An unconventional military weapon designed to create extremely strong overpressures over a wide area of targeted terrain; for use against exposed personnel, combat equipment, fortified areas and individual defensive fortifications; clearing minefields; clearing landing sites for helicopters; destroying communication centers; and neutralizing strongholds in house-to-house urban fighting. Essentially a shockwave and flame weapon delivered from helicopters, rocket trucks, or shoulder-held bazookas. Aka thermobaric weapons, "vacuum bombs".

The operating principle is that air will act as oxidizer to a aerosol of fuel in a volume of atmosphere near the ground when the fuel is dispersed and ignited with precision. In military ordnance a conventional primary explosive ruptures the weapon container and disperses the fuel, and secondary explosive(s) detonate the mixture after a precise delay, producing overpressures up to 30 kg/cm2 in a blast wave that moves at 3 km/sec and and a few dozen microseconds later reverses to a brief hard vacuum.

In an accidental, low-efficiency civilian instance, someone lights a cigarette inside a silo full of fine wheat chaff, or natural gas from a leaking cooking bottle in an apartment floods its way down to a candle on the floor below.

Developed extensively by Honeywell for American use in Vietnam clearing helicopter landing zones and Viet Cong tunnels, FAE's were quickly adopted by the Soviet military for clearing minefields, were then extended to substituting for the thousands of artillery rounds needed to punch holes in massed NATO forward defenses, and are now believed to be held by the United States, Russia, China, India, and possibly Israel and Iraq. Soviet FAE's were reportedly used against the Chinese as early as 1969 and are now in their third generation, having been extensively field-tested in Afghanistan.

Military FAE's are twelve to sixteen times more powerful than conventional munitions against targets with large surface areas such as frame buildings, bunkers and vehicle shelters. They are more effective against fortifications not only because overpressures from FAE's travel through such fortifications more pervasively than the blast from point-source explosions, but because the major detonation can be delayed until the fuel aerosol itself has saturated the target. Several can also be exploded in near-simultaneous ripples that reinforce each other's blast waves. This makes fuel-air explosives a nearly unparalleled destructive force, and an effective if brutal alternative to the vicious room-by-room, block-by-block infantry tactics that are the traditional paradigm for urban operations.


In urban settings it is very difficult to limit the effect of this weapon to combatants, and the nature of FAE explosions makes it virtually impossible for civilians to take shelter from their destructive effect.
From a 1993 DIA study:
The (blast) kill mechanism against living targets is unique, and unpleasant... What kills is the pressure wave, and more importantly, the subsequent rarefaction (vacuum), which ruptures the lungs. If the fuel deflagrates but does not detonate, victims will be severely burned and will probably also inhale the burning fuel. Since the most common FAE fuels, ethylene oxide and propylene oxide, are highly toxic, undetonated FAE should prove as lethal to personnel caught within the cloud as most chemical agents.

FAE's are not currently banned under international humanitarian law.

I was noding a response to this and it growed. It is Armistice Day and I feel an obligation not to squeam, for the sake of those who had and have no choice but pro patria mori, and for those who chose anyway.

Thanks Rancid_Pickle for amplification.

Update 22 December 2001 US forces hunting Al-Qaeda in Afghanistan are now using thermobaric bombs to "suck the air out of caves" in the Tora Bora complex.