Risk analysis is a way to anticipate the identification and classification of risks in an industrial facility by properly defining the frequency (likelihood) of occurrence versus the severity of a scenario. Therefore, the scenario to be analyzed does not need to have already occurred in the company (evaluating past incidents is indeed valid), as risk analysis focuses on assessing potential problems, which allows for preventive measures. It is not advisable to persuade the team to stop the study during a risk analysis meeting by pointing to the lack of previous scenarios since this would preclude thorough examination.
Once a deviation and its causes are identified, the hazard’s consequence must be defined if it is released. It is the team’s responsibility to properly identify the plausible consequence of the accidental event; for example, if a flammable liquid leaks and may form a cloud of flammable vapors, one must consider a pool fire, a cloud fire, the possibility of an explosion, or even a jet fire if it forms two phases upon losing containment. With these effects, it is possible to clearly define the maximum consequences.
Safeguards usually do not reduce the severity of the scenario; they reduce the risk by decreasing the frequency of occurrence based on the probabilities of failure in demand for each of them. Risk analysis specialists should be attentive when guiding the team regarding this fact; otherwise, they may have a false picture of the installation’s risks. This condition will mistakenly indicate that the plant only faces low-severity risks, resulting in the loss of the opportunity to implement effective risk management.
When can we reduce the severity? The answer is when it is possible to apply the inherently safer process (as the late Trevor Kletz already discussed in detail on this subject), for example, by reducing inventory, reducing pressure and temperature, replacing flammable solvents with non-flammable ones, and so on.