Cascading Bow-Tie Analysis

One method that has received attention lately is Bow Tie Analysis partially due to its ability to show the whole picture of a specific hazardous event. A conventional Bow-Tie Analysis is a combination of a fault tree analysis (left side of bow-tie) and event tree analysis (right side) used to provide a clear illustration of the risk pathways and control measures in place for situations that do not require a full quantitative fault tree analysis. Two short-comings of the Bow-Tie analysis are that it typically lacks a risk scoring mechanism, and that the effectiveness of control measures is not reflected in the analysis (higher level controls such as elimination, substitution and engineering are not distinguished from lower level controls such as administrative and PPE.) To address these shortfalls, the authors have modified the method to include a risk scoring system, the Hierarchy of Controls and Layers of Protection Analysis (LOPA) which is referred to as a Striped Bow Tie Risk Assessment. For complex situations, a cascading Bow-Tie can be used where the consequences of one event may be the cause or trigger of a secondary event. In addition, business consequences as a result of SH&E related incidents can be integrated into the cascading Bow-Ties methodology. A cascading Bow-Tie risk assessment example using the bio diesel production operation is presented here.