Refinery accidents were analyzed, combining data from the accident database ENSAD with information on refinery configuration. Refinerieswere also assigned to four clusters reflecting different operating practices (USA, Europe, Russia, Other). The main objectives were to calculate cluster accident frequencies and trends, assess a potential relation between the units present in a refinery and the accident risk, and compare cluster differences in accident frequencies and consequences. Although mean accident frequencies were highest in the clusters USA and Europe, their trend parameters were lower than for the other clusters, indicating a smaller increase over time. The hazard coefficients of the classes H3 and H2 contributed most to the observed accident frequencies. The fatality and injury rates as well as corresponding maximum consequences were highest in the clusters Other and USA, respectively. In summary, refinery configuration and regional differences reflecting the mode of operation are important factors potentially affecting overall refinery risk.

Comparative assessment of accident risks in the energy sector is a key aspect in a comprehensive evaluation of sustainability and energy security concerns. Safety performance of energy systems can have important implications on the environmental, economic and social dimensions of sustainability as well as availability, acceptability and accessibility aspects of energy security. Therefore, this study provides a broad comparison of energy technologies based on the objective expression of accident risks for complete energy chains. For fossil chains and hydropower the extensive historical experience available in PSI's Energy-related Severe Accident Database (ENSAD) is used, whereas for nuclear a simplified probabilistic safety assessment (PSA) is applied, and evaluations of new renewables are based on a combination of available data, modeling, and expert judgment. Generally, OECD and EU 27 countries perform better than non-OECD. Fatality rates are lowest for Western hydropower and nuclear as well as for new renewables. In contrast, maximum consequences can be by far highest for nuclear and hydro, intermediate for fossil, and very small for new renewables, which are less prone to severe accidents. Centralized, low-carbon technology options could generally contribute to achieve large reductions in CO2-emissions; however, the principal challenge for both fossil with Carbon Capture and Storage and nuclear is public acceptance. Although, external costs of severe accidents are significantly smaller than those caused by air pollution, accidents can have disastrous and long-term impacts. Overall, no technology performs best or worst in all respects, thus tradeoffs and priorities are needed to balance the conflicting objectives such as energy security, sustainability and risk aversion to support rationale

We analyze the risk of severe fatal accidents causing five or more fatalities and for nine different activities covering the entire oil chain. Included are exploration and extraction, transport by different modes, refining and final end use in power plants, heating or gas stations. The risks are quantified separately for OECD and non‐OECD countries and trends are calculated. Risk is analyzed by employing a Bayesian hierarchical model yielding analytical functions for both frequency (Poisson) and severity distributions (Generalized Pareto) as well as frequency trends. This approach addresses a key problem in risk estimation—namely the scarcity of data resulting in high uncertainties in particular for the risk of extreme events, where the risk is extrapolated beyond the historically most severe accidents. Bayesian data analysis allows the pooling of information from different data sets covering, for example, the different stages of the energy chains or different modes of transportation. In addition, it also inherently delivers a measure of uncertainty. This approach provides a framework, which comprehensively covers risk throughout the oil chain, allowing the allocation of risk in sustainability assessments. It also permits the progressive addition of new data to refine the risk estimates. Frequency, severity, and trends show substantial differences between the activities, emphasizing the need for detailed risk analysis.

This study compared severe accident risks of fossil energy chains (coal, oil and natural gas), based on the historical experience contained in the comprehensive database ENSAD. Considered risk indicators focused on human health impacts, i.e., fatality rates and maximum consequences were calculated for a broad range of country groups. Generally, expected fatality rates were lowest for natural gas, intermediate for oil and highest for coal. Concerning maximum consequences of a single accident, natural gas also performed best, followed by coal, whereas accidents in the oil chain can claim significantly more fatalities. In general, OECD and EU 27 ranked top, while non-OECD countries and China in the case of coal were worst. The consideration of numerous additional country groups enabled a more detailed differentiation within the main bounding groups. Furthermore, differences among country groups are distinctly decreasing from coal to oil and natural gas, both for fatality rates and maximum consequences. The use of import adjusted-fatality rates indicates that fatality risks in supply countries are an essential aspect to understand how specific risk reduction strategies may affect other components of energy security, and thus tradeoffs and compromises are necessary. Finally, the proposed fatality risk score for fossil chains (FRSF) allows a comparison of the combined accident risk for the considered fossil energy chains across individual countries, which can be visualized using risk mapping.

The oil spill in the Gulf of Mexico that followed the explosion of the exploration platform Deepwater Horizon on 20 April 2010 was the largest accidental oil spill so far. In this paper we evaluate the risk of such very severe oil spills based on global historical data from our Energy-Related Severe Accident Database (ENSAD) and investigate if an accident of this size could have been "expected". We also compare the risk of oil spills from such accidents in exploration and production to accidental spills from other activities in the oil chain (tanker ship transport, pipelines, storage/refinery) and analyze the two components of risk, frequency and severity (quantity of oil spilled) separately. This detailed analysis reveals the differences in the structure of the risk between different spill sources, differences in trends over time and it allows in particular assessing the risk of very severe events such as the Deepwater Horizon spill. Such top down risk assessment can serve as an important input to decision making by complementing bottom up engineering risk assessment and can be combined with impact assessment in environmental risk analysis.

Risks of severe accidents provide an essential element in the assessment of major centralized energy technologies including fossil (coal, oil, natural gas), hydro and nuclear power, but also for new renewable technologies because of their increasing market share. Comparative risk indicators are presented for human health effects (e.g. fatality rates), risk aversion expressed as maximum consequences of a single accident, and environmental impacts (e.g. land and water contamination). In the second part scenario analysis, based on Multi-Criteria Decision Analysis, is applied to evaluate the performance of these risk indicators under different stakeholder perspectives. In summary, the results indicate that climate policy goals and reduction of severe accidents risks could be achieved together, although specific stakeholder preferences (e.g. risk aversion) may lead to certain restrictions in the available technology portfolio.

Attosecond angular streaking is a new technique to achieve unsurpassed time accuracy of only a few attoseconds. Recently this has been successfully used to set an upper limit on the electron tunneling delay time in strong laser field ionization. The measurement technique can be modeled with either the time-dependent Schrödinger equation (TDSE) or a more simple semiclassical approach that describes the process in two steps in analogy to the three-step model in high harmonic generation (HHG): step one is the tunnel ionization and step two is the classical motion in the strong laser field. Here we describe in detail a semiclassical model which is based on the ADK theory for the tunneling step, with subsequent classical propagation of the electron in the laser field. We take into account different ellipticities of the laser field and a possible wavelength-dependent ellipticity that is typically observed for pulses in the two-optical-cycle regime. This semiclassical model shows excellent agreement with the experimental result.

We use attosecond angular streaking to place an intensity-averaged upper limit of 12 attoseconds on the tunneling delay time in strong field ionization of a helium atom. This is much shorter than the Keldysh time.

Unter dem Einfluss starker Laserfelder kann das Potential eines Atomkerns so stark verformt werden, dass die Elektronen sich durch Tunnelionisation vom Atom lösen. Die Frage nach der Dauer dieses Prozesses ist immer wieder Gegenstand von Diskussionen. Jüngst ist unserer Gruppe an der ETH Zürich eine zeitliche Messung mit Attosekundengenauigkeit gelungen. Das Ergebnis: Null.

We used attosecond angular streaking to measure attosecond ionization dynamics in the non-adiabatic tunneling regime of helium using slightly elliptically polarized 5.9 fs pulses with a peak intensity ranging from 2.3 to 3.5 x 1014 W/cm2 (corresponding to a Keldysh parameter variation of 1.45 to 1.17). With our technique we could demonstrate intensityindependent “instantaneous” ionization with an accuracy of 50 as. Numerical simulations based on the time-dependent Schrödinger equation confirm such ionization behavior with no distinct electron wave packets. This implies that we would not expect a tunneling time or multi-photon ionization delay in the ionization dynamics

In this paper we measured an "instantaneous" intensity independent tunneling delay time with an upper limit of 12 as [3]. Our experiments have given us direct access to the tunneling delay time with an unprecedented time accuracy of a few tens of attoseconds using attosecond angular streaking. Our results give strong indication that there is no real tunneling delay time and we expect that this will shed some light on the ongoing theoretical discussion on tunneling time and tunnel ionization in strong field physics.

We use attosecond angular streaking to place an intensity-averaged upper limit of 12 attoseconds on the tunneling delay time in strong field ionization of helium. This is far shorter than most tunneling times discussed before.

We report experimental measurements of high-order harmonic spectra generated in Ar using a carrier-envelope-offset (CEO) stabilized 12 fs, 800 nm laser field and a fraction (less than 10%) of its second harmonic. Additional spectral peaks are observed between the harmonic peaks, which are due to interferences between multiple pulses in the train. The position of these peaks varies with the CEO and their number is directly related to the number of pulses in the train. An analytical model, as well as numerical simulations, support our interpretation.

It is well established that electrons can escape from atoms through tunneling under the influence of strong laser fields, but the timing of the process has been controversial and far too rapid to probe in detail. We used attosecond angular streaking to place an upper limit of 34 attoseconds and an intensity-averaged upper limit of 12 attoseconds on the tunneling delay time in strong field ionization of a helium atom. The ionization field derives from 5.5-femtosecond-long near-infrared laser pulses with peak intensities ranging from 2.3 × 1014 to 3.5 × 1014 watts per square centimeter (corresponding to a Keldysh parameter variation from 1.45 to 1.17, associated with the onset of efficient tunneling). The technique relies on establishing an absolute reference point in the laboratory frame by elliptical polarization of the laser pulse, from which field-induced momentum shifts of the emergent electron can be assigned to a temporal delay on the basis of the known oscillation of the field vector.

Ultrashort measurement-time resolution is traditionally obtained in pump–probe experiments, for which two ultrashort light pulses are required; the time resolution is then determined by the pulse duration. But although pulses of subfemtosecond duration are available, so far the energy of these pulses is too low to fully implement the traditional pump–probe technique. Here, we demonstrate ‘attosecond angular streaking’, an alternative approach to achieving attosecond time resolution. The method uses the rotating electric-field vector of an intense circularly polarized pulse to deflect photo-ionized electrons in the radial spatial direction; the instant of ionization is then mapped to the final angle of the momentum vector in the polarization plane. We resolved subcycle dynamics in tunnelling ionization by the streaking field alone and demonstrate a temporal localization accuracy of 24 as r.m.s. and an estimated resolution of ≈200 as. The demonstrated accuracy should enable the study of one of the fundamental aspects of quantum physics: the process of tunnelling of an electron through an energetically forbidden region. A technique that uses the rotating electric-field vector of a circularly polarized laser pulse as a ‘clock’ provides a fresh approach to measuring electron dynamics with attosecond time resolution.

The intensity distribution in momentum space of He, ionized with circularly polarized ultrashort laser pulses, shows a clear dependence on the carrier-envelope phase of the pulse. A numerical simulation reproduces the characteristics found in the experiment.

Intense 5.1-fs pulses were generated through filamentation in argon while maintaining the CEO phase. The benefits to CEO phase control of using the generated octave-spanning spectrum for single shot f-2f spectral interferometry are also presented.

Intense 5.1 fs CEO (carrier envelope offset) phase stable pulses were generated through two-fold filamentation in a noble gas at atmospheric pressure. The preservation of the CEO phase during the filamentation process was investigated. We show that generating these short pulses using filaments is not detrimental for the CEO phase stabilization, and that the more than one octave-spanning spectrum intrinsically generated by the process is feasible, and offers certain benefits, for direct use in single shot f-2f spectral interferometry.

Intense 5.1-fs pulses were generated through filamentation in argon. The CEO (carrier envelope offset) phase control is investigated of using the intense, octave-spanning spectrum generated during this process, directly for single shot f-2f spectral interferometry.