What are PHA and HAZOP?

What are PHA and HAZOP?

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What is PHA?

Process Hazard Analysis (PHA) is an in-depth and systematic effort to identify and analyze potential hazards’ impact on industrial processes. The findings from a PHA assist corporate executives and the Board to make informed decisions to improve plant safety and to prevent or mitigate catastrophic accidents.

A PHA study evaluates potential sources and consequences of catastrophic events such as chemical spills, flammable or toxic releases, fires, and explosions. PHA focuses on every element of the process equipment, instrumentation and controls, and human actions. It is applied to determine and communicate that the elements either pose no hazard, pose uncontrolled hazards, or pose hazards controlled with the proper mitigations.

Methods of PHA

The US Department of Labor’s Occupational Safety and Health Administration (OSHA) has identified several ways to conduct process hazard analysis:

  • What-if
  • Hazard and Operability Study (HAZOP)
  • Failure Mode and Effect Analysis (FMEA)
  • Fault Tree Analysis

The particular PHA method applied is influenced by the complexity of the analyzed process and the organization’s experience with the process. HAZOP is the most widely utilized PHA method for performing a detailed analysis of a wide range of hazards from the design phase to routine operations.

HAZOP study

The HAZOP study, described in detail in the guidelines issued by the US Department of Labor, Occupational Safety and Health Administration (OSHA), follows a structured and thorough method to:

  • Identify possible deviations from normal operations,
  • Assess their impact, and
  • Ensure suitable safeguards are in place to prevent accidents from occurring.

The HAZOP study uses quantitative adjectives (such as “more,” “less,” “no”), called guide words, together with process conditions (such as speed, flow, or pressure) to describe all credible deviations from normal conditions. The study also goes through every possible variation in parameters for each process segment to determine what could go wrong.

HAZOP has been applied primarily in chemical production and piping systems where hazardous chemicals can cause environmental disasters or loss of life.

The characteristics of HAZOP analysis can be summarized as follows:

  • Systematic and detailed examination of processes that are structured around HAZOP guide words and operating parameters for a comprehensive review and coverage of all foreseeable hazardous events
  • Usually performed by specialized personnel with experience and insight into the facility and from various engineering and operational disciplines
  • A scalable method for evaluation of hazards at the facility, process system, or project design level
  • Generally, a qualitative assessment based on consequences, causes, and protection requirements

HAZOP Strengths and Limitations

Before employing the HAZOP process, organizations need to be aware of its strengths and limitations.


Manufacturing, pharmaceuticals, nuclear, power, chemical, and oil and gas industries apply HAZOP study to their operation and processes because it offers:

  • Structured and detailed methodology: HAZOP identifies the chain of cause-to-consequence of hazards and operability issues such as human error, procedural error, equipment/system reliability issues. It aids the design of preventative and mitigating responses.
  • Synergistic approach: HAZOP encourages viewpoints from expert team members with diverse disciplines. The interaction cultivates creativity and ensures a wide range of potential consequences can input into the analysis.
  • Good economics: It saves substantial money from the costs of catastrophic accidents and inefficient plant operability. A well-done HAZOP assures accident avoidance during the lifetime of the operating plant from the processes under review.
  • Time savings: It saves time through a more streamlined and safer start-up, quicker attainment of production levels, and incident-free operations.


However, a HAZOP study is not a foolproof method of identifying every possible hazard or operability problem during the actual operations. The outcome of the HAZOP is dependent on:

  • The level of information available: The accuracy and the extent of the system information, such as process & instrumentation diagrams (P&ID), known to the team, influence its success.
  • The expertise of the team: The technical knowledge and experience related to engineering, operations, maintenance and inspection, safety and emergency response within the HAZOP team is crucial to the quality and completeness of a study

The HAZOP workshop process

The HAZOP workshop is performed in the following sequence:

  1. Define the system, its subsections, and nodes: Select the system’s boundaries, divide it into manageable subsections, identify nodes under consideration, and understand each node’s intended process parameters (flow, pressure, etc.).
  2. Define the problems of interest: Specify the Health, Safety, and Environment (HSE) problems of interest that the analysis will address.
  3. Apply deviations for each node: Develop meaningful deviation (high, low, etc.) scenarios from the intended process parameters.
  4. Examine the consequences: Identify all significant implications for each deviation without regard to any existing safeguards.
  5. Examine the causes: Identify potential causes of the deviations.
  6. Calculate the unmitigated risk: Assess the likelihood and impact of this deviation.
  7. Identify safeguards: Determine the most robust safeguards against each consequence.
  8. Calculate the residual risk: Re-assess likelihood and impact of deviation with existing safeguards.
  9. Identify and recommend additional safeguards: Specify other safeguards for risk reduction to acceptable (tolerable) level.
  10. Calculate the residual risk: Re-assess the likelihood and impact of deviation with additional safeguards.
  11. Prepare a report: Finalize listing of safeguard recommendations in priority sequence.
HAZOP analysis
Figure 1: HAZOP analysis. Image courtesy of US Department of Labor, Occupational Safety and Health Administration

Results of a HAZOP

When a HAZOP analysis is performed in the planning stage of a new or greenfield facility, all potential causes of failure would be identified well in advance.

Implementing the engineering and administrative controls recommended in the HAZOP would now result in an inherently safer plant and help avoid costly modifications in the future.

For existing or brownfield facilities, a HAZOP analysis is performed in 3-year or 5-year intervals. The subsequent HAZOP studies demonstrate that all possible recommendation actions on hazards identified in the previous HAZOP have been implemented.

Recommendations are precise and include a reference to specific equipment. They can be categorized into one of the following:

  • Review or modify system design
  • Conduct a detailed safety or security review
  • Develop or update a procedure (operational, preventive maintenance)
  • Improve inventory management and asset lifecycle
  • Improve alarm management
  • Enhance fire or explosion protection
  • Improve disaster recovery and emergency response
  • Improve employee and contractor screening and observation program
  • Enhance physical perimeter security

Further reading

Process Safety Management Guidelines for Compliance, US Department of Labor, Occupational Safety and Health Administration.

How ORIGNIX helps

ORIGNIX leverages the results of HAZOP studies to conduct cyberHAZOP studies. The cyberHAZOP study is an integral part of our cyber Process Risk Assessment (cyberPRA) methodology based on ISA/IEC 62443 and ISA/IEC 61511 industry standards. The assessment identifies potential gaps, hazards, vulnerabilities, independent protection layers associated with engineered industrial processes at plant facilities. The identified cyber risks are prioritized based on realistic cost-benefit analysis.

To learn how our customers benefit, visit our website

Authors note: This blog was co-authored between Saif Shariff  and Anastasios Arampatzis