Thermobaric Bomb

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 and last longer 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.

## Overview

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.

While most conventional explosives consist of a fuel–oxidizer premix such as black powder, which contains 25% fuel and 75% oxidizer, or a decomposition-type explosive such as RDX, thermobaric weapons are almost 100% fuel and as a result are significantly more energetic than conventional explosives of equal weight. Despite the fact their reliance on atmospheric oxygen makes them unsuitable for use under water, at high altitude, and in adverse weather, they are, however, considerably more destructive when used against field fortifications such as foxholes, tunnels, bunkers, and caves.

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. Also explained as, the flame front is confined to the pressure wave of the initial explosion, creating much greater energy release.

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 fully empty oil tankers, refinery tanks, and vessels, such as the Buncefield fire in the United Kingdom in 2005, where the blast wave woke people 150 kilometers (93 mi) 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 like 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 auto-ignites 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 additional 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.

## Thermobaric Weapons in the New World

### Japan

As an additional countermeasure against the revival of the Yamato no Orochi, the Japanese government instructed the Ministry of Defense to take measures. This included the development of Bunker Busters and Thermobaric Bombs, with samples provided by the USFJ. Such weapons will also be helpful against the Gra Valkas Empire once the preparations for the battle are complete.