Hazard and Operability study (HAZOP)

Hazard and Operability study (HAZOP)

          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 developed to Chemical process systems, other types of systems, complex operations and software systems.

A HAZOP study is a qualitative technique and is carried out by multi-disciplinary team (HAZOP) during a set of meetings.

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. 

  HAZOP Team & Meetings

HAZOP Team Leader:

Responsibilities:

•  Define the scope for the analysis
•  Select HAZOP team members
•  Plan and prepare the study
•  Chair the HAZOP meetings

1.  Trigger the discussion using guide-words and parameters
2.  Follow up progress according to schedule/agenda
3.  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 Participant:

• Be active! Everybody’s contribution is important
• Be to the point. Avoid endless discussion of details
• Be critical in a positive way - not negative, but constructive
• Be responsible. He who knows should let the others know

HAZOP Meeting:

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

HAZOP Recording:

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)

Process HAZOP

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

1. Process flow diagrams
2. Piping and instrumentation diagrams (P&IDs)
3. Layout diagrams
4. Material safety data sheets
5. Provisional operating instructions
6. Heat and material balances
7. 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)

Modes of operation:

The following modes of plant operation should be considered for

each node:

1. Normal operation
2. Reduced throughput operation
3. Routine start-up
4. Routine shutdown
5. Emergency shutdown
6. Commissioning
7. Special operating modes

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.

Process Parameters:

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:

1. Instrumentation
2. Relief
3. Start-up / shutdown
4. Maintenance
5. Safety / contingency
6. Sampling

HAZOP PROCEDURE

A procedure HAZOP is an examination of an existing or planned operation (work) procedure to identify hazards and causes for operational problems, quality problems, and delays.

• Can be applied to all sequences of operations
• Focus on both human errors and failures of technical systems
• Best suited for detailed assessments, but can also be used for coarse preliminary assessments
• Flexible approach with respect to use of guide-words

Procedure:

1. Breakdown of operation (work) procedure to suitable steps
2. Define intention of each step
3. Establish boundary conditions 
   else as 
   conventional Process HAZOP
4. Apply guide-words to intention and boundary conditions for 
   each step.

Guide words

Guide words	Meaning
No (not, none)	None of the design intent is achieved
More(more of, higher)	Quantitative increase in a parameter
Less (lessof, lower)	Quantitative decrease in a parameter
As well as(more than)	An additional activity occurs
Part of	Only some of the design intention is achieved
Reverse	Logical opposite of the design intention occurs
Other than(other)	Complete substitution - another activity takes place

Reporting:

Report Contents:

Summary

1. Introduction

2. System definition and delimitation

3. Documents (on which the analysis is based)

4. Methodology

5. Team members

6. HAZOP results

– Reporting principles

– Classification of recordings

– Main results

Appendix 1: HAZOP work-sheets

Appendix 2: P&IDs (marked)

Review Meetings:

Review meetings should be arranged to monitor completion of

agreed actions that have been recorded. The review meeting 

should involve the whole HAZOP team. A summary of actions 

should be noted and classified as:

• Action is complete
• Action is in progress
• Action is incomplete, awaiting further information

HAZOP Results:

• Improvement of system or operations

             – Reduced risk and better contingency
             – More efficient operations

• Improvement of procedures

             – Logical order
             – Completeness

• General awareness among involved parties
• Team

Advantages:

• Systematic examination
• Multidisciplinary study
• Utilizes operational experience
• Covers safety as well as operational aspects
• Solutions to the problems identified may be indicated
• Considers operational procedures
• Covers human errors
• Study led by independent person
• Results are recorded

Pitfalls and Objections:

• Time consuming
• Focusing too much on solutions
• Team members allowed to divert into endless discussions of details
• A few of the team members dominate the discussion
• “This is my design/procedure”

           – Defending a design/procedure
           – HAZOP is not an audit

• “No problem”
• “Wasted time”

Standards & Guidelines

1. IEC 61882. “Hazard and operability studies (HAZOP studies)

– Application guide”. International Electrotechnical Commission, Geneva.

2. Crawley, F., M. Preston, and B. Tyler: “HAZOP: Guide to best practice. Guidelines to best practice for the process and chemical industries”. European Process Safety Centre and Institution of Chemical Engineers, 2000

3.Kyriakdis, I.: “HAZOP - Comprehensive Guide to HAZOP in CSIRO”, CSIRO Minerals, National Safety Council of Australia, 2003