An Incident Investigation system based on a combination of Fault Tree Analysis logic and the Deming Principles of Systems and Quality was developed during a three-year period. The system was given an excellent test in the investigation of the explosion of a tank car filled with methacrylic acid. In this case, the Event Tree constructed during the investigation was easily converted into a Fault Tree. The Fault Tree so constructed was then used to evaluate the effectiveness of proposed corrective changes to the production, loading, and analytical systems before the changes were actually implemented. By making use of these tools to guide the addition of feedback loops (“And” Gates in fault Tree terminology), the intrinsic safety of the methacrylic acid production and shipping system was greatly enhanced at a relatively low cost.