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Let’s think together....identify the potential hazards

Chapter 6

Hazard Identification

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Let’s think together....identify the potential hazards

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Contents Objectives
 Introduction of Hazard Identifications  Identify study nodes and decide on possible
 Hazard and Operability Studies (HAZOP) hazards based on HAZOP guidewords
 HAZOP guidewords  Construct HAZOP review table subsequently
assess the hazard’s cause, consequence and action
required.

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What is Hazard Identification?

 Questions that must be asked for each process in
chemical plant
 What are the hazards?
 What can go wrong and how?

 What are the chances?

 What are the consequences?

 Provide basic information for risk assessment

Figure 10-1 Hazards identification and risk assessment procedure

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When it should be performed? Who should perform?

It usually requires a committee which composed of cross-section
 At any stage during the initial design or ongoing 
of experienced plant, laboratory, technical and safety professional
operation of a process.  One individual must be a trained safety personnel and serves as
the committee chair. He will lead the discussion and must be
 It serves to enables modifications to be easily expert in the chemical process under review
 One individual must also be assigned the task of recording the
incorporated into the final design and to operate results
the ongoing process better in terms of safety.  The meeting duration must be short enough to ensure continuing
interest and input from all committee members
 It takes a large investment of time and effort, but the results are
well worth the effort

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How to perform? 1. Process hazard checklists

1. Process hazard checklists A classic example is an automobile checklist that one might review before driving away on
a vacation. This checklist might contain the following items:

 provide a list of items and possible problems in the  Check oil in engine.
Check air pressure in tires.
process that must be checked.


 Check fluid level in radiator.

 should only be applied during the preliminary stage of

 Check air filter.
 Check fluid level in windshield washer tank.
hazard identification and not be used as a  Check headlights and taillights.

replacement for a more complete hazard procedure. 


Check exhaust system for leaks.
Check fluid levels in brake system.
 Check gasoline level in tank.
Checklists for chemical processes can be detailed, involving hundreds or even thousands
of items.

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2. Hazard surveys How to perform?

1. Hazards surveys 3. Safety review
 It is more like to inventory of  It is a method used to identify safety problems in laboratory and
process area and to develop solutions.
hazardous materials, or, it
 Two (2) types
can be detailed as the Dow
 Informal: small changes to existing processes
Fire & Explosion Index.
 Formal: new process, substantial changes to existing processes
 use a rating form 4. Hazard and operability studies (HAZOP)
 is a formal systematic procedure used to identify hazards in a
chemical process facility
 very effective in identifying hazard

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What is HAZOP
Hazard and Operability Studies A Hazard and Operability (HAZOP) study is a structured and systematic
examination of a planned or existing process or operation in order to identify and
evaluate problems that may represent risks to personnel or equipment, or prevent
efficient operation.

The HAZOP technique was initially developed to analyze chemical process

systems, but has later been extended to other types of systems and also to
complex operations and to software systems.

A HAZOP is a qualitative technique based on guide-words and is carried out by a

multi-disciplinary team (HAZOP team) during a set of meetings.

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When to perform HAZOP ? When to perform HAZOP ?

HAZOP studies may also be used more extensively, including:
The HAZOP study should preferably be carried out as early in the design phase
as possible - to have influence on the design. On the other hand; to carry out a  At the initial concept stage when design drawings are available
HAZOP we need a rather complete design. As a compromise, the HAZOP is
usually carried out as a final check when the detailed design has been completed. When the final piping and instrumentation diagrams (P&ID) are available

A HAZOP study may also be conducted on an existing facility to identify During construction and installation to ensure that recommendations are
modifications that should be implemented to reduce risk and operability problems. implemented

During commissioning

During operation to ensure that plant emergency and operating procedures are
regularly reviewed and updated as required

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Type of HAZOP Objective of HAZOP

 Process HAZOP
The HAZOP technique was originally developed to assess plants and
 For identifying causes and the consequences of
process systems perceived mal operations of equipment and
 Human HAZOP
A “family” of specialized HAZOPs. More focused on human errors than associated operator interfaces in the context of
technical failures
 Procedure HAZOP
the complete system.
Review of procedures or operational sequences
Sometimes denoted SAFOP - SAFe Operation Study
 Software HAZOP
Identification of possible errors in the development of software

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Why & How HAZOP Is Used? Features of HAZOP Study

 Identifies potential hazards, failures and operability problems.  Subsystems of interest
 Recommended as a principal method by professional institutions  line and valve, etc
and legislators on the basis of proven capabilities for over 40
years.  Equipment, Vessels

 Most effective as a team effort consists of plant designers,  Modes of operation

operating personnel, control and instrumentation engineer etc.  Normal operation
 Encourages creativity in design concept evaluation.  Start -up mode
 Results in fewer commissioning and operational problems and  Shutdown mode
better informed personnel, thus confirming overall cost
effectiveness improvement.  Maintenance/construction/inspection mode

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Features of HAZOP Study Features of HAZOP Study

 Trigger events  Effects within plant
 Changes in chemical conditions
 Human failure
 Changes in inventory
 Equipment /instrument/component failure  Change in chemical physical conditions
 Supply failure  Hazardous conditions
 Emergency environment event  Release of material
 Changes in material hazard characteristics
 Other causes of abnormal operation, including
 Operating limit reached
instrument disturbance  Energy source exposed etc.

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Features of HAZOP Study Features of HAZOP Study

 Corrective actions  How would hazardous conditions detected?
 Change of process design  During normal operation
 Change of operating limits  Upon human failure
 Change of system reliability  Upon component failure
 Improvement of material containment  In other circumstances
 Change control system  Contingency actions
 Add/remove materials  Improve isolation
 Improve protection

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What is needed to perform HAZOP? HAZOP Procedures

For Detailed HAZOP 1. Detailed flow sheet, break into process units, select a unit
 For preliminary HAZOP 
 Piping and Instrumentation
2. Choose study node (vessel, line, operating instruction)
Describe the intent of study node (vessel: to store)
 Process Flow Sheet (PFS Diagram ( P & ID ) 3.

Process Calculations 4. Pick a process parameter: flow, level, temperature, pressure, etc.
or PFD) 
Apply guide words to generate deviations from normal operation corresponding
 Process Data Sheets 5.
to all conceivable possibilities such as NO or NOT, MORE, LESS, AS WELL AS,
 Description of the  Instrument Data Sheets PART OF, REVERSE, OTHER THAN.
Process  Interlock Schedules 6. If deviation is applicable, determine possible causes and note any protective
 Layout Requirements systems
 Hazardous Area Classification 7. Evaluate consequences
 Operating instructions 8. Recommend actions
9. Record information

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Process flow for HAZOP Guidelines for Division into Sections

Select Line
 Choices of lines – P&ID must be divided logically, not too
Select deviation (eg. MORE flow) many sections
Move on to next deviation Is more flow possible?  Factors to be considered:
Is it hazardous or does it prevent efficient operation? Consider other causes of
 Each section should contain active components, which gives
more flow rise to deviations. E.g piping which contains control valves can
What change in plant will tell him ? Will the operator know that there is more flow?
give rise to flow deviations, heat exchangers can cause T
What changes in plant or method will prevent the deviation or make it Consider other changes or agreed deviations.
less likely or protect against the consequences? to accept hazard
 Materials in section – contain significant amount of hazardous
Is the cost of the change justified?
materials.
Agree change(s), who is responsible for action  Section based on process and states of materials. Only one
Follow up to see action has been taken
process operation per section.

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Guidelines for Division into Sections Guidelines for Division into Sections
 General guidelines:  Supplementary guidelines
 Define each major process component as a section.  Define only one process section for equipment in identical
Usually anything assigned equipment number should be service. However, pumps in different service with a
considered a major process component. common spare must be treated separately.
 Define one line section between each major process  Define only one line at the end of a series of components if
component. there are no other flow paths.
 Define additional line sections for each branches off the  Define only one additional line section if there are
main process flow. alternative flow paths, regardless of how many branches
 Define a process section at each connection to existing there are.
equipment.

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Guidelines for Division into Sections Guide Words

 Do not define line between major equipment items if NONE No forward flow when there should be
there are no single active components that could MORE More of any parameter than there should be, e.g
more flow, more pressure, more temperature, etc.
cause deviations. LESS As above, but "less of" in each instance
 Do not define sections for existing equipment that is PART System composition difference from what it should
upstream of new or modified equipment. Address be
malfunctions of such upstream equipment as MORE THAN More "components" present than there should be for
example, extra phase, impurities
deviations in the new or modified equipment.
OTHER What needs to happen other than normal operation,
e.g. start up,shutdown, maintenance

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Guide Words Guide Words

NONE e.g., NO FLOW caused by blockage; pump failure; valve MORE OF MORE TEMPERATURE, pressure caused by external fires;
closed or jammed : leak: valve open ;suction vessel blockage ; shot spots; loss of control ; foaming; gas release;
empty; delivery side over - pressurized : vapor lock ; reaction;explosion; valve closed; loss of level in heater; sun.
control failure LESS OF e.g., LESS FLOW caused by pump failure; leak; scale in
REVERSE e.g., REVERSE FLOW caused by pump failure : NRV delivery; partial blockage ; sediments ; poor suction head;
failure or wrongly inserted ; wrong routing; delivery over process turndown.
pressured; back- siphoning ; pump reversed LESS e.g., low temperature, pressure caused by Heat loss;
MORE OF e.g., MORE FLOW caused by reduced delivery head ; vaporisation ; ambient conditions; rain ; imbalance of input
surging ; suction pressurised ; controller failure ; valve and output ; sealing ; blocked vent .
stuck open leak ; incorrect instrument reading. PART OF Change in composition high or low concentration of mixture;
additional reactions in reactor or other location ; feed change.

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Guide Words Guide Words

MORE THAN Impurities or extra phase Ingress of contaminants such  The application of each guide word to a process line to generate
as air, water, lube oils; corrosion products; presence of all conceivable deviations must be thorough and exhaustive.
other process materials due to internal leakage ; failure
 For each deviation generated the cause and the consequences
of isolation ; start-up features.
must be determined . Typical questions which could arise are:
OTHER Activities other than normal operation start-up and
shutdown of plant ; testing and inspection ; sampling ;  Do we need a high liquid level alarm as well as a level indicator?
maintenance; activating catalyst; removing blockage or  Is a single non-return valve sufficient ?
scale ; corrosion; process emergency ; safety
 Is the vent big enough ?
procedures activated ; failure of power, fuel, steam , air,
water or inert gas; emissions and lack of compatibility
with other emission and effluents.

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HAZOP Study Form Strengths of HAZOP

HAZOP Study Report Form
 Systematic, reasonably comprehensive and flexible
Project Date Sheet 1 of 12  suitable mainly for team use whereby it is possible to incorporate
Process Section
the general experience available
GUIDE DEVIATION CAUSES CONSEQUENCES ACTIONS, OR  gives good identification of cause and excellent identification of
WORDS RECOMMENDATIONS critical deviations
 use of keywords is effective and the whole group is able to
participate
 excellent well-proven method for studying large plant in a specific
manner
 Table 10-6 (page 451)  identifies virtually all significant deviations on the plant, all major
accidents should be identified but not necessarily their causes.

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Weaknesses of HAZOP Weaknesses of HAZOP

 Time consuming and can be laborious with a tendency for  Takes little account of the probabilities of events or consequences,
boredom for analysts although quantitative assessment are sometime added. The group
 Tends to be hardware-oriented and process-oriented, although generally let their collective experiences decide whether
the technique should be amenable to human error application deviations are meaningful
 Tends to generate many failure events with insignificance  Poor where multiple-combination events can have severe effects
consequences and generate many failure events which have the  Tends to assume defects or deterioration of materials of
same consequences construction will not arise
 Stifles brainstorming although this is not required at the late stage  When identifying consequences, HAZOP tends to encourage
of design when it is normally applied listing these as resulting in action by emergency control measures
 Does not identify all causes of deviations and therefore omits without considering that such action might fail. It tends to ignore
many scenarios. the contribution which can be made by operator interventions

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HAZOP Example HAZOP Example

Description of the process
 Exothermic reaction controlled by cooling water 
 The reaction is exothermic. A cooling system is provided to remove
Cooling Coils the excess energy of reaction. In the event of cooling function is lost,
Monomer the temperature of reactor would increase. This would lead to an
Feed
increase in reaction rate leading to additional energy release. The
Cooling Water to Sewer result would be a runaway reaction with pressures exceeding the
Cooling bursting pressure of the reactor. The temperature within the reactor is
Water In measured and is used to control the cooling water flow rate by a valve.
Perform the HAZOP study on this unit to improve the safety of the
process

TC
 HAZOP study as in Table 10-7 (page 453) : handout
Thermocouple

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See the Figure. An alkene / alkane fraction containing small amounts of suspended water is


continuously pumped from a bulk intermediate storage tank via a half-mile pipeline into a  Node is flow
buffer / settling tank where residual water is settled out prior to passing via a feed / product
heat exchanger and preheater to the reaction section. The water, which has an adverse effect
in pipe
on the dimerization reaction, is run off manually from the settling tank at intervals. Residence
time in the reaction section must be held within closely defined limits to ensure adequate
conversion of the alkene and to avoid excessive formation of polymer.

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Factors for a Successful HAZOP Study

 Throughout the study
 Should be an integral part of an overall safety
management system
 Process must have full backing and support of senior
management

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Factors for a Successful HAZOP Study Factors for a Successful HAZOP Study
 Before the study  During the study
 Must be initiated by a person with authority, who will  Team must be motivated and have adequate time to complete
receive and implement the actions the task
 The design must be well developed and firm, drawings  The boundary of the study must be clearly analyzed and studied
must be well prepared  Must have clear process description, design intent and design
 Skilled and suitably experienced team leader should be envelope
chosen  The study uses a creative thought process. Should fatigue sets
 Team must be balanced and well chosen to combine in, study must be halted and resumed when the team is
knowledge and experience refreshed

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Factors for a Successful HAZOP Study Summary

 After the study  Hazard identifications is one of the most
 Every action raised must be analyzed and answered important tasks for a process plant
accurately  HAZOP is a mature and most popular tool for
 Those which require a positive change should be identifying hazards without waiting for an
subject to a management of change process accident to occur

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Thanks…..

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