This engineering guide provides a methodology to define and quantify the fire development and ensuing conditions within the room of fire origin from the fire incipient stage through its full development. The approach presented in this guide was developed using the framework set forth in the SFPE Engineering Guide to Performance-Based Fire Protection. 2nd ed., Quincy, Mass.: National Fire Protection Association, 2007.) It consists of three distinct parts: 1. Approach selection 2. Input definition and data collection 3. Results computation Specifically, this guide was developed for use as a means to implement the requirements presented in Chapter 10 of the SFPE Engineering Guide to Performance-Based Fire Protection. However, material within this guide has broader applicability and is therefore not limited to performance-based design applications.