To reveal clearly the effects of particle thermal characteristics on flame structures during organic dust explosions, the flame structures in the dust clouds and liquid mist observed during the combustion of several long-chain monobasic alcohols in an open space chamber were recorded using an approach combining high-speed photography and a band-pass filter. From direct-light-emission photographs and CH-emission photographs, it was demonstrated experimentally that the structures of propagating flames changed as the thermal characteristics of the dust clouds and liquid mist varied. For methanol and propanol mist combustion, the flame structures were similar to the premixed gas explosion; in contrast, from hexanol mist combustion to eicosanol dust combustion, the flame formed a complicated structure that exhibited heterogeneous combustion characteristics. The estimated results of the combustion reaction's final state show that all of the materials should react in the gas phase and that the comparative relationship between the characteristic time for the heating and devolatilisation of dust particles and the characteristic time for the gas-phase combustion of the premixed volatiles is a critical condition for the flame structure transition from homogeneous combustion to heterogeneous combustion in different materials. (C) 2013 Elsevier Ltd. All rights reserved.