This book presents a theoretical framework for the quantitative calculation of casualties and damage from jet fires caused by high-pressure gas leaks in pressure vessels or pipelines. The framework incorporates gas leakage models, combustion dynamics models, thermal radiation models, and thermal damage criteria. It conducts sensitivity and uncertainty analyses for the input parameters of the theoretical framework. The robustness of the theoretical framework is verified through field tests. Ultimately, the theoretical framework is used to quantitatively analyze the accidents involving jet fires due to the rupture of natural gas transmission pipelines. The sub-models within the theoretical framework are developed using the fundamental principles of thermodynamics, combustion, fluid dynamics, and heat transfer, and have been validated by small-scale laboratory tests. However, the theoretical framework receives the validation of field tests and real-world case studies. The theoretical deductions in this book offer significant guidance for scaling up from the laboratory experiments to field applications. The book is intended for anyone interested in understanding the risks associated with gas leaks and jet fires. The methodology enables the calculation of hazards for specific processes in isolation or their integration to assess overall consequences.