EHSQ -HAZOP STUDY GUIDELINE

 

 

Quality, Health safety and Environment

Table of contents

Hazop Study Guidelines. 1

Table of contents. 2

1    Introduction. 3

1.1    Document Purpose and Applicability. 3

1.2    Definition. 3

1.3    Limitations. 4

1.4    Hazop and Other Hazard Identification Techniques. 4

1.5    General Application of Hazop. 5

1.6    Application to Existing Facilities. 7

1.7    Scope. 8

1.8    HAZOP Objectives. 9

1.9   Contractor Conducted HAZOP. 9

1.10    Vendor Equipment 10

2    Team Composition. 11

2.1    Importance of the HAZOP Study Chairman. 11

2.2    The Team.. 11

2.3    Competency of Team Members. 12

3    Preparation & planning. 14

3.1    Timing and Programme. 14

3.2    Drawings and Information Required. 15

3.3    Venue. 15

4    Hazop study method. 16

4.1    Selecting Key Elements to Hazop. 16

4.2    Selecting and Applying Guidewords. 17

4.3   Identifying Causes of Deviations. 18

4.4    Defining Consequences. 18

4.5    Considering Existing Safeguards. 18

4.6    Agreeing Action Required. 18

4.7    Recording. 19

4.8    Issuing Worksheets. 20

5    Batch operations. 21

6    Programmable systems. 22

7    Report preparation and issue. 23

7.1    Report Contents. 23

7.2    Report Draft Issue. 24

7.3    Report Authorisation. 24

7.4    Archiving of Report and Drawings. 24

8    Follow-up. 25

9    Computer recording of Hazop studies. 26

10    References. 28

11. Appendices. 29

11.1 Appendix 1 Hazop Study Guideword Checklists. 29

11.1.1 GUIDEWORD CHECKLIST – Core set example. 29

11.1.2 GUIDEWORD CHECKLIST – Supplementary set 30

11.1.3 GUIDEWORD CHECKLIST - Supplement set for sequential ops. 31

11.1.4 GUIDEWORD CHECKLIST – Supplementary set for well operations. 33

11.2 Appendix 2   Completed HAZOP study worksheet. 34

 1    Introduction

1.1    Document Purpose and Applicability

This document would be typically issued by the operator’s health safety and/or environment department as part of their safety management system.

This supplement outlines guidance on conducting a Hazop Study as a means to ensuring that a well design, construction and/or technical operations integrity is meet to the requirements to Drill and deliver a well safely and within the assurance systems needed.

This guide would be used in conjunction with the accumulated knowledge and experience of the Hazop chairmen and the selected or invited Hazop team to define ‘best practice’ for conducting the required Hazop study unless an equivalent and/or an equally as effective approach can be demonstrated. 

Guidance is also provided on applicability, methodology and organisation of Hazop Studies, referencing other related hazard identification methods. 

1.2    Definition

A HAZOP study is carried out by a team led by an independent chairman, team leader, designated person, and other key team members.

It is a formalised and systematic technique for identifying work related hazards and operating problems ‘i.e. risks’; and note, not for solving or quantifying them (Ref. 1). 

The subject and work related matters to be studied and assessed are divided into smaller elements with the well design and operational delivery intention of each of these elements then being explained to the team. 

A checklist of Guidewords is systematically used to identify the potential hazards and operability problems ‘i.e. risks’ arising from deviations that result when assessing work and operations to be conducted.

From this probabilistic cause recognition and analysis of deviations identified are listed together with the likely consequences. Existing safeguards and the teams’ recommendations to mitigate and/or reduce the possibility of hazards and risks arising are then reviewed, evaluated determined with recommendations ultimately resulting.

1.3    Limitations

Hazop methodology is primarily designed to review historic and/or current information that exists pertaining to all associated operating procedures, instructions and standards requirement to be implemented.

Note: Information not covered during such implementation needing to be highlighted and perhaps covered by separate Hazops.

Hazop studies usually only consider the hazards known to arise from the most likely or consequential failures that exist: e.g. previous or likely equipment failure, wellbore difficulties, people or process related difficulties.

Hazops tend not to cover lower frequency catastrophic or multiple failure events. These if identified are covered through a top down approach such as a Hazid (Ref. 2) or Fault Tree Analysis.

Most importantly is the fact that the effectiveness of a Hazop study to identifying and assess credible hazards relies on the knowledge, experience and motivation of the team members as well as the competence of the chairman leading the study. 

1.4    Hazop and Other Hazard Identification Techniques

The term Hazop has special significance in that it implies that the operating procedures, standards and compliance to these have to rigorously recognised, analysed and assessed for hazards.

The Hazop methodology, as defined in section 1.2 of these guidelines, is therefore a powerful tool because particularly in a discipline such as drilling, as it involves a systematic analysis of the well design, planning, execution and what/it as things go wrong. It is equally applicable to batch/sequential operations when analysis may include further systematic review of simultaneous procedures. Here, studies may also be conducted on critical subsystems such as well testing, logging while drilling that may not fully represented in the main drilling Hazop study.

The term Preliminary Hazop, if used, should be limited to the use of the above methodology with the understanding that a full Hazop will be done at a later stage) but is particularly applicable to novel design features because problems can then be eliminated at an early stage with minimal impact on project cost . For these and similar non standard applications of Hazop type methodology i.e. which do not meet the full intent of these guidelines it is recommended that the term Critical Safety Review (Reference 4) is used to avoid confusion. 

Other hazard identification methodologies can be applied at different stages in development and address different representations of the well lie cycle and well management process. They may well involve subdividing the area to be studied into manageable elements and applying a checklist to each of these elements but they should not be called Hazop Studies. 

Some techniques also look at broader issues in less detail e.g. concept, feasibility reviews during initial stages of development; others analyse highly specific issues in detail e.g. FMEA's.  Note: A comparison of some of these other hazard identification techniques with the terminology, as currently used by HSEQA, is summarised in table 1. 

1.5    General Application of Hazop

HAZOP technique were essentially developed to identify the hazards associated with complex chemical processes but today are now applied throughout industries that have a process and flow sequence to them e.g. where drilling and completion operations are no exception.

It can also be applied to batch or sequential operations, (see Section 5) and by careful selection of guidewords, to the review such procedures.

It is equally applicable to all well operations particularly where novel techniques are to be employed (Ref. 3). 

Table 1.  HAZOP AND OTHER HAZARD IDENTIFICATION TECHNIQUES

Method	Application	Advantages	Limitations	Ref
Hazop	Review associated procedures. Normally applied to approved for construction issue.	Powerful systematic technique.	Information not on P & ID's. Operating modes not covered by procedures.  Catastrophic/multiple failures Team knowledge/experience.	1
Critical Safety Review	Review of P & ID's & associated procedures	Flexible use of Hazop technique & other hazard identification methods	Less structured and possibly less rigorous. Relies on leader/team judgement to adjust scope of review.	4
Simple Checklist	Can be applied to any operation at any stage from concept to abandonment. (eg pre-commissioning checklist, stage 1 task risk assessments)	Flexible approach with guideword selection which can be specific to the nature of the operation and its status	Can be superficial in the absence of a technique .for supporting the systematic application of appropriate guidewords.	5,6
What If	At any stage. Can be applied in a structured manner to selected areas	Brainstorming technique. Novel hazards not previously considered. Supplement to more rigorous approaches. Good forum for operational input.	Difficult to structure to ensure systematic coverage of hazards.  Strongly reliant on the imagination of team and leader facilitation of the process
Hazid Study	Top level identification of major hazards.  Application of guidewords to process units or offshore modules	Formal recording of hazards for subsequent detailed analysis.Can be applied at any stage and updated in the course of the project	Uses checklist but relies strongly on the experience of the team to identify the less obvious hazards. Causation mechanism not necessarily defined	2
Task Analysis	Review of procedures using checklists. Applicable to procedures including those not associated with P & ID's	Good forum for operator input, development of written procedures and training aids	Needs prioritised selective use on most critical activities. Association with the process/P & ID requires more structured Hazop approach	5,6
Concept Safety Review	Application of a broad range of project specific guidewords to PFD's, schematics etc	A wide range of hazards identified early in the project. Inherently safer options selection.	Study structure and selection of appropriate elements & guidewords relies strongly on team leader	6
Failure Modes & Effects Analysis (FMEA)	Considers component failure modes of (eg mechanical or electronic devices) and potential consequences. Applied at detailed design	Detailed analysis of potential critical system components failures (eg programmable systems, hydraulic systems)	All failure modes considered and hence time consuming and only applicable to critical devices and systems.	6

1.6    Application to Existing Facilities

The Hazop technique can also be applied to existing wells, equipment or procedures to identify potential hazards or operability problems which have not already become evident through previous operating experiences or to review non standard operations or procedures not previously covered. 

Modifications involving significant changes to equipment, changes to how the process operates and/or changes to the associated safety systems should also be the subject of HAZOP studies. 

The scope should clearly indicate whether the HAZOP is to be limited to the modifications only or applied to the whole operating system. All interfaces e.g. process/flow/drilling utilities between existing and modifications should be identified and reviewed.

Particular attention should be paid to tie-ins to existing operating systems. 

Minor changes to equipment and operations can be subject to a Critical Safety Review (Ref. 4) whereby the review team decide on the selective use of Hazop techniques appropriate to the change. 

Hazop techniques are also applicable as a means of hazard identification in carrying out a Task Risk Assessment of operational changes and non standard operations.  

The operators ‘Management of Change’ procedures should give guidance on the mechanism whereby appropriate use is made of Hazop and other hazard identification techniques. 

1.7    Scope

The scope should formally be agreed between the client/project and the HAZOP Study Chairman before the study commences. It should not be assumed that the client always knows what a HAZOP study is, the requirements for an effective study, the limitations of the technique or the extent of the responsibilities of the HAZOP team. In particular it should be emphasised that the HAZOP study is primarily concerned with identifying hazards and operability problems; not solving them or quantifying risks.  

If the client requires the HAZOP team to carry out further HAZOP studies on solutions to the identified problems proposed by the project this requirement should be covered at the outset. Follow up studies should only be undertaken when the main study is completed and must not be allowed to disrupt the main study. 

The briefing memo and subsequent report should identify the scope of the study including the extent of coverage of: 

• Process and Utility Drawings
• Drilling Equipment;
• Vendor Packages;
• Operating Procedures;
• Batch or Sequential Operations (eg. Pigging, Well Intervention);
• Various Modes of Operation:
• Start up/Shutdown
• Preparation for Maintenance
• Construction and Commissioning

It is equally important to identify areas and levels of detail not covered by the study e.g. utilities such as HVAC equipment, hydraulic systems etc; perhaps they are not hazardous, not safety critical or being covered by other reviews.

The inclusion of guidewords for the various modes of operation will ensure that some attention is given to these aspects but it should be understood that a full review of the start-up and shutdown operations, for example, can only be done when procedures are available. 

Cause and Effect charts will be used for reference in the Hazop study to check that appropriate action is taken, (as represented on the charts), to control the hazards identified in the course of the systems, equipment, process and procedure review. A complete review of the charts, logic diagrams or indeed the overall control of systems is not normally included in the scope of a conventional Hazop. Such supplementary requirements should therefore be separately identified in the Hazop terms of reference. 

1.8    HAZOP Objectives

The objective of a Hazop study is to check overall well design, construction and intended delivery  to search for operating deviations and undue process interactions which could lead to hazardous situations and/or operating problems. These might include: 

• Safety and Occupational Health hazards to workers;
• Damage to equipment/asset;
• Operability/Maintainability problems;
• Plant non-availability;
• Product ‘wellbore’ quality;
• Environmental spills discharges, issues;
• Well integrity, well control, and/or deliverability e.g. productivity hazards.

Any particular areas to be included/omitted from the scope of the study or particular sensitivities arising from, for example, the materials handled or the well location should be identified in the scope and briefed to the team prior to the start of the study. 

1.9   Contractor Conducted HAZOP

In most major projects the responsibility for the conduct of HAZOP studies is that of the operator as part of the well design and construction review. It is strongly recommended that QHSE guidance is sought by the project regarding the following: 

• Detailed HAZOP study procedure including design change review, follow-up HAZOP studies and acceptance procedure for responses to HAZOP recommendations.
• The individual proposed as chairman of the HAZOP team, normally selected from an approved list of experienced Hazop chairman.
• The HAZOP team composition; in particular to ensure a measure of independent OPERATOR involvement and operational input.
• The HAZOP study reporting procedure.

Where long term partnering contracts are established alliance procedures should be updated to reflect the contents of these guidelines and be audited as part of a typical safety management system. 

1.10    Vendor Equipment

Vendor packages should be integrated into the main Hazop study where possible with the appropriate vendor representative present for the review of large or specialist packages. Where this is not practicable then individual vendor package

Hazops should be conducted by the same core team with the vendor representative in the main contractors office to ensure consistency and coverage of package interfaces. 

Similarly well completion / tree details and the various well intervention activities should be integrated with topsides Hazops as far as possible with appropriate well operations personnel on the Hazop team. 

2    Team Composition

The HAZOP study technique cannot compensate for lack of knowledge or experience so the study team should include the various disciplines appropriate to the system/procedure being studied.  

Typically for drilling Hazops, well, completion, subsea engineering, drilling contractor and 3^rd party vendor operations expertise would be required. Other specialists e.g. Geologists, Petroleum engineers etc, may be required part time or throughout depending on the system being reviewed. 

A secretary leaves the other team members free to concentrate on the details of the study without the added burden of completing the log sheets. The secretary may also deal with other administrative matters, such as, organisation of meetings, circulation of typed log sheets, reports, etc.  

2.1    Importance of the HAZOP Study Chairman

The Chairman must be independent from the design of the system. It's his job is to ensure that the technique is systematically applied, that the team members are motivated and that their expertise is used effectively. He does not need expert knowledge of the system being studied since this is provided by the technical members of the team. However, Chairmen with process design or operating backgrounds and a basic level of understanding of the system being studied are usually more readily accepted by the other team members. 

The chairman must have proven study chairing ability appropriate for the complexity of the study and be able to plan and lead the whole HAZOP study through its various stages.  

He must also ensure that clear and precise records and reports are prepared and should take formal responsibility for the recommendations which he should agree with his team. 

The OPERATOR Project Team/Client may not be able to judge the acceptability of a proposed HAZOP study Chairman. They should be encouraged to take advice on this from HSEQA who can provide an approved list of suitably qualified chairmen. 

2.2    The Team

The team needs to be a balanced mix of knowledgeable project personnel and external experienced personnel who are independent from the project. 

An independent team member is defined for the purposes of these guidelines as one who has had no direct role in the design of the system being reviewed and has no reporting relationship with the design organisation which could degrade objectivity in reviewing the design. 

The typical core study team for a Drilling Hazop should be: 

• Independent Chairman;
• Secretary;
• Independent Senior Drilling person
• Operations Representative;
• Project Well Engineer(s).
• Drilling contractor representation
• Key 3^rd party vendor representation.

This core team should be supplemented by other project discipline engineers (full time or part-time), appropriate to the nature of the study. 

The team should be as small as possible for each review session and preferably no larger than six people.

For small studies on minor modifications a smaller team can be achieved by some combination of roles. 

A key member of every HAZOP team is the Independent Engineer who leads the role of "free thinking". 

2.3    Competency of Team Members

2.3.1    Chairman

The Chairman should typically be a chartered engineer or similar with at least 10 years experience in subject matter at hand and able to demonstrate, through HAZOP study training and experience, the ability to lead HAZOP studies in oil and gas related systems and should have the motivation and leadership capabilities to chair an exhaustive multi-discipline review of the technical information presented.  

Because of the crucial role of the chairman, where appropriate an experienced chairman can be used to participate in the study sessions and review the Hazop report as a means of confirming their suitability. 

Where Assets and their alliance contractors wish to use other personnel to lead safety studies, a similar procedure should be followed to develop the approved list of study leaders for Hazop studies and other similar safety studies e.g. Critical Safety Reviews and Hazid Studies). It is recommended that QHSE is involved in this selection and approval procedure. 

The route to qualification and inclusion on a list of approved Hazop chairman should include attendance at a Hazop training course, participation in Hazops in other roles, leading similar safety studies and perhaps assignments chairing small Hazop studies supported by an experienced chairman.  

 

 

2.3.2    Secretary

The secretary should be sufficiently familiar with the technology/terminology of the study and competent to accurately record the proceedings on the study worksheets with minimum guidance from the chairman so as not to delay the progress of the study. For computer worksheet production the secretary must also have keyboard skills and be familiar with the package used. 

2.3.3    Independent Engineer

The experience and discipline requirements should match the system/procedure being studied. For a drilling Hazop the independent engineer should typically have a degree in mechanical or related engineering degree and/or be a chartered engineer with at least five years experience (more for major projects or innovative technology), preferably in the oil and gas sectors. Should preferably have attended a Hazop training course or at the very least have been thoroughly briefed in the study technique before embarking on the study. 

2.3.4    Operations Representative

Should have experience equivalent to the Independent Engineer, and particular operating expertise in systems of the type being studied. For changes to existing systems the Operations Representative must be familiar with the installation being changed. The Operations Representative would invariably have served as an Offshore Production Engineer or a Production Supervisor or in similar appointments on an onshore installation as appropriate for the design to be reviewed. 

2.3.5    Project Engineer (Designer)

Normally the Lead Process Engineer for the design and may be from the engineering design contractor or OPERATOR. On some projects this could be the Project Engineer. Will be required to explain the design intention for every part of the system to be reviewed and have the authority to obtain the assistance/attendance of other project disciplines as required. 

2.3.6    Discipline Specialists

Additional project discipline specialists knowledgeable in the design must be available as full or part time members of the team to support the project process engineer and help the team understand the design intention and the inbuilt safeguards. 

The project discipline engineers on the team will need be familiar with the reference documentation listed in section 3.2. 

3    Preparation & planning

3.1    Timing and Programme

For major projects it is not possible to have a "one-bite" HAZOP study. Due to the ongoing development of the design it is necessary to plan for at least three phases of HAZOP study: 

1. Well design outline for main initial HAZOP study.
2. Well design finalised with work-scope changed significantly since initial HAZOP study.
3. Late design changes including those if any made during well execution.

For some projects an additional preliminary HAZOP study may be justified at an early stage (see 1.4). 

A specific programme should be issued to team members before the first HAZOP study meeting. The programme should include a schedule of all the data to be studied and reviewed and the approximate time allocated. 

At the first meeting of the HAZOP team a thorough briefing on the design and operation should be provided by the Project Engineer. 

The Chairman should ensure that all team members understand the scope of the study and brief any members not familiar with the Hazop technique. 

3.2    Drawings and Information Required

Full size HAZOP master ‘data sheets’ should be tabled for the HAZOP study. It is important that all members focus on one drawing that can be seen clearly from their positions at the table. 

The team will also require additional reference documentation to be available, with project personnel present familiar with their contents, typically including: 

• Well schematic
• General arrangement drawings 
• Engineering design data sheets (including relief valve data sheets)
• Well timings
• Clear work-scope definition and outline.
• Materials and equipment inventories to be used and applied
• Emergency and safety systems
• Commissioning procedures if new equipment being installed.
• Start-up procedures
• Operating procedures
• Shutdown, emergency, contingent  procedures
• Specialist Studies conducted, e.g. well control, vibration analysis etc.
• Operating and Maintenance Philosophy
• Safety Philosophy
• Design Philosophies
• Material Safety Data Sheets.

3.3    Venue

A dedicated room should be provided for Hazop sessions with the following attributes: 

• sufficient room and tabletop lay down area for team members to deploy drawings and documents;
• flipcharts, whiteboards etc to allow presentations and explanations to be made;
• wall area to pin up master copies of drawings;
• paper, pencils, dry marker and highlight pens, sticky labels etc;
• acceptable levels of noise, lighting, temperature, humidity etc.

Ideally the team should have access to a model of the plant being studied and be able to visit and photograph the site if it already exists. If the study is carried out on an existing site then Operations Representatives should not be "on duty" or prone to being called away from study sessions. 

4    Hazop study method

Following the design briefing by the project process engineer it may be appropriate to formally or informally review some general aspects of the well design and operating procedures prior to starting the conventional Hazop process. Topics might include: 

• Specialist studies and resulted conducted. E.g. Offset study.
• Specialised equipment, new technologies to be adopted.
• Materials of Construction/Corrosion Prevention;
• Well objectives and strategy document.
• Pressure/ stability management modelling.
• Geological risks and uncertainties.
• Environmental concerns.

This initial review will help the team understand the overall picture and if the general findings are recorded in the normal manner it may reduce the need for repetition of general concerns in the main part of the study. 

The conclusion of this initial review may redefine the scope of the study and/or recommend that separate reviews are required to cover some of these aspects in more detail. 

Following completion of the initial briefings and other general team discussions the chairman will initiate the Hazop process by selecting a starting point for the study; typically one of the main process feed lines. 

4.1    Selecting Key Elements to Hazop

The first step in applying the HAZOP study technique is to select an element of the system, i.e. a line, vessel or procedural step. The function of this element should be described by the process design specialist in the team. 

To ensure that the design intentions/functions of each element can be easily and clearly understood by the team only small elements of the system should be considered. There is a temptation to consider larger elements to speed up the process but this typically results in confusion during the study, ambiguity in the study records and failure to consider properly the potential deviations and associated hazards. 

THE CRITERION FOR SELECTING AN ELEMENT OF THE PROCESS FOR STUDY IS THAT THE GUIDE WORDS SHOULD APPLY UNIFORMLY THROUGHOUT EVERY PART OF THE ELEMENT. 

Any relaxation of this criterion, at the discretion of the Hazop chairman, should only be adopted for simple or low hazard systems. 

Particular care is required on pipeline manifold systems where for example 'reverse flow' will have different implications for different branches on the system. 

Similarly in reviewing, for example well operations, the status of valves/well barriers may change if too large a procedural step is selected for review. 

4.2    Selecting and Applying Guidewords

The Hazop technique was founded on an original list of guidewords that was composed of deviations of the main process parameters: e.g.

• Flow
• Temperature
• Pressure
• Composition

For batch, sequential or well related drilling operations, deviations from the intended Sequential Step were added to the list. 

The success of the technique has resulted in the scope being extended by a growing list of guidewords and reference documents to review. To some extent this is justified in that it is unlikely that the original process (i.e. P&IDs and Procedures) will receive the same degree of detailed analysis at any other stage. 

However, given that the basic Hazop methodology is already an exhausting, intensive exercise, there is a danger that the team will be overloaded and/or lose confidence in the value of the technique if the list of guidewords is excessive and/or largely irrelevant. 

Further, the inclusion of too many guidewords may result in a more rigorous review of these aspects than may be practicable given the information (procedures) available to the team. Early identification of problems is valuable but further review is likely always to be required.

The list of guidewords appropriate to the system being studied should thus be presented by the chairman and agreed by the team at the start of the study.

Once agreed the list will be applied to all elements of the Hazop. Where several systems are being reviewed, the team may wish to tailor the list of guidewords for one or more of the systems, e.g. if batch operations were involved.  

Since the list of guidewords impacts on the scope of the study this should be planned in advance, agreed with the client where appropriate and clearly documented in the Hazop report. 

The list of guidewords included in Appendix 1 contains a core and a supplementary set which should be used selectively along with any other additional system specific guidewords based on the scope of the study and the nature of the systems being studied. 

For new or unusual applications, the list of guidewords should be discussed with QHSE advisors. This can act as a way of updating the list of supplementary guidewords in Appendix 1 for selective use.

Hazop studies applied to procedures can be expected to have a reduced set of process guidewords with the emphasis on sequential step deviations in order to identify the potential for human errors of omission etc and other concerns specific to the procedure step being considered. 

4.3   Identifying Causes of Deviations

Realistic causes should be established for the deviations proposed and appropriately grouped. For example causes of no flow are likely to include upstream supply failures and downstream blockages which may have different consequences and safeguards. 

4.4    Defining Consequences

The Chairman should challenge the HAZOP team members to identify all credible hazard and operability consequences of the deviation. It is good practice at this point to discount the safeguards to ensure a full discussion of the inherent consequences of the deviation. 

4.5    Considering Existing Safeguards

The next step is to judge whether the engineering, safety systems and all other information as presented and reviewed, can cope with the consequences of all deviations.  

4.6    Agreeing Action Required

If the team judges that the engineering and safety systems are unlikely to cope with the consequences of all deviations, or an operability feature requires attention, then a recommendation should be made. 

Recommendations can be specific hardware or procedural items for action or consideration. Alternatively the Hazop team may have no specific solutions and rather than waste time trying to redesign the plant they should recommend that the project team review the concern and take appropriate action or that further studies are conducted to resolve the concern. 

The recommendations should be worded so as to be reasonably stand alone because they may become detached from the remaining contents of the worksheet during the follow up process. 

The Chairman should have every recommendation read out at the time it is raised in the session. The team members should be obliged to agree it at the time. Note that the use of computer Hazop recording packages greatly assists this process. The chairman/secretary may wish to reword the Hazop records to improve their clarity and this is quite acceptable as long as this does not change the essence of recommendations. The worksheets should be circulated to all team members for comments after the review sessions. Assigning responsibility for action is normally done by the client (Asset/Project) as part of the follow up procedure. 

Risk ranking can be used as a means of prioritising actions or cost benefit analysis, particularly on existing facilities (see reference 8). It can be done by the Hazop team or as part of the follow up procedure; possibly only on items where the balance of cost benefit is not obvious. 

4.7    Recording

"Full Recording" of all deviations, causes and consequences on worksheets provides a record for audit of HAZOP study proceedings but is very time consuming and wasteful of resources. "Recording by exception" is recommended. Reliance is then placed on selection of a competent experienced chairman to apply all the necessary guidewords/deviations and ensure that all valid concerns are recorded. 

However, the general approach should be to endeavour to record all significant hazards/concerns even when the subsequent discussion accepts the effectiveness of the safeguards provided and hence makes no further recommendation. With this approach the team will often find that the process of recording the concerns and existing safeguards reveals important recommendations which would have otherwise been missed. 

For manual recording the HAZOP Worksheet should be A3 size, the most suitable for the Secretary to fill in during study sessions. 

It is often necessary to use a large area of the worksheet to record a detailed "design intention" and this may include a description of a "mode of use" of the system studied. This is particularly relevant when reviewing changes to existing plant. Any computerised HAZOP study package should have the flexibility for recording such information (see Section 9). The discipline of recording such information serves to clarify for the team the exact modes of use of the engineering system (see Section 4.2 regarding treatment of multiple operating modes). 

Each recommendation must be sequentially numbered. If the same recommendation applies to another section of the P&ID studied later, it should be given a separate unique number, albeit with a note referring to the initial recommendation. 

The names of all team members and participants should be recorded on the initial worksheet for each review session (see Appendix 2). 

The HAZOP master P&IDs should be clearly marked up by the chairman (using suitable coloured highlighters) and archived for future reference by OPERATOR. It is very helpful for the Chairman or Secretary to mark on the drawings the number of each recommendation close to the relevant point on the P&ID. This may be done outside review sessions. 

The Chairman should sign and date all HAZOP master P&IDs 

4.8    Issuing Worksheets

Worksheets should be checked by the Hazop team preferably on a daily basis to ensure that they are complete and readily understood. (This particularly applies on a large study when otherwise considerable time may elapse between creating and checking the worksheets.) Otherwise, team members should be invited to comment on worksheets on completion of the study or when issued in the draft report. 

As soon as possible after the final HAZOP review session the HAZOP Worksheets should be issued in draft manuscript form to the Project and/or Asset Team Job Officer. 

The recommendations should not be altered by the Chairman outside the review sessions without team consultation except for improving clarity and making factual or grammatical corrections. 

If the chairman wishes to make supplementary recommendations (eg. regarding additional studies) these should be recorded in the main report but it is suggested that for the purposes of follow up any such recommendations should also be numbered and included as an attachment to the worksheets. 

5    Batch operations

Batch operations should be identified before HAZOP studies commence as the application of guidewords/deviations to batch operation systems is more complex than their application to continuous systems. Examples are the launching and receiving of pipeline pigs. It normally requires the simultaneous application of guidewords to both the procedural step and the associated equipment used for the step. The Hazop is in fact normally driven by a review of the procedural steps with the P&ID review resulting as a natural consequence of this process. 

The HAZOP Chairman should develop a batch operations HAZOP technique applicable to the operation/system to be reviewed. Further guidance on the use of such techniques is available from HSEQA. Some components of batch HAZOP techniques are given below: 

1. Review the physical location of the operation and the relevant engineering equipment/instruments.

Consider the nature and proximity of neighbouring plant/operations. 

2. Select a set of guidewords based on the list for sequential operations supplemented by the main process parameter guidewords of Flow, Temperature, Pressure appropriate to the nature of the operation (see checklists in Appendix 1).
3. Follow step-by-step operating procedures and identify the system used, including the process/utilities interfaces, and mark up the P&ID as appropriate.
4. Define the design intention for each step including the intended condition of the relevant equipment on P&IDs and/or layout drawings.

For example coloured discs can be placed on valves to show positions (green for open, orange for "in-position" and red for closed). If items are being moved during the batch process use "models" on the layout drawings, eg. show railcars with counters or coloured blocks. 

5. Having defined the design intention, apply the selected set of guidewords to identify deviations and potential hazards.
6. Consider existing safeguards referring as necessary to the Cause and Effect Diagrams and make further recommendations as appropriate.
7. Complete the Hazop of the P&ID for sections not covered by the review of the procedures.

6    Programmable systems

One of the limitations of Hazop studies is that they consider only one or possibly two coincident failures. For conventional control systems this will involve considering single control loop failures leading to process deviations and single common cause failures such as loss of power/instrument air and associated valve fail safe positions. 

For programmable systems there is a similar potential for single loop failures and service failures which can be addressed in the Hazop in the normal way but there are also additional failure modes which may lead to multiple loop failures (Ref 7). 

However, given independent hard wired safety systems designed to cater for control system failures, these types of failure on well designed programmable control systems are not normally of concern in a conventional process design Hazop. 

To reduce the demand rate on safety systems the control system needs to be of high reliability and this is achieved by building in redundancy and diversity into the critical areas of the system design. Potential hardware failures are normally assessed by Failure Modes and Effects Analysis (FMEA) which analyses the potential failure modes of the system components and their effects on the performance of the system. 

Software failures are minimised by function testing but because of the difficulty in eliminating software errors, programmable systems are not normally used for safety critical systems. Whilst this remains the case there is no requirement for the conventional process Hazop to review such systems.  

It is however appropriate that the output of the FMEA of the control system should be available as a reference document and that the Hazop team are informed of any residual areas of concern for review prior the start of the conventional process Hazop.  

Pilot studies have used Hazop type techniques to review the consequences of multiple failures by selectively applying guidewords to the programmable systems. If this approach is adopted it is recommended that this review is considered as a separate exercise preceding the conventional Hazop of the process design (See Guidelines Ref 9).  

7    Report preparation and issue

7.1    Report Contents

A typical Hazop report should consist of the following Sections: 

1. Contents list
2. Summary
• E.g. Usually no more than half a page, highlighting any major concerns, general comments on the design and recommendations for further studies. 
3. Introduction
• This should include: reference to the formal initiation document for the study, scope of study, the team members, study session dates.
• This section should cover the study methodology particularly any novel aspects. It should identify difficulties in meeting the terms of reference e.g. deficiencies in documentation available for review and include recommendations for any further studies.
4. Description of the Systems
• This is a brief description of the process studied and the modes of operation. 
5. Principal recommendations from the Hazop study
• 5.1 General Recommendation and findings not specific to any single element of the design, e.g. discrepancies, general design and operating features. 
• 5.2 Recommendations relating to Specific Worksheet Actions. These are groupings of principal recommendations some of which refer to several well design operating elements, eg. Well control, stability management issues. 

Note however, that for follow up/action tracking purposes it is suggested that all recommendations should be numbered and included on the worksheets including any supplementary chairman recommendations. 

6. References
• List of data and documents subjected to HAZOP Study including Rev no’s. 
• List of Other Drawings and Documents Consulted 
7. Hazop Checklist
• As a basis for selecting the guidewords the Hazop Chairman should use the check lists given in Appendix 1 together with any additional guidewords added to reflect the particular nature of the system studied. 
8. Hazop Team Worksheets
• All worksheets should be typed and included as A4 copies of the original A3 masters. 
9. Distribution List
• Distribution lists will be specific for different studies, however distribution should typically include: 
1. Project Engineer
2. Asset/Client
3. Hazop Chairman
4. Library Copy HSEQA, Asset and/or Project
10. Appendices which should be included are: 
• formal terms of reference/proposal memorandum for the HAZOP study
• reference reports/items (if any).
11. Report Numbers
• Each report should have a unique number provided by the Project, Asset or HSEQA as appropriate.  

7.2    Report Draft Issue

Draft record sheets should preferably be issued to the team for comment at the end of each session and at the end of the study. A draft report should be issued for review and comment to the following: 

• Project Engineer
• Asset/Client
• Chairman
• Selected Team Members
• Head of Safety Engineering (if organised by HSEQA).

The purpose of this draft review is mainly to correct any factual errors and ensure that the identified hazards and associated recommendations are clearly stated and understood. 

7.3    Report Authorisation

All reports should be signed by the HAZOP Chairman. 

All QHSE organised HAZOP study reports should be authorised by Head of Safety and the Project. 

All Project/Asset organised HAZOP study reports should be authorised by the Project/Asset Manager or his appointee. 

7.4    Archiving of Report and Drawings

A master copy of the Hazop Study Report and Hazop Master should be archived by Project/Asset Team or QHSE person as appropriate. 

  8    Follow-up

It is the responsibility of the Well Engineer and/or the project leader (if appropriate) to formally follow-up the actions arising from a HAZOP study. 

Recommendations may be accepted, modified, referred to further consideration or rejected. The reasons for not accepting the recommendation should be recorded as part of the follow up documentation. Care should be taken that any modified recommendations still fully address the concern identified by the Hazop team. 

The study client (Project or Asset Team) should assign responsibility for assessing the responses to all HAZOP study recommendations to ensure they have been accurately interpreted by Project, whether further Studies are required and whether responses can be closed-out. 

Normally the Project response will be audited as part of the OPERATOR Technical Safety Audit Procedure. 

Project should establish a design change procedure which should include a sequential design change list. All design changes after the main HAZOP should be assessed and perhaps Peer reviewed and the appropriate discipline engineer to determine if fresh HAZOP studies are required or need to be revisited. 

To maintain an auditable record, all report recommendations and Project and/or Asset Group responses must be retained.

It is quite helpful for the Hazop chairman to be involved in the early stages of the actions close out procedure to help ensure that the hazards are understood and to assist in the review of the project responses to the Hazop team recommendations. If such additional involvement of the chairman is required, then this should be made clear in the terms of reference. 

9    Computer recording of Hazop studies

The use of computer recording packages can offer significant advantages. These include: 

• completion of the record sheets is visible to the Hazop team so that the logic and accuracy of the study process is readily understood by the team members and agreed actions are clearly displayed;
• printed copies of record sheets available at the end of each session;
• some packages include documentation for closing out the actions;
• some packages lead the progression through the guidewords freeing the chairman to concentrate on the other matters and also adding to the credibility of reporting by exception.

With the improving keyboard skills of engineers and the ease of computer editing there is also the potential advantage in speeding up the completion of the record sheets. For this to be realised however, the secretary or administrator needs to have good keyboard skills and be familiar with the computer package being used. Some packages are often not very user friendly and would require a significant period of familiarisation prior to the Hazop. 

The potential disadvantages of using computer recording mainly relate to the deficiencies in the design of the package software. These might include: 

• secretary lacking in keyboard skills;
• team overly concerned with correcting typing errors (note: minor corrections are easily made outside the main Hazop sessions);
• secretary and/or chairman unfamiliar with package; package not user friendly;
• risk of loss of data if computer or package fails (package design and auto save should ensure that data lost is minimal);
• inflexibility in the package which interferes with the Hazop process;
• lack of overall visibility of record sheets and package scanning limitations when referring to previous entries (periodic printing out and flexible package scanning capability overcome this potential problem).

Such problems to be addressed so that the team is not distracted from the purpose of the study and can realise the benefits of using this method of recording outlined above. 

The longer the duration of the study the greater the advantage in using a computer recording package. Short studies, i.e. less than one day duration, may not justify the effort involved in package familiarisation, setting up computer equipment prior to study etc. 

A standard VDU screen is quite acceptable for a short study involving a small team of 4/5 people. However for a larger and longer study e.g. 5/6 people or more, a larger screen should be used to enable all members of the team to see the screen whilst enabling the secretary/admin to have a comfortable arrangement. 

Devices designed to be placed on top of overhead projectors are not recommended as they are too intrusive in terms of space, noise and lighting requirements and can be of poor optical quality particularly after extended use/overheating. 

The venue and room arrangement/lighting need to take into account the use of computer recording. 

A number of computer packages and systems are available for conducting a Hazop with each package having their own particular advantages and disadvantages.

Probably the most important factor is that the administrator, technical support and/or and Chairman are familiar with the software and can use it effectively. 

Some of the advantages of computer recording can be obtained by simply using a pre-prepared set of tables in a standard mouse operated software package such as Word for Windows/Word for Mac etc.

This simplifies the package familiarisation aspects and is perhaps appropriate for studies of short duration. It also has the advantage that the record sheets can be imported directly into the Hazop report and any close out documentation. 

Further advice on the selection and use of computer recording packages can be obtained from QHSE specialists. 

10    References

1. A Guide to Hazard and Operability Studies, Chemical Industries Association Limited, London, CIA, 1981.
2. HSEQA Guidelines for HAZID studies (HSQ 01.05.01).
3. Hazop Study Techniques for Well Operations. Report No. WEO/HP/93/024.
4. HSEQA Guidelines for Critical Safety Reviews (HSQ 01.05.16).
5. XEU HSE Task Risk Assessment Practice No. 9.
6. Loss Prevention in the Process Industries, F P Lees, ISBN 0 408 10604 2
7. Programmable Electronic Systems in Safety Related Applications (Parts I and II), Health and Safety Executive.
8. HSEQA Guidelines on the Loss Potential Matrix (HSQ 01.05.05)
9. Guidelines on the Application of Hazop Techniques to Systems containing Programmable Systems  

 

11. Appendices

11.1 Appendix 1 Hazop Study Guideword Checklists

11.1.1 GUIDEWORD CHECKLIST – Core set example

This core set of guidewords should be used for all process design Hazop studies. 

GUIDEWORD	DEVIATION	EXAMPLES OF POTENTIAL PROBLEMS
FLOW	NO/LESS	High pressure; stagnant lines, line/instrument tapping blockages, filter blockages
	MORE	Undesirable flow, leakages, high velocity/erosion, vents & overflows, draining/sampling, flexible failure, seal/gasket failure, environmental emissions, inventory minimisation / isolation, well barrier failure/testing
	REVERSE	Utilities contamination/overpressure, reverse rotation, NRV failure, vessel overfill
	MISDIRECTED	Unexpected routings, transfer errors, interlocks & locked valves, identification & labelling, operational flexibility/complexity
TEMPERATURE	HIGH	Elastomeric materials, corrosion, thermal expansion/creep, location of temperature probes, decomposition, personnel protection, fire
	LOW	Embrittlement, hydrates/freezing, flashing liquids, depressurisation, low ambient temperatures
PRESSURE	HIGH	HP/LP interfaces, hydraulic surge, explosive boiling, gas breakthrough, liquid overfill, compressor settle out, tube rupture, deadheaded pump, thermal expansion, chemical reaction, fire exposure, vent/relief blockages, restriction orifice corrosion / erosion / removal
LEVEL/ELEVATION	HIGH LOW	Vessel overfill, high static head Line routing, deadlegs, liquid accumulation, cavitation, gas blowby, loss of interface
COMPOSITION VISCOSITY/DENSITY	CHANGE	Contamination with air, water, liquids/gases/ solids, slugging,chemical additives, corrosion products, sand, mol sieve, lost circulating fluids etc
EROSION	HIGH	Localised failure, choked valves, straight tees, unbalanced flows
DEPOSITION	PROBLEMS	Radioactive scale, pyrophoric scale, sand, wax, asphaltenes hydrate, ice, debris etc
CORROSION	HIGH	Dissimilar materials, stress corrosion cracking, H2S, CO2 composition/contamination/temperature/pressure effects, blockages due to buildup of corrosion scale, under lagging corrosion, pitting, stray currents, SRB activity
SERVICES	FAILURE	Power, heating/cooling medium, instrument air, hydraulics, nitrogen/fuel gas purge
MAINTENANCE INSPECTION	PROBLEMS & REQUIREMENTS TESTING	Access, layout, isolation, draining/venting/ purging, pyrophorics/ radioactivity maintainability/reliability, lifting, vessel entry, pressure/leak/function testing, condition monitoring, spares
STARTUP/SHUTDOWN	PROBLEMS & REQUIREMENTS	Non-standard conditions, human errors Emergency shutdown requirements, sequential operations
OTHER		An opportunity for chairman to prompt team members to raise any other concerns.

11.1.2 GUIDEWORD CHECKLIST – Supplementary set

Guidewords should be selected from this supplementary set as appropriate to the nature of the system and scope of the Hazop. 

GUIDEWORD	DEVIATION	EXAMPLES OF POTENTIAL PROBLEMS
CHEMICAL	MORE/LESS	Unexpected chemical/biological reaction, incomplete reaction
REACTION / BIOLOGICAL FOAMING	PROBLEMS	Level /interface measurement problems
IMPACT	EXTERNAL	Dropped objects, small bore fittings. swinging loads, ships/helicopters
	INTERNAL	Pig operations, hydrate plug, loose internals
HAMMER	PROBLEMS	Steam hammer, hydraulic surge
VIBRATION	MORE	Fatigue failures, thermal well failures, critical speed, well movement
IGNITION	SOURCES	Uncertified equipment, static, hot surfaces
CATALYST	REGENERATION CHANGE	Sequential operation
VENTILATION	LESS	Gas accumulation, fumes, oxygen enrichment, oxygen deficiency, pressurisation
RELIABILITY	LOW	Instruments/equipment reliability
OPERABILITY	PROBLEMS	Equipment operability / suitability, ergonomics, system complexity/flexibility, potential for human error / exposure, instrument visibility, procedures, critical information/alarms presentation, response time/action, manning
HUMAN	FACTORS	Supervision, handover, training, clear responsibilities, remote/local control
SAMPLING	PROBLEMS	Provision of sampling/draining/venting facilities, routing
DRAINING/VENTING		Batch operation, human error, uncontrolled release, filter change
SIMOP's	PROBLEMS	Well intervention, drilling, well test, construction, commissioning / decommissioning, maintenance
LAYOUT/ACCESS	PROBLEMS	Maintenance, operations, emergency escape routes
CONSTRUCTION	PROBLEMS
COMMISSIONING	PROBLEMS
ENVIRONMENTAL	CONCERNS	Emissions/spills to air, land, water
HEALTH	CONCERNS	Toxic materials in process, additives, construction materials, sampling/draining/venting procedures. Noise, radioactivity
NOISE	HIGH	Pumps, compressors, engines, high velocities, chokes, vents, exhausts
CRACKING	PROBLEMS	Thermal decomposition, stress corrosion cracking, Brittle fracture, weld quality
RADIATION	THERMAL IONISING	Personnel protection, flare LSA Scale, nucleonic instruments
VELOCITY/SPEED	HIGH LOW	Erosion, noise Deposition
DRAWING	ERRORS
WEATHER	PROBLEMS	Severe weather conditions, high/low winds, high/low temperatures, tides, flooding, combined loads etc

11.1.3 GUIDEWORD CHECKLIST - Supplement set for sequential ops

These guidewords should be used when Hazop sequential operations (procedures) supplemented by a selection of guidewords from the preceding core and supplementary sets appropriate to the nature of the operations and scope of the Hazop. 

GUIDEWORD	DEVIATION	EXAMPLES OF POTENTIAL PROBLEMS
SEQUENCE STEP	OMITTED	Step not done, handover, split responsibilities
	INCOMPLETE	Step only partially completed or delayed
	VALVE ERRORS	Valve open or closed in error prior to/during step
	TOO SHORT/LONG	Operation completed too slowly or too quickly
	TOO LATE/EARLY	Insufficient or excessive delay before moving on to the next step or following completion of previous step
	WRONG ORDER	Step done out of sequence
	WRONG ACTION	An incorrect action substituted for the correct action
	EXTRA ACTION	Another action completed as well as the action intended
	SIMOPS	Any other simultaneous activity which may impact on the overall safety of the operations

11.1.4 GUIDEWORD CHECKLIST – Supplementary set for well operations

Well operations should be viewed as batch/sequential operations and hence the procedures should be reviewed using the guidewords for sequential operations (eg. step omitted) with a small selection of core process parameter guidewords (eg. more flow, high pressure, high temperature) and supplementary guidewords (eg SIMOPS, layout, access problems) which specifically address the nature of operation and the scope of the study. For example, the following supplementary guidewords might be included in the list used to Hazop a drilling operation. 

GUIDEWORD	DEVIATION	EXAMPLES OF POTENTIAL PROBLEMS
RATE OF PENETRATION	NONE/LESS/MORE
WEIGHT ON BIT	NONE/LESS/MORE  REVERSE
VIBRATION
PRESSURE
HOOK LOAD	NONE/LESS/MORE
ELEVATION	MORE / LESS
ORIENTATION	OTHER THAN
TORQUE	NONE/LESS  MORE	Slipping  Jamming
POOH RATE	NONE/LESS / MORE	Stuck pipe
WEAR	MORE
BARRIERS	FAILURE	Lack of testing, fluid level, straddling
EQUIPMENT	OPRABILITY  FAILURE	Visibility, height/clearance maintenance, certification, jamming, slipping
SUPERVISION	PROBLEMS	Handover, remote/local control, communications

Note: drilling operations also include process type topsides equipment (eg mud tanks) and links to hydrocarbon processing systems which need to be reviewed as part of the drilling operation. 

11.2 Appendix 2   Completed HAZOP study worksheet.

TABLE NO: 1-0	DOCUMENT REF;	REVISION
DOCUMENT TITLE: Gas Import Thistle Alpha - Let Down Heater Replacement

PLANT SECTION: Import Gas Supply Line 4" 1A15B1-3204-GP, 4" 1A115b1-3205-GP, and 4"-1A6B1-32-7-GP.

DESIGN INTENT: Import of gas through the 1st stage letdown heater and 2nd stage letdown heater.

Inlet conditions 2000psi 5C

Discharge from 1st stage 1980psi 60C

Inlet to 2nd stage heater 1000pis 35C

TEAM MEMBERS: DRC, DA, WG, CHWT, NW

DEVIATION	CAUSE	CONSEQUENCE	SAFEGUARDS	ACTION
Flow   No/Less	Failed closed XCV 2016 and XCV 2002.	Closure of XCV 2016 and simultaneous opening of PCV's 2939 and 2943 potentially causing overpressure.	RV 2912/3 and 2910/1 and blow down valve XCV 2015	Confirm suitability of fail-open mode on PCV's which requires RV operation to protect HP/LP interfaces.
ACTION: 1	ON: Project to liaise with Asset
Flow  No/Less	Partial blockage of heat exchanger passages. Debris arising from previous use as export line maybe dislodged by planned pigging operation.	Progressive loss of heat exchanger surface/performance. Possible erosional effects.	DPI across exhangers and TSLL's downstream of PCV's  Witches hat strainers.	Ensure DPI's performance is reliable at the high operating pressures. Ensure double block and bleed available for DPI in view of potential reliability problems. Check operational experience of heaters with Gyda and Wytch Farm with particular reference to sizing of witches hat. Ensure pigging procedures are such that they minimise the potential to block.
ACTION: 2	ON: Project
Flow  More	Fail open of PCV 2939 system and hence operation of RV 2910 and 2911.  Similar for PCV 2943.	Potential overpressure. As above.  Very high velocities in exchangers.  Entrainment of debris.	High pressure and high flow alarms requiring manual intervention.	Consider changing fail status of PCV's 2939 and 2943. (The team acknowledge there is a possible adverse affect on security of gas supply.)
ACTION: 3	ON: Project