Vacuum bombs

A thermobaric weapon is a type of explosive that utilizes oxygen from the surrounding air to generate an intense, high-temperature explosion, and in practice the blast wave typically produced by such a weapon is of a significantly longer duration than a conventional condensed explosive. The fuel-air bomb is one of the most well-known types of thermobaric weapons.

Most conventional explosives consist of a fuel-oxidizer premix (gunpowder, for example, contains 25% fuel and 75% oxidizer), whereas thermobaric weapons are almost 100% fuel, so thermobaric weapons are significantly more energetic than conventional condensed explosives of equal weight. Their reliance on atmospheric oxygen makes them unsuitable for use underwater, at high altitude, and in adverse weather. They do, however, cause considerably more destruction when used against field fortifications such as foxholes, tunnels, bunkers, and caves—partly due to the sustained blast wave, and partly by consuming the available oxygen inside. Thermobaric weapons have the longest sustained blast wave and most destructive force of any known explosive, excluding nuclear weapons.

There are many different types of thermobaric weapons rounds that can be fitted to hand-held launchers.

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).

In contrast to condensed explosive, where oxidation in a confined region produces a blast front from essentially a point source, a flame front accelerates to a large volume producing pressure fronts both within the mixture of fuel and oxidant and then 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. Previously, such explosions were most often encountered in flour mills and their storage containers, and later in coal mines; but, now, most commonly in discharged oil tankers and refineries, including an incident at Buncefield in the UK in 2005 where the blast wave woke people 150 kilometres (93 mi) from its centre.

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