Societal Risk

Definition

​Societal Risk is the cumulative probability per year, that at least 10, 100, or 1000 people are killed as a direct result of their presence within the impact area of an establishment where the release of a dangerous chemical is involved.​ In contrast to Individual Risk, Societal Risk considers population density.

Societal risk takes into account stationary activities as well as transport activities. Transport activities present a risk of 1/km/year.​

Calculation

Societal Risk is typically presented as an fN curve, a graphical representation of the probability vs the number of fatalities.

​In this graph, the cumulated frequency is plotted versus the corresponding number of fatalities. 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. The graph consists of 3 main elements:

• Guide Value: The curve is assessed against a Guide Value.

  • If the fN curve is above the guide value the risk is deemed not acceptable.

  • If the fN curve is below the guide value the risk is considered acceptable.

• Guide Ratio (R): This ratio indicates the distance from the fN 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. 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 the area under the fN curve and is calculated as: Total Fatalities x Total Frequency

Application

• Developing safety regulations: Establish guidelines and standards to minimize the risk of events that could cause widespread harm.

• Urban planning: Aid in the design and development of infrastructure to ensure safe distances between hazardous facilities and populated areas.

• Emergency response planning: Formulate effective emergency response strategies to manage and mitigate the impact of large-scale incidents.

• Risk communication: Provide clear and comprehensible risk information to the public and stakeholders to ensure informed decision-making.

• Risk reduction measures: identify areas that may benefit from risk reduction measures. These measures could include process modifications or the relocation of hazardous activities away from populated areas.

Societal Risk in RISKCURVES

RISKCURVES calculates and presents Societal Risk in various ways, to help professionals efficiently analyse and communicate the risk. The presentation of Societal Risk consists of the fN curve and Societal Risk maps.

fN curve

• fN curves are available for particular equipment, all scenarios, or when selecting a particular subset of scenarios/equipment.

• ​The fN graph does not provide information on where the risk accumulates (which population contributes to this Societal Risk) or which areas are safer or less affected by Societal Risk (still having the possibility for urban development).

Societal Risk maps

• Societal Risk maps are area-specific visualisations for Societal Risks.

• They provide information on where the risk accumulates (which population contributes to this Societal Risk) or which areas are safer or less affected by Societal Risk (still having the possibility for urban development).

Societal Risk Area map

• A Societal Risk Area map exposes geographical areas where Societal Risk exceeds the Guide Value.

• It highlights regions where the societal risk exceeds the risk acceptance criteria.

Societal Risk Contribution map

• The Societal Risk Contribution map is based on the Expected Value (E) of an fN curve, also known as the “Potential Loss of Life” (PLL). The colours translate the number of fatalities expected in a given ​accident scenario and expose areas contributing the most to the Societal Risk. The areas with the highest contributions to the Societal Risk will be red.

• However, those red areas do not necessarily mean their corresponding fN curve exceeds the risk acceptance criterion (i.e., Guide Value). A red area merely indicates a high relative contribution to the existing Societal Risk around that location.

For more information about how to calculate Societal Risk in RISKCURVES, please refer to the article “Calculating Societal Risk in RISKCURVES” and “Interpreting Societal Risk Maps in RISKCURVES”.