Thermobaric explosives, also called fuel-air explosives (FAE), use oxygen around them to generate a high-temperature blast. The blast wave typically lasts longer than a conventional explosive and has the ability to vaporize people.
"The [blast] kill mechanism against living targets is unique--and unpleasant...." reads a
1993 U.S. Defense Intelligence Agency study. "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."
Using such explosives is a breach of the Geneva Convention, which established guidelines for humanitarian treatment of populations in war.