Problems reported by emergency response personnel in developing pre-emergency plans and making tactical decisions during hazardous materials transportation emergencies prompted the Safety Board to conduct this special investigation. The investigation disclosed a need to improve methods for predicting the expected behavior of hazardous materials in emergencies, for both preplanning and tactical uses. Existing information sources were found to be inadequate for these purposes. A method to improve the recording of hazardous materials behavior in accident investigations that will improve preplanning and tactical decisionmaking for hazardous materials emergencies was identified and has been adopted as a tentative accident reporting standard by the Safety Board for accidents involving hazardous materials. Immediate and potential uses for the standardized hazardous materials behavior maps are identified and implementation problems are discussed.