Risk Reduction Potential of Accident Prevention and Mitigation Features

Quantitative Risk Assessment (QRA) can help to establish a set of design and operational requirements in hydrogen codes and standards that will ensure safe operation of hydrogen facilities. By analyzing a complete set of possible accidents in a QRA, the risk drivers for these facilities can be identified. Accident prevention and mitigation features can then be analyzed to determine which are the most effective in addressing these risk drivers and thus reduce the risk from possible accidents. Accident prevention features/methods such as proper material selection and preventative maintenance are included in the design and operation of facilities. Accident mitigation features are included to reduce or terminate the potential consequences from unintended releases of hydrogen. Mitigation features can be either passive or active in nature. Passive features do not require any component to function in order to prevent or mitigate a hydrogen release. Examples of passive mitigation features include the use of separation distances, barriers, and flow limiting orifices. Active mitigation features initiate when specific conditions occur during an accident in order to terminate an accident or reduce its consequences. Examples of active mitigation features include detection and isolation systems, fire suppression systems, and purging systems. A concept being pursued by the National Fire Protection Association (NFPA) hydrogen standard development is to take credit for prevention and mitigation features as a means to reduce separation distances at hydrogen facilities. By utilizing other mitigation features, the risk from accidents can be decreased and risk-informed separation distances can be reduced. This paper presents some preliminary QRA results where the risk reduction potential for several active and passive mitigation features was evaluated. These measures include automatic leak detection and isolation systems, the use of flow limiting orifices, and the use of barriers. Reducing the number of risk-significant components in a system was also evaluated as an accident prevention method. In addition, the potential reduction in separation distances if such measures were incorporated at a facility was also determined.