Aerosols of hydrocarbon/air may be formed on accidental release of product in the chemical and process industries and pose a fire and explosion hazard. Some very large-scale accidents involving such systems have been reported. This paper reports a series of novel scouting experiments in a purpose-built medium-scale facility, designed to throw light on this category of hazard. Results show that significant flame accelerations only occurred for volatile fuels in the empty vented enclosure utilised. Furthermore, while the primary diagnostic of peak overpressure suggested that heptane, propane vapour and heptane/propane mixtures could be considered of similar reactivity, by decoupling the effects of the ＇internal＇ and ＇external＇ explosions and determining flamespeeds inside the enclosure, it is shown that explosions involving heptane were indeed more severe. Further fundamental research is required before meaningful analysis of this complex category of hazard can be offered. Other more general explosion trends recorded are discussed briefly.