Advances in Determining the Flammability Limits of Combustible Gases: Standard Methods, Temperature–Pressure Effects, Emerging Fuels, and Outlook

The flammability limits (FLs) of combustible gases are critical parameters for assessing fire and explosion risks in industrial processes. This review provides a comprehensive and up-to-date synthesis of recent advances in the determination and interpretation of FL, with a particular focus on conditions of elevated temperature and pressure that are increasingly relevant in emerging energy systems. Compared to previous reviews, this paper offers three key contributions: (1) it compiles the latest experimental data and methods for FL determination under nonambient conditions, highlighting methodological differences across international standards (e.g., ASTM, EN, GB) and their implications for reproducibility; (2) it critically examines the flammability behavior of next-generation fuels─including hydrogen, ammonia, and their mixtures─while identifying the limitations of conventional predictive tools such as Le Chatelier’s law; (3) it proposes prioritized future research directions based on the urgency of addressing experimental, regulatory, and kinetic knowledge gaps. By bridging experimental findings, standardization challenges, and industrial safety needs, this review aims to guide future efforts in developing safer, more accurate, and application-driven approaches to FL evaluation.