Thermobaric weapon

A thermobaric weapon, also called an aerosol bomb, or erroneously a vacuum bomb, is a type of explosive munition that works by dispersing an aerosol cloud of gas, liquid or powdered explosive. This allows the chemical combustion to proceed using atmospheric oxygen, so that the weapon does not need to include an oxidizer.

The fuel is usually a single compound, rather than a mixture of multiple substances. Many types of thermobaric weapons can be fitted to hand-held launchers, and can also be launched from airplanes.

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 (FAE).

Most conventional explosives consist of a fuel–oxidiser 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, 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 that 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, grain bins (corn silos etc.), and earlier 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 150 kilometres (93 mi) from its centre.