(81aq) Hydrogen Disposal Flare System Hazard Identification and Mitigation Analysis

The Air Force Research Laboratory (AFRL), Propulsion Directorate of Edwards AFB, CA recently conducted a hazard assessment on a hydrogen flare system in preparation for an upcoming turbopump test. These turbopump operations required the disposal of large quantities of liquid and gaseous hydrogen through a commercial flare system to prevent the formation of an explosive environment. As part of this hazard assessment, each major step in the operational process was evaluated for the formation of a potential hazard by looking at each associated failure mode and the resulting effect on personnel and facilities. Evaluation of each operational step was conducted in a Process Failure Modes and Effects Analysis (PFMEA) that identified the probability and severity of the identified effects and associated hazards. If the probability and severity were unacceptable, mitigating steps were applied until the overall risks were reduced to acceptable levels. The results of this process were incorporated into both the system design and the operational procedures prior to test stand activation with hydrogen. This paper outlines the following results of the PFMEA processes: Identification of the effects/hazards, finding of available risk-mitigating techniques, and implementation of these techniques used for the mitigation of the identified hazards. The majority of all identified flare system effects were categorized into four main groups: Internal explosions, obstructions, external explosions, and maintenance degradation. AFRL's test team took a number of corrective actions towards mitigating both the probability and severity of the identified hazards that could be controlled and minimized. This paper discusses the installation on the flare system of purge system status alarms, oxygen monitoring systems, determination of appropriate purge requirements, incorporation of a triple redundant flare ignition system with status indicators, and a number of other hazard risk mitigation techniques.