Quality, Health safety and
Environment
Table of contents
Hazop Study Guidelines
Table of contents
1 Introduction
1.1 Document Purpose and Applicability
1.2 Definition
1.3 Limitations
1.4 Hazop and Other Hazard
Identification Techniques
1.5 General Application of Hazop
1.6 Application to Existing
Facilities
1.7 Scope
1.8 HAZOP Objectives
1.9 Contractor Conducted HAZOP
1.10 Vendor Equipment
2 Team Composition
2.1 Importance of the HAZOP Study
Chairman
2.2 The Team
2.3 Competency of Team Members
3 Preparation & planning
3.1 Timing and Programme
3.2 Drawings and Information
Required
3.3 Venue
4 Hazop study method
4.1 Selecting Key Elements to
Hazop
4.2 Selecting and Applying
Guidewords
4.3 Identifying Causes of Deviations
4.4 Defining Consequences
4.5 Considering Existing
Safeguards
4.6 Agreeing Action Required
4.7 Recording
4.8 Issuing Worksheets
5 Batch operations
6 Programmable systems
7 Report preparation and issue
7.1 Report Contents
7.2 Report Draft Issue
7.3 Report Authorisation
7.4 Archiving of Report and
Drawings
8 Follow-up
9 Computer recording of Hazop
studies
10 References
11. Appendices
11.1 Appendix 1 Hazop Study Guideword Checklists
11.1.1 GUIDEWORD CHECKLIST – Core set example
11.1.2 GUIDEWORD CHECKLIST – Supplementary set
11.1.3 GUIDEWORD CHECKLIST - Supplement set for
sequential ops
11.1.4 GUIDEWORD CHECKLIST – Supplementary set for well
operations
11.2 Appendix 2 Completed HAZOP study
worksheet.
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
3rd 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 3rd 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:
- Well design outline for main initial HAZOP study.
- Well design finalised with work-scope changed significantly since initial HAZOP study.
- 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:
- Review the physical location of the operation and the relevant engineering equipment/instruments.
Consider the nature and proximity
of neighbouring plant/operations.
- 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).
- Follow step-by-step operating procedures and identify the system used, including the process/utilities interfaces, and mark up the P&ID as appropriate.
- 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.
- Having defined the design intention, apply the selected set of guidewords to identify deviations and potential hazards.
- Consider existing safeguards referring as necessary to the Cause and Effect Diagrams and make further recommendations as appropriate.
- 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:
- Contents list
- Summary
- E.g. Usually no more than half a page, highlighting any major concerns, general comments on the design and recommendations for further studies.
- 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.
- Description of the Systems
- This is a brief description of the process studied and the modes of operation.
- 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.
- References
- List of data and documents subjected to HAZOP Study including Rev no’s.
- List of Other Drawings and Documents Consulted
- 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.
- Hazop Team Worksheets
- All worksheets should be typed and included as A4 copies of the original A3 masters.
- Distribution List
- Distribution lists will be specific for different studies, however distribution should typically include:
- Project Engineer
- Asset/Client
- Hazop Chairman
- Library Copy HSEQA, Asset and/or Project
- Appendices which should be included are:
- formal terms of reference/proposal memorandum for the HAZOP study
- reference reports/items (if any).
- 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
- A Guide to Hazard and Operability Studies, Chemical Industries Association Limited, London, CIA, 1981.
- HSEQA Guidelines for HAZID studies (HSQ 01.05.01).
- Hazop Study Techniques for Well Operations. Report No. WEO/HP/93/024.
- HSEQA Guidelines for Critical Safety Reviews (HSQ 01.05.16).
- XEU HSE Task Risk Assessment Practice No. 9.
- Loss Prevention in the Process Industries, F P Lees, ISBN 0 408 10604 2
- Programmable Electronic Systems in Safety Related Applications (Parts I and II), Health and Safety Executive.
- HSEQA Guidelines on the Loss Potential Matrix (HSQ 01.05.05)
- 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 |
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