HAZOP analysis

What is HAZOP analysis?

An industrial process is designed with a specific intention: that each stream has a defined flow rate, pressure, temperature, and composition; that each piece of equipment operates under specific conditions; and that each sequence occurs in a specific order. Process accidents arise when reality deviates from this intention and safeguards fail to detect or correct the deviation in time. HAZOP is based on this idea: instead of openly asking what could go wrong, it systematically examines each part of the process, applying guide words (no, more, less, in addition to, part of, reverse, different from, before, after) to each relevant parameter (flow rate, pressure, temperature, level, composition, time, sequence) to generate plausible deviations.

For each deviation, the team identifies the possible causes (pump failure, closed valve, operating error, loss of service), the consequences of inaction (overpressure, toxic leak, runaway reaction, equipment damage), existing safeguards (alarms, interlocks, safety valves, procedures), and, when the remaining risk is unacceptable, recommendations for improvement. All of this is documented in worksheets that serve as evidence of the study and the basis for the action plan.

HAZOP is a qualitative, team-based technique: its value lies in the input of a multidisciplinary group (process, operations, maintenance, instrumentation, safety) guided by an experienced facilitator. It is applied in the design of new facilities, in modifications, in the periodic review of existing facilities, and as part of change management. It is complemented by quantitative techniques (fault tree analysis, layer of protection analysis) when safeguards need to be sized.

Methodology

• Preparation. Definition of scope and objectives, collection of documentation (piping and instrumentation diagrams, data sheets, procedures), division of the process into nodes and selection of the team and facilitator.
• Analysis sessions. For each node, description of the design intent, application of the guide words to each parameter, identification of causes, consequences and safeguards, risk assessment (often with a matrix) and formulation of recommendations.
• Record. Worksheets with the traceability of each deviation, the team’s decisions and actions, numbered and assigned.
• Report and follow-up. Final report with prioritized recommendations, the organization’s response to each (acceptance, alternative, or justification for rejection), implementation plan, and verification of closure.
• Revalidation. Review of the study in response to modifications, incidents or after a period of time has elapsed (usually five years in facilities affected by serious accidents), and verification that the safeguards are still operational.

Applications and variants

• Continuous and batch processes. Chemical, petrochemical, pharmaceutical, food, water treatment, and energy plants; in batch processes, sequence and time parameters are added.
• Procedures and operations. HAZOP procedures for start-ups, shutdowns, cleaning and maintenance, analyzing each step.
• Control and safety systems. Evaluation of safety instrumented systems and determination of safety integrity levels according to the IEC 61511 series, based on the identified scenarios.
• Major accidents. Basis of the risk analyses required in the policy for the prevention of major accidents, the safety management system and the safety report of Royal Decree 840/2015.
• Other related techniques include What-if, checklists, Failure Mode and Effects Analysis (FMEA), Fault Tree Analysis, Layers of Protection Analysis (LOPA), and bow-tie analysis, which are combined according to the phase and level of detail.

Organizational application: how to perform a HAZOP

1. Define the scope, timing (design, modification, revalidation) and objectives of the study, and appoint an experienced facilitator and a secretary.
2. Gather up-to-date documentation (piping and instrumentation diagrams, balances, data sheets, procedures, incident history) and verify that it reflects the actual installation.
3. Divide the process into manageable nodes and form a multidisciplinary team with guaranteed dedication during the sessions.
4. Systematically apply the guide words to each parameter of each node, recording causes, consequences, safeguards, risk assessment, and recommendations.
5. Issue the report, assign each recommendation to a responsible party with a deadline, and record the management’s response.
6. Execute and verify the closure of actions, integrate them into change management and risk assessment, and inform representatives.
7. Schedule periodic revalidation and after relevant modifications or incidents.

Preventive management software allows you to record HAZOP recommendations as actions with responsible party, deadline and evidence of closure, link them to the affected equipment and processes and plan the revalidations.

Limits and common mistakes

1. Conducting the study with outdated documentation or without reflecting the modifications to the installation.
2. Incomplete equipment, without operating or maintenance personnel, or without an independent and experienced facilitator.
3. Excessively long sessions that degrade attention and the quality of analysis.
4. Relying on safeguards that are not proven, maintained, or of the same nature as the cause (common dependency).
5. Not finalizing the recommendations or verifying their effectiveness, turning HAZOP into a documentary exercise.
6. Apply HAZOP to conventional occupational risks for which there are more suitable methods, or use it as the sole technique without quantification when the consequences are severe.

HAZOP requires specific training and experience in the process being analyzed; this sheet is for informational purposes only.

Regulatory and reference framework

• IEC 61882:2016 . Hazard and operability studies (HAZOP studies): application guide for the technique.
• Royal Decree 840/2015, of September 21. Measures for the control of risks inherent in major accidents involving hazardous substances: risk analysis, management system and safety report.
• Law 31/1995, articles 15 and 16. Principles of preventive action and risk assessment, which HAZOP feeds into process facilities.
• Directive 2012/18/EU (Seveso III) . Control of major-accident hazards involving dangerous substances.
• NTP 238 of the INSST . Hazard and operability analyses in process installations.

The technique is internationally applicable; in Colombia, Decree 1072 of 2015 and the regulations on major accidents require the identification of process hazards in facilities with hazardous substances.