Hazop study

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A Hazard and Operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation.

The HAZOP technique was initially developed to analyze chemical process systems, but has later been extended to other types of systems and also to complex operations and to software systems.

The HAZOP study should preferably be carried out as early in the design phase as possible - to have influence on the design. On the other hand; to carry out a HAZOP we need a rather complete design. As a compromise, the HAZOP is usually carried out as a final check when the detailed design has been completed. A HAZOP study may also be conducted on an existing facility to identify modifications that should be implemented to reduce risk and operability problems.


A HAZOP is a qualitative technique based on guide-words and is carried out by a multi-disciplinary team (HAZOP team) during a set of meetings. HAZOP( Hazard and Operability Study) and What-If reviews are two of the most common petrochemical industry qualitative methods used to conduct process hazard analyses. Up to 80% of a company’s process hazard analyses may consist of HAZOP and What-If reviews with the remainder 20% from Checklist, Fault Tree Analysis, Event Tree, Failure Mode and Effects Analysis, etc. An experienced review team can use the analysis to generate possible deviations from design, construction, modification, and operating intent that define potential consequences. These consequences can then be prevented or mitigated by the application of the appropriate safeguards.

HAZOP studies may also be used more extensively, including:

• At the initial concept stage when design drawings are available.
• When the final piping and instrumentation diagrams (P&ID) are available.
• During construction and installation to ensure that recommendations are implemented
• During commissioning
• During operation to ensure that plant emergency and operating procedures are regularly reviewed and updated as required

A HAZOP or What-If report is a living document for a facility. As changes are made to a facility or its procedures the HAZOP or What-If review(s) will be updated to represent the current facility. Process hazard analysis reviews are also required to be updated and revalidated every five years as a minimum by U.S. regulations (OSHA and EPA).

Types of HAZOP

• Process HAZOP
  HAZOP technique was originally developed to assess plants and process systems
• Human HAZOP
  A “family” of specialized HAZOPs. More focused on human errors than technical failures
• Procedure HAZOP
  Review of procedures or operational sequences Sometimes denoted SAFOP - SAFe Operation Study
• Software HAZOP
  Identification of possible errors in the development of software

HAZOP Team Members

HAZOP team leader Responsibilities:

• Define the scope for the analysis
• Select HAZOP team members
• Plan and prepare the study
• Chair the HAZOP meetings
• Trigger the discussion using guide-words and parameters
• Follow up progress according to schedule/agenda
• Ensure completeness of the analysis
• The team leader should be independent (i.e., no responsibility for the process and/or the performance of operations)

HAZOP secretary/Scribe Responsibilities:

• Prepare HAZOP worksheets
• Record the discussion in the HAZOP meetings
• Prepare draft report(s)

HAZOP team members

The basic team for a process plant will be:

• Project engineer
• Commissioning manager
• Process engineer
• Instrument/electrical engineer
• Safety engineer

Depending on the actual process the team may be enhanced by:

• Operating team leader
• Maintenance engineer
• Suppliers representative
• Other specialists as appropriate

HAZOP Meetings:

Proposed agenda:
1. Introduction and presentation of participants
2. Overall presentation of the system/operation to be analyzed
3. Description of the HAZOP approach
4. Presentation of the first node or logical part of the operation
5. Analyze the first node/part using the guide-words and
parameters
6. Continue presentation and analysis (steps 4 and 5)
7. Coarse summary of findings
Focus should be on potential hazards as well as potential
operational problems
Each session of the HAZOP meeting should not exceed two hours.

The findings are recorded during the meeting(s) using a HAZOP work-sheet, either by filling in paper copies, or by using a computer connected to a projector (recommended).

The HAZOP work-sheets may be different depending on the scope of the study - generally the following entries (columns) are included:
1. Ref. no.
2. Guide-word
3. Deviation
4. Possible causes
5. Consequences
6. Safeguards
7. Actions required (or, recommendations)
8. Actions allocated to (follow-up responsibility)

Data Required for a HAZOP Study

As a basis for the HAZOP study the following information should
be available:

• Process flow diagrams
• Piping and instrumentation diagrams (P&IDs)
• Layout diagrams
• Material safety data sheets
• Provisional operating instructions
• Heat and material balances
• Equipment data sheets Start-up and emergency shut-down procedures

HAZOP Procedure

1.Divide the system into sections (i.e., reactor, storage)
2. Choose a study node (i.e., line, vessel, pump, operating instruction)
3. Describe the design intent
4. Select a process parameter
5. Apply a guide-word
6. Determine cause(s)
7. Evaluate consequences/problems
8. Recommend action: What? When? Who?
9. Record information
10. Repeat procedure (from step 2)

Illustration of the HAZOP Procedure

The following modes of plant operation should be considered for
each node:

• Normal operation
• Reduced throughput operation
• Routine start-up
• Routine shutdown
• Emergency shutdown
• Commissioning
• Special operating modes

Process HAZOP Worksheet
Worksheet Entries

Node
A node is a specific location in the process in which (the deviations of) the design/process intent are evaluated.

Examples might be: separators, heat exchangers, scrubbers, pumps, compressors, and interconnecting pipes with equipment.

Design Intent
The design intent is a description of how the process is expected to behave at the node; this is qualitatively described as an activity (e.g., feed, reaction, sedimentation) and/or
quantitatively in the process parameters, like temperature, flow rate, pressure, composition, etc.

Deviation
A deviation is a way in which the process conditions may depart from their design/process intent.

Parameter
The relevant parameter for the condition(s) of the process (e.g. pressure, temperature, composition).

Guideword
A short word to create the imagination of a deviation of the design/process intent. The most commonly used set of guide-words is: no, more, less, as well as, part of, other than,
and reverse. In addition, guidewords like too early, too late, instead of, are used; the latter mainly for batch-like processes.

The guidewords are applied, in turn, to all the parameters, inorder to identify unexpected and yet credible deviations from the design/process intent.

Guide-word + Parameter = Deviation

Cause
The reason(s) why the deviation could occur. Several causes may be identified for one deviation. It is often recommended to start with the causes that may result in the worst possible
consequence.

Consequence
The results of the deviation, in case it occurs. Consequences may both comprise process hazards and operability problems, like plant shut-down or reduced quality of the product.
Several consequences may follow from one cause and, in turn, one consequence can have several causes.

Safeguard

Facilities that help to reduce the occurrence frequency of the deviation or to mitigate its consequences. There are, in principle, five types of safeguards that:
1. Identify the deviation (e.g., detectors and alarms, and human operator detection)
2. Compensate for the deviation (e.g., an automatic control system that reduces the feed to a vessel in case of overfilling it. These are usually an integrated part of the process control)
3. Prevent the deviation from occurring (e.g., an inert gas blancket in storages of flammable substances)
4. Prevent further escalation of the deviation (e.g., by (total) trip of the activity. These facilities are often interlocked with several units in the process, often controlled by computers)
5. Relieve the process from the hazardous deviation (e.g., pressure safety valves (PSV) and vent systems)

Process parameters may generally be classified into the following groups:

• Physical parameters related to input medium properties
• Physical parameters related to input medium conditions
• Physical parameters related to system dynamics
• Non-physical tangible parameters related to batch type processes
• Parameters related to system operations

These parameters are not necessarily used in conjunction with guide-words:

• Instrumentation
• Relief
• Start-up / shutdown
• Maintenance
• Safety / contingency
• Sampling

Some Parameters:
Flow, Composition, pH,Pressure, Addition, Sequence,Temperature, Separation, Signal,Mixing, Time, Start/stop,Stirring, Phase, Operate,Transfer, Speed, Maintain,Level, Particle size, Services,Viscosity, Measure, Communication,Reaction Control


Basic HAZOP Study Guidewords:

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