The emission of clusters in nuclear dissociation was investigated within the framework of the isospin dependent lattice gas model. As observed in the recent experimental data, it was found that the emission probability of individual clusters is Poissonian and thermal scaling was observed in the linear Arrhenius plots made from the average multiplicity of each cluster as a function of the inverse temperature. The `emission barriers' were extracted from the slopes of the Arrhenius plots and mainly depend on the surface energy of the cluster.