Fault tree and event analysis
Most companies operating hazardous industrial facilities conduct research in the field of occupational health, environment and safety (OH&S) during design, construction, as well as during operation. Hazard identification (HAZID), conducted before or during the design phase of hazardous industrial facilities, as well as Hazard and Operability Studies (HAZOP), often identify problems in safety and environmental protection systems that are highly likely to cause project delivery delays or costly design changes. Therefore, most industrial companies conduct hazard studies at the early design stage to avoid and/or reduce risks during project implementation.
According to GOST R ISO 31000-2010, the concept of risk identification represents a process of discovering and defining risks. Identification also assumes that characterization of events, risk sources, causes and their possible consequences should be carried out. Risk identification typically may also include archival data, analysis of theoretical data, expert opinions of specialists and other aspects.
There are real and potential risk scenarios that need to be identified, and there are many technologies for this purpose. Let's consider two of the main ones:
- Fault tree analysis and event tree analysis.
- HAZID "checklist" method.
Fault Tree Analysis and Event Tree Analysis
Fault tree analysis is a deductive approach to risk identification (analysis of information from general to specific), focusing on the causes of events that suggest an undesirable negative outcome.
From the English "event tree" – this is an event tree that visually represents all possible chains of events that lead to probability, for example, of ignition, and which are used to show how various individual event probabilities should be combined to calculate the probability of an entire chain of events.
Each outcome represents a result of such an event tree. Event trees, as shown in Figure 1, were used to visually depict possible chains of events leading to each individual outcome.
Application of this approach is a labor-intensive process, but can yield very useful results in certain situations. This approach is particularly effective in revealing risks from secondary causes or third-order causes. However, very often for these purposes, another more familiar method is used, which is called the "checklist" method. Pre-prepared checklists represent a convenient way to identify hazards. Checklists are typically applied at various stages of the project lifecycle: from design, construction, commissioning to equipment dismantling and facility conservation.
Checklists are prepared by experienced specialists responsible for equipment and building structure operation or design, for safe operation and functioning.
Checklists need to be regularly analyzed (minimum once every 2 years) and updated to reflect changes in systems and new industry requirements. Updates should also include results of investigations of any workplace accidents or incidents at similar facilities.
Checklists can be general or detailed depending on the set goal for risk analysis and the chosen system. Today, the "checklist" method is the fastest and simplest method for hazard identification and risk assessment.
HAZID "Checklist" Method
Issues related to hazard/dangerous risk factor identification/detection require increased attention. As a result, this task is the most important of all numerous methodologies that form the basis of risk management. Potential possible scenarios of dangerous risk factors must be identified, and there are many methodologies for this purpose.
At the beginning of work, it is necessary to identify any possible consequences that may occur and cause an undesirable effect, then highlight the hazards causing them.
According to GOST R ISO 17776-2012 (Petroleum and natural gas industries - Offshore production installations - Methods and techniques for hazard identification and risk assessment - Guidelines), hazard identification must be carried out at all stages of the project lifecycle. This refers to identification of hazards related to well operation, complex technological equipment, engineering systems, helicopter operation, service personnel, lifting operations and cargo movement, material and technical supply, environmental conditions, etc.