Thermobaric weapon
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Thermobaric weapons distinguish themselves from conventional weapons by using atmospheric oxygen, instead of carrying an oxidizer in their explosives. They are also called high-impulse thermobaric weapons (HITs), fuel-air explosives (FAE or FAX) or sometimes "fuel-air munitions", "heat and pressure" weapons, or vacuum bombs.
They produce more explosive energy for a given size than do other explosives.
Some thermobaric weapons work by first expelling a cloud of explosive mist using a small charge, then igniting it with a second charge. These consist of a container of a volatile liquid (or a finely powdered explosive or a metal powder) and, typically, two separate explosive charges. After the munition is dropped or fired, the first explosive charge (or some other dispersal mechanism) bursts open the container at a predetermined height and disperses the fuel in a cloud that mixes with atmospheric oxygen. Once the fuel is appropriately mixed, the second charge detonates, propagating an explosion (blast wave) through the cloud.
An accidental fuel-air explosion may occur as a result of a boiling liquid expanding vapor explosion (BLEVE), for example when a tank containing liquified petroleum gas burst. Silo explosions, caused by the ignition of finely-powdered atmospheric dust, are another example.
Many newer types of thermobaric weapons do not disperse the fuel before igniting it, but are "single stage" bombs which have one explosive charge that both ignites and disperses the fuel.
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Note on terminology
Template:SectOR From the open literature it appears that some experts draw a distinction between the terms thermobaric weapon and fuel-air explosive based on the primary intended effects: "thermobaric" relating to closed-zone convection or air displacement as the primary objective, and "fuel-air" for use as area-denial or "daisy cutter"–like ordnance through blast and combustion, in a role somewhat similar to that of cluster bomb weapons. Other sources use "fuel-air" as the general case, subsuming "thermobaric" as previously detailed; still others use the two terms interchangeably. The term "thermobaric" appears to be of Russian/Soviet origin.
Weapon effects
The blast wave destroys unreinforced buildings and equipment. Unprotected personnel are injured or killed as well. The antipersonnel effect of the blast wave is more severe in foxholes, on personnel with body armor, and in "stiff" enclosed spaces such as caves, buildings, and bunkers.
The overpressure within the detonation can reach 3 MPa (430 lbf/in²) and the temperature can be 2500 to 3000 °C. Outside the cloud the blast wave travels at over 3 km/s. Following the initial blast is a phase in which the pressure drops below atmospheric pressure creating an airflow back to the center of the explosion strong enough to lift and throw a human. It draws in the unexploded burning fuel to create almost complete penetration of all non-airtight objects within the blast radius, which are then incinerated. Asphyxiation and internal damage can also occur to personnel outside the highest blast effect zone, e.g. in deeper tunnels, as a result of the blast wave, the heat, or the following air draw.
The effects produced by FAEs (a long high duration pressure and heat impulse) are often likened to the effects produced by low-yield nuclear weapons, but without the problems of radiation—although this is inexact; for all current and foreseen subkiloton yield nuclear weapon designs, prompt radiation effects predominate, producing some secondary heating—very little of the nominal yield is actually delivered as blast. The significant injury dealt by either weapon on a targeted population is nonetheless great.
Some fuels used, such as ethylene oxide and propylene oxide, are highly toxic. A device using such fuels is very dangerous even if the fuel fails to ignite; the device then becomes essentially a chemical weapon.
History
Image:Rpo.jpg Arguably, the use of flamethrowers in the trench warfare of World War I (the flamethrower was a German invention) could constitute the first use of a primitive "vacuum weapon", in that they could suffocate people protected from the direct weapon effects inside a pillbox or bunker. Other such effects were seen to occur in the firestorms at Dresden and elsewhere.
In the form that exists today, these devices (often dubbed Fuel-Air Munitions) are said to have been developed in the 1960s and used by the United States during the Vietnam War to destroy Viet Cong tunnels, clear forest for helicopter landing sites and to clear minefields. However, it is not clear that this is entirely the case; in particular, the very large parachute-delivered "Daisy Cutter" bomb used for this purpose was suspected to have been such a weapon but the current published details indicate that it was not (it seems to be filled with ANFO, a mixture of ammonium nitrate and jet fuel, instead). FAMs are certainly in published literature available to English-speaking readers by the mid-1970s (Cite to come).
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 meters. [1] The thermobaric explosive used in this weapon, PBXIH-135 or a variant, was developed at the Naval Surface Warfare Center (NSWC) Indian Head Division and had previously been used in BLU-118/B air-dropped bombs against al Qaeda and Taliban forces in Afghanistan in early March, 2002.
The Soviet armed forces also developed FAE weapons, including thermobaric warheads for shoulder-launched RPGs (RPO-A Shmel Bumblebee). Russian forces have a wide array of these weapons ([2]) and reportedly used them against Chinese forces in a 1969 border conflict, and certainly used them in Afghanistan and in Chechnya. Russian troops report that a single RPO-A round in an urban environment has an equivalent effect to a 156mm artillery round.
An FAE system from Israel was developed for minefield clearing. The system uses a small rocket propelled thermobaric charge which explodes over the minefield and activates exposed or buried mines.
Thermobaric weapons in fiction
Such a bomb was used at the beginning of the movie Outbreak, starring Dustin Hoffman and Rene Russo, and threatened to be used at the end to wipe out a quarantined town.
A fuel-air device was used to destroy the submarine USS Ethan Allen in the novel The Hunt for Red October, to cover the escape of the defecting Soviet submarine.
A fuel-air bomb can be ordered in the game Mercenaries: Playground of Destruction. For destroying enemy personnel and light-armour vehicles such as Jeeps and some APCs, it is the most powerful weapon available, and has a large price tag attached.
Fuel-air bombs are mentioned in Stealth.
In the game Command & Conquer: Generals, a fuel-air bomb strike can be called in by the US Forces.
In the sci-fi novel Gust Front by John Ringo, US forces used an FAE, consisting of a propane-filled office building, to destroy the city of Fredericksburg in an attempt to stop an invading alien army.
Johann Vierziger uses a fuel air hand grenade, referred to as a bunker buster, in David Drake's sci-fi action/adventure novel The Sharp End. First Sergeant Bradley uses a similar device in Drake's short story Teem Effort
The video game Resident Evil 4 features incendiary grenades as weapons which appear to contain napalm or a similarly volatile fuel.
The bombers in Battalion Wars are described as carrying "fuel-air bombs".
An Urban Myth exists about a man attempting to play a practical joke on his newlywed friends, consisting of an acetylene filled waterbed in their new house, accidentally destroying the house and surrounds for some distance and putting the local security forces on alert due to the sheer loudness of the explosion. In the myth fortune prevails and nobody is actually injured.