Whilst the current recording style of a HAZOP is relatively easy to interpret, it does not provide immediate clarity – particularly for those who were not present during the study, or when reviewing or revalidating studies at regular intervals. In this blog, we will elaborate on why it can be useful to create bowties from HAZOP studies.

Limitations of HAZOP

HAZOP (Hazard and Operability) is a methodology which uses a structured, deviation-based approach to identify possible causes and potential consequences and assign or propose appropriate safeguards to eliminate or reduce the risk associated with the respective hazard scenario. The HAZOP technique is typically documented in a tabular form using either a generic worksheet e.g. Microsoft Excel spreadsheet or Word table or commercially available HAZOP (or PHA – Process Hazard Analysis) software. An example of an HAZOP study is in the figure below.

Figure 1: example of a HAZOP study

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 2: bowtie without mitigation safeguards


Figure 3: bowtie with mitigation safeguard

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.

Learn how to turn your HAZOP into a bowtie diagram

Learn how to convert your HAZOP study into a bowtie diagram and join one of our webinars on the 12th of October 2017:

From HAZOP to BowTieXP – 1-2 pm, UTC+8/ 7-8am CEST

From HAZOP to BowTieXP – 1-2pm, UTC+2/ 1-2pm CEST

From HAZOP to BowTieXP – 10-11am, UTC-7/ 7-8pm CEST