Fuel Air Explosives (and the irony of protection)

I've known of this class of bomb since I was around 8 : that's how hardcore a military spec fan I was. So indulge me. Also known as thermobaric weapons. But such weapons of mass destruction are very rarely used. Off the top of my head : used by the Russians against Chechnya, by the US against targets in Afghanistan more recently. Perhaps during the first Gulf War.

This bomb kills by overpressure effects, and also incineration. It contains a two stage fuze : first the canister explodes, distributing a mist of highly volatile particles into the air around the target, then the second fuze ignites.

Such flash ignitions occur catastrophically in civilian installations as well. The explosion is far more powerful than usual because of the high degree of pre-mixing of the fuel and oxygen. Milk powder factory explosions (in India) and grain silo explosions (in Canada and America) come to mind, as well as coal dust explosions in mines : anywhere where fine combustible particles are suspended in the air.

But done deliberately in a bomb : well. Upon ignition, overpressure reaches roughly 400 pounds per square inch, with the blastwave travelling at three kilometers per second. After that, the pressure drops far below normal, creating a vacuum and sucking everything back towards the blast zone. The massive overpressure and underpressure effects force unburnt fuel air mixture into every nook and cranny, incinerating everything at a temperature of 3000 degrees.

This effect is further magnified in confined spaces. Hence the use of FAE bombs against buildings, soldiers hiding in basements and caves, crew in non airtight vehicles - anywhere that the extreme high pressure air can force itself into. The more enclosed the area, the more devastating the effects. Ironically the best chance of survival for a soldier is to be standing in the open wearing no body armour (even the enclosed space between the armour you are wearing and your body magnifies the overpressure and acts as a space where the fuel-air mixture will penetrate).

This strange irony is also seen in the case of land mines. A soldier walking around barefoot that steps on a land mine might escape just losing a toe or two. If he's wearing steel jacketed boots it has been known for a land mine to slice off his leg mid calf where the boots end. In this case explosive force follows the path of least resistance, see.