Estimation of Risk Levels
Risk is a function of frequency and consequence. For calculating risk levels to people, BC estimates what are named Location Specific Risk (LSR) and Societal Risk (SR).
LSR: frequency (per year) that a person (assumed to be outdoors and present during the total exposure time) will become a victim of an accident if the person is unprotected in a certain location. The LSR is presented as a risk contour level, which is the sum of the risk of fatality from each Loss Of Containment (LOC) scenario considered in the analysis.
SR: frequency (per year) that a group of people of at least a certain size will at one time become victims of an accident. The people involved are assumed to have some means of protection. The SR is presented as an FN Curve, where N is the number of deaths, and F the cumulative frequency of accidents with N or more deaths.
The risk-based approach is an aid to the decision-making process, and BC is convinced that the more specific and detailed results are provided, the better cost-effective solutions are considered. Accordingly, BC generates specific results/information (graphical and numeric) that can be analyzed for an effective decision-making process.
The main process/system results can be graphically represented as:
Hazard Contours (e.g., overpressure above a frequency threshold);
Frequency Contours (e.g., flammable gas frequency)
Risk Contours (e.g., total risk contour level)
FN Curve for the whole area, which can include on-site and/or off-site population.
Some of the specific results at target locations are the following:
List of effects/consequences (e.g., toxic, flame, gas), and related information to each effect; e.g., associated LOCs causing the effect, effect frequency/risk.
Thermal exceedance, plotting the cumulative frequency of each of the thermal hits that the target could be exposed.
Pressure and Impulse exceedance, which are graphs that plot the cumulative frequency as a function of maximum overpressure or maximum impulse that the target could be exposed too.
FN Curve and Risk Indices for target locations defined as buildings; i.e., locations defined with people.