Flame propagation behaviours in 40 nm titanium, aluminium and iron dust clouds were investigated by highspeed photography. 40 rim titanium, aluminium and iron dust flames were all characterized by discrete single glowing burning particles with smoothly spherical front. "Micro explosions" caused by the fragment ejection occurred in both 40 nm titanium and aluminium particles burning processes. At nano scales, the heat and mass transfer regimes were absolutely different with micro particles, which resulted in different propagation velocities. The average pulsating flame propagation velocities of 40 nm titanium, aluminium and iron dust clouds were 0.565 m/s, 0.189 m/s and 0.035 m/s, respectively. From SEM analysis, it was inferred that 40 nm titanium, aluminium and iron particles were burnt in liquid, gas, and solid-phase, respectively. From XPS analysis, it was found that N-2 played a significant role in titanium particles combustion. 40 nm titanium combustion products contained 43% TiO2 (Ti4+), 27% Ti2O3 (Ti3+), 21%TiO (Ti2+) and 9%TiN (Ti3+). While 40 nm aluminium combustion products just contained 100% Al2O3 (Al3+), and 40 nm iron combustion products contained 49% Fe2O3 (Fe3+), 26% Fe3O4 (Fe3+/Fe2+), 15% FeO (Fe2+) and 10% iron nonoxides. Inerted by nitrogen for preventing nano titanium dust explosions was inadvisable. (C) 2017 Elsevier B.V. All rights reserved.