In order to get a safer and more reproducible slag yard practice, the cooling of slags from stainless steel production in a slag yard was studied. A numerical 1D model was used to predict the spatial and temporal evolution of the temperature in the yard. This model has been validated based on temperature measurements at the surface and in the bulk of an industrial yard consisting of 22 layers. Each new layer initially cools down, but is heated again as additional layers are poured on top. In the bulk of the yard, temperatures of over 1273 K can be maintained throughout the filling of the yard. This temperature is a function of the process parameters. The validated model was used to quantify the influence of the layer thickness and the interval between subsequent layers on the temperature evolution within the yard.