Bowtie Analysis and Barrier-Based Risk Management - Part 4

This article was originally published in the January-February 2018 issue of Pharmaceutical Engineering® magazine.  Catch up on this series by reading:

Every business has legal, economical, and ethical objectives that range from mandatory safety to commercial goals to corporate citizenship. Businesses undertake a certain amount of risk to achieve these objectives. The balance between risk and reward is an ongoing challenge regardless of the activities involved. The bowtie technique can be used to visualize, assess, and manage risk.

By: David Hatch


Bowties offer the following advantages:

  • Visualization and communication: Knowing, showing and sharing the basis of integrity
  • Risk-based decision-making: Are there enough barriers to mitigate the risk appropriately?
  • Barrier dependency visualization: What if the resource responsible for multiple barriers is compromised, e.g., the engineering manager is ill or power is lost?
  • Display risk assurance: How are the barriers performing?
  • Informed decision-making (change management): What happens if a barrier is removed or degraded?
  • Risk-based management: Identification, analysis, evaluation, and treatment

An alternative view on risk management could simply be "failure management." Failures often begin as threats that start a chain of undesirable events; they must be stopped or slowed by measures that themselves have the potential to fail.

New projects may be able to implement additional barriers. Established facilities may only be able to improve existing barriers. When resources are limited, management must be confident that they are investing in improvements (training, maintenance, inspection, etc.) that can deliver results.

Existing Methods

The pharmaceutical industry is not unfamiliar with hazard and risk analysis tools and techniques. The most common, from ICH-Q9, are listed below.1

  • Failure mode effects analysis
  • Failure mode, effects and criticality analysis
  • Fault tree analysis
  • Hazard analysis and critical control points
  • Hazard operability analysis (HAZOP)
  • Preliminary hazard analysis (PHA)

A more extensive list is available from the Center for Chemical Process Safety.5

All these methods have strengths and weaknesses, which are documented in a UK Health and Safety Laboratory research report.6 HAZOP, for example, is a widely used hazard-identification methodology; it is not effective in identifying where multiple cause can lead to the same consequence, however.

Bowtie analysis is not intended to replace existing tools and techniques, but to enhance them by helping those involved in the original identification or analysis studies to confirm their discussion, and those not involved in the studies (but still responsible for managing risk) to understand and address relevant issues.

One major limitation of most common techniques is that they are typically performed by specialists and documented in a technical language and format that does not easily support communication and ongoing collaboration. The UK Health and Safety Executive recognizes that a barrier (bowtie) approach is a useful tool in communicating major hazards information to the workforce.7

The clarity that bowties provide can also be used to validate existing studies more efficiently, e.g., to identify errors or omissions in the causes, effects, and control measures associated with particular scenarios. This is a key issue in high-hazard facilities that are mandated to revisit their PHA or HAZOP every five years under regulations such as the US Occupational Safety and Health Administration or the Seveso Directive.