A new algorithm, based on the thermodynamic model proposed by Schotte (1987), has been developed to simulate the mixing of HF with moist air. This process can deviate considerably from ideal mixing and lead to the formation of a cool gas-fog mixture which disperses asa heavy gas. The new algorithm reduces the calculation time necessary to compute-the composition, temperature, and density of the resulting mixture. The results compare very well with experimental data presented by Schotte.