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HAZard & OPerability (HAZOP)

HAZOP Objective

The primary objective of the HAZOP study is to identify and evaluate HSE hazards due to
process deviations/system failures/human error and to identify operability issues which,
although not hazardous, could compromise the plant’s ability to achieve its design intent and
The secondary objective of the HAZOP is to confirm the adequacy of detection of deviations
and controls safeguarding the process. The review is based on P&IDs. HAZOP Study enables to identify corrective actions in the form of additional controls and recommendations to be placed either to eliminate or mitigate hazards.

Where is HAZOP applicable?

HAZOP study procedure is applicable to every definite operational sequences in planned and existing systems. HAZOP Analysis is most effective when held during the conceptual design stage in which recommendations impacting the general design may be fabricated.

HAZOP study in chemical plant

HAZOP Study determines the Process Hazards which may incur sufficient damage or injury if not appropriately controlled. It is also used for determining equipment failures that would result in process failures or accidents inside the Plant which is being examined during a HAZOP Study. A HAZOP analysis is applicable to any level of an organization from a small Unit process to entire Plant

When is HAZOP done

As depicted in the below held Flow Chart, HAZOP Analysis should be completed in stages inside a risk management project. Generally HAZOP analysis is initiated immediately upon a new process or a process that has brought a change in the working environment.

HAZOP methodology

The HAZOP technique consists of a systematic analysis of the design in order to assess any
operability problems or process-related hazards. The HAZOP Review is developed reviewing
each P&ID using a structured step-by-step approach that allow to comprehensively analyses
the whole process via suitable guidewords, used to identify credible deviations from the design
The method identifies hazards and suggests possible accident sequences resulting from such
hazards; innovative thinking then identifies the consequences of these scenarios.
A summary flow chart of the HAZOP process

In this each node, deviation, safeguards available and mitigation measures & recommendations will be recorded

HAZOP Basic Rules and Assumptions

The following ground rules were set before proceeding with the HAZOP Session, and the HAZOP Chairman presented a summary at the start of the first day of the workshop:

  • Equipment has been designed with adequate design envelopes for start-up,
  • operation and shutdown;
  • Equipment is designed and installed as per installation code requirements;
  • Equipment and instrumentation are selected and installed compatible to local conditions;
  • Double jeopardy’ failures are not considered. Common mode failures are assessed as they are considered a ‘single jeopardy’ failure;
  • Flange/gasket leakages are not considered as a cause;
  • Spontaneous pipe or vessel rupture is not considered as a cause;
  • Single check valves are not generally considered an adequate safeguard against a hazardous backflow on their own; nevertheless, since they provide mitigation against it, they have been recorded as safeguard, when present;
  • Minor changes to the P&IDs will be noted clearly on the master P&IDs in red pen, instead of recording as a recommendation at each occurrence; however, when the change is deemed to be significant, this will be also recorded in the HAZOP log sheets;
  • Prolonged & side discussion shall be avoided. The objective is to identify potential hazards not to design them out during the workshop; when disagreement arises, a recommendation will be issued;
  • Time will not be spent on finding solutions, unless solution is obvious;
  • Sections of the existing plant will not be considered in detail; only impacts to/ from the new Project facilities to these sections will be assessed.

HAZOP Guidewords

The following table summarizes the main guidewords that were applied and the typical deviations obtained combining the guidewords and the process parameters.

Flow􀁸 More
􀁸 Less
􀁸 Reverse
􀁸 No
􀁸 Other than
􀁸 As well as
􀁸 Misdirected
􀁸 Quantitative Increase
􀁸 Quantitative decrease, includes
no flow
􀁸 Reverse/ opposite direction
􀁸 Complete negation of the
􀁸 Design intent
􀁸 Complete substitution
􀁸 Qualitative modification/ increase
Pressure􀁸 More
􀁸 Less
􀁸 No
􀁸 More than normal operating
􀁸 Less than normal operating
􀁸 Vacuum
Temperature􀁸 More
􀁸 Less
􀁸 More than normal
􀁸 Less than normal
Level􀁸 More
􀁸 Less
􀁸 More than normal
􀁸 Less than normal
Composition􀁸 Change
􀁸 Contamination
􀁸 Corrosive
􀁸 Contamination
􀁸 Out of specifications
Others􀁸 Start-up/ Shutdown
􀁸 Maintenance
􀁸 Corrosion
􀁸 Utilities Failure
􀁸 Vent/Drain
􀁸 Safety
􀁸 Leakage or release to atmosphere
􀁸 Deviations related to mentioned

How is HAZOP performed?

An Online brainstorming session will be held with the multidisciplinary team accompanied by the HAZOP Chairman and Scribe. The session is led by discussion for each node, deviation, safeguards available and thereby preventive measures & recommendations will be recorded using the Software PHA Pro.

The Input documents required by the HAZOP team are as follows

  • PFD’s
  • P&IDs for Process & Utilities
  • HSE Risk Matrix and Response Chart
  • Heat and Mass balances
  • Plot Plans or General Equipment Arrangements & Elevation Drawings
  • Material Specifications and Selection Charts
  • Cause and Effect Diagrams
  • Process Design Basis
  • Process Operation & Control Philosophy
  • Operations and Maintenance Manual

A brainstorming session will be held onsite with the multidisciplinary team along with the HAZOP Chairman and Scribe. The session will be discussed for each node, deviation, safeguards available and mitigation measures & recommendations will be recorded with the help of software PHA Pro.

The Team indulged in HAZOP Analysis has a good knowledge of Plant Operation. Hence there wouldn’t be any chance of Field Survey as all required information can be obtained from Operating Personnel through discussions. Interviewing the Plant Operators in their working Day for few Hours will yield relevant information required to make a Hazard List which will be categorized based on frequency and Severity attributes using Checklists.

iFluids Engineering have done numerous projects on HAZOP Study in India, Qatar, Oman, Tunisia and various other countries.

Take a look at our case studies some of projects done by iFluids on HAZOP Study in India and other countries by clicking the below link

Case Studies on HAZOP Study

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