HAZARD & OPERABILITY STUDIES

INTRODUCTION

The technique of Hazard and Operability Studies, or in more common

terms HAZOPS, has been used and developed over approximately four

decades for 'identifying potential hazards and operability problems' caused

by 'deviations from the design intent' in both new and existing process

plants. Before progressing further, it might be as well to clarify some

aspects of these statements.

Potential Hazard AND Operability Problems

You will note the capitalised 'AND' in the heading above. Because of the

high profile of production plant accidents, emphasis is too often placed

upon the identification of hazards to the neglect of potential operability

problems. Yet it is in the latter area that benefits of a Hazop Study are

usually the greatest. To quote an example, a study was commissioned for

a new plant. Some two years previously, and for the first time, a similar

study had been carried out on different plant at the same site that was

then in the process of being designed. Before the latest review

commenced, the Production Manager expressed the hope that the same

benefits would accrue as before, stating that "in his twenty years of

experience, never had a new plant been commissioned with so few

problems, and no other plant had ever achieved its production targets and

break-even position in so short a time".

Deviation from Design Intent

To deal firstly with 'design intent', all industrial plant is designed with an

overall purpose in mind. It may be to produce a certain tonnage per year

of a particular chemical, to manufacture a specified number of cars, to

process and dispose of a certain volume of effluent per annum, etc. That

could be said to be the main design intent of the plant, but in the vast

majority of cases it would also be understood that an important subsidiary

intent would be to conduct the operation in the safest and most efficient

manner possible.

With this in mind equipment is designed and constructed which, when it is

all assembled and working together, will achieve the desired

goals. However, in order to do so, each item of equipment, each pump

and length of pipework, will need to consistently function in a particular

manner. It is this manner that could be classified as the 'design intent' for

that particular item. To illustrate, imagine that as part of the overall

production requirement we needed a cooling water facility. For this we

would almost certainly have cooling water circuit pipework in which would

be installed a pump as very roughly illustrated below.

A much simplified statement as to the design intent of this small section of

the plant would be "to continuously circulate cooling water at an initial

temperature of xx°C and at a rate of xxx litres per hour". It is usually at

this low level of design intent that a Hazop Study is directed. The use of

the word 'deviation' now becomes more easy to understand. A deviation

or departure from the design intent in the case of our cooling facility

would be a cessation of circulation, or the water being at too high an

initial temperature. Note the difference between adeviation and

its cause. In the case above, failure of the pump would be a cause, not a

deviation.

Industries in which the technique is employed

Hazops were initially 'invented' by ICI in the United Kingdom, but the

technique only started to be more widely used within the chemical process

industry after the Flixborough disaster in 1974. This chemical plant

explosion killed twenty eight people and injured scores of others, many of

those being members of the public living nearby. Through the general

exchange of ideas and personnel, the system was then adopted by the

petroleum industry, which has a similar potential for major disasters. This

was then followed by the food and water industries, where the hazard

potential is as great, but of a different nature, the concerns being more to

do with contamination rather than explosions or chemical releases.

The reasons for such widespread use of Hazops

Safety and reliability in the design of plant initially relies upon the

application of various codes of practise, or design codes and

standards. These represent the accumulation of knowledge and

experience of both individual experts and the industry as a whole. Such

application is usually backed up by the experience of the engineers

involved, who might well have been previously concerned with the design,

commissioning or operation of similar plant.

However, it is considered that although codes of practise are extremely

valuable, it is important to supplement them with an imaginative

anticipation of deviations that might occur because of, for example,

equipment malfunction or operator error. In addition, most companies

will admit to the fact that for a new plant, design personnel are under

pressure to keep the project on schedule. This pressure always results in

errors and oversights. The Hazop Study is an opportunity to correct these

before such changes become too expensive, or 'impossible' to accomplish.

Although no statistics are available to verify the claim, it is believed that

the Hazop methodology is perhaps the most widely used aid to loss

prevention. The reason for this can most probably be summarised as

follows:

It is easy to learn.

It can be easily adapted to almost all the operations that are carried

out within process industries.

No special level of academic qualification is required. One does not

need to be a university graduate to participate in a study.

THE BASIC CONCEPT

Essentially the Hazops procedure involves taking a full description of a

process and systematically questioning every part of it to establish how

deviations from the design intent can arise. Once identified, an

assessment is made as to whether such deviations and their consequences

can have a negative effect upon the safe and efficient operation of the

plant. If considered necessary, action is then taken to remedy the

situation.

This critical analysis is applied in a structured way by the Hazop team, and

it relies upon them releasing their imagination in an effort to discover

credible causes of deviations. In practice, many of the causes will be

fairly obvious, such as pump failure causing a loss of circulation in the

cooling water facility mentioned above. However, the great advantage of

the technique is that it encourages the team to consider other less obvious

ways in which a deviation may occur, however unlikely they may seem at

first consideration. In this way the study becomes much more than a

mechanistic check-list type of review. The result is that there is a good

chance that potential failures and problems will be identified that had not

previously been experienced in the type of plant being studied.

Keywords

An essential feature in this process of questioning and systematic analysis

is the use of keywords to focus the attention of the team upon deviations

and their possible causes. These keywords are divided into two sub-sets:

Primary Keywords that focus attention upon a particular aspect

of the design intent or an associated process condition or

parameter.

Secondary Keywords that, when combined with a primary

keyword, suggest possible deviations.

The entire technique of Hazops revolves around the effective use of these

keywords, so their meaning and use must be clearly understood by the

team. Examples of often used keywords are listed below.

Primary Keywords

These reflect both the process design intent and operational aspects of the

plant being studied. Typical process oriented words might be as

follows. The list below is purely illustrative, as the words employed in a

review will depend upon the plant being studied.

Flow Temperature

Pressure Level

Composition Separate (settle, filter,

centrifuge)

React Mix

Reduce (grind, crush, etc.) Absorb

Corrode Erode

Note that some words may be included that appear at first glance to be

completely unrelated to any reasonable interpretation of the design intent

of a process. For example, one may question the use of the word

Corrode, on the assumption that no one would intend that corrosion

should occur. Bear in mind, however, that most plant is designed with a

certain life span in mind, and implicit in the design intent is that corrosion

should not occur, or if it is expected, it should not exceed a certain

rate. An increased corrosion rate in such circumstances would be a

deviation from the design intent.

Remembering that the technique is called Hazard & Operability Studies,

added to the above might be relevant operational words such as:

Isolate Drain

Vent Purge

Inspect Maintain

Startup Shutdown

This latter type of Primary Keyword is sometimes either overlooked or

given secondary importance. This can result in the plant operator having,

for example, to devise impromptu and sometimes hazardous means of

taking a non-essential item of equipment off-line for running repairs

because no secure means of isolation has been provided. Alternatively, it

may be discovered that it is necessary to shut down the entire plant just

to re-calibrate or replace a pressure gauge. Or perhaps during

commissioning it is found that the plant cannot be brought on-stream

because no provision for safe manual override of the safety system trips

has been provided.

Secondary Keywords

As mentioned above, when applied in conjunction with a Primary Keyword,

these suggest potential deviations or problems. They tend to be a

standard set as listed below:

Word Meaning

No The design intent does not occur (e.g. Flow/No), or the

operational aspect is not achievable (Isolate/No)

Less A quantitative decrease in the design intent occurs (e.g.

Pressure/Less)

More A quantitative increase in the design intent occurs (e.g.

Temperature/More)

Reverse The opposite of the design intent occurs (e.g. Flow/Reverse)

Also The design intent is completely fulfilled, but in addition some

other related activity occurs (e.g. Flow/Also indicating

contamination in a product stream, or Level/Also meaning

material in a tank or vessel that should not be there)

Other The activity occurs, but not in the way intended (e.g.

Flow/Other could indicate a leak or product flowing where it

should not, or Composition/Other might suggest unexpected

proportions in a feedstock)

Fluctuation The design intention is achieved only part of the time (e.g. an

air-lock in a pipeline might result in Flow/Fluctuation)

Early Usually used when studying sequential operations, this would

indicate that a step is started at the wrong time or done out

of sequence

Late As for Early

It should be noted that not all combinations of Primary/Secondary words

are appropriate. For example, Temperature/No (absolute zero or -273°C

!) or Pressure/Reverse could be considered as meaningless.

HAZOP STUDY METHODOLOGY

In simple terms, the Hazop study process involves applying in a

systematic way all relevant keyword combinations to the plant in question

in an effort to uncover potential problems. The results are recorded in

columnar format under the following headings:

DEVIATION CAUSE CONSEQUENCE SAFEGUARDS ACTION

In considering the information to be recorded in each of these columns, it

may be helpful to take as an example the simple schematic below. Note

that this is purely representational, and not intended to illustrate an actual

system.

DEVIATION

The keyword combination being applied (e.g. Flow/No).

CAUSE

Potential causes that would result in the deviation occurring. For example

"Strainer S1 blockage due to impurities in Dosing Tank T1" might be a

cause of Flow/No.

CONSEQUENCE

The consequences that would arise, both from the effect of the deviation

such as "Loss of dosing results in incomplete separation in V1" and if

appropriate, from the cause itself, for example "Cavitation in Pump P1,

with possible damage if prolonged".

Always be explicit in recording the consequences. Do not assume that the

reader at some later date will be fully aware of the significance of a

statement such as "No dosing chemical to Mixer". It is much better to add

the explanation as set out above.

When assessing the consequences, one should not take any credit for

protective systems or instruments that are already included in the

design. For example, suppose the team had identified a cause of Flow/No

(in a system that has nothing to do with the one illustrated above) as

being spurious closure of an actuated valve. It is noticed that there is

valve position indication within the Central Control Room, with a software

alarm on spurious closure. They may be tempted to curtail consideration

of the problem immediately, recording something to the effect of "Minimal

consequences, alarm would allow operator to take remedial

action". However, had they investigated further they might have found

that the result of that spurious valve closure would be overpressure of an

upstream system, leading to a loss of containment and risk of fire if the

cause is not rectified within three minutes. It only then becomes apparent

how inadequate is the protection afforded by this software alarm.

SAFEGUARDS

Any existing protective devices that either prevent the cause or safeguard

against the adverse consequences would be recorded in this column. For

example, you may consider recording "Local pressure gauge in discharge

from pump might indicate problem was arising". Note that safeguards

need not be restricted to hardware… where appropriate, credit can be

taken for procedural aspects such as regular plant inspections (if you are

sure that they will actually be carried out!).

ACTION

Where a credible cause results in a negative consequence, it must be

decided whether some action should be taken. It is at this stage that

consequences and associated safeguards are considered. If it is deemed

that the protective measures are adequate, then no action need be taken,

and words to that effect are recorded in the Action column.

Actions fall into two groups:

1. Actions that remove the cause.

2. Actions that mitigate or eliminate the consequences.

Whereas the former is to be preferred, it is not always possible, especially

when dealing with equipment malfunction. However, always investigate

removing the cause first, and only where necessary mitigate the

consequences. For example, to return to the "Strainer S1 blockage due to

impurities etc." entry referred to above, we might approach the problem

in a number of ways:

Ensure that impurities cannot get into T1 by fitting a strainer in

the road tanker offloading line.

Consider carefully whether a strainer is required in the suction to

the pump. Will particulate matter pass through the pump without

causing any damage, and is it necessary to ensure that no such

matter gets into V1. If we can dispense with the strainer

altogether, we have removed the cause of the problem.

Fit a differential pressure gauge across the strainer, with perhaps

a high dP alarm to give clear indication that a total blockage is

imminent.

Fit a duplex strainer, with a regular schedule of changeover and

cleaning of the standby unit.

Three notes of caution need to be borne in mind when formulating

actions. Do not automatically opt for an engineered solution, adding

additional instrumentation, alarms, trips, etc. Due regard must be taken

of the reliability of such devices, and their potential for spurious operation

causing unnecessary plant down-time. In addition, the increased

operational cost in terms of maintenance, regular calibration, etc. should

also be considered (the lifetime cost of a simple instrument will be at least

twice its purchase price… for more complex instrumentation this figure

would be significantly greater). It is not unknown for an over-engineered

solution to be less reliable than the original design because of inadequate

testing and maintenance.

Finally, always take into account the level of training and experience of

the personnel who will be operating the plant. Actions that call for

elaborate and sophisticated protective systems are wasted, as well as

being inherently dangerous, if operators do not, and never will,

understand how they function. It is not unknown for such devices to be

disabled, either deliberately or in error, because no one knows how to

maintain or calibrate them.

Considering all Keywords - The Hazop procedure

Having gone through the operations involved in recording a single

deviation, these can now be put into the context of the actual study

meeting procedure. From the flow diagram below it can be seen that it is

very much an iterative process, applying in a structured and systematic

way the relevant keyword combinations in order to identify potential

problems.

FULL RECORDING versus RECORDING BY EXCEPTION

In the early days of Hazop Studies, it was usual to record only the

potential deviations that carried with them some negative

consequence. This might well have been because such studies were only

for internal use within a company. Also, with manually handwritten

records, it certainly reduced the time taken, both in the study itself and

the subsequent production of the Hazop Report. Such methodology is

classed as "Recording by exception", where it is assumed that anything

not included is deemed to be satisfactory.

Latterly, it has become more the accepted practice to set down

everything, stating clearly each keyword combination applied to the

system. Where applicable, this would be followed by a statement

indicating either that no Cause could be identified, or alternatively that no

Consequence arose from the Cause recorded. This is classified as "Full

recording", and it results in a Hazop Report that demonstrates

unambiguously to outside parties that a rigorous study has been

undertaken. In addition, it produces a comprehensive document that will

greatly assist in the speedy assessment of the safety and operability of

later plant modifications (do they impinge upon a potential deviation that

was originally recognised as being credible, but which involved at that

time no negative consequences ?).

Bearing the above in mind, it is recommended that "Full recording" is

instituted. With the use of a computer, the previous concern regarding

time, both in the study and the reporting, is all but eliminated. To make

this methodology easier to handle efficiently, text macros should be set up

as follows:

1. No potential causes identified.

2. No significant negative consequences identified.

3. No action required - existing safeguards considered adequate.

These macros can be used in the appropriate circumstances to quickly

record the reason for not pursuing a keyword combination.

In addition to the above, the pseudo Secondary

words 'All' and 'Remainder' are often used. These are employed in the

following circumstances:

For a particular Primary Keyword (e.g. Flow), some combinations

have been identified as having credible Causes (e.g. Flow/No,

Flow/Reverse). Having explored all other relevant combinations

(Flow/Less, Flow/More, Flow/Other, etc.), no other Causes could

be identified. The combination "Flow/Remainder" is therefore

used, with the macro in (1) above.

Having explored all relevant combinations for a particular Primary

word, no potential deviations could be identified. The

combination "Flow/All" is therefore used, with the macro in (1)

above.

Use of these pseudo Secondary Keywords greatly improves the readability

of the final report, as it eliminates countless repetitive entries, all with a

similar format (i.e. Keyword combination with "No potential causes

identified"). However, to make it a robust system, the introduction to the

Hazop Report must list clearly the Secondary Keywords that were globally

applied to each Primary Keyword; in other words, the 'relevant

combinations'. This will give an unambiguous meaning to the words 'All'

and 'Remainder'.

Note that such an approach should only be adopted where no credible

Cause is identified. In cases where the potential deviation is considered

possible, but no significant consequence ensues, then both keywords

should be recorded, together with the actual Cause identified, and macro

(2) in the Consequence column.

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 that

might 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 that

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.

(Note to the reader: The above few paragraphs, as well as some that follow, are rather

male-specific, referring as they do to 'he', ' him' and 'his'. This is purely to avoid the

grammatical contortions involved with repeatedly referring to 'he or she', 'his or her',

etc., up to three times in a single sentence. Note that there are many excellent female

Study Leaders and Secretaries, who have organised, guided and participated in very successful Hazop Reviews).

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:

1. Assemble the data

2. Understand the subject

3. Subdivide the plant and plan the sequence

4. Mark-up the drawings

5. Devise a list of appropriate Keywords

6. Prepare Node Headings and an Agenda

7. Prepare a timetable

8. Select the team

Assemble the data

All relevant documentation should be collected beforehand. Typically this

might consist of:

1. A Process Flow Diagram.

2. A comprehensive Process Description containing operating

parameters, flow rates, volumes, etc., as well as a brief summary

of how each plant item functions.

3. P&IDs.

4. Cause & Effect Charts setting out how control and trip systems

operate.

5. Details of vendor packages if available.

6. 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 status within the group

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

person 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 that 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 that 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 that has been so

carefully 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 and 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:

o "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.

o 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.

o 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 that 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 that 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, or perhaps some electronic form of

storage. 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 folder. 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 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.