Explosives engineer Jerome Stofleth of Sandia National Laboratories calls the fuel-air bomb a specialty weapon, excellent at collapsing tunnels and bunkers because its shock waves can easily penetrate small spaces. But fuel-air weapons have a few serious drawbacks that limit their potential usefulness on the battlefield. First, they are notoriously difficult to build. "It's more of an art than a science to get the right concentration of fuel and air," says Van Romero, a weapons expert at New Mexico Tech. What's more, wind can blow away the fuel cloud before it ignites, leaving the target unharmed. And explosives inside the weapon, often magnesium and isopropyl nitrate, can be unstable, giving the bomb an impossibly short shelf life (in some cases, days compared with decades for a TNT bomb).