Ensuring the operational safety of gaseous fuel containers for hydrogen and natural gas vehicles requires robust and validated protective devices capable of responding reliably under diverse operating and accident scenarios. This paper presents the design considerations, test methodology, and validation outcomes for safety subsystems integrated into modern compressed gas storage vessels, with emphasis on pressure relief devices (PRDs), thermal protection systems, and valve assemblies. Drawing on experimental insights from previous studies of hydrogen and natural gas fueling systems and fire-resistance assessments, the work defines safety-critical conditions such as rapid temperature rise during bonfire exposure, localized flame impingement, over-pressurization from fast filling, and mixed-gas operation. A comprehensive validation protocol was established, combining standardized regulatory tests with additional stress profiles replicating service-realistic environments. These included thermal cycling of fusible alloy elements, repeated actuation of burst disks, endurance cycling of valves under hydrogen and HCNG atmospheres, and fault-injection scenarios such as blocked vent paths. Particular attention was given to triggering thresholds, repeatability, venting efficiency, and prevention of catastrophic vessel rupture. Results confirm that correctly dimensioned PRDs and venting configurations can maintain vessel integrity under extreme heat loads, but highlight the sensitivity of actuation timing to installation geometry and material aging. The study concludes with recommendations for integrated diagnostic approaches and predictive maintenance of safety devices in vehicle fleets. Overall, the findings provide a validated framework for implementing reliable, regulation-compliant protection systems that enable safe adoption of high-pressure hydrogen and natural gas storage in modern mobility.