Calculating Societal Risk

About Societal Risk

Societal Risk (SR), also known as "Group Risk," is the annual probability that a group of a specific size becomes victims of a fatal accident involving hazardous substances. This measure is critical in understanding the broader impact of potential incidents on a population.

Calculating Societal Risk

To include Societal Risk in your risk calculations, follow these steps:

• Enable Societal Risk calculation: In the Calculation Set, enable Societal Risk calculation as shown below:

  

  Optionally, enable the creation of Societal Risk Maps to generate Societal Risk Area and Societal Risk Contribution maps.

• Define population distribution: Add a population distribution to specify how the population is distributed in the area of interest. Accurate population distribution data is essential for meaningful Societal Risk calculations.

• Perform Societal Risk calculation: This allows the calculation of the fN curve and related Societal Risk Maps.

Results interpretation

The primary output of a Societal Risk calculation is the f-N curve. These graphs are available on the level of a calculation set, cumulation sets, comparison sets and individual equipment.

Additional outputs include Societal Risk maps, which provide a geographical representation of risk, highlighting areas of concern.

f-N Curve

• Description: The f-N curve represents the cumulative risk that a group of a specific size will be killed in an accident. It is depicted as a two-dimensional graph with a logarithmic scale: frequency (f) on the Y-axis and the number of victims (N) on the X-axis.

• Guide Value: The curve is assessed against a Guide Value. If the f-N curve is above the guide value the risk is deemed not acceptable. If the f-N curve is below the guide value the risk is considered acceptable. The slope of the guide value can be adjusted according to local legislation in "presentation settings".

• Guide Ratio (R): This ratio indicates the distance from the f-N curve to the Guide Value. It is expressed as the ratio of “ the nearest point f-N curve” / “Guide value level”. For example, a Guide Ratio > 1 implies that the Guide Value has been exceeded. For example, a Guide Ratio of 10 indicates that the Societal Risk exceeds the acceptance criteria (i.e., the Guide Value) by 10 times.

• Expected Value (E): Also known as Potential Loss of Life (PLL), this value represents the total expected fatalities from an accident scenario. It is area under the f-N curve and is calculated as:

  E = Total Fatalities * Total Frequency

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Societal Risk Maps

• Description: Societal Risk maps provide a geographical representation of risk, helping identify areas of concern. These maps answer critical questions such as "Do we have a problem?", "Where is this problem?", and "What is causing this problem?" An f-N curve may be challenging to understand or explain to non-experts. Therefore, Societal Risk is also reported through these maps, making it easier to visualise and communicate the risk.

• Societal Risk Area Map: Shows geographical areas where Societal Risk exceeds the Guide Value (or also known as risk acceptance criteria).

• Societal Risk Contribution Map: Identifies specific areas and factors contributing most to the overall Societal Risk.

• For more information about how to interpret Societal Risk maps, please refer to the article “Interpreting Societal Risk Maps“.

Conclusion

Calculating Societal Risk in RISKCURVES involves enabling the calculation in the software, defining population distributions, performing the calculation, and interpreting the results through FN curves and Societal Risk maps. These tools help assess and visualise the potential impact of hazardous substance accidents on a population, aiding in risk management and decision-making.