Process Hazard Analysis


The Process Hazard Analysis (PHA) is a legal requirement in the UK under the Health & Safety at Work Act and The Health and Safety Regulations in that employers and employees should ensure that a suitable and sufficient Risk Assessment is in place prior to the commencement of tasks/ processes. In terms of Functional Safety the PHA is required to describe the cause  / consequence pairs to be carried through to SIL Allocation. The PHA is developed during phase 1 of the Functional Safety lifecycle, and must be available throughout the lifecycle.


The PHA is the first step in the Functional Safety Lifecycle and using a systematic and detailed methodology (Hazop, Hazid, What If, Check List etc) to describe the unmitigated consequences of deviations in process control, operator actions, equipment failure and within reason natural disasters. By clearly identifying the causes that can lead to Health & Safety incidents, Environmental incidents and on occasions business and asset incidents, the existing safeguards can be identified and any shortfall in risk reduction requirements highlighted. This risk reduction gap may be filled with changes to the design to increase inherent safety, passive safeguards such as bunds, active safeguards such as relief devices and ultimately safety instrumented systems.

Where Safety Instrumented Systems are identified the PHA leader would note the causes and unmitigated consequences and pass them on to the SIL Allocation Process.

The PHA process depends on a multi functional team from across the operations, design and engineering discipline that can review the P&ID’s, Layouts, Operating Instructions and Engineering Specifications and by asking and answering a series of questions on selected scenarios can identify the residual hazards left in the design and allow them to be examined in a more formal manner at the next phase of the lifecycle.


ProSalus has assisted a number of our clients in carrying out PHAs using the Hazop, Hazid, Checklist and What If tools.