by the dispersal charge.^[16][17][18]

In confined spaces, the availability of oxygen is limited, which further extends the pulse of the detonation. Furthermore the confined explosion generates a series of reflective shock waves, which maintain the hot environment (fireball) and permit extended combustion. This further-delayed combustion process produces the pressure wave over a significantly longer time duration (10–50 msec), which is generally referred to as after-burning or late-time impulse.^[19]

Furthermore, when the super-heated gas inside the fireball cools the pressure drops sharply. This causes a partial vacuum, which can be powerful enough to cause physical damage to people and structures. This effect has given rise to the misnomer "vacuum bomb".

A thermobaric explosion in a confined area such as a tunnel often creates an asphyxiation effect, when the fireball consumes all available oxygen and prevents fresh oxygen from reaching interior spaces for a time.

If the walls of the confinement are strong, such as with defensive bunkers and tunnel systems, the over-pressure is contained and the blast effect is prolonged and channelled rather than dispersing evenly through the atmosphere. This can create a piston-type afterburn reaction in enclosed structures, with the flame-front progressing rapidly through the system "seeking" fresh oxygen.^[20][21]

The overpressure within the detonation can reach 430 lbf/in² (3 MPa, 30 bar) and the temperature can be 4,500 to 5,400 °F (2,482 to 2,982 °C). Outside the cloud the blast wave travels at over 2 mi/s (3 km/s).

[edit] History

In 1944 the Germans experimented with the development of a fuel-air bomb, using 40% liquid oxygen^[22] mixed with 60% dry brown coal powder. In a test of an 8 kg charge near Doberitz, trees were reportedly destroyed within a 600 meter radius, with shock effects being felt as far away as 2 km.^[23] The extent of the described destruction radius is not considered plausible for the stated mass of the charge.^[24][25]

Fuel-Air Munitions were in published literature available to English-speaking readers by the mid-1970s.^[26]

[edit] USA developments

Current US FAE munitions include:

• BLU-73 FAE I
• BLU-95 500-lb (FAE-II)
• BLU-96 2,000-lb (FAE-II)
• CBU-55 FAE I
• CBU-72 FAE I

The XM1060 40-mm grenade is a small-arms thermobaric device, which was delivered to U.S. forces in April 2003.^[27] In 2003, United States Marines used a thermobaric version of their Shoulder-Launched Multipurpose Assault Weapon, called a Shoulder-Launched Multipurpose Assault Weapon-Novel Explosion (SMAW-NE), in the Invasion of Iraq. One team of Marines reported that they had destroyed a large one-story masonry type building with one round from 100 yards.^[28]

The 48-lb (22 kg) AGM-114N Hellfire Metal Augmented Charge introduced in 2003 in Iraq contains a thermobaric explosive fill, using fluoridated aluminium 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 resultant sustained high pressure is extremely effective against enemy personnel and structures.^[29]

[edit] Russian developments

The Soviet armed forces extensively developed FAE weapons,^[30] and are known to have used them in Chechnya.^[31]

In September 2007 Russia successfully exploded the largest vacuum bomb ever made, leveling a multi-story block of apartment buildings with a power reportedly greater than that of the smallest dial-a-yield nuclear weapons at their lowest settings.^[32][33] Russia named this particular ordnance the "Father of All Bombs" in response to the United States developed "Massive Ordnance Air Blast" (MOAB) bomb whose backronym is the "Mother of All Bombs", and which previously held the accolade of the most powerful non-nuclear weapon in history.^[34] The bomb contains a 14,000 pound (6,400 kilogram) charge of a liquid fuel such as ethylene oxide, mixed with an energetic nanoparticle such as aluminium, surrounding a high explosive burster.^[35] See film here.

[edit] British developments

In June 2008, the United Kingdom revealed that its forces had used thermobaric munitions in Afghanistan. The munitions were delivered by the Hellfire AGM-114N from WAH-64 Apache attack helicopters. American forces have also apparently been employing the weapons in Afghanistan from Apaches and from unmanned drones. The UK stated that the weapon will also be configured to be delivered from its own MQ-9 Reaper drones.^[36]

[edit] Use by terrorists

Thermobaric and fuel-air explosives have been used by terrorists since the 1983 Beirut barracks bombing in Lebanon which used a gas-enhanced explosive mechanism, probably propane, butane or acetylene.^[37] The explosive used by the bombers in the 1993 World Trade Center bombing incorporated the FAE principle, using three tanks of bottled hydrogen gas to enhance the blast.^[38][39] In 2002, Jemaah Islamiyah bombers used a shocked dispersed solid fuel charge,^[40] based on the thermobaric principle,^[41] to attack the Sari nightclub in the 2002 Bali bombings.^[42]

[edit] See also

• Dust explosion
• FOAB
• Flame Fougasse
• MOAB
• SMAW
• Wax burning

[edit] Footnotes

[edit] External links

• Fuel/Air Explosive (FAE)
• Thermobaric Explosive (Global Security)
• Aspects of thermobaric weaponry (PDF) - Dr. Anna E Wildegger-Gaissmaier, Australian Defence Force Health
• Thermobaric warhead for RPG-7
• Defense Update: Fuel-Air Explosive Mine Clearing System
• Foreign Military Studies Office - A 'Crushing' Victory: Fuel-Air Explosives and Grozny 2000
• TOS-1 "Buratino" 220 mm Multiple Rocket Launcher (Global Security)
• XM1060 40 mm Thermobaric Grenade (Global Security)
• Soon to make a comeback in Afghanistan
• animation
• Russia claims to have tested the most powerful "Vacuum" weapon
• "Dad of all Bombs" - Russia's new super-weapon.INFOgraphics