The availability, collection, and proper application of accurate and complete Basic Design Data (BDD) are essential aspects of Loss Prevention practice. This article presents a case study to illustrate the importance of properly collecting and applying accurate BDD when designing Fired Equipment. In the case study presented, an explosion occurred inside a newly installed Catalytic Thermal Oxidizer (CatOx) shortly after initial start-up. Root cause investigation revealed that the project team, in the design and specification of the CatOx control system, had misapplied the BDD. Consequently, this led to operation of the CatOx within the flammability envelope of the particular system, resulting in an explosion. This article provides a brief discussion of BDD and its application. The case study is presented in detail using flammability diagrams for the system to demonstrate where the CatOx was intended to operate versus where it actually operated during the incident. The discussion leads the reader through the incident lifecycle, from the conceptual design of the CatOx, through the Engineering and Commissioning phases, and into the Incident Investigation. The conclusions drawn from this incident further emphasize the value of accurate BDD to the design and operation of Fired Equipment.