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| 2. |
- Back, Pär-Erik, 1961, et al.
(författare)
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Value of Information Analysis in Remedial Investigations
- 2007
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 36:6, s. 486-493
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Tidskriftsartikel (refereegranskat)abstract
- Site investigations of contaminated land are associated with high costs. From a societal perspective, just enough economic resources should be spent on investigations so that society's limited resources can be used optimally. The solution is to design investigation programs that are cost-effective, which can be performed using Value of Information Analysis (VOIA). The principle of VOIA is to compare the benefit at the present state of knowledge with the benefit that is expected after an investigation has been performed. A framework for VOIA of site investigations is presented based on Bayesian risk-cost-benefit decision analysis. The result is an estimate of the value of an investigation program, and for specific problems, the optimal number of samples. The main strength of the methodology is that it promotes clear thinking and forces the decision-maker to reflect on issues that otherwise would be ignored. The main weakness is the complexity of VOIA models.
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| 3. |
- Hernqvist, Lisa, 1968, et al.
(författare)
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A statistical grouting decision method based on water pressure tests for the tunnel construction stage - A case study
- 2013
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798. ; 33, s. 54-62
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Tidskriftsartikel (refereegranskat)abstract
- In tunnel construction, a common method to reduce water inflow is pre-grouting. There is a need for a practical method, based on information about the rock mass, to assess whether inflow will remain below the set inflow requirements q(A), to form the basis for deciding at each tunnel front whether to grout or to proceed with excavation. The aim of this paper is to present a method for use at the tunnel construction stage to decide whether to grout or not. On the one hand, the aim is for it to be practical to use whilst on the other hand it must be scientifically founded and independent of the experience of the person responsible for making the decision. The input for the decision method consists of evaluated results from water pressure tests in a small number of tunnel front boreholes in combination with the specified inflow requirement for the tunnel. The method is statistically supported and is based on an equation for inflow prediction. To illustrate the decision method, it was applied to a 1 km section of the Onkalo Tunnel (built for Finland's spent nuclear fuel repository). The decision method results were compared with the results of decisions taken during the construction of the tunnel section and agreement between the two was investigated. The main findings of the paper are: For the case study tunnel section the same decisions would for the most part have been reached using the suggested decision method compared to the method that was actually used. The tunnel achieves the inflow requirement, indicating that the decision method would have led to satisfactory results. Further, a key advantage of the method is that it is transparent and scientifically based. Finally, one constraint on the method is that it is not recommended if a large part of the flow takes place in flow channels or if the probe holes are unlikely to intersect the water-bearing fractures. To increase the understanding of grouting in the Onkalo Tunnel, the grouting pressures were compared to the rock stress and a study was made of grout take in relation to the estimated hydraulic apertures of each grouting fan and to the expected grout penetrability.
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| 4. |
- Landquist, Hanna, 1984, et al.
(författare)
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A fault tree model to assess probability of contaminant discharge from shipwrecks
- 2014
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Ingår i: Marine Pollution Bulletin. - : Elsevier BV. - 0025-326X .- 1879-3363. ; 88:1-2, s. 239-248
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Tidskriftsartikel (refereegranskat)abstract
- Shipwrecks on the sea floor around the world may contain hazardous substances that can cause harm to the marine environment. Today there are no comprehensive methods for environmental risk assessment of shipwrecks, and thus there is poor support for decision-making on prioritization of mitigation measures. The purpose of this study was to develop a tool for quantitative risk estimation of potentially polluting shipwrecks, and in particular an estimation of the annual probability of hazardous substance discharge. The assessment of the probability of discharge is performed using fault tree analysis, facilitating quantification of the probability with respect to a set of identified hazardous events. This approach enables a structured assessment providing transparent uncertainty and sensitivity analyses. The model facilitates quantification of risk, quantification of the uncertainties in the risk calculation and identification of parameters to be investigated further in order to obtain a more reliable risk calculation.
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| 5. |
- Landquist, Hanna, 1984, et al.
(författare)
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Bayesian updating in a fault tree model for shipwreck risk assessment
- 2017
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 590, s. 80-91
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Tidskriftsartikel (refereegranskat)abstract
- Shipwrecks containing oil and other hazardous substances have been deteriorating on the seabeds of the world for many years and are threatening to pollute the marine environment. The status of the wrecks and the potential volume of harmful substances present in the wrecks are affected by a multitude of uncertainties. Each shipwreck poses a unique threat, the nature of which is determined by the structural status of the wreck and possible damage resulting from hazardous activities that could potentially cause a discharge. Decision support is required to ensure the efficiency of the prioritisation process and the allocation of resources required to carry out risk mitigation measures. Whilst risk assessments can provide the requisite decision support, comprehensive methods that take into account key uncertainties related to shipwrecks are limited. The aim of this paper was to develop a method for estimating the probability of discharge of hazardous substances from shipwrecks. The method is based on Bayesian updating of generic information on the hazards posed by different activities in the surroundings of the wreck, with information on site-specific and wreck-specific conditions in a fault tree model. Bayesian updating is performed using Monte Carlo simulations for estimating the probability of a discharge of hazardous substances and formal handling of intrinsic uncertainties. An example application involving two wrecks located off the Swedish coast is presented. Results show the estimated probability of opening, discharge and volume of the discharge for the two wrecks and illustrate the capability of the model to provide decision support. Together with consequence estimations of a discharge of hazardous substances, the suggested model enables comprehensive and probabilistic risk assessments of shipwrecks to be made.
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| 6. |
- Landquist, Hanna, 1984, et al.
(författare)
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Environmental Risk Assessment of Shipwrecks: a fault-tree model to assess probability of contaminant release
- 2012
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Ingår i: SETAC North America 33rd Annual Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- RP247 Environmental risk assessment for shipwrecks: a fault-tree model to assess probability of contaminant release H. Landquist, I. Hassellov, Chalmers University of Technology / Shipping and Marine Technology; L. Rosen, Chalmers University of Technology / Civil and Environmental Engineering; F. Lindgren, Chalmers University of Technology / Shipping and Marine Technology; I. Dahllof, The University of Gothenburg; T. Norberg, Chalmers University of Technology / Mathematical Sciences; A. Lindhe, Chalmers University of Technology / Civil and Environmental Engineering. Shipwrecks lying on the sea floor around the world may contain hazardous substances which can cause harm to the maritime environment. Today there are no comprehensive methods for environmental risk assessment of shipwrecks and thus there is poor support for decision-making on prioritisation of mitigation measures. The purpose of this study has been to develop a framework for risk assessment of potentially polluting shipwrecks, focusing on a detailed probabilistic assessment of the release of hazardous substances. The framework is based on international standards for risk management and the assessment of the probability for release was done using fault-tree analysis. This approach enables a structure assessment and provides an excellent possibility of uncertainty and sensitivity analysis. The fault tree model was tested by groups of experts in the field of maritime administration, maritime archaeology and in other areas to validate the method. The developed framework facilitates risk assessment of potentially polluting shipwrecks and can support risk management as well as provide well founded input for decision-making. In particular the fault-tree analysis provides a quantitative method for assessing the probability of leakage and can facilitate uncertainty and sensitivity analyses.
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| 7. |
- Landquist, Hanna, 1984, et al.
(författare)
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Expert elicitation for deriving input data for probabilistic risk assessment of shipwrecks
- 2017
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Ingår i: Marine Pollution Bulletin. - : Elsevier BV. - 0025-326X .- 1879-3363. ; 125:1-2, s. 399-415
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Tidskriftsartikel (refereegranskat)abstract
- The necessity of having a process in place for adequate risk assessment of shipwrecks that pose a threat to the marine environment is today internationally acknowledged. However, retrieving the desired data for such a risk assessment can prove challenging. One means of addressing this problem is to make use of experts' knowledge and experience. The purpose of this paper is therefore to present and analyse data for risk assessment of shipwrecks derived by expert elicitation. The main outcome is the experts' estimations of (i) the generic probability of an opening in a shipwreck due to the occurrence of a number of activities and (ii) estimations of the degree to which site-specific and wreck-specific indicators affect the probability of opening. Results show that the derived information is applicable in probabilistic shipwreck risk assessment and that the VRAKA framework now contains needed information for integrating generic and site-specific information using Bayesian updating.
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| 8. |
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| 9. |
- Lindhe, Andreas, 1981, et al.
(författare)
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Approximate dynamic fault tree calculations for modelling water supply risks
- 2012
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Ingår i: Reliability Engineering and System Safety. - : Elsevier BV. - 0951-8320. ; 106:2012, s. 61-71
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Tidskriftsartikel (refereegranskat)abstract
- Traditional fault tree analysis is not always sufficient when analysing complex systems. To overcome the limitations dynamic fault tree (DFT) analysis is suggested in the literature as well as different approaches for how to solve DFTs. For added value in fault tree analysis, approximate DFT calculations based on a Markovian approach are presented and evaluated here. The approximate DFT calculations are performed using standard Monte Carlo simulations and do not require simulations of the full Markov models, which simplifies model building and in particular calculations. It is shown how to extend the calculations of the traditional OR- and AND-gates, so that information is available on the failure probability, the failure rate and the mean downtime at all levels in the fault tree. Two additional logic gates are presented that make it possible to model a system’s ability to compensate for failures. This work was initiated to enable correct analyses of water supply risks. Drinking water systems are typically complex with an inherent ability to compensate for failures that is not easily modelled using traditional logic gates. The approximate DFT calculations are compared to results from simulations of theorresponding Markov models for three water supply examples. For the traditional OR- and AND-gates, and one gate modelling compensation, the errors in the results are small. For the other gate modelling compensation, the error increases with the number of compensating components. The errors are, however, in most cases acceptable with respect to uncertainties in input data. The approximate DFT calculations improve the capabilities of fault tree analysis of drinking water systems since they provide additional and important information and are simple and practically applicable.
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| 10. |
- Lindhe, Andreas, 1981, et al.
(författare)
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Cost-effectiveness analysis of risk-reduction measures to reach water safety targets
- 2011
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 45:1, s. 241-253
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Tidskriftsartikel (refereegranskat)abstract
- Identifying the most suitable risk-reduction measures in drinking water systems requires a thorough analysis of possible alternatives. In addition to the effects on the risk level, also the economic aspects of the risk-reduction alternatives are commonly considered important. Drinking water supplies are complex systems and to avoid sub-optimisation of risk-reduction measures, the entire system from source to tap needs to be considered. There is a lack of methods for quantification of water supply risk reduction in an economic context for entire drinking water systems. The aim of this paper is to present a novel approach for risk assessment in combination with economic analysis to evaluate risk-reduction measures based on a source-to-tap approach. The approach combines a probabilistic and dynamic fault tree method with cost-effectiveness analysis (CEA). The developed approach comprises the following main parts: (1) quantification of risk reduction of alternatives using a probabilistic fault tree model of the entire system; (2) combination of the modelling results with CEA; and (3) evaluation of the alternatives with respect to the risk reduction, the probability of not reaching water safety targets and the cost-effectiveness. The fault tree method and CEA enable comparison of risk-reduction measures in the same quantitative unit and consider costs and uncertainties. The approach provides a structured and thorough analysis of risk-reduction measures that facilitates transparency and long-term planning of drinking water systems in order to avoid sub-optimisation of available resources for risk reduction.
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