Dust is defined as a teeny solid less than 420 microns in diameter, but that does not cover the nanoscale world. Nanodust, and its potential explosive properties, is relatively under-studied. A general rule of thumb in the world of dust research holds that the smaller the particle size and the greater its surface area, the more explosive it is. Nanoparticles are tiny, but have a large relative surface area because of the way atoms are arranged in them. They also tend to want to clump together, and this is one of the properties that makes items like carbon nanotubes and graphene so interesting to study. But these large agglomerations of nanoparticles, called nanpowders, are also pretty explosive, igniting with just 1 millijoule of energy. They could ignite with a spark, a collision or mere friction, according to Worsfold and colleagues. And because they're so small, nanoparticles can remain suspended in the air for days or weeks and you would never know it.