Basics of HAZOP

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Basics of HAZOP 6 1

C H P T E R 6

Basics of HAZOPWhat Did we Do Before HAZOP Came Along

We relied upon:

Good enginee ring practices

Codes of practice such as ASME API NFPA etc.

Informal safety reviews

So what slips through the cracks?

Interface problem s between equipment and systems

Abnormal conditions not envisioned during design

Human error in design operation maintenance

How Do We Know If a Plant Is Safe

Historical record of plant incidents and near misses

History of inciden ts on similar plants

Record of onstream time

Can apply som e risk ranking e.g., Dow/Mond indices

Ask: What guarantee d o we have that there isn t a serious accident about to happen?

If there is O guarantee:

What can w e do about it?

=3 Increase Hazards Risk Awareness

by:

Process Safety Management Program .

© 2003 by CRC Prcss LLC



Basics of HAZOP -2

HAZOP Methodology

HAZOP

Acronym for HAZards and Operability Analysis.

Originated by Imperial Chem ical Industries ICI) in Mond Division.

Basic Concept

Simulate abnormal behavior by considering deviations and disturbances due to causes

likely to impact immediate and surrounding plant resulting in consequences. Then decide

whether the design has adequate features i.e., safeguards that can prevent occurrence or

limit the consequential effects. If no such safeguards exist, then con sider what actions are

needed to remedy the situation.

High Deviation

Normal Design Intention)

Low Deviation

Other D eviations typically include:

Reverse of what was intended.

What else can happen?

System only partially functions.

What additional things can occur?




Basics of HAZO P 3

Methodology for Generating Deviations

G u i d e W o r d P r o p e r t y = D e v i a t i o n

For example

When Property = Parameter

High Flow

Low PressureMore Reaction

When Property = Operation

No Transfer

Less Empty

When Property = Material

No Steam

More iluent

High Flow

Low PressureGreater R eactivity

No Transfer

Residue Remaining

No Steam

More iluent

YADEM




Basicsof HAZOP 6 4

hat Type of HAZOP Should You Use

Parametric Deviation e.g., High pressure, Low temperature, etc.)

Good for continuous processes.

Most widely used in world today.

Critical Examination

The approach examines:

Material

Activities

Sources and Destinations

Good for batch operations, start-up, shut down.

Procedural Methodology

Useful far HAZOPing:

Operating manuals, procedures

Batch operations

Start-up, shut down

Knowledge Based HAZOP (more like What i f with established Checklist)

Mainly applicable to:

Well established continuous) processes

Organizations with very high quality engineering practices standards




Basics of HAZOP 6 5

Steps in the H ZOP Process

1 Preparation

Assemble:

P IDs (Full size and reduced copies for the team)

PFDs plus material and ene rgy balances

Equipment specifications

Layout drawings

2 Facilitator and Process E ngineer

Break P IDs down into Nodes.

Nodes are equipment items (or numbers of items).

If nodes are too small you can loose sense of analysis and incur excessive

repetition.

If nodes are too large, hard to handle, becomes confusing.

Questio n: How d o you size a node?

Answ er: Based on system function.

Example: Reactor feed system may consist of Pump Line Exchanger

3 Prepare HAZOP Outline with List of Deviations

4 Assemble HAZOP Team

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5. Facilitator Explains

The facilitator or one of the team members explains the purpose and scope of the

HAZOP and sets the rules for the study

6. Process Engineer Explains

Process in general

Immediate Node being HAZOPed

7. HAZUP Each Node Using Deviations Listed in Outline Working Throughthe P ZD.

Produce HAZOP worksheet recording the following:

Causes

Consequences

Safeguards

Actions/Recommendations

Remarks

8 At the End of HAZOP, the Facilitator Issues Preliminary HAZOP Report(issuance is optional) consisting of

Attendance

Outline

Detail Report

Action/Recommendations Register

9. Issue Final Report Giving Full Details

A sample of table of conten ts is given in page 6 11




Basics of HAZOP 6 7

Variations in HAZOP Types

Thre e basic types:

Guide Word HA ZOP

Knowledge Based HAZO P

Creative Checklist

The Guide Word method is the most accepted method. The re are five main variations:

Cause-by-cause

Consequence-by-consequenceDeviation-by-deviation

Exception only

Action/Recommendation item only

Cause By Cause Methodology

Correlates Consequences, Safeguards and Actions to each particular Cause of a Deviation.

Precise method

Reduces ambiguity

Detail print-out can be followed, is fully auditable

Example: Deviation: Line Rupture

Cause-By-Cause p rovides ull cross-referencing.

Action

Check fire protection

Action

Check fire protection

Action

Provide crash barrier

Safeguard

Pipe stress analysis

Safeguard

Charpee tested steel

Safeguard

None

Cause ILine overstressed

Cause 2

Brittle fracture

Cause 3

Vehicular impact

Consequence

Flammable release fire

Consequence


Consequence





asicsof HAZOP 6 8

Consequence By Consequence ethodology

Correlates Consequences Safeguards and Actions to each particular Consequence o a

Deviation.Precise method

Reduces ambiguity

Detail print-out can be followed is fully auditable


Consequence-By-Consequence providesfull cross-referencing.

Cause I

Line overstressed

Cause 2

Brittlefracture

Cause 3

Vehicularimpact

Deviation By DeviationMethodology

All Causes Consequences Safeguards and Actions are related only to a particular

Deviation.

Consequence

Flammable release

Fire

Consequence

Flammable release

Fire

Consequence

Flammable release

Fire

Fairly simple to execute

Some ambiguity

Fairly rapid

Detail print-out hard to follow

Safeguard


Safeguard


Safeguard

None

ction

Check ire protection

ction

CheckJre protection

Action

Provide crash burrier





Basics o HAZOP 6 9


Deviation-By-Deviation provides no cross-referencing.

Exception Only Methodology Not Recommended)

Causes

Line overstressed

Brittle fiacture

Vehicular impact

Includes only those deviations for which team believes there are credible causes.

Safeguards



Consequences

Flammable release, fire

Reduces time

Cannot be audited

Actions


Provide crash barrier

Citations have been issued by OSH A in the U SA against covered facilities using this

method.

ActiorulCecommendations Item O nly Methodo logy Not Recomm ended)

Only suggestions that team makes for action items are recorded. No proper analysis).

Not auditable

YADEM




Basics of HAZOP 6 10

Preparation of HAZOP Reports

asic Report Should Consist of

1 HAZO P O utline

Nodes

Deviations

Guide Words

Parameters

Design Intent

Design Conditions

2 Detail Report

Lists output of session s.

For each No de and Deviation lists:

Causes

Consequences + Risk Ranking)

Safeguards

Actions/Recommendations

Remarks

3 Attendance Register

Facility, Unit

Location

Team members and expertise

Attendanc e Present/Absent/N ot required/Part-time)

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4. Action/Recommendations Register

Action/Recomm endations Item

Person s) responsible for follow-up

Prioritization

Status

Target date for completion Resolution)

Other

Risk ranking

Categorization

Final Report

1 Executive Summary

2. Introduction

3 Process Description

4. Hazards of the process

5. Hazard and Operability Methodology

6. Conclusions and Recomm endations

ppendices

o Outline of Hazard and Operability Study

o Drawings

o Project Information Report

o Drawing Report

o Team Mem bers Report

o Risk Matrix Report

o Worksheet Report

o Action~RecommendationsReport

o Computer files

YADEM





HAZOP Example

Table 6-1: Scope ofHAZOP and Process Description

E?&&pslqkXY rocessing Corporationt

LPenibw b y p l a c e

Pm a3 IR: A X W l

Start Date: If2IReMI;I;

end'rnk 1r

C-t: LIGHT ENDS RECOVERY UNIT (See Figures 6- 1 and 6-2)

To muam th li hta pottion of a liquid feed stream containing 50 , by weight, of ight 4 s s& a

d m M 6 m t ~ . he eed rate is 100,000 lbhour and the intent is ta r-wr 81 af the light em ,kh in orderto prpduue a1W h y weight, light ends distillate.

RYP ess Description:

The lmit isW QX aq uptream &d dnxm V- 101. Liquid feed is sqpplied at ab t w@ Mpdgdat 22Q P. The f Is pre-heated by heat exchange with the light mis wippwrbmggp m @ QQF, inth t M m ~~b EX-101, before it enters the light ends stripper, C-101..

The light end t@l~per -Q l , s a 22 plate fractionation column, u s h g valve-type h y s w l i h b ~ P m d ImWdon plate 12.

Overhead vapors from the light ends stripper, C- 101, pass to the light ends condenser, EX-102, which is watercooled. Fluids from this condenser flow to the reflux drum, V-102. Non condensible vapors entering the refluxdrum V-102, are vented to the flare system while the condensed liquids pass to the reflux pump, P-101 or spare.The total distillate is split so that product distillate is sent directly to storage while the main portioo is reflusedbaakto the top of the light ends stripper,C-101.

At the base of the light ends stripper, C-10 1, there is a vertical thermosiphonreboiler, EX-103 hich is heated by3 psig steam on the shell side. Bottoms liquid from the base of the light ends stripper, C-101, is pumped by abottoms pump, P-102 or spare, to the tube side of the feedhottoms exchanger, EX-101, in which it is cooled by feed

before passing to storage.

Process Controls:

The feed to column is under flow control via loop FRC-10 1.

The reflux flow is under flow control via loop FRC-116.

Distillate withdrawal is under level control via loop LlC-107, from the reflux drum level.

Non-condensibles bleed off under pressure control via loop PIC- 106 based on the overheads column pressure

> YADEM




Basics of HAZOP 6 1

The rate of bottoms withdrawal is under level control via loop LIC-119 based on the column bottom level.

The steam flow to the reboiler is under composition control via temperature control loop TRC-126 based on the

process side of the reboiler outlet.

Protective Devices:

Relief valve PSV-105, protects against overpressuring of the light ends stripper and connected components.

Relief valve, PSV-106, protects against thermal expansion on the cooling water side of the light ends condenser.

High and low level conditions, LAH -120, LAL-12 1 and LAH LAL -107, are alarmed respectively on the lightends stripper and the reflux drum. The low level condition, LSL-12 1, on the stripper is also interlock ed to stop the

bottoms pump. The low low level condition on the reflux drum stops the reflux pump.

In even t of failure of the bottoms pump, the spare pum p is started by a low low pressu re switch, PSLL -125. The

same arrangement, for the reflux pump, is also supplied by a low low pressure switch, PSLL-109.

High or low column pressures are alarmed by PAH PAL- 106 respectively.

Loss of reflux is alarm ed by FAL- 116.

Loss of steam to the reboiler is alarmed by TAL - 126.

A minimum flow bypass on the bottoms pump protects against the no flow condition.

Remotely operable motor operated valve, MOV-122, can be manually initiated in an emergency, such as bottomsline leaklfiacture, to prevent significant flamm ables inventory loss and fire.

The instrume nt air failure positions of the control valves a re indicated as F.C. (fail close) or F.O. (fail open).

Car seal open (CSO) valves are as indicated.

Assumptions:

During a normal HAZOP you would normally have access to full equipment specifications, plant layout drawings,

piping specifications, line lists, tie points and other pertinent docum ents. As this samp le demonstrates PHA -Pro,rather than being an exercise in design, such documents are not included. Therefore make whatever assumptions

you think reasonable if you wish to modify or extend the HAZOP as shown.

Normal Operating Conditions:

Stream 1, Feed 220 F, 90 PSIG, 100,000 LbIHour, 50% Light EndsStream 2, Overhead 200 F, 75 PSIG, 135,000 LbIHour, 90.2% Light Ends

Stream 3, Bottoms 300 F, 120 PSIG, 50,000 LbIHour, 9.5% Light EndsStream 4, Reflux 200 F, 75 PSIG, 85,000 LbIHour, 90% Light Ends

Stream 5, Non Condensibles 200 F, 75 PSIG, 5,000 LbM our, 95% Light EndsStream 6, Distillate 200 F, 150 PSIG, 45,000 LbIH our, 90% L ight Ends

Stream 7, Reboiler Feed 300 F, 80 PSIG, 185,000 LbIHour, 9.5% Light Ends

Stream 8, Steam Flow 420 F, 300 PSIG, 25,000 LbIHour

YADEM




Basics of H ZOP 6 14

T . ,---. . l .l... ..

Heat Exchanger Duties

Condenser EX- 102: 19.5 MMB TUIHR

FeedlBottoms Exchanger EX -] 01 1.9 MM BTUIHR

Reboiler EX-103: 19.9 MM BTUIHR

Y DE M





Figure 6-1: P ID of Light Ends Process

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Basics of HAZOP 6 1

Figure 6 2: Process Flow Diagram

FOR L I G H T S W O V E B Y m

HE T ONDENSER 19 5 MMBTUl?W

FEEDIBCYITOMSEXCHANGER 1 9 MM TUlRR

REBOILER 19 9 MM TUIISR





Table 6 2: List of Dev iations

Node: 1. Light Ends Recovery Unit Drawings: 1. Process Flow Sketch of Light EndsI Recovery Unit; 2. Piping Instrumentation Dia gra~

Types: Centrifugal Pump Column Heat Exchanger Line PCD-A1Maintenance problems Vessel

' ~ ~ u i ~ r n e n tD: Distillation unit with heat recovery from

bottoms heating feedstream

Design ConditionsIParameters: Design conditions are listedin Process Flow Sketch of Light Ends Recovery Unit~ r o v i d e d

Deviation

1.1. High Flow

1.2. LowIN o Flow

1.3. ReverseJMisdirected Flow

1.4. Other than Flow

1.5. High Temperature

1.6. Low Temperature

1.7. High Pressure

1.8. Low Pressure

1.9. High L evel

1.10. Low L evel

1.1 1. Cavitation

1.12. Column Flooding

---

1 13 Low Tray Level

1.14. High Concentration of

Impuritiest

1.15. Leak

Guid e Word Parameter Sessio Revision Design Intent

High Flow

In

1 As per Process Flow

DiagramILowIN o As per Process Flow

Diagram

ReverseIMisdirecte Flow I oAs per Process Flow

d Diagram

Other than

--7 -7;As per Process Flow

Diagram

YADEM




Basics of HAZOP 6-18

. - - -

D e v ~ a t i o n G u ~ d eWord

I

1.16. Rupture I Other than

I-- - - -

l Parameter Sessio Revision De sign Intent

, DYADEM

1.17. Start-~ip1Shutdown I Other than start- 0 As per Op erating

Hazards ~~plshutdown Ins t ruc t ions. .

1.18.Maintenance Hazards Other than Maintenance 12 O1As per Maintenance

Data2-w-sik- &> bSa-& @&~&&SYR~&QSI>a3k b d k , It L 53 wLk%**~~Q, SI - $-&&V. ~V& fik bbAi3ba2&.& *& &&~-~t & *>ihaw- k 2





Table 6 3: Sam ple Worksheet

Node: 1. Light Ends Recovery Unit Drawings: 1. Process

ypes: Centrifugal Pump, Column, Heat Exchanger, Line, Flow Sketch of LightEnds Recovery Unit,

Equipme nt ID: Distillation unit with heat recovery from bottoms heating feedstream 2. PipingInstrumentation

Design ConditionslParameters: Design conditions are listed in Process Flow S ketch ofDiagram PCD-A

Light Ends Recovery Unit provided

1 1 High Flow

2. Investigate recyclingline and/or additional

101 dwg. no. PCD-AA1) to trip FV- 101

closed using solenoid

3?DYADEM





- -- -.- *-

Causes Consequen ces Safeguards S

room monitored as

opposed to local device

and add high

temperature switch and

control v alve TV- 126

so that on fill1 open ing

column will be in likely

to flood due to excess

vapor flow

Responsible

4. Control j 4.1. High bottoms 14.1. PSV-105 j I ' Tom Volkevalve or ' temperature Ifails CV ' i ; f f - spe c P roduc ts

ITV-126 Iopen or

bypass leftPhillip

Smithpen j I I

I1 ,

14.3. Over-pressuring 14.2. TI- 1 17

of column

8. Add high

temperature alarm,

TAH - 126

To111 Volke

of c o l ~ ~ m n- - i

5 Cont ro l 5 . 1 Colum n will 15.1. PAL-10 6 I 9. Add independent

pressure monitor on

column overheads with

high and low pressure

switches and a la r~n s

Tom Volke

valve or i depressure to flare / (provided 1controller ; w -

fails CV, 5.2. Loss of products

PV- 106 5.3. Off-spec products /open or ibypass left

open- --- -" - - -- - - - - II ---- -

6. Control 6.1. Loss of products 6.1. L AL- 12 1

-- --16.1.

SafegilardsfI are I.<r9

, [adequa te

I $.9

I =,

Ii i

k1

;:

1.:I

i\s

iII

18.1, dSafeguards

are

adequate '

ik A A ,4 &< W 2 h A, - & *

, v a l v e or - - - - -

I6.2. Off-spec prodi~ctscontroller ,

falls CV

LV- 107

open or -

bypass left 6.3. Low level in

6.2. LSL- I2

trips P-1021s

ope n c olumn c o ~ ~ l d II

I bottoms pumps P-

, 1021s- -

7. Control 7.1. Excess reflux to 7.1. None 4 10. Add h igh flow

alarm to FR C- I 16

1. Consider

monitoring steam flow

to column by addingi flow indicator on 3"-S-

i 10 as check on energy

, consumption

valve or column i II controller

I

I 7.2. Unecononiical

CV performance 1FV-116open or ;bypass leftopen I

I

8. PSV-10 5 8.1. Column will

fails open depressure to flare

8.1. Block

and bypass

' due to valves I8.2. Loss of products PSV

spring . .-failure ,8. 3. Off-spec products nl ~l r I 4

Y A D E M




Basics of HAZOP 6 2 1

auses

. Steamtrap on 3 -S-102 sticksopen

Consequences Safeguards

8 4 [Failure too for manualinfrequent to raise pressuresignificant concerns] relief when

PSV-105 isremoved for

repair

9.1. Steam wastage 9.1. None

9.2. Uneconomical

Recommendations

1 1. Consider

monitoring steam flowto column by addingflow indicator on 3 -S-10 1 as check on energyconsumption

Responsible

Tom Volke

CarlHanks

Remarks

1.2. Low/No Flow

Imaintenance inspection offlow devices, such as FE-

system to make up in the

event of sudden loss ofsteam to reboiler

YADEM




Basics o HAZOP 6 22

--- .-

Causes

-- 1 - -Conseq~~ences Safeguards

4.2. Poss~ble " -I

L ' R R Responsible , Remarks- - -- --

Tom Volkelosed 14. Interlock reflux return,

FV- 16, and feed, FV- I0

to close wh en PA L- 106 is

act uated

1 vacuum in I

column causing

tray dam age

I -5. Control 5. I . Column will 15. I. PAH-106

- -Tom Volke. Add independent

pressure m onitor on

column overheads with


switches and alarms

valve or

controller

fails CV PV-

106 closed

overpressure (provided

P1C- 106 is

f i~nc tonal).2. Loss of

products

- - 16. Control 16.1. Loss of 6. I . LAH - 107 15. Add high level switch

and alarm on reflux drumv - 102

Tom Volke

valve or products 1 (providedcontroller

fails CV

LV- 107

closed. - -7. Control

valve or

' controller

fails CV FV-

16 closed

- - - .

7.1. Loss of 17 .1 . AL- I16

. . -1. Consider monitoring

st ea m flo w to c o l ~ ~ m ny

adding flow indicator on

3 -S- 10 as check on

16. Add independent

pressure mo nitor onco1~11nnverheads w ith


switches and alarms

Tom Volke

& Carl

Hanks

reflux to column 1 (provided- - "

' F I C - 1 1 6 i s7 .2 Off-spec fLlnctional)products

Tom Volke

. -

1 7.3. Over-

/ columnf - --

8.1. None 1. Consider monitoring

steam flow to column by

adding flow indicator on

3 -S-101 as check on

energy consumption- - - -

Tom Volke

& Carl

Hanks02 sticks 8.2 Lois of

closed 1 products

' 9 . 1 .

Safegnards

l are

I ' - __" -9. Bottom s 19.1. No

pump P- withdrawal of

1021s stops j bottoms product- . .19.2. Loss of 9.2. Spare

products

9.3. High level in

base of column" .

10.1. Loss of

9.3. LG- 8

10. Reflux

pump P-

o IS stops

10.1. FAL-

116

j 10.1.

1 Safeguardseflux to column; are

10.2. PSV-

105t asP&42- :,34 w

productsE had

Y ADE M




Basics o HAZOP6 23

auses1

1 MOV-122 fails

closed

12.Temporarystrainers on

P-1011s

plugged13. Loss ofoverheadcondenser.

pressuring ofcolumn

wouldcavitateldamagebottoms pumps P-1021s

wouldcavitateldamage

bottoms pumps P-

1021s13.1.Overpressuring ofcolumn to reliefcondition.

10.3. Spare

11.1.Interlock on

MOV-122positionerstops bottomspumps whenvalve closes

13.1. Low 2 3flow alarmFAL-116 onloss of reflux.

13.2. Pressurerelief valve

106 PV-106 opening

to flare.

MOV- 122 positioner ZC-

122 to stop bottoms pumpswhen MOV - 122 valve

closes

strainers on P- 10 1 S arecleaned and removed whenno longer required

19. Check PSV-105 forcontrolling case for sizingvalve. Must handle firecase tube rupture inreboiler total loss of refluxloss of cooling medium

instrument or controllerfailure instrument air

failure power failure etc.

20. PV-106 to be checkedfor maximum discharge

flow in event of coolingwater failure to EX-102.

Responsible Remarks

Phillip

Smith

1.3. ReverseIMisdirected F low

1.1. Possible explosive

YADEM




Basics of H ZOP 6 24

Table 6 4: List of Recommen dations

- . . .- ...

. .. . . .

nsider monitoring stea

3 -S-101 as check on

/ _._

17. Provide interlock on M

nu discharge flow in event of

Y DE M





Recomm endation Resp Status

22. Check on flow regime in 6 -P-113 to

slugging'23. Check that line 3 -P-104 is both self-ven ting and is not pocketed Phillip ~ m i t h Fr24. Evaluate need for emergency depressuring to prevent BLEVE in Phillip Smith Study

event of fire

25. Provide sample point on inlet feed. Also consider need for on-line Tom Volke Incomplete

analyzer for column feed.

' 26.1 Provide quality control check o n feed stream to column Carl Hanks 1 Study

Add high temperature alarm on overheads to indicate trend towards Tom Volke Incomplete

off-spec distillate

TR- 103 only Phillip Smith Incomplete

29.1 Add low temperature alarm to TR- 103. Tom Volke

30. Consider adding independent high high level switch and alarm on Tom Volkereflux rum

Incomplete

Study

1. Check sizing of control valve TV-126 s o that CV is not oversized Phillip Smithand could cause column flooding when fully open. If necessary Tomconsider adding upper limit stop on control valve. Volke

Study

Check as to whether upstream water separationRecon vene meeting if not met.

33. Provide bolt torquing procedure as part of34. Consider need for environmental monitors. Mary Incomplete

Patterson

Add isolation valve immediately upstream of stripper on reflux line

2 -P- 110.

36. Make valve on 3 -P-102 feed to column car seal open. Phillip Smith Incomplete

37. Add check valve to 3 -P-102 , close to stripper feed inlet. Allen Brown Incomplete

rm that C-101 a

Pri Place(sUsed

7 1.4.1

YADEM




Basics of HAZOP 6-26

SUGGE STED READING URLs current at time of publication

"Guidelines for Hazard Evaluation Procedures" by A IChE , CCP S, 2"d edition, 1992 plus

"Guidelines for Hazard Evaluation Procedures" by AlCh E, CC PS, I st edition, 1985

w w w . a i c h e . o r r / p u L > c a t / s e a d t l . a s ~ ' ? A c ~ k 4 i n = 2 i ~

"HAZOP and HAZAN" by T.Kletz, published by IChemE, 1992

www icl1e1ne or~/framesetsiia1~o~1ti1~S~iiii~estt n ~

"Size u p plant hazards tllis way" by H .G.Lawley, H ydrocarbon Processing, April 1976, pages

247 to 258

www.livdrocarbon~~rocessin~.co~n~conte~~ts/pul~lcatiotis,:'hp/

"Eliminating Potential Process Hazards" by T.Kletz, Chem ical Eng ineering, April 1, 1985, pages

48 to 59www.che.com/

"An Introduction to Hazard and Operability Studies Th e Guid e Word Approach" by

R.E.Know lton, published by Che metic s International, 198 1

www vaerner.co~n/co~i~pa~~ics co~iipanesdcta i I.asp'?id::.::.79(i

"A Manual of Hazard & Operability Studies Th e Creative Identification of Deviations and

Disturbances", published by Chemetics International, 1992

w~vw.kvae1ner.con1/co11i~.~atii~s/~o1ii~~ai1iesdetai.asp~ id=796

"Some Features of and Activities in Hazard and Operability (Hazop ) Studies", by J.R .Roach andF.P.Lees, Th e Chemical Engineer,October, 198 1, pages 456 to 462

\vwcv.ichenie.or~/fr~1111esets/i1bo~1tus f ra~nese ttln

"HAZOP: Guide to best practice" by F .Crawley, M.Preston, B.Tyler, IChernE, 2000

~vww icherne o~/fi amesets/aboutusframesct l~t~n

"The HAZOP (Hazard and Operability) Method" (Website)

w~\~\\ .acusafc.co~n/Iazard_A~ialysis/l AZ0 PTcc lir iiquc.pd f

"Hazard and Operability Studies", by M.Lihou (Website)

M M W. l i l ~ o i ~ t e c I ~ . c o ~ ~ i / h ~ pfi.m.htm

"Hazard and Operability Studies", University of Florida, (Web site)

litt~:l.'pie.clie.i~fl.edi~/~i~ideslhazopiindex.litn~l

"Process H azards Analysis" by I.Sutton, published by SW ISutton & Associates, 2002

litt~~://ww~~~ swbooks co~i~/bool~~/bo~~k~~~prI~~tslitml

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Basics of HAZOP