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1 Hazard Evaluation, HE, Techniques

The following HE, techniques have been used in chronological order:

1960 - 2001 1960 - 2001 1965 - 2001 1970 - 2001 1972 - 1974 1974 - 2001

Safety Check Lists Relative PHA What if HAZOP

Review Ranking

Walk Historical ICI Mond Preliminary Brainstorming Hazards

Through Lists Index Hazard Operability

Inspection Analysis Analysis

Yes / No Dow FEI

Hazardous Mtls Line by Line

Hazardous Opns Deviation

Analysis

This presentation only considers the HAZOP technique.

Press Page Down for 9 pages of further information on HAZOPS.

(Best viewed with 24 lines per screen - adjust your Zoom% to suit)

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2 HAZOP Hazards and Operability Analysis

HAZOP was developed by Lawley (1974) of ICI. Based on early account by Elliott & Owen (1968)

Hazop studies are carried out by an experienced, multidisciplanary team, who review all physical

aspects of a process (lines, equipment, instrumentation) to discover potential hazards and

operability problems using a check list approach.

The basis for a HAZOP is a critical examination of information found in a word model, a process

flowsheet, a plant layout, equipment specification or a P&ID, (Piping and Instrument Drawing).

The principals of examination include: See tabs D1 to D3 for examples of computer forms.

1 Intention

2 Deviation

3 Causes

4 Consequences

(a) hazards

(b) operating difficulties

5 Safeguards

6 Recommendations / Actionscontinue to page 3

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3 Early HAZOP studies used the following set ofGuide Words to systematically review the process:

NO or NOT Negation of intention No Flow of A

MORE Quantitative increase Flow of A greater than design flow

LESS Quantitative decrease Flow of A less than design flow

AS WELL AS Quantitative increase Transfer of some component additional to A

PART OF Quantitative decrease Failure to transfer all components of A

REVERSE Logical opposite of intention Flow of A in direction opposite to design direction

OTHER THAN Complete substitution Transfer of some material other than A

More recent computerization techniques use a Standard Set Of Generic Deviations

For Specific Section Types. See Dev'ns tab for examples.

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4 Some Common HAZOP Analysis Process Parameters

Flow Time Frequency Mixing

Pressure Composition Viscosity Addition

Temperature pH Voltage Separation

Level Speed Toxicity Reaction

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5 Prepare for the review

Attitude

Preparation Meeting Leadership

HAZOP

Review By Documentation Follow-up

Team

Knowledge Info for study

Experience Teams HAZOP P&Ids, Layout

Experience

Table

Deviation Causes Consequences Safeguards Action

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6 HAZOP analysis method flow diagram

Select a process

section or

operating step

Explain design Repeat for all

intention process sections

Select a process Repeat for all

variable or task process variables

Apply guide word Repeat for all

to process variable guide words

Examine Develop action

Consequences items

associated withcontiue page down deviation

6 con't

List possible Assess acceptability

causes of of risk based on

deviation consequences

Identify existing

safeguards to

prevent deviation

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7 Potential HAZOP Pitfalls

1 Poor understanding by management of the HAZOP procedure

An Ethylene plant has 100 P&IDs, 625 equip't items. 625 items a

Consider 5 variables, Pressure, Temperature, Flow

Composition and Function. 5 variables b

Consider 6 Guidewords, None, More of, Less of

Part of, More than and Other than. 6 guide words c

Questions to be answered = 18750 questions d = axbxc

Consider 5 minutes per question = 5 min./question e

Time for ethylene plant HAZOP study = 93750 minutes f = dxe

4 hour, 240 minutes sessions per day = 250 minutes/day g

No. working of days = 375 days h = f / g

Days per week = 5 days/week I

No. of weeks to complete HAZOP for plant = 75 weeks j = h / I

2 Inexperienced HAZOP team

3 Inadequately trained or in-experienced leader

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8 Common Mistakes

1 Failing to establish a "safe" environment for team members

2 Consequences of events not carried to conclusion.

3 Taking unwarranted credit for safeguards See example on page 9 - one page down

4 Too little credit given for safeguards

5 Making recommendations as specific as possible

6 Poor recording of HAZOPS

7 Failure to HAZOP start-up and shut-down procedures

8 Poorly up-dated P&IDs

9 A HAZOP is performed in lieu of properly executed design reviews

10 Wrong technique for system being reviewed (See spreadsheet titled Fig 5.3)continue to page 9

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9 HAZOP Example See page 8 - item No. 3

To Compressor Inlet

Teams tend to quickly identify alarms, shut-downs

and controls, and claim them for safeguards.

An alarm not tested may not work when called upon

Inlet Line to do so.

Nuisance alarms are frequently bypassed and are

not effective as safeguards.

Often operators are not monitoring control panel.

Valve in manual Automatic control routines are often set in manual

mode.

end See tab D1 for computer documentation example

FV1

LAH

LIC1

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Dev'ns

Table 1 Example Standard Set Of Generic Deviations For Process Section Types

Source Lessons Learned From HAZOPS Reviews of FCCUs by P.E. McCluer et al, Hydrocarbon Processing, Aug 1992, p-140-C

Tank or Heat

ID No. Deviation Column Vessel Line Exchanger Pump Compressor

1 High Flow X

2 High Level X X

3 High Interface X4 High Pressure X X X X

5 High Temperature X X X X

6 High Concentration X X X

7 Low / No Flow X X

8 Low Level X X

9 Low Interface X

10 Low Pressure X X X X

11 Low Temperature X X X X

12 Low Concentration X X X

13 Reverse / Misdirected Flow X X

14 Tube Leak X

15 Tube Rupture X

16 Leak X X X X X X

17 Rupture X X X X X X

Some other typical HAZOP deviations Press Page Down

More Flow

Less Flow

More Pressure

Less Pressure

More Level

Less Level

Part of, wrong concentration

As well as, contaminants

other than, wrong material

More Reaction

Less Reaction

No Reaction

More Mixing

Less Mixing

More Corrosion

More Erosion

Sampling

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D1

Company Nova Revision 0 Date 2-Jun-97

Location Corunna Dwg No. Cor -123-4567 Page 1

Leader RAH Proc Des JB Research Op Tech

Scribe GFR Instr'ts GH Electrical HH Other

Prod'n PM Mech FD Safety MN Other

Node No. 1 Describe Transfer Ethane from Deethanizer to C2 KO Pot

Intention The intent is to transfer 150,000 lb/hr of C2/C2= mix at 300 psig and at -30 F for the startup period.

Guide Wrd High Param Flow Dev'n High Flow

Possible Causes

1 FV-1 Wide open

2 Line break.

3

Consequences

1 High level in KO pot with liquid carry-over to compressor with serious damage to rotor. Potential hydrocarbons release.

2 Potential hydrocarbon release.3

Safeguards1 High level alarm LAH-1

2 High - High level alarm HHLA - 1 shutdown.

3 Vessel inspection yearly.

Recommendation / Actions Respib By Date

1 Consider limiting flow orifice, auto SD trip on High-High level, smart check valve. 1 JB 1-Jan-99

2 Determine extent of typical hydrocarbon release. 2 PM #######

3 Set-up vessel inspection yearly. 3 FD #######

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D2

Company Nova Revision 0 Date 2-Jun-97

Location Corunna Dwg No. Cor -123-4567 Page 2

Leader RAH Proc Des JB Research 0 Op Tech 0

Scribe GFR Instr'ts GH Electrical HH Other 0

Prod'n PM Mech FD Safety MN Other 0

Node No. 1 Describe Transfer Ethane from Deethanizer to C2 KO Pot

Intention The intent is to transfer 150,000 lb/hr of C2/C2= mix at 300 psig and at -30 F for the startup period.

0

0

Guide Wrd Low Param Flow Dev'n Low Flow

Possible Causes

1

2

3

Consequences

1

2

3Safeguards

1

2

3

Rec / Actions Respib By Date

1 1

2 2

3 3

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D3

Company Revision Date

Location Dwg No. Page

Leader Proc Des Research Op Tech

Scribe Instr'ts Electrical Other

Prod'n Mech Safety Other

Node No. Describe

Intention

Guide Wrd Param Dev'n

Possible Causes

1

2

3

Consequences

1

2

3Safeguards

1

2

3

Rec / Actions Respib By Date

1 1

2 2

3 3

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Chk List

Hazard & Operability Studies Check List Example

1 Changes In Quantity a High Flow 1 Pump racing, delivery vessel pressure lost,

suction pressurized, scale dislodged, leak in

heat exchanger

Loss of automatic

control

b Low Flow 2 Pump failure, scaling of delivery, presence

of foreign body, poor suction condition,

cavitation, leak in heat exchanger, drainleak, valve jammed

Operator error

c No Flow 3 Pump failure, delivery vessel

overpressurized, gas blockage, presence of

foreign body, scale, sediment, suction vessel

empty.

Failure of joint, pipe,

valve, trap, bursting

disc, relief valve.

d Reverse Flow 4 Pump failure, pump reversed, delivery

vessel over pressurized, poor isolation, gas

locking, surging, back siphoning.

2 Changes in physical

condition

a High or Low

pressure

1 Boiling, cavitation, freezing, chemical

breakdown, flashing, condensation,

sedimentation, scaling, foaming, gas

release, priming, exploding, imploding.

Changes in viscosity, density. External Fire,

Weather conditions, Hammer.

b High or Low

Temperature

2 same as 1

c Static buildup 3 Source of Ignition, Personnel shock.

3 Changes in chemical

condition

a High or Low

Conentration

1 Changes in proportion of mixture, in water or

solvent content.

b Contaminants 2 Ingress of air, water, steam, fuel, lubricant,

corrosion products, other process materials

from high pressure system, leakage through

heat exchangers. gas entrainment, spray,

mist.

4 Startup and

Shutdown Condition.

a Testing 1 Vacuum, pressure testing with with harmless

material.

b Commissioning 2 Concentration of reactants, intermediates

c Maintenance 3 Purging, venting, sweetening, drying,

warming. Access, spares.

5 Hazardous Pipelines a Pipeline

registration

1 Should this pipe be considered for

registration?

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