Quantitative Risk Analysis (QRA)
The objective of this Quantitative Risk Analysis are :
- Address the definition of important terms used in QRA study
- Identifies documents based on which QRA study to be carried out;
- Methodology in which QRA study will be carried out.
The Purpose of QRA study are:
- To assess the risks to personnel, assets, and production posed by the Facility and determine their significance. This will help to decide how best the risks can be reduced.
- To determine the acceptability of the calculated risk at the Facility and identification of the key risk contributors. Risk contributors shall be identified by source and location.
- Comparing risks of the design options being considered. This process facilitates the identification of design alternatives with minimal risk and enables the selection of the most optimal option based on considerations of risk and other technological and commercial factors.
- For risk prioritization and resource allocation for implementation of safety measures;
- Assess individual risks associated within the Facility.
- Evaluate the potential societal hazards linked to the set up.
- To critically evaluate the existing safeguards and determine their adequacy in relation to identified risk.
- The aim is to furnish precise and unequivocal suggestions for mitigating risks, if deemed necessary, in order to ensure that the risks associated with the Facility are managed within acceptable thresholds.
- Applying the principle of ALARP to demonstrate the Regulator Management that the risk levels are in the tolerable region and that the practicality of incorporating any additional risk reduction measures or potential design.
- Evaluating risk reduction measures by cost-benefit analysis, to help choose cost effective ways of reducing the risk. Changes is disproportionate to the benefit obtained.
Quantitative risk assessment (QRA) is a systematic approach utilized to analyze the potential risks associated with hazardous activities. The aim is to provide a rational evaluation of the risks significance, which can be used as input for decision-making processes. The QRA process is presented below in Figure
The following key activities are performed during QRA:
- Identification of Credible Accident Scenario.
- Based on the documents, the facility can be split into multiple isolatable sections (IS); For each IS, the inventory is calculated based on material properties and operating parameters
- The consequence modelling has been performed to evaluate the resulting effects of toxic effects if the accidents occur, and their impact on personnel. Estimation of the consequences of each possible event is performed.
- Frequency analysis assesses the probability of accidents occurring. The leak frequencies for each Isolatable Sections are obtained from relevant database.
- Risk modelling is performed to combine the results of consequence analysis and frequency analysis. Risk modelling is performed using DNV SAFETI software. The risk results are expressed in two forms:
- Individual Risk: the risk experienced by an individual e.g., IRPA, LSIR contours
- Societal Risk: F-N Curve/PLL
- The risk results were compared against the criteria
- Risk Reduction Measures (RRMs) have been identified to reduce the risk.
The hazardous scenarios considered in the risk analysis for the facility covered under scope of the project will be identified based on the properties of the materials handled and the identification of the potential hazards in the systems which could lead to loss of containment events.
The results of hazard identification is a list of credible accident scenarios (CASs) that may occur at the facility, which could lead to event such as, jet, pool, flash fires, vapour cloud explosion and toxic cloud dispersion. Natural calamity such as earthquake, sandstorms and lightning are not considered for frequency assessment. However, impact of these could lead to leak or rupture which are considered in consequence analysis.
In any risk assessment study, it is required to make certain assumptions. The assumptions can be in the development of a rule set and use of judgment data. In this study also, the assumptions will be made to enable the modelling of complex systems through simplification and approximations. This is a necessary part of the assessment and the quality of the assumptions influences the outcome, as well as the level of uncertainty in the assessment.
The evaluation of the impact of identified loss of containment (LOC) scenarios on individuals will be carried out through consequence modelling. The analysis will focus on assessing the effect distances of these scenarios. The project will undertake consequence analyses encompassing the subsequent activities:
- The utilisation of source term modelling is employed for the purpose of ascertaining the rate of release.
- Physical effects modelling to determine the size of the hazard that is associated with the released fluid (for example heat radiation, flammable gas dispersion and toxic gas dispersion);
- This study aims to compare the physical effects model with the impact criteria.
The consequence modeling will be performed using DNV PHAST software.
The hazard consequence assessment based on the consequence modeling includes
- Release of hazardous and toxic materials
- Gas dispersion
- Flame Geometry
- Thermal Intensity
- Overpressure magnitude
- Structural failure /damage
- Equipment damage
- Personnel evacuation
After identifying probable release situations, international standard database is used to assess failure frequencies. The procedure for conducting the frequency analysis is as follows:
- Identification of the base failure frequencies applicable to the pipelines, vessels and the storage tanks from relevant international standard database using parts count method
- The total failure frequencies will be derived from the base failure frequency data along with the consideration of Risk Reduction factors if applicable.
Generic Failure data will be applied if site specific or company data is not available. In general, OGP Risk Assessment Data Directory, Process Release Frequencies shall be used. Risk assessment will be undertaken to evaluate the risk associated with the project facility. The risk shall be typically presented as Individual Risk and Societal Risk.
Risk evaluation involves the evaluation of the individual risk results against the Risk Acceptance Criteria to determine whether the risks are broadly acceptable, ALARP or unacceptable. Sensitivity Analysis will be carried out on assumptions made to model inputs. Comparison of evaluated risk in the sensitivity analysis with acceptance criteria will be carried out.
As per Risk assessment, if calculated risks fall within the unacceptable range, it becomes imperative to implement risk mitigation measures to reduce risks to a level that is tolerable or as low as reasonably practicable (ALARP). It is imperative to identify all feasible measures for mitigating risks, including novel interventions or enhancements to pre-existing interventions that have been implemented or installed.
Cost Benefit Analysis (CBA) is a technique for comparing the costs and benefits of additional safety measures by comparing the cost of implementing the measure with the benefit of the measure, in terms of the risk-factored cost of accidents it will avert.
Cost-benefit analysis (CBA) serves the purpose of evaluating whether the advantages of a particular course of action exceeds its drawbacks, thereby determining the suitability of implementing said course of action.
The CBA approach requires monetary evaluation of the risks or the monetary evaluation of the loss of life. The evaluation of measures to avert loss of life requires ‘Valuation of life’ criterion and the ‘Valuation of life’ shall be used for the study.
The comprehensive report will encompass the methodology, study findings, and recommendations derived from the QRA study. The report will be structured into distinct sections, which are outlined as follows.
- Executive Summary
- Introduction / Objectives
- Facility Description
- Hazard Identification / Assessment of Scenario
- QRA Assumptions / Basis
- Consequence Analysis
- Failure Frequencies / Event Trees
- Risk Assessment
- Recommendations / RRMs
The following are the deliverables for QRA study:
- QRA Assumption register presentation
- QRA Assumption Register
- ALARP Workshop & Draft report presentation
- Initial/Draft QRA Report
- Incorporation of Company Comments
- Final QRA Report