Fire whirls are often reported in forest and urban fires with devastating damage to life and property. This work conducted experiments using a medium-scale facility to study the initiation mechanism, the vertical velocity and radiative heat transfer of fire whirls. Heptane was used as the fuel in the experiments. The variations of burning rates versus time indicate that the drag force on the root of the flame plays an important role in the initiation and decay of a fire whirl. Analyses show that the pressure difference due to whirling, characterized by the circulation  , significantly affects the vertical centerline velocity. The variation of the vertical centerline velocity is correlated by , where m is nearly 1.1 for both fire whirls and general pool fires. It is also found that the radiative fraction of fire whirls is nearly 42 %, 1.4 times as large as that for general pool fires. The radiative heat feedback fraction is shown to increase with pool diameter, similarly as for general pool fires. KEYWORDS: fire whirl, radiation, centerline velocity, burning rate, pool fires. NOMENCLATURE LISTING