MIKE3 test apparatus. (image taken from "Fire and explosion properties of nanopowders", Research Report RR782, UK Health and Safety Executive)

Michael Berger at Nanowerk has written a Spotlight essay on the explosivity of nanoparticles. From the March 20, 2012 essay,

Recent studies have found that nanomaterials – in this case dusts and powders having nanosize particles – exhibit an explosion severity which is not disproportionate to micrometer-sized materials, but the likelihood of explosion is quite high due to very low ignition energies and temperatures.

…

The review concludes that nanomaterials present a dust explosion hazard, with metallic nanoparticles being particularly reactive. Nanomaterials have been shown to display lower ignition energy and temperature requirements than larger particles. Due to this high sensitivity, explosion hazards may exist for many processes including, but not limited to, mixing, grinding, drilling, sanding, and cleaning.

The essay is well worth a read as Berger synthesizes information from more than one study and he provides some technical detail.