Thermobaric weapons have been around for decades, and reportedly used to clear helicopter landing zones by US forces in Vietnam. They have come to be known under many names – enhanced blast weapons, vacuum bombs, or even a ‘poor man’s nuclear weapon’, because of the dramatic impact that they can have upon combatants, especially those in confined spaces. Russia, in particular, has been an enthusiastic adopter of such weapon systems.
How it works
The name thermobaric is indicative of what these weapons deliver; Thermos from the Greek word meaning heat, and baros meaning pressure. They are often likened to an incendiary munition, which is designed to ignite a fire that burns for some time, when in fact, thermobarics are best thought of as a modified conventional explosive weapon. This means that they create a wave of overpressure and heat, followed by negative pressure.
The key differentiator between a thermobaric weapon and a conventional high explosive is the length of time that each of these effects lasts. A high explosive might last just milliseconds with a much higher peak force than a thermobaric, which can last tens of milliseconds with a lower, but still significant peak force.
A thermobaric weapon consists of a container filled with a fuel – which may be a form of aerosolised aluminium, magnesium, silicon, which is dispersed into the air to mix with atmospheric oxygen and detonated by a small explosive charge at its centre. The fuel description can be misleading – the fuel is not a liquid and is either a solid in most modern systems or may be a paste in some older designs.
The energy produced by the charge both scatters and ignites the fuel as it expands. The shock wave expands from the point of detonation with the thermobaric mixture combusting behind it, maintaining the pressure of the shock wave. The pressure created is uniform and may last for up to one second, creating an effect of significant lethality.
Whilst the explosion uses the oxygen available in the air for fuel, the metal component may also be coated in an oxidiser such as liquid nitrate esters, which have a low combustion point and produce hot gases to help all of the metal to burn. Without the oxidisers, there may be inefficient burning of the metal components.
There are a number of different types of thermobaric weapon and include the Fuel Air Explosive (FAE). An FAE warhead consists of the fuel and two explosive charges with the munition fuzed to detonate above the ground with the first charge dispersing the fuel over a wide area. The second charge then detonates the fuel within milliseconds.
Other variants are the Slurry Explosive Warhead, which consists of a combustible liquid mixed with a high explosive or solid explosive compound, and the Reactive Surround Warhead, which is a thin-walled container filled with combustible aluminium and nitrocellulose.
Thermobarics are used by Russian forces in urban environments, a key reason being the way in which the weapon functions, as explosive fuel is capable of creating a comprehensive area of effect, filling in the gaps, before detonating. If used in a building it will move around walls, instead of its explosive force being blocked by them, and may even be reflected off surfaces.
The length of time that the shock wave endures also creates multiple types of trauma. The result of a thermobaric blast is a very high peak temperature of 1,900 degrees celsius or higher, a long peak blast wave, and an extensive area of damage. The projectiles do not rely on fragmentation to create their lethal effect and are primarily reliant upon the blast.
For comparison, the pressure of a fuel air explosive weapon may produce a blast overpressure of 2,000kilopascals (kPa) (290psi), whereas a conventional high explosive at the same distance from the blast would produce an overpressure of 200kPa. A blast overpressure of 1,380kPa in the open is uniformly fatal, according to a 2005 paper published by Toney Baskin and John Holcomb.
The enormous pressure of the blast will impact human organs that include air – such as the lungs and bowel – and shear forces where soft tissues interact with firmer tissues. For example, a blast might rupture the alveoli within the lungs which can then leak fluid into the lungs leading to a condition known as blast lung. In the event that an injury is not immediately fatal, a patient may not present symptoms for several hours, or as long as 48 hours in some cases.
In the cardiovascular system, the blast might cause air embolisms and damage to the muscular layer of the heart. As one US Air Force special operations controller described it in an article in Scientific American in 2017, “it just blows your lungs out of your mouth. It kind of turns you inside out”.
The gastrointestinal system is also vulnerable as the shock wave passes over pockets of air in the bowel, it can cause perforations and haemorrhaging. The Central Nervous System may also suffer from air embolisms in the cerebral artery, which can lead to a rapid deterioration of a patient and death.
In addition to the effects of the blast, there are of course the flash burn effects of a thermobaric weapon to consider. Furthermore, the blast can turn materials like wood and concrete into fragments, leading to the risk of penetrating wounds.
Russian thermobaric weapons
The Soviet Union was an enthusiastic adopter of thermobaric weapons and has developed them in multiple guises from shoulder-launched rockets, to multiple rocket launchers, and air-dropped bombs. They have also been deployed in combat from Afghanistan, to Chechnya, throughout the war in Ukraine and in Syria too.
Bumblebee is the original Russian thermobaric weapon and is known by its formal name of RPO-Shmel. Its development in the 1980s eventually fed into the design of what became the TOS-1. The RPO-A Schmel is a shoulder fired weapon designed to deliver the effects of a 152mm howitzer round during close combat. The 93mm rocket carries a 2.1kg thermobaric warhead initially filled with a semi-liquid paste made up of RDX, aluminium and isopropyl nitrate. It is attributed with a maximum range of 1,000m and a sighting range of 600m.
The original TOS multiple rocket launcher was developed to meet the needs of Soviet forces deployed to Afghanistan and borrowed from the Bumblebee. They would often form part of a convoy and provide direct fire support in the event of an ambush. The long fuze at the nose of the rockets lent itself to the nickname of “Pinocchio” according to some sources.
Pinocchio carried 30 220mm rockets but had a limited range of 2,700m, it was developed into its current form which is TOS-1A which carries 24 rockets with a maximum range of 6km. It fires its rockets in pairs or singles and can discharge all 24 200kg rockets in six seconds covering an area of 40,000m2.
The ODAB-500PMV is an air-dropped FAE with a weight of 525kg, 193kg of which is the explosive content. It can be carried by fixed- or rotary-wing aircraft and deployed from heights of 200-12,000m and 220-5,000m respectively. A Su-34 ground attack aircraft can carry as many as four ODAB-500PMVs, leaving hardpoints for air-to-air missiles and other munitions. Some Syrian Su-22Ms have been observed with six ODABs fitted to their under-wing pylons.
The above covers a small selection of the thermobaric weapons employed by Russian forces, which are used extensively and have formed an integral element of Russian assaults in Ukraine. One source observes that when a Ukrainian trench is identified, it is common practice for some commanders to suppress them with artillery until a TOS-1A can be brought to bear to end the engagement.
The TOS-1A has been widely exported, as have other Russian thermobaric weapons, making them an important type of munition for modern militaries to understand and consider as a potential future risk.