HAZOP : Hazard Operability Study


  • Hazard and Operability Analysis (HAZOP) is a structured and systematic technique for system examination and risk management.
  • In particular, HAZOP is often used as a technique for identifying potential hazards in a system and identifying operability problems likely to lead to nonconforming products.   
  • HAZOP is based on a theory that assumes risk events are caused by deviations from design or operating intentions.
  • Identification of such deviations is facilitated by using sets of “guide words” (such as no, less, more, part of, as well as, reverse, other than) as a systematic list of deviation perspectives.
  • This approach is a unique feature of the HAZOP methodology that helps stimulate the imagination of team members when exploring potential deviations.
  • The HAZOP is a qualitative technique based on guide-words and is carried out by a multidisciplinary team (HAZOP team) during a set of meetings.
  • HAZOP is also commonly used in risk assessments for industrial and environmental health and safety applications.

Definition :

  • Hazard – Potential source of harm. Deviations from design or operational intent may constitute or produce a hazard. Hazards are the focus of HAZOP studies, and it should be noted that a single hazard could potentially lead to multiple forms of harm.

HAZOP Characteristics

  • HAZOP is best suited for assessing hazards in facilities, equipment, and processes and is capable of assessing systems from multiple perspectives.
  1. Design ­ assessing system design capability to meet user specifications and safety standards & identifying weaknesses in systems
  2. Physical and Operational Environments ­ assessing environment to ensure system is appropriately situated, supported, serviced, contained, etc.
  3. Operational and Procedural Controls ­ assessing engineered controls (ex: automation), sequences of operations, procedural controls (ex: human interactions) etc.
  4. Assessing Different Operational Modes – start-up, standby, normal operation, steady & unsteady states, normal shutdown, emergency shutdown, etc.


1.Helpful when confronting hazards that are difficult to quantify, i.e

-Hazards rooted in human performance and behaviours

-Hazards that are difficult to detect, analyze, isolate, count, predict,etc

-Methodology doesn’t force you to explicitly rate or measure deviation probability of occurrence, severity of impact, or ability to detect

2. Built-in brainstorming methodology

3. Systematic & comprehensive methodology

4. More simple and intuitive than other commonly used risk management tools


  1. No means to assess hazards involving interactions between different parts of  a system or process
  2. No risk ranking or prioritization capability ­ teams may optionally build-in such capability as required
  3. No means to assess effectiveness of existing or proposed controls (safeguards) ­ may need to interface HAZOP with other risk management tools


The effectiveness of a HAZOP will depend on:

  1. the accuracy of information (including P&IDs) available to the team — information
  2. should be complete and up-to-date
  3. The skills and insights of the team members
  4. how well the team is able to use the systematic method as an aid to identifying
  5. deviations
  6. The maintaining of a sense of proportion in assessing the seriousness of a hazard
  7. The expenditure of resources in reducing its likelihood
  8. the competence of the chairperson in ensuring the study team rigorously follows
  9. Sound procedures.

Key elements of  HAZOP

  • HAZOP team
  • Full Description Of Process
  • Relevant Guide Words (no, less, more, part of, as well as, reverse, other than)
  • Conditions Conducive To Brainstorming
  • Recording of Meeting
  • Follow Up Plan

HAZOP Methodology

  1. Definition Phase 
  • The Definition Phase typically begins with preliminary identification of risk assessment team members.
  • HAZOP is intended to be a cross-functional team effort, and relies on specialists (SMEs) from various disciplines with appropriate skills and experience who display intuition and good judgment.
  • SMEs should be carefully chosen to include those with a broad and current knowledge of system deviations.
  • HAZOP should always be carried out in a climate of positive thinking and frank discussion.
  • During the Definition Phase, the risk assessment team must identify the assessment scope carefully in order to focus effort.
  • This includes defining study boundaries and key interfaces as well as key assumptions that the assessment will be performed under.

2. Preparation Phase

The Preparation Phase typically includes the following activities: 

  • Identifying and locating supporting data and information 
  • Identification of the audience and users of the study outputs
  • Project management preparations
  • Consensus on template format for recording study outputs
  • Consensus on HAZOP guide words to be used during the study

3. Examination Phase

  • The Examination Phase begins with identification of all elements (parts or steps) of the system or process to be examined.
  • The HAZOP guide words (no, less, more, part of, as well as, reverse, other than) are then applied to each of the elements.
  • In this fashion a thorough search for deviations is carried out in a systematic manner.
  • It must be noted that not all combinations of guide words and elements are expected to yield sensible or credible deviation possibilities.
  • As a general rule, all reasonable use and misuse conditions which are expected by the user should be identified and subsequently challenged to determine if they are “credible” and whether they should be assessed any further.
  • There is no need to explicitly document the instances when combinations of elements and guide words do not yield any credible deviations.
  • The analysis should follow the flow or sequence related to the subject of the analysis, tracing inputs to outputs in a logical sequence.
  • Hazard identification techniques such as HAZOP derive their power from a disciplined step by step examination process.

4. Documentation & Follow-up Phase

  • The documentation of HAZOP analyses is often facilitated by utilizing a template recording form as detailed in IEC Standard 61882.
  • Risk assessment teams may modify the template as necessary based on factors such as:
  • Regulatory requirements
  • Need for more explicit risk rating or prioritization
  • Company documentation policies
  • Needs for traceability or audit readiness


  • HAZOP is a powerful tool. The output of the tool should always be presented at a level of detail appropriate for the various stakeholders.
  • This is important not just for presenting results, but also for obtaining early buy-in on the approach.
  • On a long-term basis, operational feedback should confirm that the assessment and control steps are adequately addressing the risk question.
  • If this is not the case, it may be necessary to review all assumptions. Feedback should correspond to ensuring that assumptions made about the level of residual risks are still valid.
  • Residual risks are risks that are expected to remain after risk control strategies have been exercised.
  • It is also important to note that new risks may arise from risk control practices.
  • Sometimes risks that were not originally identified or may have been filtered out during the initial risk assessment can become aggravating factors due to the implementation of risk control measures

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