Hazard Operability Review (HAZOP)
1.0 Introduction to HAZOP
HAZOP (Hazard and Operability) review/study is a method for a qualitative assessment of hazards associated with the operation and maintenance of a system or facility. Due to its nature a HAZOP is to be conducted by a HAZOP team since individual input, exchange of ideas and interactions between the team members are essential components of its effectiveness. The objective of an HAZOP is not to generate cost figures related to loss of production or capital, however indicative cost figures associated with the consequences of occcurances of adverse events may be included if so desired by the proponent.
A HAZOP study focuses on deviations from the intended use of the system or facility, the assessment of the consequences and operational hazards that may then occur, as well as review of the safeguards and adequacy of safeguards (LOPA) and acceptable risk (ALARP). It also establishes actions required for mitigating, or preventing the occurrence of an hazardous situation.
This purpose of this introduction is to present an excerpt on how an HAZOP study can be conducted in a controlled systematic and comprehensive plan of action.
Hazard and operability studies CEI/IEC 61882
European commission: Chemical Accidents (Seveso I,II & III) –International co-operation.
Analysis of an hazard (HAZAN), i.e. assessing the probability of the occurrence of an adverse event, is a quantitative risk assessment process and therefore not part of the scope of this introduction. Contrary to a qualitative risk assessment, a quantitative risk assessment can be performed by a single individual. Guidelines for quantitative analysis are published in the Netherlands under the CRP 18 “Guidelines for Quantitative Analysis”.
The objective of a HAZOP is to qualitatively analyse possibilities of potential deviations from the intended use or deviation from the normal operating conditions of a production process cycle, scheme, system design or equipment. Deviations are typically addressed, as appropriate, as more/high and less/low.
A HAZOP study applies brain storming techniques involving a team of professionals with roles from diffferent disciplines and skills. For facilitating the conduct of a HAZOP study, common practice is the application of generally accepted guide words.
A HAZOP study model can be applied to the operation of equipment, facilities, processes; etc.It includes human actions and behaviour and can be carried out at any stage of a life cycle of a facility from the conceptual stage through operation.
The HAZOP model presented in this introduction can be applied to any HAZOP. It is recommended that an HAZOP review is considered in the every Project Execution Plan (and performed during the course of project execution). This introduction addresses sequence of actions, evaluation criteria, and role of partipants. Definitions, key issues and abbrieviations, generally applied during the course of conduct of an HAZOP study.
Following are some commonly used defitions:
● Risk: The measure of probability of an adverse event.
● Hazard : The inherent attribute or feature that has the potential to cause an adverse event.
Issues to be addressed during a HAZOP study are:
● BPCS:Basic Process Control System. The BPCS is the control system that monitors and controls the process for ensuring that the process conditions for producing the material are maintained for its intended use.
● FMEA: Failure mode and effect analysis. Assessment of the effects and consequential damages in case of equipment/system failure.
● LOPA: Level of Protection Assessment.
● BLEVE: Boiling Liquid Expansion Vapor Cloud Explosion.
● ALARP: As Low as Reasonably Practical. When starting any enterprise or action there is a potential risk for failure. Establishment of the acceptable level of risk is an essential part of assessment and subsequent mitigation.
● SIS: Safety Instrument System.
● SIL: Safety Integrity Level.
● HIPPS: High Integrity Process Protection System.
A HAZOP study team generally consists of the following team members:
● HAZOP Chairman/facilitator.
● HAZOP Secretary.
● HAZOP Team members.
The HAZOP chairman leads the HAZOP, he interprets the findings and recommendations, acts as an arbiter in the discussions and arranges the documentation before and after the HAZOP. He also writes the HAZOP report.
The HAZOP secretary or scribe records the agreed outcome of the discussion, e.g. deviations, mitigations and consequences in reference to the guide words. He must be familiar with the HAZOP terminology and competent at writing and recording minutes in an electronic format. Minutes of a HAZOP session can be recorded on a preformatted Excel spread sheet or by using dedicated HAZOP software. Although not recommended, the HAZOP chairman can be acting as secretary. The HAZOP team members are to provide discipline expertise, and respond to questions and issues raised related to their function or discipline.
The sequence of actions of a HAZOP study related to the assessment of a potential deviation from its intended use are reflected in the diagram below.
Key Documents required for performing a HAZOP study on a process facility are:
● Process and Intrumention Diagrams (P&ID)
● Process Flow Diagrams (PFD)
● Cause and Effect Charts (E&C)
● Equipment and Instrument datasheets
● Process data sheets
● Preformatted HAZOP work sheets.
4.0 Guide words
Guide Words that can be used appropriate to the process conditions are listed below:
● Flow - More/High-Less/Low-Reverse
● Pressure -More/High-Less/Low
● Temperature - More/High-Less/Low
● Level -More/High-Less/Low
● Composition change
● Service Failure