Protecting the public from an airborne hazardous chemical release requires that appropriate protective actions be selected quickly. When deciding whether to recommend evacuation or shelter-in-place, decision makers must weigh the interaction of numerous factors that characterize the release, the meteorological conditions, and the populations that may be affected. This article examines the components of the protective action decision process and describes steps that should be taken in a planning context to prepare for efficient decision making during an emergency. Methods of organizing information to facilitate decision making are identified, and a model useful for detailed analysis of specific emergency scenarios is described. (C) 2004 Elsevier B.V. All rights reserved.