What are the most common process safety management risk assessment methods?

1 Hazard and operability study (HAZOP)

HAZOP is a structured and systematic technique that uses a set of guidewords (such as no, more, less, as well as, part of, etc.) to examine the deviations from the intended design or operation of a process and their causes and consequences. HAZOP is usually performed by a multidisciplinary team that includes process engineers, operators, safety specialists, and others. HAZOP is best suited for complex and novel processes that have not been fully tested or operated before.

3 Failure mode and effects analysis (FMEA)

FMEA is a bottom-up technique that focuses on the individual components or functions of a process and analyzes how they can fail, why they can fail, and what are the consequences and detection methods of their failure. FMEA assigns a numerical rating to each failure mode based on its severity, occurrence, and detectability, and calculates a risk priority number (RPN) to prioritize the corrective actions. FMEA is useful for evaluating the reliability and maintainability of a process, but it can also be time-consuming and tedious.

4 Fault tree analysis (FTA)

FTA is a top-down technique that uses logic diagrams and symbols to represent the causal relationships between a specific undesired event (such as fire, explosion, spill, etc.) and the basic events or faults that can lead to it. FTA can quantify the probability of the top event by using mathematical formulas and data from historical records or experiments. FTA can provide a clear and visual representation of the fault scenarios and their interactions, but it can also be complex and demanding.

5 Layer of protection analysis (LOPA)

LOPA is a semi-quantitative technique that combines the qualitative aspects of HAZOP or what-if analysis with the quantitative aspects of FTA or FMEA. LOPA evaluates the frequency and severity of a hazardous scenario and compares it with the existing or proposed layers of protection (such as alarms, relief valves, emergency shutdown systems, etc.) that can prevent or mitigate it. LOPA can determine the adequacy or gap of the protection layers and recommend the necessary improvements or changes. LOPA is a pragmatic and efficient technique, but it can also be subjective and dependent on the assumptions and data used.