Book Description

The Ocean Breeze-Dry Gulch (OB/DG) atmospheric dispersion model is used extensively by the USAF Air Weather Service for predicting the hazard zone resulting from an accidental toxic chemical spill. This model is an empirical and statistical model derived from the Ocean Breeze, Dry Gulch, and Prairie Grass experiments conducted in the late 50's and early 60's. the USAF Scientific Advisory Board recently recommended that the OB/DG model be replaced with a current state-of-the-art dispersion model. This report represents the first step toward evaluating the OB/DG model and finding a suitable replacement. The hazard distances computed from the OB/DG model for different meteorological conditions are compared with the hazard distances calculated with the Shell Oil co. SPILLS model and a modified version of the model. In the modified Shell model, the discrete Pasquill stability categories are replaced with a continuous stability parameter, and surface roughness is included as a factor in defining the rate of cloud growth. The OB/DG model agrees quite favorably with the modified Shell model except at low wind speeds where it predicts considerably lower distances. The Shell model calculates generally larger distances and much greater fluctuations with wind speed, and therefore does not agree as well with the OB/DG model. The similarity in output between the modified Shell model and the OB/DG model lends support to further consideration of this model as a possible replacement to the OB/DG model.