Bow tie technique

The bow tie technique is being used increasingly within the process industries not only to analyze risk but also to communicate hazard and risk findings to a broad audience. It can be used not only in hazards analysis but also in incident investigations. 

In Figure 15.36 the fault tree (which is left to right rather than the normal bottom to top) generates a top event. This event is, in turn, the initiating event for the event tree that follows. For example, a series of equipment, human and instrument failures could lead to the top event of Liquid overflow from a tank. The safeguards to mitigate the top event are shown in the event tree. The bow tie technique uses the same structure as Figure 15.36. 

In Section 11.3 we stated that Design Organisations are at the heart of safety because the design solution determines the manner in which the system is operated and maintained . A useful technique which can be used to illustrate this principle (and drive the required Design Organisations behaviours in the handshake with the user s SMS) is the Bow Tie Analyses (see Fig. 11.5), where ... 

The standard reference for the offshore oil and gas industry is API RP 14J. However, as already noted, this standard does not provide guidance on some of the latest techniques being used, such as Bow-Tie Analysis. 

A hazards analysis technique that is widely used on offshore facilities is known as Bow-Tie Analysis. The name is based on the shape of the final analysis product as shown in Figure 5.1. The method is used not only to identify risks, but also to assess the effectiveness of the system s safeguards. 

SCEs are generally identified during the hazard analysis sessions (HAZID and HAZOP) and Bow-Tie analyses. Their effectiveness is evaluated through a range of Quantitative Risk Analysis (QRA) techniques. 

Literature on the many techniques for making risk assessments is abundant. For example, in ANSI/ASSE Z690.3. Risk Assessment Techniques—reviews are included of 31 techniques. Examples are such as Primary Hazard Analysis, Fault Tree Analysis, Hazard and Operably Studies, Bow Tie Analysis, Markov Analysis, and Bayesian Statistics. Uncomplicated systems that could be introduced to supervisors and front-line employees are not as prevalent. Such a system is contained in an extension of the previously cited European Community bulletin. It follows. 

Bow-Tie Analysis (BTA) a type of qualitative process hazard analysis.The methodology is an adaptation of three conventional system safety techniques Fault Tree Analysis, Causal Factors Charting, and Event Tree Analysis. Existing safeguards (barriers) are identified and evaluated for adequacy... 

Bow tie analysis is a qualitative, iterative technique often conducted by a team. It unifies fault tree analysis and event tree analysis. This technique visualizes all effects leading to a top event and all consequences which result from the top event (Badreddine and Ben Amor, 2010). 

Bow-tie analysis is an analysis technique that combines FTA and ETA together to evaluate multiple possible outcomes from an undesired IE. The various outcomes result from the operation or failure of barriers intended to prevent a mishap. The analysis begins with identification of the IE of concern in the... 

Rgure 2.68 shows a bow-tie analysis model (also referred to as X-tree analysis) of barriers. This analysis technique is a combination of FTA and ETA. The analysis begins with identification of the IE of concern in the center. An FTA is performed to identify the causal factors and probability of this event. Then an ETA is performed on all the barriers associated with the IE, and the possibilities of each barrier function failing. The various different failure combinations provide the various outcomes possible, along with the probability of each outcome. 

The only standardized test is the wet-treeing test for cable, EIC CS5-79, of the Association of Edison Illuminating Company. Both initiation and rate of wettree growth are important. Among other accepted techniques, one uses a compression-molded plastic specimen with sharp conical depressions, which are filled with water or electrolyte. The pie-plate specimen is then placed in water and different voltages are appUed between the water in the specimen and the surrounding water. The number, size, and nature of the trees, eg, bush, fan, bow-tie, etc, are observed periodically. The complexity of such observations. 

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