With the release of the technical report, ISA-TR84.00.07-2018, Guidance on the Evaluation of Fire, Combustible Gas, and Toxic Gas System Effectiveness, on performance-based design of fire and gas detection systems for process industries, risk-based techniques for detector placement have become prevalent in fire and gas system (FGS) design. While the technical report addresses designing the FGS based on the users risk profile and performance requirements, it does not provide any guidance on implementing the FGS lifecycle. The Performance-based Fire and Gas Systems Engineering Handbook provides a thorough overview of the FGS design lifecycle presented in the technical report, examining each lifecycle phase and the practical activities required to develop an FGS design. In addition to discussing the design process, this handbook provides valuable appendices containing data for FGS system risk analysis, FGS risk grading procedures and a discussion of the FGS mapping techniques used to verify the achievement of the newly defined coverage targets.