Abstract <p>Processes in which solid or liquid cylindrical objects or spherical drops heated to high temperature fall into a cooling liquid are of great interest in developing safety methods for nuclear power facilities. Since the direct laboratory simulation of potential emergencies is impossible, relevant experiments described today in the international literature deal with processes taking place when high-temperature cylindrical or spherical liquid-metal objects fall into water. Hot metal drops, falling into a liquid, generate a vapor layer (film) between the surface of the high-temperature drop and liquid−vapor phase boundary. In this study, we have considered the properties of a spherical vapor−liquid interface in the presence of a heat flux from the drop. Based on experimental data currently available it has been shown that the interface consists of stationary and oscillationg parts. For the stationary part of the vapor film, a general relation with regard for molecular and radiation heat transfer components has been derived. It has been found that in many cases the radiation heat transfer can be estimated by thoroughly analyzing radiation processes inside the vapor space. Specifically, the optical thickness of the vapor film should be estimated. For the case of moderate temperatures, when transfer by radiation can be neglected, a simple estimating expression was obtained that gives vapor film thickness values don’t contradict with respective scarce data currently available (the dependences of the film thickness on the heat flux from the hot body and its temperature). A review of research articles (see the Introduction) shows that there exists an alternative approach based on describing the phase boundary dynamics using the modified Rayleigh‒Lamb equation.</p>