Challenges to improve confidence level of risk assessment of hydrogen technologies

Abstract

Making large-scale distribution and use of hydrogen successful will require adequate risk control. In turn, control requires risk assessment. Despite many years of experience, in general, methods to determine risk lack still robustness: results being much too dependent on choices made by the analyst due to uncertainties, lack of data and different views. This can create frustration amongst people dependent on results. HySafe and other groups work in the right direction. This paper will review existing methodological weaknesses, current improvements in e.g. the context of developing risk-informed standards and emphasize the challenges to raise quality further. The Standard Benchmark Exercise Problems, SBEPs, were a good start but shall produce recommendations for CFD use or even certification of models. Scenario generation shall take advantage of historical incident data and newer methods such as Bayesian belief nets, and cover the entire hydrogen distribution system and not only garages and refueling stations; the analyses shall more explicitly present confidence intervals on results. Knowledge gaps on e.g. ignition probability shall be defined and filled.

Introduction

The perspectives for hydrogen as an energy carrier look great. The world feels a real need to reduce carbon dioxide emissions and to become less dependent on oil. There will be however a transition period of considerable duration in which perception of the hazards of hydrogen may develop one way or the other.

Hydrogen is not toxic, but its eagerness to combine with oxygen can turn into a hazard. Safety records of hydrogen processing in process industry are generally well. On the other hand, introduction of production, storage, transportation and use on the widespread scale required to replace present hydrocarbons will undoubtedly bring incidents. The large scale introduction will unavoidably bring many people in touch with the technology and standards of engineering are not everywhere at the high level of present day petrochemical complexes. The energy carrier is needed not only in industry districts but also in densely populated areas. So, in incidents people may become hurt. Experience shows that one large scale incident with fatalities can throw a new technology backwards for years. The psychological impact of risk, once shown somewhere to occur and witnessed by TV is difficult to erase. Old, misunderstood stories like the one on the Hindenburg will be remembered by the media after an accident happened and will add to fear. Such situation will be worsened if ‘experts’ contradict each other, express misbelieve in models or show uncertainty.

For adequate risk control it will pay to invest in reliable risk analysis methodology. It will help to improve operational safety by designing and installing preventive and protective measures where appropriate and economical, also embodied by standards and codes. Risk-informed standards form key to permitting hydrogen refueling stations [1]. In addition for the purpose of public safety risk analysis will help in land use planning, licensing of installations and emergency planning; the latter with respect to self rescue and effective deployment of emergency response units.

The HySafe community already has taken initiatives in drafting standards, educating and training people, performing risk studies and organizing three ICHS safety conferences. There have been numerous papers addressing an aspect of hydrogen risk but there are few attempts to perform overall risk assessments. The reports on risk assessment methods (DNV Research & Innovation, 2008 [2]), and risk studies on refueling stations e.g. IEA [3] and other facilities e.g. [4] are certainly a good step, but cannot be considered matured. Moreover, to remain critical remains necessary as quality standards for risk assessments have not become common yet. Below will be shown why vigilance is needed.