Abstract: The present invention provides a calculated protective action zone, such as a safety zone which can be used for evacuation purposes, using simplified input methods and systems and simplified internal calculation methods to model the chemical data. Yet, it uniquely retains a significantly high degree of accuracy corresponding to more expensive, complicated, time consuming state of the art models for the chemical releases as described above. It may be used for dense gas dispersion and other releases. To accomplish this, the methods and systems of the present invention may use a post-processed modeled data base and selected multi-variable equations combined with qualitative and quantitative input and may include default values for various factors. The system may include a small, hand-held electronic calculating element such as a palmtop computer, with extended battery life for portability, although it is equally applicable for high end processors on stationary computers.