Risk is generally defined as a function of Consequence × Frequency. The CPQRA guidelines provide mathematical models (such as Fault Trees and Event Trees) to combine the likelihood of an accident with the severity of its outcome. The result is a numerical risk estimate, often expressed as individual risk contours (lines of equal risk around a facility) or societal risk FN-curves, which plot the frequency of incidents causing a given number of fatalities.
Use industry-standard failure rate databases (like OREDA or CCPS data) for components like valves, flanges, and pumps. Risk is generally defined as a function of