Process Hazards Analysis
Operating companies are often challenged with making the right decision in balancing safe and reliable plants with limited labor and financial resources. Additionally, many operating companies in the United States have specific requirements to perform Process Hazards Analysis (PHAs) that conform to national or local statutory regulations. A PHA is a form of hazard analysis that can take many forms, from qualitative to semi-quantitative to fully quantitative. Examples of PHAs include:
- Hazard and Operability (HazOp) Studies
- Layers of Protection Analysis (LOPA)
- Event Tree
- Fault Tree
- What-If and Structured What-If (SWIF)
- Failure Mode and Effects Analysis (FMEA)
- Quantitative Risk Assessment (QRA)
PHAs can save companies money by not only averting risks, but also by identifying opportunities to prioritize safeguards through risk-ranking techniques. BakerRisk’s experienced staff can assist clients in selecting and implementing the right method to evaluate activities as varied as traditional process, offshore/onshore production, pipeline, instrumented and electrical distribution systems, as well as specific activities such as written procedures, crane operations, among many others.
Uniquely among major process risk consultancies, BakerRisk’s PHA staff has an average of more than 25 years of experience in the process industry and PHA activities, and many also have related certifications. Thus we are able to draw upon past experiences that may well be beyond the background of the members of the client PHA team, enhancing the knowledge and depth of the analysis.
BakerRisk studies are fully compliant with OSHA PSM 29 CFR 1910.119 requirements, and are based on the methodologies described by the American Institute of Chemical Engineers’ Center for Chemical Process Safety. BakerRisk licenses the most popular PHA recording software packages in order to match the client’s in-house tools.
Apart from being a valuable tool to assess risk, the various methods of PHA can also be utilized to resolve risk concerns related to specific scenarios. Often these are high-risk or extremely complicated scenarios, which could require integrating several analysis methods. BakerRisk assists clients by providing the most experienced risk analysts in the industry, along with best-in-breed quantitative tools that can resolve questions about event severity and likelihood as part of the study.
Hazard and Operability Study (HazOp)
A HAZOP is a qualitative study used to identify potential hazards and operability concerns, and to facilitate consensus on recommendations that arise. The study identifies process deviations from design intent and their potential consequences.
The “guideword” HAZOP technique is the most widely applied in industry. In a guideword HAZOP, a dedicated team studies available process information (such as Process and Instrumentation Diagrams) and systematically applies the guidewords with appropriate parameters to the various lines and vessels in the process to determine if a deviation from the design intent or normal process condition is possible. The cause, consequence, safeguards, and recommendations, if needed, are documented for each piece of equipment discussed.
A HAZOP team is typically composed of individuals representing a variety of technical specialties. Each session should include representations from the following areas:
- Process Engineering
Additional specialized team members may be required when effective discussion of the events and consequences in that node depend on an individual’s experience or knowledge, such as the disciplines of:
- Inspection / Materials
- Safety / Loss Prevention
- Packaged Equipment
The guidewords and parameters used in a HAZOP depend on the study, and can also vary by operating company. Additional guidewords and parameters may be added to the PHA, if appropriate for the process being studied.
Layers of Protection Analysis (LOPA)
Layers of Protection Analysis (LOPA) is a semi-quantitative risk analysis tool used to determine the risk of individual hazard scenarios. As part of the analysis, safeguards that meet specific criteria are identified as Independent Protection Layers (IPLs). IPLs are assigned, directly or indirectly, a performance factor that reflects the reliability of the protection layer. LOPA also supports the use of mitigating factors or conditional modifiers that are not strictly protection layers but do affect the likelihood of the event.
Advantages of LOPA include:
- It allows a rough estimation of the likelihood of an event that, in combination with an estimate of event consequence, can be compared to corporate risk criteria to determine tolerability.
- It allows an objective determination of risk using a consistent set of rules (as compared to other purely qualitative methods of risk analysis).
- It allows for determination of IPL effectiveness, which can be used to set performance requirements (such as Safety Integrity Level [SIL] for safety functions).
- It can function as a screening tool for more advanced risk analysis methods, such as Quantitative Risk Analysis (QRA) or Fault Tree.
LOPA differs from a Process Hazards Analysis (PHA) method such as HAZOP, which is a qualitative risk analysis method. Whereas a HAZOP asks the team to mentally combine all the safeguards into an overall risk for a given scenario, a LOPA identifies each protection layer individually, and estimates a likelihood of an event in a conservative and simplified manner. A LOPA should not be construed as being an analysis tool that is “strictly better” than a PHA – each method has strengths and weaknesses.
Operating companies typically use LOPA for either of two reasons:
- As the primary SIL selection method for their Safety Instrumented Systems (SIS)
- An alternate risk analysis to confirm a PHA team is consistently identifying risk for “high risk” or “high consequence” scenarios.
BakerRisk facilitators have extensive experience in performing LOPA in support of other PHA methods (such as HazOp), standalone, or to determine SIL targets for safety functions.
Event Tree Analysis (ETA)
Event Tree Analysis is a quantitative method of fault propagation modeling. ETA starts with an initiating event and defines possible outcomes for each sequence of events. Safeguards are modeled into the event tree, with corresponding modal outcomes that relate to the effectiveness of the safeguards in preventing or mitigating the consequence. When the frequency of the initiating event is combined with the probability of each modal outcome in the tree, a frequency estimate is calculated for each consequence of interest.
Advantages of using ETA include:
- It estimates a frequency of occurrence for key accident scenarios
- It can be employed to determine the likelihood of multiple consequences within the same analysis
- It provides a visual model that can be used to qualitatively understand the sequence of events
- The effect of recommended actions can be immediately incorporated into the model to evaluate their effectiveness
BakerRisk has performed numerous event tree analyses to predict outcomes of release or rupture for multiple sites around the world
Fault Tree Analysis (FTA)
FTA is a deductive technique, by which all of the combinations of initiating and contributing events and conditions that can lead to a particular effect (called the “Top Event”) are considered. A fault tree is a common method of determining the probability or frequency of an unwanted event. FTA can also be used to assess performance of instrumented systems such as safety functions to determine probability of failure on demand (PFD).
Advantages of FTA over other qualitative and semi-qualitative PHA methods are:
- FTA provides a diagrammatic logical view of the failure and interactions with individual components in a top-down fashion
- Fault tree can also incorporate interaction with operator action and predict human error probability (HEP) based on client operating procedures
- Detailed cutset and importance analysis measures can be employed to identify components contributing the most to the frequency of the unwanted top event.
BakerRisk has extensive experience performing fault tree analysis to estimate frequency from simple to complex scenarios:
- What-If and Structured What-If (SWIF)
- Failure Modes and Effects Analysis (FMEA)