The paper shows how fault tree analysis (FTA) of a process system can be used to compare the relative effectiveness of various equipment, design, and operating measures for release prevention and protection applied to process streams. It also shows how the costs of various safety control measures can be estimated and combined with accident frequency estimates to provide a basis for efficiently allocating financial resources for safety. In addition to the positive aspects of the methodology shown, limitations of the methodology and needs for future investigations are highlighted. Attempting to prevent and protect against an accidental or emergency release of a toxic gas or vapor is preferable to actions taken after such a release. Of the various formal, quantitative methods for estimating how releases might occur and their probability for process systems, FTA is being used more frequently. While there are current limitations to the method, due to a lack of adequate reliability data for process system components, it can still be used to provide valuable information to planners.