Quantitative Risk Assessment

rifle contour

ESR’s Safety and Risk Management business has extensive experience of carrying out Quantitative Risk Assessments (QRAs) and associated safety studies, and has worked with most major oil and gas operators in the UK and overseas. The QRAs and safety studies are carried out using our in-house RISK and RIFLE tools for a wide range of onshore and offshore facilities worldwide. The underlying consequence models for fires, explosions and gas dispersion have been extensively validated against experimental data. Over the last 10 years alone we have successfully completed more than 150 QRA studies for the oil & gas industry.


Frequency and Event Analysis

Event trees are used in the QRA to consider a range of possible outcomes, given an initiating event (generally a leak). ESR Technology has been heavily involved in the interpretation of relevant data sources for many years on behalf of the UK HSE and the United Kingdom Offshore Operators Association (UKOOA – now Oil & Gas UK). Industry standard data sources used by ESR Technology include the UK HSE HCR (hydrocarbon release) database, OREDA, E&P Forum, and the EGIG (European gas pipeline) database.

Ignition probability is assessed using either ignition density or mass flow approaches, applying time dependency and flow decay where appropriate for the fluid and scenario.

In assessing the probability of specific hazardous outcomes, account is taken of prevention, control and mitigating factors such as shutdown, blowdown, fire and gas detection/protection and mustering, as well as operator response. Estimates of system failure probabilities are determined from generic data (e.g. from OREDA), human factors HEART methodologies and simplified fault tree techniques, as appropriate.


Risk Assessment

QRA Analysis Software

RIFLE LSIR MapESR Technology’s RISK (Offshore) and RIFLE (Onshore) QRA software is capable of undertaking detailed risk modelling, taking into account both the likelihood and consequence of potential events. Risks are typically interpreted in terms of individual risk (IR) and Potential Loss of Life (PLL) by worker group (e.g. maintenance, operation, administration etc). Risk associated with offsite populations is assessed using both risk contouring and societal risk (FN) techniques.

Our RISK Software is a spreadsheet based model used for assessing risks numerically on offshore installations. Where risk contouring is appropriate, calculations are performed using ESR Technology’s RIFLE software.

RIFLE processes information on the frequency and consequences of the individual events and calculates the risk level at any specified location. The overall risk profile is then generated by combining the contributions from individual events at each point on a two-dimensional grid. The result is a complex risk profile, with the overall risk dependent on the geographical location relative to the centres of risk and the variation of risk with distance for the different events. The overall risk is displayed as risk contours (lines of equal risk) superimposed onto a map of the area. RIFLE can also undertake detailed societal risk calculations and generate F-N curves for exposed populations. By suitable choice of harm criteria, the software can be used to assess risk to assets and occupied building, as well as the risk to people.



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