Use of Bowties for Pipeline Safety Management

Bowtie diagrams have become a widely-used method for demonstrating the relationship between the causes and consequences of hazardous events following the identification of Major Accident Hazards (MAHs). They are particularly useful for illustrating how safeguarding measures protect against particular threats or mitigate the various consequences of an incident. Bowtie diagrams have been widely used in a range of industries for over twenty years and are widespread in the upstream oil and gas industry, as well as other high hazard industries such as mining and nuclear. Bowtie diagrams are used for a range of purposes. At their simplest, they provide an overview of the measures in place to prevent and mitigate hazardous events, and as such are valuable additions to training programmes. A bowtie diagram provides an excellent platform to show regulatory authorities, trainees and new employees the various threats to a pipeline system, and what barriers are in place to prevent and control major accidents, such that the risks are as low as reasonably practicable. The bowtie process may be used during design, construction, operations and decommissioning. The bowtie for construction is different to that for design and operations, being more to do with occupational safety rather that loss of containment. However, the construction bowtie diagram still plays a vital role in minimising risk. Whilst the typical failure mechanisms for pipelines are generally well-established during operations, bowties have a key role in informing senior management of the measures in place to reduce risk. Furthermore, a large proportion of major accidents may occur at above ground installations (AGIs), and bowtie diagrams provide a mechanism to help management in the protection of personnel and potentially of nearby populations. For both cross-country pipelines and AGIs, the effectiveness of each barrier can be established to ensure that the risk of loss of containment is minimised. More detailed bowties may be used to assist in identifying safety critical elements (SCEs) or safety critical tasks; developing performance standards and defining process safety performance indicators. Often, the hardware shown by the barriers may be considered as SCEs, particularly in the case of effective barriers, such as vibration detection along the right-of-way (RoW) (prevention) or gas detection at AGIs (recovery). Where such barriers are defined as key to a major threat, the bowtie diagram illustrates the importance of good maintenance systems to ensure that the barriers have a high reliability. Thus, by defining the SCEs in a logical manner, bowties may be a key element in managing the risk from a pipeline system.