Individual Risk

Definition

Individual Risk (IR) represents the annual probability that one individual continuously present without protection at a specific location outside a facility will be fatally harmed as a consequence of an event inside the establishment leading to the release of a dangerous chemical, dangerous waste or a pesticide. ​

It is expressed in units of per year (/year).

In some regions, Individual Risk is also referred to as Location Specific Individual Risk (LSIR), indicating its relevance to a specific coordinate or location.

The concept of Individual Risk assumes that the entire population remains unprotected and outdoors, although, in reality, most individuals spend a significant portion of their time indoors and only occasionally venture outside. Therefore, the criteria outlined here can sometimes be overly conservative.

Calculation

Various countries have specific definitions and calculation methods for Individual Risk. For instance, Singapore employs a distinct approach in calculating this risk measure.

In general, IR is calculated as the sum of all failure frequencies for each scenario, which is then:

• Multiplied by the probability of an effect (such as the probability of direct and delayed ignition, probability of confinement, probability of a certain weather condition occurring, etc.).

• Multiplied by the probability of exposure (which is influenced by factors such as the probability of a certain wind direction, or the probably of escaping)​.

• Multiplied by the probability of getting killed by exposure (which is determined by the Probit function used to translate physical effect to a damage footprint)​.

Applications

Individual Risk assessments are crucial in ensuring the safety and health of workers and individuals in environments where hazardous substances and processes are present. Individual Risk is often presented as iso-risk contours to aid in land-use planning. These contours help visualize risk levels across different areas, guiding decisions on where to develop or restrict certain activities.

Individual Risk in RISKCURVES

In RISKCURVES, the Individual Risk criteria assume 100% presence and an unprotected situation outside. A so-called “Iso Risk Contour” is drawn by connecting all points with equal Individual Risk (see figure below). Additionaly, the Individual Risk values can be also displayed by a grid presenting IR value in each grid cell. The Individual Risk can also be expressed in a so-called FX curve, which presents the fraction lethal versus distance from the release point, for different wind-directions.

An additional functionality is a risk transect, which shows how the individual risk changes as a function of the distance along the drawn transect.

For more information about how to calculate Individual Risk in RISKCURVES, please refer to the article “Calculating Individual Risk in RISKCURVES”.