A process and apparatus for regasifying a cryogenic liquid to gaseous form are described. Heat is transferred from ambient air to the cryogenic liquid across a heat transfer surface by circulating cryogenic liquid or an intermediate fluid through an atmospheric vaporizer, wherein the ambient air and the cryogenic fluid or intermediate fluid are not in direct contact. A layer of ice is allowed to form, in use, on at least that external portion of the heat transfer surface exposed to the atmosphere where the temperature at the heat transfer surface is below the freezing temperature of water. The layer of ice is dislodged intermittently from the vaporizer using a source of heat operatively associated with a control device, the control device arranged to generate a signal when de-icing is required. The source of heat being directed at the interface between the layer of ice and the heat transfer surface.