Bow-tie diagram

Interestingly, controls can come in two flavours depending on which part of the storyboard they interact with. The distinction between the two can be neatly articulated in a bow-tie diagram as shown below (Fig. 12.1). 

Fig. 12.1 Bow-tie diagram showing how causes, hazards, impacts and controls relate...

The risk analysis procedure is outUned once again in Fig. 8.2 using the so-called bow-tie diagram, which is frequently found in the literature. 

As already mentioned, the scope and depth of the analyses may differ. If only the left-hand side of the bow-tie diagram is treated, we are dealing with a probabilistic safety analysis. Its results are the expected frequencies of undesired events. The objectives then are to identify weak points and imbalances in the engineered safety systems as weU as to indicate ways for eliminating them. This is the most work-intensive part of a risk analysis. 

A Fimctional Process Analysis (FRA) is first undertaken to identify hazards and their causes in terms of technical and human elements using plant diagrams, safety procedures, incident records and inter-views/observations of operational people. Bow-tie diagrams can be used to develop a graphical representation of hazards and potential barriers that can prevent or mitigate failure consequences. The next step involves the analysis of human-related barriers (e.g., operator visual checks, operator procedures etc) in Older to identify possible task deviations and human errors that may diminish the efficiency of barriers or make them fad. The analysis of human barriers and task deviations is done with the support of Task... 

Potential human errors and equipment failures are combined in dynamic event trees for the final evaluation of event probabilities as identified initially from the bow tie diagrams. Data about Human Error Probabilities (HEPs) are estimated with the use of the FPE tool on the basis of expert judgement and theoretical insight (i.e., the CREAM methodology HoUnagel 1998) applied in combination with fuzzy logic principles (Zadeh 2008). 

Figure 1 shows a simplified bow-tie diagram with an initiating event (A ) and its causes and consequences. There are uncertainties associated with A as well as with the causes and consequences, including the performance of barriers (for example alarms on the causes side and back-up plans on the consequences side ). Step 1 and 2 analyse the bow-tie using probabilities and expected values. This analysis is based on a number of assumption and suppositions, and uncertainties may be hidden. The purpose of Step 3 is to reveal and analyse such uncertainties. 

Figure 1. Basic features of a bow-tie diagram including uncertainties.

Figure 5.1 shows the stmcture of a bow-tie diagram, which consists of an event tree that creates a top event and the safeguards and controls which are analyzed with a fault tree. On the left side of the figure is the hazard, say a vessel... 

A bow-tie diagram is a means of representing the causes and consequences of a hazardous occurrence, together with the elements in place to prevent or mitigate the event. The knot in the middle of the bow-tie represents the hazardous event itself. Such an event might be Eoss of containment or Storage tank overfill etc. 

Bow-tie diagrams can be used as a stand-alone qualitative hazard identification tool or as the first step in a quantified risk assessment. Depending on the software used, the data on a bow-tie diagram may be output as a hazard register and responsibilities for ensuring that barriers are effective may be assigned. 

The chosen approach means that what enters as initiating events in the National risk picture (risk areas/scenarios), and are thus implicitly placed in the middle of a bow-tie diagram, may instead enter as causes in the regional RVA. 

The three scenarios above were visualized in preliminary bow-tie diagrams as preparation for further analysis. The respective TOP events were then ... 

Step-4 Identification of barriers Barrier identification and analyses were conducted in a Workshop (WS) with marine experts from Statoil and partners. Results from the WS were documented in the prepared STEP diagrams, preliminary Bow-tie diagrams and work sheets for further analysis. Only scenarios with end consequences implying a major accident potential were focused. 

In the subsequent analysis the most important barriers were identified in revised bow-tie diagrams for the respective positioning failure- and collision scenarios. Color codes were applied to better differentiate between onshore and offshore barriers (activities) in the Bow-tie figures. 

Badreddine, A. Ben Amor, N. 2010. A New Approach to Construct Optimal Bow Tie Diagrams for Risk Analysis. In Garcia-pedrajas, N., Herrera, F, Fyfe, C., Benitez, J. Ali, M. (eds.) Trends in Applied Intelligent Systems. Springer Berlin Heidelberg. 

In the following sections the case-study and the related scenario are described in detail by means of a bow-tie diagram. A methodology is then proposed for dynamically assessing the risk connected. To conclude, a set of simulation results are shown in order to illustrate the application of the methodology. 

A bow-tie diagram was used to visualize the case-study (Fig. 1—the terminology follows the one... 

Figure 1. Bow-tie diagram illustrating the case-study (adapted from the result obtained with BowTieXP ).

From a safety point of view, sand production is critical because it is threatening the integrity of the pipeline and to some extent also safety valves. If these threats are not stopped by the safety barriers mentioned, they can lead to material degradation, (shown in the middle of the bow-tie diagram as top event—Fig. 1). 

The framework of IT RA is mainly influenced by IT security analyses dealing with Confidentiality, Integrity, and Availability (CIA) of data or assets. Major goals are the identification of external threats on and weak points of an IT infrastructure network. In fact, IT RA is a vulnerability analysis concordant with (ISOTECGuide73b 2009) and (NIST 2012). It also comprises control analyses similarly to Bow Tie Diagrams. Following the definition of the NIST Guide, risk is ... 

Ferdous, R., Khan, F., Sadiq, R., Amyotte, P. Veitch, B. 2013. Analyzing system safety and risks imder uncertainty using a bow-tie diagram An innovative approach. Process Safety and Environmental Protection 91 1-18. 

Figure 4.8 shows the structure of a bow-tie diagram, which consists of an event tree that creates a top event, the safeguards and controls for which are analyzed with a fault tree. At the left of the diagram is the hazard, say a vessel containing hydrocarbons stored under pressure. Threats are events such as corrosion, external impact, and operating error, which could create an undesired event, in this case a release of hydrocarbons from the vessel. Between the threats and the undesired outcome are barriers such as operator training, relief valves and instrumentation. 

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