HAZARD & OPERABILITY STUDIES (2 of
2)
Mike Lihou - Lihou Technical & Software Services
THE HAZOP TEAM
The team who will conduct the Hazop study should consist of personnel with a
good understanding of the process and plant to be reviewed. The group
should ideally contain about six members, with perhaps an absolute upper limit
being set at nine. In a study in which both contractor and client are
participating, it is desirable to maintain a balance between the two in terms
of team membership so that neither side feels outnumbered.
The participants should consist of people from a range of disciplines, and
this aspect is one of the strengths of the Hazop methodology:
- With a team of people, each with differing backgrounds and experience,
potential problems are likely to be identified which would be missed by one or
two people working on their own.
- It is often the case that one person's solution can become a problem to
another department within the project. For example, a Process Engineer
conducting his own review in isolation may identify a potential problem for
which he considers that another instrument and alarm would be desirable.
When this requirement is passed to the Control & Instrumentation Engineer,
it transpires that no suitable channels are available within the appropriate
section of the electronic control system, which has already been ordered and is
currently being manufactured by the vendor. A protracted
inter-departmental discussion and correspondence then ensues as to possible
alternative remedies, and the potential cost penalty of re-specifying the
control system. All of this could have been settled within a few minutes
had both departments participated in the study.
- A spirit of co-operation and common purpose is engendered which crosses
departmental boundaries, and this will persist even after the Hazop Study has
been completed. Personnel will understand better the views, concerns and
constraints within which other disciplines have to work, and will take these
into account when making decisions affecting the project.
The actual composition of the Hazop team will vary according to the type of
plant being reviewed. One person who should always be included is a
representative from Operations. He or she should have first hand
experience of day-to-day operations on either the plant being reviewed, or one
that is very similar in nature. The contribution of this team member to
the discussion can be invaluable, as it introduces an operational perspective
to other participants who may have never, for example, had to climb down into a
vessel wearing breathing apparatus to carry out repairs or an inspection.
To summarise, a team should be selected so that a balanced approach to the
study is ensured. In addition, the intention should be that questions
raised during the meeting can be answered immediately, rather than having to
resort to the time consuming process of referring to outside expertise.
It is not of course necessary for the same people to participate in the study
from beginning to end. If the "core" of the group consisted of
five people, for example, additional members could be called in from session to
session as and when their particular expertise was needed.
As with all group activities, there needs to be a person appointed who will
be in overall charge; with Hazop Studies this person is usually called the
Chairman or Study Leader. Ideally, he should not have been too closely
associated with the project under review as there might be a risk of him not
being sufficiently objective in his direction of the team. As the
Chairman's role is of vital importance in the smooth and efficient progress of
the study, he should be carefully chosen and be fully conversant with the Hazop
methodology.
Another important member of the team will be the Secretary. His
contribution to the discussion may well be minimal, as his main function during
the sessions will be to record the study as it proceeds. He will
therefore need to have sufficient technical knowledge to be able to understand
what is being discussed.
PREPARATORY WORK
It is most important that, before a study commences, work that can be
conveniently done beforehand is carried out. This is not only essential
in some respects for the proper structuring of the study and the team, but will
also greatly increase the efficiency of the Hazop and thus retain the interest
and enthusiasm of the participants.
This preparatory work will be the responsibility of the Chairman, and the
requirements can be summarised as follows:
- Assemble the data
- Understand the subject
- Subdivide the plant and plan the sequence
- Mark-up the drawings
- Devise a list of appropriate Keywords
- Prepare Node Headings and an Agenda
- Prepare a timetable
- Select the team
Assemble the data
All relevant documentation should be collected beforehand. Typically
this might consist of:
- A Process Flow Diagram.
- A comprehensive Process Description containing operating parameters, flow
rates, volumes, etc., as well as a brief summary of how each plant item
functions.
- P&IDs.
- Cause & Effect Charts setting out how control and trip systems operate.
- Details of vendor packages if available.
- Plant layout diagrams.
Understand the
subject
The Chairman should take as much time as is necessary to gain a good
understanding of how the plant is meant to operate, by studying the assembled
data and if necessary talking to the design personnel involved. As he
performs this task, it is very likely that he will notice potential problem
areas. Private notes should be made of these, as they might possibly be
missed during the course of the study. In such an event, it can only
serve to enhance the Chairman's standing if he demonstrates his grasp of the
subject by pointing out potential problems that the team have overlooked.
This stage of preparation is perhaps the most important, because it is the
foundation upon which the other steps in the preparation process will be
built. Without a reasonable understanding of how the plant functions, it
will be impossible to plan a sensible study strategy, decide how long the
review is likely to take, or who needs to be included in the study team.
Some proponents of the Hazop methodology state that there is no need for the
Chairman to have any knowledge of the plant being reviewed, his function being
only to ensure that the meeting progresses smoothly. An analogy to this
approach would be a leader attempting to guide an expedition without a map, no
plan of action other than to get to the destination, and with no knowledge of
the terrain to be traversed. Such a leader would command very little
respect from other members of the team, and at the first sign of trouble he
would likely be sidelined and marginalised by those with a better understanding
of the situation. Once that has happened it will be almost impossible for
him to regain control of the group.
Subdivide the plant and plan
the sequence
In all but the simplest of plants, it is too much to expect any study team
to deal with all aspects and operations in the process simultaneously.
Therefore, it must be split into manageable sections (commonly referred to as
Nodes, but sometimes called Tables because of the tabular means of recording
the study). Also, the sequence in which these sections are studied is
important.
With continuous plant, one usually progresses from upstream to downstream,
with services such as drains, vent headers, instrument air, cooling water, etc.
being considered separately and last. With regard to splitting the plant
into sections, there is no need to consider each line and every single minor
item of equipment under a separate Node. This will be wasteful of time,
and boring and tedious for the team.
Instead, endeavour to group smaller items into logical units.
Therefore, a minor pump with its suction, discharge and kick-back lines might
be grouped together in a Node. However, with a major compressor, the
recycle line and its in-line cooler should perhaps be studied separately.
Also, when studying a vessel the Node should encompass those inlet/outlet lines
up to and including any control/isolation valve/s, all level bridles, as well
as vent lines up to the PSV.
If a number of streams converge on a vessel, the study sequence should if at
all possible deal with all of those streams before the vessel is
considered. The rule is "never study a vessel until the incoming
deviations are known".
With batch operations, an entirely different approach is needed. In
such a case the plant drawings are an accessory rather than the prime focus of
the study. Of greater importance instead will be a detailed flowchart or
operational sequence of steps to be accomplished. It is these batch
sequences which will need to be split into manageable sections, and keywords
may well target sequential operations such as Prepare, Charge, React, Transfer,
Centrifuge, Dry etc. This methodology is required because an individual
plant item is very likely to be put into differing states and serve different
purposes at various stages of the sequence.
Mark the drawings
When the study strategy has been decided, the plant items encompassed by
each Node should be marked in distinctive and separate colours, with the Node
Numbers alongside in the same colour. Lines should be paralleled, and
equipment and vessels outlined in the chosen colour. Where a Node spans
two or more drawings, the colour used should remain constant.
This prior marking is a departure from the more usual practise of doing such
work whilst the study progresses. However, it serves two purposes.
Firstly, it will save time during the meeting, both in the actual marking and
the discussion as to where a Node should begin and end. Secondly, the
Chairman will be assured that in planning the study strategy nothing has been
inadvertently missed.
Devise a list of
appropriate Keywords
Having completed the work above, it will be a simple matter to formulate a
comprehensive list of the Keywords required to cover all aspects of the process
to be studied.
Some companies, because most of the plant that they operate is of a similar
nature, will have a standard set of Keywords. Such a list should be
checked to ensure that it is covers all aspects of the system to be
studied. Any redundant Keywords should be removed. For example, if
the subject of the review is to be a pumping station, the inclusion of a
keyword such as 'Absorb' is unnecessary.
The finalised list should be duplicated and a copy given to every team
member. Also included should be a schedule of appropriate keyword
combinations (i.e. which Secondary keywords will be applied with each Primary
keyword). Where there are likely to be semantic problems as to what
meaning/s a particular combination is intended to convey, then a full
explanation should be given.
When devising the list, bear in mind that the smaller the number of words
utilised, the more speedy the study. That is not to say that aspects of
the process should be discounted. Instead, to illustrate what is meant,
imagine a plant containing a separation vessel, some pump suction filters, and
an environmental scrubber. Rather than have three keywords 'Separate',
'Filter', 'Absorb', have instead one keyword 'Separate'... that, after all, is
the basic function of all those equipment items. Similarly, 'Temperature'
can cover heat transfer aspects of Heaters, Coolers, and Heat Exchangers.
Prepare Node Headings and
Agenda
Node Headings reference the relevant drawings, and contain a brief
description of the design intent of the relevant plant section, with process
parameters, flow rates, and any other potentially informative details.
The agenda is a list of those headings. A copy should be handed to
each team member. In addition to being informative and an aid to full
participation, it will serve to put into perspective the amount of work to be
accomplished in the time allotted. Hopefully this will induce an
appropriate sense of urgency.
Prepare a timetable
For all but a one day study, the Chairman should devise a timetable showing
what needs to be accomplished at each study meeting if the schedule is to be
maintained. In devising this schedule he will need to call upon his
experience when assessing how much time the review will take. A great
deal will depend upon the complexity of the plant as well as the experience of
the team.
As a rough guide, with straightforward plant and with P&IDs which are
not too 'cluttered', on average three drawings can be studied in a day.
If the system to be reviewed is complex, or if each P&ID seems to have been
drawn with the intention of not wasting any space (i.e. as many plant items as
would fit are included on the drawing), then almost certainly only two or
perhaps even one drawing will be completed in a day.
Be prepared for time slippage at the start of the study. Progress is
always slow to begin with, whilst the team are acclimatising themselves to this
novel role of casting critical eyes over their own or their colleague's design
efforts. After the first day everything will speed up, and the schedule
should be on target by the end of the week. Do not, however, allow the
timetable to reflect this expectation of a slow start... better for the team to
realise that they must increase their efforts, rather than go home thinking
that this first slow day is the norm.
Select the team
Having gained a good appreciation of what will be involved in the study,
both in terms of content and timetable, the Chairman can ensure that the core
team members have suitable expertise and will be available for the duration of
the review. In addition, he can also ascertain which personnel with
additional expertise are likely to be needed during the course of the meetings,
and when their assistance will be required. With regard to the latter
aspect, in certain circumstances the study sequence may need to be tailored
around the availability of such personnel.
RUNNING A HAZOP
STUDY
After all the above preparation, the Chairman should be in a position to
easily guide an efficient and comprehensive study through to a successful
conclusion. However, there are a few guidelines to remember:
- It is always a temptation for team members to illustrate their ideas by
quickly drawing on the master P&ID which has been so painstakingly marked
up. Establish the rule right at the beginning that this is forbidden,
even in pencil.
- Similarly, with tie-ins and vendor packages, a team member may endeavour to
help by roughly illustrating the upstream/downstream plant or the internal
workings of the package. Be firm in the rejection of such help... it is
dangerous to pretend to have studied something when all that is available is a
few scribblings on a sheet of paper.
- If the schedule is slipping, resist the temptation to hasten the process by
listing potential causes/consequences yourself. All that results is that
the team sits back and listens to you dictating to the Secretary, and they will
continue to do so until you force them to participate again.
- Do not allow a separate meeting to develop, with two team members
conversing in low voices at the corner of the table. If this happens,
stop the general discussion and ask them to share with the rest of the team the
benefit of their deliberations (always assume that they are discussing
something directly relevant to the study, although the likelihood is
otherwise). This will usually elicit an apology and bring them back to
full participation.
If they persist, request that the rest of the team members be completely silent
whilst the private discussion continues. If even this does not produce
the required result, call a coffee break. Then speaking privately to the
persons concerned, politely but firmly insist that they leave the
meeting. Such members usually have nothing to contribute to the study,
and they will only irritate and demotivate the remainder of the team.
- Ensure that all team members participate, even those who might well feel
unsure of themselves. Do this by asking questions such as "Do you
agree with that solution, Bob?", or "What severity would you attach
to this consequence, Fred?". Alternatively, and less potentially
contentious, you could request "John, could you help the Secretary by
summarising in a few words the agreed action". Once such team
members realise that they are not going to be contradicted as soon as they open
their mouths, they participate to the best of their ability.
- Recognise and reward with praise the team member/s who contribute to the
discussion wholeheartedly and sensibly. However, do not allow them to
overshadow the rest of the team.
- If discussion wanders away from the matter under consideration, re-focus
the attention of the team either by requesting that the Secretary read out what
he has recorded, or by asking for an action to be formulated. The latter
usually concentrates the mind and encourages the team members to get to the
heart of the problem.
- Where a particularly intractable problem arises, or consequences of a
serious nature are uncovered, too often an inordinate amount of time is devoted
to formulating potential remedies. Solutions and counter solutions are
proposed and discussed, there is much speculation as to costs and other related
aspects, and generally no satisfactory conclusion is reached. Before too
much time is wasted, such situations should be dealt with by placing an action
upon a specific person to investigate and report upon what alternatives are
available, together with the advantages/disadvantages of each. Any
discussion, gathering of additional data, reliability calculations, etc. can
thereby be accomplished outside of the Hazop meeting, allowing the team to
progress steadily with the review.
- The Chairman should be independent and unbiased, and should not be
perceived as constantly favouring one section of the team as opposed to
another. This is of particular importance when personnel from both client
and contractor are participating. If a difficult situation arises, where,
for example, there is a heated dispute over whether an action should be
undertaken, in some cases one of the parties to the dispute will request that
the Chairman makes the final decision. If, in the Chairman's estimation,
the reasons on one side of the argument are so strong as to be indisputable,
then he should say so. On the other hand, should the situation be finely
balanced, then the dispute can be defused by careful wording of an action.
Take as an example the situation where the client wishes to have an additional
High Level Alarm, but the contractor strongly disputes its necessity.
Consider the following actions:
- "Fit a High Level Alarm". In the view of the contractor,
the Chairman has sided with the client. He may, wrongly or otherwise,
perceive this to be a biased decision.
- The action "Justify the requirement for a High Level Alarm" is
addressed to the client. The Chairman favours the contractor's argument,
but is not dismissing altogether the views of the client. Both parties
are likely to be content with this formula.
- The action "Justify the absence of a High Level Alarm" is
addressed to the contractor. The Chairman favours the client's argument,
but is not dismissing altogether the views of the contractor. As before,
neither party will have cause to feel aggrieved.
By effectively postponing a final decision until a later review of Action
Responses, it is often the case that the two sides will get together after
passions have cooled to discuss the matter rationally. Almost invariably
the situation will then be amicably resolved.
THE REPORT
The Hazop Report is a key document pertaining to the safety of the
plant. The number of man-hours spent on the study is usually
considerable. It is crucial that the benefit of this expert study is
easily accessible and comprehensible for future reference in case the need
arises to alter the plant or its operating conditions.
The major part of such a report is of course the printed Minutes, in which
is listed the team members, meeting dates, Keywords applied, and of course
every detail of the study teams findings. However, it is usual to include
with this a general summary. The contents of such a summary might
typically be:
- An outline of the terms of reference and scope of the study.
- A very brief description of the process which was studied.
- The procedures and protocol employed. The Keyword combinations
applied should be listed, together with the explanatory meanings given to the
team at the start of the study. Also the fact that Action Sheets have
been produced and responses will be recorded should be explained. A brief
description of the Action File (described in the following section) should be
included.
- General comments. If, for example, the team were assured that high
point vents and low point drains would be universally provided, mention that
statement and its source. If certain details of vendor packages were not
available, explain and list the items which were not reviewed.
- Results. This usually states the number of recommended actions.
Also included in the Hazop Report would be an Appendix containing:
- Master copies of the drawings studied.
- Copies of technical data used.
- Cause and Effect charts (i.e. matrices showing the executive action of
safety related instruments and trips).
- Any calculations produced.
- Relevant correspondence between departments, from contractor to vendor, or
client to contractor.
Each of the above should be signed and dated by the Chairman.
THE ACTION FILE AND REVIEW
MEETINGS
The Hazop Report is compiled as soon as possible after the end of the study,
and once completed does not change. On the other hand the Action File is
only started at the end of the study, and its contents will continue to change
perhaps for many months, until the very last action has been reviewed and
accepted as having been satisfactorily discharged.
Essentially, this Action File is a binder. Initially, at the end of
the study, it will be empty. As completed and signed Action Response
Sheets are returned, they are housed in the binder. Periodically, the
returned responses will be input into the data file (either manually or
electronically, according to the system being used).
By the time the first review meeting is convened there should be no
outstanding (i.e. overdue) responses. The Secretary would prepare a
listing of all responses received, making a copy for each review team
member. During the review meeting responses will either be accepted and
marked as having been discharged, or in a small number of cases further action
would need to be taken.
At the end of the first review, where further action had been required,
Action Sheets for these would be produced for distribution. In due course
these would be completed, signed and returned, and these further responses
would be input into the data file and housed in the Action File as before.
The procedure for the second review meeting is the same as for the first,
except that the number of responses would of course be much smaller. If
some of those responses were still not found to be satisfactory, then the
process as outlined above would be carried out again.
It can be seen that the Action File represents a hard copy record of the
state of completion of Hazop recommendations at any point in time. When
all action responses have been reviewed and accepted, it finally becomes a
static record containing the complete history of the implementation of the
Hazop Study's findings.
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