Analyses to support development of risk-informed separation distances for hydrogen codes and standards.

Abstract

The development of a set of safety codes and standards for hydrogen facilities is necessary to ensure they are designed and operated safely. To help ensure that a hydrogen facility meets an acceptable level of risk, code and standard development organizations are utilizing risk-informed concepts in developing hydrogen codes and standards.This report describes the application of a risk-informed process to establish one code requirement: the separation distances between a bulk gaseous hydrogen storage facility and the public at large. A risk-informed process, as opposed to a risk-based process, utilizes risk insights obtained from quantitative risk assessments (QRAs) combined with other considerations to establish code requirements. The QRAs are used to identify and quantify scenarios for the unintended release of hydrogen, identify the significant risk contributors at different types of hydrogen facilities, and to identify potential accident prevention and mitigation strategies to reduce the risk to acceptable levels. Other considerations used in this risk-informed process include the results of deterministic analyses of selected accidents scenarios, the frequency of leakage events at hydrogen facilities, and the use of safety margins to account for uncertainties.The risk-informed approach results in a defensible technical basis for specifying separation distances for hydrogen facilities. The results also demonstrate that separation distances for hydrogen facilities can be significantly affected by facility design parameters such as the system operating pressure and available mitigating features, component leakage frequency data, and the selected consequence measures and risk guidelines used in the evaluation. The separation distances generated in this report have been accepted for incorporation into revisions of several hydrogen facility standards.iv

Early-stage quantitative risk assessment to support development of codes and standard requirements for indoor fueling of hydrogen vehicles.

“…NFPA 2 selected a fatality risk guideline of 2×10 −5 /yr for members of the public for use in the separation distance work documented in [7]. This value is consistent with the risk at existing gasoline stations, is in general agreement with criteria being utilized in several countries, and is approximately twice the value recommended by European Industrial Gas Association (EIGA) for hydrogen facilities.…”

“…A risk-informed approach had previously been used to establish the separation distances for bulk gaseous hydrogen storage areas [6,7]. The goal of the current work was to extend this approach in a way that could be used to inform codes and standards for indoor fueling, and to provide an initial assessment of fatality risks for a generic system.…”

“…For indoor hydrogen applications the unacceptable level of risk is an AIR greater than 1×10 −4 /yr for a worker or a fatality rate greater than 1×10 −5 /yr for a member of the public; these risk acceptance criteria were established by the International Energy Agency (IEA) and were used in previous work [7]. NFPA 2 selected a fatality risk guideline of 2×10 −5 /yr for members of the public for use in the separation distance work documented in [7].…”

“…However, sources from commercial operations may be used as a baseline for a frequency analysis. SAND2009-0874 [7] documents a Bayesian approach for predicting the frequency of leaks from hydrogen components using the power function relationship in Equation 3. This approach generated leak frequency distributions for each leak size, for each component in the analysis.…”

Safety of Hydrogen Systems Installed in Outdoor Enclosures

“…Although some work has been done to define leak probabilities and credible leak sizes (LaChance et al 2009), more work is needed.…”