From Hazop to Bowtie

^{Figure 1: example of a HAZOP study, click here for full image}

The major limitation of the most common worksheet format is often the inability to unambiguously match prevention safeguards to ‘causes’ and mitigation safeguards to ‘consequences’ which can lead to incomplete or inconsistent studies as the line of sight between ‘cause’ (threat) and ‘consequence’ is not clearly defined such that the safeguards can be properly identified and managed.

In this HAZOP study, it seems like there are enough safeguards to cover the causes and consequences of higher or lower pressure within the chlorine rail car. The bowtie method also helps to analyze deviations from normal operations and therefore we put the elements of this HAZOP study into a bowtie diagram.

The benefits of making bowties out of HAZOP

Bowties allow you to link safeguards to specific causes (threats) and consequences, as shown below. When you look at the bowtie diagram below, the left-hand side is preventing the threat from leading to the loss of control (top event). The right-hand side of the bowtie is for recovering from the top event or mitigating the consequences. In the same figure, the safeguards (barriers) are mostly on the left-hand side, which means this operation proactively managed with preventative safeguards. Which is, of course, a good safety approach, but what happens if there is a higher or lower pressure. When no mitigation safeguards are being managed, the top event could directly lead to consequences.

^{Figure 3: bowtie with mitigation safeguard, click here for full image}

Where HAZOP studies stops, barrier-based risk management just starts. Once you have completed the main components of the bowtie diagram, BowTieXP allows you to add additional management data of your organization to your barriers. For example, adding job titles and accountabilities to know who is responsible for each barrier. A barrier may also require training or maintenance, which is also possible to link to each barrier. Managing risks can be done by either a proactive way in terms of audits and inspections or reactive way with incident and accident data. Knowing what barriers are more effective than others allows you to make risk-based decisions, by adding or improving barriers and deciding what barriers are more critical than others.

In BowTieXP, it is possible to link existing HAZOP studies from various tools like PHAWorks™, LEADER™PHA and HAZOP Manager as well as simple Excel and Word formats, without having to copy/paste between applications. Linking your existing HAZOP studies to bowties gives you insight in what safeguards are actually protecting your operations and the opportunity to manage these safeguards effectively.